Kinetics and morphological characteristics of struvite (MgNH4PO4.6H2O) under the influence of maleic acid

Abstract

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.

Thermodynamics and Kinetics of Struvite Crystallization from Hydrothermal Liquefaction Aqueous-Phase Considering Hydroxyapatite and Organics Coprecipitation

“…22,23 In addition, crystallization kinetic parameters were determined by fitting the proposed kinetic model to observed concentration data of only one of the reacting ions, e.g., either Mg 2+ or phosphate ion, ignoring the presence of the other contributing ions and the formation of struvite and nonstruvite minerals. 16,33,39 Finally, the existing models assume no coprecipitation of organic compounds, despite the fact that phosphate minerals offer active polar surfaces that can adsorb polar organic compounds. 40−42 While previous studies provided a fundamental reference and define the boundaries for optimal ranges of the parameters that rule struvite crystallization, more efforts are required to comprehensively understand the thermodynamic and kinetic behavior of struvite crystallization and coprecipitation of nonstruvite minerals, e.g., via hydroxyapatite crystallization, and organic compounds, e.g., via adsorption.…”

“…Few studies have investigated the struvite crystallization thermodynamics and kinetics in real wastewaters, adopting different kinetic models, e.g., linear growth rate, first-order kinetics, population balance, and size-dependent growth models. To design a fluidized bed reactor for struvite production, a recent study proposed three solid–liquid flow models, i.e., complete mixing of liquid and bed, plug flow of liquid and perfect classification of the bed, and plug flow of liquid and complete mixing of the bed, incorporated with reduced thermodynamic and growth kinetic models; the aim of the study was to improve previously proposed flow models by Rahaman et al and Burns et al However, those studies assume an ideal condition, neglecting the change of chemical thermodynamic properties at different temperatures and pH, e.g., ionic strength and effective concentration or activity of the reacting ions, during crystallization and the possibility of side reactions caused by foreign ions, e.g., hydroxyapatite formation due to Ca 2+ presence. , In addition, crystallization kinetic parameters were determined by fitting the proposed kinetic model to observed concentration data of only one of the reacting ions, e.g., either Mg 2+ or phosphate ion, ignoring the presence of the other contributing ions and the formation of struvite and nonstruvite minerals. ,, Finally, the existing models assume no coprecipitation of organic compounds, despite the fact that phosphate minerals offer active polar surfaces that can adsorb polar organic compounds. − …”

Potentially Probiotic Lactobacillus Strains Derived from Food Intensify Crystallization Caused by Proteus mirabilis in Urine

“…The increase in the intensity of crystallization was manifested by both the formation of bigger crystals and the crystallization of larger amounts Table 3 Crystallization intensity occurring in synthetic urine in the presence of P. mirabilis or P. mirabilis with various Lactobacillus strains during incubation at 37°C for 24 h of calcium and magnesium phosphates. The intensity of crystallization in such conditions may depend on the rate of pH increase, which affects the degree of supersaturation of urine [9]. The increase in the concentration of ammonium ions and pH play a key role in inducing struvite and apatite crystallization, and in the presence of the appropriate concentration of calcium and magnesium, ions also have an impact on the crystallization rate [40].…”

Effects of Physicochemical Parameters on Struvite Crystallization Based on Kinetics

“…The first-order kinetic model is used to assess the growth rate of struvite crystallization, which can be further described as follows [ 19 , 34 ]: where is the concentration of the substrate at time t; is the equilibrium concentration of the substrate; is initial concentration of substrate; is the rate constant of first-order reaction. The parameter values in some studies are summarized in Table 2 .…”

“…Currently, the dynamic kinetics of struvite crystallization are described by the following models: the population density model [ 17 ], the surface growth model [ 18 ], and the first-order dynamic model of substrate concentration [ 19 ]. Furthermore, the population density model describes how the total rate of change in the crystal number occurs due to variations in following parameters: diameter, surface area, volume, shape, etc.…”