Effect of Calcium Additive on the Crystallization of Struvite

Abstract

Crystallization of struvite [MgNH4PO4.6H2O] may lead to the deposition of scale which may create significant problems in the process pipes, pumps and other industrial equipment. However, struvite precipitation can be benefited for phosphate recovery for use of fertilizer. The aim at the present work was to investigate calcium additive on struvite precipitation. The experiment was carried out in a batch mode using a 1-liter Pyrex glass vessel mechanically agitated for 200 rpm. The scale-forming solution was prepared for mixing solutions to MgCl2 and NH4H2PO4 with Mg +2 , NH4 + and PO4 -3 in a molar ratio of 1: 1:1. The crystallization temperature of 30 and 40 O C was selected. Ca was added into the crystallizing solution to chloride dihydrate 0.4M (CaCl2•2H2O). Then each solution was pH adjusted to 9 by addition of KOH. The crystals obtained were characterized using SEM for morphology, EDS for elemental analysis as well as XRPD Rietveld analysis for crystaline phases. The induction periods varied from 10 to 90 min, which means that the struvite crystals began forming 10 to 90 min after mixing of the solution. It was observed that the Ca additive may inhibit the struvite crystallization. SEM analysis revealed that the struvite crystals obtained were predominantly of irregular prismatic morphology. Furthermore, the EDS pattern revealed that the elemental composition of the crystals consisted of Ca, Cl, S Mg, N, and P, providing that many crystalline phase found in the crystals such as Gypsum, CaCl2, struvite, struvite-(K) and sylvite. It was observed that the Ca additive appeared to inhibit the struvite crystallization.

Study of Potassium Recovery from Biomass Ash Using Tartaric Acid and Syngenite Method

“…The molar ratio of Ca and K in syngenite based on EDX analysis for additional magnesium doses of 5 mmol/l, 10 mmol/l and 15 mmol/l at pH 11.0 were 1:2.1, 1:2.8 and 1:3.2 respectively with the best %K and %Ca are 42% and 31%. The phosphate value in this study is also quite high, because besides being able to react with syngenite, calcium ions can also actively react with phosphate to form calcium phosphates [24].…”

“…However, in the study only Ca and K, the S ion can not identified as crystals formed because these minerals may precipitate in the order of days and are influenced by the pH of the solution and the concentration of magnesium and phosphate [24]. The molar ratio of Ca and K in syngenite based on EDX analysis for additional magnesium doses of 5 mmol/l, 10 mmol/l and 15 mmol/l at pH 11.0 were 1:2.1, 1:2.8 and 1:3.2 respectively with the best %K and %Ca are 42% and 31%.…”

A General Review of the Current Development of Mechanically Agitated Vessels

“…The vessels with single [89] mechanical agitator or multiple agitators systems are often used in various configurations in three-phase or two-phase mixing processes [90], such as catalysed oxidation, polymerisation, evaporative crystallization [91], aerobic fermentation, [92] froth flotation [93], flocculation [94], microbial coal desulphurisation, gold leaching, bacterial, sulphide oxidations or separation processes etc. In all these applications, simultaneous dispersion of gas and the suspension of the solids have crucial meaning.…”