A Comparative Study of the Adsorption of Crystal Violet Dye from Aqueous Solution on Rice Husk and Charcoal

In this work, the adsorption of crystal violet dye from aqueous solution on charcoal and rice husk has been investigated, where the impact of variable factors (contact time; the dosage of adsorbent, pH, temperature, and ionic strength) have been studied. It has been found that charcoal and rice husk have an appropriate adsorption limit with regards to the expulsion of crystal violet dye from fluid arrangements. The harmony adsorption is for all intents and purposes accomplished in 45 min for charcoal and 60 min for rice husk. The amount of crystal violet dye adsorbed (0.4 g of charcoal and 0.5 g of rice husk) increased with an increasing pH and the value of 11 is the best. The effect of temperature on the adsorption process was studied at the range (298-323) K. The test comes about were broken down by utilizing Freundlich and Tempkin isotherm models, where the Freundlich and Tempkin factors were determined, and it has been found that the adsorption isotherm obey the Freundlich isotherm. The effect of ionic strength on the adsorption process was studied also via sodium chloride electrolyte solution; the results have been revaled that the sodium ion has a positive impact on the adsorption process. The thermodynamic parameters are shown estimated as ∆H values were 2.8012 kJ mol -1 and 5.8252 kJ mol -1 for charcoal and rice husk, respectively; this behavior referred to endothermic adsorption.

Nonetheless, the utilization of untreated plant squanders adsorbent can likewise bring a few issues, for example, bring down adsorption limit, higher synthetic oxygen request and natural substance request and also add up to natural carbon due to the discharged of the solvent natural compound contained in the plant material (9,10). A few plants were utilized as adsorbent surfaces to expel a few colors, for example, a novel horticultural (11), malvaparviflora and different plants (12). The crystal violet (CV) dye (Fig.1) is a water-soluble cationic dye (13) and is widely used in textile dyeing. The dye has a brightness and high color intensity, even at low concentration. The CV is easily absorbed by the creatures in the water and affected their lives; therefore the waste water containing crystal violet dye needs to be treated before it is discharged into water bodies (14). The present work involves using plant rice husk and charcoal as a reasonable sorbent for the removal of crystal violet from aqueous solutions and check the freundlich and Temkin isotherms. The thermodynamic parameters and pH values have been calculated.

Chemicals and Apparatus
Crystal violet dye was supplied from the HIMEDIA company, rice husk was provided from Al-Najaf Analysis factory, charcoal was provided from (BDH) with purity 99.7%. Hydrochloric acid was provided from BDH with purity 37% and sodium hydroxide was supplied from Riedel-De Haen AG Seelze-Hannover with purity 99%.Visible spectrophotometer model 721 -China was used to record absorbance of crystal violet before and after adsorption experiments. Thermostated Shaker water bath model JEIOTECH (BS-11)-Germany was used to shake the aqueous solutions of dye with adsorbents, while Remi Centrifuge model R&C.Bombay-Japan was utilized to separate the adsorbents from the aqueous solution of dye and pH-mater model Hanna-HI-8417-England was used to adjust the pH of the solutions.

Absorbed Substance
The crystal violet dye stock arrangement was set up by dissolving precisely weighted color in refined water to the centralization of 8 ppm, was utilized without assist cleansing at λ max (585 nm), (Fig.2) shows the absorption spectrum of dye. The arrangements were gotten by weakening the color stock arrangement in precise extents to various beginning focuses from (0.4-10 ppm). Figure 3 shows the calibration curve, which was used to convert the absorbance value of dye to concentration According to Beer-Lambert law.

Rice Husk
The dry rice husks were washed with excessive amounts of distilled water, several washings were performed to remove dust and soluble materials. Washed surfaces were then dried under sunlight and in an oven at 105C˚ for a period of 12 hours and kept in airtight containers. The surfaces were then ground and sieved by using a 75 µ sieve.

Batch Adsorption Experiment
Group tests were done to decide the impacts of pH, contact time, beginning color focus and adsorbent dosage by differing the factors under examination and saving different factors steady. The feed arrangement was set up by dissolving a precisely measured amount 0.1 g of strong color in 1liter of water. The exploratory arrangement of wanted focus was acquired by progressive weakening of stock arrangement. The pH of every one of these arrangements was kept up by including 0.1N hydrochloric acid or 0.1N sodium hydroxide. where C 0 and C e are the primary and the equanimity concentrations (mg/l) of dye, respectively. Q e is the quantity of dye adsorbed on the adsorbent at the time of equanimity (mg/g), V is volume (l) of solution and W is the mass of adsorbent (g).

Results and Discussion: Adsorbent Dosage
The adsorbent dosage is an imperative parameter in the adsorption process; the experiments were done by using different amounts of the charcoal and rice husk for a given initial concentration of dye solution 8ppm at 25 • C. Figure  4 shows the effect of dosage of charcoal and rice husk on the adsorption capacity of crystal violet dye. It is clear that the Q e of the color increments with the expansion in adsorbent measurements, however an estimation of 0.5 and 0.4 g for charcoal and rice husk respectively. The rate evacuation comes to right around the greatest esteem. This is most likely because of the more prominent accessibility of the replaceable destinations or the expanded surface territory where the adsorption happens (16).

Equanimity Time
The effect of contact time on the amount of crystal violet adsorbed per unit of adsorbent was investigated under 25°C at dye concentration of 8ppm and used the optimum values of adsorbents (0.5 and 0.4 g for charcoal and rice husk respectively). Figure 5 shows the results of equilibrium time for crystal violet on charcoal and rice husk. It can be observed that the adsorption process exhibits immediate rapid adsorption and reaches equilibrium within a short period of 45 min for charcoal and 60 min for rice husk (16). The Effect of pH Figure 6 demonstrates the take-up of crystal violet dye expanded with diminishing starting pH and was the best at pH 11. At low pH esteems the practical gatherings of charcoal and rice husk would be protonated and result in a more grounded fascination for adversely charged particles in the adsorption medium. The pH basically influences the level of ionization of the crystal violet and the surface properties of charcoal and rice husk. As appeared in Fig. 6 that, the adsorption of cationic crystal violet dye was increased with expanded the pH. It can be noticed that the best adsorption was at pH 11 as the surfaces of the adsorbents become negatively charge and resultantly high interaction between the dye and the surface of the adsorbents. The low adsorption of crystal violet adsorption under acidic may be correlated with lyophobic behavior between adsorbate and adsorbents and resultantly, the forces between adsorbate and adsorbent may change (17).

Adsorption Isotherms
Adsorption properties and balance parameters, normally known as adsorption isotherms, which show how the adsorbate interfaces with adsorbents, and complete comprehension of the idea of cooperation. Tow famous isotherm, the Freundlich and Temkin were examined. The Freundlich isotherm was utilized for the adsorption of crystal violet on the adsorbents. The Freundlich isotherm was calculated by the following equation: where Q e is the measure of crystal violet dye adsorbed (mg/g), C e is the balance grouping of color in the arrangement (mg/l), K f and 1/n are constants fusing the elements influencing the adsorption limit and force of adsorption, separately.  where K T and B T is the equilibrium binding constant (l /g) As appeared from Figures 11,12,13,and 14 with the calculated results in Table ( 1) and (2) that, the estimations of R 2 coefficient were near to be 1, for both isotherms, which means that there is a good corresponding in the relationship between Q e and ln C e at different temperatures which showing the helpful estimations of its constants. The adsorption isotherm for is clarified better by Freundlich isotherm demonstrates.

Thermodynamic Parameters
The thermodynamics factors identified with the adsorption of color. For example, enthalpy change, entropy change and Gibbs free energy change ∆Gº. ∆Hº has been computed for all adsorption forms, as indicated by Van't Hoff equation 6 by means of plotting of the adsorption equilibrium constant (K eq ) as (ln Q e /C e ) against the temperature as (1/T) (22). The outcomes are recorded in Table 3 and Fig. 15 where K eq is adsorption equilibrium constant and R is the gas constant.   The adsorption of color increments quickly with an expansion in temperature. The expansion in adsorption limit of charcoal and rice husk was attributed to the development of pore size and initiation of the sorbent surface with temperature. Additionally ascend in temperature builds the versatility of the vast color particles and decreases the swelling impact in this manner empowering the substantial color atom to enter encourage (23). The positive estimation of ΔH shows that the adsorption of crystal violet dye onto charcoal and rice husk is an endothermic response. It can be noticed from ΔH values that the force driving the adsorption process is physics-sorption process.All estimations of ∆G values released that the adsorption procedure went with the procedure of assimilation, where the adsorbed particles spread inside the pores of the charcoal and rice husk and expands speed of organization with expanding temperature this conduct is inferable from extra assimilation. The negative values of ΔS indicate that the regularity of the dye particles on the surface more than they are in the solution and it was higher in charcoal than in rice husk.

Conclusions:
The adsorption of crystal violet by charcoal and rice husk has been studied. The adsorption was considered as an element of adsorbent measurements, contact time, pH, temperature and ionic quality, it has been found that the optimum values of the adsorbents were 0.5 and 0.4 g for charcoal and rice husk respectively, while the solutions get rapid adsorption and reaches equilibrium within of 45 min for charcoal and 60 min for rice husk, furthermore the best media for the adsorption process was at pH 11, in addition, the ionic strength was examined and it has been shown a positive effect on the adsorption process. The balance information fit with Freundlich and Tekmin equations of adsorption and the straight relapse factors R 2 was utilized to clarify the best fitting isotherm demonstrate. Diverse thermodynamic factors, similar to ΔG o vitality, ΔH o and ΔS o of the on-going adsorption operation have additionally been assessed. The thermodynamic examinations of the color adsorption on charcoal and rice husk store demonstrated that the framework was endothermic in nature.