Scientists from Perm National Research Polytechnic University (PNIPU) have proposed an integrated, waste-free technology for producing useful materials from rice husks for various areas of production, such as construction and repair, surface protection from corrosion, and others, the service reported on July 8.
For all rice-producing countries, the disposal of large tonnes of waste in the form of rice husk remains an unsolved problem, even though up to 40 million tonnes are produced annually in China alone.
This is due to the fact that rice husk contains a significant amount of inorganic impurities, which does not allow its disposal using traditional agricultural waste composting technology. It does not easily biodegrade naturally in landfills, becoming a serious environmental pollutant.
Burning the shell allows energy to be obtained, but due to the same impurities (calcium and magnesium oxides), complete combustion does not occur. At the same time, a significant amount of ash is formed, but the presence of residual carbon impurities and calcium and magnesium oxides does not allow processing this ash into pure silicon oxide, which is in demand in industry, including for the production of various types of glass.
PNRPU scientists presented the results of a study of the proposed technology that solves this problem in the article “Recycling rice husk ash to obtain popular silicate materials”, published in the Construction and Geotechnics journal, Volume 15 No. 1, 2024.
In ordinary wood or straw, the content of inorganic impurities does not exceed 5-7% by weight, and in rice husk – up to 19-21% by weight. Therefore, it burns poorly and a high proportion of unburned carbon remains in the ash.
The resulting material is amorphous silicon dioxide (amorphous silica) with impurities of calcium and magnesium oxides and unburned carbon. Amorphous silicon oxide is a valuable raw material for a number of industrial products, but rice husk ash is currently being eliminated by adding it to asphalt concrete instead of sand, as it contains, in addition to amorphous silicon oxide, many impurities.
Scientists from Perm Polytechnic University decided to change this wasteful situation, as hundreds of thousands of tons of natural minerals composed of amorphous silicon oxide, such as tripoli and diatomite, are mined, and rice husk ash, a renewable source of the same, mostly ends up in landfills.
Natural silica minerals are widely used to produce an important industrial product: liquid glass (silicate glue), which is used in the manufacture of heat- and acid-resistant materials, paints and decorative coatings that protect against corrosion, and in many other areas.
The technology developed by scientists from the PNRPU allows obtaining liquid glass from rice husk ash as the main product. At the same time, during technological operations, impurities are separated and converted into another valuable product – granulated foam glass. It can be used as a thermal insulation layer in residential, commercial and industrial construction projects.
Carbon present in rice husk ash is also used. It is oxidized to form gases that are used to make foam in foamed glass.
The head of the Department of Construction Production and Geotechnics of the PNIPU, Doctor of Technical Sciences Vadim Ofrichter, explained the problem that the researchers are solving:
“The annual production of ash can be compared with the production of its mineral analogue, diatomite, which is a valuable mineral raw material, and mining companies incur high costs for its extraction. Meanwhile, rice husk ash is considered a useless waste. We propose to consider it as a valuable resource of silicon oxide, which, unlike its analogue, is renewable. Therefore, we should focus not on the destruction of rice husk ash, but on the full use of all its components and obtaining the most sought-after products.”.
The method of processing rice husk ash proposed by Perm scientists is a comprehensive and effective solution to both the environmental problem of recycling rice production waste and the economically viable production of valuable products from a renewable source.
Source: Rossa Primavera
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