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Removal of metal ions from industrial effluents and acid mine drainage by metal sulphide precipitation
Expanded Title:The purpose of this research was to further the understanding of metal sulphide precipitation in the treatment of acid mine drainage and metal ion impregnated industrial wastewater. During the process of metal sulphide precipitation the physicochemical properties of the precipitant material had a significant effect on the overall viability of the metal removal process. The aim of the work was to ascertain the conditions necessary for optimal metal ion removal. The work showed that metal sulphide precipitation has shown potential as a method for the removal of metals from industrial pollutant streams. Although its relatively low solubility products and fast reaction kinetics mean that the process has a number of challenges, it is still a superior choice to that of metal hydroxide precipitation. The findings of the work were, firstly, that that metal sulphide particles obey the DLVO theory. However, the reported threshold value for the promotion of aggregation of about -38 mV is difficult to achieve under viable operational conditions. The pH during precipitation either has to be very high, resulting in the need for a high dosage of pH modifiers, or the colloidal suspension has to be treated with significant amounts of coagulants. This reduces the viability of sulphide precipitation as a precipitation method. This work has also shown that other mechanisms of inducing settling, such as partial oxidation of precipitant material, are effective, but only in synthetic mono-component streams. The consequence of using such a technique for typical industrial multicomponent streams and acid mine drainage is that altering the solution redox not only affects the target material, but may induce catalytic reactions that may transform the precipitant material into an undesired product. Further studies with multicomponent systems would be required. The last major finding of this work is that using FeS as a slow sulphide release source for the precipitation of lower solubility product metal sulphides suffers from limitations that render it not viable for industrial use. The encapsulation of FeS by ZnS that was observed in the current process inhibited further dissolution of the sulphide source, thus stopping the precipitation process.
Date Published:01/09/2014
Document Type:Research Report
Document Subjects:Mine water - Mine water treatment
Document Keywords:Pollution control
Document Format:Report
Document File Type:pdf
Research Report Type:Technical
WRC Report No:2108/1/14
ISBN No:978-1-4312-0588-2
Authors:Nduna M; Lewis A
Project No:K5/2108
Organizations:University of Cape Town
Document Size:856 KB
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