DETERMINATION OF SOME METALS IN RICE HUSK ASH

DETERMINATION OF SOME METALS IN RICE HUSK ASH

ABSTRACT

The technological trend towards waste utilization and cost reduction in industrial processing has attracted the use of rice husk ash as a value added material. Both rice husk and rice husk ash has been found suitable for wide range of domestic as well as industrial applications. This research work covers the determination of the element present in the rice husk ash using atomic absorption spectrometer showing that leaching of rice husk with nitric acid was superior. This is seen that agricultural waste can be converted into viable product, economically advantageous and also for future use.

 
CHAPTER ONE

1.0            INTRODUCTION

Rice husk is one of the most widely available agricultural wastes in many rice producing countries around the world. Globally, approximately 600 millions tons of rice paddy is produced each year. On average 20% of the rice paddy is husk giving an annual total production of 120 million tons. In majority of rice producing countries much of the husk produced from processing of rice is either burnt or dumped as waste. (Giddel M.R and Jivan A.P 2006).

Burning of rice husk in ambient atmosphere leaves a residence called rice husk ash, for every 1000kgs of paddy milled, about 220kgs (22%) of husk is produced and when this husk is produced and the boilers, about 55kgs (25%) of rice husk ash is generated. (Koteswara Rao.D and Prav 2007).

1.1     RICE HUSK

Rice husk contain 75-90% organic matter such as cellulose, ligmin e.t.c and mineral components such as silica, alkalis and trace element. It’s silica content is position highest among all of them. Nigeria produces about 4 million tons of paddy every year from which 0.8 million tons of rice husk are separated as by-product.

Chemical composition of rice husk ash (RHA) depends on the type of soil for growing rice plants, the fertilizing practices, environment, temperature and duration of burning. These factors influence the percentage of silica and its mineralogical nature. The heap burning method produces poor quantity of rice husk ash. (Mehtel et al 1975)

It consist of large amount of unburnt carbon which lowers the silica content secondly the original amorphous nature of silica is destroyed and resulting ash is largely of crystalline character consequently it becomes comparatively less reactive regarding the anticipated chemical combination (Kotsis et al 1989).

1.2     APPLICATION OF RICE HUSK ASH

1.           Rice husk ash in steel industry. RHA is used during the production of high qualify flat steel. The ash also finds application as an excellent insulator having fine insulating properties including low thermal conductivity, a high melting point, low bulk density and high porosity. It is used as tundish powder to insulate the tundish container, prevent rapid cooling of steel and ensure uniform solidification in casting process. Rice husk ash is also used as a coating over the molten metal in the tundish and in ladle which acts as a very good insulator and does not allow quick cooling of metal. (The uk steel Association www.uksteel).

2.           Use in ceramic and refracting industry: RHA is used in the manufacture of refractory bricks because of its insulating properties. It has been used in the manufacture of low cost, high weight insulating boards. RHA has been used as silica source for cordierite production. Replacement of kaolinite with rice husk silica in the mixture composition, yields higher cordierite with a lower crystallize temperature and decrease in activation energy of crystallization. (Fadaly et al 2004).

3.           Use of rice husk ash as silica source: due to presence of large silica content in ash, extraction of silica is economical. Silica is also precipitated in customized forms to meet the requirements of various uses. Silica can be used in rubber industry as reinforcing agent, in cosmetics, in toothpaste as a cleaning agent and in the food industry as an anti-caking agent. There is a growing demand for fine amorphous silica in the production of high performance cement and concrete, use in budges, manure environments, nuclear power plants e.t.c (Chandrasekar S, Satyanarayana KG 2003).

1.3     FACTORS INFLUENCING ASH PROPERTY

1.3.1  TEMPARATURE

A series of experiment using a laboratory oven under conditions design to stimulate the conditions of combustion from a rural facility were carried out.

Atomic absorption spectrometer analysis of the ash found that the (globular) amorphous silica, increase in size from 5-10µm to 10-50 µm with rising combustion temperature from 500 ⁰ C-600 ⁰ C the transition to complete by 900⁰C.

These change affect the structure of the ash as such, the grind ability and therefore reactivity of the ash is affected since, after grinding, a greater surface area, is available for chemical reaction if the ash is to be used as a pozzolan. For the steel industry, more crystalline ash is preferred as this increases its refractory properties. (Christiana Dolly Granados, Rosa Ventuni 2008)

         

1.3.2    GEOGRAPHICAL REGION

It has been reported that chemicals variation in husk composition land consequently ash composition are influenced by such things as the soil chemistry, paddy variety and climate. However, only one report of a change in the physical and chemical properties of ash influence by region was found. A variation in colour and trace metal was found in ash from husk from northern India resulting in a much darker ash than husk from Nasarawa. The colour variation was not related to difference in mineral composition of ash, but cultivation, with phosphate having a negative effect on the quality of the ash in terms of its ability to act as a pozzolan. It has also been said that the K₂O found in some ashes could be a consequent of k-rich fertilizers used during the paddy cultivation. (Cordeiro, G.C Toledo Filho 2008).

1.4            AIMS AND OBJECTIVES OF THE STUDY

1.     To determine the presence of element/ metals in rice husk ash using AAS.

2.     To notify industries of the economic importance of rice husk ash such as in:

a.     Ceramic and refracting industry

b.     Silica source.

c.      Production of high quality flat steel.

1.5            SCOPE OF THE STUDY

The present studies, in the above perspective, were carried out consequently, the first and foremost aim is to analyze the presence of some metals from rice husk ash.

The possibility of utilizing rice husk, yielding ash demand a number of special processing considerations like burning environment, temperature and time plays a very important role of optimum yield of rice husk ash. Simple supply of fresh air helps in oxidizing the rice husk carbon to carbon dioxide; this result in lowest residual carbon percentage and highest ash content.

1.6     PROBLEM OF STUDY

Ø Rice husk removal during rice refining creates disposal problem due to less commercial interest.

Ø Handling and transportation of rice husk due to it’s low density could also be a problem.

Ø Rice husk ash is a great environment threat causing damage to land and surrounding area where it is dumped.

Ø The high cost of machine for analysis carried out in rice husk ash and the difficulty in getting the machine.

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