ADSORPTION POTENTIAL FOR A MIXTURE OF CHEMICALLY AND THERMALLY TREATED CLAYS TO REMOVE ORANGE G DYE FROM WASTEWATER

This study examined the adsorption behavior of anionic dye (orange G) from aqueous solution onto the raw and activated a mixture of illite, kaolinite and chlorite clays from area of Zorbatiya (east of Iraq).The chemical treatment involved alkali and acid activation. The alkali activation obtained by treated the raw clay (RC) with 5M NaOH (ACSO) and the acid activation founded by treated it with 0.25M HCl (ACH) and 0.25M (ACS). The thermal treatment carried out by calcination the produce activated clay at 750 o C for acid activation and 105 o C for alkali activation. Batch adsorption method was used to study the adsorption of orange G dye onto raw and activated clays. The impact of different factors related to the adsorption process was studied such as: agitation time, clay dosage, solution pH, starting OG dye concentration, temperature and ionic strength. The adsorption process was described by using Langmuir, Freundlich, Temkin and Dubinin-Raduchkevish isotherm models. Thermodynamic in Hoff


Clays
The raw clay used in the study was collected from Zorbatiya area (east of Iraq). The clay has the following composition: 19 19.6%. The clay mineral analysis of this clay showed that this clay is a mixture of illite, kaolinite and chlorite (Al-Dabbagh 2018).
The acidification of the clays was performed by using 37% hydrochloric acid and 98% sulfuric acid supplied by Fluka, also alkali activated of clay was carried out using 99% sodium hydroxide supplied by BDH.

Raw clay
30 g of the raw clay was mixed with 100 mL distilled water, the mixture was shaking for one hour at room temperature, then filtered by using Buckner funnel and oven dried at 120 o C for 7 hr, then allowed to cool and keep in a dry place. The obtained clay labeled as RC.

Activation with NaOH, HCl and
The activated clay with NaOHa volume of 70 mL from 5 M NaOH was added to five grams pretreated raw clay under 800 rpm mechanical stirring for 4 hr to yield a homogenous suspension, by using centrifugation at 5000 rpm, the product was separated, washed with distilled water several times and dried at 105 o C for 4 hr. The result sample marked as ACSO.
To prepare acid activated clay with HCl 20 g of the raw clay was mixed with 67 mL 0.25 M HCl by using a thermo stated shaker type (Gallenkamp, England) for 2 hr. The resulting clay was filtered by using a Buckner funnel, the residue slurry washed with distilled water until it becomes neutral. The prepared sample was dried at 120 o C for 2 hr, the activated clay was calcinate in muffle furnace type (BS32C, Korea) at 750 o C for 4 hr. The obtained clay labeled as ACH.
The acid activated clay with carried out by mixing 20 g of raw clay with 200 mL 0.25 M in a shaking water bath for 6 hr at 70 o C, then the sample was allowed to stand for fourteen hours in solution. Finally, the precipitate was filtered and washed for many times with distilled water till reaching a natural pH. The sample was dried at 120 o C for 2 hr, then calcinate at 750 o C for 4 hr. The obtained clay marked as ACS.

Batch adsorption studies
Batch experiments were carried out to study the adsorption of OG on RC, alkali and acid activated clays ACSO, ACH, ACS. A known quantity of the clay was added to 20 mL dye solution in 100 mL Erlenmeyer flask. The mixture was agitated by using a shaker with water bath type (JTYS-1000, China) at pre-determined speed, time and temperature. Centrifugation with 1000 rpm was used for 5 min to separate the supernatant, the residual OG dye concentration was determined by UV-Vis -Spectrophotometer model( Shimadzu UV 1800, Japan) at = 476 nm. The removal percentage R% and the amount of the OG dye adsorbed at equilibrium in (mg/g) were calculated by using equations: Where , are the starting concentration and the concentration at equilibrium (mg/L), V is the volume of the working solution (L) and M is the mass of the clay (g).

Optimum conditions Influence of adsorption time
The influence of adsorption time on the removal efficiency carried out at various adsorption time (5-60) minute, with 100mg/L starting concentration at 288 K, PH=7, clay dosage = 0.2 g/ 50mL and agitation speed 150 rpm, as shown in (Figure 1). It is found that the adsorption reaches equilibrium after 30 min for all clay samples. According to this statistic, adsorption was found to be rapid within the first minutes of adsorbent/ adsorbate interaction. This can be explained by the fact that the amount of active sites accessible on the surface of the adsorbent material at the beginning of the adsorption is much higher than that of the sites remaining after a certain period of time.Furthermore, the ACS sample has interesting basal spacing that favors the phenomenon of adsorption

Influence of clay dosage
The impact of clay dosage on removal of OG dye was tested using different quantities of clay (0.025, 0.05 , 0.1, 0.15, 0.2, 0.3, and 0.5 g) in 20 mL of 100 mg/L OG dye at 288 K, pH=7 and shaking speed (150 rpm). As seen in (Figure 2), the removal efficiency increased with increasing the clay dosage for all samples till reaches a constant values at clay dosage equal to 0.2 g, then the removal kept constant. Increasing the R% may be resulted from the abundance of more available adsorption sites. Unless too much adsorbent has been applied to the dye solution, the transport of dye ions to the active adsorption sites would also be reduced, thereby reducing the efficiency of adsorption (Seey & Kassim 2012).Therefore 0.2 g of clay was selected as the optimum weight for the further experiments. The same results was found by

Influence of Ph:
Batch experiments were performed for the adsorption of OG dye onto the clay samples by varying the pH levels from 2.17 to 11.24 a fixed adsorption time of 36 min, starting OG concentration 100 mg/L at 288 K and agitation speed 150 rpm as shown in (Figure 3), it is evident that the removal efficiency of OG increased in acidic medium pH=2.17 to 5 and reaches to 66.89 for RC and 67.2, 67.85, 69.03 for ACSO, ACH, ACS. As the pH increase there is a decrease in the R% reaches to 66.13 for RC and 66.33, 67.14, 67.93 for ACSO, ACH, ACS. The higher values of R% noticed in the acidic solution may be related to the electrostatic attractions between the negative charge of the functional groups of the OG dye and a positive charged of clay surfaces also the H⁺ acts a bridging ligand between the OG and the clay surfaces. The abundance of OH¯ ions in the simple solution also creates a competitive environment which causes anionic OG ions to decrease adsorption in the adsorption sites

Influence of initial OG dye concentration
Influence

Influence of temperature
Temperature effect was tested for initial OG dye (100 mg/L) at temperature range (288-328 K), clay dosage (0.2g /20 mL), PH=7, shaking time 36 min and agitation speed (150 rpm), the findings results are seen in ( Figure 5).The results showed that the R% for all samples decrease with increases thetemperature from 288 to 328 K, thus suggested that the adsorption of OG dye on the clay samples can be imparts an exothermic naturefor the adsorption process. It means that when the temperature rise the adsorption forces betweenthe dye moleculesand the

Influence of solution ionic strength
The effect of ionic activity on the adsorption of OG dye was tested by adding sodium chloride salt within the range 0.2-1.0 mg/L, OG concentration is 100 mg/L, clay dosage 0.2 g, pH=7, shaking time equal to 36 min at 288K and shaking speed (150 rpm). The presence of salts in water can contribute to high ionic strength and effective to the efficiency for adsorption process. As seen in (Figure 6

RESULTS AND DISCUSSION Adsorption isotherm
The experiments of isotherm were carried out at five temperatures in the range of (288, 298, 308, 318 and 328K), clay dosage 0.2 g/20 mL, shaking time 36 min for all types of clay, pH=7, shaking speed 150 rpm and the concentration of OG dye in the range of (50, 75, 100, 150 and 200 mg/L).

Langmuir adsorption isotherm
The Langmuir isotherm model postulation the maximum adsorption agrees to a saturated monolayer of solute molecular on the adsorbent surface. Linear form of Langmuir model is (Bouatay et al., 2014).
Where: is the equilibrium concentration for OG dye (mg/L). And is the amount of adsorbate per gram of adsorbent at equilibrium (mg/g).
The values of (mg/g) and (L/mg) are the Langmuir constants associated to adsorption capacity, and rate of adsorption were resolute from the linear plot of specific adsorption ⁄ against . (Figures 7, 8, 9 and 10) show the Langmuir isotherm plots for the adsorption of OG dye onto RC ACSO, ACH and ACS respectively.    arranged as ACS>ACH>ACSO>RC, this indicated that the adsorption capacity for acid and alkali activated clay is higher than raw clay. The same result was noticed by (Sarma et al., 2018). The separation factor can be calculated from the equation: Table 2) shows the values of separation factor for the adsorption of 50 mg/L OG dye onto clay samples at different temperatures. The calculated values are lies between o and 1 indicate that the adsorption process is favorable.

Freundlich adsorption isotherm
Freundlich model assumes OG dye adsorption takes place on sites with various adsorption energies or at heterogeneous clay surfaces, and can be applied to multilayer adsorption (Gbajiet al., 2019).It usually written as (Miyahet al., 2017): ⁄ ------------------(5) and n are freundlich constants related to adsorption capacity and adsorption intensity respectively. The values of these constants were estimated from the intercept and slope of the plot between Ln vs Ln . (Figures 11, 12, 13 and 14), these values are illustrate in (Table 2). The values of n identify the favorability of the sorption process.    ( Table, 2) shows that the values of n<1 that indicates cooperative adsorption. The value of lies between 0.9511-0.9832, 0.9317-0.9859, 0.9368-0.9694 and 0.9768-0.9878 for RC, ACSO, ACH and ACS respectively, these values show a reasonable fit to Freundlich model plots for the adsorption of OG dye onto different clay samples, which predicted that the adsorption process carried out on a heterogeneous surface and this process is reversible (Sejie & Nadiye-Tabbiruka 2016). The similar results was found by (Nadiye-Tabbiruka et al., 2018).

Temkin isotherm
This model based on the effect of the indirect dye-clay interactions on sorption leads to, linearly decreasing the heat of adsorption with the surface coverage. The linear equation for this isotherm was expressed as equation (Bouatay et al., 2014).
-       (Table, 2) shows the Temkin constants for the adsorption of OG dye onto RC, ACSO, ACH and ACS at different temperatures. In this Table increasing in temperature leads to decreases in the values of that indicates the adsorption process is an exothermic, the values of are less than 8 kJ/mol suggesting a weak interaction between OG dye ions and clay surface indicating that the adsorption process is likely physi-sorption. The values of correlation coefficient lies between 0.9103-0.9460, 0.9112-0.9692, 0.9223-0.9779 and 0.9343-0.9544 for RC, ACSO, ACH and ACS respectively. The highest values of relatively predicted a uniform distribution for the binding energies a rises during the adsorption of OG dye onto clays samples (Okoli et al., 2015).

Dubinin-Radushkevich (D-R) isotherm:
The Dubinin-Radushkevich isotherm was applied to study the adsorption on micro porous materials based on the potential theory of adsorption. The linear form of D-R model written as (Emeniru et al., 2015).     As shown in (Table, 2) the values of R² lies between 0.9041-0.9662, 0.9019-0.9632, 0.9037-0.9552 and 0.9194-0.9797 for RC, ACSO, ACH and ACS clays, this values indicate a good fitting for the adsorption of OG dye onto four types of clays. At all temperatures the highest values of mean free energy (E) were (0.1174, 0.1307, 0.1216 and 2.082 kJ/mol) for RC, ACSO, ACH and ACS respectively (less than 8kJ/mol). The low values of mean free energy predicting that the adsorption of OG dye onto four types of clays is Physi-sorption in nature (Dada et al., 2012). From the values of correlation coefficient, the following order to fit the isotherm: Freundlich>Temkin>Dubinin-radushkevich>Langmuir. It was obvious that Freundlich isotherm described better the dye uptake with the higher correlation coefficient R² values for the RC, ACSO, ACH and ACS samples in comparison with that of the other adsorption isotherm model.

Adsorption thermodynamic
The thermodynamic parameters for the adsorption of OG dye were evaluated by using the following equations: ₌   (Table, 3) shows the thermodynamic parameters ( ) for the adsorption of OG dye onto four types of clays at different temperatures. In this Table the negative values  of confirm the spontaneous and thermodynamically favorable characteristic for the adsorption of OG dye onto the clays samples at low temperatures and the negative values of indicating that the adsorption of OG dye onto clays is exothermic the positive values of represents the adsorption of OG dye onto RC, ACSO, ACH and ASC is reversible (Akbartabar et al., 2017), and occurs with a good affinity of OG dye towards the clay samples, that leads to an increased at the solid/liquid interfere during dye adsorption onto the clay samples and it remain randomly on the each surface (Al-Timimi et al., 2016).

CONCLUSION
In this article we can concluded that: 1. The percentage removal for OG dye onto raw and activated clays were varied with clay dosage, agitation time, starting dye concentration, temperature, ionic strength and initial pH, the adsorption process was carried out 0.2 g clay dosage, equilibrium time was 36 min, pH 5, the adsorption process increased when increase the dye concentration from 50 to 200 mg/L, when the temperature increased from 288K to 328K the adsorption decrease and for ionic strength when the concentration of sodium chloride increased, the adsorption increased for ACSO, ACH and ACS and decreased for RC. 2. The adsorption isotherm models indicates the adsorption of OG dye onto four types of clays was fitted with Freundlich isotherm model. 3. The maximum mono layer capacity that estimated from Langmuir model increased from RC to ACS respectively, this indicates that the activation leads to increase the adsorption capacity for ACSO, ACH and ACS clays. 4. The values of thermodynamic parameters suggested that the adsorption of OG dye onto clays is spontaneous, exothermic and reversible. 5. From the isotherm models analysis and experimental data we can concluded the removal efficiency of color pollutants from water for the alkali and acid activated clay is more than raw clay. 6. It is recommended to apply this clay as adsorbent to remove other types of dyes and other environmental pollutants such as phenols, heavy metals and toxic organic compounds.