基于配位理论的碱性硫脲选择性溶金机理

Mechanism of gold dissolution selectively in alkaline thiourea solutions based on complex theory

采用电化学方法研究了金及常见伴生金属元素银、铜、镍、铁在高稳定性碱性溶液中阳极溶解的电化学行为,及碱性硫脲浸金的选择性。结果表明:在最佳溶金电势0.42 V时,金在碱性硫脲溶液的溶解电流密度分别是银、铜、镍和铁的3.4,5.2,27.3和42.6倍;而且碱性硫脲体系进行矿物浸出时金的伴生元素浸出率均小于0.1%,浸金具有显著的选择性。采用配合物的化学键理论、配位理论等分析了碱性硫脲选择性溶金的机理。碱性硫脲溶液中金、银、铜、镍和铁分别以Au(TU)2+,Ag(TU)3+,Cu(TU)42+,Ni(TU)42+和Fe(TU)62+的形式存在,Au(TU)2+中反馈σ—π配键的形成显著增强了其稳定性。配合物Ni(TU)42+和Fe(TU)62+中,由于硫脲分子的特殊性,各配位体间硫原子和氮原子上电子云互相排斥,使其稳定性有所降低。而且碱性硫脲溶液中,Ag,Cu,Ni,Fe易于形成致密的硫化物钝化膜,在一定程度上也阻碍了金属的进一步溶解。

Electrochemical behaviors of gold and the co-existing elements, such as silver, copper, nickel and iron dissolving in alkaline thiourea solution with high stability, and gold leaching selectively in alkaline thiourea solution were studied by the methods of electrochemistry. The results indicate that at the optimal potential of 0.42 V, the anodic current density of gold in alkaline thiourea solution is 2.4, 4.2, 26.3 and 41.6 times as big as that of silver, copper, nickel and iron, respectively. Additionally, the leaching rates of the coexisting metals are less than 0. 1% when gold ore is leaching in alkaline thiourea system, which indicates that gold leaching in alkaline thiourea solution shows excellent selectivity. The mechanism of gold dissolution selectively in alkaline thiourea solution was anatomied based on chemical bond theory and complex theory. The results indicate that Au, Ag, Cu, Ni and Fe exist in alkaline thiourea solution in the form of Au（TU）2^＋ , Ag（TU）3^＋ , Cu（TU）4^2＋ , Ni（TU）4^2＋ and Fe（TU）6^2＋ , respectively. σ-π bond is formed in Au（TU）2^＋ , which strengthens its stability markedly. In Ni（TU）4^2＋ and Fe（TU）6^2＋ , repulsion of electron clouds between S atom and N atom amongst complexes decreases their stabilities owning to the particularity of thiourea molecular. Moreover, the compact sulphides passivation layers of Ag^＋ , Cu^2＋ , Ni^2＋ , Fe^2＋ with S^2- , being prone to form in alkaline thiourea solution, prevent their further dissolution to some extend.