The Oxidation And Passivation Of Chalcopyrite

In the process of ore mining, plenty of sulfide riched tailings are open pit and exposed towater and air under natural conditions. Weathering and biological oxidation of sulfide in thetailings trigger the production of acidic mine drainage (AMD), which has the characteristicsof low pH value, high concentrations of heavy metal and sulfate ions. AMD is regarded as thebiggest problem for mining industry. Seepage of AMD into stream and soil leads to severepollution problems and damages the ecosystems. Therefore, the control technology of AMD isurgent to develop and apply. Among various technologies for controlling AMD, passivation isan promising source control method by using a coating agent to inhibit the oxidation ofsulfide in the tailing ore.In this paper, Acidithiobacillus ferrooxidans (represented as A.ferrooxidans) bacteriascreened from surface mine water in Dabaoshan was used to investigate the effect ofmicroorganism on the oxidation of chalcopyrite, which is a common sulfide ore. In addition, acoating agent sodium triethylenetetramine bisdithiocarbamate (DTC-TETA) was used toprevent the oxidation of chalcopyrite. The main work was concluded as follows:(1) Study on the oxidation of chalcopyrite by acclimated A.ferrooxidans bacteria. Thescreened species was acclimated and used to preliminarily investigate the effect of bacteria onthe oxidation of chalcopyrite through shaking experiments. The result showed that the growthof A.ferrooxidans reached to a stable stage within10day. High concentration of copper ioncould be detected in solution, showing the positive effect of A.ferrooxidans on the oxidationof chalcopyrite. Adsorption of copper ion by A.ferrooxidans was much higher than that oftotal iron ion, while absorption of copper ion was lower than that of total iron ion. Surfaceoxidation of chalcopyrite was verified by scanning electron microscope (SEM) observation,possibly due to the adhesion and direct oxidation by A.ferrooxidans.(2) Comparative study on the chemical and biological oxidation of chalcopyrite. Shakingexperiments with and without A.ferrooxidans bacteria was carried out to understand thechemical and biological oxidation process of chalcopyrite in20day. The oxidation wasassessed by the chemical parameters, including pH value, copper ion and iron ion content, thecomponent analysis detected by X-ray diffraction (XRD) and other analytical methods.Results showed that the concentrations of copper ion and total iron ion in biological oxidationwere5.0and9.3times as high as those in chemical oxidation. Also, higher SO42-content wasobserved in biological oxidation. These results demonstrated that A.ferrooxidans could accelerate the oxidation of chalcopyrite. In the process of oxidation, less iron ion was releasedinto solution, which might be due to the production of cubanite (CuFe2S3) and the absorptionof iron by A.ferrooxidans.(3) Investigation on the inhibitive effect of the passivator on the chemical and biologicaloxidation of chalcopyrite. For this purpose, the passivator DTC-TETA was applied in surfacecoating of chalcopyrite before the chemical and biological oxidation in a shaking experiment.Results showed that the concentrations of copper ions in the system treated with and withoutbacteria were only17%and48%of the corresponding controls, indicating the passivator hadsignificant inhibition on the chemical and biological oxidation of chalcopyrite. However, theproduction of cobalt phosphide sulfide (CoPS), cobalt phosphate (Co3(PO4)2) and ironphosphate hydroxide (Fe4(PO4)3(OH)3) which were detected by XRD after chalcopyriteoxidation，did not affect the oxidation rate. From the analysis of chalcopyrite samples byX-ray photoelectron spectroscopy (XPS), the transformation of iron from Fe2+to Fe3+-SO42-and Fe3+-O, and sulfur from reduction state to oxidation state were detected, but the coppervalence did not change. The observation by SEM showed that the surface of coatedchalcopyrite was smooth after chemical oxidation, owing to the protection ability of thesurface coating.(4) Electrochemical studies of the oxidation and passivation of chalcopyrite.Electrochemical analysis methods, including open circuit potential (OCP), cyclic voltammetry(CV) and Tafel polarization curves were used to investigate electrochemical behavior ofchalcopyrite in systems with and without bacteria, revealing the mechanism of chalcopyrite’schemical and biological oxidations. On these bases, the feasibility of DTC-TETA to inhibitthe chemical and biological oxidation of chalcopyrite had also been discussed.The electrochemical behavior of a chalcopyrite carbon paste electrode in the systemswith and without A.ferrooxidans bacteria was also investigated. The results showed that theaddition of A.ferrooxidans could enhance the corrosion current density of chalcopyriteelectrode greatly. From cyclic voltammetry curves, the current of oxidative and reproductivepeaks of chalcopyrite electrode enhanced in the system with baterial, but the numbers ofpeaks did not change, indicating A.ferrooxidans could increasethe rate of oxidation ofchalcopyrite but not change its oxidation mechanism.Passivator DTC-TETA was used to investigate the passivation effects on chalcopyriteoxidation with different concentrations of0.1%,0.2%,0.8%and4%. Coating agentDTC-TETA effectively inhibited the chemical oxidation and biological oxidation ofchalcopyrite, but the passivation did not increased with increasing concentrations of the coating agent. Experimental results showed that, the effect in concentration of0.2%wasbetter than those in other concentrations. Compared to other coating treatments, the use ofcoating agent by DTC-TETA could limit both the chemical and biological oxidations ofchalcopyrite. Therefore, using DTC-TETA could represent a simple, cost-effective method toreduce the production.