Influence of Citric Acid on Struvite Precipitation

Struvite (MgNH4PO4 center dot 6H(2)O) is a mineral deposit which can be commonly crystallized on the surface of process pipes, pumps, and other industrial equipment and hence influence the performance and maintenance cost. However, struvite is also phosphate minerals that can be used as resources in an industrial fertilizer. This paper presents results of study on examining the controlled parameter (chemical additives) on struvite precipitation. MgCl2 center dot 6H(2)O and NH4H2PO4 crystals were separately dissolved in doubly-distilled water to provide the struvite crystallizing solution of 0.03 M. The magnesium chloride and the ammonium dihydrogen phosphate salts would provide the struvite components i.e., Mg2+, NH4+ and PO4-3, respectively. The experiments for struvite crystallization was conducted at ambient temperature of about 30 degrees C. It was done by mixing the two solutions in a glass beaker with stirring at 400 rpm. The acids were added in ppm amounts: 1.00; 10.00 and 20.00 ppm, respectively. The crystallization process was subsequently evaluated by the induction time through observing the pH reduction over time. It was shown that in all the experiments, the pH decreased over time depending on the parameters investigated. SEM analysis revealed that the struvite crystal has prismatic-shaped morphology. Struvite was the major crystalline phase found in the crystals as confirmed by XRPD Rietveld analysis. This study indicated that the citric acid can be beneficial for the mitigation of struvite scale.