clay and perfluorooctanoic-acid

The need for the efficient remediation of soils impacted by per- and polyfluoroalkyl substances (PFAS) is substantially growing because of the notable upsurge in societal and regulatory awareness of this class of chemicals. To remediate PFAS-contaminated soils using mobilization approaches, the choice of appropriate techniques highly depends on the soil's composition, particularly the clay content, which significantly affects the soil's permeability. Here, we investigated the PFAS mobilization efficiency from soils with different clay contents by using two techniques: electrokinetic (EK) remediation and hydraulic flushing. Artificial kaolinite was added to a loamy sand soil to prepare four soil blends with clay contents of 5, 25, 50, and 75%, each contaminated with perfluorooctanoic acid (PFOA) and perfulorooctanesulfonic acid (PFOA) at 10,000 μg/kg. EK remediation was conducted by applying a low voltage (30 V) with a current of 100 mA, and hydraulic flushing was carried out by applying a hydraulic gradient (HG) with a slope of 6.7%. Results show that, with a 14-day treatment duration, the EK-mobilization efficiency was enhanced substantially with the increase of clay content (removal of PFOS increased from 20% at 5% clay to 80% at 75% clay), most likely due to the increase of electroosmotic flow due to the higher content of particles having a zeta potential (i.e., clay). For HG, increasing the clay content significantly suppressed the mobilization of PFAS (removal of PFOS decreased from 40% at 5% clay to 10% at 75% clay) due to a notable decrease in the soil's permeability. Based on the results, applying hydraulic flushing and washing techniques for mobilizing PFAS would be appropriate when treating permeable soils with a maximum clay content of about 25%; otherwise, other suitable mobilization techniques such as EKs should be considered.

Topics: Clay; Environmental Pollution; Fluorocarbons; Soil; Soil Pollutants

Perfluorooctanoic acid (PFOA) in the ecosystem, resulting from industrial effluent and water bodies, has attracted greater concern. An economical treatment is in demand to optimize the current issue. In this research work, Perfluorooctanoic Acid was treated from drinking water sources with nano-ceramic clay. The ceramic clay was synthesized and characterized with Fourier infrared transformation, scanning electron micrograph, transmission electron micrograph, x-ray diffraction, and thermal analysis. An adsorption process was performed in batch and continuous modes for the effective conditions for maximum removal. In batch mode 82 ± 12 nm ceramic clay particle size; 3.0 initial pH; 210 rpm agitation 1.2 mg/L PFOA concentration; 100 mg/L clay dosage; 27 °C temperature, and 20hrs experimental time shows maximum 99.15% adsorption. The experimental data is well fitted with kinetics, isotherms, and thermodynamics calculated data. In fixed bed, continuous column study 10 h treatment time, 10 cm of bed height, and 2 ml/min were adsorbed 99.99% of PFOA. The experimental data from the fixed bed adsorption equipment was correlated using a number of different mathematical models, including the Thomas, Adams-Bohart, Yoon-Nelson, and Clark models. Overall nano ceramic clay was found to potential adsorbent for Perfluorooctanoic acid removal.

Topics: Adsorption; Caprylates; Clay; Ecosystem; Kinetics; Thermodynamics; Water Pollutants, Chemical; Water Purification

We examined the effects of representative clay minerals, montmorillonite (M) and kaolin (K), on perfluorooctanoic acid (PFOA) transport under saturated conditions. Results showed that low amounts of M or K addition increased and high addition amounts reduced PFOA retardation in quartz sand during the transport. With increasing addition of clay minerals (0-50%, weight ratio), the retardation factor of the M-added system increased from 1.03±0.00 to 1.31±0.03 and then decreased to 0.72±0.06, while that of the K-added system increased to 1.30±0.02 and then decreased to 0.49±0.11. Results of the tracer experiment showed that low amount of M or K addition did not produce preferential flow, while high amount addition induced obvious preferential flow, which resulted in the decrease in PFOA retardation. In addition, due to limitations of the highly negative-charged surface of the M or K modified sand and the solid-liquid ratio of column experiment, the modified M or K sand had low adsorption capacity of PFOA and thus almost did not affect PFOA retention. However, the adsorption and desorption of PFOA by clay minerals might still be responsible for the increases in PFOA retardation with low amount of M or K addition. The results are of great significance for accurately assessing the transport process and eco-environmental risks of PFOA in soil-groundwater systems.. 本研究以蒙脱石(M)和高岭土(K)为代表性黏土矿物,探究了饱和条件下黏土矿物对全氟辛酸(PFOA)运移行为的影响。结果表明: 较低量的M或K添加增强了石英砂中PFOA的运移阻滞,较高量添加则减弱其阻滞。随黏土矿物添加量的增加(0～50%,重量比),添加M的PFOA阻滞系数由1.03±0.00增至1.31±0.03后降至0.72±0.06;添加K的PFOA阻滞系数增至1.30±0.02后降至0.49±0.11。示踪试验结果显示,较低量的M或K添加未形成优先流,而较高量的M或K添加产生了明显的优先流,该条件下PFOA阻滞减弱。此外,受M或K改性石英砂电负性强及柱试验固液比等限制,试验条件下M或K改性石英砂对PFOA吸附量较低,几乎未影响PFOA滞留,但黏土矿物对PFOA的吸附和脱附作用仍可能是较低量的M或K添加增强PFOA运移阻滞的原因。本研究结果对准确评估土壤-地下水系统中PFOA的迁移过程和生态环境风险具有重要意义。.

Topics: Adsorption; Clay; Minerals; Porosity; Sand; Silicon Dioxide

The widespread use of perfluoroalkylated acids (PFAAs) has led to a global presence in the environment, in which they accumulate and may cause detrimental effects. Although soils are known sinks for many persistent organic pollutants, still little is known on the behaviour of PFAAs in soils. Furthermore, studies that examine the relationships between PFAA concentrations and soil microbial parameters are scarce. The 3 M fluorochemical plant near Antwerp has been characterized as a PFAAs hotspot. In the present study, we examined the vertical distribution of 15 PFAAs and their associations with multiple physicochemical soil properties along a distance gradient from this hotspot. Additionally, we tested the relationships between PFAA concentrations in the top soil with soil respiration, microbial activity and microbial biomass. Our results show that both perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) concentrations were elevated in the subsurface layer (up to 50 cm), after which concentrations decreased again, suggesting a downward migration of both analytes in the soil. This downward movement might pose a potential threat for the contamination of the groundwater and, consequently, organisms that rely on this water for consumption. The soil concentrations were influenced by multiple physicochemical properties of the soil, which suggests differences in bioavailability and sorption/desorption capacities between different soil types. We did not observe any influence of PFAA contamination in the top soil on microbial activity and biomass nor soil respiration.

Topics: Alkanesulfonic Acids; Belgium; Caprylates; Carbon; Chemical Industry; Clay; Fluorocarbons; Hydrogen-Ion Concentration; Soil; Soil Microbiology; Soil Pollutants; Temperature

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a class of highly persistent contaminants with high bioaccumulation and toxicity. Our previous studies showed that perfluorooctanoic acid (PFOA) can be completely defluorinated under UV irradiation in organo-montmorillonite/indole acetic acid (IAA) system. However, there is still lack of information for the degradation mechanism and the test for wastewater treatment. Here, we systematically investigated the defluorination reaction in the presence of different organo-montmorillonites and found that the degradation process was apparently controlled by the configuration of surfactants. In hexadecyltrimethyl ammonium (HDTMA)-modified montmorillonite, HDTMA exists as a tilt conformation and isolated clay interlayer from the aqueous solution, protecting hydrated electrons generated by photo-irradiation of IAA from quenching by oxygen. Defluorination hydrogenation process was the dominant degradation pathway. While in poly-4-vinylpyridine-co-styrene (PVPcoS)-modified montmorillonite, due to the multiple charges of PVPcoS, a flat conformation parallel to clay surface was expected. Hydroxyl radicals, which were generated by the reaction of hydrated electrons with oxygen molecules diffused into clay interlayer, are also involved in the degradation process. Our results further demonstrate that mixture modified montmorillonite could combine the advantages of both modifications, thus showing superior reactivity even for actual industrial wastewater without any pretreatment. This technique would have great potential for treatment of actual wastewater.

Topics: Adsorption; Bentonite; Caprylates; Clay; Electrons; Fluorocarbons; Hydroxyl Radical; Molecular Conformation; Surface-Active Agents; Water Purification

The sorption of four perfluoroalkyl acids (PFAAs) [perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA) and perfluorohexanoic acid (PFHxA)] on three typical minerals [montmorillonite (MM), kaolinite (KL) and hematite (HM)] was studied. The sorption of PFOS and PFHxS was much stronger than PFOA and PFHxA. The sorption of each PFAA on the minerals followed an order of HM>KL>MM, even though MM was positively while KL and HM were negatively charged, implying that the sorption is driven by some other interactions besides electrostatic attraction. The sorption decreased with an increase in pH and a decrease in ionic strength of the solution, and their impacts on PFOS were much stronger than other three PFAAs. Surface complexing and hydrogen-bonding could make great contributions to the sorption of PFOS on the minerals. The results are important for understanding the transport and fate of PFAAs in sediment and ground water.

Topics: Adsorption; Alkanesulfonic Acids; Aluminum Silicates; Bentonite; Caproates; Caprylates; Clay; Ferric Compounds; Fluorocarbons; Hydrogen Bonding; Kaolin; Osmolar Concentration; Static Electricity

The influence of salinity and organic matter on the distribution coefficient (K(d)) for perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in a brackish water-clay system was studied. The distribution coefficients (K(d)) for PFAs onto inorganic clay surfaces increased with salinity, providing evidence for electrostatic interaction for the sorption of PFAs, whereas the relationship between K(d) and organic carbon content (f(oc)) suggested that hydrophobic interaction is the primary driving force for the sorption of PFAs onto organic matter. The organic carbon normalized adsorption coefficient (K(oc)) of PFAs can be slightly overestimated due to the electrostatic interaction within uncoated inorganic surfaces. In addition, the dissolved organic matter released from coated clay particles seemed to solvate PFA molecules in solution, which contributed to a decrease in K(d). A positive relationship between K(d) and salinity was apparent, but an empirical relationship for the 'salting-out' effect was not evident. The K(d) values of PFAs are relatively small compared with those reported for persistent organic pollutants. Thus, sorption may not be a significant route of mass transfer of PFAs from water columns in estuarine environments. However, enhancement of sorption of PFAs to particulate matter at high salinity values could evoke potential risks to benthic organisms in estuarine areas.

Topics: Alkanesulfonic Acids; Aluminum Silicates; Caprylates; Clay; Fluorocarbons; Geologic Sediments; Kinetics; Salinity; Seawater; Water Pollutants, Chemical