FLSmidth‘s MRC reactor-clarifier technology commissioned to be installed at a greenfield copper mine in the Democratic Republic of the Congo (DRC) is the first of its kind and is the biggest in Africa.FLSmidth describes it as the “renaissance” of this technology and says it will set a benchmark in the African hydrometallurgical sector wherever solvent extraction is being used to recover any type of metal. FLSmidth global manager hydromet, Ron Klepper, says “This technology minimises extraction losses and maximises the quality of the product being produced.” Klepper, who is based in Utah in the USA and was instrumental in the mine’s decision to install this technology, explains that metallurgists at the mine are experiencing high levels of suspended solids in the leach liquor — as high as 2 000 ppm. This, in turn hasled to the formation of “crud”, a solid stabilised aqueous/organic emulsion that created imbalances in the SXcircuit. The original pin bed clarifiers have not succeeded in reducing the pregnant leach solution (PLS) suspended solids to levels that make it possible to meet the mine’s commitment to produce LME grade copper. The MRC reactor-clarifiers now enable the production of copper of the highest purity (99.9999%), which will attract a premium price on the world market.
“Although it is a far newer technology, pin bed clarifiers are limited by the fact that they are only successful over a narrow range of suspended solids and the levels at this copper mine exceed this range,” Klepper continues. “A far more robust system is needed and, with MRC Reactor-Clarifiers already proven in other parts of the world, we have absolute confidence that the technology will meet, and indeed exceed, the mine’s expectations. This technology has a tremendous buffering capacity that absorbs any variation, both in start-up conditions and during day-to-day operations.”The order for a complete “process island” was placed with FLSmidth towards the end of 2011. Fabrication was carried out in South Africa and a sub-contractor installed the system on-site under the supervision of FLSmidth representatives and the EPCM contractor during 2012. Klepper was on-site in November2012 to oversee the final mechanical check, which was conducted according to the stringent FLSmidth quality assurance/quality control procedure, before the system went into operation. At the mine, MRC reactor-clarifier solids contact units combine mixing, solids-contact flocculation, clarification and raked sludge removal in a single basin, achieving the efficient removal of hard-to-settle suspended solids. A variable speed turbine maintains a large volume of flocculated solids circulating within the feedwell and underflow is recycled to the feedwell to increase the solids concentration. The mixing, combined with an optimal solids concentration, greatly improves flocculation and effluent clarity. The larger, heavy particles settle out at a high rate and are collected by rake arms, while the clarified solution passes to the clarification zone for collection in a launder system. The process of solids-contact flocculation enhances the settling rate of suspended solids and is well suited to a variable solids concentration feed, because the concentration maintained in the reaction zone – where flocculation takes place–is substantially greater than the highest solids concentration expected in the feed liquor. “This project is an excellent example of FLSmidth’s ongoing commitment to identify technologies that have been proven in other industrial sectors and transfer them to the hydrometallurgical industry. “This creates very low risk options for our customers. In this case, even though the MRC reactor-clarifier process is new to the base metals industry, we have a thorough understanding of its capabilities and have demonstrated this in the water sector over many decades,” concludes Klepper.