Study of malachite green dye biosorption on acerola (Malpighia emarginata) seeds for the treatment of coloured wastewater: kinetics, equilibrium, and experimental design

Abstract

In this work, malachite green dye was removed from an aqueous effluent using acerola seed as an adsorbent. The adsorbent was characterized by Fourier transform infrared (FTIR), X-ray diffraction, zero charge potential, and acid group concentration techniques. The findings revealed that the adsorbent has a characteristic composition of lignocellulosic materials, as described by the FTIR data, besides having a pH-PZC of 3.5 and a concentration of acid groups of 0.2313 mmol g−1. The central composite design was used for batch experiments, and the effects of three variables were analysed. The optimum conditions (pH, particle size, and adsorbent mass) were 10.0, 600 μm, and 0.8 g, respectively, for 97.52% dye removal. Redlich–Peterson isotherm fitted well to the experimental data (R2 = 0.997 and root-mean-square error (RMSE) = 1.168). From the Langmuir isotherm, the maximum adsorption capacity obtained for dye was 103.50 mg g−1. As for the adsorption kinetics, it was found that the pseudo-second-order model sufficiently describes the experimental data (R2 = 0.999 and RMSE = 0.018). Thus, the acerola seed has excellent properties as an adsorbent, demonstrating a remarkable performance and a great capacity to be used in the treatment of aqueous effluents contaminated by dyes.