Adsorption of Aqueous solution of NO₂ by certain waste materials

 

K. Mamatha¹, N. Gandhi² and D. Sirisha³*

Centre for Environment and Climate Change, Jawaharlal Nehru Institute of Advanced Studies, 6^th floor, Buddha Bhavan, Secunderabad – 500003, Andhra Pradesh, India.

Corresponding author: sirishadavid@gmail.com

ABSTRACT:

Nitrogen oxides are formed during high temperature combustion processes from the oxidation of nitrogen in the air or fuel. The principal source of nitrogen oxides - nitric oxide (NO) and nitrogen dioxide (NO₂), collectively known as NO_x - is road traffic. NO and NO₂ concentrations are therefore greatest in urban areas where traffic is heaviest. Other important sources are power stations, heating plants and industrial processes. Long-term exposure to nitrogen dioxide may affect lung function and that exposure to nitrogen dioxide enhances the response to allergens in sensitized individuals. The feasibility of using waste materials as adsorbent for air pollutant NOx was evaluated in the present study. The experiments were carried out in laboratory on certain waste materials like Neem wood, brick powder, Coal and paper pulp. The experimental investigations were carried out by traditional adsorption studies and it showed that all substances have certain capacity to adsorb the NO_x from aqueous solution of NO_x. The adsorption of NO_x due to Neem dust is 100%. The adsorption due to paper pulp is in the range of 85-100%. The adsorption by brick powder is about 85%. At lower concentration the adsorption is more compared to higher concentration. It is found that the adsorption increases with increase in surface area.

 

 

 

INTRODUCTION:

NOx is the collective term for the environmental pollutants nitrogen oxide and nitrogen dioxide. At high temperatures, nitrogen and oxygen react to create the pollutants. Together, NO and NO₂ contribute to the creation of smog and acid rain as well as the formation of ozone. NOx form when fuel is burned at high temperatures, as in a combustion process. The primary sources of NOx are motor vehicles, electric utilities, Power plants and other industrial, commercial, and residential sources that burn fuels. Oxides of nitrogen in the atmosphere, when exposed to sunlight, react chemically with other gaseous compounds in the atmosphere such as "volatile organic compounds" (VOCs) through photosynthesis to form a brownish yellow cloud of gases commonly referred to as smog. Excess air also plays a major part in the creation of NOx. Greater excess air represents greater access to oxygen not taken up in burning the fuel, and it is therefore available to combine with the 80% nitrogen that is available in fresh combustion air.

 

Saw dust from Neem bark is used as low cost biosorbent for adsorptive removal of heavy metals such as Zn and Cd from aqueous solutions (Tarun Kumar; etal.,2008), Cr(VI) (Vinodhini and Nilanjana Das, 2009), Mercury from water (Ansari M.H.; etal., 2000) . Brick powder can be effectively used as a low cost adsorbent for minimization of organic chemical load in dye effluents (C.P. Kaushik; et al., 2009) and deflouridation of ground water (Asheesh Kumar Yadav; et al., 2005). Chalk powder can be used as one of the low cost adsorbent for removal of trihalomethanes from drinking water (Mohamed Suhail. T, N. Vijayan). Coal was used as one of the effective adsorbents from long time. Coal is used in removal of heavy metals like chromium (III) (Jamil Anwar; et al., 2009) and for the removal of sulphur dioxide from stack gases emitted to the atmosphere by different industries (A. K. Kotb, 2007). Coal can also be effectively used for removing organic contaminants from secondary municipal effluents (G. J. Johnson; et al., 1965) and mineral oil from wastewater (Branislav R. Simonović; et al., 2009).

 

MATERIALS AND METHODS:

In this paper an attempt has been made to suggest certain waste materials as effective adsorbents of NO_x.  The adsorbents primarily screened were Neem dust, Paper pulp, Brick powder, Coal, Concrete and Chalk powder. Initially, all the sorbents are screened by adding 1 gm of each adsorbent to 100 mL of aqueous solution of NO₂ gas.

 

Adsorption methods are adopted for non-combustible gas and these methods are suitable when pollutant gases are present in low concentrations. For this purpose, an aqueous solution of 100 mL of NO₂ of various concentrations is taken in 100 mL stoppered bottles and 1 gm of adsorbent is added to the solutions. Batch adsorption experiments are carried out at room temperature, a contact time of 24 hrs is maintained. The initial and final concentrations of aqueous solutions solution of NO₂ were determined by colorimeter and percentage removal of NO₂ was determined.

 

RESULTS AND DISCUSSION:

Table 1: Adsorbents and Sampling Sites

Adsorbent	Sampling Site
Brick Powder	Construction site at Hyderabad
Neem bark dust	Timber Industry
Coal	Singareni Coaleries
Paper pulp	Badrachalam Paper Mills
Chalk powder	Class room
Concrete	Construction site at Hyderabad

 

The adsorbents selected for the present study are brick powder, Neem bark dust, Paper waste, Chalk powder, Coal and Concrete and the sampling sites are tabulated in Table 1. From Table 2 it is observed that the order of adsorption is Neem bark dust, Paper waste, Brick powder, Chalk powder, Coal and Concrete. The adsorption capacity is more at lower concentrations compared to higher concentration. In the present study, it is observed that physical adsorption is taking place. Neem bark dust is a waste material collected from the Timber industry. Neem bark dust is a bio adsorbent and it consists of lignin and cellulose and many hydroxyl groups such as lumins or phenolic compounds.

 

The composition of Neem bark dust is given by Cellulose – 36.5% and Lignin – 49.5%. The ligno-cellulosic components present in the Neem bark dust are responsible for complete adsorption observed in the present study. Neem bark dust is a cheap material and the adsorption capacity of the Neem bark dust is high compared to other adsorbents, hence, it can be used as an effective adsorbent for removal of NO₂.

 

Brick powder is the waste material collected from construction sites and it is used as the adsorbent. It has a high porosity and it is made from the local red mud from Hyderabad which has iron oxide, which helps in adsorption of NO₂.

 

Paper consists of organic and inorganic material. Organic portion consists of cellulose, hemi cellulose and lignin. Inorganic portion consists of mainly filling material such as CaCO₃ and TiO₂, may be of 30% of paper. As the paper waste material also have porosity, cellulose and lignin compounds, it is also good adsorbent.

 

Chalk powder is the waste material collected from classrooms. Chalk is the form of Calcium carbonate with minor amount of silt and clay. As Calcium carbonate decomposes only at 900⁰C, the adsorption taking place in the present study is physical adsorption. Chalk powder due to certain porosity adsorbs NO₂ from aqueous solution of NO₂.

 

Concrete material is a mixture of silica, stones and cement in the ratio of 1:2:4. As the material consists of all these substances, it is selected as adsorbent. Concrete powder which is a mixture of Portland cement, sand stones in the required strength has adsorption capacity and has shown less adsorption capacity when compared to other adsorbents.

 

 

Order of Effectiveness of the Adsorbents Neem bark dust > Brick powder > Paper pulp > Chalk powder > Concrete > Coal

 

Table 2: Percentage removal of NO₂ with different Adsorbents

S. No.	Concentration of NO2 µg/m3	Brick Powder	Neem bark dust	Coal	Paper pulp	Chalk Powder	Concrete
1.	10	88	100	40	100	40	35
2.	20	85	100	20	85	30	20
3.	30	44	100	16	83.3	25	16.6
4.	40	26	100	14.2	87.5	25	12.5
5.	50	13	100	11.6	90	25	8
6.	60	5	100	8.8	-	6.6	-
7.	70	-	100	8	-	5.7	-
8.	80	-	100	-	-	-	-
9.	90	-	100	-	-	-	-
10.	100	-	100	-	-	-	-

 

 

In most of adsorption process commercially available activated charcoals are used to study the adsorption. In the present study the adsorption found is very less because of less porosity and hardness of coal.

 

CONCLUSION:

It is necessary for the environmental researcher to control the ill effects caused by air pollution for survival of the mankind. So the present study has helped to control the air pollution caused by NOx. Among six different adsorbents studied, Neem bark dust proved to be the most effective adsorbent of NO₂ from aqueous solution of NO₂. Thus, our study proves that the effect of harmful chemicals like NOx can be reduced by using naturally available waste materials like Neem bark dust, Brick powder, Concrete, Paper pulp, Chalk powder and Coal. Hence, this study provides an economic solution for cleaning up environmental pollutant NOx and it is recommended to use these adsorbents in industries.

 

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Received on 19.12.2011         Modified on 04.01.2011

Accepted on 15.01.2012         © AJRC All right reserved