CONTAINMENT OF CHROMIUM AND ZINC IN FERROCHROMIUM FLUE DUSTS BY CEMENT-BASED SOLIDIFICATION

A physico-chemical model is proposed for the immobilisation of soluble metal species contained in cement-based solidification products where the primary constituent is a ferro-alloy flue dust. Particular attent ion has been given to the fate of chromium - in both Cr(III) and Cr(VI ) forms - and zinc. Whilst metal retention can be achieved by a combin ation of physical and chemical processes, experimental work has shown that the alkaline nature of the cementitious product pore solution red uces the solubility of Cr(III) and zinc species to retard their mobili ty. Cr(VI) remains mobile over the likely pH range. Effective setting of the cement-waste product requires a preliminary wash of the untreat ed dust to remove much of this soluble chromium and other salts. The p ermeability of the final product is much reduced by effective cross-li nking of cement hydration products within the aggregate pore spaces. T his inhibits liquid migration through the cement-waste product and ass ists in physically containing residual Cr(VI), Cr(III), Zn and Mg. Pub lished by Elsevier Science Ltd. All rights reserved.