Co-Conversion Mechanisms of Boron and Iron Components of Ludwigite Ore during Reductive Soda-Ash Roasting

Abstract

Ludwigite ore is a typical intergrown mineral resource found in China. Reductive soda-ash roasting followed by water leaching is an innovative process for the high-efficiency separation and recovery of boron and iron. In this study, the co-conversion mechanism of boron activation and iron reduction during soda-ash reductive roasting for boron-bearing iron concentrate was clarified. When the boron-bearing iron concentrate was reduced in the presence of Na2CO3, szaibelyite (Mg2(OH)(B2O4) (OH)) was activated to sodium metaborate (NaBO2) and, meanwhile, magnetite (Fe3O4) was reduced to metallic iron (MFe). Boron activation promoted iron-oxide reduction effectively, while the latter could only slightly influence the former. The promotion occurred through (1) a facilitated generation of sodium magnesium silicate (Na2MgSiO4) and a hindering of the formation of olivine (MgxFe2-x(SiO4)). (2) The newly generated NaBO2 promoted iron-oxide reduction. (3) The low melting point of the NaBO2 (966 °C) favored particle migration, which accelerated metallic iron particle aggregation.