Resource preparation of poly-Al–Zn–Fe (PAZF) coagulant from galvanized aluminum slag: Characteristics, simultaneous removal efficiency and mechanism of nitrogen and organic matters

Abstract

A poly-Al–Zn–Fe (PAZF) coagulant was prepared using a galvanized aluminum slag as main raw material, and was characterized by Scanning Electron Microscopy (SEM), Infrared Spectroscopy (IR) and X-ray Diffraction (XRD). Simultaneous removal efficiency and mechanism of nitrogen (as NH3–N) and organic matters (as CODCr) during coagulation process in treating simulated fountain water by PAZF were investigated compared to those by poly-aluminum–chloride (PAC). The results indicated that PAZF has better coagulation performance than PAC: PAZF gave the greatest NH3–N and CODCr removal of 82% and 89% over the whole dosage range, respectively, in comparison with 17% and 57% by PAC. PAZF has stronger adsorption than PAC: PAZF has a large surface area which consisted of series of cauliflower head structure having some pleated ditches with different width and depth, in comparison with an irregular mountain appearance of convex–concave structure of PAC having a small surface area. PAZF has greater capability of neutralization/destabilization for pollutants than PAC: the amount of positive charge carried by the hydrolysis products of PAZF was more than that of PAC because PAZF was composed of more crystalline and amorphous substances and was a co-polymer of three metals of Al, Zn and Fe. PAZF gave higher nitrogen removal than PAC: PAZF was a coagulant containing much zinc (w(Zn)=30.25%), so one of its hydrolysis products of “zinc of hydroxide system” can react with NH4+ and NH3 to give “zinc-ammonia ion complexing system” positively charged. Nitrogen removal mechanism by PAZF was a comprehensive action of coagulation and chemical reaction.