Removal of heavy metals from contaminated water using industrial wastes containing calcium and magnesium

Two industrial wastes (IW1 and IW2) were investigated as potential sorbents to retain cadmium and lead from contaminated water. The sorption experiments have been conducted through lab-engineered cartridge filtration system in order to get as close as possible to industrial processes. The effectiveness of IW1 and IW2 were compared to that of activated charcoal Norit® (AC), the best-known matrix for its excellent retention capacity. The sorption isotherms of metals on the three solid sorbents (IW1, IW2 and AC) were built, and then mathematically modelled. Free Gibbs energy (ΔG°) of the sorption processes as well as the equilibrium parameter (RL) have been calculated for each pollutant-sorbent couple. The study revealed that: i) for cadmium sorption, IW2 was much more effective than IW1 and especially than AC (18-fold higher in term of maximal sorption capacity); ii) if IW2 was slightly less effective than AC to retain lead, it can be still considered as an interesting sorbent due to its low cost; iii) the sorption of cadmium was as spontaneous on AC as on IW1, and almost half as much on IW2; iv) regarding lead retention, the sorption on the three sorbents was spontaneous; (v) the retention of cadmium and lead was mainly explained by precipitation since otavite, cerussite and hydrocerussite were identified and characterized by X-ray diffraction of used sorbents. The study showed that the industrial wastes studied stood out as new efficient materials with sorption power equal to or greater than the reference material AC. The prospect of a new generation of industrial wastes with lasting efficiency as contaminated water depollution agents comes at a key moment in the search for new perspectives in the circular economy.