Silica extraction from Biomass
Many plants contain silica, and some products of agriculture, for example, rice husks, contain as much as 10% silica by dry weight. Rice husk is the outermost layer of rice grain that is separated from the food product in a milling process. Around 20% of rice harvest weight is husk. Rice production in Asia alone produces about 770 million tons of husk annually.
The processing capacity of commercial rice mills range from 400 to 10,000 tonnes/day. The largest mills produce 2,000 tonnes of husk per day. This large biomass resource is available at milling sites at little or no cost as rice husks have limited use.
The uses of rice husks include combustion for local electricity generation at smaller mills in Asia to pasteurisation and bagging for home gardening at larger mills in the USA. In many rice growing regions rice husks are waste sent to landfill or burned.
Precipitated silica, an amorphous form of silicon dioxide, is versatile product with many uses. For example, it is used as a filler, and a substitute for carbon black, in the manufacture of tyres and other rubber goods. It is also used in nutrition and health products, paints, inks and coatings, paper manufacture and toothpaste formulations.
Precipitated silica is typically made from quartz sand via a sodium silicate intermediate product. It may also be made from the ash of silica containing plant materials. Both processes consume large amounts of energy and produce waste streams.
Leaf Resources is researching and developing new low-energy processes for extracting silica from rice husks and other plant materials, especially the by-products of agriculture. Leaf aims for these processes to use much less energy than the conventional processes and produce very little waste. Leaf is evaluation co-products including the biomass residue and its potential as a feedstock for the Glycell process.