Blast-Furnace Sludge as Sorbent Material for Multi-Metal Contaminated Water

Alternative and waste product materials are much in demand for use as sorbent material for contaminated water due to lower costs as well as the sustainability aspects of recycling industrial waste products. In this project batch tests were carried out to evaluate the capacity of blast-furnace sludge to remove Cd, Cr, Cs, Cu, Mo, Ni, Pb, Sn, V and Zn in multi-metal solutions. The sorption tests were conducted on different metal concentrations and pH values. Old sludge deposited at a landfill was also tested, using real leachate from the landfill area spiked with the multi-metal solutions. The data were evaluated by means of calculations of removal/sorption capacities, construction of Freundlich adsorption isotherms and speciation of the metal forms with CHEAQS software. The mineral composition of the sludge was determined qualitatively using XRD. At pH 7 – 9, the sludge had a high removal capacity for the majority of the specific metals in the multi solutions. The capacity of the old sludge with multi metals in real leachate was lower. The isotherms reveal that sorption could be the main mechanism for the removal of Cd, Cu, Mo, Ni and Pb. At pH < 7 there is a risk of leaching of V and Cs, and at pH 5.6 the capacity to remove all metals was low; Zn, Cs and Pb could be leached. The sludge was composed of different iron hydr/oxides, carbonates and silicates, and the active surfaces of the iron hydr/oxides may explain the good sorption capacity for metals. The carbonates endowed the material with a high buffer capacity and the risk of a decrease of pH in water in contact with the material is low