Recovery Of Gold By Cementation From From Thiourea And Thiosulfate Leaching Solutions

Since M. C. Arthur and Forrest invented the technology of recoverying gold by cyanidation, for itsmature technology, flexible process, low cost, strong adaptability and so on, cyanidation has been thedominant means of recovering gold in hydrometallurgy. However, because of the poor performance of theconventional cyanidation in smelting of unmanageable ores, the lower speed of leaching, the highly toxic ofcyanide, etc., non-cyanide leaching of gold is gaining popularity and the rationale underlying non-cyanideleaching of gold has come to be known in part. Several methods have been proposed for the recovery ofgold from gold leaching solutions: that is, adsorption, flotation, electrowinning, solvent extraction, ionexchange, and cementation. Among those methods, cementation is considered as an important reaction inhydrometallurgical processing and in winning metals. This paper introduces the common gold leachingsystem,at the same time,researches the recovery of gold with cementation from two typical gold leachingsystem:acid thiourea solution and thiosulfate solution. The leaching of gold is an oxidation–complexationprocess and the gold leaching systems are usually composed of ligand and suitable oxidant. The presence ofthe oxidant in the corresponding leach solutions should be considered no matter what technique is used torecover the gold. It is clear that the oxidants present in corresponding leach solutions negatively affect thegold cementation reaction. In general, the negative effects of oxidants would result in both the higherconsumption of cementation agents and the lower gold recovery. Thus, it is necessary to minimize thenegative effects of the oxidants on the gold cementation reaction. This paper is divided into five chapters:In the first chapter, the common gold leaching method, and the technology of winning gold wereintroduced. On the basis of a large number of literatures, the experiment scheme and experimental purposeswere presented of this paper.In the second chapter, the gold cementation by iron powder from thiourea solutions was investigatedin the absence and presence of ferric ion. Ferric ion affects significantly the cementation reaction kinetics.The gold cementationwithout the presence of ferric ion obeys the first-order kinetics and is a diffusioncontrolled process. Ferric ion increases significantly the redox potential of the solutions, which results inthe remarkable decrease of gold recovery. Tri-sodium citrate was used to overcome the negative effect of ferric ion on gold cementation reaction, which is attributed to its role of lowering the redox potential of thesolutions with the formation of iron (III)-citrate complexes.In the third chapter, the gold cementation reaction was discussed with using aluminium as areplacement agent, displace gold from acid thiourea solutions.Experiments show that, gold recovery closeto100％in the absence of ferric ion. The redox potential of the solutions increases significantly in thepresence of ferric ion, and gold recovery decreases observably. When added fluoride, due to the stablecomplex of fluorine (Ⅰ) and iron (Ⅲ),and overcome the negative effect of ferric ion on gold cementationreaction.In the fourth chapter, cementation of gold from thiosulfate solutions using copper powder wasstudided. Investigated the effect of gold cementation reaction on temperature, stirring speed, goldconcentration, etc., in the absence of copper ion, and optimized the best reaction condition. In the presenceof copper ion,the recovery of gold decreases significantly.When added EDTA, for EDTA and copper(Ⅱ)form stable complex, so overcome the negative effect of copper ion on gold cementation reaction.In the fifth chapter, the effect of temperature, pH, gold concentration and aluminium/gold mass ratioon gold cementation reaction were investigated detailedly. Experiments show that copper ion produceadverse effect on gold cementation reaction, influence the recovery of gold. When added EDTA, goldrecovery increase observably, and gold recovery close to100％.