Efficient and selective phosphate removal from wastewater using surface-modified spent bleaching earth from palm oil refineries: A zero-waste approach

This research employs a zero-waste approach by utilizing the surfactant-modified spent bleaching earth (SBE) waste from palm oil refineries for phosphate removal from wastewater. Various mass ratios of n-hexane to SBE (r(hex)), CTAB loading (mc), and temperature (Ti) is studied to obtain the reactivated SBE with the highest phosphate removal - which is obtained at r(hex) = 1:5, mc = 0.5 wt%, and T-i = 30 C and is referred to as RSBEm. A 97.7 wt% removal of phosphate and 194.6 mg/g adsorption capacity can be successfully achieved at pH = 7, C-o = 150 mg/L, t = 150 min, T = 30 C, RSBEm loading = 0.1 wt%. The kinetic, isotherm, and thermodynamic studies suggest that the phosphate uptake follows the monolayer mechanism. The studies also show that the adsorption is spontaneous, endothermic, and mainly driven by the electrostatic interaction between the cationic head of CTAB attached to the interlayer spacing of RSBEm and negative phosphate ion. RSBEm shows good reusability with the phosphate removal rate > 80 wt% until four cycles. Based on the selectivity study using the single compound and binary system approach, RSBEm also has a good selectivity towards phosphate in the presence of various co-existing anions.