Study on modification of colloidal silica surface with magnesium ions.

The prepared colloidal silica via ion exchange was modified by adding Mg(+2) ions in the surface growth process of colloidal silica. The particle size of the modified colloidal silica was decreased by increasing the seed concentration, whereas that of colloidal silica was slightly increased as the seeds concentration exceed 15 wt%. But the trend of changes in surface area was completely reversed. Magnesium ions on surface of the modified colloidal silica were identified by the measurement of energy-dispersive X-ray spectrometry (EDS). After modifying with Mg(+2) ions, the iso-electric point (IEP) of colloidal silica in pH approximately 2 without modification, disappears over the whole pH range.