Characterization and calcination behavior of a low-grade manganese ore

Abstract

Characterization and calcination behavior of a low-grade manganese ore, as a part of Mn ferroalloys production, was studied by XRF, ex-situ XRD, in-situ XRD, and SEM-EDS techniques. Calcination experiments were carried out at and up to 900 °C (1173 K) in air and argon atmospheres. The samples were in particles and powder forms. The results indicated that both quartz and calcite phases in the ore exhibit a bimodal spatial distribution; as relatively large regions and finely distributed in the Mn- and Fe-containing phases. By Rietveld analysis of the in-situ XRD data, the reactions occurring upon heating during the calcination process were deduced. Thermal decomposition and reactive diffusion were found to be the dominant mechanisms in the calcination process. The results demonstrated that there were some phases forming and vanishing during the calcination process in air, such as calcium ferrites, calcium oxide, and bixbyite. While Fe-containing bixbyite was thermally decomposed to hausmannite at low temperatures, magnetite was the product at higher temperatures. However, magnetite was also formed through the diffusion between hematite and hausmannite phases. Reactive diffusion was much more prevalent in fine ore powder form than particles. Formation of complex phases such as (di-)calcium ferrite and bustamite was the result of the reactive diffusion mechanism. Although thermal decomposition of Mn and Fe oxides was not influenced by particle size, the final product of calcination was highly affected by the particle size, as a result of reactive diffusion.