Removal of anionic dyes by rice milling waste from synthetic effluents: equilibrium and thermodynamic studies

This study describes the removal of Everdirect Orange-3GL and Direct Blue-67 by low cost rice milling waste in a batch mode. The effect of various process parameters like solution pH, particle size, biosorbent dose, initial dyes concentration, contact time and temperature on the removal of anionic dyes was investigated. Maximum biosorption capacity of rice milling waste was observed at pH 1 and 3 for Everdirect Orange-3GL and Direct Blue-67, respectively. The results showed that the biosorption capacity of rice milling waste decreased with increase in biosorbent dose and increased with increase in initial dyes concentration and temperature. A maximum biosorption capacity of 31.44 and 52.63 mg/g was observed for Everdirect Orange-3GL and Direct Blue-67, respectively. Analysis of equilibrium data was done by commonly used isotherms. The experimental data followed the Langmuir, Freundlich and Temkin isotherm models very well. Adsorption data of both dyes was better described by the pseudo-second-order kinetic model. Thermodynamic study revealed that the process was feasible and spontaneous at higher temperatures. Positive value of Delta H degrees (13.31 and 40.64 kJ/mol) showed that the process was endothermic in nature. FT-IR spectrum was also taken to investigate the functional groups involved in the biosorption of anionic dyes. The results suggested the applicability of rice milling waste in industrial processes for remediation of industrial effluents.