Profitable Project Investment Opportunity in Extraction of Ultrapure Silicon from Rice Husk Ash

Description:

Silicon, the second most abundantelement on earth, is an essential part of the mineral world. Its stabletetrahedral configuration makes it incredibly versatile and is used in variousway in our everyday lives. Burning the  fuel,  rice husk  to  generate energy  results  in  the  waste product  called  rice husk  ash (RHA). RHA is an abundantagricultural by-product. It is rich in silica (about 60%) and can be made intoeconomically viable raw material which can be used for production of ultrapuresilica. The present work deals with the production of silica particles.

Properties of Silicon

Silicon is a crystalline semi-metalor metalloid. One of its forms is shiny, grey and very brittle (it will shatterwhen struck with a hammer). It is a group 14 element in the same periodic groupas carbon, but chemically behaves distinctly from all of its groupcounterparts. Silicon shares the bonding versatility of carbon, with its fourvalence electrons, but is otherwise a relatively inert element.

Process of extraction

1. Digestion: This involves the digestion of the rice husk ash withcaustic at specific conditions. In this process the silica in the ash is getsextracted with caustic to form sodium solution. After the completion of thedigestion the solution is filtered for the residual undigested ash present inthe solution. The clear filtrate is taken for precipitation.

2. Precipitation: This step involves precipitation of silica from thesodium silicate solution. Carbon dioxide at a specific flow rate is passedthrough the silicate solution at design conditions. Continuous stirring isemployed during the operation. The precipitated silica is filtered, washed withwater to remove the soluble salts and dried. The filtrate containing sodiumcarbonate is taken for regeneration.

3. Regeneration: Regeneration is the step where calcium compoundreacts with the sodium carbonate to form calcium carbonate and sodiumhydroxide. The resulting solution is filtered to remove the solid calciumcarbonate and aqueous sodium hydroxide is used for digestion again. The calciumcarbonate is washed with water and dried. The dried calcium carbonate can beeither calcined to get calcium oxide, which is reused, for regeneration or thecalcium carbonate is sold and fresh calcium hydroxide is used for regenerationwhich gives an option of one more value addition.

4. Production of Ultrapure Silicon:  A chlorine based system is used inthe method of transferring silicon from SiO2 to polysilicon. The process isflexible enough to allow the use of chlorine as the halide conversion medium bymodifying the process, hydrogen, argon and a silicon chloride containing gasare injected into inductively coupled plasma operating at a temperature ofapproximately 2500°C.

Under these conditions, the siliconchlorides decompose to silicon, chlorine, and possibly hydrogen ions, and thegaseous product flows into a baffled cold trap held at approximately 1500°C. byresistance heating. 

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