Effect of Continuous Crystallizer Performance on Struvite Crystals Produced in Reaction Crystallization From Solutions Containing Phosphate(v) and Zinc(ii) Ions

Abstract

-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 m were produced. An increase in Zn 2+ 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.

Recovery of phosphates(V) from wastewaters of different chemical composition

“…aluminum [22], copper [23], potassium [24], as well as boron, cobalt and molybdenum ions [17]), in other cases -unfavorable (e.g. calcium [11,12], manganese [17], iron [25], zinc [26] ions). Calcium [9,12] and zinc [26] ions are especially disadvantageous in respect to struvite crystals growth and their size-homogeneity.…”

“…calcium [11,12], manganese [17], iron [25], zinc [26] ions). Calcium [9,12] and zinc [26] ions are especially disadvantageous in respect to struvite crystals growth and their size-homogeneity. Calcium ions also co-precipitate forming phosphates [11] of smaller sizes than struvite crystals.…”

“…The shifting of the mean product size towards smaller values was reported. Zinc ions [26], similar to iron [25] and manganese [17] ions, precipitate in a form of hydroxide, also of small size. Their net effect is usually unfavorable [11,19].…”

Effect of Copper and Zinc Ions on Struvite Nucleation and Crystal Growth Kinetics in Various Process Environments

“…The SIG (size-independent growth) kinetic model frame was applied [8,9]. Research results demonstrating and quantifying the effects of copper [10,11] and zinc ions [12,13] on the quality of struvite crystals manufactured in their presence, as well as on the chemical and phase compositions of final products, were also introduced into discussion. O or/and zinc chloride ZnCl 2 was used as the crystallizer feed.…”

“…Characteristic of the crystallizer unit, details of its work mode, method of determination of crystal size distribution (CSD) and its recalculation into corresponding population density distribution (PDD, n i (L), L -crystal size), estimation of struvite crystal shape (crystal length to width ratio L a /L b , crystal shape coefficient k v ) and analytical determination of chemical/phase composition of the products are presented elsewhere [10][11][12][13][14]. Selected experimental results [10][11][12][13] were supplemented with new measurements and presented together in Table 2. Exemplary scanning microscope images of struvite crystals manufactured in the presence of copper [11] or zinc [12] ions are demonstrated in Fig.…”