Optimization, equilibrium, kinetic and thermodynamic studies of malachite green biosorption using Pisum sativum L. pods powder as a low-cost biosorbent

Different countries occupy a good position in pea production and cultivation. In this research, pea ( Pisum sativum ) shells are low or no-cost material used for the removal of malachite green from water, which are otherwise discarded as waste or used as animal fodder or their pods are used as vegetables. Minimum research is available on the use of pea shells for the removal of dyes from the water. Hence, this was a better opportunity to work on it. The shells of P. sativum were dried, crushed into a fine powder and used for the removal of MG from its aqueous solution. Solutions of different concentrations from 10 to 80 mg/L of MG were prepared from its stock solutions. The pea shell adsorbent powder was pre-treated under different conditions to enhance its efficiency, e.g., boiling in water, treatment with benzoic acid, and microwave oven exposure. Different doses from 0.04 g to 0.24 g of biosorbent were added in 20 mL of solution and effects of different parameters like dose (0.24 g), concentration of MG (10 mg/L), contact time (30 min), and pH (7.0) were studied to get the maximum % sorption of MG. Compared with untreated Pisum sativum pod powder (7.42 mg g⁻ 1 ), pretreatment with 0.1 N benzoic acid increased the maximum adsorption capacity to 9.19 mg g⁻ 1 (23.8%), while boiling water pretreatment increased it to 8.12 mg g⁻ 1 (9.43%). In contrast, microwave pretreatment slightly reduced the adsorption capacity to 7.95 mg g⁻ 1 (7.14% decrease), indicating no improvement over the untreated biosorbent. The equilibrium models showed that data was best fitted in Freundlich isothermal model and all adsorptions followed the pseudo-second order of kinetics and thermodynamic studies.