Amino acid mediated hydration of caustic calcined magnesia: dual-function for efficient conversion and purification

Caustic calcined magnesia (MgO) hydration to magnesium hydroxide (Mg(OH)₂) is fundamental in magnesium chemical engineering, yet it faces kinetic limitations from the dense product layer forming on unreacted MgO and persistent impurity challenges from natural magnesite. This study has presented an approach for synchronous enhancement of MgO hydration and in-situ purification via amino acid mediation. Screening eight amino acids across non-polar, polar neutral, basic, and acidic categories revealed that non-polar amino acids (e.g., glycine) notably promoted hydration and impurity separation, whereas polar basic amino acids hinder hydration due to strong surface adsorption. Mechanistic characterization showed amino acids regulated the Mg²⁺ dissolution-precipitation pathway through carboxyl-group-mediated electrostatic adsorption and hydrogen bonding with the MgO surface, facilitating heterogeneous nucleation of Mg(OH)₂ for effective separation from high-density impurities. Optimized by response surface methodology, the process achieved 99.12 % hydration efficiency and 99.03 % pure Mg(OH)₂ with low impurity levels. Pilot-scale experiments demonstrated a profit of 395 US dollars per ton of MgO, establishing a viable technical route for high-value utilization of low-grade magnesite. This work uncovered the dual role of amino acids in mediating both hydration kinetics and impurity segregation, offering an innovative solution for efficient high-purity Mg(OH)₂ production.