Study on chemical compatibility of bentonite under the action of cation and stress of hazardous waste leachate
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摘要:
膨润土因其优异的防渗性能被用于危险废物填埋场防渗屏障的构筑,但其防渗性能通常会受到渗滤液和应力的影响。通过渗滤液采样分析设置不同浓度阳离子溶液,系统探究实际渗滤液组分对膨润土防渗性能的影响规律;选用Ca2+作为特征阳离子研究不同应力条件下膨润土渗透系数变化规律;同时结合Zeta电位和DLVO理论计算,阐明渗滤液组分和应力作用对膨润土化学相容性影响规律。结果表明,渗滤液中Al3+、Fe3+、Zn2+、Ni2+、Cu2+、Fe2+、Mn2+浓度为0~0.20 mmol/L时,对膨润土膨胀特性和渗透特性影响较小。Mg2+、Ca2+、K+、Na+浓度为0.20~50 mmol/L时,Ca2+对膨润土膨胀特性和渗透特性影响较大,Ca2+浓度由1 mmol/L上升到50 mmol/L时,渗透系数由1.15×10−7 cm/s急速上升到6.34×10−6 cm/s。Ca2+浓度和应力通常通过影响水化后膨润土孔隙比进而影响其渗透特性,相同Ca2+浓度条件下,渗透系数随应力增加而逐渐降低。Zeta电位和DLVO理论分析表明,Ca2+浓度增大会导致膨润土表面负电势减弱,引起膨润土双电层厚度减小,使膨润土中蒙脱石的层间距变小,导致膨润土膨胀特性和渗透特性降低。因此,填埋过程中应优化危险废物固化稳定化工艺,从源头减少渗滤液中Ca2+浓度;同时还应研发新型膨润土复合材料,提高膨润土在Ca2+等高浓度盐溶液中的防渗性能,防控危险废物填埋场渗漏风险。
Abstract:Bentonite is widely used for the construction of anti-seepage barriers in hazardous waste landfills due to its excellent anti-seepage performance, but its impermeability is usually affected by leachate and stress. Different concentrations of cationic solutions were set up by leachate sampling and analysis to investigate the influence law of actual leachate components on the anti-seepage performance of bentonite. Ca2+ was chosen as the characteristic cation, and the variation rule of the bentonite permeability coefficient under different stress conditions was studied. Meanwhile, the influence law of chemical compatibility of bentonite was elucidated under the action of leachate composition and stress combined with Zeta potential and DLVO theoretical calculation. The results show that the concentration of Al3+, Fe3+, Zn2+, Ni2+, Cu2+, Fe2+, Mn2+ in the leachate is in the range of 0-0.20 mmol/L, which has less influence on the expansion and permeability characteristics of bentonite. The concentration of Mg2+, Ca2+, K+, Na+ is in the range of 0.20-50 mmol/L, and Ca2+ has more influence on the expansion capacity and permeability characteristics of bentonite. When the concentration increases from 1 mmol/L to 50 mmol/L, the permeability coefficient rapidly increases from 1.15×10−7 cm/s to 6.34×10−6 cm/s. Ca2+ concentration and stress usually affect the permeability characteristics of hydrated bentonite by affecting its porosity, and the permeability coefficient gradually decreases with increasing pressure under the same Ca2+ concentration conditions. Zeta potential and DLVO theoretical analysis indicate that the increase in Ca2+ concentration leads to a decrease in the negative potential on the surface of bentonite and thickness of the double layer of bentonite, which decreases the interlayer spacing of montmorillonite in bentonite, and then depress the swelling and permeability characteristics of bentonite. Therefore, the solidification and stabilization process of hazardous waste during the landfill process should be optimized, to reduce Ca2+ content in the leachate at the source. Meanwhile, new bentonite composite materials should be developed to improve the impermeability of bentonite in Ca2+ as well as other salt solutions to prevent and control the risk of leakage of hazardous waste landfills.
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Key words:
- bentonite /
- hazardous waste leachate /
- chemical compatibility /
- permeability /
- stress
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表 1 膨润土物理化学指标
Table 1. Physical and chemical indexes of bentonite
蒙脱石
含量/%胶质价/
(mL/g)液限/% 塑限/% 比表面积/
(m2/g)膨胀容/
(mL/g)75 6.68 269.4 34 252 19.8 表 2 不同阳离子溶液作用下膨润土Zeta电位
Table 2. Bentonite zeta potential under the action of different cationic solutions
mV 离子浓度/(mmol/L) Na+ K+ Ca2+ Ni2+ Cu2+ Zn2+ Fe2+ Fe3+ Al3+ 0.05 — — — −33.37 −33.87 −34.60 −32.13 −37.83 −34.77 0.20 — — — −32.90 −24.23 −34.60 −32.53 −32.43 −30.30 5 −36.63 — — — — — — — — 10 — −36.33 −10.95 — — — — — — 50 −42.53 −38.20 −8.83 — — — — — — 注:—表示未检测。 -
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