The metal mining of certain minerals is associated with the generation of acid mine drainage waters and effluents containing cyanides that can have long-term negative impacts on waterways and biodiversity. Obtaining valuable components from those effluents would improve the resource efficiency and the environmental performance of mining. This paper reviews the main separation processes cited in literature for the purification of real acid mine drainage waters and cyanide tailings, and for the recovery of heavy metals and cyanides from those effluents. The processes used are adsorption and membrane technology to obtain valuable compounds from acid mine drainage waters and ion-exchange, acidification-volatilization-reneutralization, sulphidization-acidification-recycling-thickening and membrane technology from cyanide tailings. Further, the use of the 12 green engineering principles for improving the environmental performance of the purification techniques is debated. This work indicates that the energy and chemical consumption and the formation of waste are the main environmental disadvantages of the purification and recovery techniques. This paper concludes that the limitations may be overcome by improving the efficiency of the processes and by using renewable energy and material. The benefits of conducting the purification and recovery techniques utilizing hybrid processes are also pointed out.

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Abstract:The application of nanofiltration membranes to remove sulfate and arsenic from wastewaters was investigated. The influence of operating parameters on the rejection and permeate flux was determined. The nanofiltration experiments carried out with NF90 and NF270 membranes showed a high rejection of sulfate ( 90 %) and arsenic ( 97 %) under the given set of experimental conditions. Better permeate flux values were obtained by NF270 membrane with a minor drop in rejections, but it proved to be better in water recovery. In FESEM analysis, the sulfate deposition on the membrane surface confirmed its well-known precipitation in desalination types of equipment. The experimental results were successfully predicted by using theoretical framework available in the literature. The simulation was carried out by using Levenberg-Marquardt with Gauss-Newton algorithm in MATLAB and the prime important parameters, viz. membrane resistance( ), permeability coefficient P m , and mass transfer coefficient (k) were established separately for each membrane. The gel layer thickness was determined to better understand the hydrodynamics over the membrane surface and it validated the assumption of negligible fouling.

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