Fundamentals Of Green Process Of Gold Leaching In Alkaline Thiourea Solution With High Stability

Dissolution of gold in thiourea solution was reported firstly in 1941, and then the theory and process of gold leaching in thiourea solution have been most widely studied throughout the world mainly because thiourea is not detrimental to the environment, non-toxic to humans, and the dissolution of gold in thiourea solutions is much faster than in cyanide solutions, however, which is limited to acidic media. There exist some problems in acidic thiourea solution, such as, higher consumption of thiourea during gold dissolution, serious corrosion of equipments in acidic solution, no selectivity of gold leaching, complicated regeneration and purify procedures of lixiviums, which are the important reasons that acidic thiourea had not been widely applied industrially. In order to overcome the above disadvantages of acidic thiourea solution, gold leaching in alkaline thiourea solution was proposed, and accordingly some research works were carried out. However, thiourea is less unstable in alkaline media than in acidic one, so resolving the stability of thiourea in alkaline media has become the first item to apply it to industry. Since gold leaching in the alkaline thiourea solution is still at the developmental stage, a better understanding of the thermodynamics, a more comprehensive summarization of the research status, and a proper discussion of prospect should be put forward. Under the financial support of the National Natural Science Foundation of China (Grant No.50004009), the stability of the alkaline thiourea system and the concerned fundamentals of green process of gold leaching were carried out. the objective of this dissertation is to offer theories for industrial application of gold leaching in alkaline thiourea solution, to insure continuous and harmonious development of gold industry through studying the fundamental and the key scientific problems of gold leaching in alkaline solution, and accordingly some innovative conclusions were obtained as follows:Based on theory of molecular mechanics (MM), a structure-property relationship between the stability of alkaline thiourea and the structure of thiourea and sodium sulfite was built by a combination of software calculation of HYPERCHEM6.0 with the experiment of infrared spectrum. A double bond between carbon and nitrogen exists in aqueous thiourea because of isomer. Hydrogen-sulfur bond formed easily decreases the energy of HOMO of thiourea molecular, resulting...