Waste basalt quarry dust for efficient adsorptive removal of malachite green dye: experimental and modeling studies

Abstract

This study investigates the adsorption performance of waste basalt quarry dust (BQD) for the removal of malachite green (MG) from aqueous solutions. The physicochemical properties of BQD were characterized using FTIR, SEM, EDS, zeta potential, BET, TGA, and XRD analyses. Single-parameter batch adsorption experiments were conducted to evaluate the effects of solution pH (1–10), adsorbent dose (0.5–5 g/L), initial MG concentration (10–80 mg/L), contact time (20–160 min), and temperature (20–55 °C). The optimum experimental conditions were identified as pH 4, adsorbent dose of 3 g/L, initial MG concentration of 50 mg/L, contact time of 80 min, and temperature of 20 °C, achieving the maximum removal efficiency of 96.45%. Subsequently, response surface methodology (RSM) and artificial neural network (ANN) models were employed for multi-parameter modeling and prediction of MG removal. The RSM and ANN models exhibited high predictive performance, with R2 values of 0.9993 and 0.9750, respectively. Adsorption kinetics were adequately described by the pseudo-first-order model, while the equilibrium data were well represented by the Sips isotherm, with the corresponding maximum adsorption capacity of 20.41 mg/g. Thermodynamic analysis indicated that MG adsorption onto BQD was spontaneous and exothermic. Regeneration experiments demonstrated that BQD retained an MG removal efficiency of 86.58% after five adsorption–desorption cycles using 0.5 M HCl. These findings demonstrate the potential of waste BQD as a reusable adsorbent for MG removal from aqueous media.