**3. Results and discussion**

### **3.1 Characterization**

### *3.1.1 Scanning electron microscopy*

The **Figure 1(a)** and **(b)** shows the scanning electron microscopy of rice biomass, with magnification of 2.000 x in (a) and 5.000 x in (b). In (c) and (d), it shows the banana biomass, with an image enlarged from 2.000 x in (c) to 5.000 x in (d). In all the images it is possible to observe a porous structure, being able to be susceptible to adsorption of metals on its surface.

### *3.1.2 Infrared spectroscopy with fourier transform*

The main adsorption bands were observed in the infrared region (500- 4000 cm−1) and compared with the literature.

In **Figure 2**, the banana peel biomass presents: the absorption band of 3200 cm-1 can be attributed to the O-H bond stretch, characteristic of functional groups of alcohols and phenols. Pino [16] as well as the presence of H2O molecules. The wavenumber 2930 cm−1 corresponds to the axial deformation of aliphatic and hydro aromatic carbon sp3 carbon bonds found in cellulose and hemicellulose [17]. In the vicinity of the range 1620 cm−1 indicates the lignin, due to the functional group C=O [18]. Finally, the peak near 1000 cm−1 is assigned to the C-O group stretching than can be observed in cellulose, hemicellulose and lignin. Thus, it can be concluded that groups alcohols/phenols, carboxyl, carbonyl, alkane, aromatic groups are present in banana bark [19].

Rice bark biomass shows major bands in the bands of 3369 cm−1 indicating O-H elongation, revealing a hydrogen bond, this structure may be due to the presence of acids or alcohols [20]. The wavelength 2900 cm−1, as well as in banana biomass,

**Figure 2.** *Results of the Fourier transform infrared analysis of rice and banana biomass.*

*Removal of Copper and Lead from Water in the Mariana Mining Disaster Using Biomass… DOI: http://dx.doi.org/10.5772/intechopen.99668*

indicates groups of C-H, from carbon sp3 , connecting to the presence of cellulose and hemicellulose. The spectral band around 1500-1640 cm−1 attributes to the functional group carbonyl (C=O) elongation associated with lignin [21]. The bands near 1100 and 800 cm−1 are characteristic of the O-Si bond in polymorphic silica, SiO2 [22].

The adsorption mechanism of the copper and lead ions in the studied biomass can be associated with the presence of functional groups that have oxygen in their constitution [23]: a two-step process: (i) the metal ions hydrolyze in the solution to form a hydrolyzed metal ion (ii) the positively charged halves interact with oxygencontaining functional groups, leading to better contact with biomass and high adsorption capacity.

#### *3.1.3 Zeta potential*

**Figure 3** show the zeta potentials of the banana and rice peel. The original peels exhibit a negative zeta potential and the used particles possess a less negative potential. All these results reveal that the waste peels had adsorbed the metal ions. The isoelectric point for banana was 6.6 – 7.0 and for rice 6.6 – 7.3.

### **3.2 Adsorption tests**

### *3.2.1 Isotherm test*

### *3.2.1.1 Copper*

In order to determine and compare the adsorption capacity of copper by the banana and rice biomass, **Figure 4** shows two graphs of the Cu (II) equilibrium concentration (Ce) as a function of the adsorption capacity (Qe) of the biomasses. **Figure 4(a)** shows a marked increase in the isotherm, indicating that the free sites of the banana biomass were empty and available for Cu (II) adsorption. While **Figure 4(b)** shows some initial oscillation in the adsorption capacity but soon after the free sites reach the saturation and, consequently, a balance in the adsorption capacity of the rice biomass.

The Langmuir and Freundlich isotherm models were tested for information on Cu (II) adsorption by banana and rice biomasses. These models describe the interaction between the adsorbent and the adsorbed material. The Langmuir model considers that the adsorption process occurs in a monolayer on a homogeneous

**Figure 3.** *Zeta potential curves obtained for (a) banana peel and (b) rice rusk.*

**Figure 4.**

*Adsorption isotherm of Cu (II) (a) by banana, (b) by rice and of Pb (II) (c) by banana, (d) by rice. Adsorbent dose: 10 mg; shaking speed:200 rpm; pH 7 ± 0.3; temperature: 25 ± 0.3°C.*

surface, that is to say, with active sites with identical energy and availability and without interaction between the adsorbed molecules [24].

The Freundlich isotherm differs from the Langmuir isotherm model, which describes multilayer adsorption on heterogeneous surfaces [25]. In the Freundlich model, when the 1/n exponent value for this model equals 1, the adsorption is considered linear, with identical adsorption energies at all sites. The higher the value of 1/n, the stronger the interaction between adsorbent and adsorbate [26].

**Table 1** shows the values of the parameters obtained by nonlinear regression of the Cu (II) adsorption by the banana and rice biomass applied to the Langmuir and Freundlich isotherm. For banana biomass, the Langmuir and Freundlich isotherms presented very close adaptations when comparing the values of the correlation coefficient (R<sup>2</sup> ): 0.99 (Langmuir) and 0.99 (Freundlich). In addition, the RL value is between 0 and 1, indicating that the Langmuir model is favorable, but Freundlich is also an accepted model for this adsorption since the value of 1/n is less than 1. For rice biomass, the Langmuir model was more favorable, with R<sup>2</sup> = 0.96 and RL = 0.99.

#### *3.2.1.2 Lead*

The **Figure 4(c)** and **(d)** illustrates the experimental data obtained in the adsorption of Pb (II) by banana and rice biomasses applied to the Langmuir and Freundlich models. For both banana and rice biomass, there was an increase in the adsorption capacity, indicating the occupation of the free sites in the material.

The adsorption of Pb (II) by banana biomass was favorable to the Langmuir isotherm model with R2 = 0.95 and RL = 0.92. For rice biomass the Freundlich model presented R2 = 0.91, but another parameter, 1/n, indicates that this model is not adequate because it has a value higher than 1. With this, the Langmuir model is the most favorable model.


*Removal of Copper and Lead from Water in the Mariana Mining Disaster Using Biomass… DOI: http://dx.doi.org/10.5772/intechopen.99668*

#### **Table 1.**

*Parameters obtained by nonlinear regression adjustment of Langmuir, Freundlich, for Cu (II) and Pb (II) isotherms by adsorption in biomass of banana and rice husk. Qm: Maximum adsorption capacity, KL: Langmuir constant, RL: Balance parameter, KF: Freundlich constant, 1/n: Adsorption intensity.*

### **3.3 pH test**

#### *3.3.1 Copper*

The effect of pH on copper (II) adsorption by banana and rice biomass at pH values of 5.0, 7.0 and 9.0 is described in **Figure 5(a)**. The adsorption capacity of the metal by the banana is higher at pH 5.0 (34.16 mg g−1) than pH 7.0 (33.80 mg g−1) and 9.0 (31.02 mg g−1). In agreement, the rice presents similar behavior where the capacity of adsorption undergoes a slight decrease with the increase of the pH, pH 5.0 (34.37 mg g−1), pH 7.0 (33.70 mg g−1) and pH 9.0 (30.81 mg g−1). As in the literature [27], the rate of Cu (II) removal has little effect on pH.

#### *3.3.2 Lead*

**Figure 5(b)** shows the effect of pH on the adsorption of Pb (II) by banana and rice biomasses. Banana biomass presented a removal rate of 91.21% (36.46 mg g−1) at pH 5, 93.88% (37.53 mg g−1) at pH 7.0 and 94.46% (37.76 mg g−1) to pH 9.0. As for banana, the adsorption capacity for rice did not have a significant effect, since at pH 5.0 it removed 93.61% (37.42 mg g−1) from Pb (II) 94.85% (37. 91 mg g−1) and 95.68% (38.25 mg g−1) to pH 7.0 and 9.0, respectively.

The behavior shown where the adsorption capacity has a small increase together with the pH value is justified by the PZC values of banana biomass (6.6 - 7.0) and rice (6.6 - 7.3) and a study [28] where it states that the negative surface charge leads to deprotonation of functional groups of the biomass as H<sup>+</sup> (aq) and H3O+ (aq) are

**Figure 5.**

*Effect of pH on (a) Cu (II) and (b) Pb (II) adsorption by banana and rice biomass. Initial [Cu2+] and [Pb2+]: 20 mg L−1; adsorbent dose: 20 mg; shaking speed: 200 rpm; temperature: 25 ± 0.3°C.*

released from them. Thus, these deprotonated functional groups serving as binding sites become readily accessible to metal ions causing better sorption.

#### **3.4 Kinetic test**

#### *3.4.1 Copper*

The results obtained from the kinetic copper adsorption test for banana and rice biomass are presented in **Figure 6(a)** and **(b)**. At pH 7.0, the results indicate a rapid removal in the first 30 minutes of contact, with approximately 53.16% for banana and 69.66% for rice. The maximum removal rate was reached at 120 minutes for banana, with 64.73% and 360 minutes for rice, with 91.72%.

The kinetic adsorption data were fitted with a pseudo first order model [12] and pseudo second order model [13].

The kinetic pseudo-first order model does not adjust to copper adsorption by banana and rice biomasses. While the pseudo-second order model based on the adsorption capacity of the solid phase shows the processes of adsorption studies in all time bands.

The kinetic data presented linearity (**Figure 6(b)**), with a correlation coefficient of 0.99 for banana and 0.99 for rice. The qe calculated with values close to experimental qe. For banana, the values qe (14.05 mg g −1), K2 (0.0012 L mg −1) and qe (29.41 mg g −1), K2 (0.0026 L mg −1) were obtained from the slope and intersection of the straight line of the graph t/qt as a function of t, according to **Figure 6(b)**.

#### *3.4.2 Lead*

**Figure 6(c)** and **(d)** shows the results obtained for the kinetic test at the times of 30, 120, 360, 720 and 1440 minutes. At pH 7.0, the data indicate a rapid adsorption of lead by banana biomass in the first 30 minutes of contact, with approximately 83% removal. While the biomass of rice removed about 75.9% in the first 120 minutes.

The kinetic adsorption data were fitted with a pseudo first order model and pseudo second order model. The pseudo-first-order kinetic model does not fit the adsorption of lead by banana or rice biomass. While the pseudo-second order model *Removal of Copper and Lead from Water in the Mariana Mining Disaster Using Biomass… DOI: http://dx.doi.org/10.5772/intechopen.99668*

#### **Figure 6.**

*(a) Kinetics of Cu (II) adsorption by banana and rice biomass (b) pseudo-second order kinetic model of Cu (II) adsorption by banana and rice biomass (c) kinetics of Pb (II) adsorption by banana and rice biomass (d) pseudo-second order kinetic model of Pb (II) adsorption by banana and rice biomass. Initial [Cu2+] and [Pb2+]: 20 mg L−1; pH: 7.0 ± 0.3; shaking speed: 200 rpm; temperature: 25.0 ± 0.3°C.*

based on the adsorption capacity of the solid phase shows the adsorption process in all time bands.

The kinetic data for the adsorption of lead by banana biomass present a high linearity (**Figure 6(d)**), with correlation coefficient close to 1 (0.99) and calculated Qe (26.60 mg g−1) with values close to experimental Qe (26.96 mg g−1). The values of calculated Qe and K2 (0.0014 L mg−1) were obtained from the slope and intersection of the straight line of the graph t/qt as a function of t.

For the rice biomass, the correlation coefficient is also close to 1 (0.99), the calculated Qe (23.81 mg g−1) presented a value close to the experimental Qe (23.92 mg g−1) at the end the K2, through the 0.0006 L mg−1 slope of the line.

The adsorption capacities of copper and lead in banana and rice biomass are compared with the studies on the types of materials of organic origin (**Table 2**). In addition to the efficiency of the removal, it is easy to obtain and handle the adsorption capacity. Considering this, it is noticed that the studied materials present great efficiency in the removal of metals from contaminated water. Worked biomasses are cheap and easy to prepare because they are reused materials from common productive activities in various regions, making this technology accessible to various social levels.

Comparing the biomaterials of this study with the values found in the literature (**Table 2**), the biomasses of banana peel and rice present better adsorption capacities, thus confirming the great potential of applying the material with real water samples.


#### **Table 2.**

*Comparison between the adsorption capacities of different materials in copper and lead removal.*
