Anti-causticization of calcium carbonate in sodium aluminate solution

Anti-causticization of calcium carbonate in sodium aluminate solution was studied. The thermodynamic calculation result shows that the degree of anti-causticization reaction of CaCO3 with NaOH solution to form Ca(OH)2 is low at low temperatures, while that of CaCO3 with Al(OH)4- to form 3CaO·Al2O3·6H2O (C3AH6) is significant. The reaction rate of CaCO3 is less than 5% in pure sodium hydroxide solution and more than 50% in sodium aluminate solution, indicating that Al(OH)4- anion can significantly promote the anti-causticization of calcium carbonate in sodium aluminate solution. The reaction rate of anti-causticization improves with the increase of temperature, increasing first and then decreasing with the increase of the mole ratio of Na2O to Al2O3 (αk), and reaches the maximum with αk of approximate 3. The results also show that C3AH6 is formed in the anti-causticization of CaCO3 in sodium aluminate solution under the atmospheric condition, causing the loss of alumina.