Studies on selenite adsorption using manganese nodule leached residues

Selenite adsorption on water-washed manganese nodule leached residues (WMNLR) was studied with the aim of detoxifying industrial effluents before their safe disposal into the environment. WMNLR, a solid waste material, was characterized with the help of XRD, FTIR, TG-DTA, pHpzc, BET surface area, surface oxygen, surface hydroxyl group, and chemical analyses. The adsorption behavior of WMNLR toward selenite was studied as a function of time, pH, temperature, and concentration of adsorbate and adsorbent. Increased adsorption capacity with rise in temperature indicates that the adsorption process was endothermic in nature. Based on the thermodynamic parameters such as the Gibbs free energy change, standard enthalpy change, and standard entropy change, the adsorption process was found to be spontaneous and endothermic in nature. Adsorption followed second-order kinetics. The adsorption capacity of the material was found to be 54.6 mg g−1 at 60 mg L−1 of selenite concentration at pH 5 in 3 h contact time.

Graphical abstractThe adsorption capacity increases with increases in temperature. The adsorption process is endothermic in nature as adsorption capacity increases with increase in temperature. The enhancement in adsorption capacity may be due to chemical interaction between adsorbate and adsorbent. Positive value of enthalpy (ΔHoΔHo) indicates the endothermic nature of the adsorption process meanwhile positive values of entropy (ΔSoΔSo) suggest the increased randomness at solid–solution interface.Figure optionsDownload full-size imageDownload as PowerPoint slide