An efficient polysilicate aluminum ferric (PSAF) for drilling wastewater treatment: Performance evaluation and coagulation mechanisms

Drilling operations generate large volumes of wastewater; inadequate treatment poses a direct threat of groundwater and soil pollution. Biological treatment is environmentally friendly, yet it is constrained by prolonged treatment times. Coagulation offers the distinct advantages of rapid processing. Nevertheless, conventional organic polyacrylamide (PAM) flocculants increase the total nitrogen concentrations in wastewater, and traditional aluminum–iron salt coagulants exhibit limited efficiency and induce pipeline corrosion owing to their low degree of polymerization and the introduction of chloride ions. Therefore, developing a green and highly efficient coagulant has become a promising solution. In this study, an efficient polysilicate aluminum ferric (PSAF) was synthesized via copolymerization and applied to treat real drilling wastewater. In comparison to commonly used polyaluminum chloride (PAC), PSAF demonstrated a 14.3–21.4 % lower effective dose, a chloride ion release 1/17 that of PAC, and a reduced SV 30 value, indicating enhanced coagulation efficiency and sludge settling performance. In addition, the microscale coagulation mechanism was explored. It was found -OH and -COOH groups contributed to the coagulation process. Organics bearing these functional groups were effectively removed, while S 1 O x surfactants exhibited resistance to removal. This selective removal led to a substantial reduction in the organic molecular formula complexity of drilling wastewater. Notably, PSAF achieved a 2.8-fold greater reduction compared to PAC. Further analysis indicated that the formation of Si-O-Al/Fe-OOC or Si-O-Al/Fe-OH bonds enhanced adsorption and net trapping bridging capacities of PSAF, thereby improving overall coagulation performance. This study provides a technical reference for on-site treatment of drilling wastewater.