Fixed-bed adsorption of Pb(ii) and Cu(ii) from multi-metal aqueous systems onto cellulose-g-hydroxyapatite granules: optimization using response surface methodology

Abstract

We prepared cellulose microfibrils-g-hydroxyapatite (CMFs-g-HAP_N (8%)) in a granular form. We evaluated the ability of these granules to eliminate Pb(II) and Cu(II) ions from aqueous solution in dynamic mode using a fixed-bed adsorption column. Several operating parameters (inlet ion concentration, feed flow rate, bed height) were optimized using response surface methodology (RSM) based on a Doehlert design. Based on ANOVA and regression analyses, adsorption was found to follow the quadratic polynomial model with p < 0.005, R² = 0.976, and R² = 0.990, respectively, for Pb(II) and Cu(II) ions. Moreover, three kinetic models (Adams–Bohart, Thomas, Yoon–Nelson) were applied to fit our experimental data. The Thomas model and Yoon–Nelson model represented appropriately the whole breakthrough curves. The Adams–Bohart model was suitable only for fitting the initial part of the same curves. Our adsorbent exhibited high selectivity towards Pb(II) over Cu(II) ions in the binary metal system, with a maximum predicted adsorption capacity of 59.59 ± 3.37 and 35.66 ± 1.34 mg g⁻¹, respectively. Under optimal conditions, multi-cycle sorption–desorption experiments indicated that the prepared adsorbent could be regenerated and reused up to four successive cycles. The prepared CMFs-g-HAP_N was an efficient and effective reusable adsorbent for removal of heavy metals from aqueous systems, and could be a suitable candidate for wastewater treatment on a large scale.