Acceleration and centralization of a back-diffusion process: Effects of EDTA-2Na on cadmium migration in high- and low-permeability systems

You, Xueji; Dai, Chaomeng; Zhong, Guangfa; Duan, Yanping; Tu, Yao-Jen

doi:10.1016/j.scitotenv.2019.135708

Cited by 14 publications

(11 citation statements)

References 71 publications

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“…This is in accord with the observation reported by a previous study (Fig. 11b1) [16]. Overall, all changes including attachment of EDTA and microparticles, agglomeration, connection and the smoother surfaces contributed to reducing specific surface areas and adsorption capability of SM2.…”

Section: Morphology Of the Soil Mineralssupporting

confidence: 93%

“…Therefore, under the effects of EDTA, the adsorption behaviors of both SM1 and SM2 for Cd and Pb conformed to the Langmuir isotherm model and it should be considered as a multilayer adsorption which occurred on energetically heterogeneous surfaces. In detail, on the one hand, some EDTA introduced into the HM-SM system could be adsorbed on and cover the surfaces of SMs [33,38]; and this made the surfaces of SMs heterogeneous, blocking some adsorption sites and making them nonuniform [16,27]. On the other hand, EDTA and HM ions were both adsorbates for SMs, and they were interactive via chelation [26,28,[39][40]; and this was accord with the mechanism of the Freundlich isotherm model.…”

Section: Isothermal Adsorptionmentioning

confidence: 53%

“…while EDTA might hinder the process of Cd adsorption onto SM, via blocking the adsorption sites and chelating Cd ions simultaneously [16,27].…”

Section: Adsorption Kineticsmentioning

confidence: 99%

“…However, there are usually some low-permeability layers in the soil and groundwater environment, which can act as principal obstacles to retard pollutant migration and serve as pollution sinks to store pollutants due to their strong adsorption capability and special diffusion properties [14][15][16][17]. On the one hand, because of their low hydraulic conductivity, water flow and solute transport in lowpermeability layers are slow [18].…”

Section: Introductionmentioning

confidence: 99%

“…As a result, a large quantity of HMs from wastewater has accumulated in the soil and groundwater system since long time ago, which enhances the hazards of heavy metal pollution and is also quite difficult to restore. Specifically, low-permeability layers serve as long-term reservoirs for pollutants, simultaneously, it also become a secondary pollutant source and constantly release pollution by back-diffusion [16,18,24]; this would greatly extend the timeframe and difficulty of remediation.…”

Section: Introductionmentioning

confidence: 99%

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Effects of EDTA on adsorption of Cd(II) and Pb(II) by low-permeability soil minerals and on their microscopic characteristics

You¹,

Dai²,

Zhong³

et al. 2020

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Background Ethylenediaminetetraacetic acid (EDTA) can serve as a washing agent in the remediation of low-permeability layers contaminated by heavy metals (HMs). Therefore, batch adsorption experiments, where quartz sands (SM1) and mineral mixtures (SM2) were used as low-permeability soil minerals (SMs), were implemented to explore the effects of different EDTA concentrations, pH and exogenous chemicals on the HM-SM-EDTA adsorption system. Changes in microscopic characterizes of SMs were determined by instrument analysis to investigate the mechanisms.Results As the EDTA concentration increased gradually, it gradually cut down the maximum Cd adsorption capacities of SM1 and SM2 from approximately 135 to 55 mg/kg and 2,660 to 1,453 mg/kg; and the maximum Pb adsorption capacities of SM1 and SM2 were reduced from 660 to 306 mg/kg and 19,677 to 19,262 mg/kg, respectively. When the mole ratio (MR = moles of HM ions / sum of moles of HM ions and EDTA) was closer to 0.5, the effect of EDTA was more effective; and Freundlich isotherm model fitted better to the data. It took 5 to 10 min for EDTA to begin taking its effect. EDTA worked well at pH below 7.0 and 4.0 for Cd and Pb, respectively. Low-molecular-weight organic acids (LMWOAs) affected the system mainly by bridging, complexation, adsorption site competition and reductive dissolution. Cu 2+ , Fe 2+ ions could greatly increase the Cd and Pb adsorption on SM2. There were feature changes in mineral particles including attachment of EDTA and microparticles, agglomeration, connection and smoother surfaces, making the specific surface area decrease from 16.73 to 12.59 m 2 /g.Conclusion All findings indicated that EDTA could effectively and economically reduce the HM adsorption capacity of SMs at the reasonable MR value, contact time and pH. The extent of the effects of LMWOAs and exogenous metal ions on the HM-SM-EDTA system depended on the synthesis of diverse effects and the selectivity of EDTA, respectively. EDTA reduced the HM adsorption capacity of SMs not only by complexation with HM ions, but also decreasing SSA and blocking active sites. Hence, the acquired insight from the presented study can help to promote the remediation of contaminated soil and groundwater.

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Section: Morphology Of the Soil Mineralssupporting

confidence: 93%