Sawdust as a low cost adsorbent can be used to remove dyes and heavy metals from wastewater due to its lignocellulosic composition. In this study, the use of kapok sawdust as an adsorbent for the removal of methyl violet from aqueous solutions was studied. To improve the adsorption capacity, chemical modification using sodium hydroxide was used. The mild alkaline treatment produced chemical changes in the sawdust resulting in acid groups release and acetyl groups elimination. The degree of change is dependent on the time, temperature and alkali concentration. Batch experiments were carried out to investigate the effect of pH, contact time and methyl violet concentration on sorption efficiency. The effect of initial pH of methyl violet solution was analyzed in the range of 3-9. The amount of dye adsorbed increase until pH 5, and then decrease with the increase of pH due to the formation of soluble hydroxy complexes between the adsorbent and the dye. For the investigated methyl violet concentration (0-100 mg/L), maximum adsorption rates were achieved almost in 10-20 min of contact. Pseudo first order, pseudo second order and Elovich models were used to fit the experimental data. Kinetic parameters were computed from linearized equations of these models in Microsoft Excel. The sorption kinetics of methyl violet onto modified kapok sawdust was very well described by the pseudo second order kinetic model with the value of regression coefficient (R2) > 0.999, the adsorption capacity at equilibrium (qe) of 5.7537 mg/L and the pseudo second order constant (ks) of 1.0002 g mg-1 min-1. It may be accepted a two partial order with respect to the free sites concentration and a zero partial with respect to the solute in the solution.
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