This contribution is a comparison study between synthetic hydroxyapatite (Sy-HAP) and commercial hydroxyapatite (C-HAP) for the removal of Pb²⁺ and Cd²⁺ ions present in wastewater from industrial effluents. The obtained results show that the equilibrium time required for complete adsorption of Pb²⁺ and Cd²⁺ ions on C-HAP and Sy-HAP is 15 min for both. The obtained removal efficiencies for Sy-HAP are 95.52% and 90.91% for Pb²⁺ and Cd²⁺ ions, respectively. Whereas, C-Hap presents lower removal efficiencies of 86.53% and 81.43% for Pb²⁺ and Cd²⁺ ions, respectively Maximum adsorption was observed at pH 5, at lower pH levels adsorption was less. The experimental kinetic data fitted with the second order kinetic model. Thermodynamically, the adsorption process was endothermic and spontaneous in nature. Isotherm adsorption studies indicated that Langmuir, Freundlich and Temkin, are the most valid models to describe and evaluate the adsorption process. The EDX results also confirmed the presence of lead and cadmium in adsorbents after adsorption. Finally, the HAP porous materials possess a great potential for the removal of Pb²⁺ and Cd²⁺ ions from aqueous solutions and wastewater from industrial effluents.

In this study, low-cost biomaterial hydroxyapatite (N-Hap) prepared from bovine bones was tested for its potential to sorb copper Cu²⁺ and Fe³⁺ from aqueous solution and was compared with commercial hydroxyapatite (C-Hap). The structural characterization of N-Hap and C-Hap were carried out by Fourier transform infrared (FTIR) analysis, textural analysis (BET), morphology, and elemental analysis via scanning electron microscopy (SEM-EDX). The results obtained show that SEM images confirmed the formation of porous N-Hap with various morphologies and the average particle size ranges from 50 to 100 nm and the CaP ratio is 1.657. The presence of functional groups on N-Hap surface was confirmed by FTIR analysis. The specific surface areas of N-Hap and C-Hap are found to be 46.87 and 40.98 m²/g, respectively. Adsorption of two metals Cu²⁺ and Fe³⁺ was fast, with equilibrium attained within 30 min. Copper ions exhibited the greatest adsorption on both adsorbents because of their size and pH conditions. Metallic ion removal efficiency was favored at a slightly acidic solution pH and low temperature. The equilibrium and kinetic data were found to fit well the Langmuir model and the pseudo second order model with intraparticle diffusion. Thermodynamic parameters (ΔH_ads < 0 and ΔG_ads < 0) involved the exothermic, spontaneous, and physical adsorption process. The adsorption interaction of Cu²⁺ and Fe³⁺ with Hap surface was investigated by theoretical density functional theory (DFT) calculations. Therefore, the porous hydroxyapatite N-Hap displays potential as a new biocompatible adsorbent, and its use seems to be an interesting solution for the treatment of industrial wastewater.

The treatment of used vegetable oil (UVO) with seven different adsorbents and through two different procedures (stirring and gravity filtration) was explored. Important differences in terms of density, turbidity, electrical resistance, free fatty acids (FFAs) content and relative fatty acid distribution were observed. Different outcomes were shown depending both on the adsorbent and on the procedure. Lower values of density and FFAs were registered for oils treated by gravity filtration with portland (respectively 0.6% and 0.81 g/ml) and celite (respectively 0.7% and 0.72 g/ml). Considering the undesired leaching from the powder to the oil, related to the turbidity, the celite resulted more suitable for the oil recycling (241 Nephelometric Turbidity Unit (NTU) for portland vs 184 NTU for celite). In addition, Fourier-transform infrared spectroscopy combined with multivariate analysis allowed to determine a chemical fingerprint relative characteristic of vegetable oils recycled by gravity or by adsorption by stirring.

The treatment of used vegetable oils (UVOs) with clays represents a pivotal step in their industrial recycling process as well as one of the most challenging topics for researchers. In particular, cheap, effective, and sustainable powders need to be explored in order to develop new processes which produce beneficial results in relation to economic and environmental aspects. In this context, five samples within commercial and waste vegetable oils were treated with two sodium- and calcium-based bentonites employing a low oil/bentonite ratio (0.15 wt%). The outcomes of the processes were monitored by FT-IR spectroscopy and compared with the data relative to the parent commercial edible oil. In particular, treatment of FT-IR data by multivariate statistical analysis allowed us to determine a chemical fingerprint characteristic of each sample. Important relationships between the overall chemical composition and the specific clay employed and the treatment time (2 or 4 h) were highlighted. Finally, N₂ physisorption, TEM microscopy, and FT-IR analyses of the more efficient Na bentonite allowed us to characterize the material and thus to furnish all the information needed to set-up a general protocol for the partial regeneration of waste vegetable oil destined for further processing.