Preparation of nesquehonite powder by solid-phase conversion of magnesite and its phase conversion mechanism

Abstract

A novel and straightforward ion-catalysed magnesite solid-phase conversion method was used to prepare nesquehonite powder. Magnesite and slaked lime were used as raw materials and MgCl₂ was used as the catalyst. Magnesite could be directly converted to magnesium hydroxide by the solid-phase conversion method, and nesquehonite crystals were prepared by carbonisation and pyrolysis. The physical composition and microscopic morphology of the products were characterised by XRD and SEM, and the solid-phase conversion mechanism was analysed. The effect of catalyst type, solid-to-liquid ratio, hydration temperature, MgCl₂ addition and magnesite ore powder to slake lime mass ratio on the magnesium conversion rate was investigated. The rod-like nesquehonite crystals with good crystalline structures were obtained when the hydration temperature was 85°C, the solid-liquid ratio was 1:40, addition of MgCl₂ was 5%, magnesite ore powder to calcium hydroxide ratio was 1:2 and magnesium conversion rate reached 20.98%. The catalyst MgCl₂ could react with Ca(OH)₂ rapidly to form CaCl₂, which improves the ionic strength in the bulk solution as an intermediate product. Consequently, the solubility of magnesite was improved due to the salt effect and the conversion rate of magnesium was further increased.