Reseach On Preparation And Application Of Non-cyanide Gold Leaching Agents Mainly From Thiourea

With the incessant exploitation and utilization of gold resources, more and more ores are unmanageable, gold ores containing arsenic, antimony, or high-sulfur and submicron-sized particulate gold ores become to be the mainly process object. Using the available technology to dispose it, low recovery will be or a number of preprocessing operations are essential to improve the recovery rate and this will result in uneconomic production index. Although classical cyanide gold leaching method is widely used, it is environmentally harmful. So the cyanide gold leaching technology is seriously constrained to be projected. Thiourea has been always concerned as one of the environmental gold leaching agents since it came out. Acidic thiourea has not been used industrially on a large scale up to now for many shortcomings, i.e., no-selective to leach metals, low gold leaching efficiency, high reagent consumption, devices are easy to be corroded, solution is difficult to be purified and reused and so on. Therefore, investigation on an environmental, efficient, low-cost, and large-scale industrial applied agents mainly from thiourea to extract low grade and unmanageable gold ores has important strategic significance.Too strong alkaline solution increases the decomposition of thiourea. The decomposition rate of thiourea was no more than22%in sodium hydroxide solution when thiourea lets sit for8h at pH value of13. The effect of different oxidizing agents and stable reagents to the stability of thiourea in alkaline solution was investigated at pH value of no more than13. The experiment results show that the oxidization capability of CaO2, K2S2O8and H2O2to thiourea heightens successively, and the capability of Na2SO3, Na2SiO3and (NaPO3)6to restrain the irreversible decomposition of thiourea weakens in sequence. After doing lots of experiments, the main components of thiourea, the stable reagents of Na2SO3and Na2Si03, the pH regulators of Na2CO3and CaO, and the leaching agents of NaBr and K4Fe(CN)6-3H2O were mixed with appropriate proportion to prepare gold leaching agents (CSU-800). The structure of CSU-800was investigated by means of FT-IR and it shows that the main structures of product, such as thiourea, were not destroyed and retained the characters of all ingredients.Main element content, mineral composition and content, as well as mineral dissemination size characteristics of a low grade micro-fine gold ore from Hunan province were investigated by some methods, such as XRD, XRF, SEM, chemical composition and laser particle size analysis. The results show that the mine is mainly an oxidized ore with low sulfur and low arsenic, the grade of gold is2.54g/t, and it belongs to a low grade faintly acid gold ore with some vanadium. Fine-grained dissemination, metallic minerals, and metalloid gangue were very difficult to be separated from each other.CSU-800was applied to the above gold ore in the addition of some appropriate oxidizing agents in alkaline media. Small agitation leaching test was conducted firstly, laboratory trickle stack immersion gold was carried out after the small technological parameter was adjusted. The influences of gold leaching rate from gold ore by grinding particle size, slurry pH, oxidizing agent species and dosages, CSU-800dosages, and mixing time were discussed in the former. The optimum process conditions of small agitation leaching test are determined as follows: liquid to solid mass ratio is2.0,91%grinding ore is less than74μm particle size, pH is about12, CaO2dosages are1kg/(t ore), CSU-800dosages are3kg/(t ore),and mixing time is7h. As a result,72.6%gold leaching rate was obtained. The latter experiment conditions are:770kg micro-fine gold with5.0%moisture content and less than50mm particle size are stacked in a1m3container. During the dump leaching process, the mean concentration of CSU-800is1.40%o, the mean trickle intensity is624.7L/(m2-d), pH is11-12, raw ore grade is2.28g/t with1.665g gold, and leaching time is27days. By the technology above, the gold grade of tailings was0.39g/t, and82.88%gold leaching rate with1.380g gold was obtained.26figures,7tables, and132references.