A novel method for preparation of polyaluminum phosphoric sulfate (PAPS) coagulant using SAPO-34 mother liquor: Characterization and coagulation performance

Abstract

Polyaluminum phosphoric sulfate (PAPS), which is a composite coagulant, was prepared using SAPO-34 mother liquor that was obtained from the process of synthesizing SAPO-34 molecular sieve. After the pretreatment of the SAPO-34 mother liquor, 80.50 % of the triethylamine in the mother liquor was recycled by fractional distillation and the residual triethylamine was oxidized and decomposed by ozone. Furthermore, during the preparation of PAPS, the effects of [P]/[Al], [OH]/[Al] molar ratios, and reaction temperature were examined, and the optimum preparation conditions were determined by response surface methodology. Results showed that the optimum PAPS preparation conditions were n(P)/n(Al)=0.25, n(OH)/n(Al)=1.05, and temperature of 85°C. In addition, the structure and morphology of PAPS were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and the coagulation performances were evaluated by kaolinite synthetic water treatment. The results indicate that complex compounds are formed in the synthesis of PAPS. Finally, on comparison with PAC and Al2(SO4)3·18H2O, PAPS exhibits better coagulation performance in removing turbidity and total phosphorus, when the dosage is 40mg/L.