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Effect of humic acid load hydroxyapatite on the adsorption of Cd²⁺ in wastewater

摘要：以硝酸钙、磷酸氢二铵和腐殖酸为原料，制备了腐殖酸负载羟基磷灰石（HA/HAP）复合吸附剂.同时，利用SEM、BET、FT-IR、XRD对复合吸附剂结构和形貌进行表征，研究了HA/HAP对废水中Cd²⁺的吸附工艺.结果表明，腐殖酸使羟基磷灰石孔容和孔径增大、比表面积减小，从而提高了羟基磷灰石的吸附性能.在pH=6、吸附剂投加量为800 mg、接触时间为180 min时吸附率最佳，为98.3%.HA/HAP对废水中Cd²⁺的吸附是自发的、吸热的、可持续的化学吸附，反应前120 min适合采用准一级动力学伴随着内扩散模型描述，后120 min适合采用准二级动力学伴随着内扩散模型描述，Dubinin-Radushkevich（D-R）等温线模型拟合的吸附数据在不同温度下效果最好（R²>0.98），吸附量分别为259.15、266.05和264.66 mg·g^-1.研究表明，静电吸附到腐殖酸活性位点后Cd²⁺主要以络合反应被吸附到羟基磷灰石的表面和两个羟基中间.

Abstract：The humic acid supported hydroxyapatite (HA/HAP) composite adsorbent was synthesized with calcium nitrate and diammonium phosphate and humic acid. The structure and morphology of the composite adsorbent were analyzed with scanning electron microscope(SEM), BET surface area(BET), Fourier Transform infrared spectroscopy(FTIR)and X-ray powder diffraction(XRD) to study the absorption mechanism for Cd²⁺. The results indicate that adsorption capacity of hydroxyapatite was improved since the volume and diameter of hydroxyapatite is enlarged by adding HA/HAP. The highest adsorption efficiency was 99.02%, under pH=6, 800 mg of adsorbent dosage, and 180 minutes of contact time. Meanwhile, the adsorption of Cd²⁺ is an spontaneous and endothermic process, of which the absorption process follows quasi-first order kinetics with internal diffusion in the first 120 minutes but follows the quasi-second order kinetics in the next 120 minutes. The dubinin-radushkevich isotherm model was employed for fitting this experiment data under different temperatures, with a high correlation coefficient (R²>0.98) and with adsorption capacities 259.15, 266.05 and 264.66 mg·g^-1, respectively. After reaching to the active site of humic acid, Cd²⁺ was mainly adsorbed to the surface of hydroxyapatite and the middle position of two hydroxyl groups by complexation reaction.