* Salinity: Seawater contains a high concentration of dissolved salts, primarily sodium chloride (NaCl). These salts increase the ionic strength of the solution, making it more difficult for SiO2 to dissolve.
* Ionic Interactions: The dissolved ions in seawater compete with SiO2 for hydration (the process of water molecules surrounding and stabilizing ions/molecules). This competition reduces the effective concentration of water available for dissolving SiO2.
* Complexation: Some of the dissolved ions in seawater, like calcium (Ca²⁺), can form complexes with dissolved silica, effectively removing it from solution.
In summary: The high salinity and ionic strength of seawater make it a less favorable environment for dissolving SiO2 compared to freshwater.
Note: While SiO2 is less soluble in seawater than in freshwater, both are still considered relatively low in solubility. The vast majority of silica in the ocean exists in the form of solid particles (e.g., diatoms).
