Evaluation of new hydrophobic association inorganic composite material as coagulant for oilfield wastewater treatment

The use of oil recovery technologies has resulted in the weakening of interfacial tension between oil and water in oilfield wastewater due to a large amount of polymer present. This leads to the formation of stable emulsified colloidal systems and increases the difficulty of oilfield wastewater treatment. This study investigated hydrophobically-modified polyaluminium silicate sulphate (PASS-C) as a coagulant for oilfield wastewater treatment. PASS-C was prepared by the condensation polymerisation of Al2(SO4)3·18H2O with dialysed and hydrolysed KH570 [3-(trimethoxysilyl)propyl methacrylate] under titration with NaAlO2 and water glass at low temperature. The zeta potential of PASS-C showed that the introduction of hydrophobic groups increased its charge neutralisation ability. Additionally, compared with conventional PASS, PASS-C showed a satisfactory oil removal rate from simulated polymer flooding oily wastewater. When the hydrophobic group content was 1% and the dosage of PASS-C was 140 mg·L–1, the optimal oil removal rate and turbidity removal rate was 95% and 98%, respectively. The particle size and morphology of the coagulated flocs were characterised by laser particle size analysis and SEM. Compared with PASS, PASS-C formed a larger and more compact floc. These findings indicated that the good flocculability of PASS-C for crude oil wastewater was attributable to the synergistic effects of charge neutralisation, hydrophobic associations and adsorption bridging.