金在黄铁矿表面沉淀机理的实验研究

EXPERIMENTAL STUDY OF THE DEPOSITION MECHANISM OF An ON PYRITE SURFACE

为了研究金在黄铁矿表面沉淀的机理，于室温、常压，在氯化物溶液中进行了黄铁矿粉末吸附金的实验。在不同ｐＨ的溶液中，黄铁矿均可吸附金，而且ｐＨ值明显地影响吸附速率。扫描电镜观察表明，反应后黄铁矿粒表面有金晶体形成。ＸＰＳ研究得知，黄铁矿光片与含金氯化物溶液反应后表面有ＡＵ存在；硫在反应初期为Ｓ０、Ｓ２Ｏ３，随后转变为ＳＯ４，而铁成为Ｆｅ３＋。黄铁矿中的Ｆｅ２＋和Ｓ２是溶液中金的还原剂。金在黄铁矿表面沉淀可能涉及吸附、还原和晶体生长等过程。

yrite is a common carrier-mineral for An in An-ore deposits.It is important to ascertain the deposition mechanism of An on pyrite surface for understanding the pattern of transport and enrichment of An and for drawing up the technology of ore dressing and recovery of An. Adsorption of An by natural pyrite powder(<75μm) was experimentally studied in chloride solutions (An=100×10-6-500×10-6) at ambient temperature and pressure, and in N2 atmosphere and under a condition of electromagnetic stirring. Two sets of experiments were completed, PH of solution was controlled with and without adding NaOH in the first and second experiment, respectively. An in solutions was determined by spectrophotometry. The results show that pyrite absorbed An from solutions with PH of 4. 50-11.00 and the reaction resulted in decrease in PH of solution. The pH significantly influenced the absorption rate. The rate in an acid solution was greater than that in an alkaline one. Crystals of An were found by SEM observation on the surface of pyrite powder reacted. After reaction of a pyrite plate polished by diamond abrasive paste with An-chloride solution (pH = 5.00 ), XPS study shows the presence of Au on pyrite surface, sulpher existed as S and S2O3 at the early stage of the reaction, and then transformed to SO4; iron -Fe3+.Both Fe2+ and S2 in pyrite play a role as reducing agent for An in solution. The general reaction in an acid environment can be written as:FeS2+ 5AuCl4 + 8H2O→Fe3+ + 2SO4.+ 16H+ + 5An + 20ClDeposition of An on pyrite surface from solution probably involved: the adsoption of An complexes in solution on mineral surface and the formation of surface complexes, the reduction of An of the surface complexes to Auo, and crystal growth of An. The present study provides an experimental basis to approach physicochemical conditions for the enrichment of An by pyrite. It is consistent with the composition determination of fluid inclusions in minerals in An ore deposits that the final oxidation product of sulpher in pyrite is SOak--. Pyrite can be considered as a potential u scavenger' of trace An in chloride-water system (e. g. seawater ).