Study On Leaching Process And Mechanism Of Refractory Gold Ore By New Non-cyanide Leaching Agent

Because the technology is mature,simple and the index is stable,Cyanidation is the main means of gold leaching.However,because deadly toxic of the cyanide,it brings huge harm to environment and human.The non-cyanide leaching method which is low toxicity,high efficiency and economic has been explored all the time.In this paper,a high sulfur and arsenic gold ore was researched,non-cyanide leaching through ammonium thiocyanate was obtained to leach the gold.It has been found through the research of process mineralogy that there were 9.206% S and 12.694% Fe in test samples.Gold grade is highly 98.34g/t.The ore contains 2.7% arsenic.Ore mineral composition is simple,the main metallic minerals are pyrite,arsenopyrite,rutile,chalcopyrite,sphalerite and trace gold.The gangue minerals are mainly quartz and feldspar,in addition there is a small amount of gangue minerals,sericite and chlorite.Gold is embedded in pyrite with irregular fine veins or flakes,or it is dense associated with arsenopyrite in the form of disseminated tectonic.Granularity of Sample ore is sross,Particle size less than 74?m is accounted for only 42.51%.The grain size can not reach the requirement of effective leaching of ores.By comparing the leaching environment and pretreatment methods,high temperature roasting-acid leaching has been adopted.Finally,the process parameters were determined by the optimization test: ore was roasted at 750? for 2 hours and was grinded for 6 min,then leached by 0.8mol/L leaching agent,0.05mol/L oxidant,4:1 of liquid-solid ratio and pH of 2 at ambient temperature,leaching rate of 94.09% can be reached.Through the study of leaching thermodynamics,Au is mainly oxidized into trivalent and complexed with SCN^-as Au?SCN?₄^-.In ammonium thiocyanate leaching gold system,there was no Au?SCN?2-and Au⁺ in solution.SCN^-is inevitable to be oxidated into SO₄^2-?CN-and H+,when the oxidant was used for leaching.So the electrode potential of oxidant should not be too high,and it should be less than 0.94-0.079pH-0.0074logSCN^-/[SO₄^2-][OCN]^-.And using Fe³⁺ as oxidant,the leaching solution pH should be kept below 3.Through the study of kinetic,it can be known that the apparent activation energy Ea of leaching is 45.7kJ/mol when ammonium thiocyanate leaching agent at the range of 0.5⁰.8mol/L,leaching temperature at the range of 15⁴5?,Oxidant concentration at the range of 0.02⁰.05mol/L,leaching time at the range of 15⁶0 min.The reaction order of ammonium thiocyanate was 1.1,and the reaction order of ferric sulfate was 0.5.It can be concluded that the gold leaching rate of ammonium thiocyanate is controlled by chemical reaction model.Therefore,there are the reaction rate equation of leaching by ammonium thiocyanate:1-?1-??^1/3=11.64e^-45700/RT?[HJ-1]^1.1?[Fe₂?SO₄?₃]^0.5.