The Theory And Process Research Of Alkaline Pressure Self-leaching Of Arsenic Bearing Refractory Gold Ore

Arsenic bearing refractory gold ores usually need to be pretreated by roasting,microbial oxidation,chemical oxidation and pressure oxidation in advance.It is difficult to achieve ideal leaching effect by direct cyanidation.The pyrite can be oxidized into thiosulfate in alkaline oxygen atmosphere.Therefore,it is significant to realize gold self-leaching by thiosulfate produced by sulfide oxidation,while the wrapped gold is released due to the sulfide ore dissolution in alkaline oxygen atmosphere.In this paper,taking refractory gold ore as the research object,the feasibility of oxygen pressure alkaline self-leaching(OPASL)was studied by the oxidation products of sulfide ore.The results show that pyrite can be oxidized to form sulfate,thiosulfate and sulfite under alkaline pressure.After pressure oxidation,the oxidation residue is mainly composed of iron oxide,ferrous oxide,hydrated iron oxide and ferric hydroxide colloid.Two different kinds of valence iron oxides form flocculent or spongy passivation layers on the mineral surface.But sodium carbonate adding can form soluble iron carbonate complexes with iron oxide in alkaline solution,which is beneficial to remove the passivated oxide layer and expose the fresh surface,so as to enhance the oxidation of pyrite.At the same time,the pH buffering capacity of sodium carbonate can be used to stabilize the solution pH in the OPASL process,which can avoid the thiosulfate decomposition and promote gold leaching.In the OPASL process,arsenopyrite can be oxidized into thiosulfate,thioarsenate,arsenate and intermediate products sulfite and arsenite.The oxidation residue is mainly composed of unreacted arsenopyrite and iron oxide,ferrous oxide,hydrated iron oxide,and a small amount of amorphous iron hydroxide with poor crystallinity.The electrochemical study on the gold dissolution by thiosulfate without copper and ammonium showed that the pyrite addition can form corrosion galvanic effect in the gold leaching process.It is helpful to the electron transfer in the gold leaching process,which makes oxygen more effective reduction on the low potential pyrite surface and improves the efficiency of gold dissolution.The existence of pyrite makes the gold corrosion potential shift negatively,and the corrosion current density increases,which enhances the corrosion degree of anode gold electrode.It is found that the gold dissolution in alkaline thioarsenate solution is more efficient than that in thiosulfate solution.The amount of gold dissolved in thioarsenate solution was 16 mg/L,while that in thiosulfate solution was only 6.3 mg/L within 24 h of leaching.The maximum gold extraction efficiency of gold-bearing flotation concentrate could achieve 91.56%under the following condition:a concentration of sodium hydroxide,sodium carbonate and sodium carboxymethyl cellulose at 0.6 M,0.3 M and 100 mg/L,respectively;stirring speed at 800 rpm;temperature at 308.15 K;oxygen pressure at 0.5 MPa;leaching time of 18 h and a liquid-solid ratio of 5:1.The OPASL of gold is an environmentally friendly and smokeless leaching process.The two stages of oxidation pretreatment and leaching can be combined to shorten the leaching process.The cost can be effectively reduced by using the oxidation products of sulfide without additional leaching agent,which provides a new technical reference for the recovery arsenic bearing refractory gold ore.