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自然界中过量的磷极易引发赤潮、水华等水体富营养化现象,给整个水生态系统带来安全隐患,如何高效降低水体磷浓度已经成为水污染防治的主要问题之一。吸附法除磷工艺由于其高效清洁、可回收磷、可重复利用、工艺简单等优点,具有广泛的应用前景[1]。黏土矿物(clay minerals)作为常见吸附剂,其独特的层间结构及离子附着现象使其通过离子交换、静电引力和配位作用拥有良好的吸附潜力[2-3],且具有无臭、无毒、比表面积大、化学稳定性高等优点[4-5]。中性条件下天然黏土矿物对离子的吸附能力由大到小分别为蒙脱石>伊利石>高岭石[6]。天然黏土矿物对磷的吸附容量不高,通常采用离子饱和、焙烧、铝铁等高价态阳离子负载方式进行预处理或改性,提高吸附剂的配位结合能力或扩大矿物层间距,更有利于离子吸附[6-7]。
目前,国内外大部分吸附除磷研究主要集中于正态磷酸盐(
${{\rm{H}}_{\rm{2}}}{\rm{PO}}_4^ - {\rm{, HPO}}_4^{2 - }{\rm{, PO}}_4^{3 - }$ )这一形态展开。但是,现实水体中水溶性磷酸盐包括正态磷酸盐和非正态磷酸盐(${{\rm{P}}_{\rm{2}}}{\rm{O}}_7^{{\rm{4 - }}}{\rm{, }}{{\rm{P}}_{\rm{3}}}{\rm{O}}_{10}^{{\rm{5 - }}}{\rm{, }}\left( {{\rm{P}}{{\rm{O}}_{\rm{3}}}} \right)_n^{n - }$ 等)。非正态磷酸盐由于较难水解或难以被传统方法测定等原因,虽广泛应用于肥料、水处理、食品、采矿、印染等行业,但在磷循环中的重要性往往被人们所忽略[8]。SUNDARESHWAR等[9]发现以焦磷酸盐为主的非正态磷酸盐在海岸湿地沉积物中含量已超过正态磷酸盐沉积物。因此,有效处理水体中的非正态磷酸盐同样是吸附除磷研究的重要内容之一。本研究以蒙脱石型黏土矿物为研究对象,利用焙烧、铝基改性、铁基改性等方式进行定向改性并开展了吸附除磷实验研究,采用吸附模型对批次动力学吸附实验、热力学吸附磷实验结果进行了拟合,分析了不同改性蒙脱石的除磷效果,探究了改性蒙脱石对正态磷酸盐和非正态磷酸盐单独存在及其混合体系下的吸附特性,以期为含磷废水吸附处理技术应用提供参考。
改性蒙脱石对正态磷酸盐和非正态磷酸盐混合体系的吸附特性
Adsorption behavior of mixture of orthophosphate and unortho phosphate by modified smectite
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摘要: 为研究吸附剂对正态磷酸盐、非正态磷酸盐的吸附特征,以及正态磷酸盐和非正态磷酸盐混合体系下的竞争吸附行为,制备出3种改性蒙脱石SWy-焙烧、SWy-Al、SWy-Fe,将其分别用于对不同形态的磷酸盐吸附实验中。结果表明,制备的3种改性蒙脱石对磷的吸附效果均有所提升。SWy-Fe的吸附效果最佳,对正态磷酸盐和非正态磷酸盐4 h吸附去除率分别提高了56.1%和55.3%,实验结果符合Ho拟二级吸附动力学方程。根据Langmuir吸附热力学方程,对正态磷酸盐和非正态磷酸盐的饱和吸附量分别为21.9 mg·g−1和18.8 mg·g−1。此外,在初始总磷浓度高于3.0 mg·L−1的条件下,正态磷酸盐和非正态磷酸盐混合体系中的非正态磷酸盐吸附量显著高于正态磷酸盐,二者单位平衡吸附量之比为2.9∶1.0。改性蒙脱石对正态磷酸盐和非正态磷酸盐的吸附结果均表现为吸附外部液膜扩散、表面吸附、颗粒内扩散等多种过程的综合作用,可交换阳离子Ca2+/Fe3+/Al3+的引入通过吸附络合作用提高了蒙脱石对磷酸盐的吸附能力。在初始总磷浓度高于3.0 mg·L−1的条件下,正态磷酸盐和非正态磷酸盐混合体系存在吸附竞争现象,这为实际处理含磷废水吸附技术的发展和应用提供了理论依据。Abstract: In order to study the adsorption characteristics of orthophosphate and unortho phosphate, and the competitive adsorption behavior under the mixture of orthophosphate and unortho phosphate, three kinds of modified smectite SWy-roasted, SWy-Al and SWy-Fe were prepared and were used to adsorb the different morphological phosphates. The experimental results showed that the phosphorus adsorption was improved by all the three kinds of modified smectite. SWy-Fe had the best performance on phosphorus adsorption, the removal rates of orthophosphate and unortho phosphate increased by 56.1% and 55.3% within 4 hours adsorption, respectively, which accords with the pseudo-second-order kinetic model. According to Langmuir adsorption thermodynamic equation, the saturated adsorption capacities toward orthophosphate and unorthophosphate by SWy-Fe were 21.9 mg·g−1 and 18.8 mg·g−1, respectively. In addition, when the initial total phosphorus concentration was higher than 3.0 mg·L−1 in the hybrid system of orthophosphate and unorthophosphate, the adsorption amount of unorthophosphate was significantly higher than that of orthophosphate, the ratio of their equilibrium adsorption amounts was 2.9∶1.0. The adsorption process of modified smectite on orthophosphate and unorthophosphate was determined as the comphrehesive functions of external liquid membrane diffusion, surface adsorption, and intraparticle diffusion. The introduction of adsorption and complexation by exchangeable cation Ca2+/Fe3+/Al3+ improved the adsorption capacity of smectite on phosphate. Under the condition of high initial total phosphorus concentration, the adsorption competition phenomenon existed in the hybrid system of orthophosphate and unorthophosphate, which can provide a theoretical basis for the development and application of adsorption technology treating the actual phosphorus-containing wastewater.
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Key words:
- modified smectite /
- orthophosphate /
- unortho phosphate /
- adsorption phosphorus
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表 1 不同改性蒙脱石对磷的吸附动力学的动力学参数
Table 1. Kinetic parameters for phosphorus adsorption by different modified smectite
磷酸盐形态 吸附剂 qe, Exp/(mg·g−1) 拟一级动力学模型 拟二级动力学模型 k1/min−1 qeq/(mg·g−1) R2 k2/(g·(mg·min)−1) qeq/(mg·g−1) R2 正态磷酸盐 SWy 3.44 0.023 3 2.43 0.98 0.049 0 3.55 0.99 SWy-离子饱和 4.90 0.017 4 3.99 0.97 0.012 0 5.12 0.99 SWy-焙烧 7.40 0.012 6 3.69 0.73 0.016 5 7.41 0.99 SWy-Al 8.84 0.022 4 6.21 0.87 0.010 7 9.20 0.99 SWy-Fe 9.39 0.015 3 7.31 0.97 0.005 6 9.83 0.99 非正态磷酸盐 SWy 4.14 0.011 2 1.98 0.67 0.020 4.20 0.99 SWy-离子饱和 3.95 0.020 2 1.79 0.74 0.037 2 4.06 0.99 SWy-焙烧 4.01 0.014 7 1.65 0.76 0.364 0 4.06 0.99 SWy-Al 6.14 0.016 2 2.80 0.78 0.029 5 6.21 0.99 SWy-Fe 9.40 0.047 0 9.50 0.89 0.068 0 10.30 0.99 -
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