**Acknowledgements**

*Water Chemistry*

the stretching of P-O (H) in the HPO**−**<sup>2</sup>

and the peaks observed at 665 and 1651 cm**−**<sup>1</sup>

*Infrared spectrum of pure nCDPD doped with Ni, Co, and Cu.*

signals obtained at 3548, 3484, 3278, and 3166 cm**−**<sup>1</sup>

the water molecule in the apatite. Finally, a band at 2944 cm**−**<sup>1</sup>

1138, 1120, 1065, and 1004 cm**−**<sup>1</sup>

these signals are related to the PO3

1215 cm**−**<sup>1</sup>

**Figure 14.**

metals directly.

**4. Conclusion**

4. On the other hand, the signals found at

are related to the binding vibrations

are related to the extension of

was also observed,

are attributed to the stretching of the P-O link. At

**−**4 and OH groups, with which it can be inferred

the signal generated by the flexion of the O-H group plane is presented,

and physical vibrations of the water molecule. Additionally, a shoulder at 1725 cm**−**<sup>1</sup> was observed, which is related to the flexural stress of the water molecule, and the

directly related to the stretching of PO-H that occurs in HPO [1, 41, 42]. In the case of the nDCPD spectra with the different metal ions, it was observed that several peaks decrease in intensity or disappear as a result of the presence of Ni, Co, and Cu;

that the groups present on the surface of this apatite participate in the adsorption of

Based on the thermodynamic parameters obtained at different temperatures and concentrations of brushite (nDCPD), used as an adsorbent material in the removal of different heavy metals (Ni, Co, and Cu), from aqueous solutions, it can be concluded that the adsorption of heavy metals with nDCPD is feasible and that the adsorption capacity of nDCPD increases at a higher temperature. The percentages of removal achieved show that nDCPD has a higher affinity for adsorbing Cu and Co compared to Ni. From the data obtained from the adsorption isotherms, it can be inferred that the process of removing the metal ions in solution on the surface of nDCPD is carried out, forming a heterogeneous monolayer since the model that best fits to the data obtained in the SIPS is a combination of the Langmuir and Freundlich models. The experimental data obtained also show that there are different models to describe the kinetic process of adsorption, such as the pseudo-firstorder model, which suggests that only one surface site is needed for adsorption to take place, as well as the pseudo-second-order model which indicates that two sites are needed for each ion molecule and that each site requires different adsorption

**106**

The authors thank the Interdisciplinary Professional Unit of Engineering Campus Guanajuato of the IPN, the Center for Nanoscience and Nanotechnology (CNyN) of the UNAM, and the Colombian Polytechnic "Jaime Isaza Cadavid" for the infrastructure provided for the realization of this project and the Research and Postgraduate Secretary for the financial support for this work (SIP: 20170577) and to the BIOCATEM Network.
