**Figure 1.**

*Crustaceans used in the preparation of raw chitin.*


#### **Table 1.**

*Systematic crustaceans used for the treatment.*

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

The raw chitin of shrimp origin (Ccre), crab origin (Ccra), and lobster origin (Clan) is extracted from the shells of these crustaceans according to the following mode: the shells are isolated from their soft parts containing the proteins, washed with bidistilled water, dried in an oven at 100°C for 48 hours, and finally they are crushed and sieved at particle size well defined.

### *2.1.2 Preparation of synthetic wastewater*

For each metal, a stock solution of 1 g/l [expressed in (g) metal cations per liter of test solution] was prepared using the metallic substances used in the most soluble mineral form (M2+, 2NO3 <sup>−</sup>) × H2O with [M = Zn (x = 6), Pb (x = 0), Cu (x = 3), and Cd (x = 4)]. For each adsorption test, the solution containing the metals to be studied is obtained from the daughter solutions.

#### **2.2 Experimental study of the adsorption phenomenon**

Adsorption is a surface phenomenon and to evaluate the adsorption of a compound on an adsorbent, it is necessary to start the following studies:

### *2.2.1 Adsorption kinetics*

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

Our study focused on an economic and abundant adsorbent, the raw chitin. This polymer exists at concentrations ranging between 20% and 50% in the skeletons of arthropods and more than 60% in the skeletons of crabs and shrimp [53, 54]. The studied crustaceans [crabs, lobsters, and shrimps (**Figure 1**)] belong to the phylum of the arthropods, it is the most important branch of the animal kingdom (75%) about 1 million species, are invertebrate animals metazoans, triploblastics, acoelomates, protostomials with metamerized body, bilateral symmetry and heteronome segmentation, covered by a protective epicuticle serving as external skeleton/exoskeleton, rigid but flexible in some places, and very rich in chitin. This richness is relative to each species. The systematics of

The selected species, Squinado, Panulirus, and Kerathurus (**Figure 1**) are the most abundant species in Moroccan markets. Their carapaces consist of an external epicuticle followed inward by a pigmented zone, a calcified layer, another noncalci-

**Crabs Lobsters Shrimps**

Branch Arthropods Arthropods Arthropods Class Shellfish Shellfish Shellfish Superorder Fucarides Fucarides Fucarides Order Decapoda Decapoda Decapoda Under order Reptantia Reptantia Natantia Section Brachyoures Macroura — Kind Maia Palinutus Pehaens

Cash Maia (Squinado) Panulirus *Penaeus kerathurus*

**2. Isothermal study of heavy metals adsorption**

**2.1 Preparations**

*2.1.1 Preparation of adsorbent carriers*

these crustaceans is summarized **Table 1**.

fied, and an epidermis.

**240**

**Table 1.**

**Figure 1.**

*Systematic crustaceans used for the treatment.*

*Crustaceans used in the preparation of raw chitin.*

The adsorption kinetics was established by stirring for varying periods of time, the M2+ solutions introduced into 250 ml Erlenmeyer flasks and added to constant amounts of the adsorbent. After a determined contact time of each suspension, they are filtered; the amount of M2+ not removed by the support is subsequently assayed.

#### *2.2.2 Adsorption isotherm*

The adsorption mechanism can be described using an adsorption isotherm. An adsorption isotherm is the curve, which represents the variation of the adsorbed quantity "Qe" as a function of the equilibrium concentration "Ce" with Eq. (1)

(1)

where, C0: initial concentration of adsorbate (mg/l); m: mass of adsorbent used (mg); v: volume of the solution (ml); and ma: mass of retained adsorbate (mg).

The adsorption can be studied, either by examining the decrease of the concentration of the adsorbate in the solution, or by a direct determination of the amount fixed on the solid; the second case requires a washing of the solid in order to remove all the unadsorbed molecules, which can cause destruction in the case of the reversible process, and thus leads to erroneous results, and for these reasons, we opted for the first possibility.

To obtain an adsorption isotherm for a solute on an adsorbent, a constant temperature was used, by mixing a determined quantity of the adsorbent with a solution whose solute concentration is known. After vigorous stirring (500 rpm) and prolonged, the equilibrium time between the solid and liquid phases is determined. The mixture is filtered, and by appropriate dosage, the residual concentration of the solute in the solution is measured. This equilibrium concentration will be noted Ce (mg/l). The amount fixed on the adsorbent is deduced, by difference with the initial concentration. This quantity will be symbolized by Qe (mg/g): amount of solute adsorbed per unit mass of the adsorbent. The measurement is repeated several times using solutions of different concentrations, which allow us to draw the isothermal curve. The operating conditions are summarized in **Table 2**. The supernatant is filtered and the equilibrium


#### **Table 2.**

*Operating conditions of adsorption isotherms.*


#### **Table 3.**

*Results of the blank tests.*

**243**

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

Percentage of reduction = percentage of abatement

concentration Ce is determined by a suitable assay. The precipitates [M2+/adsorbent] are dried in an oven for 24 hours to be mineralized. The percentage of elimination is

Blank tests are carried out by stirring the same adsorbent solution (Cd2+, Pb2+, Cu2+, and Zn2+) at a concentration of 100 mg/l during equilibrium time,

According to this table, we can neglect the amount retained by the filter

To demonstrate the effectiveness of the Ccre in retaining the metal ions, we proceeded to a simple treatment using 500 mg of the chitin and a series treatment using amounts of adsorbent whose sum is equal to 500 mg. Starting with an initial concentration of 100 mg/l M2+, after each adsorption test, the measured filtrate is again adsorbed on the material. This operation is repeated four times for four metals

Depending on the results sought and also to cross-check the information

• Atomic absorption spectrophotometry with flame (cadmium, copper, lead, and zinc) by spectrophotometers VARIAN AA-475, PHLIPS PU-900, PERKIN

• Graphite furnace atomic absorption spectrophotometry (lead and cadmium)

Prior to the adsorption experiments of heavy metals, it appeared useful to follow

their adsorption kinetics to determine the times required to reach equilibrium.

To determine the time required to reach the Cd2+ adsorption equilibrium, we monitored the change in Cd2+ concentration as a function of time. The results are

This study shows that equilibrium is established rapidly for all adsorbents (**Figure 3**). It reaches its maximum for 30 and 20 minutes, respectively for Ccra and

From these curves, it is also found that 50% of Cd2+ is adsorbed on the Ccre before the equilibrium reached 20 minutes. The equilibrium times (teq) are

Ccre, while the adsorption kinetics of Cd2+ on Clan is relatively slow.

and this is filtered. Then dosed to determine the amount of adsorbate retained by the Erlenmeyer flasks and the filter, the results of these tests are

= percentage of elimination = (Co − Ce/Co).100 (2)

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

calculate according to Eq. (2):

grouped in **Table 3**.

**2.3 Serial metal ion adsorption test**

**2.4 Dosage of heavy metals**

according to the following flowchart **Figure 2**.

obtained, we used different techniques and equipment:

ELMER 305, and SHIMADZU AA-680.

type SHIMADZU GFA-4B.

**3. Study of cadmium adsorption**

shown in **Figure 3**.

**3.1 Kinetic study of the Cd2+ adsorption**

accessories.

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

concentration Ce is determined by a suitable assay. The precipitates [M2+/adsorbent] are dried in an oven for 24 hours to be mineralized. The percentage of elimination is calculate according to Eq. (2):

 Percentage of reduction = percentage of abatement = percentage of elimination = (Co − Ce/Co).100 (2)

Blank tests are carried out by stirring the same adsorbent solution (Cd2+, Pb2+, Cu2+, and Zn2+) at a concentration of 100 mg/l during equilibrium time, and this is filtered. Then dosed to determine the amount of adsorbate retained by the Erlenmeyer flasks and the filter, the results of these tests are grouped in **Table 3**.

According to this table, we can neglect the amount retained by the filter accessories.

### **2.3 Serial metal ion adsorption test**

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

**Concentration of the material 1 g/l** Granulometry 100 μ ≤ Φ ≤ μ 125 m Concentration range 10–100 mg/l Stirring speed 500 rpm Temperature 20 ± 2°C

**Metals Pb2+ Cd2+ Cu2+ Zn2+** Co (mg/l) 100.02 100.05 99.99 99.98 This (mg/l) 99.98 99.97 99.97 99.92

Stirring time Equilibrium time of each metal

**242**

**Figure 2.**

*Serial adsorption process.*

**Table 3.**

**Table 2.**

*Results of the blank tests.*

*Operating conditions of adsorption isotherms.*

To demonstrate the effectiveness of the Ccre in retaining the metal ions, we proceeded to a simple treatment using 500 mg of the chitin and a series treatment using amounts of adsorbent whose sum is equal to 500 mg. Starting with an initial concentration of 100 mg/l M2+, after each adsorption test, the measured filtrate is again adsorbed on the material. This operation is repeated four times for four metals according to the following flowchart **Figure 2**.

#### **2.4 Dosage of heavy metals**

Depending on the results sought and also to cross-check the information obtained, we used different techniques and equipment:


Prior to the adsorption experiments of heavy metals, it appeared useful to follow their adsorption kinetics to determine the times required to reach equilibrium.
