Rice husk is the “skin” that wraps rice grains, which become waste after the rice milling process by dismantling itself from the rice. This waste ranges from 15-20 percent of the total mass of rice mills product.
In Indonesia, most of the rice husks exterminated by burning. Even though, the ash from burning process has high mineral content! The following is data on the mineral composition of rice husk ash:
Imagine these ashes are left alone and fly, inhaled, and entering your respiratory tract!
Then what can be done with these rice husk ashes? The P (Phosphorus) and K (Potassium) mineral content in rice husk ash is quite high, so it can be used to add N-P-K values to organic fertilizers. In addition, Hisham et al examined that the silica content in rice husk ash can also be utilized for improving the composting process by maintaining the moisture content and water holding capacity of compost within 50–60% and 61-73% (https://doi.org/10.22146/ijc.39704)
The silica that makes up 86.9 - 97.3 percent of rice husk ash can be extracted into silica gel, mesoporous silica, nano-silica, etc. This sustainable mineral processing has been researched and practiced in various publications and conferences.
Research on the process of forming silica gel from rice husk ash could be traced back to 1998 by Kamath, et al (https://doi.org/10.1094/CCHEM.19184.108.40.2064). They synthesized rice husk ash with NaOH, then adding H2SO4 so the pH turned back into neutral. Turns out both surface area and chemical composition were similar with the commercial silica gel.
The synthesis of nano-silica, another product of silica from rice husk ash can be carried out by the sol-gel method. Nanosilica could be used for promoting bean seed germination researched by Nguyen, et al (doi:10.1088/1755-1315/266/1/012007); nanofluids for various application by Ong, et al (doi: 10.5772/intechopen.89904); additive for ordinary portland cement to increase its compressive strength (https://doi.org/10.30736/teknika.v9i2.58); mesoporous silica for aqueous pollutant adsorbent; etc
So what can be done if you don’t want to burn the husk? You can put it around the soil in your potted plants to prevent snails from eating the plant’s leaf because the snail’s soft gastropod body is sensitive to the spiky structure of rice husk. This structure also prevents cats to defecate!