Recycling silica from rice husk and its application in liquid chromatography

  Rice husk production is about 482 million tons per yer all over the world. The compounds of the rice husk can be divided into organic and inorganic parts. The organic part contains cellulose, hemicellulose, and lignin and its mineral part consists of silica and metal oxides. One of the most abundant ingredients in the rice husk is silica. Twenty percent of the rice husk is white ash, which is obtained after complete burning of the rice husk in controlled time and temperatures and is a rich source of silica (more than 90 percent). In other countries, this type of recycled silica has many applications ranging from cosmetics to electronic industries, yet in Iran, recycling of silica does not happen. The aim of this work is silica production from rice husk, which is used as packing material in high-performance liquid chromatography (HPLC) column. As a result, this recycled silica from the rice husk is considered as valuable and cost-effective silica.
Material and For the synthesis of spherical porous silica gel from the rice husk, the physical preparation of the husk was done by burning and acidifying, adjusting the pH, and then heating (burning) at high temperatures to obtain a white powder. Then, in the alkaline conditions, the powder was converted into sodium silicate solution. Spherical porous silica gel was produced by the sol-gel method. HPLC columns were prepared by filling the column with bare silica and in the next step, silica was coated by vancomycin. Bare silica column was used for flavonoids analysis and vancomycin coated silica was tested for propranolol analysis. The results obtained from the separation of flavonoids and propranolol showed that the prepared silica could be a very suitable substrate for the settlement of functional groups. Therefore, the recycling was done successfully and can be used as a column stationary phase. Our country is one of the largest rice producers. Rice husk silica sources (such as mineral silica) can be recycled, purified, and can have various applications such as chromatography stationary phases.