| The arsenic bearing gold ores is abundance and distributing abroad in China.The bio-pretreatment—cyanidation technique has advantage of higher leaching,lower cost and no pollution,so it is gradually a hot research subject.Howerever,it has long periods and there are still very important unknown mechanisms,which affects its large scale application. In this research,electro-methods were used to investigat the bio-oxidation action and corrosion mechanism with or without bacteria in acidic solution.Based on the electrochemical results,the solution chemistry of bio-oxidation As(Ⅲ)to As(Ⅴ)and arsenopyrite oxidation kinetics were studied.At the same time,the process of bio-pretreatment—cyanidation leaching was investigated with arsenical antimony concentrates.The arsenopyrite oxidation action was investigated by various methods of electrochemistry(such as Tafel,liner polarization,AC impedance)and using Carbon- Paste-Electrode simulating the bacteria leaching system.In the acdic solution without bacteria,arsenopyrite was fistlly oxidated to As2S2 at the potential of 0.2～0.3v(vsSHE),which covered the electrode and blocked the process continuesly,and At higher potential,As2S2 was oxidated to H3AsO3,when the potential is over 0.8v (vsSHE),H3AsO3 was then oxidated to H3AsO4.The results showed the mechanism of arsenopyrite oxidation in acidic solution.Adding bateria in the system,the electrostatic potential of arsenopyrite was reduced,and arsenopyrite was dedirectly oxidated to H3AsO3 and no intermediate product As2S2,which tesitified that bacteria is directly action on the surface of the ore.The mechanism of adding bacteria and irons is the same as acidic solution without bacteria,the pasivation film is As2S2, which discovered the mechanism of biooxidation passivation.The current density is two times of the biooxidation,which shown that iron is the main oxidants to oxidate arsenopyrite.The result of AC impedance is the same as that of liner polarization,which made sure that As2S2 passivation film was the main matter to block the arsenopyrite to be further oxidated. In order to avoild to form As2S2,the potential must be higher than 0.3v(vsSHE),however,in the range of 0.3V to 0.8V(vsSHE),arsenic is mainly as As(Ⅲ)in the solution,which would lead bacteria to death.The results of kinetics of bio-oxidation As(Ⅲ)to As(Ⅴ)indicated that the bacteria activity decrease with As(Ⅲ)concentratin increasing. Fe(Ⅲ)can oxidate As(Ⅲ)to As(Ⅴ),but the oxidation rate is very solly and the activity of bacteria decreased with As(Ⅲ)concentration increasing.As(Ⅲ)is mainly oxidated by Fe(Ⅲ)on the early stage when adding Fe(Ⅲ),When bacteria survive,As(Ⅲ)is oxidated by inderect mechanism.There were relationship between As(Ⅲ)oxidation and initial As(Ⅲ)concentration,Fe(Ⅱ)and Fe(Ⅲ)concentration in the solution. Keeping iron concentration and avoilding iron deposition can intensify As(Ⅲ)oxidation.The results of arsenopyrite oxidation kinetics showed that in the bio-oxidation system the solution potential is 0.5v or so,avoiding the As2S2 passivation but arsenic is mainly the As(Ⅲ)form,which can lead bacteria to death and affect arsenopyrit to oxide.Fe(Ⅲ)firstly oxidized arsenopyrite.Suitable amount of pyrite will form galvanic cell and also supply nutrient source,which could intensify the bio-oxidation of arsenopyrite.when pH is over 2.0,The passivation film is jarrosite which would affect the arsenopyrite to be further oxidated.Suitable temperature and shaking table speed is advantageous for biooxidation.The theory of bioxidation arsenopyrite kinetics can direct the bio-oxidation arsenic bearing gold ores.If the ore,of which contain 10.37%arsenic,is not pretreatment,gold leaching is about 41%,after 12days oxidation,the result is about 76.55%,which improved about 35.62 points.The bio-pretreatment greatly intensified the cynidation of arsenic bearing gold ores.The raelationship between gold leaching and arsenic oxidation is direct proportion,furthermore,it needs only partly oxidateand higher gold leaching could be get,for example,gold leaching is over 90%when asenic oxidation is 60%.This investigation provided new theory and technique for the bio-pretreatment—cyanidation leaching technology.The research is supported by the National Natural Science Foundation of China(50321402)and Major State Basic Research Development Program of China(2004CB619204).
|
PDF Full Text Request