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

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, R-2 = 0.976, and R-2 = 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.