The identification and characterization of silicate complexes in calcium chloride solution using fast atom bombardment mass spectrometry Original Research Article

The chemical species of silica dissolved in calcium chloride (CaCl2) solution were identified using fast atom bombardment mass spectrometry (negative ion mode) equipment. The chemical species dissolved in CaCl2 solution were compared with those in the sodium chloride (NaCl) solution to discuss the stability of the complex in CaCl2 solution. In 0.1 mol dm−3 (M) CaCl2 solution, some new species of silica complexes were identified. The chemical species of silica dissolved in CaCl2 solution were as follows: silica monomer, Si(OH)3O− and Si(OH)O3Ca−, the dimer species such as Si2(OH)5O2−, Si2(OH)3O4Ca−, the linear tetramer such as Si4(OH)9O4−, Si4(OH)7O6Ca−, Si4(OH)5O8Ca2−, Si4(OH)3O10Ca3− and Si4(OH)O12Ca4−, and the cyclic tetramer such as Si4(OH)7O5−, Si4(OH)5O7Ca−, Si4(OH)3O9Ca2− and Si4(OH)O11Ca3−. The linear tetramer silica complexes were contained in the 0.1 M CaCl2 solution, and the eight protons of the linear tetramer silicate Si4(OH)9O4− are all exchangeable with Ca2+, while the linear tetramer silica complexes were not identified in 0.1 M NaCl solution. This indicates that the Ca-silicate complex is more stable than Na-silicate complex in each chloride solution, and that Ca2+ should assist in the two intra-molecular bondings of Si-O−.