Alumina–Hydroxyapatite Millimetric Spheres for Cadmium(II) Removal in Aqueous Medium

Heavy metals can act as selective agents in the development and proliferation of antibiotic-resistant bacteria through a process called coselection. In the year 2050, an estimated 10 million deaths will be caused by antibiotic-resistant bacteria; therefore, the presence of heavy metals in bodies of water represents an environmental and sanitary threat that requires efficient treatment processes and/or materials for their removal. In the present study, the effect of the hydroxyapatite coating on the adsorbent capacity of cadmium in alumina spheres was evaluated. The hydroxyapatite coating on the alumina sphere increased the surface area from 0.66 to 0.96 m²/g and the number of acid sites from 0.064 to 0.306 meq/g and displaced the IEP of hydroxyapatite from 5.37 to 4.2, increasing the Cd²⁺ adsorbing capacity from 59.87 mg/g to 89.37 mg/g and promoting adsorption by surface complexation. Alumina-hydroxyapatite spheres stand out for their improved adsorbent properties and easy handling, which positioned this material as a potential alternative in adsorption processes.