Effect of continuous crystallizer performance on struvite crystals produced in reaction crystallization from solutions containing phosphate(V) and ZINC(II) IONS

Continuous reaction crystallization of struvite from aqueous solutions containing phosphate(V) (1.0 mass %) and zinc(II) ions (from 0.1 to 2.0 mg kg-¹) in a continuous DT MSMPR crystallizer was investigated. The influence of pH (9-11) and mean residence time (900-3600 s) on the product characteristics and its chemical composition was tested. Struvite crystals of mean size 22-41 um were produced. An increase in Zn²⁺ concentration decreased the mean crystal size and homogeneity. An elevation of the pH also decreased the struvite crystal size. Augmenting the mean residence time influenced product quality advantageously. Coexistence of struvite and Zn(OH)₂ in the product was confirmed analytically.