How to make silicic acid, potassium silicate or calcium silicate? I am a student of tropical agriculture. I am taking the class of agronomic chemistry and plant nutrition. I want to make use of silicate source I have at home for e.g. zeolite, wood ashes, diatomaceous earth, silica sand. I have hydroxide of calcium, potassium and sodium. Can I use any of these to make silicate for use on plant nutrition ?
You can make the silicates by fusing the hydroxides with silica. Potassium silicate fertilizer grade are successfully produced by direct fusion of silica ($\ce{SiO2}$) and potasium compounds($\ce{KOH}$ and $\ce{K2CO3}$) in furnaces at temperatures up to melting point of mixture. The fusion temperature reaches around 1350 °C.
$$\ce{SiO2 + 2 KOH -&gt;[\Delta] K2SiO3 + H2O}$$
$$\ce{SiO2 + K2CO3 -&gt;[\Delta] K2SiO3 + CO2}$$
Calcium silicate is prepared by reacting calcium hydroxide and silica. This paper1 discussed the reaction at 30-85 °C.
References

https://www.matec-conferences.org/articles/matecconf/pdf/2016/21/matecconf_bisstech2016_01021.pdf
REACTION BETWEEN SILICA AND CALCIUM HYDROXIDE SOLUTIONS. I. KINETICS IN THE TEMPERATURE RANGE 30 TO 85°, S. A. Greenberg, The Journal of Physical Chemistry 1961 65 (1), 12-16, DOI: 10.1021/j100819a005