Rice husk is rich in silica content and is a biomass. 

The ash of rice husk is very rich source of silica. The challenge is to recover high purity silica. I will let you know about the details of nanosilica.

ball milling may help!

Preparation of nanosilica you can make with foolowing stages:

1. The dried husk (50 gr) were stirred in 500 ml (10% NaOH) solution and boiled in beaker glass for 1 h. The mixture was allowed to cool to room temperature for 24 h. . Then, the mixture was filtered through a Millipore filter to separate the filtrate which contained silica (silica sol). To obtain solid silica, the sol The mixture was drop slowly with 5% HCL until the pH 7.5-9. The precipitated silica was washed repeatedly with warm deionised water until the filtrate became completely alkali free. The washing process continued by deionised water repeatedly and dried at 110o C for 24 h in the oven.

2. Pure silica was extracted by refluxing with 6 N HCI for 4h and then washed repeatedly using deionised water to make it acid free. It was then dissolved in 2.5N NaOH by continuous stirring for 10 h on a magnetic stirrer and then concentrated H2SO4 was added to adjust pH in the range of 7.5-9. The precipitated silica was washed repeatedly with warm deionised water until the filtrate became completely alkali free. The washing process continued by deionised water repeatedly and dried at 50o C for 48 h in the oven.

Also you can search and read this paper, thanks

STUDYING OF NANO SiO2PREPARATION FROM RICE HUSK ASH BY USING HIGH GRAVITY REACTION  PRECIPITATION TECHNOLOGY

Nguyen Thanh Chung, Tran Ngoc Ha and Hoang Van Duc

Center for Material Technology, ITRRE, Vietnam Atomic Energy Institute

48 Lang Ha, Dong Da, Hanoi, Vietnam

Process of the nano SiO

preparation from rice husk ash by using high -gravity reactive

precipitation technology

2

The process of the preparation nano SiO

included 2 steps

 Leaching rice husk ash (RHA) with sodium hydroxide (NaOH) for producing liquid

2

glass. The furnace and a high pressure stainless steel equipment was shown in Fig.1

The procedure of leaching rice husk ash with NaOH to prepare liquid glass was as following.

2 kg of husk ash and a certain amount of NaOH solution were added in the reaction vessel (5).

Close the vessel and turn on the mixer (3). Then gradually increase the reaction temperature of the

furnace (2) by the control system (6) at a certain period of time. The reaction was undergone under

5 atm and secured with a pressure gauge (4). After the reaction completed, the solution of liquid

glass was extracted as a raw material for the preparation of silica by high-gravity reactive

precipitation equipment.

 Preparation of nano SiO

from liquid glass by using high gravity precipitation

technology (Higee method).

2

As shown in Fig.2, liquid glass presented initially in the stirred tank (1) was pumped through

the distributor (5) into the rotating packed bed (6), where it reacted with CO

2

to form SiO

particles.

The mixture slurry of SiO

flowed back into the stirred tank 1, where it was re-pumped into the

rotating packed bed and reacted with CO

2

again. This recycling process was ended when the pH of

the slurry reached the value about 8,3. At this moment SiO

2

was completely converted from liquid

glass.

2

2

Dear Simon,

Thank you for answering.

I suggest you contact Dr Haoran Chen at Texas State University ([email protected]); his thesis, BIOGENIC SILICA NANOPARTICLES DERIVED FROM RICE HUSK BIOMASS AND THEIR APPLICATIONS, covers the topic of your interest. Also see: Haoran Chen et al., J Pet Environ Biotechnol 2012, 3:7. Dr Chen is CTO of a start-up company aiming to make and sell such silica here in the States.

Firstly you have to isolate silica from the associated rice husk ash, and then please solubilize the isolated silica into a suitable solvent and mix with emulsifier. Subsequently treat the mixture with high frequency ultrasound to reduce the size become nano scale (less than 100 nm)