CLEVR Process™—Parametric and Technology Transfer Interlaboratory Study

This study was done in collaboration with a world’s leading gold mining company to evaluate the technical applicability of DST’s CLEVR Process™ as an alternative to cyanidation for gold extraction at one of its deposit projects located in South America, a region known for its opposition with the use of cyanides due to environmental risks associated with the process. The CLEVR Process™ is a hydrometallurgical process operating in a closed-loop circuit and using in-situ chlorine and bromine generation from sodium hypochlorite and halides salts in acidic media for the purpose of gold and platinoids extraction. Its fast reaction kinetics, high efficiency, relatively low waste production and health, safety and environment (HSE) risk makes it a favorable option for gold miners when compared to the traditional cyanidation. An extensive series of tests were performed at the laboratory scale on 4 typical low-bearing sulzides materials ranging from 1.7 to 6 g/t of gold supplied by the miner (2 feed ores and 2 gravimetric tails). A parametric study was performed to better define the impact of the following conditions on the process efficiency: hypochlorite concentration, operating pH, contact time, particle size, solids percentage and material. Gold extraction efficiency under optimized conditions reached above 97% for the oxide material tested without pre-treatment ([NaOCl] = 4%wt, [NaCl] = 70 g/L, [NaBr] = 10 g/L, pH < 1, ORP > 950 mV, contact time = 2 h, P90 = 80 µm, %solids = 45%, room temperature). The solid residue resulting from the CLEVR Process™ is one of the few waste streams generated in the process. Consequently, its characterization is of obvious interest and presented in this paper. The residue was found to be non-hazardous, based on the Toxicity Characteristic Leaching Procedure (TCLP—EPA1311). An interlaboratory study based on ASTM E2935-15 Standard Practice for Conducting Equivalence Testing in Laboratory Applications was also conducted in the scope of the study with the gold mining company. Relevant documents (SOPs, control sheets, visual support, etc.) were shared between both laboratories and 10 representative sub-samples issued from the same material (5 for each lab.) were prepared and used for the technology transfer. Analytical and operational results were compared for 7 tests (3 performed by DST and 4 performed by the gold mining company).