1、PDF外文：http:/ 录 Anaerobic Thiosulfate Leaching: Development Of In Situ Gold Leaching Systems J.A. Heath, M.I. Jeffrey *, H.G. Zhang, J.A. Rumball Abstract Ferric EDTA and ferric oxalate complexes are both effective oxidants for the aerobic and anaerobic dissolution of gold in thios
2、ulfate solutions, and therefore are potential candidates for the development of an in situ leaching system. The thiosulfate and polythionates were quantified during leaching using HPLC with perchlorate eluent and an anion exchange column, and it was found that both the iron EDTA and oxalate complexe
3、s have a low reactivity with thiosulfate, and they do not react with thiourea when it is added as a leaching catalyst. Anaerobic leaching experiments showed that both systems were still active after seven days leaching, and when 1 mM thiourea was present, there was significant gold dissolution. Howe
4、ver in the absence of thiourea, the gold leaching was very slow, and hence the addition of thiourea as a gold oxidation catalyst is required for the iron(III) leaching systems. When anaerobic leaching was carried out in the presence of finely ground pyrite, the iron(III) complex was rapidly reduced
5、to iron(II) as a result of the pyrite catalysed oxidation of thiosulfate. Pyrrhotite was also found to be problematic as it directly reduced the iron(III) complex, and therefore the quantity of gold leached was significantly lower in the presence of both these sulfide minerals. These problems associ
6、ated need to be overcome if such a system is to be used in an in situ leach environment. 1. Introduction In situ leaching has been in use since the mid 1970s inthe United States and the former Soviet Union for producing refined uranium (Mudd, 2001a, b). It has recently been implemented at Beve
7、rley (2000), and is soon to be used at Honeymoon Well in South Australia. It has also been utilised to recover copper (DAndrea et al., 1977), and soluble salts such as halite, trona, and boron (Bartlett, 1992), and potash from phosphate rock (Habashi and Awadalla,1988). The famous Frasch process for
8、 mining sulfur with superheated water may also be consider as an in situ leaching process. However, in situ leaching technology has not been adopted for the recovery of gold, even though there are a number of deposits which have favourable characteristics, including the Victorian Deep Leads. The Vic
9、torian Deep Leads are buried alluvial gold bearing gravels, deposited in ancient valleys about 3060 million years ago. Since that time the valleys have filled with sand, gravel, water, clay and other minerals, and the leads now lie up to 100 m below the surface. They are below the water table, howev
10、er the water is slow moving at only a few meters per year (Anon, 1982). The resource is very extensive at least 700 km are known to exist in Victoria around the Bendigo, Ballarat and Avoca areas. As it is an alluvial gold deposit, the content is highly variable, but averages approximately 4 g/m3. Th
11、e thickness of the leads varies up to 5 m, and the width up to 1 km (Anon, 1982). The sulfur content is typically low, varying from 1% to 5% (Phillips and Hughes, 1996), with marcasite being the major sulfide present with some pyrrhotite. A further complication is the presence of lignite, which has
12、the potential ofpre- robbing gold from cyanide solutions. During the early1980, CRA Limited undertook extensive research into theuse of in situ leaching with cyanide to mine gold from theVictorian Deep Leads. This work was unsuccessful forboth technical reasons (availability of oxidant) and dueto en
13、vironmental concerns with pumping cyanide underground.Any future development of the Leads would needto be compa- tible with the current use of the groundwaterresource in farming, as well as having strategies for environmentalmonitoring and rehabilitation in place. Thisleads to the visualisation of a
14、 process which uses a relativelybenign gold leaching system, potentially based on thiosulfate as a ligand. The copper-ammonia-thiosulfate system suffers from several drawbacks, most notably, the reduction of copper(II) ammine by thiosulfate, producing copper(I) thiosulfate and tetrathionate (Byerley et al., 1973). This causes the gold leach rate to
