Preparation Of Arsenic Hydroxyapatite And Its Arsenic Toxicity Leaching

Arsenic and its compounds are a class of chemical substances having high toxic ity and carcinogenicity. They are very harmful to the environment and threaten human survival and development. With the rapid development of the high arsenic industries （such as mining, metallurgy, chemical industry et）, arsenic contamination control has become a hot global research. A great deal of effort have been done, but most have little effects, cause high leaching of As or have lower stability, so we desperately need a workable method to solve the problem. Because As0₄^3- are sinilar to PO₄^3-, so the more stable arsenate-phosphate solid solutions are often formed. The insolubility of inorganic arsenic compounds can be used to remove the arsenic, which will become the most promising technique for the treatment of the arsenic.In this paper, arsenate-substituted hydroxyapatite （As-HA） and arsenate-silicon-substituted hydroxyapatite （As-Si-HA） were synthesized successfully by hydrothermal method. The main factors influencing the process of synthetic was discussed to obtain the best solution. At the same time, the stability of solid solution was discussed by leaching toxicity method, in which leaching concentration of As was measured in a regular time. The main results are as follows:1. A series of arsenate-substituted hydroxyapatite and a series of arsenate-silicon-substituted hydroxyapatite were prepared by hydrothermal method using Ca（NO₃）₂·4H₂O, （NH₄）₂HPO₄, Na₃AsO₄·12H₂O and Si（OCH-2CH₃）₄ as reagents. Through discussion, the best solution were obtained: the reaction temperature was 200 ℃, the reaction time was 8h and the content of Si was y=1[Caio（PO₄）_6-x-y（AsO₄）x（SiO₄）y（OH）_2-y].2. X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Fourier transform infrared spectroscopy （FTER） were used to characterize the crystalline phase, chemical composition and surface morphology of the arsenate-substituted hydroxyapatite. The results showed that the solid solution of As-HA was irregular block, the crystal structure of As-HA was similar to the crystal structure of HA, other structures were not be found in the solid solution. Arsenic was incorporated in HA lattice by partially replacing phosphate groups ( PO₄^3-)with arsenic groups (As0₄^3-),the maximum content of As was 27.720%.3. X-ray diffraction （XRD）, Scanning electron microscopy （SEM） and Fourier transform infrared spectroscopy （FTIR） were used to characterize the crystalline phase, chemical composition and surface morphology of the arsenate-silicon-substituted hydroxyapatite. The results showed that the solid solution of As-Si-HA was irregular block, the crystal structure of As-Si-HA was similar to the crystal structure of HA, other structures were not be found in the solid solution. Arsenic was incorporated in HA lattice by partially replacing phosphate groups( PO₄^3-) with arsenic groups (As0₄^3-).The substitution of phosphate groups by silicate groups caused some OH- loss to maintain the charge balance, which brought a obvious decrease in crystallinity.The maximum content of As was 19.928%（y=1）.4. The leaching concentration of As was influenced by pH. In acidic conditions, the leaching concentration of As was the highest and in neutral condition, the teaching concentration of As was the lowest, which proved that solid solution had more stability in neutral condition.5. In solution, As-Si-HA showed lower leaching concentration of As than As-HA, which proved that arsenate-silicon-substituted hydroxyapatite is more stable than arsenate-substituted hydroxyapatite.6. The leaching rate of arsenate solid solution is relatively lower than other materials containing arsenic, which proved that solid solution had stable crystal structure and arsenic can be embedded into crystal lattice of HA by a effective method.7. The crystalline phase, chemical composition and surface morphology of the solid samples before and after dissolution were analysised by XRD、SEM and FTIR, the results showed that the solid solution had no change.