Preparation of novel CS/SiO2-EDTA nanocomposite from ash of rice straw pellets for enhanced removal efficiency of heavy metal ions in aqueous medium

The production valuable materials from waste for environmental treatment have attracted considerable attention worldwide. In this study, porous silica was produced from the ash of rice straw pellets. The porous silica was then modified with chitosan (CS) and ethylenediaminetetraacetic acid (EDTA) to produce novel CS/SiO2-EDTA nanocomposites for the removal of heavy metals in aqueous medium. The adsorption of Pb2+ was investigated to evaluate the effectiveness of the composite and the effects of reaction parameters on the adsorption process were extensively explored. The adsorption is fast in the initial 5 min, then almost reaches equilibrium in 10 min. The conditions for the highest adsorption capacity are an EDTA content of 1.0 M, a pH of 6, an adsorbent dosage of 0.1 g/L, and a Pb2+ concentration of 100 ppm. The removal efficiency, adsorption capacity, and rate constant are 70.39 %, 703.9 +/- 21.1 mg/g, and 0.012 +/- 0.003 g/mg & sdot;min, respectively. The conditions for the highest adsorption efficiency are an EDTA content of 1.0 M, a pH of 6, an adsorbent dosage of 0.5 g/L, and a Pb2+ concentration of 40 ppm, where the adsorption efficiency, adsorption capacity, and rate constant are 89.88 %, 71.91 +/- 1.86 mg/g, and 0.013 +/- 0.002 g/mg & sdot;min, respectively. The selectivity of the composite was investigated by using Ni2+, Cu2+ and Fe2+ ions under the same experimental conditions. In multi-metal solutions, the adsorbent showed the highest affinity for Pb2+. In addition, the adsorption isotherms and thermodynamics were investigated and an adsorption mechanism was proposed.