Christophe Pochari, Pochari Technologies, Bodega Bay, CA.
707 774 3024, firstname.lastname@example.org
In this text, we discuss the possibilities of both extracting nickel from ultramafic by using closed-loop acid leaching and carbonation, as well as by using centrifuges for density-based segregation.
Note to the reader: The method proposed below (centrifugal separation) is purely theoretical, it is not a technology in strict terms such as our pneumatic tower or aluminum oxide heat exchanger which can be calculated to exacting precision and whose real world performance can be confidently predicted. This inquiry falls under the category of research interest, for the sake of probing what is possible with current human knowledge. We do not know precisely to what extent different forms of ultramafic rock hosts nickel bearing minerals in “clusters” or inclusions, and to what extent nickel is widely diffused through the host mineral at the atomic scale or even nanoscale. This question represents the major unknown with respect to the viability of the proposed concept. The only way to determine this is to scan a sample of ultramafic rock with an mass spectrometer and perform a color-coded map of the crystal because optimal microscopy alone is insufficient. An alternative method may simply involve crushing a representative sample of ultramafic rock and measuring the variance in particle density through settling. Until this is performed, all discussion is purely theoretical. For the proposed method to work, fine comminution, up to 10 micron, must be able to produce particles of discrete density, however minute this difference, to gravitationally segregate. The basic assumption made is that because nickel has an atomic weight of 58.7 while magnesium and silicon are 24 and 28 respectively, a micron size particle carrying even slightly higher diffused nickel will possess more mass than one carrying slightly less. This small differences in mass will allow segregation, so while we can calculate the energy consumption of the centrifuge and comminution, we cannot calculate the segregation efficiency because we cannot know the diffusiveness of the nickel within the host rock because no data can be found. While we believe it is possible to liberate sufficient discrete particles of more nickel-concentrated rock, we cannot be certain so we treat the entire proposal hereinafter as conceptually feasible but unproven.
Note: this treatise is a speculative effort to evaluate whether a non-chemical means of ore separation is possible. It may very well be the case, and probably is, that chemical separation is the only possible method, in that case a method should be developed to employ a close-cycle system where the acid reactant is recycled continuously. Lower grade ores mean acid consumption grows proportionally to the ore grade, in the absence of an effect regeneration scheme, it is economically absurd. In our opinion, in light of the ability to regenerate the sulfur/nitric and carbon dioxide use in nickel extraction, it makes little sense to pursue centrifugation. Efforts have been made to extract nickel from ultramafic rocks, for example the Chinese patent CN102517445A Method for extracting minerals from olivine-serpentine ore deals with a acid leach method, and another Chinese patent CN1972870B Process for complete utilization of olivine constituents, deals with a similar method. The discussion of centrifugation below is thus merely an intellectual inquiry. Such a scheme could operate at the expense of energy alone, namely comminution and crushing. Sulfuric acid does not react with silica, silica only reacts with bases, being acidic, it does not react with an acid. Thus only the magnesium oxide will react with the acid, along with the trace metals. When magnesium oxide reacts with sulfuric acid, it yields magnesium sulfate. Magnesium sulfate can then be reacted with water to yield brucite (magnesium hydroxide) and sulfuric acid in the following reaction MgSO4 + 2H2O → Mg(OH)2 + H2SO4. Sulfuric acid will first react with magnesium carbonate according to the following reaction: MgCO3 + H2SO4 → MgSO4 + CO2 + H2O. The rest of the metal oxides, if one excludes silica which is inert, are negligible by mass so might as well be ignored for the sake of this analysis. In the case of nickel minerals, sulfuric acid will react with the nickel to produce a nickel sulfide compound which can then be decomposed to liberate the sulfur and pure nickel oxide. In a perfect cycle, all the sulfur can be recovered reducing the cost of the acid procurement, sulfur costs $183/ton to purchase in bulk so it must be procured each time, the cost per kg of nickel would be exceedingly high in the absence of recovery. Sulfur is not a widely abundant element, occurring in the crust at a concentration of only 350 mg/kg. It must be remembered that these are chemical, there is no destruction of matter, only rearrangement, this is something Lavoisier knew in the 18th century! Carbon dioxide can be used to carbonate the magnesium, increasing the nickel extraction yield. The paper Nickel Extraction from Olivine: Effect of Carbonation Pre-Treatment, by Rafael M. Santos, suggests that with carbonation of the ultramafic rock (olivine), nickel yields of over 90% can be achieved with nitric acid and a particle size of 35 microns.
Sulfuric acid is not the only acid that can be used, nitric or hydrochloric acid could be used as well, but in the case of nitric, its inability to be easily regenerated hampers its use As long as the temperatures are not brought high enough to catalyze the decomposition of the nitrogen oxide bond, nitric acid can be recovered. Upon reacting with nitric acid, magnesium turns to magnesium nitrate via the following reaction: MgO + 2 HNO3 → Mg(NO3)2 + H2O. The magnesium nitrate can then be decomposed upon reacting with water to form magnesium oxide yielding nitrogen dioxide and oxygen in the following reaction: Mg(NO3)2 → MgO + NO2 + O2. Iron oxide will be attacked by nitric acid and form ferric nitrate via the reaction: Fe2O3 + 6HNO3 → 2 Fe(NO3)3 + 3H2O. Ferric nitrate can then be decomposed to yield iron oxide and nitric acid: Fe(NO3)3 + 3H2O → Fe(OH)3 + 3HNO3. Iron(III) oxide-hydroxide (Fe(OH)3) will then decompose into iron oxide and water: 2 Fe(OH)3 → Fe2O3 + 3H2O. The above reaction suggests half of the nitric acid is destroyed, prompting the use of sulfuric acid instead since sulfur is easily converted back to sulfuric acid through its own combustion with air and water using a simple vanadium oxide catalyst, so called “wet sulfuric acid process”. Upon reacting with sulfuric acid, iron oxide forms a sulfate salt: Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O. This iron sulfate then reacts with water to yield ferrous hydroxide: FeSO4 + 2 H2O → Fe(OH)2 + H2SO4. Ferrous hydroxide then reacts with water to yield magnetite and hydrogen via the Schikorr reaction: 3 Fe(OH)2 → Fe3O4 + H2 + 2 H2O. None of the elemental sulfur is lost, but much of the acid itself is decomposed into via these oxide-salt-oxide reactions. These reaction pathways are very elegant, the salts selectively strip oxides into their own salts and back, allowing very efficient separation provided the operation features an in-house sulfuric acid reactor to operate closed-loop. The catalyst for sulfuric acid production is 6-8% wt. vanadium pentoxide supported on diatomaceous earth. Catalyst consumption is around 0.26 kg V2O5/ton-H2SO4/yr. In the case of hydrochloric acid, the reaction is: MgCO3 + 2HCl → MgCl2 + CO2 + H2O. The magnesium chlorides then reacts with water yielding magnesium hydroxide: MgCl2 + 2H2O → Mg(OH)2 + 2HCl. No hydrogen is lost in the magnesium reaction. The magnesium hydroxide then liberates water and yields magnesium oxide Mg(OH)2 → MgO + H2O. In the above reaction pathway, there has been no oxidization of hydrogen. In the case of iron oxide, the reaction is: Fe2O3 + 6 HCl → 2 FeCl3 + 3 H2O. The ferric chloride then reacts with water to yield iron hydroxide: 2 FeCl3 + 6 H2O → 2 Fe(OH)3 + 3 H2 + 3 Cl2. The iron hydroxide then decomposes: 2Fe(OH)3 → Fe2O3 + 3H2O. Half of the hydrochloric acid is lost, requiring newly produced hydrogen to regenerate the chlorine. Hydrochloric acid 1300 is times more powerful than sulfuric acid on the acid dissociation constant (Ka) scale. Hydrochloric acid can be regenerated using sulfuric acid via the following reaction: 2Cl + H2SO4 → 2HCl + SO4.
In contrast to sulfuric acid, nitric acid must be produced from fixed nitrogen, an energetically intensive pathway. The attractiveness of acid leaching is that the acid reacts with only one element at a time, it does not form “intermediate compounds”, for example “magnesium-nickel sulfate”, such a compound is not stable or energetically favored. For example, let’s say one dissolves iron in a strong acid, the acid will form a salt of the iron and leave a residue of carbon. To the result of acid leaching is streams of separate metal “salts”, while still oxidized, are distinct compounds capable of being precipitated. Nickel and magnesium can only form a compound in the host rock crystal. For example, in our case, the sulfuric or nitric acid will attack the chemical bond between nickel and magnesium within the ultramafic rock, namely (liebenbergite Ni,Mg2SiO4), and form separate compounds of nickel sulfide or nickel nitrate. The tiny dimensions of the comminuted particles generates large surfaces areas for the acid to attack these chemical bonds. The reactors are usually operated at considerable pressure to intensify these reactions. Acid leaching can thus be thought of as a process of splitting the chemical bonds of the ore to yield distinct separable metal compounds. Once these distinct metal compounds are separated and their acids removed and return to their original oxides, reduction can begun and the only the desired metal is reduced, leaving the iron, magnesium, aluminum as oxides. These oxides can then be sold or used elsewhere.
The carbon dioxide used to carbonate the magnesium oxide, which comprises 48% of the rock (silica does not react with CO2), can be released upon heating. MgCO3 → MgO + CO 2 (ΔH = +118 kJ/mol), the decomposition temperature is 350°C. The reaction is exothermic so heat is not needed. In theory, with acid separation and a complete or close to complete recycling of the sulfur, a nickel cost of the base crushing and ore extraction cost can be achieved. If 3.5 kg of valuable transition metals are yielded per ton, as long as the ore processing cost do not exceed $10 per ton, the nickel cost is only $2.85. It is uncertain whether centrifugation can compete with an optimized closed-cycle acid leaching method. We can roughly calculate the cost of ore extraction using a moderate depth open-bit mining strategy. The cost of rock extraction is principally found as fuel, operator wages, and equipment amortization. Comminution CAPEX costs are exceedingly low, for example, a one ton per hour 35 micron Raymond mill costs only $22,000, or $0.16/ton over a 15 year amortization time.
Blasting costs are virtually nothing, one kg of ammonium nitrate can yield 10 tons of rock (Geology for Civil Engineers By C. Gribble, A. McLean, 2017 pp 239). Since ammonium nitrate costs around $500/ton, this is less than 5 cents per ton of rock liberated. Excavation and transportation are more variable and difficult to calculate, since they depend on geography, distance, and terrain. Taking a more small-scale example since this is our ideal customer base, a typical 50 ton excavator (i,e Caterpillar 345) has a cycle time of around 18 seconds, with a bucket volume of 2.45 m3 and a rock density of 50% of original (due to large void volume), the hourly tonnage processed is 734 tons. The fuel consumption of the excavator is 27 kg/hr, or around $33/hr, or $0.05/ton. The operator wage is $23.2/hr or $0.03/ton. (https://www.bls.gov/ooh/construction-and-extraction/construction-equipment-operators.htm). The rock density assumes a mean fragment size from rock blasting of around 150mm and an ultramafic rock density of 2.82 to 3.3 g/cm3. (U.S. Geological Survey Bulletin, Volume 2044 pp 10, Measurement of Size Distribution of Blasted Rock Using Digital Image Processing, Siddiqui et al). In short, the bulk of the cost is expected to lie in the reactor vessel for carbonation, the sulfuric acid regeneration, and component replacement due to corrosion form the acidic substances. The cost of ore processing is virtually nothing if minimal transportation is performed, on the other hand, if large distances must be traveled, it becomes uneconomic. Therefore, it is essential the processing take place close to the ultramafic deposits. The lifespan of the reactor is assumed to be 10 years. Below is a map of global ultramafic rock deposits, notice the U.S Appalachian mountain, it has been known for a long time that the Appalachian mountains contain rich deposit of ultramafic rocks. The Piedmont plateau covers 210,000 km2 and consists of a deep layer of oceanic crust below the Appalachian mountain range, (Ultramafic Rocks of the Appalachian Piedmont, Steven K. Mittwede). From a mining perspective, this site is ideal since most of the land is privately owned and can be mined on a small scale without multi-decade environmental approval. Christophe Pochari Engineering strongly believes in Rudolf Diesel’s idea of “Solidarismus”, a political philosophy favoring small scale, decentralized independent producers and craftsman free from the exploitation of monopolist corporate entities, (Solidarismus: Natürliche wirtschaftliche Erlösung des Menschen, Solidarity: Natural economic salvation of man, Rudolf Diesel, 1903). By allowing the extraction of these valuable materials from more abundant and widely distributed rocks, manufactures can bypass the markup charged by the monopoly held by multinational mining companies who must constantly generate large returns to shareholders. For example, if we look at the Rio Tinto stock, we find a net profit margin of 30%! Fortescue Metal Group boasts a net profit of 36%! A healthy competitive industry should not feature net margins above 5%, much work needs to be done to lower these obscene profit margins so that manufactures can access the materials they need for the cost of actually producing them, not to make ticker symbols on trading floors.
The resource potential of this region is virtually unlimited.
The vast majority of land owned by the federal government is virtually worthless desert. A few national parks in Appalachia belong to federal lands, but the bulk of the Piedmont plateau is private hands, with relatively low land-costs and low population density. Using Zillow, Landwatch, and other websites, we have estimated land costs in the region, most large plots seem to sell for $2500-5000/acre. For a hypothetical 800 acre site (3.25 km2), if excavation takes place at a depth of 100 meters excluding the sedimentary layer, a total of 9 × 108 tons of rock could be generated. Assuming only 15% is actually ultramafic, the potential nickel, chromium and cobalt yield would be 472,500 tons, worth approximately 7 billion USD at current market prices assuming an average sale price of $15000, since not all of it is nickel, around half is chromium which is only worth $10/kg. So evidently land costs place a very small role in the cost of mining. California also possesses some very interesting ultramafic geologies, predominantly in the Northerly Coast. Unfortunately for California, most of the ultramafic deposits appear to fall right into federal land, so mining will never happen, and if it does, it will be hoarded by greedy mining companies!
Reactor design considerations for the sulfuric/nitric ultramafic leaching system
In the regenerated sulfuric process, a corrosion resistant reactor is filled with comminuted ultramafic rock powder, the reactor is filled with CO2 and carbonated if hydrochloric or nitric acid is used. Once carbonation is performed, the reactor is filled with sulfuric acid. The purpose behind carbonation is the selective removal of magnesia (nickel bearing) from the inert silica. This allows the sulfuric acid to preferentially target the acid since more of the nickel bearing mineral is exposed. Designing a non-glass coated reactor to be handle sulfuric acid, hydrochloric, or nitric acid, is indeed challenging. Most alloys are intensely attacked by this acid, tantalum and Hastelloy provide the best protection. The reactor serves two purposes. First, it is used to introduce carbon dioxide pressurized to 30 bar or more to strip much of the magnesium from the silica and generate a high surface area magnesium carbonate mineral that can be more effectively leached by acid. Secondly, the reactor vessel must then be able to withstand the highly corrosive sulfuric acid bath that will be pressurized to the same 30 bar. The residence time of the carbonation and acid leaching may be several hours or more per batch. The reactor cost is around $2500-3000/m3 depending on size, that is a 30 cubic meter reactor sells for $76,000 (Weihai Huixin Chemical Machinery Co.,Ltd). The leaching and carbonation period is set at 12 hours, so assuming the reactor contents an 80% slurry content at a density of 2000 kg/m3, it will yield 2920 kg of metal annually, resulting in a reactor CAPEX cost of only $0.885/kg-metal assuming the lifespan of the reactor is 10 years.
Returning to the possibility of centrifugation, in the event acid leaching employing a closed-cycle for recovering the sulfur is not viable whatever reason (unlikely), we may be able to extract nickel by density-gradient centrifugation. Most of the article deals with this method since it is “new” and worth investigating. It should be emphasized that regenerated sulfuric acid leaching is a very simple and very crude technology, dating back centuries to the days of alchemy. Centrifuge is a “high-tech” and one could say “exotic” method, and while unproven, has the upside of being extremely clean and easily down-scaled. But it’s not without its downsides, leaving aside fundamentally feasibility concerns, the cost of carbon fiber centrifuges, high speed bearing, motors, vibrational issues, sieves, etc, the cost may not competitive with regenerated acid leaching.
Liberation of minerals from gangue is predicated on the assumption that the mineral occurs as discrete pockets or parcels within the host. The principle behind liberation through comminution relies on the difference between the mean size of the discrete mineral pocket and the mean size of the final comminuted particle. If the size of the mineral pocket is greater than the size of the comminuted particle, then by definition comminution will possess either a larger or greater fraction of the mineral pocket. On the other hand, if the element desired is entirely diffused atom by atom in every 100 atoms of the host oxide, then by definition it is physically impossible to separate the material in question from the host rock, because no matter how small the particle is, the mineral can never be concentrated. But evidence suggests few elements are distributed atomically this way, most form isolated mineral formulations that are disparate from the host mineral as veins or tiny aggregates within the “mother” crystal. Liberation through comminution represents the basis of modern mining technology. In our case, the method proposed here relies even more heavily on very fine comminution to liberate nickel-rich particles that are conducive to centrifugal separation. Below are some schematics to illustrate the principle of mineral liberation with comminution. Comminution energies as high as 200 kWh/ton of rock are tolerable for the economic production of nickel, chromium, and cobalt from ultramafic rock. 200 kWh/ton is roughly equivalent to a minuscule 5-micron particle size.
The word metal derives from the Greek word “metallon”, which meant “mine or “quarry”. Mining is mankind’s oldest industry after agriculture. Entire historical epochs were named after metals or alloys of metals, a testament to the immense role they played in these early settled civilizations. The mining profession as we know it began on a large scale in Bohemia (today known as Czechoslovakia) in the 16th century. The town of St. Joachimsthal/Jáchymov operated very productive silver mining operations generating great wealth for their prospectors. Georgius Agricola wrote the world’s authoritative book on the subject. De re metallica (On the nature of metals) was published a year after Agricola died in 1556. The knowledge he accrued in this book still forms the basis of modern metallurgical technique and mining. The foundation of modern civilization lies in the efficient and cost effective extraction of materially useful elements from the crust, principally metals but also metalloids, which allows for the construction of virtually every heavily-loaded precisely manufactured component in use today. Without metals, man would evidently still be living in the “stone” age, forced to construct everything around him with wood or brittle stones. Metals are also useful as catalysts, catalyzing essential chemical reactions for hundreds of different compounds. The role of metal is so deeply cemented in modern civilization that one could argue we still live in the “metallurgical age” which started sometime in the 18th century. Metallurgy made the jet engine possible, and in some way or another facilitates virtually every high-tech process known to man. The only engineer to ever be elected U.S president was a mining expert.
But over the course of the global expansion of techno-civilization in the past century, many of the more useful elements which are not copiously distributed have been depleted. While civilization has not even begun to deplete these elements as the share of the earth’s gigantic crust, it has quite severely in the form of highly concentrated ores. Most conventional mining restricts itself to a select few highly propitious formations, which due to sheer luck, host large concentrations of the desired elements. In light of this, a number of technically dubious mining ideas have been proposed recently. The first of these ideas involves mining the seabed for manganese nodules, which contain substantial nickel and cobalt. The second is perhaps so preposterous as to not warrant mentioning but we feel the need to because some credible individuals continue to give it credence. This preposterous idea is to “mine” asteroids using probes that will somehow grapple onto these massive rocks darting through space at phenomenal speeds. Somehow, their advocates claim, these little probes will take off and make their way back to earth carrying platinum and iridium! It is obvious that the latter idea is fiction and can be rightly ignored. But the former is not really preposterous at all, and is indeed technically possible with current technology, but the deeper question pertains to its practicality and whether it would actually produce lower cost metals. It seems only obvious to mine the 75% of the earth that is submerged in water. After all, if we assume the current reserves on earth are equally represented in the oceanic crust (they are likely overrepresented due to the oceanic crust being more mafic), we can assume a 4-fold increase in available supplies if the seabed were mined. But the situation is perhaps less exciting than it seems due to a number of technical limitations. Reliable machinery must be developed to both excavate, consolidate, and transport this rock to a surface vessel. The expense of constructing these machines for hyperbaric environments including the corrosion, degradation, and their total reliance on remote control, is yet to be proven. Any breakdown or the rupturing of even a single hydraulic hose will require the machine to be lifted as much a few thousand meters to the surface to be repaired. Any operator of heavy earth moving equipment will attest to their maintenance intensity and proneness to breakdown. Without personnel to attend to these machines, it is not certain that automation alone can perform the critical coordination functions required for them to operate effectively. Very heavy winches will be required on the vessels to lift this ore to the surface, requiring specialized vessels. Although this criticisms is valid, surely many believed it impossible to extract oil from the deep oceans when the idea was first proposed in the 1940s. But while this is surely true, there is a notable difference. Oil occurs in concentrated pockets or reservoirs that are easily tapped and drained once a hole is drilled, metals occurs as sparsely distributed oxides in the host rock, requiring large amounts of material to be processed underwater, while for oil rigs, the bulk of the work is done in the safety and comfort of the floating rig. This is a major difference and has pronounced implications for seabed mining. Moreover, while strictly non-technical, international waters are an inherently nebulous and contested concept, so only major nation-states will have the ability to carry out these endeavors, almost certainly leading to gigantic monopolies no better than current mining which offers no benefit to users of the material. Additionally, once the “low hanging fruit”, namely the shallow seabed packed with these nodules is scraped clean, deeper inhospitable waters will need to be trekked, which is beyond the capabilities of present technogenic civilization. Smaller private companies will likely be left out and the fruits of these seabed elements will be hogged by states and large corporations, providing little tangible economic benefit to most users of these metals. We can thus conclude that these current alternative mining ideas are unlikely to transpire anytime soon leaving improved methods of “terrestrial mining” as the only plausible candidate. Christophe Pochari Energy Engineering has proposed a very modest and technically conservative solution. Rather than engage in highly technically daunting schemes, we can simply turn our eyes to the massive ultramafic rock reserves that sit beneath our feet. Current nickel mining companies harvest ores with 1% Ni content, considering ultramafic rock contains 0.2% Ni, it is not outlandish to propose mining these ores, since after, it is only a 5-fold increase in material processing required. A 0.2% concentration is not exactly like proposing to extract uranium from seawater which occurs at an infinitesimally small concentration of 3.3 parts per billion! Imagine the amount of brine that must be processed to produce a ton of uranium? If more effective non-chemical and thermal methods of separating the metal oxides from the host silicate and magnesia are developed, this increase in material volume adds surprisingly little cost to the final product. Better yet, since ultramafic rocks occur quite copiously across the earth, plots of land can be purchased allowing small companies to mine them, without the bothersome regulatory issues faced by large scale mines. In essence, we have proposed to use ultra-high g gravity separation to dramatically reduce energy consumption, paired with efficient comminution and particle-size filtration, we can afford to process five fold more rock, especially with low-cost solar energy at the source.
The significance of nickel
While a truly rigorous analysis would include chromium and cobalt (the two other extractable elements found within ultramafic rock), for this study we briefly look at nickel as the sole element of interest. Nickel is an indispensable alloying agent for high-strength corrosion-resistant steels, a catalyst for hydrogen production, and as a cathode for batteries. If hydrogen production is to significantly grow to replace hydrocarbons via ammonia, a large expansion of alkaline electrolysis will be required. Alkaline electrolyzers use nearly pure nickel anodes, with current densities of only <0.2 watts/cm2, nickel loadings of up to 8 kg/kW are common. For example, if the entirety of present ammonia production were to be replaced with electrolyzed hydrogen, a total of 40,000 MW of electrolyzer capacity would be needed, totaling 320,000 tons of nickel alone. Some may view this as a small number compared to global nickel production of 2.2 million tons, but such an increase in demand will place considerable strain on existing mines sending the price soaring, in turn making these electrolyzers uneconomic and forcing less active substitute catalysts. Moreover, ammonia production is not the only sector that will need hydrogen, much of commercial transportation, if it is to become hydrocarbon-free, will need energy-dense chemical fuels like ammonia. Presently, 69% of nickel consumption goes to stainless steel, batteries 13%, and superalloys (Inconel, Incoloy, Hastelloy) 7%, with the balance electroplating.
The principal motivation of this study was Christophe Pochari Engineering’s keen interest in ultra-high strength nickel cobalt alloys for high ductility, high strength, yet machinable components. It has been shown that an alloy of equal molar ratios of nickel, chromium, cobalt, and nickel with small amounts of silicon achieves 1000 MPa tensile strength and 500 MPa yield strength while boasting unprecedented ductility and fracture toughness. Such a metal is ideal for high-fatigue components. (Novel Si-added CrCoNi medium entropy alloys achieving the breakthrough of strength-ductility trade-off, Chang et al 2021). Additionally, conventional high strength steel alloys like 40Ni2Cr1Mo28 can have their molybdenum replaced with cobalt, these alloys typically have at least 1.6% nickel, 0.9% chromium, and 0.3% molybdenum. But with existing nickel costs, these alloys are somewhat too expensive for liberal use. A molybdenum free nickel-cobalt-chromium ferrous alloy is the ideal future material for highly loaded components. Unfortunately, these three metals are presently too expensive for widespread use in a wind turbines. But unlike carbon fiber whose cost is dominated by production technologies, these three elements are by no means scarce in the true sense of the definition. With more intelligent operations and the breaking of the monopoly of existing mines, the production of these three elements becomes almost unlimited and at a fraction of the current cost. Metal costs have been escalating recently due not only to growing demand primarily from Asia, but a disturbing trend of regulatory smothering and a veritable “war on mining”. While this term is perhaps a bit too extreme, the realities on the ground testify to this problem. In 1983, there were 940 metal mines operating in the U.S, today the number is only 270. Many may argue this is due to a decline in silver mines in Nevada, and while this is probably true, there still has been a decline in U.S mining activity overall. This disturbing situation has led many Western countries to become heavily dependent on China, Russia, and many other countries, for its critical metal needs. Environmental activists, unresponsive federal lease programs, long approval times etc, make it difficult for new mines to be opened in the West, so vast resource deposits hiding beneath our feet are squandered. To fill the gap, expensive imports from Asia are used to fill the gap. https://www.texaspolicy.com/how-environmentalists-are-making-it-harder-to-produce-the-green-energy-they-claim-to-love/
Alternatives to either ocean floor mining and centrifugation of ultramafic rocks do exist, and that is “phytomining” or “agromining”. Ultramafic rock can be crushed and artificial serpentine soils can be produced to grow nickel hyperaccumulator plants in green-houses that mimic the optimal climate that fosters growth of the assorted 450 nickel hyperaccumulator plants known to exist. Pycnandra acuminata is known to excrete green resin in New Caledonia, this green resin is rich in nickel oxide. A protein coded in the “ZIP gene” appears to facilitate extremely high uptake of nickel and other heavy metals in these plants. Thlaspi cypricum, 52120 mg/kg, Thlaspi oxyceras, 35600 mg/kg, Peltaria emarginata, 34400 mg/kg, Bornmuellaria tymphea, 31200 mg/kg, Thlaspi sylvium, 31000 mg/kg, Alyssum argenteum, 29400 mg/kg, Thlaspi jaubertii, 26900 mg/kg, Alyssum masmenkaeum, 24300 mg/kg, Alyssum cypricum, 23600 mg/kg, Alyssum lesbiacum, 22400 mg/kg, Alyssum pterocarpum, 22200 mg/kg, Stackhousia tryonii, 21,500 mg/kg, and Bornmuellaria baldacii, 21300 mg/kg. The mg/kg number refers to the concentration of nickel in the plant’s leaves, chloroplast, and stem. By increasing CO2 concentrations in a greenhouse, plant growth can be rapidly accelerated. Regions where land costs are cheap can be employed. If it proves too difficult to sufficiently enrich nickel using centrifuges, we can instead turn to agromining using greenhouses as a way to produce nickel for a fraction of its current cost. Growing lettuce in vertical farms requires around 2000 kWh/m2/yr, so if we had to provide artificial light to grow nickel hyperaccumulators vertically, 1,380,000 kWh/kg of nickel would have to be expended on LED lighting. Thus it is impossible to increase the production density of agromining, so a method must be developed to utilize low cost land. Agromining using the best nickel accumulators typically yields relatively small amounts of nickel per hectare, around 100 kg or less annually. Although experimental efforts suggest yields up to 300 kg per hectare are possible in tropical regions.
“Early results from the pot trial suggest that a Ni yield of 200–300 kg/ha can be achieved under appropriate agronomic systems—the highest so far achieved with agromining, which is indicative of the hitherto untapped metal resources in tropical regions”. Agromining: Farming for Metals. Extracting Unconventional Resources Using Plants, Alan J.M. Baker, Antony van der Ent, Guillaume Echevarria, Jean Louis Morel, Marie-Odile Simonnot.
To produce 2 million tons of nickel annually assuming 150 kg/hectare, 1.33 million square kilometers would be needed, or 13.5% of the total U.S landmass. The average cost of land in the U.S is $4000/acre, one acre is 0.40 hectare, so the economics as far as land are definitely viable, but not stellar. Desert regions where land costs are only $500/acre could be used provided water can be produced. When fertilizer and greenhouse costs are taken into account, agromining may not seem terribly competitive, but it is a potentially more mature option than centrifugation since there is no technical risk, but it cannot scale or lower the cost much below the current spot price. But we can confidently conclude that once the basic operational efficacy of centrifugal separation of nickel bearing minerals from ultramafic with fine comminution is proven, it will be the only way other than re-generated sulfuric leaching to expand nickel production or to lower its cost. If these methods should fail for whichever reason, human civilization will remain metallurgically constrained for millennia to come.
It is important to state that even in the event that mining the lower concentration ultramafic rock for nickel is not desirable, this comminution-centrifugation-sifting technology can still be used very effectively by small companies to directly extract nickel oxide from existing laterite ores without the use of any acid or floatation agents. Centrifugation technology is inherently more small-scale friendly, all one would need is to produce the raw laterite ore in bulk and simply install a comminutor, centrifuge, and sifting machine at the factory, to satisfy all the nickel needs for stainless steel production. Such a scheme would eliminate the need for the complex equipment needed at present nickel processing facilities, such as rotary kilns. There exists massive reserves, likely hundreds of years of laterite ore with concentrations between 0.5-1.5% that have relatively low market value, around a a third of the retail price of nickel metal. Laterite ores containing a high concentration of garnierite can be bought cheaply for <$150/ton and processed indigenously allowing for a non-trivial cost reduction since expensive acid and pyrometallurgical techniques are not needed. The cost of the ore has surprisingly small effect on the price of the final product, nickel’s selling price of $26000 is much higher than the ore equivalent of around $10,000/ton. This can be explained by the high cost of acid leaching or floatation. If we are ever to markedly increase the global availability of nickel, we must develop a method that can separate the ore via other less chemically intensive methods. To extract nickel from an ore, excluding the floatation process, acids of sulfur or nitrogen oxides must be used to leach the metals from the rock. Consumption of acid may reach 1-1.5 tons/ton of ore, since most of the acid is consumed leaching the iron, magnesium and aluminum. If the acid cost is $200/ton, the cost per kg of nickel may reach $20/kg for the acid alone for a 1% Ni ore grade if it is not recycled in a closed-loop. This clearly shows that it is economically impossible to extract nickel from ultramafic rock at 0.2% concentrations without a closed-loop sulfuric acid system.
But provided sufficient comminution and particle size homogeneity can be achieved, gravitation through centrifugation emerges as an interesting option if acid regeneration cannot be performed. Christophe Pochari Engineering employs a strategy of optionality to reduce risk.
“The application of centrifugal force in separating immiscible liquids or separating solids from liquids is well established, and there is abundant literature on the subject. Outside of patent records, however, there is practically no literature dealing with the principles that relate to the centrifugal separation of solid particles having different densities”.
Centrifugal Concentration: its Theory, Mechanical Development and Experimental Results, January 1, 1929, H. A. Doerner.
Christophe Pochari Engineering has applied a physics and fluid mechanics based approach to the problem of critical metal depletion. By using ultra-high G force centrifugation, widely distributed ultramafic rocks (dunites, peridotites, pyroxenites, troctolite), can be mined for trillions worth of nickel and chromium. These respective transition metal oxides could be separated from their light silica and magnesia hosts using proven centrifugation technology.
Images below show the occurrence of ultramafic rock in various geological bodies and the concentration of nickel and chromium.
The idea that some essential technogenic elements, such as nickel, chromium, or even cobalt, are scarce, is theoretically incorrect if lower grade rocks can be harvested. Of course, not all elements are equally abundant, stellar nucleosynthesis, cosmic ray spallation, and beta decay did not result in equal distributions of the elements, no sound person would claim platinum is abundant! Different ionization potentials resulted in elemental segregation during the formation of the earth in the protoplanetary (accretion) disk. Many elements farther up the atomic weight scale are truly scarce and can never be made more abundant with technology, but many could, and the ones that can happen to the most valuable for technical alloys. To argue that ultramafic rock, which contains an average of 0.2% nickel, cannot be “economically” is guaranteed to be true. As technology evolves, the concept of an ore grade “cut-off” becomes nebulous. A mine is a perfect monopoly, one cannot “start” a new mine because by definition they are not created but rather discovered in rare and highly propitious mineral concentration sites. The price of a mine can reach billions, making it impossible for small players to compete. But with a combination of technology and ingenuity, small companies can mine the unlimited supply of ultramafic rocks for nickel, chromium, and cobalt from the oceanic crust that made its way onto continents. There are an estimated 90 teratonnes (90 trillion metric tons) of ultramafic rock easily extractable in ophiolite mountain belts (The variation in composition of ultramafic rocks and the effect on their suitability for carbon dioxide sequestration by mineralization following acid leaching, M. T. Styles). Once the oxide is crushed down to small fragments using advanced comminution machines, the metals of interest are liberated since the desired metal are chalcophiles and siderophiles, while the base metals (silicon and magnesium) are not. High-speed centrifugal separation in a gaseous or liquid medium permits rapid agglomeration of high-mass micron-size particles on the walls of the centrifuge allowing for effective separation after multiple stages. The energy needed to spin these centrifuges is very small. Once the iron oxide is removed, the only heavy elements left are nickel, chromium, and cobalt. By mixing the micron size particles in a gaseous or liquid media, they are free to float due to the high frictional resistance, even small differences in settling velocity both horizontally due to gravity or laterally due to artificial acceleration will cause gravity-determined sorting. The rate at which these particles propagate is a function of Stokes’s law, which is used to predict the terminal velocity of spherical particles in a viscous media at a low Reynolds number. If the particle density difference is 1.2x, the terminal velocity, regardless of g forces applied, fluid viscosity and particle size, will always differ by exactly 1.2x. To maximize the throughput of the centrifuge, we want a medium viscosity as low as possible. If water is used over gases, the water can be pressurized to 25 bar and warmed to 220°C to lower its viscosity from 1 centipoises to 0.14, but a gas would be far superior. The terminal velocity difference of the micron fragments suspended in water with a viscosity of 0.14 cP and liquid density of 870 kg/m3 under an acceleration of 400,000 g (60,000 rpm, 200mm diameter centrifuge) would be 6650 m/s. Such a high velocity difference results in rapid sedimentation. Using a lower viscosity medium the velocity differences between the different mass particles is 18,500 m/s. During each centrifugation cycle, the slightly heavier fraction deposits on the wall, the reactor is then purged and this heavier deposit is re-fed into the centrifuge, a staged system will experience progressively higher separation until concentrations of 90% are reached, which allows reduction operations to begin. Before this mixture of metallic oxides are reduced, it is desirable to remove the iron magnetically since we do not want to expend excessive amounts of hydrogen producing iron. If magnetic separation is undesirable, they can be separated by precisely adjusting the melt temperature to precipitate each metal.
Just because the existing mining industry ignores this immense potential reserve because their current assumption forbids them from extracting “low-grade reserves”, not mean that it is not technically possible according to physics, whether this is acid leaching with regenerated sulfuric acid or through centrifugation. The ore is not crushed to micron sizes making centrifugal separation impractical. Micron-sized comminution is not considered “cost-effective” presently, but if one performs a basic energetic analysis using the Rittinger curve, one can easily see that it is.
With Raymond mills, crushing energies of around 25 kWh/ton are required. Note that the hardness of the brittle oxide makes very little difference on the energy consumption, so the numbers above for calcium carbonate are not increased very much for magnesium oxide or silica. As previously mentioned, ultramafic rock reserves have been estimated to be over 90 terratonnes of readily accessible deposits at shallow depths, but the real reserves are much larger because excavation can be performed to greater depths. The concentration of ultramafic rock in the upper continental crust is estimated to be 5%, the theoretical reserves are thus so huge a calculation is redundant since industrial civilization would not been able to utilize such a quantity of material nor possess the necessary excavation abilities. Taking the 90 terratonnes estimated, if we assume the nickel content of ultramafic rock is only 1500 mg/kg (the actual number is 2000, so we are being conservative), then the total reserves of nickel in this magnesia-rich rock is 135 billion tons, or equal to 67,500 years at current nickel consumption rates of 2 million tons per year. It would be a great tragedy if we failed to harness this untold fortune. If we manage to develop such a methodology, we could increase nickel consumption by over a thousandfold and replace much of the present low-grade steels with nickel and chromium alloys like stainless steel or Inconel. The implications for this centrifugal low grade ore extraction technology are immense, by making nickel not only much cheaper but close to infinitely available, structures could be left unpainted in corrosive environments, bridges, skyscrapers, and most terrestrial structures including residential homes could be constructed entirely of stainless steel. Without engaging in fantastical speculation, one could imagine large permanent ocean settlements or perhaps highways constructed over large bodies of water, connecting the continents. Offshore structures allowing for sea-steading communities now become possible since their cost would be competitive with land-based structures, allowing the formation of private libertarian states in international waters. Vehicles, including tractors, trucks, cars earthmoving equipment, could improve durability and corrosion resistance thanks to stainless steel’s extremely high ductility. Ships could be constructed entirely out of stainless steel and last for centuries, the painting of ships would become entirely redundant. But beyond mere speculation, what can be said is that with the techno-economics of centrifugal ultramafic rock powder separation, nickel production can satisfy current global production for millennia to come at a cost not much higher than aluminum.
Centrifugal separation is a proven technology and the physics behind it are very intuitive, but success is dependent on the ability to liberate nickel minerals from the host silicate and magnesia
Centrifugal separation conjures up images of gigantic farms of vertical tubes spinning at high speed to produce highly enriched uranium for fission bombs, but the principle of centrifugal separation is applied in a number of disparate domains. Zippe style centrifuges, invented by Gernot Zippe, used in uranium enrichment for both nuclear weapons manufacturing and civilization nuclear power, spin at speeds up to 90,000 rpm. Separative work increases with the 4th power of peripheral velocity. By doubling the speed of the centrifuge, the intensity of this artificial gravity grows to the square of the chosen speed, and by doubling the gravity generated, the acceleration of the mass in question grows to the square of this new gravity, so that’s how we get a 16 time increase in separative work from a doubling of the initial peripheral velocity. Spinning a large mass at high speeds requires surprisingly little energy, for example, spinning a 200mm diameter 15 kg centrifuge at 70,000 rpm uses only 1.3 kWh. If such a size centrifuge can process 1000 kg of rock per hour, the energy consumption is less than 1.3 kWh per ton of rock per stage. Assuming around 10-20 stages is needed to raise the concentration of metallic oxides from around 0.35% of the rock by mass to 90%, the energy consumption increases to only 5.6 kWh per kg of metal.
Comparison of uranium isotope separation technologies, notice that centrifugation is by far the most effective.
Proteins, blood, and serums for preparing vaccines, and even cream, are separated centrifugally relying on small mass differences (isopycnic centrifugation) to facilitate agglomeration. Such techniques are capable of separating particles with specific gravity differences as little as 0.05. But centrifugation, while not used for existing ore separation, has been successfully applied to battery recycling, proving the viability of our concept. German researchers created a small high speed 20,000 rpm centrifuge to separate lithium-iron phosphate (density of 3.57 g/cm3), from carbon black (density of 1.9 g/cm3). The same team also separated zinc oxide nanoparticles from polymer particles, although the density gradient was larger, the same principles apply. Smaller density differentials simply mean more stages, and as long as the power consumption of each centrifuge is kept low (using CFRP rotors and gas over water) we could use up to 40 stages without using excessive energy, allowing the separation of tiny mass differences, mass differences far lower than what will be encountered in the field. With the high density differences of phosphate and carbon, they achieved recovery rates of up to 90% with one stage immersed in a solvent, note that these mass differences are quite close to the silica-magnesia/nickel oxide values. Uranium in a gas form as UF6 (uranium hexafluoride) possesses a tiny mass difference of barely 0.85 percent, but with enough stages (40-90), it can almost miraculously be purified to over 90%. Note that uranium 235 and 238 have a mass difference of 1.3%, but because uranium hexafluoride is 32.4% fluorine, the difference is further “diluted” to 0.87%. Assuming roughly linear correlations between mass differences and stage count, only a few stages are required in the case of these large mass differences of nearly two-fold. The average density of magnesium-oxide and silica, which comprises 90% of the mass of ultramafic rock is 3.11 g/cm3, while in theory, nickel sulfide, nickel oxide, and chromite have an average density of 5.75 g/cm3, or a 63x greater mass difference than uranium isotopes of fluorine. Of course, in reality, nickel does not exist as a sole oxide of NiO, except in highly weathered laterite ores. It typically occurs as pentlandite (FeNi9S8) and liebenbergite (Ni,Mg2SiO4), with a specific gravity gravity of 4.6. Nickel occurs in these minerals within the host rock, pentlandite has a higher specific gravity than liebenbergite at 4.8, but still well over 1.54x times that of SiO2 and MgO alone. Cobalt occurs as the mineral Cobaltite (CoAsS), with a specific gravity of 6.33, 2.03x more than the host rock. The predominant chromium mineral is the least dense, with the mineral magnesiochromite (MgCr2O4) and ferrous chromite (FeCr2O4), with average specific gravities of 4.2 and 4.6, but still over 1.42x times. The number of centrifuge stages is reduced proportionally to the mass differences and the number of g’s generated. While some may express skepticism that uranium gas separation and solid powder separation share any commonality, the actual kinetics are very homologous. Comminuted powder is either immersed in a low-viscosity liquid or air, and as the fine rock powder sloshes around within the centrifuge, the heavier metallic oxides tend to move towards the perimeter. The concentration of powder in the liquid or gas bath is low enough so that collisions between fragments does not dramatically slow down the separation process. There is a clear trade-off between energy consumption and solid concentration, too high a solid concentration and interference between particles becomes an issue, and too low a solid concentration and excessive energy inputs are required. A a relatively low solid concentration of 5% in air is used for our models.
The above images are from a German study on recycling lithium batteries, the fundamental physics apply equally to ore separation, the only difference is that the concentrations of the heavier particles are smaller so more stages are needed. Centrifugation can apply to any physical compound that has a consistent difference in density, perhaps the only thing that cannot be gravitationally separated is plasma due to its instability.
The average concentration of nickel in ultramafic rock is usually measured to be around 2000 mg/kg, or 2 kg per ton of rock.
Current nickel mining operations make use of ores with a concentration of over 1%, or five times greater. The current justification for this strategy is that less ore needs to be processed, but the result is a much more limited reserve and a far from sustainable future supply, which risks thwarting new industrial and technological developments which heavily rely on nickel. Recycling alone cannot meet the demand of a large expansion in nickel use. Existing ores, mainly laterite and sulfide, are formed from the natural weathering of ultramafic rocks exposed in ophiolite belts, but these reserves are finite and are being rapidly drawdown, which partially explains the presently high cost of nickel. Weathering is a very slow process and technogenic extraction can rapidly deplete what took nature millions of years to achieve. For example, when nickel mining first began in New Caledonia in 1875, ore grades were over 10%, today they are barely above 1.5%. Such a strategy of picking earth’s “low-hanging fruit” is by no means sustainable, as it will force less consumption of this critical element, and in turn, lower the quality of civilization. There is no physical law that states lower grade host rocks cannot be harvested, while thermal separation is certainly energy intensive, gravitational means are not, allowing large volumes of rock to be processed without too much concern for energy consumption. If nickel atoms replace a magnesium in the crystal interstices, this particle will have more mass, this is the principle of centrifugal separation. Ultramafic rock can be crushed down to sub 40-micron size particles using only 20-40 kWh per ton of ore using advanced Raymond roller crushers. This fine dust can then be placed inside a high-speed centrifuge (spinning at 70,000 rpm to generate g forces of over 500,000), this powder when immersed in a gas or liquid will quickly segregate by mass resulting in the selective accumulation of iron, nickel, and chromium oxides on the walls of the centrifuge, while the lighter fragments of silica and magnesia will travel straight through. Once a sufficient accumulation of heavy fragments occurs on the walls of the centrifuge, the device is stopped and emptied since there is no practical way to continuously clear the buildup of heavier deposits. With theoretical centrifugal recovery rates of 90% percent, over 3.7 kg of valuable metal (excluding iron, around 9.6 kg/ton) would be produced per ton of rock, including nearly 2 kg of nickel, 1.6 kg of chromium and 0.15 kg of cobalt. These numbers are from a dataset collected in Finland (http://weppi.gtk.fi/publ/foregsatlas/text/), they do not represent selected commercial mining ores such as laterite, they are samples of regular ultramafic rock that occurs in the ophiolites of mountain belts. The Finnish dataset cites the 1970s text Review of research on modern problems in geochemistry Corporate author : International Association of Geochemistry and Cosmochemistry, Frederic R. Siegel. https://unesdoc.unesco.org/ark:/48223/pf0000037516
Ultramafic rock is simply oceanic crust (which is highly mafic) that has been pushed up below the continental crust through obduction (oceanic crust scrapped off and buried underneath the continental crust with some of it being exposed, mainly in ophiolite belts). Magma bubbles up in the oceanic ridges and spreads laterally, forming the oceanic crust. The mantle is 0.2% nickel by mass while the core is 5.3% nickel). Separating magnesium and aluminum is more difficult due to the low density difference of these oxides relative to the principal silicon oxide. Fortunately, the heavy metals we are after will produce heavier particles since a transition metal element, nickel chromium or cobalt, with atomic weights of just under 60, will replace the light magnesium and silicon atoms with the oxide.
Optimal centrifuge design, material, and operational parameters
To maximize the segregation efficiency of the different density metal oxides, we desire the highest g force practically attainable. In order to achieve very high g forces without placing excessive stress on the material, we must employ a material with very low density. Carbon fiber emerges as the obvious candidate. But an additional factor is the mass of the spinning medium inside the cylinder. The rock powder cannot be suspended in a vacuum, it will simply fall to the bottom of the centrifuge. A medium of some kind is required to suspend the solids and carry them through the centrifuge. Since the media inside the cylinder is spinning at the rotational velocity of the cylinder, it requires additional energy to rotate. Since water is very dense, the use of water requires around 3 times more energy than gas for the same g force. Therefore, a simple analysis suggests that a carbon fiber centrifuge, spinning at up to 70000 rpm, is optimal. Note that the rotational speed is decreased proportionally with an increase in centrifuge radius, so lower speed large diameter centrifuges may be optimal, making bearing design less difficult. As long as particles enjoy unencumbered mobility within the medium, different-weight particles are free to move toward the perimeter of the centrifuge due to their greater settling velocities, this is important as if the particles were too concentrated, this would impede their sorting efficiency. A low concentration, such as 5% solids in the medium, permits a large degree of mobility, preventing excessive particle collision and minimizing pressure drop of the delivery gas. Centrifuges work by spinning a mass of gas or liquid by exploiting the high skin friction between the surface of the cylinder and the medium exposed to this surface. The total skin friction encountered by a 6 kg/m3 gas along the wall of the cylinder is in excess of 400 kg at the peripheral velocities encountered. Skin friction coefficients of 0.0031 are encountered at a Reynolds number of 9 million, corresponding to the peripheral velocity of the spinning cylinder. This high skin friction experienced by the gas body within the cylinder causes it to acquire the entire velocity of the spinning cylinder, subjecting all its content to artificial gravity. For ultra-high throughput, low-viscosity gaseous media is employed at moderate pressures and low temperatures. Nitrogen gas is used at 15°C and 10 bar, with a viscosity of only 0.016 cP and a density of 12 kg/m3. The particle size is between 30 and 40 microns, or a standard mesh size of 400, but if mineral liberation is not effective enough at this size, sizes as small as 10-15 micron may be used at the expense of centrifugation throughput. By operating at low temperatures, carbon fiber can be used as the centrifuge cylinder material, reducing the power demand greatly. If water is used, it has to be heated for optimal performance which restricts the material choice to titanium, which has 2.5x the mass of carbon fiber, but only half the strength. Since air has very low density, the terminal velocity of the 35-micron particles is an extraordinary 69,000 m/s and 82,800 m/s respectively, for 3.10 and 3.72 g/cm3 oxides. While the separation efficiency never changes by definition (the mass difference is the sole determinant) the throughput per centrifuge (and hence the energy consumption) is controllable since faster settling velocities result in quicker sedimentation. A lightweight carbon fiber centrifuge can be constructed to offer spectacular efficiency. A centrifuge 200mm in diameter and 1.2 m long weighs less than 9 kg and requires only 1200 watts to spin at 70,000 rpm, generating 535,000 g. The shear stress on the rim is only 1088 MPa, well within the limit of T1100 carbon fiber with a tensile strength of over 3460 MPa. The centrifuge could be made even lighter but we are including the weight of an interior metal liner and the mounting shafts. The higher the g force the higher the gas flow rate through the cylinder and thus the higher the throughput of each centrifuge, which reduces the power used per mass of rock powder separated. If the throughput per cylinder can be brought to 1 ton of rock powder at a 5% loading factor, the pressure drop of the nitrogen at 10 bar is only 0.0018 bar per stage. From experimental data, a solids concentration of 4% at 100-micron particle size adds an additional 2.53x to the baseline pressure drop assuming a smooth pipe. We can thus calculate the gas pumping power per centrifuge. If one centrifuge processes one ton of rock, the compression power is virtually zero and not worth including in our analysis. Since 10 ten stages are assumed to be required for complete separation, the total pressure drop is barely 0.09 bar per centrifuge, this includes an additional margin for bends. Compressing 20,000 kg, (1666 m3) of air to 0.10 bar requires only 5 kWh. We can clearly show the immense techno-energetic potential of this system by simply calculating the relative electricity value of one kilogram of the metal yielded. If we use non-baseload photovoltaic energy at 3 cents/kWh, we can afford to expend 166,000 kWh/ton of metal yielded if the price is to be kept to $5/kg.
An energetic analysis for producing 10 million tons of nickel annually
Centrifugation requires around 26 kWh/kg-metal (assuming a maximum of 40 centrifuge stages assuming the worst case scenario of weak mass differences), and comminuting to 10-35 microns requires another 22.33, yielding a total of 48.33 kWh/kg-metal. To produce 1 ton of nickel, we must expend 48,000 kWh, or still less than $1440 per ton if we used photovoltaic energy, less than 5% of the current spot price. Note that with the current spot price, we could easily expend 3 time the energy and still arrive at a direct production cost of $4300/ton. The total energy consumption to produce 10 million metric tons of nickel annually is thus only 48 GW, or 0.41% of global primary energy consumption. Note that the above estimates are highly conservative, uranium isotope separation with minuscule sub 1% mass difference use only 60 stages, and we basing our numbers on 40 stages! even though the mass difference is at least 25%! We do not engage in ridiculous optimism! these numbers are extremely conservative. We are also using an aggressive number for comminution, since an average of 22 microns is substantially smaller than any current ore crushing. The use of this very small number is due to the concern that without excessive comminution, the liberation of the nickel bearing minerals from the host rock will be less efficient, resulting in small mass differences. Note that a mass difference of as low as 1% is tolerable since we can afford to use 60 stages.
Are there any technical impediments?
As we have already mention, this proposed method will only work if the nickel bearing minerals are mechanically liberated upon ultra-fine comminution to form somewhat higher density grains that can be centrifugally separated. While the theory and mathematics suggest that separation can be very effective provided there is effective liberation of the nickel bearing minerals, we do not exactly know to what extent nickel is highly diffused throughout the rock, if it so highly diffused as to produce only miniscule mass differences between one particle and another, clearly this cannot work. By tiny we mean less than the difference between U-235 and U-238. But the Goldschmidt classification insists that nickel will prefer to form compounds with either iron or sulfur, it is not a lithophilic element, so we are thus able to confidently make these claims: that assuming a minimum amount of comminution, a substantial recovery of the sidero and chalcophile elements will be possible. The fact is magnesium and silicon are highly lithophilic, and so will be almost exclusively found as silicates, with much higher reactivity, for example both silicon and magnesium cannot be reduced with hydrogen. From a purely technical and operational perspective, centrifugation and vibratory sieve separation can indeed work very effectively, so this is not where criticism is due. The fundamental uncertainty is: how effectively can fine comminution, even as fine as 10 microns, produce a high degree of isolated nickel minerals from the preponderance of light magnesia and silicates particles? Some may say: “this sounds good and all, but why hasn’t it been done before?”. Strictly speaking, it is impossible to answer such a question, if the idea in question proposed satisfies the basic mechanics, thermodynamics, or physical principles required for operation, then a technology can be called a proven theoretical concept, with the only risk being a lack of practicality, but not lack of basic functioning. Such a case study might be a flying car, it is perfectly possible to construct one using foldable propellers and micro-gas turbines, but it may not be practical or safe, therefor we do not see them used. A more serious example might be using projectile launchers to fire payloads into space, an idea proposed by Gerald Bull, while the physics is perfectly sound, its practicality compared to rockets has yet to be proven. A new invention cannot by definition have priority, so there may be a genuine chance a new idea works but has never been attempted or considered before. From this perspective, since we have ruled out fundamental operational impossibilities (being physically impossible, i,e perpetual motion machines), it is merely a matter of engineering and economics. As long as the basic physics and working principle can be conceptually evaluated and falsified with respect to a particular application, then it can be assumed the lack of adoption is due to non-technical reasons. We can answer the above question by simply resorting to reasons of industry dogmatism, conservatism, and or outright lack of inventive talent. Industries tend to become large, sclerotic, and generally self-perpetuating systems with little incentive to improve methodology unless it is forced on by competition. Most new ideas promoted today consists of highly uncertain technologies with unproven underlying physics, often with very lofty assumptions of future breakthroughs that will somehow make up for their present shortcoming. Prevailing attitudes tend to dominate and few small companies with visionary individuals offering differing methods can truly compete. As long as different mass particles can be segregated due to different settling velocities, by definition, the process can “work”, but it does not mean it is automatically rendered practical. Practical and possible are two different criteria, but in the case of rock powder separation, we know that spinning a carbon fiber tube with magnetic bearings and high speed electric motors is more than practical, it is proven and works quite well. Of course, the actual engineering details are more unpredictable in this particular application, since rock powder is different from uranium gas or separating sludge from oil. For example, abrasion of the centrifuge by the rock powder or potential vibrational concerns exist if there is an uneven accumulation of sediment along the wall of the centrifuge. But industry experience with solid liquid centrifuges find little issue with uneven solid accumulation.
The essential enabling feature of centrifugal metal extraction from rock powder
Leaving aside the known of metal diffusivity, the critical requirement that must be met for centrifugal separation of rock powder by density difference to work is very high particle size homogeneity. This requirement is unique for our methodology, conventional comminution of ores can tolerate a high degree of particle heterogeneity. The Achilles’ heel of centrifugal separation of different density particles is a lack of size homogeneity, if such a homogenization cannot be effectively achieved, the method will not work. An inherent difficulty of particle separation through gravity is that larger particles of lighter material can attain higher velocities than smaller particles of the denser material, severely hampering segregation efficacy. This becomes more severe as the density differences diminishes, and when this occurs, small difference in particle size can override the difference in settling velocity due to density. It is thus critical to prevent larger magnesia and silica particles from being drawn to the smaller heavier nickel oxide and chromium particles towards the periphery of the centrifuge. Fortunately, a technical solution exists for almost every practical problem. Numerous sectors make use of powder, ranging from baking to high end manufacturing, require highly fine materials of roughly uniform size. A number of effective separation technologies, mainly sieve based, have been developed. The highest performance is by far ultrasonic multi-stage vibratory sifter technology, which can be effectively employed to facilitate high degrees of homogenization. Ultrasonic piezo crystal vibrators are extremely effective at dislodging particles and encouraging the tumbling of particles slightly smaller than the mesh aperture. As a consequence of the intense yet small amplitude vibration afforded by the ultrasonic generator, a high throughput per mesh can be maintained. Using highly precise electroforming micro-mesh technology, a structurally robust and uniform filtration sieve can sort particles according to their sizes to extreme accuracy. These multi-stage vibratory sifters can produce batches of homogenized powder streams by employing the simple principle of successive filtration according to minimum and maximum particle diameters. These segregated and homogenized powders are then sent to a separate centrifuge array for density gradient separation. Each pair of meshes produces a homogenized powder size which is sent to dedicated centrifuges to process this material. It is inherently impossible to generate a homogenous size powder for the entire rock batch, since by definition the comminutor will generate a wide range of particle sizes in the micron range. It is the job of the ultrasonic multi-stage sifter to generate separate streams of highly uniform particle diameters by classifying the initial heterogenous stream. By employing a stack of sieves each vibrating to encourage particle tumbling, by passing the comminuted powder through two sieves, all the particles that fall through the first but do not fall past the second will have a mean size equal to the exact difference in size between the two respective meshes. It is impossible for larger particles to fall through unless they break, but the fracture toughness of the material is greater than the stresses generated during the churning of these ultra-light particles, so very little comminution takes place with vibratory sifters. The inherent springiness of the ductile electroformed nickel mesh prevents particle breaking. But even if some degree of particle crushing takes place, all particles freshly broken off will tumble through the mesh with the larger particles remaining trapped, so size segregation will still occur between two meshes. If the difference in size between the primary and secondary mesh is very small, the particles will converge toward an equilibrium of the two sizes. For example, suppose we want most particles to congregate to 44-46 micron mean size. If we employ a 46-micron mesh at the first stage, all particles smaller or just below 46 microns will tumble through. The second mesh is then set at 44 microns, all particles smaller than 44 microns will tumble through, leaving only 44-micron particles preventing smaller particles from being sent to the centrifuge even if we filtered out all the larger ones. We can then calculate the maximum tolerable difference in particle size that will still yield density segregation in the centrifuge with Stokes’s law. For hypothetical 15 micron particles, the maximum difference in particle size for effective separation is plus or minus 1.5 microns, which still generates a 600 m/s velocity difference between a 3.58 g/m3 magnesium oxide particle and a 4.6 g/cm3 mineral of the desired metal. This means any mesh stack that can maintain a sub-1.5 micron particle size difference will still result in very effective density gradient separation. Current electroforming technology can achieve tolerances of 0.1 micron, so it is well within the capabilities of modern manufacturing. Differential comminution of the transition metal bearing oxide and the silicon and magnesia oxide can influence the density-dependent particle size distribution. If the transition metal minerals are more easily crushed, they will form a smaller mean fragment size than the magnesia and silica, and vice versa.
In summary, it appears that there is no fundamental opposing technical hurdle that cannot be overcome provided micron size comminution and extremely precise filtration is achieved.