Leachability of heavy metals from cement mortar bricks modified with water treatment alum sludge

Abstract

Leachability profiles of aluminium (Al), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) from raw drinking water treatment sludge (WTS), laboratory produced sludge and WTS-cement solidified bricks (CMWTS) were studied to determine the potential of reusing WTS in brick manufacturing. The leachability of the heavy metals was investigated using the extraction method. Leach Tests were performed on WTS obtained from the Semanggar Water Treatment Plant, Kota Tinggi, Johore, Malaysia; laboratory produced sludge, and CMWTS produced using the solidification-stabilization (S/S) technique. Structural identity, chemical composition, effectiveness of the solidification-stabilization (S/S) technique and strengths of bricks were also investigated. Surface and other physicochemical properties were studied using FESEM, SEM, BET-surface area analyzer, XRD, FTIR, TOC, compressive strength test and TG analyzer. Leach tests showed that some heavy metals were leached out from samples in acidic solution but very low levels of heavy metals were leached in water and basic conditions and indicating that the WTS was safe for reuse. When the WTS was solidified in cement mortar, the compressive strength of the bricks increased with increasing curing time, pH of the curing solution and amount of WTS added. However, a reduction of compressive strength was observed at 20% WTS in the CMWTS bricks. It can be concluded that WTS has the potential for reuse in brick manufacturing as the addition of up to 20% WTS in cement mortar produced bricks with good strength properties as well as reduced leachability of the selected heavy metals from WTS.