Removal of Malachite Green Dye by Adsorption Method using Activated Carbon (AC)

Removal of Malachite Green Dye by Adsorption Method using Activated Carbon (AC)

Ch. J. Pavany

Civil Engineering Svecw, Bhimavaram, India

S. Harika

Civil Engineering Svecw, Bhimavaram, India

Samuel D

Civil Engineering

Abstract:- The objective of this work is to study the adsorption of Malachite Green Dye using Activated Carbon (AC). This is a cheap and eco-friendly adsorbent. Liquid phase batch operations were carried out to observe the effect of various experimental parameters such as Contact Time, Adsorbate Dose, Initial Concentration along with Langmuir and Frendlich Isotherm models. Here, the optimum conditions for the Contact Time and the Dosage were evaluated using above adsorbent. This work is helpful to design a low cost adsorption columns for treating effluent water in industries or other adsorption processes.

1. INTRODUCTION

   A dye is generally a substance that bears an affinity to the substrate to which it is being applied which is often applied in aqueous solution. It appears to be coloured because they absorb some wavelengths of light in particular than other. Various industries like chemical, refineries, textile, plastic and food processing plants discharge wastewaters. These wastewaters include dyes as residues which cause many hazards. Such residual dyes are non- biodegradable due to their complex molecular structures making them more stable and hard to biodegrade. They cause water pollution and also pose a serious threat to the environment. These coloured stuffs along with being aesthetically displeasing also inhibit sunlight penetration into water bodies and thus affect aquatic ecosystem. Many of them are also toxic in nature and can cause direct destruction or can affect catalytic capabilities of various microorganisms.

   Textile industries are the main sources of discharge of dyes. They are used to colour the products. Today there are over 1,00,000 dyes for commercial use and around 700 tons of dyestuffs are produced annually. The types of dyes are mainly basic, acidic, direct, reactive, mordant, azonic, disperse, sulphur and vat dyes. Most of the dyes are toxic and have carcinogenic properties hence they make water bodies inhibitory to aquatic systems. They dont fade by water or sunlight owing to their complexity in structures. They cant be adequately treated in conventional treatment plants for waste waters.

   Coloured water is not aesthetically acceptable to the general public though it may not be toxic. In fact, given a choice, consumers tend to choose clear, non coloured water of otherwise poor quality over treated potable water

   with an objectionable colour. Highly coloured water is unsuitable for laundering, dyeing, paper making, beverage, textile, plastic, dairy and other food-processing industries. Recent reports suggest that colour-causing substances are microtoxic to aquaic biota. Colour acquired by a river through the discharge of coloured industrial effluents, inhibits growth of the desirable aquatic biota necessary for self- purification-oxygenation) by reducing penetration of sunlight and consequent reduction in photosynthetic activity and primary production.

   There are various ways to remove dyes from wastewater discharges like adsorption, coagulation, electrochemical process, membrane separation process, chemical oxidation, reverse osmosis, aerobic and anaerobic microbial degradation. Many of these processes are not so popular due to their economic disadvantages and inefficiency. Coagulations, chemical and electrochemical oxidations have low feasibility on large scale plants. There by Adsorption process is only preferred over these processes and is widely used due to its low cost and high performance. Some of the common adsorbents are activated carbon, alumina silica, saw dust, zeolite, char, metal hydroxides etc., Economic advantages, performance efficiencies and the environment are the main concerns when selecting any adsorbent. Due to this reason most of the researchers generally go for low-cost adsorbents.

2. MATERIALS AND METHODOLOGY

Activated Carbon (AC):

Activated carbon, also called activated charcoal, activated coal, or carboactivatus, is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Activated is sometimes substituted with active. Due to its high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m2, as determined by gas adsorption. An activation level sufficient for useful application may be attained solely from high surface area; however, further chemical treatment often enhances adsorption properties. Activated carbon is usually derived from charcoal and increasingly, high-porosity biochar.

Malachite Green dye

Malachite green was first prepared by Fischer in 1877 by condensing benzaldehyde and dimethylaniline in the molecular ratio 1:2 and in the presence of a dehydrating agent.

Malachite green dye is basically a cationic dye and is an

organic compound that is used as a dyestuff and has emerged as a controversial agent in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper. Although called malachite green, the compound is not related to the mineralmalachite the name just comes from the similarity of colour.

Fig A. Activated Carbon Fig B. Malachite Green Dye Adsorption

Adsorption is a surface phenomenon which results out of binding forces between atoms, molecules and ions of adsorbate and the surface of adsorbent. It is the process of formation of a layer of solid or gas on the substrate. It involves separation of a substance from fluid phase by accumulation on the substrate of solid phase.

Factors affecting adsorption

1. Surface area of the adsorbent

2. Contact time

3. Particle size of the adsorbent

4. Solubility of the adsorbate in waste water

5. Degree of ionization of the adsorbate molecule

6. Number of carbon atoms

7. Size of molecule with respect to the size of the pores

8. Temperature

9. pH

   out of which the following were studied along with adsorption isotherms

   1. Contact time

   2. Dosage

   3. Initial Concentration

   Adsorption Isotherms

   Adsorption isotherms help in describing how molecules of adsorbate interact with adsorbent surface. The adsorption processes are generally described by the Langmuir and the Freundlich isotherm models.

   The Langmuir equation is based on the fact that there is no interaction between the adsorbate molecules and that the adsorption process is localized in a monolayer. It then assumes that once a dye molecule occupies a given site, no more adsorption can take place at that site. The Langmuir equation is commonly expressed as in the linear form

   1 1 1

   qe b*q0 *Ce q0

   where Ce is the equilibrium concentration of dye solution (mg L1), qe is the equilibrium

   capacity of dye on the adsorbent (mg g1), qo is the monolayer adsorption capacity of the adsorbent (mg g1), and b is the Langmuir adsorption constant (L mg1) and is related to the free energy of adsorption.

   The Freundlich adsorption model assumes that adsorption takes place on heterogeneous surfaces. Its linear form can be written as:

   ln qe ln K f 1

   n * ln Ce

   where Kf and n (dimensionless constants ) are the Freundlich adsorption isotherm constants, which indicates the capacity and intensity of the adsorption, respectivey.

   Isotherms study

   Adsorption isotherms are mathematical models that describe the distribution of the adsorbate species among liquid and adsorbent, based on a set of assumptions that are mainly related to the heterogeneity/homogeneity of adsorbents, the type of coverage and possibility of interaction between the adsorbate species. Adsorption is usually described by adsorption isotherms, such as Langmuir, Freundlich isotherms. These isotherms relate metal uptake per unit mass of adsorbent qe, to the equilibrium adsorbate concentration in the bulk fluid phase Ce.

   Experimental methodology:

   In this experimental methodology, the experimental procedures are detailed in four phases. In Phase I – stock solution, in Phase II determination of optimum time, in Phase III

   determination of optimum dosage, in Phase IV initial dye concentration are described below.

   Phase I :Stock solution: It is prepared by diluting 1g of Malachite green dye in 1 litre of distilled water. And afterwards, it was diluted in distilled water as per our requirement.The entire experimental procedure was carried out with the concentration of 10ppm or 10mg/l.

   Phase II: Determination of optimum time

   100 ml of dye solution with dye concentration (10mg/L) was prepared in a 250ml conical flask with adsorbent concentration (g/L) and placed on the shaker. The samples were withdrawn from the shaker (orbital shaker) at predetermined time intervals. Keeping the concentration (10mg/l) constant and varying the time from 0 150 minutes, it was observed until it reached equilibrium to find the optimum time. The dye concentrations were measured after 1,3,5,10,15,30,60,90,120 and 150 minutes until equilibrium reached. The dye solutions were taken by the help of micropipettes and % absorbances were estimated by using Spectrophotometer (Lovibond PC) at the wavelength corresponding to maximum absorbance, (max=618).

   Phase III: Determination of optimum dosage

   100 ml of dye solution with dye concentration (10mg/L) was prepared in a 250ml conical flask with adsorbent concentration (g/L) and placed on the shaker (orbital Shaker). The samples were withdrawn from the shaker at predetermined time intervals (RPM=120, temp=(271) oC) . Keeping the time constant (optimum time) and varying the dose from 2-

   4.5 mg/100ml, it was observed until it reached equilibrium to find the optimum dosage and % absorbances were measured by using Spectrophotometer at the wavelength corresponding to maximum absorbance, (max=618). The dye solutions were taken by the help of micropipettes. The dye concentrations were measured after 2.0, 2.5, 3.0, 3.5, 4, 4.5 and 5mg/100ml until equilibrium was reached.

   Phase IV: Initial dye concentration

   Eleven solutions of dye in distilled water were prepared in conical flasks with varying concentrations of dye – 2, 4, 6, 8, 10, 15, 20, 25, 30, 40 and 50mg/l. Accurately weighed adsorbent was put into the solutions in the conical flasks at optimum dosage and were placed on the shaker (RPM=120, temp=(271) oC) until optimum time was reached. Their % absorbances were determined using spectrophotometer (max=618) and the removal efficiency was calculated. The dye solutions were taken by the help of micropipettes. The dye concentrations were measured at every 2,4,6,8,10,15,20,25,30,40 and 50mg/l respectively.

   Calibration Curve:

   Dye solutions were prepared with concentrations required and their % absorbances were found out by UV spectrophotometer (max=618) with these values a standard calibration curve was plotted. The equation of the curve was used to calculate the concentrations for various % absorbances of all the adsorbents.Calibration Curve is shown below.

   Table 1.0: Dye Concentrations and Absorbance Values

   Conc. of dye(mg/L)	%Absorbance
   0	0.000
   2	0.320
   4	0.632
   6	0.946
   8	1.261
   10	1.565
   15	2.351
   20	3.131
   25	3.912
   30	4.724
   40	6.263
   50	7.826

   Calibration Curve

   10

   y= 0.156x + 0.004 R² = 1

   Calibration Curve

   10

   y= 0.156x + 0.004 R² = 1

   0

   10

   20

   30

   40

   50

   60

   0

   10

   20

   30

   40

   50

   60

   Dye Concentration in mg/l

   Dye Concentration in mg/l

   5

   0

   5

   0

   % Absorbance

   % Absorbance

   Fig 1.0 : Standard calibration curve

   Equation from the above graph is y= 0.156x+0.004 which is of the form y=mx+c Now from this equation, concentrations can be calculated.

   Where x= concentration, y=% absorbance

   Moreover, according to Beer Lamberts law, absorbance is the product of slope and concentration. The Removal Efficiency (RE) was determined as follows Removal efficiency (%) = (C0-Ce) / C0*100

   The amount of adsorption at equilibrium qe (mg/g) was calculated by the following equation qe=(Co-Ce)*V/m where, Co is the initial dye concentration (mg/L),

   Ce is the equilibrium (or) final dye concentration (mg/L),

   V is the volume of the solution (L) and m is the amount of adsorbent used (g).

   Effect of Time

   The effect of contact time was studied at1,3,5,10,30,60,90,120 and 150minutes. Fig

   2.0 shows the relationship between contact time and colour removal efficiency. Observation reveals that the removal of colour improved by increasing the contact time. The percentage colour removal approached equilibrium 90 minutes. Further increase in contact time does not show significant change in colour. This might be due to fact that, large number of vacant surface sites is available for the adsorption during the initial stage and with the passage of time. After some times, repulsive forces between solute molecules on solid phase and liquid phase create difficultness for the solute molecules to occupy remaining vacant surface sites.

   Table 2.0 : Data for the effect of contact time on colour removal by AC

   AC
   Time(min)	Ce(mg/l)	% Removal
   1	8.324	16.76
   3	7.564	24.36
   5	4.231	57.69
   10	3.048	69.52
   30	2.336	76.64
   60	1.506	84.94
   90	1.077	89.23
   120	1.063	89.37
   150	1.071	89.29

   TIME 90

   TIME 90

   100

   100

   90

   90

   80

   80

   70

   70

   60

   60

   50

   50

   40

   40

   30

   30

   20

   20

   10

   10

   0

   1

   0

   1

   3

   3

   5

   5

   10 30 60 90 120 150

   10 30 60 90 120 150

   Time (t) inmin

   Time (t) inmin

   % Removal efficiency

   % Removal efficiency

   Fig 2.0: Removal Efficiency Vs Contact Time of AC

   Effect of Dose

   The effect of the adsorbent dose on colour removal is shown in Fig 3.0. Adsorbent dose was varied between 2 and 4.5 mg/100mL and it was indicated that the removal efficiency of colour improved by increasing the adsorbent dose up to 3mg/100mL where further dose increase yields negligile adsorption. Greater availability of exchangeable sites at higher concentration of adsorbent is the reason for the increase in colour removal with the increase in adsorbent dose. Thats why beyond 3mg/100mL, the adsorption found to be constant. At fixed optimum time, the optimum dosage found was 3 mg/100ml. The percentage removal of colour at various mix dosages for an initial dye concentration 10mg/L by Activated Carbon is given by following table followed by a graph.

   Table 3.0 : Data for the effect of adsorbent dose on colour removal by AC

   AC

   Dose (mg/100ml)

   Ce (mg/l) % Removal

   2 1.851 81.49

   2.5 1.589 84.11

   3 1.295 87.05

   3.5 1.282 87.18

   4 1.268 87.32

   85

   80

   75

   85

   80

   75

   % Removal Efficiency

   % Removal Efficiency

   4.5 1.264 87.36

   90

   Dose 3

   90

   Dose 3

   2

   Am2o.u5nt of adsor3bent in mg/31.050ml

   4

   2

   Am2o.u5nt of adsor3bent in mg/31.050ml

   4

   Fig 3.0: Removal Efficiency Vs Dosage of AC Effect of Initial Concentration

   The effect of the Initial Concentration of the dye on colour removal is shown in Fig

   4.0 . The initial concentration was varied between 2 and 50 mg/l and it was indicated that the removal efficiency decreases by increasing the initial dye concentration.

   Table 4.0: Data for the effect of initial concentration on colour removal by AC

   AC
   Initial Conc(mg/l)	Final Conc.(mg/l)	% Removal
   2	0.681	93.19
   4	0.724	92.76
   6	0.785	92.15
   8	0.828	91.72
   10	1.002	89.98
   15	1.525	84.75
   20	1.948	80.52
   25	2.356	76.44
   30	2.803	71.97
   40	3.397	66.03
   50	3.876	61.24

   AC

   AC

   100

   50

   0

   100

   50

   0

   2

   2

   4

   4

   6

   6

   8 10 15 20 25 30 40 50

   8 10 15 20 25 30 40 50

   Initial Concentration

   Initial Concentration

   % Removal Efficiency

   % Removal Efficiency

   Isotherm Models

   Fig 4.0: Effect of initial dye concentration on colour removal by AC

   Langmuir & Freundlich Isotherms of AC are shown in the graphs along with the values in the table below.

   Table 5.0: Data for Langmuir & Freundlich Isotherms of AC

   Dose	Ce	qe	1/ce	1/qe	log ce	log qe
   2	1.851	407.45	0.540249	0.002454	0.267406	2.610074
   2.5	1.589	336.44	0.629327	0.002972	0.201124	2.526908
   3	1.295	290.1667	0.772201	0.003446	0.11227	2.462648
   3.5	1.282	249.0857	0.780031	0.004015	0.107888	2.396349
   4	1.268	218.3	0.788644	0.004581	0.103119	2.339054
   4.5	1.264	194.1333	0.791139	0.005151	0.101747	2.2881

   0.002

   0

   0.002

   0

   1/qe

   1/qe

   A curve 1/qevs 1/Ce is plotted, the intercept gives the q0 value and slope gives the KL value

   0.006

   0.004

   Langmuir

   y=0.006x-0.001 R² = 0.812

   0.006

   0.004

   Langmuir

   y=0.006x-0.001 R² = 0.812

   AC 1/Ce

   0.6

   0.8

   1

   AC 1/Ce

   0.6

   0.8

   1

   0

   0

   0.2

   0.2

   0.4

   0.4

   Fig 5.0: Langmuir isotherm curve of AC

   The observed values of R2, q0and KL of AC from the following plot that are 0.812,

   log qe

   log qe

   166.67 and 0.0012 respectively. A curve ln(qe) vs ln(Ce) is plotted , the slope gives n value and intercept gives Kf value.

   Freundlich

   y= 1.352x+ 2.252 R² = 0.863

   2.65

   2.6

   2.55

   2.5

   2.45

   2.4

   2.35

   2.3

   Freundlich

   y= 1.352x+ 2.252 R² = 0.863

   2.65

   2.6

   2.55

   2.5

   2.45

   2.4

   2.35

   2.3

   0 0.05 0.1

   0.15

   LogCe

   0.2

   0.25

   0.3

   AC

   0 0.05 0.1

   0.15

   LogCe

   0.2

   0.25

   0.3

   AC

   Fig 6.0: Freundlich isotherm curve of AC

   The observed values of R2, n and KL of AC from the following plot that are 0.863, 0.739 and 0.2529 respectively.

   3. RESULTS AND CONCLUSIONS

   Experimental studies were conducted to remove M.G dye using Activated Carbon (AC) as an adsorbent and it can be extended for the different adsorbents for future scope.

   1. The maximum removal efficiency of the adsorbent AC was found to be 89% when treated for contact time.

   2. The maximum removal efficiency of the adsorbent AC was found to be 87% when treated for adsorbent dosage.

   3. The maximum removal efficiency of the adsorbent AC was found to be 89% when treated for initial dye concentration.

   4. The minimum and maximum removal efficiencies of the adsorbent AC were found to be 61% and 93% respectively.

   5. The removal efficiency increased with time and adsorbent dosage but it decreased with the increase in initial dye concentration.

   6. Removal efficiency was found to be increasing till it reached the optimum time and the optimum dosage. Since then, it was found to be negligible.

   7. We observe that both Isotherm curves fit well with the adsorption system as their R2 values are quite near and both gives reasonable values of rate constants. However, Freundlich isotherm model fits well as its correlation coefficients R2values are higher than the Langmuir.

4. REFERENCES

1. ChetnaParasharet al. (2008), submitted a thesis on adsorption of Malachite Green dye using char.

2. Goswami, A.K. Kulkarni, S.J. etal., Fly Ash as Low Cost Adsorbent to Remove Dyes, International Journal of Scientific Research and Management(IJSRM), Vol. 2, 2014.

3. GrabowskaEwaLorenc, GryglewiczGra_zyna. Adsorption characteristics of Congo red on coal-based mesoporous activated carbon, Dyes and Pigments 74,2007.