Evaluating solubility of Zn, Pb, Cu and Cd in pyrite cinder using leaching tests and geochemical modelling

Production of sulfuric acid by roasting of pyrite (Fe sulfide) produces a Fe rich waste product, pyrite cinder (or pyrite ash), which often contains high levels of trace metals such as Zn and Pb. The chemical forms of the metals and their solubility in these materials are poorly known. To evaluate the risks associated with pyrite cinder and manage cinder contaminated sites efficiently more knowledge on the chemical processes in pyrite cinder is needed. In this study the solubility of Zn, Pb, Cu and Cd in a pyrite cinder from Bergvik, Sweden, was investigated. The objectives were to (i) identify the solubility controlling processes for Zn, Pb, Cu, and Cd in the pH range 3-9, (ii) characterize the Fe (hydr) oxides present in these materials and (iii) to identify implications for management strategies of pyrite cinder contaminated sites. This was done using a combination of batch experiments, selective extractions, X-ray absorption spectroscopy and geochemical modelling. Hematite was identified as the dominating Fe mineral in the cinder. A geochemical model using generic binding parameters could describe the solubility of Zn, Cu and Cd in the cinder well, while Pb concentrations were generally underestimated. The modelling indicated that adsorption to Fe (hydr) oxides was the most important solubility controlling mechanism for all metals, except for Zn at pH > 6, where Zn minerals seemed to control the concentrations of Zn. To minimize leaching of Zn, Pb, Cu and Cd from cinder materials, remediation strategies should be focused on keeping the pH > 6. (C) 2017 The Authors. Published by Elsevier Ltd.