Study On The Controllable Preparation Of Hydroxyapatite Microspheres And Their Adsorption Properties For Pb²⁺

As the industrialization process accelerating ceaselessly,lead pollution has penetrated into all aspects of our life.Lead containing wastewater would harm to the human beings' health if it is discharged without effective treatment.Hydroxyapatite?HAP?is a new adsorbent which has high adsorption efficiency or Pb²⁺,and it can be applied into the removal of Pb²⁺ from lead containing wastewater.In this dissertation,CaCO₃ microspheres were synthesized via the precipitation method,and then HAP microspheres were synthesized on the basis of the CaCO₃ microspheres with the help of hydrothermal treatment.After that,the adsorption properties of the HAP microspheres for Pb²⁺ were also studied.And the obtained main results are as follows:Firstly,the CaCO₃ microspheres have been synthesized from CaCl₂,Na₂CO₃ and water via the precipitation method without the addition of surfactant.These CaCO₃ microspheres were assembled by CaCO₃ nanoparticles,and the diameter of the CaCO₃ microspheres was about 3-5 ?m.The influences of the reactant concentration and reaction time on the formation of CaCO₃ microspheres were studied,and the optimal experimental conditions for the synthesis of CaCO₃ microspheres are as follows: CaCl₂ concentration of 0.3 mol/L,Na₂CO₃ concentration of 0.3 mol/L,reaction temperature of 25?,and reaction time of 30 min.Then,the HAP microspheres have been synthesized successfully from the obtained CaCO₃ microspheres,Na₂HPO₄·12H₂O and water with the help of hydrothermal treatment.These pompon-like HAP microspheres were composed of nanoplatelets,and the diameter of the microspheres was about 3-6 ?m.The influences of the Na₂HPO₄·12H₂O dosage,hydrothermal reaction temperature and hydrothermal reaction time on the formation of HAP microspheres were studied,and the optimal experimental conditions for the synthesis of HAP microspheres when the CaCO₃ microspheres dosage was 2.0 g and water dosage was 50 ml are as follows: Na₂HPO₄·12H₂O dosage of 0.024 mol,hydrothermal reaction temperature of 160? and hydrothermal reaction time of 60 h.The adsorption properties of the HAP microspheres for Pb²⁺ were studied,and the effects of the adsorption time,initial p H value,adsorption temperature and initial Pb²⁺ concentration on the adsorption of Pb²⁺ were also investigated.Results showed that the maximum removal rate was as high as 93.44% when the initial Pb²⁺ concentration was 200 mg/L and adsorbing material dosage was 1.0 g/L under the optimum conditions: the adsorption time of 1 h,initial pH value of 2.5,adsorption temperature of 30?.The adsorption process of Pb²⁺ onto the HAP microspheres was consistent with the Langmuir isothermal adsorption model,and the saturation adsorption capacity was 248.76 mg/g.The results reveal that these HAP microspheres have good adsorption performances and have potential as an adsorbent in the treatment of lead containing wastewater.