Adsorptive removal of cadmium from aqueous medium-a critical review

Cadmium is widely distributed in the environment and is basically a non-essential element in cellular metabolism for most life forms. Both geogenic and anthropological sources contribute to cadmium emission and eventual contamination of soil and water. The elevated amounts of cadmium in various environmental resources such as drinking water pose a toxic threat to all the life forms that depend on these resources to sustain life. Cadmium contamination in groundwater is increasing at an alarming rate along with other more prevalent toxicants especially in underdeveloped countries. It is gradually entering our system by consuming contaminated food and water and is spreading in food chain. Along with various health hazards cadmium is basically a potent carcinogen. According to the guideline value recommended by the World Health Organization (2017) (WHO) the presence of 0.003 mg/l (ppm) of cadmium in drinking water is acceptable. Adsorptive removal of cadmium has much been overshadowed by the conventional removal technique (precipitation/coagulation/floatation/membrane separation). Previous reviews have seldom focused on both available and developed sorption techniques for cadmium removal. A vast tabular representation has been representing the sorption capacities of various adsorbents. Cadmium remediation by both activated carbon and other low cost adsorbents has critically been surveyed. Various low cost adsorbents such as biosorbents along with modified activated carbon have shown sufficient high sorption capacity. Desorption techniques for sorbent regeneration after cadmium removal have also been discussed. Treatment of cadmium concentrate and disposal has also been addressed which is much less focused till date.