Reutilization of granite powder as a component of permeable reactive barriers for the treatment of Cr(VI)-contaminated waters

Permeable reactive barriers (PRBs) are efficient and cost- effective systems for groundwater remediation. Different types of material have been tested as reactive media for constructing PRBs. To this purpose, the use of waste materials is of particular interest, provided they meet some permeability and reactivity requirements. In the present study, the use of granite powder, a waste generated during the process of cutting granite, was evaluated as a component of PRB filler, mixed in different proportions with compost. The Cr(VI) adsorption capacity and desorption behaviour of granite powder, pine bark compost, composted municipal solid waste and mixtures containing different proportions of granite powder and compost was compared. Individually, the granite powder was not suitable for use as PRB filler because of its moderate permeability and Cr(VI) adsorption capacity. The addition of pine bark compost increased the hydraulic conductivity and improved the Cr(VI) adsorption capacity of the material, while decreasing Cr desorption. In turn, the addition of compost derived from municipal solid waste did not have the same beneficial effect, as it decreased the hydraulic conductivity of the mixtures and only slightly improved the adsorption capacity. In summary, mixtures containing 50 or 25% granite powder and 50 or 75% pine bark compost (v/v), respectively, were the best materials for use as a PRB in relation to cost/effectiveness.