Factors affecting the mechanism of the adsorption of arsenic species on activated carbon
The development of carbon-in-pulp (CIP) and resin-in-pulp (RIP) processes sparked off intensive investigations into the kinetics and mechanism of adsorption of various species onto activated carbon. The increased processing of complex sulphide ores (e.g. the bacterial oxidation of gold-bearing arsenopyrite) has led to higher levels of impurities such as arsenic in process streams. The removal of such impurities could become a new field of application for activated carbon. It was found that As(V) is more effectively removed from solution by using activated carbon with a high ash content. Pretreatment of the carbon with Cu(II) solutions improves its arsenic removal capacity. The optimum pH for arsenic adsorption by pretreated carbon is approximately 6. There are two mechanisms of arsenic adsorption which occur simultaneously. The arsenic in solution can form insoluble metal arsenates with the copper impregnated in the carbon. Arsenic is also adsorbed independently of the impregnated copper. Ion pair formation has been ruled out in the latter case. Arsenic desorption is easily achieved using strong acidic or alkaline solutions. When acidic solutions are used, copper is also eluted. © 1995.