Preparation and coagulation behavior of poly-Al-Zn-Fe coagulant from galvanized-aluminum-slag

Key words:  galvanized-aluminum-slag  poly-Al-Zn-Fe (PAZF) coagulant  micro-properties  coagulation behavior

Abstract:

Poly-Al-Zn-Fe (PAZF) coagulant was prepared by a two-stage method of leaching with mixed acid and polymerizing with alkali using galvanized-aluminum-slag (GAS). Its micro-properties during preparation were conducted using UV-vis spectrophotometer (UV) and scanning electron microscopy (SEM). Coagulation behavior of PAZF was tested by Jar tests in treating a simulated dyeing wastewater compared with that of poly-aluminum-chloride (PAC). The results show that the optimal leaching time and polymerizing time are 3and 5hours, respectively. The acid leaching substances mainly contain zinc, aluminum and iron salts and polymers of these three metals of chloride-sulfate. Many types of polymeric substances with different absorption wavelengths were formed while their copolymer structures with characteristic absorption-peak of aluminum, zinc and iron were adjusted continuously with the increase of polymerizing time. The surface morphology of PAZF changed a lot at different magnification times, while PAC changed a little. PAZF appeared to have a kind of uniform pleated structure having larger surface area at 4000magnification times. However, it has a series of cauliflower head structure with some pleated ditch having different width and depth at magnification of 8000times. PAZF dosage range showing excellent coagulation efficiency in treating complicated qualities of water samples was wider than PAC. It had a consistent optimal pH range for removal of turbidity and organic matters compared with PAC showing different pH ranges. The distinctive coagulation behavior of PAZF was determined by its special micro-properties.