Electrochemical crystallization for phosphate recovery from an electronic industry wastewater effluent using sacrificial iron anodes

Abstract

With the circular economy in mind, recovery of iron phosphate, i.e., ferric phosphate or ferrous phosphate, from industrial wastewater is realized and the products recovered could be used in the synthesis of lithium iron phosphate for Li-ion secondary batteries. The formation of iron phosphate highly depends on pH and dissolved oxygen (DO) level. The present study focused on the phosphorus removal and recovery from the industrial wastewater effluent of a semiconductor plant by crystallization of iron phosphate. P recovery as iron phosphate was explored by means of electrochemical crystallization using a sacrificial iron anode under various DO levels (air sparging, mechanical mixing, and N2 purging) and pH values (both initial and fixed pH). Under the nitrogen purging condition, the P removal linearly increased with increasing of the Fe:P molar ratios, reaching 100% when the Fe:P molar ratio equals 1.5, which is the stoichiometric molar ratio of ferrous phosphate. The ferrous phosphate particles quickly settled and the crystalline structure was confirmed as vivianite. The final product obtained at pH 6.0 was composed of 82 wt% of vivianite. The operational cost of the electrochemical process was estimated to be only 23.5% of the costs required by the fluidized chemical crystallization process reported in the literature.