Dissolution mechanism of colemanite in sulphuric acid solutions

Boron compounds are very important raw materials in many branches of industry and their uses have been increasing and expanding continuously. Colemanite, one of the most common boron minerals, has a monoclinic crystal structure with a chemical formula of 2CaO·3B₂O₃·5H₂O and is used usually in the production of boric acid. The present study concerns and investigation of the dissolution mechanism of colemanite in H₂SO₄ solution and the effect of acid concentration, the effect of SO₄⁻² ion on the dissolution process, using H₂SO₄, HCI+H₂SO₄ and H₂SO₄+Na₂SO₄ solutions. The analysis of the experimental data shows that increasing H₃O⁺ acid concentration increased the dissolution rate, but increasing SO₄⁻² concentration reduced dissolution rate because of the precipitation of a solid film of CaSO₄ and CaSO₄·H₂O.