Activity calculation and phase transformation predication for heavy metals with slag activity calculation model during using electroplating sludge in production of bricks

Abstract

Electroplating sludge is usually regarded as the hazardous waste because of the considerable amount of heavy metals. The vitrification process or firing clay bricks mixing of electroplating sludge is an alternative way to disposal it. The reaction behaviors of heavy metals in electroplating sludge at high temperature are closely associated with the leachability of heavy metals from fired products. In this work, an available thermodynamic model, slag activity calculation model, was used to examine the reaction behaviors and predicate the phase transformation of heavy metals under different conditions. CaO would preferably combine with SiO2 and form CaSiO3 at 1100–1500 K. Most of Cr, Zn and Cu would exist in a form of oxides and spinel phases. Cr would be preferably incorporated into ZnO·Cr2O3 and CaO·Cr2O3 rather than CuO·Cr2O3 except metal oxide; Zn would be preferably incorporated into ZnO·Cr2O3 and ZnO·Fe2O3 rather than 2ZuO·SiO2 and ZnO·Al2O3; Cu would be preferably incorporated into CuO·Al2O3 and CuO·Fe2O3 rather than CuO·Cr2O3. Elevating the basicity facilitated Zn to transform into ZnO·Al2O3, ZnO·Fe2O3 and CuO·Fe2O3, while hindered Zn and Cu being incorporating into 2ZnO·SiO2 and CuO·Cr2O3. Increasing the amount of Fe2O3 in system suppressed the formation of heavy metal oxides (i.e. Cr2O3, ZnO and CuO) and spinel species containing Cr, while promoted the formation of spinel species containing Fe, especially for ZnO·Fe2O3 and CuO·Fe2O3. This work can provide some useful information for reaction behaviors and phase transformation of heavy metals during heating solid waste containing heavy metals.