Low-cost composites based on porous titania-apatite surfaces for the removal of patent blue V from water: Effect of chemical structure of dye.

Hydroxyapatite/titania nanocomposites (TiHAp) were synthesized from a mixture of a titanium alkoxide solution and dissolution products of a Moroccan natural phosphate. The simultaneous gelation and precipitation processes occurring at room temperature led to the formation of TiHAp nanocomposites. X-ray diffraction results indicated that hydroxyapatite and anatase (TiO2) were the major crystalline phases. The specific surface area of the nanocomposites increased with the TiO2 content. Resulting TiHAp powders were assessed for the removal of the patent blue V dye from water. Kinetic experiments suggested that a sequence of adsorption and photodegradation is responsible for discoloration of dye solutions. These results suggest that such hydroxyapatite/titania nanocomposites constitute attractive low-cost materials for the removal of dyes from industrial textile effluent.

Parameters influencing ciprofloxacin, ofloxacin, amoxicillin and sulfamethoxazole retention by natural and converted calcium phosphates.

The retention of four antibiotics, ciprofloxacin, ofloxacin, amoxicillin and sulfamethoxazole by a natural phosphate rock (francolite) was studied and compared with a converted hydroxyapatite powder. The maximum sorption capacities were found to correlate with the molecular weight of the molecules. The mechanisms of sorption depended mostly on the charge of the antibiotic whereas the kinetics of the process was sensitive to their hydrophobic/hydrophilic character. The two materials showed slightly distinct affinities for the various antibiotics but exhibited similar maximum sorption capacities despite different specific surface areas. This was mainly attributed to the more pronounced hydrophobic character of the francolite phase constituting the natural phosphate. These data enlighten that the retention properties of these mineral phases depend on a complex interplay between the inter-molecular and molecule-solid interactions. These findings are relevant to understand better the contribution of calcium phosphates in the fate and retention of antibiotics in soils.

Lead and zinc removal from aqueous solutions by aminotriphosphonate-modified converted natural phosphates.

Apatite particles prepared from natural phosphate rock and grafted with nitrilotris(methylene)triphosphonate (NTP) were evaluated for Pb2+ and Zn2+ sorption from aqueous solutions. Sorption capacities as high as 640 mg.g-1 and 300 mg.g-1 could be obtained for the highest organic content (10 wt%). Analysis of the sorption isotherms using Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich models revealed that Pb2+ ions have a larger affinity for apatite (sorption energy ≈ 8 kJ.mol-1) than for NTP so that organo-modified surfaces led to a heterogenous adsorption process. In contrast, Zn2+ interacts weakly (sorption energy ≈ 1 kJ.mol-1) and similarly with the mineral surface and the organic moieties following a homogenous sorption process. Such an association of organic metal ligands with reactive apatite surfaces within porous materials appears as a promising strategy to obtain efficient adsorbents at low cost and limited environmental impact.

Pyridine and phenol removal using natural and synthetic apatites as low cost sorbents: influence of porosity and surface interactions.

A natural phosphate rock and two synthetic mesoporous hydroxyapatites were evaluated for the removal of pyridine and phenol from aqueous solutions. Experiments performed by the batch method showed that the sorption process occurs by a first order reaction for both pyridine and phenol. In contrast, the Freundlich model was able to describe sorption isotherms for phenol but not for pyridine. In parallel, the three apatites exhibit similar pyridine sorption capacities whereas phenol loading was in agreement with their respective specific surface area. This was attributed to the strong interaction arising between pyridine and apatite surface that hinders further inter-particular diffusion. This study suggests that, despite its low specific surface area, natural phosphate rock may be used as an efficient sorbent material for specific organic pollutants, with comparable efficiency and lower processing costs than some activated carbons.

Adsorption of phenol from an aqueous solution by selected apatite adsorbents: kinetic process and impact of the surface properties.

Batch adsorption experiments were conducted to investigate the removal of phenol from wastewater by addition of three apatites (porous hydroxyapatite (PHAp) and crystalline hydroxyl- (HAp) and fluoroapatite (FAp)). The best performances were obtained with porous hydroxyapatite PHAp, which presented higher adsorption capacities (experimental: 8.2mgg(-1); calculated 9.2mgg(-1)) than HAp and FAp (3-4mgg(-1)). Different models of adsorption were used to describe the kinetics data, to calculate corresponding rate constants and to predict the theoretical capacities of apatite surfaces for phenol adsorption. A mechanism of phenol adsorption associating chemisorption and physisorption processes is presented allowing the discussion of the variations in adsorption behavior between these materials in terms of specific surface area and chemical composition. These data suggest that apatites are promising materials for phenol sorption.

Retention of fluoride ions from aqueous solution using porous hydroxyapatite. Structure and conduction properties.

Synthetic porous calcium hydroxyapatite (noted p-HAp) treated with different fluoride concentrations at room temperature in the presence of carbonate, sodium chloride and phosphate-rich media was investigated. The fluoridation rate of the porous calcium hydroxyapatite was 89% using 1 mol/L [F(-)] solution compared with 30% for crystalline hydroxyapatite (c-HAp). The high specific surface area of p-HAp (235 m(2)g(-1)) compared with c-HAp sample (47 m(2)g(-1)) has an important effect on the removal of fluoride ions from aqueous solution, when p-HAp was treated with high fluoride concentration to produce calcium fluorohydroxyapatite materials. Fluoride adsorption on porous hydroxyapatites (p-HAp) modified their structural and conduction properties.