The base metals refinery (BMR) is adjacent to the smelter at the Company’s metallurgical complex in Columbus. Montana. Converter matte from the smelter that contains nickel, copper and PGMs is transported from the smelter to the BMR. The matte is then sampled, weighed and assayed before being fed to the refinery.
The objective of the BMR is to extract the base metals (nickel and copper) and upgrade the PGM content of the matte. This process utilizes a sulfuric acid media that will effectively leach only the nickel and copper while the PGMs remain inert to the leach process. This occurs in a three-step leach process which is initiated by first conducting a nickel atmospheric leach (NAL) utilizing sulfuric acid, oxygen and elevated temperatures to preferentially leach the nickel. The nickel-laden solution is then directed to a crystallization circuit where a crude nickel sulfate crystal is produced and sold as a product.
The remaining copper/PGM matte proceeds to the second step or the copper dissolve autoclave, which also utilizes sulfuric acid, oxygen and elevated temperatures along with elevated pressure to leach the copper. Once complete, the copper-laden solution is directed to an electro-winning circuit that removes the copper from solution as an impure copper cathode that is then sold as a product.
Once the bulk of the nickel and copper have been removed, the matte proceeds to the third and final step, or the polish leach, that again utilizes sulfuric acid, oxygen and elevated temperatures and pressure to remove any copper and nickel not leached in the first two leaches. After completion of the polish leach, the PGMs in the matte have been upgraded such that this material is ready to be shipped for final metal refinement as PGM-rich filter cake.
Through this state-of-the-art process, the BMR is able to maintain a zero-discharge facility.