A Proposal for Measuring Solubility of the Silica in Rice Husk Ash

Aims: At present, rice husk is being used in many applications as a biomass resource. The method of rice husk quality evaluation, especially solubility, is not codified and therefore values cannot be compared across regions and institutions. In this study, the solubility of silica in rice husk ash was analyzed, and a systematic measurement process was proposed so as to make global sharing of data easier.

Study Design: Producing black and white ash using a boiler in the field and an electric furnace in a laboratory, respectively, the solubility of silica in rice husk ash and those physical properties were analized.

Place and Duration of Study: Rice husk incineration: a local agricultural association located in Imizu, Toyama, Sample analysis: Toyama Prefectural University.

Methodology: The Japanese standard method 4.4.1.c was evaluated for measuring the solubility of silica in rice husk. The current study also assessed the physical state and solubility of silica in both white and black rice husk ash.

Results and Conclusion: From the analysis results, we determined that the Japanese standard method 4.4.1.c could be simplified to reduce the complexity of the measurement procedure. For a consistent and high accuracy measurement of the solubility of silica in rice husk ash, an acid treatment procedure is necessary. Since solubility increases as the surface area of ash decreases, powdering of samples is not necessary and ash can be used as-is for solubility measurements. Ash became bulky as the burning temperature increased, indicating that the silica did not fully transit to crystalline state in the conditions tested. Fixed carbon, volatile matter, and moisture content may also affect solubility up to 800°C. Additional factors that we did not study may also affect the solubility of silica in rice husk.