Morphology-tunable anhydrous MgCO3 synthesis from magnesite solid waste via salicylic acid-Na2EDTA synergistic leaching and carbonation

Abstract

Magnesite solid waste (MSW) is typically discarded during magnesite mining, leading to significant resource waste and environmental pollution. This study introduces a synergistic salicylic acid (SA)-Na₂EDTA system for efficient Mg²⁺ leaching from MSW and subsequent synthesis of high-purity anhydrous MgCO₃ (MC). The effects of reagent type, concentration, and leaching/carbonation temperature on Mg²⁺ leaching and carbonation behaviors were investigated. Under optimized leaching conditions (0.55 M reagent concentration, 70 °C), SA achieved a Mg²⁺ leaching efficiency of 97.08 %, comparable to the 98.24 % efficiency obtained with H₂SO₄, demonstrating the feasibility of substituting strong acids with weak acids for Mg²⁺ extraction. The Mg²⁺ leaching efficiency was further enhanced to 99.64 % by introducing Na₂EDTA. SA degradation provided a carbon source during carbonation, while Na₂EDTA acted as a crystal control agent. Under carbonation conditions of 150 °C for 12 h, MC morphology transitioned from rod-like to flower-like spherical with increasing Na₂EDTA addition, achieving a high purity of 99.1 %. The mechanism of synergistic leaching and morphology modulation was analyzed by characterization techniques and DFT calculations. The results indicate that H-O bond formation between SA and magnesite induced O-Mg bond cleavage, releasing Mg²⁺, which EDTA^2- subsequently chelated to promote leaching. As carbonation proceeds, EDTA^2- adsorbed onto the MC surface through chemisorption, mediating oriented growth and assembly to regulate its morphology. This work presents a streamlined process for controllable synthesis of high-purity MC with multiple morphologies, offering a sustainable strategy for MSW resource recovery and environmental remediation.