Adsorption of a basic organic dye methylene blue from aqueous solution onto a low-cost bio sorbent made from peanut (Arachis Hypogea) shells

Organic dyes are among the refractory and persistent pollutants of water. Methylene blue (MB) is one of the organic dyes widely used in the textile and other industries. In this study the removal of methylene blue in aqueous solution was studied by adsorption using a biosorbent prepared from peanut (Arachis hypogea) shells (AHB). After characterising the biosorbent, the adsorption tests were carried out in batch tests by varying the following parameters: mass of the biosorbent, contact time, initial concentration and pH of methylene blue solution. The results obtained show that the AHB biosorbent has a pHZPC of 6.74, a specific surface area of 55.96 m2 g-1 and a maximum observed adsorption capacity (Qmo) of 19.95mg/g. The maximum adsorption capacity of AHB decrease from   46.50 mg/ g to 4.62 mg/g when the amount of the biosorbent increases from  10 g to 1000 g ; in the other hand, the maximum adsorption capacity increases from 9.30% to 92.4%with the increasing of the  mass of the biosorbent. The optimal adsorption weight was evaluated to be 800 mg, with a % Ads of 89.12% at pH 10, after 210 min. The results obtained show an increase in the maximum adsorption capacity and the maximum adsorption percentage of the biosorbent with the AHB-MB contact time and pH solution and tend to constants. The modeling of the kinetic and equilibrium of adsorption shows that the pseudo-first-order kineticmodel (Rg2=0.9536) and the Freundlich equilibrium model (Rg2=0.9466) are better suited to describe the adsorption of MB on AHB compared to the pseudo-second-order kinetic model (Rg2=0.9009)and the Langmuir model(Rg2=0.8903).Adsorption is therefore governed by the attachment of the MB particles to the surface of AHB and occurs through the formation of multilayers. The values of RL and 1/n lower than 1 indicate that the adsorption of MB on the AHB biosorbent is favorable. This suggests that biosorbent from peanut shells is effective for the removal of organic dyes from wastewater.