Carbonate hydroxyapatite (CHAP) was synthesized from domestic hen egg shells. The obtained CHAP was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy and investigated as metal adsorption for Pb 2+ from aqueous solutions. The effect of various parameters on the adsorption process such as contact time, solution pH, and temperature was studied to optimize the conditions for maximum adsorption. The results showed that the removal efficiency of Pb 2+ by carbonate hydroxyapatite calcined at 600°C (CHAPF) reached 99.78 %, with an initial Pb 2+ concentration of 200 mg · L -1 , pH ) 3, and a solid/liquid ratio of 1 g · L -1 . The equilibrium removal process of lead ions by CHAPF foam at pH ) 3 was well described by the Langmuir isotherm model, with a maximum adsorption capacity of 500 mg · g -1 at (25 and 35)°C. The removal mechanism of Pb 2+ by the CHAPF varies, depending on the initial concentration of lead in the aqueous solution: the dissolution of CHAPF and precipitation of hydropyromorphite (Pb 10 (PO 4 ) 6 (OH) 2 ) is dominant at low concentration [(20 to 200) mg · L -1 ], and the adsorption mechanism of Pb 2+ on the CHAPF surface and ion exchange reaction between Ca 2+ of hydroxyapatite and Pb 2+ in aqueous solution is dominant at high concentration [(500 to 700) mg · L -1 ]. The thermodynamics of the immobilization process indicates an exothermic sorption process of Pb 2+ .

No abstract

Pure and doped hydroxyapatite (HA) nanocrystalline powders (Ca10‐xMgx(PO4)6OH2) were synthesized using sol‐gel process. For this, calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and phosphorous pentoxide were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg+2) especially from 0 to 10% (molar ratio) were incorporated as dopant into the calcium sol solution. The structure and morphology of the gels obtained after mixing the phosphorous and (calcium + magnesium) sol solution were different, and their condensations in time depend on the quantities of magnesium added. The several powders resulting from the gels dried and sintered at 500°C for 1 h were characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and inductively coupled plasma (ICP). Additionally, their agglomeration, morphology, and particle size were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area of each sample was measured by the Brunauer–Emmett–Teller (BET) gas adsorption technique. The results of XRD, FTIR, and ICP values ranged between 0.45 and 2.11 mg/L indicated that the magnesium added in the calcium solution was incorporated in the lattice structure of HA so prepared, while those obtained by SEM and TEM confirmed the influence of Mg on their morphology (needle and irregular shape) and crystallite size, which is about 30–60 nm. The as‐prepared powders had a specific surface area ranged between 6.37 and 27.60 m2/g.

No abstract

We report the synthesis of hydroxyapatite (HAP) powder from waste mussel shells (decomposed to CaO) and phosphoric acid at room temperature without pH control. The powder synthesized was utilized for cadmium removal from aqueous solutions using the batch technique. The effects of solution pH, adsorbent dose; initial Cd2+ concentration, contact time, and temperatures were examined. Furthermore, the adsorption process revealed a pseudo-second-order reaction model and the Langmuir isotherm is the best-fit model to predict the experimental data and adsorption capacity was found to be 62.5 mg/g. Thermodynamic analysis revealed that because of the negative values of ΔGo and the positive value of ΔHo, the adsorption process was spontaneous and endothermic. Cadmium immobilization occurs through a two step mechanism: rapid ion exchange followed by partial dissolution of hydroxapatite and precipitation of cadmium containing hydroxyapatite.