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Struvite (NH4MgPO4•6H2O) is a mineral often found as a scale deposit in an industrial process and piping. The common occurrence of struvite formation is a wide variety of environments. pH solution and environmental temperature are important parameters that control precipitation and subsequent decomposition of struvite. The study aims to characterise the struvite precipitated out the solution through chemical and mineralogical analysis. In this work, struvite solution was prepared by mixing NH4OH , MgCl2 and H3PO4 with the different purity grade (A and B) in the mol ratio of 1 : 1 : 1 in the stirred glass vessel tank with volume of 500 ml, and then stirred at 200 rpm for 70 minutes. Temperature of 30 O C and an initial pH of 10 were selected. The precipitated deposit was dried at room temperature for 48 hours of being analyzed. Material characterization of the deposits was conducted using XRPD Rietveld method of qualitative and quantitative mineralogical phase analysis. XRF was employed for bulk chemical elemental analysis of the scale obtained. The sample A using analytical grade powder provided the major phases of struvite-(K) and struvite. In constrast, the major phase of newberyite and minor phases of lepidocrocite (FeOOH) and niter (KNO3) was observed by following changes in the lowest purity of powder (Sample B). Analysis of the experimental data suggests a solution mediated transformation process as a possible mechanism of struvite transformation.

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Precipitation strategy of struvite-family crystals is presented in this paper to recover phosphate and potassium from a synthetic wastewater in the presence of citric acid at elevated temperature. The crystal-forming solutions were prepared from crystals of MgCl and NHHPO with a molar ratio of 1:1:1 for Mg, [Formula: see text], and [Formula: see text], and the citric acid (CHO) was prepared (1.00 and 20.00 ppm) from citric acid crystals. The Rietveld analysis of X-ray powder diffraction pattern confirmed a mixed product of struvite, struvite-(K), and newberyite crystallized at 30°C in the absence of citric acid. In the presence of citric acid at 30° and 40°C, an abundance of struvite and struvite-(K) were observed. A minute impurity of sylvite and potassium peroxide was unexpectedly found in certain precipitates. The crystal solids have irregular flake-shaped morphology, as shown by scanning electron microscopy micrograph. All parameters (citric acid, temperature, pH, Mg/P, and N/P) were deliberately arranged to control struvite-family crystals precipitation.

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This work reports a stirred-batch lab crystallization to examine the influence of maleic acid (HO 2 CCHCHCO 2 H), and temperatures (30 and 40 C) on crystallization kinetics and morphology of struvite. The crystallization was followed by measuring the pH change up to 70 min. The pH decreased drastically for the first 5 min of the run, then started to tail off. It was found that the crystallization rate constants range from 1.608 to 6.534 per hour, which agrees with the most published value. Higher maleic acid concentrations resulted in greater growth retardation; the highest retardation was 74.21%, which was achieved for 30 C with 20.00 ppm maleic acid. SEM imaging of the obtained precipitates showed irregular prismatic morphology, and the associated EDX confirmed that the precipitates were struvite (MgNH 4 PO 4 ⋅6H 2 O). As checked through XRD, the crystalline nature of the struvite was further confirmed, and that co-precipitation of struvite with struvite-K was observed. The coprecipitation was the result of K þ adsorption onto the crystal surface. Temperatures had less influence on struvite crystallization. At 40 o C and 20.00 ppm the rate constant was 1.332 per hour; whereas at 30 o C and 0.00 ppm) the corresponding was 1.776 per hour, indicating the retardation of about 25%. Thus, the temperature effect is only 1/3 of the maleic acid effect. The current findings suggest that the presence of maleic acid can be used to elucidate the mechanism of crystallization as well as the crystalline phase transformation of struvite. In practical terms, maleic acid could be potential as a scale inhibitor.