摘要
选择Mg2+为掺杂离子,通过溶胶-凝胶法制备了不同比例的镁-钙羟基磷灰石吸附剂,研究其对水溶液中Pb~(2+)的去除特性和过程机制.结果表明,吸附剂表面以羟基磷铅矿化合物[Pb10(PO4)6(OH)2]为主,其晶体结构由短棒状转变为针状结构;在温度25℃,p H为5时,镁-钙羟基磷灰石吸附Pb~(2+)在720 min内达到平衡,吸附剂的最佳投加量为0. 6 g·L-1,最大吸附量为813. 17 mg·g-1;热力学实验结果:ΔGθ<0、ΔSθ> 0和ΔHθ> 0,表明镁-钙羟基磷灰石吸附Pb~(2+)的过程是自发的吸热、熵增的过程,升温有利于吸附;吸附过程符合伪二级动力学方程,Langmuir吸附模型能更好地描述等温吸附行为;材料表征与吸附实验分析表明,表面络合与溶解-沉淀是镁-钙羟基磷灰石去除Pb~(2+)的主要机制.
A novel magnesium-calcium hydroxyapatite adsorbent was prepared by the Sol-gel method with different proportions of Mg/( Ca + Mg) using Mg2 +as doped ions,and the removal characteristics and process mechanism of Pb~(2+)on the magnesium-calcium hydroxyapatite in an aqueous solutions were studied. The results show that the surface of the adsorbent is composed mainly of a hydroxyphosphonite compound [Pb10( PO4)6( OH)2],The morphological characteristics of the magnesium-calcium hydroxyapatite adsorbent surface was investigated as crystal structure changes from short rods to needle structures according to scanning electron microscopy( SEM). Testing at a temperature of 25℃ and p H of 5 showed that the adsorption of Pb~(2+)by magnesium-calcium hydroxyapatite reached equilibrium within 720 min. The adsorption capacity was determined to be 813. 17 mg·g-1 at a dosage of 0. 6 g·L-1. The thermodynamic test results of ΔGθ< 0,ΔSθ> 0,and ΔHθ> 0 indicated that the adsorption process of Pb~(2+)by magnesiumcalcium hydroxyapatite is a spontaneous process with endothermic reaction and entropy increments,and higher temperatures were considered be favorable for adsorption at a range of 25-45℃. The adsorption could be effectively described by a pseudo-second-order kinetic equation. The equilibrium data were found to follow the Langmuir adsorption model. Material characterization and adsorption tests showed that surface complexation and dissolution-precipitation were the main mechanisms for the removal of Pb~(2+)by magnesiumcalcium hydroxyapatite in an aqueous solution.
引文
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