Hydrolysis performance of poly-Al-Fe containing zinc (PAZF) coagulant and its removal of color and organic matters

A novel poly-Al-Fe coagulant containing zinc (PAZF) was prepared from a solid waste of galvanized-aluminum slag and its hydrolysis performance was studied. The coagulation behavior by PAZF was investigated in treating different wastewater samples compared to that by poly-aluminum-chloride (PAC). The results showed that PAZF hydrolysis could be seen as a hydrolysis process of complex salt and appeared to be characteristics of different types of salt at various concentrations. PAZF showed the nature of “strong acid and weak base salt” or “strong base and weak acid salt” at lower or higher PAZF level, respectively. For different types of wastewaters, PAZF yielded better removal of color and organic matters than PAC. For dyeing, papermaking, sugar, pharmaceutical and simulated wastewater samples, the removal of color and chemical oxygen demand (CODCr) by PAZF were up to 60.3%, 97.3%, 60%, 78.3% and 98.5%, and 32.5%, 48.1%, 41.6%, 45.4% and 82%, respectively. PAZF gave more 23%, 5%, 5%, 19% and 4%, and 8.1%, 6%, −1%, 7.2% and 18.4% than PAC in removing color and CODCr, respectively. The best pH for removing color by PAZF was different for different wastewater samples. PAZF could withstand great impact load of wastewater qualities.