Phosphate recovery through struvite-family crystals precipitated in the presence of citric acid: mineralogical phase and morphology evaluation

Abstract

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.

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

“…Increasing awareness on sustainable practices in industry, which subsequently leads to environmentally friendly methods has encouraged extensive research on struvite precipitation using additives of organic origin. Our work on struvite precipitation [12] has revealed that minute amounts of citric acid (1.00-20.00 ppm) were able to significantly retard the growth of the crystals. The effect, however, was not notably obvious for the change in morphology.…”

“…Further experimental errors in the current experiments have been taken into account according to the methodology that has been implemented for the author's work previously [2,12] as follows; Firstly, error in weighing the chemicals: MgCl 2 and NH 4 H 2 PO 4 have been covered by using an analytical balance with four-digit accuracy i.e. 0.0001 g. This is commonly used in experiments involving chemicals weighing.…”

“…Scale formation of struvite is initiated by crystallization, a process which is significantly subject to a number of physical-chemical parameters. Among these parameters are pH level of the solution [1,11,12], and the presence of foreign ions [2,3,12].…”

Optimization of Key Parameters in Struvite (K) Production for Phosphorus and Potassium Recovery Using a Batch Crystallizer

“…Correspondingly, the MAP crystallization reaction could be completely inhibited by the presence of citric acid with high concentration. Moreover, the MAP precipitation with citric and succinic acid present in the solution leads to the change in morphology and size of the crystallized products 20,21 . Correspondingly, tight aggregates of crystals with fine and uniform morphology would have good solubility in water, which is favorable for use as fertilizer.…”

Optimized Phosphate Recovery Through MAP Precipitation in an Air Agitated Column Reactor

“…Furthermore, the chemical composition of wastewater can control the final results of the struvite reaction crystallization process 8 . Impurities, namely metal ions, sulfates, nitrates, carbonates may also control struvite crystallization in wastewater, which in turn plays a critical role in the nucleation and its crystal growth, shape and agglomeration, chemical composition of the final product in addition to co-precipitated sparingly soluble hydroxides or phosphates of the selected metal ions 10,11 . Moreover, catalyst or chemical inhibitor of individual ionic impurities 12 has a significant effect on the struvite reaction crystallization mode, which may change crystallized type and the operational parameters to be selected.…”