Removal of Congo Red Fron Solution by Adsorption

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Removal of anionic dye Congo Red from aqueous solution by adsorption

Abstract

The removal of Congo Red (CR) dyes from wastewater effluents is an important topic due to the

health and environmental risks if left untreated. In lot of developing areas in the world removal of

CR dyes by conventional means is still expensive. This has been motivation for research to be

carried out in order to find low cost alternatives. The use of agricultural wastes as adsorbents has

shown to be a promising avenue to remove dyes such as CR. This report investigates results of four

different studies on the low cost adsorbents: Chitosan Hydrogel Beads, Bagasse Fly Ash, Cattail

Root and Bael Shell Carbon. Conclusions are then drawn from the results of these studies.

1. IntroductionDyes have been used by humans for thousands of years to colour fibrous materials such as fabrics.

Prior to 1856 humans were only using dyes from natural sources, until the discovery of synthetic

dyes was made (Clark 2011, 3). The aim of a dye is to uniformly colour a substrate permanently,

hence the dye should also be resistant to such things as moisture, light, heat and washing methods

once applied (Chatwal 2009). According to the Britannica encyclopaedia the dyeing process places

the dye molecules within the microstructure of the substrate via various mechanisms depending on

the specific dye and substrate.

Congo Red (CR) also known as Direct Red 28 is a synthetic, anionic benzidine based dye, with the

chemical formula . CR can metabolize to benzidine which is a known human

carcinogen. CR is also known to be toxic to plants and animals which is another reason why CR

effluents entering wastewater streams is a major environmental, ecological and health concern

(Ahmad and Kumar 2010).

There are several immediate dangers to CR exposure, which are as follows: Eye irritation and the

possibility of chemical conjunctivitis or corneal damage. Skin irritation (possibly burns) with the

possibility of an allergic reaction, which would become evident upon re-exposure to CR. If ingested

(large quantity) CR may cause gastrointestinal irritation with nausea, vomiting and diarrhoea. If

inhaled respiratory tract irritation may result. Olfactory fatigue may occur and possibly delayed

pulmonary edema (Congo Red MSDS. 2005).

The long term health risks are much more dangerous, some of these are: Possibility to cause

adverse reproductive effects (fetotoxicity, female and male fertility) and birth defects (teratogenic developmental abnormalities) based on animal data. May cause genitic mutations based on animal


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data. Congo Red is a benzidine-based dye and benzidine has been classified by IARC as Group 1

carcinogen (Congo Red MSDS. 2005).

Some of the environmental impacts of CR effluents in wastewater are: negativily affecting

photosynthetic processes of aquatic plants, reducing the oxygen levels in water and in some

extreme cases suffocating of aquatic flora and fauna has occurred (Chatterjee et al. 2009).

According to Mall et al. (2005) CR effluents are most commonly produced from textiles, printing

and dyeing, paper, rubber and plastics industries however because of the structural stability of CR it

can be difficult to biodegrade. This being the case there are still various ways to treat the CR

wastewaters so that the associated risks can be reduced.

CR dye wastewater can still be treated by conventional means such as coagulation and flocculation

membrane separation, activated carbon adsorption, electrochemical removal and photochemical

degradation (Hu et al. 2010). According to Gupta and Suhas (2009) biological treatment is the

most common and wide spread technique used in dye wastewater treatment. Biological treatments

can be aerobic, anaerobic or combined aerobicanaerobic, which can offer flexibility for treating a

range of dyes and reasonably cost effective (Gupta and Suhas 2009). However this method isnt

very effective for dyes such as CR that have low biodegradability also it requires a large area of

land and requires a long time to ferment which means it cannot be done on a continuous process.

Chatterjee et al. (2009) explains that activated carbon is the most common adsorbent used for

removing dye from waste water, however it is difficult to to dispose of and regenerate. Mall et al.

(2005) also states that granular activated carbon is a very popular and successful adsorbent, but

costly too.

The main problem the methods mentioned above have is that they can be quite costly and are

therefore too expensive to be used in a lot of developing countries. This has been motivation forresearch into low cost adsorbents that can be used to treat wastewaters containing CR (Ahmad and

Kumar 2010). Some of the research has looked into the use of low-cost agricultural adsorbents such

as: coir pith, anaerobic granular sludge, hazelnut shells, bottom ash and de-oiled soya, carbon

slurry, hen feathers along with other waste materials however the adsorption capacities of most of

the materials mentioned are limited (Hu et al. 2010). Other low cost agricultural adsorbents have

greater adsorption capacities, which could be promising, such as: Pine dust, chitosan, rice husks,

activated clay and cane pith, all with different contact times and pH (Gupta and Suhas 2009).


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Darwood and Sen (2012) along with many others believe adsorption to be superior to other

separation techniques in terms of initial cost, simplicity of design, ease of operation and insensitive

to toxic substances.

According Sen (2013) adsorption is defined as the selective retention of one or more components

of a mixture on a solid surface (pore wall). There are two types of adsorption, physical or

physisorption and chemical or chemisorption. The attractive forces occurring in physisorption

between adsorbed molecules and the solid surface are van der Waals forces. These forces are

usually weak which can allow in reversible adsorption. Attraction forces in chemisorption are

generally stronger than physisorption, hence it is difficult to remove chemisorbed species from the

solid surface (Sen 2013). In the case of anionic dyes such as CR electron transfer between the

adsorbent and adsorbate take place to form chemical bonds.

Good adsorbents should have the following characteristics, high surface area (increases the

adsorption capacity), small particle size, time taken for adsorption equilibrium should be as short as

possible, good affinity for solute and correct pH which will affect the degree of ionisation.

According to Gupta and Suhas (2009) some common adsorbents used to remove dyes from waste

water are:Alumina, which is a synthetic porous crystalline gel, available in the form of granules of different

sizes having surface area ranging from 200 to 300 m2g-1.

Silica Gel, prepared by the coagulation of colloidal silicic acid results in the formation of porous

and non-crystalline granules of different sizes. Silica Gel has a higher surface area than to alumina,

ranging from 250 to 900 m2g-1, however it is an expensive option.

Zeolites, are micro porous adsorbents, which can be found naturally and prepared synthetically

also. They are also considered as selective adsorbents and show ion exchange properties.

Activated carbon, very effective, normally has a very porous structure with a large surface area

ranging from 500 to 2000 m2g-1. However time and expensive are required to first activate the

carbon through and then regenerate it after it has been exhausted.


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2. Previous ResearchAs previously mentioned there is a great need for CR dyes to be removed from wastewater because

of the risks associated however many conventional methods of removal can be expensive for

developing countries. This section of the report will investigate previous research done on low cost

adsorption solutions for the removal of CR dyes.

Chitosan Hydrogel Beads

Chatterjee et al. (2009) investigated the effectiveness of using Chitosan hydrogel beads

impregnated with nonionic or anionic surfactants. Chitosan (CS), is a linear biopolymer of

glucosamine that exhibits a high adsorption capacity towards many classes of dyes especially

anionic dyes because of its high amino and hydroxyl functional group content (Chatterjee et al.

2009). CS can be obtained at an industrial level by chemical de-acetylation of crustacean chitin (a

major component of exoskeletons of crustaceans such as crayfish, prawns and crabs, also on

insects), which is the second most abundant biopolymer in nature. In their report Chatterjee et al.

(2009) investigated the effect of impregnation of CS beads with two surfactant types, non-ionic

[triton X-100 (TX-100)] and anionic [sodium dodecyl sulphate (SDS)], for the removal of anionic

dye CR from aqueous solution. Table 1 below shows the properties of the different beads used for

the study, notice the very similar physical properties.

Table 1: General properties of different types of beads (Chatterjee et al. 2009)

Figure 1 below shows that CS/TX-100 increases in equilibrium absorption capacity, (mg/g), with

increasing surfactant concentration of beads up to 0.02 % where slowly decreases. CS/SDS also

increases but starts to decrease rapidly at about 0.01 % surfactant concentration.


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Figure 1: Effect of Surfactant Impregnation on CR adsorption with initial concentration of 500mg/l

(Chatterjee et al. 2009)

Figure 2 below shows how the equilibrium absorption capacity , decreases with initial pH of

solution with all bead types.

Figure 2: Effect of pH on CR adsorption with initial concentration of 500 mg/l (Chatterjee et al.

2009).

Through their experiments Chatterjee et al. (2009) found that not only could CS beads be an

effective adsorbent for CR dye but surfactant impregnation at a low dosage could greatly improve

performance. With an initial CR concentration of 500 mg/l, the experiments showed a maximum

adsorption (mg/g) of CS, CS/TX-100 and CS/SDS beads to be, 160.19, 302.05 and 223.35

respectively. All beads reached maximum adsorption capacity between 480-600 minutes with

CS/TX-100 beads having the highest mass transfer rate also. These findings by Chatterjee et al.

(2009) are quite promising however no costing estimates were included in their study.


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Bagasse Fly Ash

Mall et al. (2005) performed a study to examine the effectiveness of bagasse fly ash (BFA) as an

adsorbent for CR dye removal in comparison to boilers, activated carbons of commercial grade

(ACC) and laboratory grade (ACL). BFA is a waste product from the sugarcane industry and can be

obtained from the particulate collection equipment attached upstream to the stacks of bagasse

(fibrous remains of sugarcane stalks) fired boilers.

Results from the study showed that CR colour removal increases, as adsorbent dosage increases, up

to a certain limit and then it remains almost constant with the optimum for BFA, ACC and ACL

dosages being 1, 20 and 2 g of adsorbents per litre of dye solution, respectively. Figure 3 shows the

results of initial CR concentration for the various adsorbates at pH= 7, temperature = 30C and

time= 4 h, demonstrating that effectiveness of adsorbents decreases with increasing initial CR

concentration.

Figure 3: Effect of initial adsorbate concentration on the adsorption of CR at optimum dosages

(Mall et al. 2005)

Figure 4 below demonstrates how the mass of CR adsorbed per unit mass of adsorbent, qt (mg/g),

increases over time.

Figure 4: (mg/g), over a 4 h period, pH= 7, temperature = 30C (Mall et al. (2005).

Summarising the study by Mall et al. (2005) it can be seen that BFA may be an effective low cost

adsorbent for the removal of CR dye from aqueous solutions and more effective than the ACC and

ACL used. The main advantage of using BFA is its low cost, which according to Gupta and Suhas

(2009) is less than $0.1 US/ per kg.


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In summary the investigation by Hu et al. (2009) produces the following results. Removal

efficiency of CR increased with increasing adsorbent dosage and decreased with increasing

temperature from 20 to 40C. The equilibrium time was about 16 h, depending on the adsorbentdosage. Over a pH range of 5.5 10.0, the removal efficiency was independent of pH at CR

concentration of 50mg/L and adsorbent dosage 5.0 g/L with a pH of 2.5 producing the best results .

The maximum adsorption capacities of CR on cattail root were 38.79, 34.59 and 30.61mg/g at 20,

30 and 40C, respectively. These results suggest that cattail root is a potential low-cost adsorbent

for the dye removal from industrial wastewater (Hu et al. (2009).

Bael Shell Carbon

Ahmad and Kumar (2010) investigated the use of Bael shell carbon (BSC) as a low cost adsorbent

for the removal of CR dye from aqueous solution. Looking into the effect of different parameters

such as pH, temperature, contact time and initial dye concentration.

Bael is a fruit that is grown throughout Southeast Asian countries such as India, Sri Lanka,

Pakistan, Bangladesh, Burma, and Thailand. The hard shell of the fruit is a waste product. For the

study the bael shell was collected locally in India after which it was washed with distilled water and

dried in sun light for 10 days. The dried shell was crushed and sieved to the appropriate particle

size then it was carbonized for 1 h at 450C in a muffle furnace. The carbonized sample was

washed with hot distilled water and dried at 60 C for 24 h after which it was used for experiments

(Ahmad and Kumar (2010).

Figure 7 below is an example of one of the results from the study performed by Ahmad and Kumar

(2010) and shows how the adsorption capacity at equilibrium, , increases with temperature.

Figure 7: Effect of temperature on CR adsorption onto BSC (Ahmad and Kumar 2010).


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Other results from the study are as follows were the adsorption of CR onto BSC was strongly pH

dependent. The maximum adsorption (92%) was observed at pH 3. The maximum adsorption

capacity or CR using BSC was 98.03 mg/g which can be seen in table 4 below along with thecomparisons to other carbons used for CR removal. Overall it can be said that BSC could be an

effective low cost adsorbent for the removal of CR dyes from wastewater.

Table 2: Comparison of maximum monolayer adsorption capacity of various carbons for CR

removal (Ahmad and Kumar 2010).

3. ConclusionEach of the four adsorbents reviewed have potential to be good low cost adsorbents. Simply

comparing the maximum equilibrium adsorption capacities of CS/TX-100, BFA, Cattail root and

BSC gives the following results respectively, 302.05, 10, 38.79, 98.03 mg/g, which shows CS/TX-

100 to be the most effective adsorbent. However the adsorption capacities are not the only factor to

choose when evaluating options for low cost adsorbents. Factors such as: Cost of obtaining the

resource, cost and time in preparing the adsorbent for use, complexity of process, space required,

availability of resource, dye removal time, batch or continuous process, concentration of CR in

solution and temperature must also be considered.


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4. References

Ahmad, Rais, and Rajeev Kumar. "Adsorptive Removal of Congo Red Dye from Aqueous Solution

Using Bael Shell Carbon."Applied Surface Science 257, no. 5 (12/15/ 2010): 1628-33.

Chatterjee, Sudipta, Dae S. Lee, Min W. Lee, and Seung H. Woo. "Congo Red Adsorption from

Aqueous Solutions by Using Chitosan Hydrogel Beads Impregnated with Nonionic or

Anionic Surfactant."Bioresource Technology 100, no. 17 (9// 2009): 3862-68.

Chatwal, Gurdeep R., and Madhu Arora. Synthetic Dyes. Mumbai, IND: Global Media, 2009.

Clark.Handbook of Textile and Industrial Dyeing, Volume 2 - Applications of Dyes. 2011.

Gupta, V. K., and Suhas. "Application of Low-Cost Adsorbents for Dye Removal a Review."

Journal of Environmental Management90, no. 8 (6// 2009): 2313-42.

Hu, Zhenhu, Hui Chen, Feng Ji, and Shoujun Yuan. "Removal of Congo Red from Aqueous

Solution by Cattail Root."Journal of Hazardous Materials 173, no. 13 (1/15/ 2010): 292-

97.

Mall, Indra Deo, Vimal Chandra Srivastava, Nitin Kumar Agarwal, and Indra Mani Mishra.

"Removal of Congo Red from Aqueous Solution by Bagasse Fly Ash and Activated Carbon:

Kinetic Study and Equilibrium Isotherm Analyses." Chemosphere 61, no. 4 (10// 2005):492-501.

Sen, Tushar Kanti. 2013 Lecture 4: Adsorption. Power Point lecture notes.

https://lms.curtin.edu.au/bbcswebdav/pid-2558151-dt-content-rid-

8200158_1/courses/313760-FacSciEng-1821132224/Adsorption_4.pdf

Removal of Congo Red Fron Solution by Adsorption

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