Pb(II) removal using calcium silicates synthesised from industrial wastes: process optimisation and kinetic modelling

Abstract

ABSTRACT This study investigates the potential of calcium silicates (CS) synthesised from granite and marble waste as an adsorbent for sustainable waste management. A simple and chemical-free synthesis method was adopted in the preparation of CS. X-ray diffraction, scanning electron microscopy, zeta potential and particle size distribution techniques were used for the characterisation of CS. As Pb(II) and its derivatives from various industrial effluents exercise significant negative impact on the environment and human health, an attempt was made to remove Pb(II) by adsorption process. Batch experiments were conducted to evaluate the feasibility of removal of pb(II) using CS. The zeta potential value of −83.7 mV and the mean particle size of 916 nm for the prepared CS can enhance adsorption process. The analysis of various adsorption kinetic models reveals that pseudo second order kinetic model exhibited a favourable level of agreement with kinetic data (R2 = 0.999). Response surface methodology utilising central composite design was employed to evaluate various process parameters, such as initial Pb(II) concentration, pH, adsorbent dosage and sonication time on adsorption process. Results from 30 experimental runs performed in accordance with model recommendations concluded that the effect of selected parameters with an R2 value of 0.937 was adequate for the current study. In order to assess the goodness of fit and statistical significance of the model’s performance, ANOVA and Lack of Fit (LOF) tests were conducted. The findings show that Pb(II) can be easily removed from the aqueous solutions using CS as an adsorbent under optimal experimental conditions of 100 mg/l Pb(II) initial concentration, 2 g/l adsorbent dosage, pH of 8 and a sonication time of 45 min.