Four composites of hydroxyapatite/hydrolyzed polyacrylamide (HAP/HPAM-n) were prepared using an in situ wet chemical method. The synthesis was performed by preparing a suspension of calcium in a copolymer solution having a known HPAM concentration. Phosphoric acid was added dropwise to each suspension to obtain HAP/HPAM-n composites. The effect of initial copolymer amount on the composite properties was investigated using XRD, FTIR, TGA, and SEM/EDS analysis. The obtained results were compared to the HAP sample synthesized under the same conditions and without copolymer. HPAM amount in the composite affects the retention of methylene blue (MB) dye. The result shows that the increase of HPAM in the material leads to the increase of the dye retention capacity. Therefore, the composite prepared with a higher copolymer amount was selected to study the effects of different parameters on the dye removal including contact time, concentration, pH, temperature, and composite regenerations. We deduce in this work that the composite HAP/HPAM-75 is a good candidate for MB dye retention from aqueous solution with a maximum removal capacity of 435.6 mg g −1 and the possibility of its reuse for several times.
In this paper, a simple method was proposed to obtain hydroxyapatite (HA) and hydroxyapatite/partially hydrolysed polyacrylamide (HA/AD37) composite materials which where applied to lead retention from aqueous solution by means of the batch method. The characterization of the materials verified that the presence of AD37 created interconnected porosity in the composite HA/AD37 giving it a good swelling properties that conducted to an easy separation of the material from aqueous solutions. Retention experiments carried out by varying the dose of lead and the contact time between adsorbent and adsorbate showed that the maximum adsorption capacity (Qmax) obtained for 2072.2 mg/L as initial concentration of Pb2 + was equal to 984.63 mg/g for HA and 924.50 mg/g for HA/AD37. Furthermore, AD37 used alone cannot retain Pb2 + ions. Indeed, the calculated Qmax of AD37 part of the composite was of 806.57 mg/g. The obtained Qmax values was elevated more than the reported values in many literatures. Based on the correlation coefficient, the kinetic study proved that pseudo-second order model agrees well with the obtained experimental data for Pb2+ retention by both HA and HA/AD37. Also, isotherm study explored that adsorption of lead was best fitted by Langmuir model for HA and Temkin model for HA/AD37. At last, the mechanism of retention was probed by characterizing the adsorbents after contact with lead ions by XRD and SEM. The results showed the transformation of calcium-hydroxyapatite to different structures of lead hydroxyapatite confirming the presence of ion exchange mechanism between Ca2+ and Pb2+.
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