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 attention 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 combination of physical and chemical processes, experimental work has shown that the alkaline nature of the cementitious product pore solution reduces the solubility of Cr(III) and zinc species to retard their mobility. Cr(VI) remains mobile over the likely pH range. Effective setting of the cement-waste product requires a preliminary wash of the untreated dust to remove much of this soluble chromium and other salts. The permeability of the final product is much reduced by effective cross-linking of cement hydration products within the aggregate pore spaces. This inhibits liquid migration through the cement-waste product and assists in physically containing residual Cr(VI), Cr(III), Zn and Mg. Published by Elsevier Science Ltd. All rights reserved.