Main species of silica dissolved in calcium chloride solution and their chemical implications for silica species in sodium chloride solution

The characterization of silica dissolved in sodium chloride (NaCl) and calcium chloride (CaCl2) solutions was performed by FAB-MS. When silica gel was dissolved into NaCl and CaCl2 solutions with shaking at 25 degreesC for 24 h, the maximum concentration of silica in CaCl2 solution was almost twice that in NaCl solution. The peak intensity ratio of the cyclic tetramer to the dimer, plotted against the concentration of CaCl2, is much higher than the peak intensity ratios of other complexes to the dimer. And the trend of the peak intensity ratio of the cyclic tetramer to the dimer is similar to that of the concentration of silica. Therefore, in CaCl2 solution, the cyclic tetramer is regarded as the main component. Comparing the silicate complexes in CaCl2 solution with those in NaCl solution, the CaCl2 solution was found to contain cyclic heptamer and linear heptamer, but the possibility of the NaCl solution containing cyclic heptamer and linear heptamer is very low, based on our FAB-MS results.