Heap bioleaching of sulfide ores (geotechnology) simulates naturally occurring processes when sulfides convert to oxides. This process is environmentally-friendly. Gold-bearing sulfide ore from a Russian deposit was studied. The samples were composed of quartz (38-48%), feldspars (22-24%) and micaceous minerals (18-21%). Carbonates occurred as ankerite, calcite, dolomite and siderite. The host minerals were pyrite (2.2-2.3%) and arsenopyrite (1.2-1/7%). The grade of gold was 1.6-2.0 g/t. Russian software package Selector was used to develop the model. Thermodynamics of the reaction pathway for the conversion of the gold-bearing sulfide ore in H2SO4 environment with and without using bacteria was calculated. Phases and their components which are able to form in these given conditions were selected during modeling. Modeling of irreversible evolution of the rocks caused by bacteria was carried out in the three reservoir system. They are interconnected by the flows of three movable phases: gases, solid phase and liquid phase. In this case, the composition of the solutions which were obtained under steady state conditions without bacteria and metastable equilibrium using bacteria can be compared. Bacterial oxidation occurs under acidic conditions. Oxidation without using bacteria occurs under more alkaline conditions. Bacteria increase the rate of sulfides oxidation and retard the formation of mixed-layer aluminum silicates (illites, montmorillomonites) and carbonates (magnesian calcite). It was found that bacteria have the potential to achieve the required destruction of sulfides in favorable environment. Bacteria make the rate of sulfide oxidation higher. In the presence of bacteria, the rate of aluminosilicates oxidation is slower compared to the conditions without using bacteria. Mineralogical analyses of the leach products confirmed this. Results show that thermodynamic approach can be successfully used for the modeling of bacterial-oxidation circuits and geology of the rocks and ores.
Developed and tested in the pilot
Nowadays, efficient recovery of base metals from the solutions when processing gold ores is a topical issue. In this connection, the focus is on the use of hydrogen sulfide produced in bioreactors using sulfate-reducing (SRB) and sulfur-reducing bacteria. A new technology of biogenic hydrogen sulfide production followed by the precipitation of base metals from the solutions as sulfides was developed. The strains of anaerobic sulfidogenic thermophilic microorganisms: Desulfurellaacetrivans and DesulfurellaKamchatkensis which were obtained at S.N.Vinogradsky Institute of Microbiology RAS, Moscow were used for these tests. They have anaerobic respiration using sodium acetate as an electron donor and elemental sulfur as an electron acceptor. In order to cut costs for biogenic hydrogen sulfide production, the possibility of using acetic acid as an electron donor was studied. Scaled-up test work was conducted in a 1.5L bioreactor at the temperature of 55°C, pH of 5.0, redox of-250mV and using POX solution with the content of C2+=5700.0 mg/L, Fe2+=4890.0 mg/L and Zn2+=1200.0 mg/ L. Selective precipitation of copper (at pH of ≤0.5), zinc (pH=1.0-2.0) and iron (II) (pH≥5.5) was carried out. Recycled gas contacted with the metals solutions (in a series of reactors for the precipitation of metals) coupled with the removal of hydrosulfuric acid from the recycled gas and the recovery of metals from the solution as sulfides. The precipitate was separated from the solutions by filtering. Then the filtrate was directed to the next stage. Carbon dioxide was removed from the recycled gas by filtrating through alkaline solution. After that, about 10% of ultra high purity nitrogen was added from the balloon and the recycled gas was again directed to the bioreactor. The average hydrogen sulfide reactor throughput was 1 g/L per day of culture medium. The total consumption of hydrogen sulfide was 1.28 g/L of the process solution. Results showed that this process can selectively recover metals from POX solutions with generation of high grade copper (50%), zinc (45%) and iron sulfide (45%) concentrates.
An optimal approach to the problem of cupriferous gold ores hydrometallurgical processing is the recycling of process solutions after copper recovery and regeneration of cyanide bound in complexes. The study focuses on the copper-cyanide solutions processing technology using biogenic hydrogen sulfide for copper recovery in the form of сhalcocite, and cyanide regeneration. The strains of anaerobic sulfidogenic thermophilic microorganisms Desulfurella acetivorans and Desulfurella Kamchatkensis were used for producing hydrogen sulfide. The studies on copper precipitation and cyanide regeneration were conducted on copper-cyanide process solutions which were obtained during cyanidation of refractory cupriferous gold-bearing flotation concentrates from one of the deposits in the South Ural (Russia). Ten cycles of "Cyanidation-Regeneration" were carried out in total. The copper recovery was 86–96 %; the cyanide regeneration obtained 96 %. On an average 8.9 kg of sodium cyanide and 4.6 kg of copper sulfide were recovered from 1 m3 of solution. The sodium cyanide consumption decreased from 25.0 kg/t to 6.0 kg/t without reducing gold recovery during the CIL (carbon-in-leach) recycling process. The gold recovery was the same 63–68 %.
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