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Batch adsorption experiment of malachite green (MG) was studied with walnut shell (WS). Adsorption of MG onto WS was confirmed by FTIR analysis. Particle size, dosage, effect of dye concentration, pH, temperature and ionic strength were investigated. The optimized conditions for adsorption process in this study was carried out using WS of dosage 0.03 g/20 mL dye, at room temperature, ambient pH and agitation rate of 250 rpm for 2 h. The kinetics of the adsorption process was studied using four models: Lagergren 1st order, pseudo 2nd order, Weber–Morris intraparticle diffusion and the Boyd models. Kinetics data is best fitted with pseudo 2nd order. Weber–Morris model showed that intraparticle diffusion may be present, but is not the rate-limiting step while Boyd model suggested that film diffusion may be the controlling mechanism. Four isotherm models namely the Langmuir, Freundlich, Redlich–Peterson …