Browsing by Author "Pretorius, Petrus Johannes"

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    Atmospheric acid leaching of oxidised and mixed copper cobalt ores mined in the Democratic Republic of the Congo
    (Stellenbosch : Stellenbosch University, 2019-04) Pretorius, Petrus Johannes; Akdogan, G.; Bradshaw, S. M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Kamoto-Oliveira-Virgule (KOV) located in the Democratic Republic of the Congo, operates its mining operation on the north-western boundary of the approximately 350km long Congolese copper belt. This deposit accounts for nearly half of all the Cu-Co resources within the DRC. The concentrator and refinery being studied was launched as a brownfields project, designed to receive concentrated copper oxides that feed the leaching circuit directly. Copper sulphide concentrate was received by the fluidized bed roasters after sulphide and oxide flotation. Current open pit operation has predominantly oxidised copper ore and mining the mineral resources from the open pit is considerably more economical than running the underground operation that produces predominantly copper sulphides. Consequently, the decision to build a Flotation Tailings Acid Leach (FTAL) plant was made which allows for the copper oxide flotation process to be eliminated completely by increasing the leach circuit capacity to process all the ore from the open pit operation, the ore will only undergo a pre-flotation process to recover the copper sulphides fraction. The justification for the FTAL plant lies with the mineral recovery gained by eliminating the copper oxide flotation circuit. The purpose of this study is to characterize the ideal leaching conditions of flotation tails for ore mined from KOV and its respective orebodies. Therefore, determining if the mining, concentration and refining operation can run a metal recovery process from mine to metal efficiently by evaluating the leach performance and characteristics of all the available resources including the ores containing dolomite and calcite. Core samples were received from FNSR, Oliveira, Virgule and Variant ore bodies in the KOV pit. The samples were crushed and milled to a desired P80 particle size followed by a 4-minute flotation step to remove the copper sulphide minerals present in the sample. The concentrate from this step was submitted to the laboratory for analysis. The flotation tailings were dried and sent for chemical analysis and labelled as the leach feed. The flotation tails were then re-pulped and vigorously agitated and leached at a controlled temperature using diluted sulphuric acid, at the desired pH for a period of 4 hours. After the leach process, the acidic slurry was filtered, and washed. The initial experimental results revealed that particle with a P80 of 75μm, 150μm and 212μm had leach recoveries of 91%, 89%, 89% respectively and average acid consumption values of 141, 132 and 128 kg/t respectively, but the sulphides fraction recovery dropped by 20% from 212μm to 150μm. The fresh acid consumption (FAC) decreased from 142kg/MT to 86kg/MT for leach tests performed at pH values of 1.0 and 2.0 respectively and leach recovery decreased from 95.4%CuOx to 93%CuOx respectively. The effect on cobalt however was much more pronounced as the total cobalt recovery dropped from 82% to 60% for pH values of 1.0 and 2.0 respectively. A change in the percentage solids in the leach slurry showed that the optimal leach conditions was at 30% solids with a copper leach recovery of 98.2%. Leaching at 30°C, 45°C and 60°C resulted in copper leach recoveries of 98.2%, 98.2% and 98.5% respectively. The leaching of cobalt was much more affected by the change in temperature, the total cobalt leach efficiency varied from 78.6% to 88.0% for tests conducted at 30°C and 60°C respectively. A very strong correlation between the contained calcium in the feed and the gangue acid consumption value was found, which would make it uncomplicated to create an advanced blending strategy if the operation would invest in online analysers placed on the conveyors that feed the stockpiles. Furthermore, the mineralogy revealed that the percentage cobalt in the ore had a profound precipitation effect on the already leached copper in solution due to the electron negativity of the Co3+ found in heterogenite. The optimised leaching conditions were used to leach a large quantity core samples to verify the results from the initial core samples.