Rice husk is a by-product of the rice milling industry. It is also abundantly available.  Rice husk is a residue produced in significant quantity on a global basis.  While they are used as a fuel in some regions, in other countries they are treated as waste, causing pollution and disposal problems.  Due to growing environmental concern, and the need to conserve energy and resources, efforts have been made to burn the husks under controlled conditions and to utilize the resultant ash as building material. South and South East Asia account for over 90 % of world’s rice production.  Like most other biomass material, rice husk contains a high amount of organic volatiles.  Thus, rice husk is recognized as a potential source of energy. This is a unique crop residue with uniform size and high content of ash (14–25%). The amorphous silica content of the rice husk ash (RHA) can be as high as 90–97% which would make the rice husk ash utilization economically attractive (Balakrishnan, 2006; Adam, 1991; Saleh, et. al.1990; Della, et. al. 2002).

Rice husks (or rice hulls) are the hard protecting coverings of grains of rice. Rice husk is an agricultural residue abundantly available in rice producing countries. Husk Produced is around 20% of total rice production. The annual rice production in India and the World is 150 MT (Million Tons) and 700 MT, respectively, and hence husk produced in India and the World, the amounts are generally approximately in the range of 30 MT and 140 MT, respectively. Rice husk is generally not recommended as cattle feed since its cellulose and other sugar contents are low means there is limited source of energy for body. Furfural and rice bran oil are extracted from rice husk. Industries use rice husk as fuel in boilers and for power generation. Among the different types of biomass used for gasification, rice husk has a high ash content varying from 18 – 20 %. Silica is the major constituent of rice husk ash and the following tables gives typical composition of rice husk and rice husk ash. With such a large ash content and silica content in the ash it becomes economical to extract silica from the ash, which has wide market and also takes care of ash disposal. The dry analysis of rice husks are as follows:

Table 1 Analysis of rice husks and its ash

Chemical analysis of rice husk

Compositional analysis of rice husk ash

Element Analysis

Mass Fraction %


Mass Fraction (%)



Silica (SiO2)

80 – 90



Alumina (Al2O3)

1 – 2.5



Ferric oxide (Fe2O3)




Calcium oxide (CaO)

1 – 2



Magnesium oxide (MgO)

0.5 – 2.0



Sodium oxide (Na2O)

  0.2 – 0.5







Loss on Ignition

10 – 20





(Kumar and Singh, 2011)





 Again, amorphous silica is well known and commonly used as a support material due to its high surface area, which will provide sufficient surface area for any metal to disperse (Mekhemer, et. al. 1999). There are very limited publications on the use of RHA as a matrix for preparing metal supported heterogeneous catalyst (Chang, et. al.1997, 2002a, 2002b, 2003a and 2003b; Chang and Tsay, 2000).  In all reported cases, the incipient-wet method and ion exchange methods were used to physically incorporate the metal into the rice husk silica matrix (Adam, et. al.2006).


From this review of literature it can concluded that:

1) RHA (Rice husk ash) has a very high active surface area.

2) RHA, thus, must have high CEC (cation exchange capacity).

3) RHA can hold a good amount of water soluble oxides of Na, Ca and Mg and can hold NO-3, thus it is a good ion-adsorbent.

   So, it has a very good buffering capacity in neutralizing both acid and alkaline soils and must have good quality in mitigating soil salinity. As such one can foresee successful application of RHA (Rice husk ash) in amelioration of problem soils like saline, alkali and acid soils without hampering nutritional balance in soil and at the same time improving physical characteristics for aeration, structure, friability, tillage, water holding capacity, etc. towards a good farming in problem soils.

Other good soils may be mixed with RHA for sustainably maintaining good soil health.

4)  Application of RHA in soil needs suitable field trial to judge its efficacy and to find out its economical use.

A proposal on field trial:

Experiment No.

Title: Laboratory experimentation on management of soil salinity through application of ash of rice husk

Objective: Improvement of a saline soil implies the reduction of the salt concentration of the soil to a level that is not harmful to the crops. Germination of seed and raising seedling are most problematic tasks towards successful cultivation in saline water inundated fields followed by drainage, as it was experienced subsequently after Aila in May 2009 in coastal areas of West Bengal. It was found that rice seeds unknowingly left over on ash of paddy husks could give good germination of seeds in those acute saline affected soils at that time for which no records were created. In this experiment, germination of rice seeds will be studied in petridishes under different levels of artificial soil salinity and doses of ash of rice husk. Availability of B and Zn will also be analysed in each experiment.


Location: Laboratory

Crop: Rice

Design: RCBD with four replications

Treatments: Artificial soil salinity will be created through application of known concentration of NaCl solution in each petridishes up to a maximum of 10dSm-1 i.e. the EC 10 to 5 times more than the EC value for critical germination.

  1. 50g soil+ no artificial salinity.
  2. 50g soil + NaCl solution (up to EC 1.00).
  3. 50g soil + NaCl solution (up to EC 2.00).
  4. 50g soil + NaCl solution (up to EC 3.00).
  5. 50g soil + NaCl solution (up to EC 4.00).
  6. 50g soil + NaCl solution (up to EC 4.00).
  7. 50g soil + NaCl solution (up to EC 5.00).
  8. 50g soil + NaCl solution (up to EC 6.00).
  9. 50g soil + NaCl solution (up to EC7.00).
  10. 50g soil + NaCl solution (up to EC 8.00).
  11. 50g soil + NaCl solution (up to EC 9.00).
  12. 50g soil + NaCl solution (up to EC 10.00).
  13. 10g ash of rice husk +no artificial salinity.
  14. 50g soil + 10g ash of rice husk + no artificial soil salinity.
  15. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 1.00).
  16. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 2.00).
  17. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 3.00).
  18. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 4.00).
  19. 50g soil + 10g ash of rice husk + NaCl solution (up to EC5.00).
  20. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 6.00).
  21. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 7.00).
  22. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 8.00).
  23. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 9.00).
  24. 50g soil + 10g ash of rice husk + NaCl solution (up to EC 10.00).


Adam, F. (1991). Preparation and adsorption studies on rice husk ash. M.Sc. thesis, Universiti         Sains Malaysia, Pulau Pinang.

Adam, F.; Balakrishnan, S. and Wong, P. L. (2006). Rice husk ash silica as a support

material for ruthenium based heterogeneous catalyst. Journal of Physical Science,  

        17(2), 1–13.


Balakrishnan, S. (2006). Rice husk ash silica as a support material for iron and ruthenium based heterogeneous catalyst. Thesis submitted in fulfillment of the requirements for the degree of Master of Science. School of Chemical Sciences, Universiti Sains Malaysia. 11800 Penang, Malaysia. October 2006.

Chang, F.W., Hsiao, T.J., Chung, S.W. & Lo, J.J. (1997). Nickel supported on RHA – Activity          and selectivity in CO2  methanation.  Applied Catalysis A: General, 146, 225.

Chang, F.W., Tsay, M.T., Kuo, M.S. & Yang, C.M. (2002)a. Characterization of nickel catalyst          on RHA-Al2O3  composite oxides prepared by ion exchange.  Applied Catalysis A:

General, 226, 213.

Chang, F.W., Tsay, M.T. & Kuo, M.S. (2002)b. Effect of thermal treatments on catalyst reducibility   and activity in nickel supported on RHA-Al2O3  systems. Thermochim. Acta, 386, 161.

Chang, F.W., Kuo, W.Y. & Lee, K.C. (2003)a. Dehydrogenation of ethanol over copper  catalyst on rice husk ash prepared by incipient  wetness impregnation. Applied Catalysis A: General, 246, 253.

Chang, F.W., Kuo, M.S., Tsay, M.T. & Hsieh, M.C. (2003)b. Hydrogenation of CO2 over Ni

catalyst on rice husk ash-alumina prepared by incipient wetness impregnation. Applied

    Catalysis A: General, 247, 309.

Chang, F.W. & Tsay, M.T. (2000). Characterization of rice husk ash- supported nickel catalyst       prepared by ion exchange. Applied Catalysis A: General , 203, 15.

Della, V.P., Kühn, I. & Hotza, D. (2002). Rice husk ash as an alternative source for active silica  production. Materials Letters, 57, 818.

Kumar, S. and Singh, B. (2011).  Study on silicon carbide produced from rice husk as a

reinforcing agent. A thesis submitted in partial fulfillment of the requirements for the degree of Bachelor of Technology in Metallurgical & Materials Engineering. Department of Metallurgical & Materials Engineering, National Institute of Technology, Rourkela, India.2011, pp. 2 – 3.

Mekhemer, G.A.H., Abd-Allah, H.M.M. & Mansour, S.A.A. (1999). Surface characterization of silica-supported cobalt oxide catalyst. Colloids and Surfaces, A160, 251.

Saleh, M.I., Farook, A. & Ab. Rahman, I. (1990). Production and characterization of rice husk

ash as a source of pure silica.  In R. Othman (Ed.). Seramik Nusantara. Pulau Pinang:

Universiti Sains Malaysia, 261– 273.

To be continued…..