**5.1 Sorption Fe3+ ions using natural quartz (NQ) and bentonite (NB))**

It is known from the chemistry view that surface of NB and NQ is ending with (Si-O) negatively charged. These negative entities might bind metal ions *via* the coordination aspects especially at lower pH values as known in the literatures. Fe3+ ions are precipitated in the basic medium. Therefore, the 1 % HNO3 stock solution is used to soluble Fe3+ ions and then achieving the maximum adsorption percentages [20].

The binding of metal ions might be influenced on the surface of NB more than NQ. This is due to the expected of following ideas: (i) NQ have pure silica entity with homogeneous negatively charged, therefore the binding will be homogeneous. (ii) The natural bentonite has silica surface including an inner-layer of alumina and iron oxide, which cause a heterogeneous negatively charged. Therefore, the binding Fe3+ ions on the surface on NB might be complicated.

The adsorption thermodynamics modelsof Fe3+ ions on NQ and NB at 30 ºC are examined [20]. The calculated results of the Langmuir and Freundlich isotherm constants are given in Table 2. The high values of *R2* (*>*95%) indicates that the adsorption of Fe3+ ions onto both NQ and NB was well described by Freundlich isotherms.It can also be seen that the max *q* and

Thermodynamics Approach in the Adsorption of Heavy Metals 751

The obtained experimental data also has well described by Freundlich isotherm model into

confirms the feasibility of the process and the spontaneous nature of adsorption with a high preference for metal ions to adsorb onto NB more easily than NQ in pseudo second order rate

> 3.4 3.6 3.8 4 4.2 4.4 4.6 **lnCe**

Fig. 9. The linearized Freundlich adsorption isotherms for Fe3+ ions adsorption by natural Quartz (NQ) and bentonite (NB) at constant temperature 30 ºC. (initial concentration: 400

**5.2 Sorption isotherms of Fe3+ ions processes using Jordanian natural zeolite (JNZ)**  Isotherm studies are conducted at 30 ºC by varying the initial concentration of Fe3+ ions [19]. Representative initial concentration (1000, 800, 600, 400 ppm) of Fe3+ ions are mixed with slurry concentrations (dose) of 20g/L for 150 min., which is the equilibrium time for the zeolite and Fe3+ ions reaction mixture. The equilibrium results are obtained at the 1% HNO3 model solution of Fe3+ ions. The Langmuir isotherm model is applied to the experimental data as presented in Figure 10. Our experimental results give correlation regression coefficient, <sup>2</sup> *R* , equals to 0.998, which are a measure of goodness-of-fit and the general

0.136 8.72 *<sup>e</sup> <sup>e</sup>*

Our results are in a good qualitatively agreements with those found from adsorption of Fe3+

*c*

*e c*

*q*

ppm, normal 1% HNO3 aqueous solution, 300 rpm, contact time: 2.5 hours).

R2

= 0.9926

*Gº* (- 13.4 and – 13.9 KJ/mol, respectively)

R2

= 0.9966

Fe-NQ Fe-NB

both NQ and NB. The negative value of

reaction.

0

empirical formula of the Langmuir model by

on the palm fruit bunch and maize cob [58]**.** 

0.2 0.4

0.6 0.8

1

**lnqe**

1.2 1.4

1.6 1.8

2

the adsorption intensity values of NB are higher than that of NQ. The calculated *b* values indicate the interaction forces between NB surface and Fe3+ ions are stronger than in case of using NQ, this is in agreement with the higher ionic potential of Fe3+. This means that the NB is more powerful adsorbent than NQ. Furthermore, based on this information, we found that the adsorption using NQ and NB is much higher as compared to carbon used by other authors [57].

Fig. 8. The linearized Langmuir adsorption isotherms for Fe3+ ions adsorption by natural quartz (NQ) and bentonite (NB) at constant temperature 30 ºC. (Initial concentration: 400 ppm, 300 rpm and contact time: 2.5 hours).


NQ = Natural Quartz

NB = Natural Bentonite

Table 2. Langmuir constants for adsorption of Fe3+ ions on NQ and NB

the adsorption intensity values of NB are higher than that of NQ. The calculated *b* values indicate the interaction forces between NB surface and Fe3+ ions are stronger than in case of using NQ, this is in agreement with the higher ionic potential of Fe3+. This means that the NB is more powerful adsorbent than NQ. Furthermore, based on this information, we found that the adsorption using NQ and NB is much higher as compared to carbon used by other

R2

= 0.9385

**qmax b (L/mol) G/1000 (kJ/mol)** 

R2

30 40 50 60 70 80 90 100 **Ce**

NQ 14.4 226.3 -13.4

NB 20.96 283.8 -13.9

Table 2. Langmuir constants for adsorption of Fe3+ ions on NQ and NB

Fig. 8. The linearized Langmuir adsorption isotherms for Fe3+ ions adsorption by natural quartz (NQ) and bentonite (NB) at constant temperature 30 ºC. (Initial concentration: 400

= 0.961

Fe-NQ Fe-NB

authors [57].

0

NQ = Natural Quartz NB = Natural Bentonite

ppm, 300 rpm and contact time: 2.5 hours).

**Langmuir Constants Adsorbent**

5

10

**Ce/qe**

15

20

25

The obtained experimental data also has well described by Freundlich isotherm model into both NQ and NB. The negative value of *Gº* (- 13.4 and – 13.9 KJ/mol, respectively) confirms the feasibility of the process and the spontaneous nature of adsorption with a high preference for metal ions to adsorb onto NB more easily than NQ in pseudo second order rate reaction.

Fig. 9. The linearized Freundlich adsorption isotherms for Fe3+ ions adsorption by natural Quartz (NQ) and bentonite (NB) at constant temperature 30 ºC. (initial concentration: 400 ppm, normal 1% HNO3 aqueous solution, 300 rpm, contact time: 2.5 hours).

**5.2 Sorption isotherms of Fe3+ ions processes using Jordanian natural zeolite (JNZ)**  Isotherm studies are conducted at 30 ºC by varying the initial concentration of Fe3+ ions [19]. Representative initial concentration (1000, 800, 600, 400 ppm) of Fe3+ ions are mixed with slurry concentrations (dose) of 20g/L for 150 min., which is the equilibrium time for the zeolite and Fe3+ ions reaction mixture. The equilibrium results are obtained at the 1% HNO3 model solution of Fe3+ ions. The Langmuir isotherm model is applied to the experimental data as presented in Figure 10. Our experimental results give correlation regression coefficient, <sup>2</sup> *R* , equals to 0.998, which are a measure of goodness-of-fit and the general empirical formula of the Langmuir model by

$$\frac{c\_e}{q\_e} = 0.136c\_e + 8.72$$

Our results are in a good qualitatively agreements with those found from adsorption of Fe3+ on the palm fruit bunch and maize cob [58]**.** 

Thermodynamics Approach in the Adsorption of Heavy Metals 753

from the slope and intercept respectively for the three isothermal lines. These values of max *q* and *b* are listed in Table 1 with their uncertainty and their regression coefficients, *R* 2 . Table 3 shows that the values of *q* max and *b* are decreased when the solution temperature increased from 28 to 45 <sup>0</sup> C. The decreasing in the values of *q* max and *b* with increasing temperature indicates that the Fe3+ ions are favorably adsorbed by olive cake at lower temperatures, which shows that the adsorption process is exothermic. In order to justify the validity of olive cake as an adsorbent for Fe3+ ions adsorption, its adsorption potential must be compared with other adsorbents like eggshells [59] and chitin [24] used for this purpose. It may be observed that the maximum sorption of Fe3+ ions on olive cake is approximately

15 20 25 30 35 40 45 50 55 60 65 70 75 80

3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4

lnCe

Fig. 13. The linearized Freundlich adsorption isotherms for Fe3+ ions adsorption by olive cake at different temperatures. (Initial concentration of Fe3+ ions: 100 ppm, Agitation speed:

Ce

Fig. 12. Langmuir isotherm model plot of *qe*/*Ce* of Fe3+ ions on olive cake *vs. Ce* (ppm) of Fe3+

greater 10 times than those on the chitin and eggshells.

1.5

 28 C 35 C 45 C

2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4

100 rpm, pH: 4.5, Contact time: 24 hr).

lnqe

ions.

2.0

2.5

Ce/qe

3.0

3.5

4.0

 28 C 35 C 45 C

Figure 11 represents the fitting data into the Freundlich model. We observe that the empirical formula of this model is found as ln 0.1058ln 1.2098 *e e q c* with <sup>2</sup> *R* value equals to 0.954. It can be seen that the Langmuir model has a better fitting model than Freundlich as the former have higher correlation regression coefficient than the latter.

The value of standard Gibbs free energy change calculated at 30 C is found to be -16.98 kJ/mol. The negative sign for <sup>0</sup> *<sup>G</sup>* indicates to the spontaneous nature of Fe3+ ions adsorption on the JNZ.

Fig. 10. Langmuir isotherm model plot of *qe*/*Ce* of Fe3+ ions on JNZ *vs. Ce* (ppm) of Fe3+ ions.

Fig. 11. Freundlich isotherm plot of *ln qe vs. ln* Ce, where *C*e is the equilibrium concentration of Fe3+ ions concentration.
