Immobilization of Heavy Metals for Building Materials in the Construction Industry – an Overview

Coal bottom ash (CBA) is a one of coal combustion by-products from the production of electricity in coal fired power plants. Although it is classified as hazardous waste and the usage of this material is very limited, it is also an alternative material that benefits the construction industry in replacing cement or fine aggregate at certain percentage. CBA contains heavy metals. The possibility of heavy metals fluxes from the concrete is of great concern as it may cause highly potential adverse environmental impacts especially if the concentration is at beyond regulated standards. This will stop the reuse of CBA in the construction industry and may lead to deficit to entities like power plants due to the high cost of CBA disposal. Thus, this paper presents an overview on the studies of heavy metals immobilization for building materials in the construction industry. Techniques applied for heavy metals immobilization during solidification and stabilization (S/S) process using alkali activation, hydration, thermal treatment and synthesis of dicalcium silicate (β-Ca2SiO4) were briefly described.