包裹纳米零价铁处理水力压裂废水的化学转化和金属（类）去除的老化效应。
Aging effects on chemical transformation and metal(loid) removal by entrapped nanoscale zero-valent iron for hydraulic fracturing wastewater treatment.
机构信息
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China; State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China; Department of Environmental Science, Zhejiang University, Hangzhou 310058, China.
出版信息
Sci Total Environ. 2018 Feb 15;615:498-507. doi: 10.1016/j.scitotenv.2017.09.332. Epub 2017 Oct 5.
In this study, alginate and polyvinyl alcohol (PVA)-alginate entrapped nanoscale zero-valent iron (nZVI) was tested for structural evolution, chemical transformation, and metals/metalloids removal (Cu(II), Cr(VI), Zn(II), and As(V)) after 1-2month passivation in model saline wastewaters from hydraulic fracturing. X-ray diffraction analysis confirmed successful prevention of Fe corrosion by polymeric entrapment. Increasing ionic strength (I) from 0 to 4.10M (deionized water to Day-90 fracturing wastewater (FWW)) with prolonged aging time induced chemical instability of alginate due to dissociation of carboxyl groups and competition for hydrogen bonding with nZVI, which caused high Na (7.17%) and total organic carbon (24.6%) dissolution from PVA-alginate entrapped nZVI after 2-month immersion in Day-90 FWW. Compared to freshly-made beads, 2-month aging of PVA-alginate entrapped nZVI in Day-90 FWW promoted Cu(II) and Cr(VI) uptake in terms of the highest removal efficiency (84.2% and 70.8%), pseudo-second-order surface area-normalized rate coefficient k (2.09×10Lmh and 1.84×10Lmh), and Fe dissolution after 8-h reaction (13.9% and 8.45%). However, the same conditions inhibited Zn(II) and As(V) sequestration in terms of the lowest removal efficiency (31.2% and 39.8%) by PVA-alginate nZVI and k (4.74×10Lmh and 6.15×10Lmh) by alginate nZVI. The X-ray spectroscopic analysis and chemical speciation modelling demonstrated that the difference in metals/metalloids removal by entrapped nZVI after aging was attributed to distinctive removal mechanisms: (i) enhanced Cu(II) and Cr(VI) removal by nZVI reduction with accelerated electron transfer after pronounced dissolution of non-conductive polymeric immobilization matrix; (ii) suppressed Zn(II) and As(V) removal by nZVI adsorption due to restrained mass transfer after blockage of surface-active micropores. Entrapped nZVI was chemically fragile and should be properly stored and regularly replaced for good performance.
在这项研究中，我们测试了海藻酸钠和聚乙烯醇（PVA）-海藻酸钠包埋的纳米零价铁（nZVI）在模型盐水中的结构演变、化学转化和金属/类金属去除（Cu（II）、Cr（VI）、Zn（II）和 As（V））后的性能，这些水样取自水力压裂产生的废弃盐水。X 射线衍射分析证实，聚合物包埋成功地防止了 Fe 的腐蚀。随着老化时间的延长，离子强度（I）从 0 增加到 4.10M（去离子水到第 90 天压裂废水（FWW）），导致由于羧基的离解和与 nZVI 的氢键竞争，海藻酸钠的化学稳定性降低，这导致 PVA-海藻酸钠包埋 nZVI 在第 90 天 FWW 中浸泡 2 个月后，有 7.17%的 Na 和 24.6%的总有机碳（TOC）溶解。与新制备的珠粒相比，在第 90 天 FWW 中老化 2 个月的 PVA-海藻酸钠包埋 nZVI 促进了 Cu（II）和 Cr（VI）的吸收，表现为最高去除效率（84.2%和 70.8%）、以比表面积归一化的准二级速率常数 k（2.09×10Lmh 和 1.84×10Lmh）和 8 小时反应后 Fe 的溶解（13.9%和 8.45%）。然而，相同的条件通过 PVA-海藻酸钠 nZVI 抑制了 Zn（II）和 As（V）的固定，表现为最低的去除效率（31.2%和 39.8%）和 k（4.74×10Lmh 和 6.15×10Lmh）。X 射线光谱分析和化学形态模拟表明，老化后包埋 nZVI 对金属/类金属的去除差异归因于不同的去除机制：（i）在非导电聚合物固定基质显著溶解后，通过 nZVI 还原加速电子转移，增强了 Cu（II）和 Cr（VI）的去除；（ii）由于表面活性微孔的传质受到限制，nZVI 的吸附抑制了 Zn（II）和 As（V）的去除。包埋的 nZVI 化学性质脆弱，应妥善储存并定期更换，以保持良好的性能。
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