Laboratory experiments show that H
4SiO
4 (monomeric silica) up to 80ppm in seawater is stable under all CO
2 pressures from 0 to 17.2 × 10
3 kg/m
2. CaCO
3, AlCl
3·6H
2O, MgCl
2, and standard clays, when added individually, did not remove silica from solutions containing silica from 50 to 80ppm under these CO
2 pressures. Addition of CaCO
3 and AlCl
3·6H
2O together, however, removed silica from solution in inverse proportion to the CO
2 pressure. CO
2 serves to inhibit the removal of silica from solution containing CaCO
3 and aluminum chloride. The CaCO
3 functions as a buffer to maintain the acid to neutral pH. The final reaction appears to follow: 2H
4SiO
4 + Al
3++ 2CaCO
3 + H
2O = AISi
2O
5(OH)·4H
2O + 2Ca
2+ + HCO
3- + CO
2. In an open system, where CO
2 can escape to the atmosphere, the removal of silica from solution is controlled by the available AlCl
3·6H
2O and CaCO
3. Electron microscopy and infrared analyses confirm that the principal precipitates were clayey sediments and trace amounts of sepiolite. This suggests an intimate interrelationship between the geochemical cycles of carbon dioxide, calcium carbonate, aluminum, and silica in nature.
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