Platinum Group Metals (PGM)
Beginning with rhodium (Rh) refining from spent autocatalysts at Tanaka and palladium (Pd) refining from primary ore at Impala in the mid-1990s, SuperLig® MRT™ systems have been installed worldwide at major primary and secondary PGM refiners for individual PGM separations including rhodium, palladium, platinum, iridium, and ruthenium.
Favorable Characteristics of MRT™ in PGM Refining include:
- Highly selective single-pass separations of 99%+ with product purities of 99.95 - 99.99%.
- Minimization of platinosis and other health and safety risks due to the non-generation of chloroplatinates and the system being self-contained, thereby greatly reducing worker exposure.
- Rapid recycling of target individual platinum group metals by reduction of total processing time.
- Reduction of platinum group metal refining costs (space, labor, materials) by elimination of and/or decreasing the number of process steps and many process chemicals.
- Reduction of labor, construction, and maintenance costs by simplification of the separation system.
- Reduction of processing pipeline time resulting in low metal financing costs and rapid release of metal for sale.
- Option to target specific, commercially important platinum group metals such as rhodium and palladium early in the flowsheet.
- Rapid kinetics for metal complexation and release enabling on-line processing.
- Efficient production of a salt product that may be sold or reduced to market-grade metal.
- Efficient, rapid, and semi-continuous separation process that may be put on-line.
- Treatment of any feed solution volume.
- High loading and elution flow rates.
- Recovery of impurity metals from raffinate for reuse or proper disposal, thus minimizing waste generation and allowing recovery of valuable resources.
- Reduction of platinum group metal security risk as the system is self-contained, thus minimizing exposure.
- Reduction of capex of SuperLig® products by their regeneration for multi-cycle use.
MRT™ Platinum Group Metal Refining Systems have Proven to be Very Advantageous for a Large Number of PGM Refining Applications
Examples of the application of MRT™ for platinum group metal refining include cost-effective, efficient and green recovery of individual platinum group metals from primary ores, copper refinery byproduct sludge and residues, spent autocatalysts, other platinum group metal-bearing catalysts, plating baths, gauzes, e-waste and other secondary materials.
Separation, recovery, and purification of individual platinum group metals from various matrices using MRT™ products.
|PGM||Separation, Recovery, Purification Event||Ref|
|Pt||Pt from spent catalytic converters
Pt from Pt/Cr/Co/Cu alloy scrap from a sputtering process
|Pd||Pd from spent catalytic converters and primary mine feed
Pd from spent petrochemical catalysts
Pd from dipping bath solutions
Pd from plating baths
|Rh||Rh from spent catalytic converters||a,b,d,e,k|
|Ir||Ir from primary mine feed matrix of Rh and base metals||l,m,n,o|
|Ru||Ru from alloy scrap||c|
aref. 48; bref. 49; cref. 50; dref. 1; eref. 4; fref. 51; gref. 52; href. 53; iref. 54; jref. 46; kref. 2; lref. 7a; mref. 47; nref. 46; oref 18. References cited are available
- A Key Advantage of the MRT™ Process is that Rhodium can be Recovered at the Beginning of the Flowsheet, Providing a Tremendous Economic Advantage
- Exceptionally High First Pass Recovery Rates Essentially Eliminate PGM Lock-up, Releasing Metal Much Earlier for Sale
- Sustainable and Circular Economy Platinum Group Metal Refining is Achieved using MRT™
- Analysis of Cost Metrics for MRT™ and Classical Methods for Platinum Group Metal Refining Show MRT™ Systems to have Superior Performance with Reduced Capex and Opex Values Compared to Classical Methods which are Profligate in Their Use of Energy, Time, and Resources.
Case Study: Iridium, Ruthenium, Platinum Recycling
Key to sustainability in the emerging green hydrogen economy is the efficient production and recycling of membrane electrode assemblies (MEAs), which are used for the electrolysis of water and contain iridium, ruthenium and platinum as catalysts.
Isondo Precious Metals has announced the selection of MRT™ for recycling of iridium, ruthenium and platinum from their planned production of Membrane Electrode Assemblies (MEA) in South Africa.
Case Study: Iridium Refining from Primary Ore
An automated SuperLig® MRT™ refining system for iridium from primary ore has been operating at Sibanye-Stillwater’s South African Precious Metals Refinery since 2015. The MRT™ process is efficient and highly selective for iridium over rhodium.
Case Study: Palladium from Primary and Secondary Sources
The first large-scale industrial MRT™ system for palladium refining was installed at Impala in the mid-1990s. Since then, MRT™ has been widely used for palladium refining from both primary and secondary sources. For example, a green chemistry SuperLig® MRT™ process is used for the highly selective separation of palladium from various primary and secondary sources in the precious metals plant at the Boliden Rönnskär copper smelter, a world leader in recycling metals from waste electronics. Highly efficient and rapid separation and high purity recovery of palladium results in a green, sustainable, circular economy recycling process.
MRT™ Platinum Group Metal Refining Processes Adhere to the Principles of Green Chemistry and Green Engineering
Green Chemistry and Green Engineering principles applied to MRT™ PGM separations include:
- No organic solvents (inherently flammable) are used in the separation process that normally operates at room temperature (~25C) and pressure (~0.1 MPa).
- No contaminants are added to the process stream during the separation process.
- Wash and eluent solutions are as simple as possible while being compatible with overall PGM refining plant operations. Washes and eluents used include H2O, HCl, NaCl, KCl, Na2SO3, (NH4)2SO3, and NH4HSO3.
- Target individual PGM are recovered in pure concentrated form following elution from the column with a small amount of eluent.
- Target individual PGM in eluates are easily precipitated to final products using common reagents. For example, HCl, air, and H2O2 are used to form palladium yellow salt. Precipitated PGM compounds are collected by filtration. No contaminating or hazardous reagents are used.
- Impurity metals, such as silver, gold, deleterious metals, and base metals are selectively separated from the raffinate and recovered either for value or safe disposal.
- Individual PGM are selectively separated. This achievement is of critical importance since it simplifies the procedure, eliminates need for multiple stages, and avoids downstream use of hazardous/contaminating chemicals for further separations.
- Individual and/or group separations are accomplished from feed solutions containing g/L to mg/L-or lower PGM concentration levels even with high concentrations of impurity metals present.
- Minimal amounts of hazardous waste are generated.
- Minimal carbon footprint is achieved
Gold (Au) and Silver (Ag)
MRT™ gold and silver applications are summarized below.
|PM||Separation, Recovery, Purification Event||Ref|
|Au||Au from mine and electronic waste cyanide solutions
Au from high copper gold ores
Au from plating solutions
Au from chloride solutions containing PGM and base metals
|Ag||Ag from cyanide solutions
Removal of impurities from Ag electrolyte
SuperLig® MRT™ systems are highly efficient for the recovery and refining of gold from various refining, recycling, plating and mining feed solutions at high gold purities (99.99-99.999%.)
Copper (Cu), when present in gold ores at high concentrations, causes many problems including very high consumption of cyanide, low extraction of gold, adsorption of copper cyanide on activated carbon and need for complex effluent treatment.
MRT™ systems are able to extract and recover gold cyanide complexes from leachates of ore bodies containing high amounts of copper and recover copper away from cyanide to allow for both copper recovery and cyanide ion recycle from the leachates of these same gold ores. Gold is recovered at high purity for subsequent reduction to the metal. Copper is then extracted and separated from cyanide for further electrowinning to grade A cathode. The cyanide is recycled to the heap leach operation. The overall process allows the processing of high copper gold ore bodies that were previously uneconomical to treat with conventional technology.
Recovery of gold from cyanide solutions is typically performed with activated carbon. However, in contrast to MRT™, activated carbon has low gold selectivity.
Low gold selectivity leads to loading of silver, copper, and other base metals that are present in the feed solution on the activated carbon. Capacity for gold is diminished and additional steps are required to obtain pure gold, resulting in extensive waste generation. The high selectivity of the gold SuperLig® MRT™ system provides a green processing alternative to activated carbon. Gold is selectively removed from impurity ions upfront, thereby avoiding the need for complex, costly and environmentally damaging processing.
MRT™ is effective in selectively separating gold from aqueous chloride solutions.
Typically, chloride ion and gold concentrations are 100-200 g/L and multi-g/L, respectively. Common impurity metals present in these solutions are PGM, selenium, and base metals, such as copper, at concentrations ranging from approximately equal to the gold concentration to twenty times larger. Gold recovery from these solutions is at least 99%+. Levels of potential impurities are low enough in the eluent that gold sponge at 99.99% or higher purity can be obtained by selective reduction of eluted gold with sodium sulfite or sulfur dioxide.
MRT™ has been employed commercially for the recycling of potassium gold cyanide (PGC) from spent gold plating solutions.
Potassium gold cyanide is the most commonly used base for the gold plating electrolyte. The specifications for the plating electrolyte solutions are particularly tight in the electronics sector and the baths must be periodically replaced due to the buildup of various impurities. The conventional process for production of potassium gold cyanide is to recover the gold from the plating solution in metallic form, refine it, and use it for the production of new potassium gold cyanide. The MRT™ process enables recovery of the potassium gold cyanide directly from the spent plating solution and direct conversion back into potassium gold cyanide. The MRT™ process eliminates a number of unit operations and greatly reduces the processing time, resulting in substantial cost savings.
- Highly selective separation of gold from both cyanide and chloride solutions
- High selectivity for gold over other contaminants such as copper, zinc, cobalt, nickel, and iron
- Economical installation and operation
- Reduction in refining cost by elimination and/or reduction of the use of process chemicals and the number of process steps
- Major reduction in process gold inventory in the process flow sheet/recovery pipeline resulting in improved cash flow, lower interest costs, and reduced security risk
- Reduction in gold loss by direct sale to the consuming markets of pure gold as ingot, sponge, or grain, thus bypassing traditional outside toll refiners
- Essentially quantitative selective gold extraction and recovery from solution
- High gold loading capacities
- Rapid metal loadings
- Wide concentration ranges for gold extraction including low mg/L levels where no other technology is effective
- Availability of compatible, low-cost elution reagents, which readily and completely strip or elute the gold at ambient pressure and temperature, and from which the gold can be readily and rapidly recovered in high purity (e.g., SuperLig® 127 uses a simple water elution)
- Capability to handle high solution volumes and high flow rates
- Use of simple, compact equipment which maximizes economy of operation and markedly reduces space requirements
- Production of a high purity, directly marketable gold product which is easily obtained
Recovery of Silver from Cyanide Solutions
The selective separation of silver at high purity from base metals in cyanide solutions is easily accomplished with MRT™.
A critical requirement for maximizing production capacity and producing high purity silver is to effectively control impurities in the silver electrolyte.
In contrast to highly selective MRT™ systems, other separation technologies require multiple stages, result in incomplete impurity recovery, and generate much waste.