Effect of time and acid concentration on metal extraction from galvanic sludges

Abstract

Galvanic sludge is a solid waste produced by the surface treatment industry, classified as hazardous because of their high concentration of heavy metals, which in its final destination is disposed in waste disposal facilities, with economic costs to the holders. Through hydrometallurgical processing, it is possible to extract valuable metals, with low costs involved, while the hazardous level of the residue is reduced. In the present work, the heap leaching method was studied as a solution to the treatment of these residues, which in order to consist in a valuable option, processing and operation costs must be kept as low as possible. For the experimental testing, a closed loop lixiviation column for hydrometallurgical treatment of galvanic sludge with possibility of continuous flow of the leachate (and static process as well) was constructed, simulating the heap leaching process. The galvanic waste in study, delivered by a local surface treatment company, was both chemically and physically characterized, proving to be rich in valuable metals like Nickel, Chromium and Copper. The waste material was characterized both for physical parameters (grain size) and chemical composition. The lixiviation trials, with a maximum duration of 1 week, were conducted. The influence upon the extraction rate of metals such as Nickel, Chromium and Copper, of parameters such as the concentration of the leaching agent (sulfuric acid) and time were tested. In order to quantify the leachate circulation effect, a static trial was conducted as well. Extraction rates of 35.5 % of Nickel, 14% of Copper and 13.6 % of Chromium were obtained after 6 hours in a dynamic trial, with 100 g/L sulfuric acid solution concentration. The acid consumption rate was correlated with the metal extraction. Finally, the results were compared with others obtained in previous galvanic sludge agitation lixiviation and laterites heap leaching works.