Removal of Chromium (III) from drinking water using ash of bark of Terminalia arjuna

 

M.N.Thakuria¹ and A. K. Talukdar²

¹Department of Chemistry, Birjhora Mahavidyalaya, Bongaigaon -783380, Assam, India

²Department of Chemistry, Gauhati University, Guwahati-781014, Assam, India

*Corresponding Author E-mail: mnt_bm@yahoo.com

 

 

Drinking water samples of 27 sources of Chirang District of Assam, India have been analyzed. Ash bark of Terminalia arjuna was studied as adsorbent for adsorption of Cr³⁺ ions from contaminated water based on these findings. Terminalia arjuna was characterized by X ray fluoresence spectroscopy for determining chemical composition, X ray diffraction to verify crystallinity, fourier transform infra red spectroscopy for residual organic species and N₂ adsorption studies to find out surface area and pore volume. The adsorption experiments were applied to evaluate the adsorption performances of Terminalia arjuna. The maximum (99%) removal of Cr (III) can be obtained if 60 mL of water containing 0.8g L^-1 of Cr (III) was passed through 5 g of Terminalia arjuna bark ash for 2 elutions. Langmuir’s and Freundlich’s adsorption isotherms gave satisfactory fitting to the adsorption isotherm data.

 

 

1. INTRODUCTION:

Chromium and its compounds are widely used in electroplating, leather tanning, cement, dyeing, metal processing, wood preservatives, paint and pigments, textile, steel fabrication and canning industries ¹. It can percolate into the soil and as a result it may contaminate groundwater, which is a major source of drinking water. Trivalent chromium is the naturally occurring state of chromium and is not considered toxic as compared to hexavalent chromium. Naturally occurring chromium can be oxidized in raw water to produce more toxic hexavalent form of chromium. Other sources of hexavalent chromium are from paint and plating wastewater contamination of waterways. Some people are extremely sensitive to both trivalent and hexavalent chromium and can develop allergic reactions consisting of severe redness and swelling of the skin. Most human exposure to chromium occurs when people eat fresh vegetables, meats, fish, and poultry. Presence of chromium ion in drinking water beyond the permissible limit (0.05 mg L^-1) causes lung disease, ulcer of mucous membrane of nose etc. Although, chromium (III) is less toxic than chromium (VI), presence of Mn (II) oxidizes trivalent chromium to hexavalent state ^{2, 3}.

 

The use of zeolites as ion exchangers has been reported as an attractive means of Cr³⁺ removal from wastewater, both in terms of removalability and cost effectiveness ^4-6. The separation of the chromium (III) dissolved in a tanning wastewater was studied by means of precipitation with calcium carbonate, reverse osmosis with polyamide membrane and adsorption on activated carbon ^{7, 8}. It has also been reported that chromium (III) could be removed by using precipitation process from aqueous solutions ⁹. Numerous studies of various unconventional adsorbents for the adsorption of heavy metals from water have been conducted recently like some natural adsorbents such as poplar and fir sawdust, pulp and Kraft lignin¹⁰, tannin immobilized mesoporous matrial ¹¹ etc. Natural materials including waste from agricultural operations are available in large quantities and they may have high potential to be used as low cost adsorbents. Moreover, they are cost effective as they represent unused resources and are environment friendly. For example, Casuarina glauca has been found to be effective for the sorption of chromium and lead ions from their mixed solutions ¹². Pomegranate husk carbon sorbents are efficient, environment friendly and can reduce the huge amount of toxic chromium ions from effluent discharges by the industries around the big cities ¹³. The phenomenon of bioseparation emerges as one of the effective techniques for separation of heavy metals from water ^{14, 15}.

 

The bark of Terminalia arjuna (family Combretaceae) is an ayurvedic remedy that has been mentioned in many ancient Indian medicinal literature including Charaka Samhita and Astang Hridayam to possess cardio protective property. A number of experimental and clinical studies have proved that dried bark powder of this plant have potent hypolipidemic and cardioprotective activity. The bark powder of Terminalia arjuna has also been found to improve antioxidant status in the patients of coronary heart disease and these beneficial effects may be related to its high flavonide content ¹⁶.  In Assam Terminalia arjuna, commonly known as Arjun tree is found in large scale. In the present work, drinking water samples of 27 sources of Chirang District of Assam, India have been analyzed. Based on these findings ash bark of Terminalia arjuna was studied as adsorbent for adsorption of Cr³⁺ ions from contaminated water. Langmuir’s and Freundlich’s adsorption isotherms are drawn on the basis of these results.

 

2. MATERIALS AND METHODS

2.1 Preparation of the adsorbents

The bark of Terminalia arjuna after cutting into pieces was washed, cleaned and burnt under normal conditions.  The adsorbent was heated at 383 K in oven for a period of 12 h before used as adsorbent.

 

2.2. Characterization of ash bark of Terminalia arjuna

Chemical composition of ash bark of Terminalia arjuna was determined by XRF (PANalytical, Model EXIOS Fluorescence Spectrometer).The material was also characterized by powdered XRD, FTIR and N₂ adsorption. XRD patterns were obtained in a Rigaku Miniflex Table Top XRD (copper source, wavelength, λ = 1.54 nm, K_α radiation) while IR spectra were recorded in a Perkin-Elmer spectrum RXIFT-IR system. Nitrogen adsorption measurements were carried out using a MICROMERITUS TRISTAR 3000 instrument at 77 K. Prior to nitrogen adsorption, samples were degassed for 2 h at 323 K.

 

2.3 Analysis of drinking water and preparation of solutions

Drinking water samples of 27 sources consisting of ring wells, tara pumps, tube wells and deep tube wells covering the Chirang district of Assam have been analyzed by standard methods ¹⁷. The highest concentration (described as highest field concentration or simply, as HFC) of Cr³⁺ ion was found to be 0.08 mgL^-1. A stock solution of Cr³⁺ was prepared using demineralized water having concentration 10 times more than that of HFC. This solution is termed as 10×HFC. The solution was then acidified with 4-5 drops of concentrated nitric acid to bring the metal completely into aqueous medium.

 

2.4 Adsorption procedure

A bed of glass-wool was made in the lower part of a uniform glass tube fitted with a stop cock. 2 g of ash of Terminalia arjuna bark was placed on the bed of adsorbent and then 60 mL of the solution (10 ×HFC) was allowed to pass through it for single elution. The process was repeated with the same volume of the solution for 2, 3 and 4 elutions taking same amount of same adsorbent separately. Identical methods were followed using 2, 3, 4 and 5 g of the same adsorbent for 1, 2 and 3 elutions. All the solutions were analyzed by Atomic Absorption Spectrophotometer (AAS) before and after passing through the adsorbent to study the extent of adsorption of Cr³⁺ ion in the water samples. 

 

3. RESULTS AND DISCUSSIONS

3.1. Adsorbent characteristics

The chemical composition of ash of bark of Terminalia arjuna on dry basis is given in Table 1.  It is observed that silica concentration is the maximum followed by calcium oxide and alumina. XRD patterns of the ash of bark of Terminalia arjuna show that all the components are in crystalline state (Fig.1). FTIR spectra of ash of bark of Terminalia arjuna are shown in Fig. 2. Appearance of different bands in the 2000-3000 and  600-1000 cm^-1 regions indicates the presence different organic species in dried sample. Pore size distribution of   ash of  bark of Terminalia arjuna from BJH adsorption data is depicted   in Fig.3. There are two types of pores one having size less than 4 nm and the other falls in the mesopore region of 60 to 200 nm. The surface area and pore volume of ash of bark of Terminalia arjuna sample has been found to be 3.6634 m²/g and 0.001878 cm³ g^-1 respectively [(Figs. 4(a) and (b)].

 

Fig1: XRD of bark ash of Terminalia arjuna

 

Table 1: XRF study results of ash bark of Terminalia arjuna (in percent  weight)

SiO2	Al2O3	MnO	CaO	Na2O	K2O	TiO2
39.08	10.01	0.02	29.32	3.01	3.30	0.10

 

Fig. 2: FTIR of Terminalia arjuna bark ash

 

 

Fig. 3 Pore size distribution of ash of bark of as obtained from BJH  Adsorption data

 

Fig4(a).   BET surface area plot of Terminalia arjuna

 

Fig. 4(b) BJH adsorption  cumulative  pore volume plot

 

3.2 Adsorption isotherm

The Langmuir adsorption model was applied to study the adsorption equilibrium of Cr (III) on ash of bark of Terminalia arjuna. The Langmuir adsorption may be expressed as:

 

C_e/x/m =1/Q₀ b+ C_e / Q₀

 

Where C_e is the residual concentration of Cr (III) at equilibrium in mg/L, x is the amount of Cr (III) adsorbed in mg/L, m is the weight of the adsorbent in gram, Q ₀ and b are Langmuir constants related to adsorption capacity and rate of adsorption respectively. The linear plot of C_e/x/m versus C_e indicates that the adsorption follows the Langmuir adsorption model for Cr(III) adsorption in the present study (Fig 5).The values of Q₀ and b calculated from the slope and the intercept respectively of the plot are found to be 0.523 mg/g and 9.1 l/g respectively..

 

The Freundlich adsorption model was also applied to study the adsorption equilibrium of Cr (III) on Terminalia arjuna bark ash .The Freundlich adsorption may be expressed as:

 

                      log x/m =log K_f +1/n log C_e

 

Where x is the amount of Cr (III) adsorbed in mg/100mL. m is the weight of the adsorbent in gram and C_e is the residual concentration of Cr (III) at equilibrium in mg/100 mL.

K_f and 1/n are Freundlich constants relating to the adsorption capacity and adsorption intensity respectively and are evaluated from the log x/m vs. log C_e plot (Fig 6) with the slope 1/n and the intercept log K_f .The value of 1/n and K_f are found to be 2.66 and 3.1189 respectively. The linearity of the curve indicates the applicability of the adsorption isotherm.

 

Fig5. Langmuir Plot

 

 

Fig 6. Freundlich Plot

 

3.3. Effect of amount of adsorbent                                             

Adsorption of Cr (III) on Terminalia arjuna bark ash for 1 elution was found to increase linearly with the amounts of the adsorbent (Fig 7).This is naturally acceptable as the availability of surface area or for that matter, number of adsorption points is more in larger amount of the adsorbent. The minimum and the maximum adsorptions of the metal ion from drinking water samples in case of single elution were seen 84% and 95% for 1 g and 5 g of the adsorbent respectively . The percentage adsorption of the metal was also found to increase almost linearly up to 5g of the adsorbent for different elution numbers ( Figs 7, 8 and 9).

 

Fig 7. Cr (III) adsorption on Terminalia arjuna bark ash for 1 elution-% adsorption vs. amount of adsorbent (g)

 

Fig 8. Cr (III) adsorption on Terminalia arjuna bark ash for  2 elution-% adsorption vs. amount of adsorbent (g)

 

Fig 9. Cr (III) adsorption on Terminalia arjuna bark ash for 3 elution-% adsorption vs. amount of adsorbent (g)

 

3.4. Effect of number of elutions

The results of adsorption studies for different number of elutions for 2g of the adsorbent are depicted in the Fig 10. It is found that the adsorption of the metal increases with increase in the number of elution for a constant amount of the adsorbent studied. This is also true for other amounts of the adsorbent (Table 2). Thus, maximum 99% removal of Cr (III) can be obtained if 60 mL of water containing 0.8g L^-1 of Cr (III) is passed through 5 g of Terminalia arjuna bark ash for of 2 elutions.

 

 

Table 2: percentage adsorption of chromium from aqueous solutions

Concentration of solution	Amount of the adsorbent(g)	Adsorption of Cr(III)			No. of elution
		Before adsorption mgL-1	After adsorption mgL-1	% adsorption
10X HFC	1	0.8	0.127	84	1
-do-	1	-do-	0.104	87	2
-do-	1	-do-	0.083	90	3
-do-	2	-do-	0.112	86	1
-do-	2	-do-	0.083	90	2
-do-	2	-do-	0.064	92	3
-do-	2	-do-	0.031	96	4
-do-	3	-do-	0.088	89	1
-do-	3	-do-	0.056	93	2
-do-	3	-do-	0.048	94	3
-do-	4	-do-	0.064	92	1
-do-	4	-do-	0.032	96	2
-do-	4	-do-	0.024	97	3
-do-	5	-do-	0.043	95	1
-do-	5	-do-	0.009	99	2
-do-	5	-do-	0.006	99	3

 

Fig 10. Cr (III) adsorption on Terminalia arjuna bark ash (2g)   %adsorption vs number of elution

 

4. CONCLUSION:

The present study follows the Langmuir and Freundlich adsorption models for Cr (III) adsorption on Terminalia arjuna bark ash. Adsorption of Cr (III) from water on Terminalia arjuna bark ash was found to increase with the amounts of the adsorbent. Again, the extent of adsorption of the metal increases with increase in the number of elution for any amount of the adsorbent studied. Terminalia arjuna can be effectively used for removal of Cr (III) from contaminate water containing at least 0.8g L^-1  of the metal ion. As the drinking water of rural tribal areas of Assam is found to be contaminated by chromium,  Terminalia arjuna can be used as a cost effective and efficient adsorbent for removal of chromium.

 

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Received on 08.03.2012         Modified on 20.03.2012

Accepted on 25.03.2012         © AJRC All right reserved