Rapid and efficient magnetically removal of heavy metals by magnetite-activated carbon composite: a statistical design approach

This study investigates the efficiency of the magnetite-powder activated carbon (M-PAC) to removal of Ni2+, Co2+ and Cd2+ ions from the aqueous solution. Response surface methodology based on the Box-Behnken design was used to evaluate the effects of independent variables such as pH, contact time, adsorbent dosage, temperature and initial concentration of metal ions on the response function and prediction of the best response values. The adsorption fitted best to the Langmuir model indicating the presence of heterogeneous sites for Ni2+, Co2+ and Cd2+ ions adsorption. The kinetics results demonstrated the adsorption process well suited with pseudo-second-order model, indicating that it was involves the formation of valency forces through the exchange or sharing of electrons between metal ions and the binding sites of M-PAC. The intraparticle diffusion model showed a low linear relationship (R-2 < 0.87), which suggests that pore diffusion is not the rate-limiting step in the adsorption process. The values of thermodynamic parameters (Delta GA degrees, Delta SA degrees and Delta HA degrees) showed that the adsorption of all studied metal ions onto M-PAC was spontaneous, feasible and endothermic. Based on these findings, it is concluded that the M-PAC could be successfully employed for adsorption of heavy metals due to simple and rapid separation and high capacity.