Kinetic and mechanism studies of the adsorption of lead onto waste cow bone powder (WCBP) surfaces

摘要

This study examines the adsorption isotherms, kinetics and mechanisms of Pb~(2+) sorption onto waste cow bone powder (WCBP) surfaces. The concentrations of Pb~(2+) in the study range from 10 to 90 mg/L. Although the sorption data follow the Lang- muir and Freundlich isotherm, a detailed examination reveals that surface sorption or complexation and co-precipitation are the most important mechanisms, along with possibly ion exchange and solid diffusion also contributing to the overall sorption process. The co-precipitation of Pb~(2+) with the calcium hydroxyap- atite (Ca-HAP) is implied by significant changes in Ca~(2+) and PC_4~(3-) concentrations during the metal sorption processes. The Pb~(2+) sorption onto the WCBP surface by metal complexation with surface functional groups such as = POH. The major metal surface species are likely to be = POPb+. The sorption isotherm results indicated that Pb~(2+) sorption onto the Langmuir and Freundlich constant q_(max) and K_F is 9.52 and 8.18 mg g~(-1), respectively. Sorption kinetics results indicated that Pb~(2+) sorption onto WCBP was pseudo-second-order rate constants K_2 was 1.12 g mg~(-1) h~(-1). The main mechanism is adsorption or surface complexation ( = POPb+: 61.6%), co-precipitation or ion exchange [Ca_(3.93) Pb_(1.07) (PO_4)_3 (OH):21.4%] and other precipitation [Pb 50 mg L~(-1) and natural pH: 17%). Sorption isotherms showed that WCBP has a much higher Pb~(2+) removal rate in an aqueous solution; the greater capability of WCBP to remove aqueous Pb~(2+) indicates its potential as another promising way to remediate Pb~(2+)-contaminated media.