Removal of malachite green from aqueous solution by kerolite/stevensite mixed-layer clay: full factorial design analysis

Abstract

ABSTRACT In this study, we have tested a mixed-layer clay to remove malachite green (MG) as a pollutant in water. The adsorbent was characterised by various techniques such as BET, DRX, and FTIR. The effects of several physico-chemical parameters (contact time, adsorbent mass, MG concentration, temperature, pH, and stirring speed) on the adsorption capacity of the clay were investigated by batch adsorption experiments. Experimental results were well described by the pseudo-second-order kinetic model with the highest correlation (R2 = 0.999). Of the three isothermal models used, the Langmuir model best describes the MG adsorption process with a coefficient of determination (R2) of 0.995, and a maximum adsorption capacity (qmax) of 100 mg/g. The thermodynamic study showed that the adsorption is endothermic (ΔH° = 44.35 kJ/mol), disordered (ΔS0 = 170 J/mol.K), and spontaneous (ΔG° < 0). Full factorial design modelling resulted in a first-degree mathematical function; the suggested regression model demonstrated excellent agreement with the experimental data. Analysis of main and interaction effects revealed that three factors, namely contact time, MG concentration, and temperature, had a positive effect on response; conversely, adsorbent mass had a negative effect on response. In addition, the model analysis revealed the existence of significant interactions among these factors. This study showed that this clay has good adsorption properties towards MG and can be applied to the decolourisation of water.