**3. Results and discussion**

#### **3.1 Adsorption isotherms**

Adsorption data obtained at different temperatures help to understand the interaction between nDCPD and Ni, Co, and Cu ions; analyzing the data with different adsorption models, the model with better fit is obtained. In **Table 1**, the most used isotherm models are described according to the literature, and in **Figures 1**–**3** for Ni, Co, and Cu, respectively, the behavior of the removal of metal ions at different temperatures is shown. The parameters derived from the adjustments together with the coefficient of determination, R2 , are shown in **Tables 2–4**, for Ni, Co, and Cu, respectively, using the SigmaPlot software (®Version 11) at a temperature of 15, 30, and 45°C. Based on the results obtained, it is observed that the most appropriate models to adjust the adsorption in nDCPD of Ni metal ions, in the three temperatures analyzed (**Figure 1** and **Table 2**), are SIPS, Redlich-Peterson, and Langmuir and Freundlich, suggesting that Ni ions are adsorbed on the surface of nDCPD causing the formation of a monolayer and that the adsorption process is physical. On the other hand, the results obtained in the removal of Co ions (**Figure 2** and **Table 3**), show that the models with the best fit of the data are SIPS, Redlich-Peterson and Langmuir in the three temperatures analyzed, which implies that the cobalt ions are adsorbed on the surface of nDCPD, in a physical process independent of temperature. Finally, in the removal of Cu ions (**Figure 3** and **Table 4**), only an appropriate fit was obtained with the SIPS model, which suggests that the removal of copper ions in equilibrium is carried out by a physisorption process on the surface of the adsorbent. The obtained results also show that the removal of all the ions analyzed using nDCPD is favored given that the *RL* values are between 0 and 1, which indicates that the adsorption is favorable; this tendency can be seen independently of the temperature used. The results of metal ion removal obtained in the present study using nDCPD are comparable with those obtained using other agroindustrial residues, since for Ni, removals between 6.88 and 120 mg/g have been obtained, while the value obtained in this work was of 22.48 mg/g. In the case of Co, a removal range of 2.55–45.44 mg/g has been reported, and in our case a value of 41.81 mg/g was obtained, finally, for Cu, removal values have been reported in the range of 0.98–163.01 mg/g, while in the present study a value of 41.88 mg/g of adsorbent was obtained [3–5, 13, 20–23, 26]. On the other hand, when comparing the results obtained with those reported by other authors who also used hydroxyapatites and brushite as adsorbent material, it was observed that the

**97**

**Figure 3.**

*temperatures.*

*The Use of Industrial Waste for the Bioremediation of Water Used in Industrial Processes*

*Adjustment of the experimental data of Ni adsorption using the different models of isotherms at different* 

*Adjustment of the experimental data of Co adsorption using the different models of isotherms at different* 

model that was best adjusted was that of Langmuir, with a capacity of Ni adsorption reported between 9.9 and 40.0 mg/g, these data are comparable with those obtained in the present work. In the case of Co, an adsorption with apatites of 8.8–20 mg/g has been reported, a value lower than that obtained with natural nDCPD obtained in the present study, which is 41.8 mg/g. Finally, in the case of Cu ions, a range of adsorption has been documented in this type of materials of 26.6–343.64 mg/g, a value comparable to that obtained in the present work with nDCPD [7, 15, 32–35]. From the results obtained, it can be inferred that brushite is a material with good characteristics for the removal of metals from wastewater; it could also be observed

*Adjustment of the experimental data of Cu adsorption using the different models of isotherms at different* 

that nDCPD favors the adsorption of Cu over Co and Ni.

*DOI: http://dx.doi.org/10.5772/intechopen.86803*

**Figure 1.**

**Figure 2.**

*temperatures.*

*temperatures.*

*The Use of Industrial Waste for the Bioremediation of Water Used in Industrial Processes DOI: http://dx.doi.org/10.5772/intechopen.86803*

#### **Figure 1.**

*Water Chemistry*

*B (kJ/mol).*

**Table 1.**

**3. Results and discussion**

*Nonlinear adsorption isotherm models [40, 41].*

**3.1 Adsorption isotherms**

the coefficient of determination, R2

Adsorption data obtained at different temperatures help to understand the interaction between nDCPD and Ni, Co, and Cu ions; analyzing the data with different adsorption models, the model with better fit is obtained. In **Table 1**, the most used isotherm models are described according to the literature, and in **Figures 1**–**3** for Ni, Co, and Cu, respectively, the behavior of the removal of metal ions at different temperatures is shown. The parameters derived from the adjustments together with

*KL (L/mg), qm (mg/g), RL (dimensionless); Freundlich: KF [(mg/g)(L/mg)]1/n, n (dimensionless); Temkin: A (L/mg),* 

**Model Equation** SIPS *qe* <sup>=</sup> *qm* (*KsCe*)

Redlich-Peterson (R-P) *qe* <sup>=</sup> \_\_\_\_\_\_ *KRCe*

Langmuir *qe* = \_\_\_\_\_\_\_

Temkin *qe* = *A* + *Bln*(*Ce*) Freundlich *qe* = *KFCe*

*SIPS: KS (L/mg), qm (mg/g), nS (dimensionless); Redlich-Peterson: KR (L/g), aR (L/mg)<sup>β</sup>*

respectively, using the SigmaPlot software (®Version 11) at a temperature of 15, 30, and 45°C. Based on the results obtained, it is observed that the most appropriate models to adjust the adsorption in nDCPD of Ni metal ions, in the three temperatures analyzed (**Figure 1** and **Table 2**), are SIPS, Redlich-Peterson, and Langmuir and Freundlich, suggesting that Ni ions are adsorbed on the surface of nDCPD causing the formation of a monolayer and that the adsorption process is physical. On the other hand, the results obtained in the removal of Co ions (**Figure 2** and **Table 3**), show that the models with the best fit of the data are SIPS, Redlich-Peterson and Langmuir in the three temperatures analyzed, which implies that the cobalt ions are adsorbed on the surface of nDCPD, in a physical process independent of temperature. Finally, in the removal of Cu ions (**Figure 3** and **Table 4**), only an appropriate fit was obtained with the SIPS model, which suggests that the removal of copper ions in equilibrium is carried out by a physisorption process on the surface of the adsorbent. The obtained results also show that the removal of all the ions analyzed using nDCPD is favored given that the *RL* values are between 0 and 1, which indicates that the adsorption is favorable; this tendency can be seen independently of the temperature used. The results of metal ion removal obtained in the present study using nDCPD are comparable with those obtained using other agroindustrial residues, since for Ni, removals between 6.88 and 120 mg/g have been obtained, while the value obtained in this work was of 22.48 mg/g. In the case of Co, a removal range of 2.55–45.44 mg/g has been reported, and in our case a value of 41.81 mg/g was obtained, finally, for Cu, removal values have been reported in the range of 0.98–163.01 mg/g, while in the present study a value of 41.88 mg/g of adsorbent was obtained [3–5, 13, 20–23, 26]. On the other hand, when comparing the results obtained with those reported by other authors who also used hydroxyapatites and brushite as adsorbent material, it was observed that the

, are shown in **Tables 2–4**, for Ni, Co, and Cu,

*ns* \_\_\_\_\_\_\_\_\_ 1 + (*KsCe*) *ns*

> 1 + *aRCe* β

*qm KLCe* 1 + *KLCe*

1 ⁄*n*

*, β (dimensionless); Langmuir:* 

**96**

*Adjustment of the experimental data of Ni adsorption using the different models of isotherms at different temperatures.*

#### **Figure 2.**

*Adjustment of the experimental data of Co adsorption using the different models of isotherms at different temperatures.*

#### **Figure 3.**

*Adjustment of the experimental data of Cu adsorption using the different models of isotherms at different temperatures.*

model that was best adjusted was that of Langmuir, with a capacity of Ni adsorption reported between 9.9 and 40.0 mg/g, these data are comparable with those obtained in the present work. In the case of Co, an adsorption with apatites of 8.8–20 mg/g has been reported, a value lower than that obtained with natural nDCPD obtained in the present study, which is 41.8 mg/g. Finally, in the case of Cu ions, a range of adsorption has been documented in this type of materials of 26.6–343.64 mg/g, a value comparable to that obtained in the present work with nDCPD [7, 15, 32–35]. From the results obtained, it can be inferred that brushite is a material with good characteristics for the removal of metals from wastewater; it could also be observed that nDCPD favors the adsorption of Cu over Co and Ni.


#### **Table 2.**

*Equilibrium parameters of adsorption models at different temperatures for Ni ions.*

#### **3.2 Effect of temperature on the removal of metal ions**

In the literature it has been widely reported that one of the most important variables in the process of solid-liquid removal is temperature, since it directly influences some thermodynamic parameters (**Table 5**) of great interest in the removal process. The negative values of Δ*G* indicate that the removal processes of the metal ions of the aqueous solutions are carried out spontaneously; the increase of the value in the negative scale parallel to the increase of the temperature shows the direct dependence with this variable. The positive value of the Δ*S* indicates that the sites of the solid-liquid interface during the uptake of metal ions increase due to the randomness in the adsorbent [4, 5, 13, 34, 37], while the positive value of Δ*H* reveals that the process has an endothermic nature, which will influence the increase in ion removal as the temperature increases, which makes the process feasible and spontaneous at temperatures above room temperature [27, 36, 37]. Several reports indicate that the metal adsorption process in brushite is spontaneous; however, some authors indicate that the heat of adsorption in this process is negative, therefore, as the temperature increases, the removal capacity decreases.

**99**

*The Use of Industrial Waste for the Bioremediation of Water Used in Industrial Processes*

*KS* 0.0470 0.0208 0.0117 *qm* 23.8607 30.1446 41.8104 *nS* 1.1294 0.8178 0.9105 R2 0.9895 0.9958 0.9895

*KR* 0.1884 0.4259 0.3462 *aR* 0.0073 0.0326 0.0089 β 1.0 0.8886 1.0 R2 0.9980 0.9953 0.9891

*KL* 0.0073 0.0089 0.0124 *qm* 25.6863 26.5263 39.0000 R2 0.9980 0.9933 0.9891 *RL* 0.121–0.578 0.101–0.529 0.075–0.447

*KF* 1.3457 2.2983 2.1685 *n* 2.2770 2.6411 2.2291 R2 0.9723 0.9773 0.9753

*A* 2.0398 × 10<sup>−</sup><sup>8</sup> 1.8935 × 10<sup>−</sup><sup>8</sup> 4.696 × 10<sup>−</sup><sup>8</sup> *B* 2.8230 3.3781 −6.3526 × 10<sup>−</sup><sup>6</sup> R2 0.8390 0.9084 0.4984

**15°C 30°C 45°C**

**Models Parameters**

[4, 5, 13], However, other authors agree with that found in this work, where the heat of adsorption is positive and, as the temperature of the process increases, the

In the process of solid-liquid adsorption, it is convenient to know the necessary contact time between the adsorbent and the adsorbate to achieve a maximum interaction between both and get removed as much metal ions as possible. **Figures 4**–**6** show the adsorption curves of each metal ion, where it is observed that about 10 h after the start of the process, the adsorption speed is high and that after this time the rate of removal of the ions. It decays, probably, because the sites where the capture of the ions is carried out are saturated, and therefore the balance is reached regardless of the concentration of absorber that has been used. This type of behavior is common among various adsorbent materials [37]. Also, it is observed that the adsorption capacity of the adsorbent material decreases significantly with the

adsorption of the ions in the material increases [32].

*Equilibrium parameters of adsorption models at different temperatures for Co ions.*

**3.3 Effect of contact time and amount of adsorbent**

*DOI: http://dx.doi.org/10.5772/intechopen.86803*

**SIPS**

**Redlich-Peterson**

**Langmuir**

**Freundlich**

*RL* **Temkin**

**Table 3.**


#### *The Use of Industrial Waste for the Bioremediation of Water Used in Industrial Processes DOI: http://dx.doi.org/10.5772/intechopen.86803*

**Table 3.**

*Water Chemistry*

**SIPS**

**Redlich-Peterson**

**Langmuir**

**Freundlich**

**Temkin**

**Table 2.**

**98**

**3.2 Effect of temperature on the removal of metal ions**

*Equilibrium parameters of adsorption models at different temperatures for Ni ions.*

**Models Parameters**

*KS* 0.005 0.016 0.0020 *qm* 18.2426 20.6152 22.4789 *nS* 1.1611 0.8644 1.3671 R2 0.9969 0.9985 0.9974

*KR* 0.0191 0.2423 0.2024 *aR* 0.007 0.0240 0.0078 β 1.0 0.9046 1.0 R2 0.9943 0.9990 0.9913

*KL* 0.0007 0.0078 0.0105 *qm* 27.7198 18.9551 25.9445 R2 0.9962 0.9975 0.9913 *RL* 0.588–0.935 0.114–0.562 0.087–0.488

*KF* 0.0552 1.6384 1.5515 *n* 1.2921 2.7263 2.3854 R2 0.9923 0.9869 0.9980

*A* 1.873 × 10<sup>−</sup><sup>8</sup> 2.683 × 10<sup>−</sup><sup>8</sup> 2.3779 × 10<sup>−</sup><sup>10</sup> *B* 1.0213 2.3617 2.8940 R2 0.6402 0.9078 0.8337

**15°C 30°C 45°C**

In the literature it has been widely reported that one of the most important variables in the process of solid-liquid removal is temperature, since it directly influences some thermodynamic parameters (**Table 5**) of great interest in the removal process. The negative values of Δ*G* indicate that the removal processes of the metal ions of the aqueous solutions are carried out spontaneously; the increase of the value in the negative scale parallel to the increase of the temperature shows the direct dependence with this variable. The positive value of the Δ*S* indicates that the sites of the solid-liquid interface during the uptake of metal ions increase due to the randomness in the adsorbent [4, 5, 13, 34, 37], while the positive value of Δ*H* reveals that the process has an endothermic nature, which will influence the increase in ion removal as the temperature increases, which makes the process feasible and spontaneous at temperatures above room temperature [27, 36, 37]. Several reports indicate that the metal adsorption process in brushite is spontaneous; however, some authors indicate that the heat of adsorption in this process is negative, therefore, as the temperature increases, the removal capacity decreases.

*Equilibrium parameters of adsorption models at different temperatures for Co ions.*

[4, 5, 13], However, other authors agree with that found in this work, where the heat of adsorption is positive and, as the temperature of the process increases, the adsorption of the ions in the material increases [32].
