According to Daniel Verwey, technology manager at Protea Mining Chemicals, “With the potential to cause loss of revenue, and in worst-case scenarios shut a mine down completely, finding innovative ways to identify and mitigate the risks associated with colloidal silica is crucial if mines want to remain operational and optimise efficiencies.”
Verwey cites a case study in the Democratic Republic of Congo as a case in point. The DRC is a leader in the production of copper and cobalt having produced 1.4 million tons and 95 000 tonnes in 2020 respectively, translating to 70% and 60% of global output of these commodities respectively. Copper and cobalt are used in many sectors of the economy, such as power generation and transmission construction, production of lithium-ion batteries and factory equipment and electronics and the price of these resources is set to continue to rise.
Copper-cobalt ores are characterised by high silica contents. These minerals partially dissolve during acidic sulphate leaching of the ores and significant amounts of silica report to the pregnant leach solution in various forms – one of them being colloidal silica. The presence of colloidal silica in the feed to the downstream solvent-extraction circuit creates extensive operating problems, including severe crud formation, difficulties in maintaining organic phase continuity, solid-liquid separation problems and poor cathode quality.
Verwey adds that this, in turn, can lead to mine downtime, loss of revenue, and in worst-case scenarios shut down of Solvent Extraction/Electrowinning (SX/EW) plants completely, thus causing massive knock-on effects economically and socially in the DRC.
The processes used to remove the ultra-fine colloidal silica particles present challenges as they are time consuming and costly due to mine downtime. These processes included maintaining a very high organic to the aqueous ratio in all the stages, at least a ratio above 2 to sustain organic phase continuity in all the SX stages, but sporadic instabilities are still observed and the SX can still not operate at its maximum capacity, says Verwey.
However, the innovation of a coagulant targeting silica molecules by Protea Mining Chemicals and Innospec, used to-date in four mines across the DRC Copperbelt, is seeing a decrease in the concentration of colloidal silica and gels in a leach solution. At one site, a mine that was experiencing substantial loss saw 20% improved copper production and improved cathode quality production rates from less than 50% LME grade copper cathode on spec to >99% on spec. By improving efficiencies, the mine showed a 9% improvement in revenue year on year from 2019 to 2020.
The product has been such a success that it is now being touted for use on any form of extraction operation that has a highly acidic leach with a solvent extraction process on it. This solution now extends beyond the borders of the DRC with plans to leach uranium and zinc operations across Zambia and Namibia in the pipeline.
This innovative technology has exponentially increased operations and maximised yields, whilst saving costs and increasing bottom lines.