Water leaching of boron from soda-ash-activated ludwigite ore

•A novel process for boron extraction from ludwigite ore was proposed.•Ludwigite ore was alkali-activated by Na2CO3 during roasting process to form sodium metaborate.•Sodium metaborate was extracted by water leaching.•The mechanism of alkali-activated ludwigite ore was elucidated.

Water leaching of boron from ludwigite ore activated by soda ash under reductive, natural and oxidative atmospheres was investigated by evaluating the effects of roasting parameters (roasting atmosphere, temperature and time) and leaching parameters (leaching temperature, leaching time, liquid-to-solid mass ratio and feed particle size) on boron leaching. The presence of CO during soda-ash activation promoted boron leaching because of the reduction of iron-bearing minerals in the ore, whereby iron species within magnetite (Fe3O4) and ludwigite ((Mg,Fe)4Fe2[B2O6]O4) transformed to metallic iron. This facilitated the reaction between B2O3 and soda ash, giving rise to the formation of water-soluble sodium metaborate. The boron of 92.7% could be extracted from the ore roasted in the presence of soda ash (25 wt.%) under the 100% CO atmosphere at optimized roasting and leaching conditions.