Cleanly Processing Limonite to Produce
27 Other Critical Metals,
Osmium, Copper, Silver, Gold,
and Carbon Steel
Limonite (or limonitic-laterite) is currently used to produce an intermediate (ferronickel) for stainless steel production. This is a bad use for limonite.
Limonite is also processed to produce an intermediate for battery-grade nickel production.
This is a worse use for limonite,
For example, the acid leaching methods of this processing are destructive to rain forests. This prompted this quote:
"It's hopeless. Zero chance that is going to succeed because, first of all, you are
destroying vast amounts of tropical jungle, and you have to justify that to the end-user
in Los Angeles, who watches Apple TV and HBO and realizes you are destroying that
forest. Secondly, they were going to put those tailings in the ocean, but that has been
banned, and when you have ferronickel, converting that ferronickel into nickel sulfate
and cobalt sulfate, the physics just doesn't work. The amount of energy required to get
there from here makes it completely non-viable. It's a ludicrous fiction guaranteed to
Robert Friedland — thoughts on High Pressure Acid Leaching (HPAL) of limonite in Indonesia for battery-grade nickel production, in February 21st, 2021 interview with Benchmark Mineral Intelligence. (Robert Friedland famously developed Voisey's Bay nickel mine and other mining ventures).
Limonite is widespread. Limonite is one layer-type of laterite. It is found in most tropical regions and many regions that were tropical in the distant past. Limonite is a potential source of diverse metals needed in a sustainable, technology-rich future.
Limonite should be processed with methods that turn the potential into potent reality.
Limonites in various locations contain:
Limonite in all locations contains many of the above 33 metals. Limonite always contains a lot of iron and some nickel and cobalt. Globally, limonite is a potentially abundant source for all 33 metals. Of these 33 metals, 28 are on the US Geological Survey's 2021 list of critical minerals "that are vital to the Nation's economic and national security interests."
Two Planet Steel is developing a process that should enable refining all 33 listed metals from limonite to high-purity, high-value metals or high-purity, high-value metal oxides.
This process mainly separates the iron, nickel, and some cobalt from the other minerals and metals in limonite. Also, it separates the iron, nickel, and cobalt from each other. The technical goals of our process development are to (i) speed up an established niche process (iron carbonylation) by a factor of more than 10 and (ii) separate close to 100% of the iron (derived from goethite) from everything else. These two goals are strongly correlated since speeding iron carbonylation improves the completeness of the separation of iron from everything else.
The pivotal role of the separation of iron stems from the broad facts that (A) the dominant minerals in limonite are goethite (FeO(OH)) and hydrated goethite (FeO(OH).nH2O), (B) most of the lists' other valuable metals, metal oxides, and metal oxyhydroxides are closely associated with the goethite, and (C) these other metal minerals are mainly not associated with the relatively small amounts (10—15 wt%) of siliceous material in the limonite (although magnesium, which is not on the list, is in siliceous minerals and also some of the aluminum).
This Two Planet Steel process is conceptually different from the acid leaching processes used in other hydrometallurgical processing. Acid leaching draws out some of the desired minor (but valuable) metals from the larger material bulk in the ore, where the desired metals are separated from the bulk as ions in acidic aqueous solutions. In contrast, the Two Planet Steel converts and separates out the dominant goethite mineral from the remainder.
The Two Planet Steel process is also different from the acid leaching processes in that it does not produce any acidic tailings and does not need any tailings dams, and it does not have the liabilities and disasters associated with dammed lakes of tailings, whereas acid leaching processes create problems and devastation with acidic tailings.
The Two Planet Steel process is also different from the acid leaching processes in that acid leaching can only separate out one or a few valuable metal species from the acidic bulk it leaves behind. In contrast, the residue left by the Two Planet Steel's iron separation can be post-processed using many refining techniques to separate all the listed valuable metals (except the nickel, which separates from the rest with the iron). So, the Two Planet Steel process has a significantly longer value chain than the processes using acid leaching.
The main fast carbonylation step in the Two Planet Steel process follows after dehydration and low-temperature reduction preprocessing. Dehydration involves (a) removing loose water, (b) removing water from hydrated minerals (mainly hydrated goethite), and (c) converting metal oxyhydroxides into oxides, particularly goethite into hematite (Fe2O3). The low-temperature reduction strips oxygen from hematite and the oxides of nickel, cobalt, copper, and silver to unoxidized metals.
The dehydrated and reduced intermediate is fed into the fast carbonylation step. This carbonylation turns the iron and nickel (and small amounts of cobalt) into vaporous carbonyls of iron, nickel, and cobalt. These vaporous carbonyls exit the reactor through a separate exit to the solid residue of everything else — this is the crucial separation step. In another separation step, the carbonyls are distilled from each other and then separately decomposed to produce high-purity powders of iron, nickel, and cobalt. The giant mining company Vale uses nickel sulfide ore processing that carries out slow nickel carbonylation and decomposition. It sells its nickel powder to lithium-ion battery manufacturers. The decomposition to iron powder induces some soot (carbon) production, so this powder actually comes out as a carbon steel powder. Small quantities of this carbon steel powder are now manufactured. It is currently post-processed to remove the carbon to produce a high purity niche iron product called carbonyl iron powder (or CIP).
The Two Planet Steel process needs to remove close to 100% of the iron from the remaining solid residue. If it does not achieve excellent separation of iron from the rest, it is more difficult and expensive to perform the downstream refining of the residue into high-purity, high-value metal and metal oxides.
Fast iron and nickel carbonylation have another excellent application on another source material called hematite blueberries. These blueberries are found on Mars. Steel-making on Mars from blueberries using fast iron and nickel carbonylation has enormous advantages: The equipment needed to carry it out is readily transportable in a rocket to Mars, and this carbonylation steel-making requires no consumables like water and slagging agents.
The pre-processing reduction step in the Two Planet Steel process requires significant energy inputs. For both environmental and customer branding reasons (see Friedland quote) this reduction should be driven by electricity generated by wind and solar power. Given this, economics demands that large-scale implementations of the Two Planet Steel should be sited close to low-cost wind and solar electricity generation.
The USA now has sufficiently low-cost wind and solar electricity generation regions to carry out the Two Planet Steel process at very-large scales with competitive costs that could (i) produce enough nickel, cobalt, and manganese from limonite to make lithium-ion batteries for more than 10 million cars a year, (ii) enough "by-product" carbon steel powder to make the carbon steel bodies for those 10+ million cars a year, with zero-CO2 emissions in steel production, and (iii) large amounts of rare earth elements, platinum group metals, gold, silver, copper, aluminum, chromium, and niobium. Low-cost renewable electricity will allow the USA to have significant advantages in automobile production, and also battery, clean steel production, and the production of the various other critical and valuable metals on the limonite list.
Two Planet Steel has enormous carbonyl chemistry talent to turn this potential into a potent reality.