Zn(II) removal from wastewater by an alkali-activated material prepared from steel industry slags: optimization and modelling of a fixed-bed process

Abstract

Removal of dissolved zinc (Zn) from water by a novel alkali-activated material (AAM) prepared from steel industry slags in a fixed-bed column was investigated. Design of experiments was used to find the optimum operation parameters [flow rate $\left(Q\right)$, adsorbent mass, ($m_{\mathrm{ads}}$), and initial Zn concentration ($C_0$)] for the removal of Zn²⁺ from a ZnCl₂ solution. Regression models for the breakthrough ($q_b$), and saturation ($q_{\mathrm{sat}}$) capacities of the bed and three other response parameters as functions of $Q$, $m_{\mathrm{ads}}$ and $C_0$ were fitted with coefficients of determination ($R^2$) ranging from 0.48 to 0.99. Experimental values of $q_b$ and $q_{\mathrm{sat}}$ varied within 1.42-7.03 mg Zn/g and 10.57-17.25 mg Zn/g, respectively. The optimum operation parameters were determined to be $Q=$ 1.64 ml/min and $m_{\mathrm{ads}}=$ 4.5 g, whereas $C_0$ had negligible effect on the response parameters in the range 73-107 mg Zn/l. Finally, three empirical breakthrough curve (BTC) models were employed to describe the individual BTCs of which the modified dose - response model was found to give the best fit (0.960 $\le$ $R^2$ $\le$ 0.998). The results of the present work demonstrate that the novel AAM has considerable potential to be utilized in water purification applications.

Keywords: Alkali-activated materials; breakthrough curve modelling; design of experiments; fixed-bed column; water treatment.