Removal of heavy metals using polyvinyl alcohol semi-IPN poly(acrylic acid)/tourmaline composite optimized with response surface methodology

The heavy metals, Pb2+ and Cu2+ adsorption was studied using polyvinyl alcohol semi-IPN poly (acrylic acid)/tourmaline (PVA semi-IPN PAA/Tm) composite as the adsorbent. During the preparation process of adsorbent, response surface methodology (RSM) based on three-variable-three-level Box–Behnken design (BBD) was employed. The effects of three variables, i.e. neutralization degree (ND) of AA, PVA:AA ratio, and Tm:AA ratio on the adsorption capacity for Pb2+ and Cu2+ (as response) were evaluated. The results indicated that ND of AA and Tm:AA were the most significant preparation variables affecting Pb2+ and Cu2+ removal. Models capable of predicting the maximum adsorption capacity were established and the optimum preparation conditions were determined as follows: ND of AA, 68–69%, PVA:AA, 0.0973, Tm:AA, 0.20. Under these conditions, the predicted values of models (3.18 mmol/g for Pb2+ and 3.00 mmol/g for Cu2+) were in good agreement with experimental results (3.12 mmol/g for Pb2+ and 2.98 mmol/g for Cu2+). The adsorption kinetics of as-prepared composite under non-competitive and competitive conditions suggested that the adsorption equilibrium could be achieved within 30 min. In addition, as-prepared composite showed good reusability with 0.1 mol/L EDTA as the desorbing agent, and the adsorption process was mainly controlled by ion exchange and chelation interaction.