Recovery valuable metals from processing gangue minerals.

Abstract

The wide use of zinc and the exhaustion of traditional sulfide zinc resources provide the motivation to consider oxide zinc mineral resources, however, it is a challenge to be separated from other carbonate minerals by flotation techniques. Therefore, calcium reverse flotation was evaluated as a new flotation method to recover zinc oxide minerals in this literature. The novel collector CaFloatA1 and CaFloatA2, a emulsion mixed by sodium oleate, kerosene and sodium hydroxide, were examined in this study. For comparison, the Ag-CuOx-Ca and Ca flotation were considered as a control tests. In the control test of Ag-CuOx-Ca, the collector sodium isopropyl xanthate, frother AF-70 and promoter AP-3418 were carried out for Ag flotation; sodium hydrosulfide, AP-6494 and sodium amyl xanthate for CuOx flotation; sodium oleate (NaOl) as a collector for Ca flotation. The results showed an insufficient recovery for Ag and CuOx, only15.7% of Ag, 2.44% of CuOx in the Ag and Cu concentrate, respectively. But we surprisingly found the Ca flotation recovered 66.46% of calcite, then the calcite recovery was examined in the further Ca flotation. Three Ca flotation stages were carried out for recovering reversely calcite. 1000 g/t NaOl was added in each Ca flotation stage. The results showed that Ca recovery increased from 61 to 78%, and the ore grade decreased from 8.69 to 1.97% of the tailings, indicating that Ca flotation could recover a large quantity of calcite. Therefore, it is proved that Ca reverse flotation was a promised method to separate calcite from zinc oxide ores. Recently, studies showed that sodium oleate mixed with the bridging liquid, such as kerosene or benzene, improved the agglomeration of calcite particles, and calcite recovery achieved 98% under the optimal process parameters. Therefore, this kind of collector was carried out to inspect calcite recovery by Ca reverse flotation in this study. The results showed that Ca, Zn recovery and grade increased with NaOl addition increased by the novel collectors (CaFloatA1) at pH 10, despite the content of zinc oxide ores of sample 1, sample 2 (willemite, Zn2SiO4) is different from sample 3, sample 4 (Zincite, ZnO). The maximum Ca recovery was over 90% with 4000 g/t NaOl additions in four samples. The acid leaching tests showed that the acid consumption of Zn pre-concentrate was decreased significantly compared to the original samples. The acid consumption of ores was introduced in this study, which demonstrated that less than 100 Kg/t sulfuric acid was consumed for extracting Zn. The CaFloatA1 had a perfect performance on the calcite flotation in this literature. The acid consumption of Zn pre-concentrate decreased significantly After Ca reverse flotation compared to the original ores, which indicated that this method can improve economic benefits and decrease the environmental footprint. Therefore, we supposed that CaFloatA1 can be applied in the separation of other metal oxide ores from calcite by froth flotation. Gold and silver in pyrite are not amenable to recovery by traditional cyanide leaching. In this literature, pyrite concentrates were roasted at different temperatures to improve the recovery of gold and silver by cyanide leaching. Gold and silver recoveries were maximum in the temperature range of 500-600oC due to the higher porosity of calcine, the Au and Ag recovery improved from 25 to 86% and 50 to 77%, respectively. Higher roasting temperatures caused the gold secondary encapsulation and formation of silver ferrite lead to the recoveries decreased. Gold secondary encapsulation was due to the sintering of the calcines. SEM characterization studies of the calcine revealed that the gold included in the pyrite occurs in sizes less than one micron and roasting produced channels in the pyrite exposing the gold particles to the leaching solution. This work also presents a brief review of the pretreatment oxidation processes currently available for the recovery of encapsulated gold in pyrite, namely bio-oxidation, atmospheric and high-pressure leaching with oxygen. Copper tailing is a solid waste produced from effluent in mining plants. However, a huge amount of copper tailings are collected and stockpiled by mining activity and process, resulting in the occurrence of failures increase worldwide, in addition, the leached heavy metals in the tailings pose serious pollution to the local resources when exposed to the weathering and natural oxidation environment. On the other hand, such a large number of tailings are regarded as a second resource to recycle valuable metals, such as iron, copper, zinc, etc. As an effective and multifunctional technology, flotation is a widely and commonly used method to treat copper tailings, recover valuable minerals and minimize the environmental footprint. This literature reviews: the potential effects of tailings in the environment, including dust emission, tailing failures, and contamination; factors that influence the performance of copper flotation, including particle size, reagent effects, and clay minerals behavior were also discussed.