Utilization of plastics shoes waste as sorbent for removal of heavy metals (Ni and Cd) from industrial wastewater

The present study was focused on the behavior of heavy metals (Ni2+ and Cd2+) uptake by the use of sorbent material of organic nature. Ni2+ and Cd2+ were released abundantly from the industries of metal plating, coating operations (including transportation equipment, machinery and baking enamels), photography, television phosphors, nickel-cadmium rechargeable batteries, solar batteries etc. For the purpose of elimination of Ni2+ and Cd2+ from wastewater two novel sorbents, polyurethane based shoe material-I and poly vinyl acetate based shoe material-2 of particle size 300mu were used for this study. Central composite rotatable design (CCRD) was applied to optimize the independent variables such as initial metal ions concentrations, pH, contact time and amount of sorbent. The optimum conditions for maximum nickel uptake for shoe material-1 was adjusted at the initial concentration of 299 ppm, pH 4.5, contact time of 934.44 minutes using 1.3 g of sorbent and initial concentration of 402 ppm, pH 4.6, contact time of 881.09 minutes using1.2 g of shoe material-2 as sorbent. Similarly the optimum conditions for maximum cadmium uptake were found at the initial concentration of 401.9 ppm, pH 5.0, contact time 881.32 minutes using 1.2 g of shoe material-1. For the shoe material-2 the initial concentration of 402 ppm, pH 4.6, contact time of 881.09 minutes using 1.2 g of sorbent found to be best. The maximum metal uptake of shoe material-1 was observed 171.99 mg/g for Ni2+ and 180.222 mg/g for Cd2+. Whereas, the maximum metal uptake of shoe material-2 was 388.08mg/g for Ni2+ and 396.312 mg/g for Cd2+. Kinetic models (pseudo first order and second order) as well as isotherms (Freundlich and Langmuir) were fitted on the data for studying sorption mechanism. For each sorption system the pseudo first order kinetics and Freundlich isotherm were found best fit. In aqueous medium these sorbents (shoe material-1 and 2) were found better to apply for the sorption of heavy metals (Ni2+ and Cd2+).