Patented platinum-group metals (PGMs) refining technology Chloroplat, which recovers PGMs from ore concentrates and yields recoveries comparable with those achieved using conventional smelting, will soon reach commercialisation.
The technology, which is a high-temperature chlorination process, was developed by alternative PGMs refining technologies developer and recycler of PGMs from PGM waste materials Talis Platinum, a subsidiary of privately owned South African minerals beneficiation company Ferminore.
The PGMs industry will inevitably shift from large-scale smelter processing to modular, cleaner, more efficient and less energy-intensive processing technologies, says Ferminore CEO Alex Andersson.
“In South Africa, the energy crisis, labour tensions and the increased processing of chromite-rich upper group two (UG2) concentrates are factors that support and drive the strategy of Ferminore,” explains Andersson.
The technology is successful because it is neither bound by the limitation of conventional PGM smelting, such as the ore’s chromium(III) oxide (Cr2O3) content, nor does it require the presence of a collector for the PGMs, and it recovers all six of the economic platinum-group elements, namely platinum, palladium, rhodium, iridium, ruthenium and gold.
“This dry chlorine metallurgy technology is suitable for PGM concentrates from the UG2 and Merensky seams, as well for the Platreef and the chromite middle-group 3 (MG3) and MG4 seams.
Chloroplat can also be used to recover PGMs from recycled catalytic converter monolith, where the PGMs are in a washcoat on a cordierite substrate, and from ore con- centrates, where the PGMs occur in a refractory matrix,” Talis Platinum MD Jacques de Villiers tells Mining Weekly.
Chlorine metallurgy is also successfully used in other sectors, such as titanium mining.
The base technology was first developed and patented by Canada-based developer of precious metals recovery technologies and processes Ressources Minières Pro-Or.
The company subsequently spent the last ten years developing this technology for the recovery of PGMs from recycled catalytic converter monolith and, after successfully operating a demonstration scale plant, the technology is in the process of being established at a commercial-scale plant for this purpose.
Ferminore acquired the worldwide rights to the base technology from Ressources Minières Pro-Or in 2007 to further develop and use the technology specifically for the recovery of PGMs from ore concentrates.
The base technology was initially tested at a demonstration-scale plant in Canada that processes catalytic converter monolith, with Talis Platinum staff assisting in the operation of the plant for six months.
Talis Platinum then refined and tested the technology on several ore concentrates of laboratory and pilot scale in South Africa, says Andersson.
Since acquiring the rights to the base tech- nology, Talis Platinum has spent the last six years refining the technology for ore concentrates to the point where it is nearing commercialisation.
The company illustrated in 2010 that a Chloroplat plant, constructed to treat PGM concentrate from a single concentrator, is viable and competitive, compared with conventional smelting.
Apart from improving the process conditions, several different reactor designs were constructed and tested between 2009 and 2012, notes De Villiers.
The next step in the commercialisation of the Chloroplat technology is to build and operate a demonstration-scale plant that will take 10 to 12 months to construct.
Once the continous operation of a closed-circuit plant is proven, a commercial-scale plant could be in operation as early as 2017, says De Villiers.
Owing to the chemical reagents required for the Chloroplat process, Talis Platinum collaborates with a local chlor-alkali producer. The demonstration-scale plant was designed with the assistance of two local engineering companies and the input of several South African PGMs experts.
Further, Talis Platinum does not plan to license the Chloroplat technology, but rather to become an owner-operator of the technology in the PGMs industry. It hopes to attract industry participation in the project and in the commercialisation of the Chloroplat technology.
How it Works
The Chloroplat process is used to upgrade a PGM concentrate of between 50 and 250 parts per million of PGMs to a mixed PGM sponge of more than 80% PGM in a once-through or single-step process, which has no PGM recycles and low PGM lockup.
The process comprises feed preparation, including drying, similar to conventional smelting. This process is then followed by the high-temperature dry chlorination step, which is used to selectively recover PGMs and base metals. A weak hydrochloric acid leaching and solid-liquid separation are applied, followed by PGM recovery from the solution through ion exchange.
In the first phase of the project, the PGMs will be recovered as a mixed PGM sponge from the ion-exchange resins, but, in a second phase, Talis Platinum will aim to produce high-purity PGMs, explains De Villiers.
“Depending on the level of base metals in the concentrate feed, a base metals recovery circuit can be added after the PGM ion exchange is complete to recover the base metals from the solution using conventional technologies,” he explains.
The technology is modular and scaleable and can be constructed competitively to process the concentrate from a single con- centrator, notes De Villiers.
“Rather than producing a PGM matte, the Chloroplat process produces a rich PGM sponge, which can be separated into high-purity individual metals using conventional technology,” he explains.
Conventional PGM Refining
The incumbent process for PGM-concentrate refining comprises smelting, converting, base metals refining and, finally, precious metals refining.
Sulphide matte smelting technology was developed and improved for Merensky reef concentrates, with the containment of sulphur emissions being a critical aspect.
UG2 and other chromite-rich concentrates, with their low sulphide and high chromite concentrations, are challenging for sulphide matte smelting to process, as it requires much higher melting temperatures.
Andersson notes that this is partially overcome by blending high chromite concentrates with Merensky or Platreef concentrates; however, the ever-increasing ratio of UG2 to Merensky concentrates makes this strategy less feasible in future.
Conventional smelting or converting produces a sulphide matte of about 0.2% PGMs, which is further treated in the base metals refinery to recover a PGM concentrate of 30% to 65% PGMs, which is then upgraded to high-purity individual PGMs in the PGM refinery.
The Chloroplat technology offers various benefits, compared with conventional smelting and alternative refining technologies under development, believes Andersson.
“The Chloroplat process is not sensitive to the Cr2O3 content in the PGM-concentrate feed, and it does not depend on the presence of collectors, making it ideally suited to UG2 and other chromite-rich concentrates. The Cr2O3 insensitivity further allows for the increased efficiency levels of high-chromite concentrator plants to improve PGM recovery.”
Further, as the Chloroplat process is not a smelting technology, energy consumption is lower and thus the electricity requirement of the process is significantly reduced.
Andersson says the Chloroplat process does not produce sulphur emissions, as sulphur is removed in its elemental form, limiting the environmental footprint of the technology.
He highlights that other PGM refining technologies under development are either variations of the energy-intensive smelting route or hydrometallurgy processes that yield lower PGM recoveries than conventional smelting, requiring multiple lixiviants (chlo- rines) to recover the PGMs and the base metals, typically at high pressure in autoclaves.
Another benefit of the process is reduced PGM pipeline costs, as PGMs are not locked up in recycles. Conventional processing leads to PGM lockup, which can range from two to six months.
The simple recycle-free flowsheet is a result of using only chlorine and operating at atmospheric pressure, which, in turn, results in lower capital expenditure.
Once demonstrated and tested in South Africa, the Chloroplat technology is aimed at helping mining companies that want access to a larger portion of the PGM value chain to process chromite-rich PGM concentrates, concludes De Villiers.