RESUMO
In recent years, extraction of zinc from low-grade mining tailings of oxidized zinc has been a matter of discussion. This is a material which can be processed by flotation and acid-leaching methods. Owing to the similarities in the physicochemical and surface chemistry of the constituent minerals, separation of zinc oxide minerals from their gangues by flotation is an extremely complex process. It appears that selective leaching is a promising method for the beneficiation of this type of ore. However, with the high consumption of leaching acid, the treatment of low-grade oxidized zinc ores by hydrometallurgical methods is expensive and complex. Hence, it is best to pre-concentrate low-grade oxidized zinc by flotation and then to employ hydrometallurgical methods. This paper presents a critical review on the zinc oxide mineral flotation technique. In this paper, the various flotation methods of zinc oxide minerals which have been proposed in the literature have been detailed with the aim of identifying the important factors involved in the flotation process. The various aspects of recovery of zinc from these minerals are also dealt with here. The literature indicates that the collector type, sulfidizing agent, pH regulator, depressants and dispersants types, temperature, solid pulp concentration, and desliming are important parameters in the process. The range and optimum values of these parameters, as also the adsorption mechanism, together with the resultant flotation of the zinc oxide minerals reported in the literature are summarized and highlighted in the paper. This review presents a comprehensive scientific guide to the effectiveness of flotation strategy.
RESUMO
Nickel extraction from hazardous waste by sulphuric acid leaching has been investigated. This study was performed to assess the effects of different parameters such as reaction time, acid concentrations, solid-liquid ratio, particle size, stirring speed and reaction temperature on nickel extraction from zinc plant residue, with the aim of recycling this waste and reducing its environmental impact. It was shown that the nickel extraction increased with increasing reaction time, acid concentration and temperature, and decreasing solid:liquid ratio and particle size. Leaching residues were subjected to chemical analysis, XRD and SEM studies, and the results indicated that it is possible to extract more than 96% nickel content by optimization of leaching conditions. These results provided important data on the recovery of nickel from toxic hazardous waste, and leaching is a suitable method for this waste management. The results also showed that this waste can be used as a secondary resource for nickel extraction.
