羟基磷灰石除氟滤料的吸附平衡及动力学
Study on equilibrium and kinetics of hydroxyapatite fluoride removal filter
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摘要: 羟基磷灰石（HAP）是一种高容量、环保型饮用水除氟材料。以氢氧化钙和磷酸为原料采用沉淀法合成了羟基磷灰石，并用红外光谱和XRD图谱进行了表征。研究了接触时间、pH值和温度等因素对羟基磷灰石吸附氟性能的影响。通过对吸附过程中的热力学动力学参数的计算来判断吸附的实质过程。研究结果表明，60 min以内吸附速率较快，在约70 min时吸附过程趋于平衡；酸性环境中的吸附效果要比在碱性环境中要好；升高温度有利于吸附的进行。吸附过程更符合Langmuir吸附模型，说明化学吸附占主导地位；吸附过程是一个自发的吸热过程，其中ΔGoΔHo为13.10 kJ/mol，Ea为15.24 kJ/mol，ΔSo为31.42 J/（mol?K）；吸附过程符合拟二级动力学模型。Abstract: Hydroxyapatite (HAP) is a new kind of defluoridation material with high capacity and friendly to the environment. HAP was synthesized by chemical precipitation method using calcium hydroxide and phosphoric acid as raw materials. The products were characterized by FTIR and XRD. The effects of contact time， pH， temperature and other factors on fluoride removal performance were explored. And thermodynamics and kinetics parameters were calculated to understand the nature of the adsorption processes. The results show that the adsorption rate is much rapid within 60 mins， the adsorption process approaches to equilibrium at about 70 mins. The adsorption results in acidic environment are better than those in an alkaline environment； and high temperature is conducive to adsorption. The adsorption process is more accord with Langmuir adsorption model， which indicates that chemical adsorption is dominant. Adsorption process is a spontaneous endothermic process， in which ΔGo is less than zero， and ΔHo is 13.10 kJ/mol， and ΔSo is 31.42 J/(mol?K) and Ea is 15.24 kJ/mol. Kinetic experiments show that the adsorption process is in line with pseudo second dynamic model.
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Key words:
- defluoridation /
- HAP /
- adsorption thermodynamics /
- adsorption kinetics
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