Study On Reclamation Of Gold And Preparation Of Polyferric Sulphate Form Pyrite Cinder

The pyrite cinder,accompanied by the production of calcining pyrite in a sulfuric acid plant in Anhui province,contains 35%to 60%iron,gold,silver and other precious metals, and the grade of gold is 3.2g/t to 6.5g/t,so such pyrite cinder possesses qualities to leach gold and synthesize polyferric sulphate.Study shows that the cinder contains harmful impurities for leaching gold such as arsenic,copper etal.,the leaching rate of gold is less than 30%only by conventional methods,therefore,a kind of particular aiding agent has been prepared to mask interaction from copper aiming at such problem.In this experiment, the cinder was fine grinded firstly,mixed 2 hours with Self-synthesized SNO promotion agent in pretreatment process,and then acceded activating agent SMD in cyanidation system keeping appropriate conditions,the leaching rate of gold can be above 80%.The optimum condition was defined as follows:fine grinded granularity is -300 mesh;20L SNO agents should be acceded and reacted for 150min with per ton cinders in pretreatment process;the amount of sodium cyanide is 3kg/t cinder in cyanidation;activating agent SMD is 3kg/t cinder;pH between 10 to 11 in cyanidation;cyanide leaching temperature maintained above 15℃;cyanide leaching time is 24 to 30h.The grade of gold would drop from 3.2 or 6.5g/t to 0.3g/t cinder.The cinder can be directly extracted iron with sulfuric acid to prepare PFS after being removed the cyanide.The preparation process was divided into three steps-acid leaching,reduction and catalylytic-oxidation polymerization.The iron in the cinder were leached out by sulfuric acid at atmospheric pressure in acid leaching process;potassium chlorate-nitrate-potassium iodide compound catalytic oxidizer was used in the catalylytic-oxidation polymerization process,it not only avoided the secondary pollution by conventional catalyst-sodium nitrite,but also shortened the reacting time to prepare qualified PFS.This paper determined the best preparation conditions by orthogonal and single factor experiments.The sulfate acid concentration is 70%in acid leaching process;excessive coefficient of sulfuric acid is1.3;acid leaching time is 40 min;the leaching rate of iron can reach 91.69%;the catalyst is potassium chlorate 4%,nitric acid 0.9%and potassium iodide 0.2%in catalylytic-oxidation polymerization process;the reactants molar ratio n(H₂SO₄)/n(Fe²⁺)=0.29-0.36;stirring reaction time is 30 min and preserves the temperature 2h.Experiments show that PFS has a good result in dealing with coal-washing waste water and kaolin suspension.All indications of PFS were qualified to reach the state standards.The best PFS dosage for Coal-washing wastewater is 2mg/L; scope of pH is 6 to 10;the best PFS dosage for kaolin suspension is 4mg/L,scope of pH is 5 to 12.The principle of cyaniding leaching gold and the influences on leaching process of iron,copper,arsenic and other impurities in the cinder was discussed.SNO agent and activating agent SMD would eliminate the influence of arsenic and copper to insure that gold can be leached out effectively.Moreover,the main reaction behaviors in the preparation process of PFS were studied so as to achieve the advancement and rationality of the preparation process.Finally,the flocculation principle of PFS was discussed.Study shows that cyaniding leaching gold is complexing reaction between gold and cyanide with the existence of oxygen in alkalescence,there are inferences in leaching gold from arsenic and copper rather than other constituents in the pyrite cinder.Furthermore,PFS has main function in adsorption electrical neutraligation,adsorption bridging and compressing electric double layer to treat with coal-washing waste water and kaolin suspension,which has importance of realistic significances in recovering and using solid waste,controlling environmental pollution and alleviating stress from the shorten of resource.