Modeling of Sorption Data for Cr (III) Adsorption onto Cabomba caroliniana from Leather Tannery Effluent Using Non-Linear and Linear Methods of Isotherm Models

Industrial effluents constitute the major source of various kinds of heavy metal pollution in natural water. Water pollution by heavy metals is dangerous because they are toxic, non-degradable by both chemically and biologically and tend to accumulate in aquatic species or deposit in sediments. Leather tannery industry discharges a large volume of untreated effluent which containing both Cr (III) and Cr (VI) in Sri Lanka. Cr (VI) is toxic, but Cr (III) in the effluent, on standing is completely oxidized by dissolved oxygen to more toxic hexavalent chromium. Adsorption is rapidly becoming a prominent process for treating aqueous effluent containing heavy metals. It depends on the ambient conditions. Batch experiments were carried out to investigate the optimum ambient conditions such as initial pH of the solution, dosage of biomass and contact time for the adsorption of Cr (III) to Cabomba caroliniana. Equilibrium isotherm study was performed for the initial concentrations varying from 30-6000 mg/L of tannery effluent. The adsorption data was modeled using widely used two parameter isotherm models such as Langmuir and Freundlich. The best fit among the isotherm models was assessed by linear and nonlinear methods. The both non-linear and linear forms of Langmuir isotherm model showed the better fit of sorption data compared to the Freundlich isotherm model suggesting a monolayer adsorption of Cr (III) onto the biosorbent Cabomba caroliniana. The maximum monolayer coverage was found to be 94.98 mg/g. The separation factor RL (0-1) reveals that the adsorption is a favorable process.