Adsorption of Bromo Phenol Red Dye from Aqueous Solution by Iraqi Bentonite Clay

This studies deals with investigated the potential of a Iraqi bentonite clay for the adsorption of bromo phenol red dye from contaminated water. Impulse adsorption experiments were performed. The contact time influence of initial dye concentration, temperature, pH, ionic strength, partical size adsorbent and adsorbent dosage on bromo phenol red adsorption are investigated in a series of batch adsorption experiments. Adsorption equilibrium data were analyzed and described by the Freundlich, Langmuir and temkin isotherms equations. Thermodynamic parameters inclusive the Gibbs free energy (∆G • ), enthalpy (∆H • ), and entropy (∆S • ), were also calculated. These parameters specified that adsorption of bromo phenol red onto bentonite was functional, more spontaneous and endothermic with increase of temperatures from 298.15 to 313.15 K.


Introduction
Many industries use dyes extensively in different operation such as textile, leather tanning, paper, plastic, food processing, cosmetics, printing etc. [1][2][3].Numerous dyes are pestilent to some microorganisms which may cause direct consuming or inhibition of their catalytic power textile industry that use dye and pigments to color their out put.Numerous techniques have proposed by various researchers for the treatment of dye effluents [4].The adsorption use the gotten adsorbent for parquet poisoning as a gastric decontaminant.Common environment instructive recommend low permeability soils, which naturally should contain bentonite as a stamping material in the construction and repair of Garbage dump to ensure the security of ground water from the contaminated.Last few years, bentonite clay was successfully used for the adsorption of metal ions and dyes as of contaminated from water [5,6].The objective of this paper is to use Iraqi bentonite clay in removing bromo phenol red dye from wastewater under different temperatures.

Experimental Materials
The bentonite clay used in the present work was supplied from Doakhla site in the west part of Iraq and chemically characterized in the state company of Geological survey and miningministry of industry using atomic absorption spectra, the chemical composition of this clay is 54.66% SiO

Prepare of Bentonite Clay Powder
The bentonite clay was supplied in powder form; it was washed with excessive amount of deionized water to remove the soluble materials than dried form (3 hours) at 150 ˚C.Coal at room temperature and milled after sieved by using the available sieves of nominal size (75, 150, 250 m).

Calibration Curve
Figure (1) the range of the concentration under study for bromo phenol red was prepared by serial dilution from the standard stock solution (100 mg/L) .Wave length of maximum absorbancy ( max ) for bromo phenol red dye was selected and found (574nm) which agree with preview studies [7].

Method
The time that is sufficient for the bromo phenol red dye adsorption process by bentonite clay to reach equilibrium at certain temperature was found (90 mint) from Figure (2).Adsorption experiments were carried out in batch system by shaking (0.2gm) bentonite samples with (10ml) of Aqueous solution of range concentrations (5-40 mg.L -1 ) of dye at a certain temperature 25 ˚C.Constant speed (100 rpm) for the required equilibrium time, the mixtures were discreted by centrifugation at (5000 rpm) (10min), the dye equilibrium concentration was measured by using double beam spectrophotometer.The adsorbed amounts of bromo phenol red dye were calculated from the concentration in solution before and after adsorption granting to the equation (1).
Where q e is equilibrium dye concentration on adsorbent (mg/g), C e and C o are the equilibrium liquid phase concentration of dye solution (mg/L), and the initial equilibrium respectively, w is the mass of bentonite sample used (mg), and V is the volume of dye solution (L).

Effect of Contact Time
The adsorption of bromo phenol red on bentonite as function of time at fixed initial concentration (40 ppm) was studied for bromo phenol red dye at different times.Figure (1), showed that the amount of adsorption (q e ) growing with time and optimum contact times was (90) min of bromo phenol red dye.The amount of adsorbed dye was found (0.56 mg/g).

Effect of Adsorbent Dosage
Adsorption of bromo phenol red on bentonite was studied at different bentonite mass (0.01, 0.04, 0.07, 0.1, 0.17 and 0.29g).Keeping initial bromo phenol red (40 mg/L), temperature (25 ˚C) and contact time (2 hour).Figure (3) showed that the percentage of dye adsorption at beginning increased with the increase of amount of bentonite, but amount of dye adsorbed per unit mass of adsorbent decreased with increase of a mount of adsorbent.The plateau value represents the amount of the adsorbent at a saturation stage, which depends on the physical properties of the clay [8].The plateau value for bentonite was (0.2g).

Adsorption Isotherms
Freundlich, Langmuir and Temkin models were allawys studied adsorption of dye from aqueous solution onto the bentonite clay.Freundlich be decided the following model [9] A more suitable form from over equation [10] ) Where is the quantity adsorebed in (mg.g -1 ), C e is the concentration of solute at equilibirium in the solution (mg/L), (1/n) refer to the heterogeneity factor, and represents empirical Freundlich constant or capacity factor (L.g -1 ).The slop and intercept of ln k. with reference to Langmuir model [11] Where q max (mg.g -1 ) is the monolayer adsorption capacity of the adsorbent, (k L ) (L.mg -1 ) is the Langmuir constant, C e (mg.L -1 ) is the equilibrium concentration of dye in solution and (mg.g -1 ) is the amount adsorbed per unit mass of adsorbent corresponding to complete coverage of sites.A linear plot of C e / q e Vs C e in Figure (4-b).The Temkin isotherm consist of agent that taking into the account of adsorbent adsorbate interaction by ignoring the frequently low and high value of concentrations, the model suppose that heat of adsorption of all molecules in the layer would reduce linearly that logarithmic with coverage [12,13].As implied in the equation its derivation is characterized by auniform distributon of binding energies.The Temkin isotherm can be qualified by equation.
Where T is the absolute temperature, R is the universal gas constant (8.314J.k -1 mol -1 ), k⊤ is equilibrium binding constant (L.g -1 ) corresponding to the maximum binding energy, and b⊤ is related to the adsorption heat.The Temkin isotherm plot between In C e and q e is shown fiqure (4-c), enables the determination of the slop and intercept these results in Table (1).Table (1) shows the account of the constant of the Freundlich isotherm at different temperatures, the values of the constant (n) in range (0-1) for all temperature suggest that the adsorption of bromo phenol red on bentonite clay is easily, The values of (k F ) and (n) increase with increase temperature and these less adsorption in high temperature , the values of (R 2 > 0.84) was not higher for all the temperarures evaluated and this indicated the Freundlich model less fitted to experimental date for not all the temperatures.Also Table (1) shows the value of the constant of the Temkin isotherm at different trumpeters.Adsorption of bromo phenol red on bentonite clay which have heat of adsorption (b⊤) within (3-12) (kJ.mol -1 ) that indicate that adsorption of bromo phenol red on bentonite clay favorable for the physical adsorption at all different the values of (R 2  0.89) for Temkin model was more than R 2 for Freundlich model for all tempearures which indicated that model fitted better to experiment data for all temperatures.As well Table (1) shows the account of the constant of the Langmuir model at various temperatures for adsorption of bromo phenol red dye on bentonite clay is not useful because the values of (R 2 = 0.20-0.46)and this model fitted to experimental data for some the temperatures [9,11].

Effect of Practical Size
The effect of particle size (surface area) of the adsorbent materials on the extent of adsorption was studied by using three different size of the studied adsorbent materials (75 m, 150 m and 250 m).These experiments were performed by using a fixed concentration (40 ppm) of bromo phenol red and the same weight of the adsorbent (0.2g) at 25 ˚C. Figure (5) showed that there is an increase in adsorption with decreasing their particles size.It is known that the break of the large particles into smaller would lead to increase in the surface area [14].

Effect of Ionic Strength
Figure (6) show The effect of (0.01-0.02M) of NaCl solution containing concentration of dye (40) mg.L -1 was added to flasks each containing (0.2g) of adsorbent, ionic strength (I) (0.078, 0.088, 0.098, 0.108, and 0.128M) at 25 ˚C the increase in ionic strength between (0.01-0.05M) has decrease the amount of adsorption between (0.487-0.409mg.g - ) this may be due to solubility of NaCl more than solubility of dye which lead to increase competition between sodium ions and dye molecules for the active sities of bentonite and these lead to decrease adsorption capacity of dye on bentoite.It found that relationship between the ionic strength (I) and the adsorption quantity (q e ) at a fixed equilibrium concentration is linear relationship as illustrate in Figure (7) , It proposed the following empirical equation between (I), (q e ).q e =q e 0 -AI -----------------------( 6) Where q e 0 the adsorption at I=zero and A is the Empirical constant for the system according to the slope and straight line intercept for linear relation between (I), (q e ) , Figure (7) and value of R 2 indicate that the equation could be applied for the adsorption of bromo phenol red on bentonite clay surface [15].

Effect of pH
Adsorption experiments were carried out as mentioned previously as function of pH by using a fixed concentration (40 mg/L) of dye in different pH media which were adjusted by using (0.1M).NaOH and (0.1) M HCl and (0.2g) of bentonite clay at temperature 25 ˚C, the pH of the system for adsorption was measured by using pH-meter .The premier pH rates of the dye solution effect the flatness of the adsorbent and thus the adsorption of the adsorbed of the charged dye groups on it , in universal the acidic pH system presented good adsorption behavior for the dye solution.The adsorption of dye excess with lowering of the pH from (1 to 11).As the pH of the system diminution, the protonated flatness groups simplify the adsorption of the negatively charged dye.The number of positively charged sities growing resulting binding sities for anionic dye molecules [16], Figure (8).

Thermodynamics of Adsorption
The Effect of temperature on the adsorption of bromo phenol red on bentonite was studied at (298.15, 303.15, 308.15 and 313.15K) the results were displayed in Figure (9).The result revealed that the amount of adsorption increase from (0.4473-1.2946 mg.g -1 )with temperatures increase from 298.15K to 313.15K.This increase in amount adsorption with temperatures indicating that the process is endothermic.This mean the high temperature are favorite for adsorption of bromo phenol red on bentonite clay.Endothermic dye adsorption may be also interpreted as consequence of possible adsorption process.This disposal imputed to adsorption operation.Which means that adsorption process may happen escorted with adsorption process.The study of the temperature effect on adsorption of bromo phenol on bentonite will help involution.The basic thermodynamic parameters such as Gibbs free energy (J/mol.K) ,enthalpy H • (J/mol) and entropy (S • ) (J/mol.K) of the adsorption process.The change in free energy (G • ) could be determined from the equation [17,18]. G • = -nRTlnk eq ------------------------(7) Where T is absolute temperatures, R is universal gas constant (8.314) (J.mol -1 K -1 ), and k e is thermodynamic equilibrium constant for the adsorption process at each temperatures was from the equation.