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随着工业的发展,石油被广泛应用于各行各业,但其带来的环境污染问题不容忽视,尤其是泄漏等生产事故诱发的土壤污染,原位化学氧化 (ISCO) 是土壤有机污染快速去除的有效方法,因具有修复效能高、成本低及操作便利等优势,常用于石油烃污染土壤修复[1-6]。近年来高锰酸钾 (KMnO4) 对石油烃的ISCO被认为是H2O2、O3/H2O2或催化H2O2氧化的良好替代品,因为其易于处理、成本低、pH范围适应性强且氧化电位 (E0=1.51 V) 相对较高[7]。然而,传统的ISCO技术在修复过程中面临着一系列挑战,特别是氧化剂的有效浓度低,难以维持长效性的问题,这使得污染物容易出现浓度反弹。
为了解决这些问题,已有报道提出了利用微囊化技术制备可控缓释材料来替代传统反应试剂,两者的主要区别在于控释材料延长了反应试剂的释放时间,降低反应物的释放速率,即控释材料具有持续释放的特点[8-10]。目前,微胶囊技术在缓释氧化材料研发领域已经取得初步的进展[11-12]。例如,有研究通过离子交联反应,将过氧化钙封装在海藻酸钙聚合物中,形成过氧化钙的释氧凝珠,为环境中的好氧微生物提供氧源用于降解1,4二恶烷,释氧凝珠可以在较长的时间内 (7 d左右) 使环境中的溶解氧保持较高的水平,并在10 d内将污染物去除近96%[13]。KAMBHU等[14]通过使用石蜡包裹KMnO4,使用模具制备了柱状KMnO4缓释材料,通过埋入表层土壤的方式对土壤多环芳烃进行降解,但是需要定期挖出去除表面石蜡,并进行再次填埋。从目前关于场地修复缓释氧化材料的研发和应用方面来看,缓释和控释技术在越来越多的研究和修复方案中得到了应用[15-16]。这些技术能够有效控制修复活性物质的释放,减少修复药剂的非选择性消耗,并提高污染物的去除效率,有望解决污染场地原位修复的长期有效性差的问题[17-19]。然而,目前所研发的控释材料缓释时长普遍处于24 h之内[19-21],其氧化活性难以维持更久,这对低渗透地层非水相污染物的原位修复功能材料提出了更大挑战。因此,需要进一步研究和开发适用于土壤修复的缓释氧化材料包覆方法,在选择包覆材料时,需要考虑其渗透性和降解性,以确保修复活性物质能够有效释放到土壤中。
本研究以硬脂酸为壳材,采用油相分离法制备了包覆型KMnO4,并通过正交实验探究最佳制备条件和实验参数。通过水相缓释实验探究缓释氧化材料的释放动力学,并根据缓释曲线拟合缓释材料的释药模型,结合表征结果探究该材料的释放机理。设计制作土柱动态淋洗实验,探究缓释氧化材料在模拟土柱中的缓释作用及其对柴油烃污染土壤的修复效果,为其在实际修复中的应用提供理论依据。
包覆型缓释氧化剂的制备及其缓释性能评价
Preparation of coated slow-release oxidants and evaluation of their slow-release performance
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摘要: 在低渗层非水相液体污染物的原位化学氧化修复过程中,土壤有机质会消耗氧化剂,导致氧化剂的有效浓度难以长期维持,从而使污染物浓度容易反弹。为了解决该问题采用硬脂酸作为壳材,通过相分离法包覆高锰酸钾制备缓释氧化材料。结果表明,硬脂酸包覆型高锰酸钾 (PP@SA) 具有良好的缓释性能,可以持续缓释120 h以上。正交实验结果显示,当芯壳比为1∶3,超声时间为15 min,搅拌速度为300 r∙min−1,粒径为1.12~4.00 mm时缓释效果最佳。并且,随着PP@SA的粒径和硬脂酸用量的增大,MnO4-的缓释机制从Fickian扩散模式向骨架溶蚀和Fickian扩散混合释放机制转变,其中骨架溶蚀释放机制逐渐起主导作用。此外,土相缓释柱实验结果表明,PP@SA在淤泥质粘土和粉质粘土两种低渗土壤中可以保持高锰酸根离子的扩散浓度在0.25 g∙L−1以上的时间分别为7和9 d,其缓释寿命远超过原高锰酸钾。Abstract: During the in-situ chemical oxidation remediation process of low-permeability non-aqueous phase liquid, the consumption of oxidants by soil organic matter is inevitable. This makes it difficult to maintain the effective concentration of oxidants in the long term, and the concentration of pollutants is prone to rebound. This study managed to prepare sustained-release oxidation materials using the phase separation method, with stearic acid as the wall material and KMnO4 as the core material. Results showed that KMnO4 coated with stearic acid (PP@SA) had good sustained-release performance, which could last for more than 120 h. The orthogonal experimental results indicated that the optimal sustained-release lifespan was achieved when the core-shell ratio was 1∶3, ultrasound time was 15 min, stirring speed was 300 r∙min−1, and the particle size ranged from 1.12 to 4.00 mm. As the particle size of PP@SA and the amount of stearic acid increased, the sustained-release mechanism shifted from the Fickian diffusion to a mixed release mechanism involving both skeleton dissolution and Fickian diffusion. Moreover, in two low permeability soils, chalky clay and silty clay, PP@SA maintained a diffusion concentration of MnO4- above 0.25 g∙ L−1 for 7 and 9 d, respectively. Its sustained release lifetime was significantly longer than that of the original potassium permanganate.
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Key words:
- in-situ chemical oxidation /
- sustained-release /
- KMnO4 /
- low permeability soil
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表 1 正交实验方案设计 (因素) 及结果
Table 1. Design and results of orthogonal test program
序号 因素实验 A芯核比 B超声时间/min C搅拌速度/(r∙min−1) D粒径/mm 材料特征及缓释性能 包封率 5 d释放量 1 1-S 1∶1 5 150 <0.6 72.88%±3.2% 101.9% 2 1-M 1∶1 10 300 1.12~4 83.90%±2.00% 77.68% 3 1-L 1∶1 15 450 0.6~1.12 72.37%±8.60% 91.78% 4 2-S 1∶2 15 300 <0.6 58.91%±2.09% 74.23% 5 2-M 1∶2 10 150 0.6~1.12 73.89%±1.29% 68.84% 6 2-L 1∶2 5 450 1.12~4 45.45%±2.25% 82.70% 7 3-S 1∶3 5 300 0.6~1.12 43.60%±6.85% 52.75% 8 3-M 1∶3 10 450 <0.6 69.32%±3.25% 73.78% 9 3-L 1∶3 15 150 1.12~4 67.79%±6.33% 52.84% 表 2 正交试验结果极差分析
Table 2. Analysis of extreme differences of orthogonal test results
K 包封率指标 释放量指标 A B C D A B C D K1j 229.2 161. 3 214.6 201.1 271.3 237.2 223.5 249.8 K2j 178.3 227.1 186.4 189.9 225.8 220.3 204.7 213.4 K3j 180.7 199.1 187.1 197.1 179.4 218.9 248.3 213.2 Rj 50.9 65.2 28.6 11.3 91.9 18.4 43.6 36.6 注:表中Kij表示第j (j=A芯壳比,B搅拌时间,C搅拌速度,D粒径)列影响因素i (i=1, 2, 3)水平所对应的试验指标的总和。Rj表示第j列影响因素所对应的试验指标的极差。 表 3 Higuchi和Ritger-Peppas方程对缓释实验数据的拟合结果
Table 3. Fitting results of Higuchi and Ritger-Peppas equation for sustained release experimental data
样品方程 1-S 1-M 1-L 2-S 2-M 2-L 3-S 3-M 3-L Higuchi 0.571 9 0.978 1 0.993 0 0.800 8 0.754 2 0.967 2 0.745 7 0.950 8 0.982 2 Ritger-Peppas 0.760 1 0.991 1 0.995 7 0.939 5 0.944 0 0.978 0 0.910 5 0.975 2 0.990 5 一级释放模型 0.986 6 0.986 0 0.975 5 0.989 3 0.988 2 0.997 6 0.963 6 0.996 2 0.992 5 -
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