Organic pollutant adsorption on clay minerals

Design of a Novel Sericite-Phosphoric Acid Framework for Enhancement of Pb(II) Adsorption

In this study, phosphoric acid was used to attach anions to the weak interlayer structure of sericite, one of the clay minerals composed of a tetrahedral structure of silicate, to increase the adsorption capacity of cations. Natural sericite beads (NSB) and activated sericite beads with phosphoric acid (PSB) were prepared as beads in order to increase reusability and facilitate the separation of adsorbates and adsorbents. Using this, lead (Pb(II)) removal efficiency from an aqueous solution was comparatively analyzed. The pHpzc was 6.43 in NSB but lowered to 3.96 in PSB, confirming that more acidic functional groups were attached to the PSB surface. According to FT-IR analysis, P=O, P-O-C, P=OOH and P-O-P bonds appeared on the surface of the PSB adsorbent, and the peaks of carboxyl groups and OH-groups were large and broad. The maximum adsorption capacity of Langmuir was 52.08 mg/g for NSB and 163.93 mg/g for PSB. The adsorption process was close to physical adsorption for NSB and chemical adsorption for PSB, and both adsorbents were endothermic reactions in nature in that the higher the temperature, the higher the adsorption efficiency. The adsorption mechanism of Pb(II) to PSB was achieved by ion exchange, electrostatic interaction, hydrogen bonding, and complexation. The adsorption of Pb(II) using PSB was not significantly affected by the adsorption of competing ions and showed a high adsorption efficiency of 94% in reuse up to 6 times. This confirms the favorable feasibility of removing Pb(II) from industrial wastewater using PSB.

Controversial Issues Related to Dye Adsorption on Clay Minerals: A Critical Review

This critical review points out the most serious and problematic issues to be found in the literature on the adsorption of dyes on clay minerals. The introduction draws attention to the fundamental problems, namely the insufficient characterization of adsorbents, the influence of impurities on the adsorption of dyes, and the choice of inappropriate models for the description of the very complex systems that clay minerals and their systems represent. This paper discusses the main processes accompanying adsorption in colloidal systems of clay minerals. The relationship between the stability of the colloidal systems and the adsorption of dye molecules is analyzed. The usual methodological procedures for determining and evaluating the adsorption of dyes are critically reviewed. A brief overview and examples of modified clay minerals and complex systems for the adsorption of organic dyes are summarized. This review is a guide for avoiding some faults in characterizing the adsorption of organic dyes on clay minerals, to improve the procedure for determining adsorption, to evaluate results correctly, and to find an appropriate theoretical interpretation. The main message of this article is a critical analysis of the current state of the research in this field, but at the same time, it is a guide on how to avoid the most common problems and mistakes.

Feasibility of soil oxidation-reduction potential in judging shear behaviour of hydrocarbon-contaminated soil

This study investigates the indicative role of oxidation-reduction potential (ORP) and pH of hydrocarbon-contaminated soils on their shear characteristics, contributing to safer and more efficient ex-situ remediation and management processes. The presence of hydrocarbons alters the soil's shear strength by affecting the hydration shell thickness, fluid's dielectric properties, and ion/electron exchange, as well as the soil's electrochemical force, which in turn affects the ORP and pH. The relationship between hydrocarbon concentrations in contaminated soils (0.1-15%) and corresponding ORP/pH values could be fitted linearly with a good correlation coefficient r (0.978), highlighting the potential of ORP/pH as an indicator for pollutant occurrence. Furthermore, the relationships between ORP/pH and shear strength, as tested in our study and obtained after processing from relevant literature sources, exhibited a strong fit (r = 0.976-0.995). The Mohr-Coulomb criterion modified using the ORP/pH parameter was established, which could improve the fitting effect of these relationships (r = 0.988-0.996), verifying the reliability of the novel criterion and application feasibility of ORP/pH. In future research, this modified criterion can be employed to conveniently assess the shear strength of contaminated soil by considering the shear behaviour of virgin soil and the ORP/pH values of the contaminated soil.

Thermal desorption mechanism of n-dodecane on unsaturated clay: Experimental study and molecular dynamics simulation

Thermal desorption technology can effectively remediate fuels-contaminated clayey soil. However, the microscopic mechanism for the contaminant desorption on clay is still unclear, especially with the existence of water on clay surfaces. In this study, a combination method including TGA experiments, multi-phase and multi-component kinetic models, and MD simulation was proposed to reveal the thermal desorption mechanism of n-dodecane in unsaturated clay. Results showed that the thermal desorption behavior of the free nonaqueous phase liquid (NAPL) and the adsorbed phase of n-dodecane or water could be identified by the multi-phase and multi-component kinetic models based on the desorption process rate obtained by thermogravimetric analysis (TGA) experiments. The activation energy of the NAPL phase (49-69.9 kJ/mol) was lower than the adsorbed phase (90 kJ/mol). The activation energy of the NAPL phase had the same linear relationship with its mass on kaolinite and montmorillonite, while adsorbed phase only existed on the kaolinite surface. MD simulation showed that water demonstrated competitive adsorption with n-dodecane on montmorillonite surfaces and prevented the formation of the adsorbed phase while having little influence on the n-dodecane adsorption on kaolinite surface, which agrees well with the kinetic analysis of the TGA experiments. With the combination of macroscopic experimental analysis and microscopic molecular simulation, it can be concluded that the mass of the NAPL phase limited the desorption behavior, while the interaction between the clay mineral surface and n-dodecane was the key factor that dominated the thermal desorption behavior of the adsorbed phase. The presented results provide new insight into the desorption mechanism of hydrocarbon on clay minerals, which is of significance for the design of thermal desorption remediation.

Adsorption of Naphthalene on Clay Minerals: A Molecular Dynamics Simulation Study

Naphthalene, as one of the representative polycyclic aromatic hydrocarbons, widely exists in contaminated sites and is a potential threat to human health due to its high mobility in soil. The interaction between naphthalene and clay minerals is of great significance to the environmental behavior of naphthalene and the design of remediation technology. In this study, montmorillonite and kaolinite were selected as representative clay minerals. Naphthalene adsorption behavior on mineral surfaces and water-wet kaolinite surfaces was investigated using molecular dynamics (MD) simulation. The interaction energy was calculated to represent the interaction between naphthalene and soil fractions, and the relative concentration and density distribution of naphthalene was analyzed to describe the distribution of naphthalene on the clay surfaces. The self-diffusion coefficient of naphthalene was obtained to represent its mobility under different water content. The electron density calculation was performed to reveal the different adsorption behavior of naphthalene on different surfaces of kaolinite. The simulation results show that montmorillonite had a stronger interaction with naphthalene due to larger electrostatic interaction energy compared to kaolinite, and naphthalene distributed more intensively on the montmorillonite surface. With regards to kaolinite, naphthalene tended to be absorbed on the alumina octahedral surface rather than the silicon tetrahedral surface due to the weak hydron bond interaction. The results indicate that water impeded the adsorption of naphthalene, and the optimal initial thickness of water film, which was 10 Å, was put forward for the application of thermal remediation technology. Furthermore, the average interaction energies between water and mineral surfaces largely depended on the water content, and the competitive adsorption between water and naphthalene only occurred under absorbed and bound water conditions. Overall, the knowledge of naphthalene–soil fractions interaction gained in this study is critical to the understanding of the environmental behavior of naphthalene and the reference for remediation technology.

A simple empirical model for phenanthrene adsorption on soil clay minerals

Soil clay minerals are effective substrate adsorbents of polycyclic aromatic hydrocarbons (PAHs) in natural soil. The adsorbed PAHs result in long-term contamination of soils. In this paper, a typical PAH phenanthrene (Phe) and nine high purity clay minerals are selected as representative PAH pollutants and adsorbents, respectively. A series of experiments have been conducted to disclose the relationship between the Phe adsorption effect of these clay minerals and their physical properties, including specific surface area (SSA), cation exchange capacity (CEC) and contact angle (CA). Molecular simulation methods are performed to explore the mechanism of clay mineral structure on Phe adsorption at the molecular level. Density functional theory (DFT) calculation suggests that the adsorption of Phe on clay minerals is mainly due to the van der Waals effect. The strength of the O-H-π effect is greater than that of the hydrophobic effect of Phe adsorption. Molecular dynamic (MD) simulations imply that the hydration effect of cations hinders the Phe hydrophobic adsorption by occupying the adsorption sites. Based on the mechanism explored, a simple empirical model is proposed, and the adsorption distribution coefficient K_d of clay mineral and water phases can be precisely predicted by the three physical properties of clay minerals, without rigorous quantitative analysis of soil clay minerals.

Assessment of Levonorgestrel Leaching in a Landfill and Its Effects on Placental Cell Lines and Sperm Cells

The Buenavista landfill is located east of the city of Medellín, but it has a slope steeper than 30% and is less than 600 m away from the Piedras River, possibly influencing the quality of the drinking water in the city. Many complex residues are disposed of in this landfill, including pharmaceuticals and personal care products (PPCPs) such as levonorgestrel (LNG), which may reach water bodies via runoff and leaching. We assessed the levels of LNG in the effluent of an upflow anaerobic sludge blanket (UASB) reactor from the Buenavista landfill by uHPLC–DAD, as well as the endocrine disruptor effect of LNG on placental cell lines (BeWo) and human sperm cells. Additionally, the potential leaching of LNG was assayed under laboratory conditions using soil layers that were sampled from the Buenavista landfill. LNG was detected at levels of 315 μg·L−1 in the effluents of the UASB reactor. Thus, the UASB reactor is not an efficient treatment method for the removal of recalcitrant pollutants. Additionally, we found that a layer of soil used as a cover material may adsorb more than 90% of LNG pollutants, but small amounts may still be leached, which means that a cover material is not a strong enough barrier to fully prevent the leaching of LNG. Finally, our results show that the leachate fraction decreased the levels of β-human chorionic gonadotropin, but not sperm motility or viability. Thus, leached LNG could trigger reproduction disorders, but further studies should be carried out to investigate its potential effects in more detail.

Understanding of the mechanism of crystal violet adsorption on modified halloysite: Hydrophobicity, performance, and interaction

Halloysite was processed at 600 °C and then by acid leaching with HCl solutions of different concentrations, i.e. 0.5, 3 and 5 N (H600-xN; x = 0.5, 3 or 5). The resulting materials underwent chemical, textural, and laser diffraction analyses and were used in crystal violet (CV) adsorption. Bath experiments were conducted to evaluate the parameters influencing adsorption. A hydrophobicity study by adsorption of water/toluene and a spectroscopic investigation by FTIR and Raman were conducted, to understand the interaction mechanism. The affinity for CV is as follows: H600-0.5N (115 m²g^-1) > H600-3N (434 m²g^-1) > H600-5N (503 m²g^-1) > H600-0N (61 m²g^-1). The maximum adsorption of H600-0.5N would be explained by optimal hydrophilic and hydrophobic properties. Dealumination leads to the creation of more silanols responsible for hydrophilicity. Dehydroxylation at 600 °C combined with dealumination would induce a partial transformation of silanols into siloxanes which are responsible for organophilicity. The CV-H600-0.5N interaction implies two mechanisms: hydrophobic interactions and hydrogen bond. This study focused on hydrophobic interaction as a non-negligible component governing the interaction of organic contaminants with 1:1 clay minerals, while it was not sufficiently considered in the scientific literature.

Influence of suspended sediment on the bioavailability of benzophenone-3: Focus on accumulation and multi-biological effects in Daphnia magna

The UV-filter benzophenone-3 (BP3) tends to associate with suspended sediment (SPS) due to hydrophobicity, which could alter its toxicological effects on non-target aquatic organisms. In this study, the freshwater cladoceran Daphnia magna (D. magna) was selected as a model organism to investigate the impacts of the source and composition of SPS on the accumulation and multiple toxicological effects (from the molecular level to individual level) of BP3. Among the three components of SPS, amorphous organic carbon (AOC) and minerals promoted the body burden of BP3, while black carbon (BC) inhibited the bioaccumulation. The inhibition effects of BP3 on swimming and feeding behaviors of D. magna were also enhanced due to the presence of AOC and BC. Compared with BP3 exposure alone, higher oxidative stress and neurotoxicity were observed in the presence of SPS containing AOC, BC and minerals, corresponding to that superoxide dismutase, catalase and glutathione-S-transferase activities were further induced, and acetylcholinesterase activity was inhibited. Furthermore, BP3 induced mRNA expression levels of the endocrine system (ecdysone receptor, cytochrome P450 CYP314) and metabolic system (toxicant nuclear receptor HR96, P-glycoprotein), and the presence of SPS containing AOC, BC and minerals exhibited an enhanced effect. Combined with all endpoints, evident relationship was observed between the bioaccumulation level and the response of individual behavior and molecular biomarkers. The results demonstrated that the effects of SPS compositions on bioaccumulation and toxicological effects of organic UV-filters should be considered in aquatic environments.

Swelling layered minerals applications: A solid state NMR overview

Swelling layered clay minerals form an important sub-group of the phyllosilicate family. They are characterized by their ability to expand or contract in the presence or absence of water. This property makes them useful for a variety of applications, ranging from environmental technologies to heterogeneous catalysis, and including pharmaceutical and industrial applications. Solid State Nuclear Magnetic Resonance (SS-NMR) has been extensively applied in the characterization of these materials, providing useful information on their dynamics and structure that is inaccessible using other characterization methods such as X-ray diffraction. In this review, we present the key contributions of SS-NMR to the understanding of the mechanisms that govern some of the main applications associated to swelling clay minerals. The article is divided in two parts. The first part presents SS-NMR conventional applications to layered clay minerals, while the second part comprises an in-depth review of the information that SS-NMR can provide about the different properties of swelling layered clay minerals.

Over-sulfated soils and sediments treatment: A brief discussion on performance disparities of biological and non-biological methods throughout the literature

High sulfate concentrations in industrial effluents as well as solid materials (excavated soils, dredged sediments, etc.) are a major hindrance for circular economy outlooks. SO₄^2- acceptability standards are indeed increasingly restrictive, given the potential outcomes for public health and ecosystems. This literature review deals with the treatment pathways relying on precipitation, adsorption and microbial redox principles. Although satisfactory removal performances can be achieved with each of them, significant yield differences are displayed throughout the bibliography. The challenge here was to identify the parameters leading to this variability and to assess their impact. The precipitation pathway is based on the formation of two main minerals (ettringite and barite). It can lead to total sulfate removal but can also be limited by aqueous wastes chemistry. Stabilizer kinetics of formation and equilibrium are highly constrained by background properties such as pH, Eh, SO₄^2- saturation state and inhibiting metal occurrences. Regarding the adsorption route, sorbents' intrinsic features such as the q_max parameter govern removal yields. Concerning the microbial pathway, the chemical oxygen demand/SO₄^2- ratio and the hydraulic retention time, which are classically evoked as yield variation factors, appear here to be weakly influential. The effect of these parameters seems to be overridden by the influence of electron donors, which constitute a first order factor of variability. A second order variability can be read according to the nature of these electron donors. Approaches using simple monomers (ethanol lactates, etc.) perform better than those using predominantly ligneous organic matter.

Adsorption of toluene on various natural soils: Influences of soil properties, mechanisms, and model

This study investigated toluene adsorption on natural soils. The linear partition model was found to represent the adsorption isotherm well (R² = 0.958-0.994), compared with the Freundlich model (R² = 0.901-0.991). Therefore, the coefficient, K_d, of the linear model indicated the adsorption capacity of soils A to F. Traditionally, K_d and the total organic carbon (TOC) content have a good linear relationship. However, this relationship was weak (correlation coefficient (r) = 0.689) when TOC values (8.43-12.9 mg/g) were low and close. To correct this deviation, this study investigated the influences of physicochemical properties, such as special surface area, mineral composition, functional groups, pH, and potentials. As soils B and C consisted of a large amount of active clayey minerals (69.4% kaolinite and 79.3% nacrite, respectively) and rich functional groups, they demonstrated the strongest adsorption capacity. Additionally, the r for pH-K_d, zeta potential-K_d, and redox potential-K_d were high, at 0.806, 0.914, and 0.932, respectively. To explore adsorption mechanisms, the adsorption thermodynamic parameter (enthalpy) was used initially to determine the forces. Combined with the analysis of soil properties, the mechanisms identified were hydrophobic interaction and hydrogen-pi bonding, involving co-adsorption with water molecules. Based on all studies, the properties were quantified and simplified by the plastic limit (PL), and TOC was simplified by soil organic matter (SOM). Then, PL and SOM were weighted by the entropy-weight method to obtain the determination factor, DF, a logarithmic parameter to replace TOC. Finally, a new model describing toluene adsorption on natural soils was established and expressed as K_d = 4.80 + 3.53DF. This new model had significantly improved the correlation between K_d and TOC (r = 0.933) and expanded the engineering adaptability.

Mineral sorbents for ammonium recycling from industry to agriculture

In tropical environments, nutrient-poor soils are commonly found, leading to high fertilizers application rates to support agricultural activities. In contrast, anthropogenic activities generate large amounts of effluents containing nitrogen. In this study, two minerals (natural zeolite and vermiculite) were tested to remove NH₄⁺ from an industrial effluent with high pH and contents in Na⁺ and K⁺. Afterwards, they were tested as an alternative slow-release fertilizer in the soil. To verify the best conditions to adsorb NH₄⁺, batch tests were conducted using synthetic solutions and an industrial effluent. In general, the efficiency of both minerals in removing NH₄⁺ was high (85% for zeolite and almost 70% for vermiculite) as well as the ability to decrease the industrial effluent pH. In this process, more NH₄⁺ and K⁺ ions were removed in comparison with Na⁺, which remained in solution. These minerals were tested as slow-release fertilizers by leaching with distilled water (both minerals releasing 2 mg L^-1 NH₄⁺) and with an acid solution (releasing 10 mg L^-1 NH₄⁺ from zeolite and 50 mg L^-1 NH₄⁺ from vermiculite-corresponding only to 12% of total NH₄⁺ retained by zeolite and 29% by vermiculite). During the test of soil incubation with zeolite-NH₄⁺, the NH₄⁺ ions of the exchangeable sites were retained for a longer period, minimizing their loss by leaching and biological nitrification. Consequently, soil acidification was prevented. Therefore, both minerals showed high efficiency in removing NH₄⁺ from solution which can then be slowly released as a nutrient in the soil.