Dissolution mechanism of ulexite in H2SO4 solution

This work comprises an investigation of the dissolution mechanism of ulexit e in H2SO4 solution and the effect of SO42- ions and acid concentration on the dissolution process, using H2SO4, HCL + H2SO4 and H2SO4 + Na2SO4 soluti ons. From the experimental observations, it can be suggested that the overa ll dissolution reaction can be written as Na2O . 2CaO . 5B(2)O(3) . 16H(2)O((s)) + 3H(2)SO(4(aq) )--> 2Na((aq))(+) + 2CaSO(4) + + 10H(3)BO(3(aq)) + SO4(aq)(2-) + 4H(2)O((1) )or Na2O . 2CaO . 5B(2)O(3) . 16H(2)O((s)) + 3H(2)SO(4(aq) )--> 2Na<INF>(aq</INF>)<SUP>+</SUP> + 2CaSO<INF>4</INF> . 2H<INF>2</INF>O<I NF>(s</INF>) + 10H<INF>3</INF>BO<INF>3(aq</INF>) + SO<INF>4(aq</INF>)<SUP>2 - </SUP>depending upon the experimental conditions. It was observed that, inc reasing H3O+ acid concentration increased the dissolution rate, but increas ing SO42- concentration reduced dissolution rate due to the precipitation o f a solid film of CaSO4 and/or CaSO4 . 2H(2)O, determined by X-ray and SEM measurement. (C) 1999 Elsevier Science B.V, All rights reserved.