An organic-inorganic hybrid coagulant containing Al, Zn and Fe (HOAZF): preparation, efficiency and mechanism of removing organic phosphorus

A polymeric-Al-Zn-Fe (PAZF) coagulant showing high removal of pollutants has been successfully developed using a galvanized slag in earlier works, but it gave less elimination of phosphorus. To improve phosphorus removal, a hybrid organic-Al-Zn-Fe (HOAZF) coagulant was prepared using PAZF and polyacrylamide (PAM) as an organic additive, and then was characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD), and Zeta potential, respectively. Removing efficiency and mechanism of organophosphorus by HOAZF was probed using jar tests in treating a simulated pesticide wastewater containing dichlorvos (DDVP), compared to that by PAZF and polyaluminum chloride. The results displayed that HOAZF having relative lower Zeta potential (compared to PAZF) exhibited complex surface morphology composited by Al, Zn and Fe and PAM, forming some new crystalline and amorphous substances different from that in PAZF. HOAZF gave higher removal of organophosphorus and far lower dosage than PAZF, and also posed a suitable wider pH range (pH = 7-12 for HOAZF and 10-11 for PAZF, respectively) and suitable wider organophosphorus level range than PAZF. Removing organophosphorus by HOAZF was a simultaneous complex process involving a non-phase transfer of adsorption/bridging/sweeping and a phase transfer of chemical precipitation.