**3.2 Study of Cd2+ adsorption isothermals on raw chitin**

The curves in **Figure 4a** show the evolution of the adsorption capacity (Qe) as a function of the equilibrium concentration (Ce) of Cd2+ and **Figure 4b** shows the removal efficiency by source of chitin.

When the residual concentration increases, the isotherm of Cd2+ on the Ccre deviates from the other two isotherms, which presents two different curvatures. For low concentrations, the slope is steep up to 40 mg/g, which shows that adsorption is important for low concentrations as for high concentrations. Indeed, the increase of the ionic strength of the system reduces the adsorption through the effect of the coefficient of activity. More than 40 mg/g, the curve no longer follows Henry's law. The Cd2+ adsorption isotherm on the Ccra is almost straight; Henry's hypothesis (low surface coverage) is true for all the concentrations studied, whereas for the Clan,

#### **Figure 4.**

*(a) Experimental isotherms of Cd (II) adsorption on raw chitin, (b) Effect of the origin of raw chitin on the removal efficiency of Cd (II).*

**245**

**Figure 5.**

*Sustainable Treatment of Heavy Metals by Adsorption on Raw Chitin/Chitosan*

the isothermal loss loses its linearity above 18 mg/g. For a residual concentration of 22 mg/l, the quantity retained depends on the origin of the raw chitin. Thus, it decreases successively from 78 mg/g for the Ccre to 57 mg/g for the Ccra and 47 mg/g for the Clan. From an initial concentration of Cd2+ equal to 100 mg/l, one can reach 22 mg/l after adsorption on the Ccre and 37 mg/l after adsorption on the Clan.

*Values of the Freundlich parameters deduced from the adsorption isotherms of Cd2+ on raw chitin.*

Ccre 34.81 0.27 0.98 Ccra 7.38 0.69 0.99 Clan 18.92 0.34 0.97

selectivity of Cd for three supports is as follows: Ccre > Clan > Ccra.

From **Figure 4b**, the percentage of removal of Cd on the Ccre reaches 90%. The

**Kf mg/g 1/n R**

The modeling of the isotherms in **Table 4** showed that the adsorption of Cd on these different supports perfectly satisfies the Freundlich model **Table 1**. The adsorption capacity of Cd on Ccre is greater than that relative to the Ccra and Clan (**Table 4**). This capacity is comparable to that found by Wales [52] by studying the

In this study **Figure 4b**, we found that the percentage of abatement decreases with increasing concentration. Thus, it varies from 78% for 100 mg/l to 98% for a

From **Figure 5**, we observe that the adsorption of Cu2+ is very fast initially and quickly reaches equilibrium time, 60 minutes for Ccra and 90 minutes for Clan. We also found that the hardness (mineral part) of the carapaces plays a role in the kinetics of the adsorption process by comparing these results with the equilibrium

According to Davis [57], the shape of these kinetic curves shows that the adsorption of Cu2+ is done according to the following model: Cu2+ binds rapidly in one time on the surface and groups co-ordinates very slowly to groups of chitin after scattering inside wall surfaces of the shells. Such adsorption kinetics is also

*DOI: http://dx.doi.org/10.5772/intechopen.88998*

**Table 4.**

adsorption of Cd2+ on chitin-rich fungi.

**4. Study of the Cu (II) adsorption**

**4.1 Kinetic study of Cu (II) adsorption**

times found by Melchor [38].

*Kinetic study of Cu (II) adsorption on raw chitin.*

concentration of 10 mg/l after adsorption on the Ccre.

*Sustainable Treatment of Heavy Metals by Adsorption on Raw Chitin/Chitosan DOI: http://dx.doi.org/10.5772/intechopen.88998*


**Table 4.**

*Trace Metals in the Environment - New Approaches and Recent Advances*

time of equilibrium (40 minutes) comparable to our result.

**3.2 Study of Cd2+ adsorption isothermals on raw chitin**

removal efficiency by source of chitin.

*Kinetic study of Cd (II) adsorption on raw chitin.*

**Figure 3.**

classified in the following order: teq Ccre < teq Ccra <teq Clan. This kinetics is very fast in comparison with other works cited in the literature concerning the adsorption of Cd2+ on mineral surfaces, which require a very large equilibrium time. For example, for the adsorption of Cd2+ on the illite, the equilibrium is reached after 54 days [1] and in the case of a natural clay [55, 56], the equilibrium is reached after 50 days. Melchor [39] having studied the adsorption of Cd2+ on chitin, mentions a

The curves in **Figure 4a** show the evolution of the adsorption capacity (Qe) as a function of the equilibrium concentration (Ce) of Cd2+ and **Figure 4b** shows the

When the residual concentration increases, the isotherm of Cd2+ on the Ccre deviates from the other two isotherms, which presents two different curvatures. For low concentrations, the slope is steep up to 40 mg/g, which shows that adsorption is important for low concentrations as for high concentrations. Indeed, the increase of the ionic strength of the system reduces the adsorption through the effect of the coefficient of activity. More than 40 mg/g, the curve no longer follows Henry's law. The Cd2+ adsorption isotherm on the Ccra is almost straight; Henry's hypothesis (low surface coverage) is true for all the concentrations studied, whereas for the Clan,

*(a) Experimental isotherms of Cd (II) adsorption on raw chitin, (b) Effect of the origin of raw chitin on the* 

**244**

**Figure 4.**

*removal efficiency of Cd (II).*

*Values of the Freundlich parameters deduced from the adsorption isotherms of Cd2+ on raw chitin.*

the isothermal loss loses its linearity above 18 mg/g. For a residual concentration of 22 mg/l, the quantity retained depends on the origin of the raw chitin. Thus, it decreases successively from 78 mg/g for the Ccre to 57 mg/g for the Ccra and 47 mg/g for the Clan. From an initial concentration of Cd2+ equal to 100 mg/l, one can reach 22 mg/l after adsorption on the Ccre and 37 mg/l after adsorption on the Clan.

From **Figure 4b**, the percentage of removal of Cd on the Ccre reaches 90%. The selectivity of Cd for three supports is as follows: Ccre > Clan > Ccra.

The modeling of the isotherms in **Table 4** showed that the adsorption of Cd on these different supports perfectly satisfies the Freundlich model **Table 1**. The adsorption capacity of Cd on Ccre is greater than that relative to the Ccra and Clan (**Table 4**). This capacity is comparable to that found by Wales [52] by studying the adsorption of Cd2+ on chitin-rich fungi.

In this study **Figure 4b**, we found that the percentage of abatement decreases with increasing concentration. Thus, it varies from 78% for 100 mg/l to 98% for a concentration of 10 mg/l after adsorption on the Ccre.

### **4. Study of the Cu (II) adsorption**

#### **4.1 Kinetic study of Cu (II) adsorption**

From **Figure 5**, we observe that the adsorption of Cu2+ is very fast initially and quickly reaches equilibrium time, 60 minutes for Ccra and 90 minutes for Clan. We also found that the hardness (mineral part) of the carapaces plays a role in the kinetics of the adsorption process by comparing these results with the equilibrium times found by Melchor [38].

According to Davis [57], the shape of these kinetic curves shows that the adsorption of Cu2+ is done according to the following model: Cu2+ binds rapidly in one time on the surface and groups co-ordinates very slowly to groups of chitin after scattering inside wall surfaces of the shells. Such adsorption kinetics is also

**Figure 5.** *Kinetic study of Cu (II) adsorption on raw chitin.*

observed in the toxicological and physiological effect of copper. A similar behavior of copper retention was observed according to Balistrieri [58] on metal oxide surfaces, according to Fisher [29] on phytoplankton, and according to Xue et al. [59] on the algae.
