Evaluation of the hydration process of an industrial magnesia compound to obtain struvite crystals: a technique for recovering nutrients

Avaliação do processo de hidratação de um composto industrial de magnésia na obtenção de cristais de estruvita: uma técnica para recuperar nutrientes

Struvite crystallization as a technique for recovering nutrients from wastewater streams has proven to be an attractive alternative to conventional treatments. The process becomes economically viable with the cost reductions related to the chemical reagents, especially magnesium ions. Thus, this study assessed the processing of a cheap and high-grade industrial magnesia compound in obtaining magnesium hydroxide slurries through a hydration reaction using different hydrating agents (magnesium acetate and sodium chloride solutions and water). The optimum hydration condition was achieved in acetate solution with a conversion rate to hydroxide about 67%. The efficiency of the obtained slurries as alternative reagents on the struvite crystallization process was evaluated in terms of the nutrient removal, NH₄⁺-N and PO₄^3--P. In experimental conditions of Mg²⁺:NH₄⁺:PO₄^3-ratio equal to 1.5:1.0:1.25 and pH equal to 8.5, the best results were achieved by using the magnesium hydroxide slurry obtained in acetate solution, which promoted removals of about 62% and 67% of NH₄⁺-N and PO₄^3--P, respectively. Finally, instrumental analysis confirmed the formation of struvite crystals in a purity degree that allows its use as a potential fertilizer.

Industrial magnesia compound; Hydration process; Magnesia hydration; Nutrient recovery; Struvite crystallization