Immobilisation of trace elements using alkaline industrial by-products

Abstract

This paper describes soil pollution with arsenic and thallium compounds, also gives a quick overview on stabilization methods and materials that can be used as trace element immobilising additives. According to published research, alkaline materials can be used for arsenic stabilization. Meanwhile, information on the immobilization of thallium in the soil is very limited. Immobilisation experiment was carried out using cement kiln dust from cement industries and lime mud obtained from sugar refinery as stabilising agents. The 20% addition of these alkaline industrial by-products to contaminated soil and sewage sludge was assessed as a possible way to reduce trace element mobility. Total amount (as aqua regia digestible) and mobile fraction (as (NH4)2EDTA extractable) of 10 trace elements (Zn, Cu, Ni, Cr, Pb, Cd, Hg, As, Se, Tl) were evaluated in four stabilised mixtures and their initial components. The highest total concentrations of trace elements was found in sewage sludge (Cu, Cd, Zn exceeding maximum permissible concentrations (MPC) up to 5.5 times), while the lowest total concentrations of trace elements was in lime mud. Results show that the addition of alkaline waste in most cases decreased available metal fractions. Immobilising effect on contaminated soil was moderate, while both alkaline byproducts effectively reduced mobility of Zn, Ni, Cr, Pb and Cd in the sludge. Mobility of Cu was reduced using lime mud, but additive of cement kiln dust even increased Cu concentration in mobile fraction. Total arsenic (28 mg/kg) exceeded the MPC by 2.8 times in contaminated soil, while the highest As mobility was found to be in the sewage sludge (31% of total). Lime mud effectively decreased As mobility in the sewage sludge (by 15%), but alkaline treatment even slightly increased the share of mobile As fraction in contaminated soil. [...]