Hydroxyapatite was obtained by bone calcinations. To study the calcination process, bovine and porcine bones were first autoclaved to remove fat and other non-bone tissues. They were then heated in an alumina pan in an oxidizing atmosphere of air, where simultaneous thermal analysis curves were recorded. To prepare the hydroxyapatites, bone samples were calcined at 850 °C and 1000 °C using a muffle furnace for 1 h. The obtained materials were powdered using mortar and pestle, and sifted in a sieve (60 mesh) without any additional purification or chemical treatment. The materials obtained were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The antimicrobial properties of these materials were determined through direct contact tests against Staphylococcus aureus. The natural hydroxyapatites obtained by bone calcination inhibited S. aureus growth, with the material obtained by calcination of bovine bones at 1000 °C, showing the best antimicrobial activity. These results indicated that bone wastes can be used to obtain hydroxyapatites with antimicrobial activity.

Sodium smectite clays were enriched with ferric ions (Argel-Fe and Volclay-Fe) to convert the surface charge of the clays from negative to positive and to use the clays in the discolouration of a synthetic effluent composed of seven anionic dyes (mixed from tartrazine, Brilliant Blue FCF and amaranth). The iron content increased from 5.99% to 11.02% for Argel-Fe and from 5.39% to 10.54% for Volclay-Fe. The efficiency of the discolouration of the anion dye mixture was evaluated by measuring the absorbance of the mixture at 562 nm, where the band with the greatest intensity was found. The contact time required for the system to reach equilibrium was ~5 min for both adsorbents. The kinetic adsorption data supported a pseudo-second-order kinetic model. The experimental data support the dual-site Langmuir–Freundlich isotherm model. The maximum adsorption capacities were 88.68 mg g–1 for Argel-Fe and 392.21 mg g–1 for Volclay-Fe. The enrichment of clays with Fe(III) added functionality to the clays and generated adsorbents with rapid adsorption abilities and high discolouration capacities.

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Akaganéite is a very rare iron oxyhydroxide in nature. It can be obtained by many synthetic routes, but thermohydrolysis is the most common method reported in the literature. In this work, akaganéite-like materials were prepared through the thermohydrolysis of FeCl(3).6H(2)O in water and suspensions containing clay minerals. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) data show that the clays determine the crystal phase and size of the iron oxyhydroxide crystals. According to XRD and FTIR data, beta-FeO(OH) (akaganéite) is the main metal oxyhydroxide phase. Considering the small basal spacing (d(001)) displacement observed when comparing the XRD patterns of pristine clays with the composites containing beta-FeO(OH), the iron oxyhydroxide should be mostly located on the basal and edge surfaces of the clay minerals. UV-Vis electronic absorption spectra indicate that the preferred phase of the iron oxyhydroxide is determined by the nature of the clay minerals.

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