Revalorization of Spent Bleaching Earth a Waste from Vegetable Oil Refinery Plant by an Efficient Solvent Extraction System

In search of an efficient method for the revalorization of spent bleaching earth (SBE), a waste from vegetable oil refinery plant, three different solvent extraction strategies were adopted. Acetone (A), n-hexane (H), and n-hexane/acetone (HA) solvent systems were used for the extraction of the remnant polar and nonpolar organic compounds of the SBE. The regenerated SBEs together with virgin bleaching earth (BE) were characterized by different characterization techniques and investigated in terms of surface morphology and chemistry. The samples were exploited as low-cost adsorbents for the depletion of methylene blue (MB) from water. The adsorption capability was scrutinized by systematic studying the effect of influential factors including pH, adsorption time, MB initial concentration, and adsorbent dose on the removal efficiency. The results indicated that the regenerated SBE by sequentially extraction system (HA-SBE) resembles BE characteristics, whereas regenerated SBE by acetone extraction system (A-SBE) is superior to the regenerated SBE by n-hexane extraction system (H-SBE) in terms of MB adsorption. The adsoprtion isotherms revealed that the adsorption process obeys Langmuir isotherm model with the maximum adsorption capacity (at pH 5.0 ± 0.1) of 138.00, 109.20, 88.78, and 70.99 mg g−1, for BE, HA-SBE, A-SBE, and H-SBE, respectively. The experimental data well fitted to the pseudo-second-order kinetic model showing that the chemical adsorption is the limiting step in the adsorption process. Considering high adsorption capacity of HA-SBE, the revalorization of SBE by the sequential extraction method could be encouraging from the environmental and industrial points of view.