Study On Alkaline Pretreatment For Refractory Gold Concentrates Under Normal Conditions And Leaching With Bromide

The sample used in the experiment came from JinChiLing concentrator belonged to Zhaojin Group. In the sample, the grade of gold was 84.37g/t and the grade of silver was 723.21 g/t, also with high content of sulfur and arsenic, they were 11.86% and 2.53%. Gold disseminates in the sulfide minerals with a very fine-grained dense, this was showed excellently by phase analysis and particle size distribution analysis. The sample were leached in excessive Br2 and NaBr solution after acid leached, leaching rate of gold and silver were less than 10%. Therefore, the sample is a typical type refractory gold ore with high sulfur and high arsenic.In the test, the sample was finely grinded, after that, it was put into single flotation machine for alkaline pretreatment. The whole process fully realized automatically inhale under normal temperature and pressure. A new type of bromide leaching oxidant carrier called DBDMH was introduced into the test of bromide leaching, which was proceeded after pretreatment and acid leaching. The property of DBDMH was tested.Mainly for the following research:(1)Alkali pretreatment test under normal temperature and pressure:To determine the impact factors of alkali pretreatment under normal temperature and pressure, including the pretreatment slurry pH value, pretreatment time, liquid to solid ratio, surfactant dosage and so on. The effect of each factor on the trend of leaching rate of gold and silver was studied by single-factor test, and the optimum conditions were obtained definitively.(2)Operation of pulp in the flotation machine:XDF-63 flotation machine was used to be the main device of pretreatment, in which, the pulp circled up and down. The phenomenon of "run trough" was prevented.(3)DBDMH bromide leaching test:To determine the factors of DBDMH bromide leaching factors, including pH value, liquid to solid ratio, DBDMH concentration, sodium bromide concentration, leaching time, leaching temperature. The effect of each factor on the trend of leaching rate of gold and silver was studied by single-factor test, and the optimum conditions were obtained definitively.(4)The mechanism of DBDMH bromide leaching:HBrO was released as DBDMH reacted with water. According to the HBrO redox half-reaction in the acidic and alkaline conditions, combining the Nernst equation under 298.15K, the electrode potential under different pH values were calculated. The best pH value was detained by comparing these electrode potentials with the electrode potential of the minimum bromine leaching requirements.Results show that:XDF-63 flotation machine fully available to the refractory gold concentrate came from JinChiLing concentrator in the alkaline pretreatment. The optimization conditions of alkali pretreatment under normal temperature and pressure were as follows:pH value of pulp 14, pretreatment time 48h, liquid to solid ratio 2:1, the amount of lignin sulfonate 1.2kg/t. The leaching rate of gold was 90% and leaching rate of silver was 99% under these optimized conditions. When DBDMH bromide leaching was processed, gold and silver could be leached as long as the slurry pH value was less than 13, but with low efficiency in the neutral or alkaline conditions. Optimum conditions of DBDMH bromide leaching were as follows:pH value-5, liquid to solid ratio 4:1, DBDMH concentration 2g/L, sodium bromide concentration 6g/L, leaching time 6h, room temperature leaching. Under optimum conditions, the total leaching rate of gold was among 90%～91% and the total leaching rate of silver was stable at 99% above.