Research On Secondary Reaction Mechanism In Leaching Process Of Calcium Aluminate Clinker

?-2CaO·SiO₂ is one of the main components of calcium aluminate clinker.In the leaching process of calcium aluminate,?-2CaO·SiO₂ reacts with adjustment liquid causing the increase of silicon content in sodium aluminate solution.When the content of SiO₂ in sodium aluminate solution exceeds its saturation concentration,it will react with Na[Al?OH?₄]to generate insoluble aluminium silicate into the red mud,resulting in the loss of Al₂O₃ and Na₂O.That's called"secondary reaction".According to the problems above,the factors such as the activity of material,sintering atmosphere and temperature schedule which effect on the stability of the synthetic clinker were studied.The influence of various factors on the stability of the clinker were analyzed by means of X-ray diffraction and laser particle size analyzer.The decomposition mechanism of?-2CaO·SiO₂in sodium aluminate solution was discussed by the combination of the simulating experimental results and the thermodynamic calculation.And the secondary reaction mechanism was disscussed according to X-ray diffraction results.The results shows that:?1?pure?-2CaO·SiO₂ can be obtained from the mixture of CaO:SiO₂=2:1?molar ratio?under 1500?for 60min.The activity of material and sintering atmosphere had no effect on the stability of the synthetic clinker.?-2CaO·SiO₂obtained under the heating rate of 10?·min^-11 and the cooling rate of 5?·min^-11 was more stable.?2?The calcium aluminate clinker whose main phases are 12CaO·7Al₂O₃ and?-2CaO·SiO₂canbeobtainedwiththerawmaterialsproportioningof CaO:Al₂O₃:SiO₂=4.26:1:1.27 under 1500?for 30min.Compared with mechanical mixed calcium aluminate,calcium aluminate has better leaching properties.The best sintering schedule of calcium aluminate is similar to that of?-2CaO·SiO₂.?3?The dissolution of?-2CaO·SiO₂ in sodium aluminate solution is influenced by the dissolution conditions and the composition of adjustment liquid.The maximum decomposition rate of?-2CaO·SiO₂can reach 8%under the condition of 80?,120min,N_C=85g·L^-1,N_K=85g·L^-1,?_K=1.6 and L/S=8.57.?4?Na₂CO₃ and Na[Al?OH?₄]are the dominant factors causing the decomposition of?-2CaO·SiO₂ into the solution.NaOH has little effect on the decomposition of?-2CaO·SiO₂.The stability of?-2CaO·SiO₂ in the three components of sodium aluminate solution is:NaOH>>Na[Al?OH?₄]>Na₂CO₃.?5?The secondary reaction products of calcium aluminate dissolution are the hydro-garnet,sodium-silicon slag and some of the intermediate phases.Prolonging the leaching time,improving the leaching temperature,increasing the alumina concentration will cause the decomposition of the hydro-garnet,and generate the sodium-silicon slag which was more stable.The secondary reaction is accelerated when liquid-solid ratio is lower.Sodium-silicon slag is stable with low sodium carbonate concentration and high liquid-solid ratio;the hydro-garnet is stable with high sodium carbonate concentration and liquid-solid ratio.