Research And Application On Two-stage Bio-Oxidation Process For Arsenic-containing Gold-bearing Concentrate

With the development of gold industry,the proportion of the refractory ore in the gold raw materials for industry gradually increased.It is more and more urgent to development efficient and environmentally friendly technology for refractory gold resources.Based on these requirements,the bio-oxidation technology for arsenic-bearing gold concentrate has been put forward.Comparing others traditional technology,bio-oxidation pretreatment technology has the advantages of environmental protection,stable production and flexible production scale and has become the greatest potentiality in development of gold extraction technology.In this paper,based on the analysis of the process mineralogy of arsenic-bearing gold concentrates,the biooxidation thermodynamics and biooxidation mechanisms of the arsenic-bearing gold concentrates are investigated.The arsenic dissolution behavior during the oxidation process is explicited.The mechanism of two-stage biological oxidation was also analyzed.In raw materials of the arsenic-containing gold concentrates,metal sulfide minerals are mainly pyrite and arsenopyrite,accounting for 66.30%of the total mineral.Gangue minerals are mainly quartz and feldspar.Gold in the concentrate is mainly micro fine granular gold and accounting for 88.7%(containing submicroscopic gold),following byfine grained gold and accounting for 9.60%,in which gold grain size are greater than 0.037mm only 1.70%.Gold is surrounded by metal sulfides accounted for 60.25%,wrapped by gangue minerals accounting for 4.06%of gold,monomer and bare gold accounting for only 35.69%.The Eh-pH diagram of pyrite and arsenopyrite system in the aqueous solution obtained through thermodynamics calculated and depicted shows that,arsenic,iron and sulfur exist in aqueous solutions by a stable form of H3AsO3,H3AsO4,H2AsO4-,Fe2+,HSO4-,SO42-respectively,under normal pressure and 313.15K temperature condition.In the bio-oxidation system,the increasing of oxidation-reduction potential and pHis conducive to the genetating of As5+ ions and the formation of iron arsenate,but the oxidation of sulfur in minerals produce acid to gradually reduce the pH value of the solution,which will do harm to the generation of As5+ and iron arsenate.Therefore,the appropriate increasing of oxidation potential and pH of the slurry can reduce the harmful ions,thereby reducing the harmful ions on the inhibition of bacterial growth and activity.The research results of bio-oxidation mechanism of arsenic-bearing gold concentrate and the oxidation behavior of arsenic show that the bio-oxidation mechanism of arsenopyrite is mainly indirect oxidation.In the process of bio-oxidation,arsenopyrite are first oxidized by Fe3+in solution to As3+and Fe2+,and then As3+ is oxidized to As5+ by surplus Fe3+in the solution,while the Fe2+ formed in oxidation process are oxidized into Fe3+ by bacteria.As5+and Fe3+ in the solution can produce iron arsenate under certain conditions.When the arsenopyrite content is too high in bio-oxidation raw materials,arsenopyrite will consume a large amount of Fe3+ in the solution,leading to a decrease in Fe3+ concentration and difficulty in oxidizing As3+,resulting in the accumulation of As3+ in the solution and inhibiting the oxidative activity of the bacteria.The rate of bio-oxidation slows or even stops.The research results of one stage bio-oxidation of the gold concentrate containing 8.31%arsenic show that,the oxidation-reduction potential decreases with the increasing of the pulp density.The conceLtration of Fe2+ in the solution decreases with the progress of the oxidation time at different pulp density,and the concentration of As3+is proportional to the concentration of the pulp.When given the oxidation time,the oxidation rate of arsenic,iron and sulfur decreases with the increase of pulp density.The oxidation rate of arsenic,iron and sulfur decreased from 83.96%,77.21%,79.96%to 77.76%?69.11%?70.21%,and the leaching rate of gold in corresponding oxidized slag decreased from 93.54%to 87.18%,when the pulp density creased from 14%to 20%.The research results of two stage bio-oxidation of the gold concentrate containing 13.84%arsenic show that the pulp density of first stage has a great influence on the bio-oxidation,and most of the arsenic in the gold concentrate are removed after the first stage,making that feasible the second stage of the biological oxidation in a higher pulp density.The leaching rates of gold in oxidized slag are 93.77%,94.87%,91.71%and 90.54%respectively when the pulp density(solid mass fraction)of first stage was 9%and the second stage were 14%,16%,18%,20%respectively,and the oxidation time of the first and second stages is 4d,6d respectively.The industrial application of the two-stage bio-oxidation process of arsenic-containing gold concentrate shows that the two-stage bio-oxidation process has the advantages of running stabilization,simple operation,low running cost,stable technical parameters and production index.The arsenic content in gold concentrate decreases from 16.09%to 4.26%after three days of first stage oxidation.The oxidation rates of arsenic,iron and sulfur in gold concentrate reache 93.20%,81.27%and 79.46%respectively after two stage bio-oxidation treatments.The leaching rate of gold in the oxidized slag produced by two stage bio-oxidation process is as high as 96.37%after 98.05h treatment by the CIL process.