Sixty-nine samples of surface sediments (0∼5 cm) recovered from the eastern Beibu Bay were analyzed for TOC and heavy metals to examine the element distribution pattern and potential pollutant sources. The sediments in the study area are characterized by variable heavy metal concentrations that are comparable with those of the surrounding regions. Obvious positive correlations were observed amongst the concentrations of Zn, Cr, Pb, Cd, Cu and the clay contents, suggesting that fine clay particles are important carriers of trace metals in the sediments. Hg and As show a considerable/low positive correlation with TOC, indicating that organic matter may play a discernible role in the sediment chemistry. Cd contamination was detected in the north of the study area primarily due to the input of phosphate fertilizers carried by rivers. In comparison, Zn, Cr, Pb, and partly Cu are predominantly sourced from lithogenic components, and Hg and As are mainly from organic matter related to anthropogenic input.

The compositional changes of saturates, aromatics, resins and asphaltenes (SARA) fractions in aqueous clay/oil microcosm experiments with a hydrocarbon-degrading microorganism community were analysed using Iatroscan. The clay mineral samples used in this study were organomontmorillonite, acid-activated montmorillonite and K, Ca, Zn and Cr montmorillonites produced by modifying the original montmorillonite sample. The evaluation and quantification of biodegradation and adsorption were carried out using a combination of the Iatroscan and gravimetric analysis. The SARA compositions in the presence of organomontmorillonite and acid-activated montmorillonite after incubation follow the same pattern in which the aromatic fraction is higher than the other fractions unlike in the presence of unmodified, K, Ca and Zn montmorillonites, where the saturates fraction is higher than the other fractions. Changes in SARA fractions due to biodegradation seemed to occur most in the presence of unmodified and calcium montmorillonites; hence, the removal of SARA fractions due to biodegradation was significant and enhanced in the presence of these two clay samples. However, biodegradation in the presence of organomontmorillonite and acid-activated and Cr montmorillonites was hindered. The study indicated that Cr montmorillonite adsorbed resins most, whereas Zn and K montmorillonites adsorbed aromatics most after incubation.

Perfluorooctane sulfonate (PFOS), which has numerous uses besides being an ingredient in the formulation of aqueous film-forming foams, is considered as an emerging pollutant of increasing public health and environmental concern due to recent reports of its worldwide distribution, environmental persistence and bioaccumulation potential. In an attempt to recommend a 'risk-based' remediation strategy, this study investigates the removal of PFOS from impacted waters and fixation of PFOS in impacted soils using a novel modified clay adsorbent (MatCARE™, patent number 2009905953). Batch adsorption tests demonstrated a much faster adsorption kinetics (only 60 min to reach equilibrium) and remarkably higher PFOS adsorption capacity (0.09 mmol g-1) of the MatCARE™ compared to a commercial activated carbon (0.07 mmol g -1). Treatability studies, performed by treating the PFOS-contaminated soils with the MatCARE™ (10 % w/w) and then incubating at 25 and 37 C temperatures maintaining 60 % of the maximum water holding capacity of the soils for a period of a year, demonstrated a negligible release (water extractable) of the contaminant (only 0.5 to 0.6 %). The fixation of PFOS in soils by the new adsorbent was exothermic in nature. Soils with higher clay and organic matter content, but lower pH values, retained PFOS to a much greater extent. A cost analyses confirmed that the MatCARETM could be an economically viable option for the 'risk-based' remediation of PFOS in contaminated waters and soils. © 2013 Springer Science+Business Media Dordrecht.

The sorption behaviors of brilliant blue FCF dye by natural clay and modified with iron chloride were determined. The materials were characterized by X-ray diffraction and scanning electron microscopy, and the zero point charges were also determined. The effects of pH, contact time, dye concentration, and temperature were considered. The results showed that clay does not suffer any important change in its structure after the chemical treatments. The pH influences the sorption of the dye in the unmodified clay, but this effect was not observed in the iron-modified clay. The equilibrium time and the sorption capacity for the unmodified clay were 48 h and 6.16 mg/g, while for the iron-modified clay, 24 h and 14.22 mg/g, respectively. The sorption kinetics results were best adjusted to the pseudo-first-order and pseudo-second-order models. Sorption isotherms were best adjusted to the Langmuir model, indicating that both clays have a homogeneous surface. Thermodynamic parameters (E, ΔS, ΔG and ΔH) were calculated for the natural clay from the data of the sorption kinetics at temperatures between 20 and 50 °C, indicating that the sorption process is exothermic. For the case of the iron-modified clay, it was not possible to calculate these thermodynamic parameters because the sorption capacities were similar in the temperature range selected.

One of the major obstacles to zerovalent iron nanoparticles (nZVI) application in soil and groundwater remediation is the limited transport, especially in low-permeability soils. In this study, direct current (constant potential of 5.0 V) was used to enhance polymer-coated nZVI mobility in different porous media, including a bed of glass beads and kaolin clay. The tests were conducted using a modified electrophoretic cell and with nZVI concentrations typical of field applications (4 g L-1). Experimental results indicate that the use of direct current can enhance the transport of the polymer-modified nanoparticles when compared with natural diffusion in low permeability or surface neutral porous medium. The applied electric field appeared to enhance the oxidation-reduction potential, creating a synergistic effect of nZVI usage with electrokinetics. Aggregation of the nanoparticles, observed near the injection point, remained unresolved. © 2013 Springer Science+Business Media Dordrecht.

Acid mine drainage (AMD) has long been a significant environmental problem that impairs water resources in historic or current mining industries throughout the world. One of the methods using passive treatment system at low cost to remove metals from solution involves the use of clays. The ability of three different adsorbents (montmorillonite K-10, bentonite (NT-25), and hydrotalcite (HT)) to remove Fe and Mn from aqueous solutions and acid mine drainage samples has been studied at different optimized conditions such as pH, amount of adsorbent and contact time. Flame atomic absorption spectrometer (FAAS) was used for measuring Fe and Mn concentrations. Langmuir and Freundlich isotherms were applied and isotherm coefficients were computed. A kinectic study was also developed for HT using the first order, second order and intraparticle diffusion models. A great amount of clay (more than 100 mg) and also contact times higher than 60 min had also no influence in the adsorption capacity for all adsorbents. HT was found to be the best among the studied clays removing more than 90 % of Fe and Mn for all AMD samples investigated. Moreover, the maximum adsorption capacity was 63.7 mg Mn g⁻¹ HT and 666.7 mg Fe g⁻¹ HT.

Sepiolite reveals as a low-cost and efficient adsorbent for the adsorption of caffeine from aqueous solutions. The characterization of this material was carried out by N₂ adsorption–desorption at 77 K, Fourier transform infrared spectroscopy, thermogravimetric analysis, and electronic microscopy. Initially, batch adsorption experiments were developed in order to determine the equilibrium time and the adsorption isotherm of the system. Pseudo–first-order, Elovich equation, pseudo–second-order, and intra-particle diffusion models were applied to the experimental data to determine the adsorption kinetics. In continuous adsorption, the influence of several operation conditions (initial caffeine concentration, volumetric flow rate, and mass of adsorbent) on the shape of breakthrough curves and the mass transfer resistance was evaluated. Experimental data were fitted to the bed-depth service-time model bed-depth service-time (BDST). Through the calculation of the adsorption, parameters as breakthrough time or caffeine removal percentage can be concluded that the removal of this compound from aqueous solutions by adsorption in sepiolite beds is an alternative technique to the current methods, in order to eliminate this micropollutant.

Removal of petroleum hydrocarbon (PHC) contamination that is hazardous and often prevalent in soils would benefit from a rapid detection technique. Visible and near-infrared spectroscopy (VIS-NIRS) has a large potential as a rapid detection technique for PHC in soils. Nevertheless, the combined influence of oil concentration, moisture content and clay content on soil reflectance spectra and the accuracy of the technique have yet received little attention. The objective of this study was to investigate the combined influence of oil concentration and moisture and clay contents on the spectral characteristics of diesel-contaminated soils and the quality of calibration models developed for polycyclic aromatic hydrocarbons (PAH) in soils using VIS-NIRS. With partial least-squares regression data from a systematic experimental design using 150 artificially contaminated soil samples, results showed that soil diffuse reflectance decreased with increasing oil concentration, clay and moisture contents. The trend was less defined in relation to moisture and clay due mainly to the interaction effects of the soil matrices as mediated by the oil. The PAH partial least squares cross-validation showed best performance with the lowest oil concentration and clay content at 20 % moisture with r ² of 0.89, root mean square error of prediction of 0.201 mg/kg and ratio of the standard error of prediction to the standard deviation of the reference data in the validation set of 2.75. Analysis of variance showed that the interaction effects of oil concentration, moisture and/or clay content significantly (p < 0.05) affected the quality of the PAH models.

Natural palygorskite was used as an adsorbent for the removal of copper, cobalt and nickel from an aqueous solution. All assays were performed under controlled conditions to establish the adsorption capacity of the solid. Initially, the clay was characterized by chemical analysis, XRD, infrared spectroscopy and thermogravimetry. Adsorption experiments for the ions in aqueous solution were carried out by a batch method through which the reaction time, initial concentration of cations, temperature and pH of the aqueous solution were systematically varied. First-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data. The results show that the processes were fitted well by the pseudo-second-order model. Moreover, the equilibrium solid–cation systems followed the Langmuir isotherm model. The results indicate that raw palygorskite could be employed as a low-cost material for the removal of heavy metals from aqueous solution.

A set of periurban calcareous agricultural Mediterranean soils was spiked with a mixture of Cd, Cu, Pb and Zn at two levels within the limit values proposed by current European legislation, incubated for up to 12 months, and subjected to various one-step extraction procedures to estimate mobile (neutral salts) and potentially mobile metal fractions (complexing and acidic extraction methods). The results obtained were used to study metal extractability patterns according to the soil characteristics. The analytical data were coupled with mineralogical investigations and speciation modelling using the Visual Minteq model. The formation of soluble metal-complexes in the complexing extracts (predicted by the Visual Minteq calculations) led to the highest extraction efficiency with complexing extractants. Metal extractability patterns were related to both content and composition of carbonate, organic matter, Fe oxide and clay fractions. Potentially mobile metal fractions were mainly affected by the finest soil fractions (recalcitrant organic matter, active lime and clay minerals). In the case of Pb, scarce correlations between extractable Pb and soil constituents were obtained which was attributed to high Pb retention due to the formation of 4PbCO3·3PbO (corroborated by X-ray diffraction). In summary, the high metal proportion extracted with complexing agents highlighted the high but finite capacity to store potentially mobilizable metals and the possible vulnerability of these soils against environmental impact from metal accumulation.