The removal of pesticide residues in soil is a research hotspot. The metolachlor (MET) adsorption by walnut shell biochar (BC) modified with montmorillonite (MBC), illite (IBC), and kaolinite (KBC), as well as the original BC (OBC) was investigated. The characteristics of samples were studied by scanning electron microscopy and mapping analysis, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry, and chemical stability analysis. The effects of the dosage, ionic strength, and pH, and determined the adsorption kinetics and isotherms for MET with the BCs were analyzed. In addition, response surface methodology regression model analysis was conducted and the adsorption mechanisms were investigated. The results showed that the thermal stability and chemical stability of MBC, IBC, and KBC were higher than those of OBC, and MBC had the greatest stability. The MET adsorption rates of OBC, MBC, IBC, and KBC were 62.15%, 92.47%, 87.97%, and 83.31%, respectively. The kinetic fitting results and adsorption mechanisms showed that the modification of BC with minerals enhanced the physical adsorption of MET. The maximum MET adsorption capacities by OBC, MBC, IBC, and KBC were 39.68 mg g⁻¹, 68.49 mg g⁻¹, 65.79 mg g⁻¹, and 65.36 mg g⁻¹, respectively. Hydrogen bonds, π–π bonds, coordination bonds, and hydrophobic interactions were the key adsorption mechanisms. Therefore, the mineral-modified BCs were characterized by high adsorption rates and stability. This approach can make BC more efficient, with higher performance as a low cost soil amendment.

The synthesis of clay-biochar composite has been recognized as an effective way to enhance the removal of pollutants. The interaction between clay mineral and biomass during thermal pyrolysis and the sorption capacity for ionic/nonionic organic containments have not been elaborated. In this study, two types of biochar were obtained from pyrolytic carbonization of the cellulosic-rich corn straw (C) and lignin-rich pine wood (P) at 500 or 700 °C. Typical clay minerals kaolinite and montmorillonite were selected to prepare clay-biochar composite. The results showed that the addition of clay mineral could strengthen dehydration reaction of corn straw biomass and reinforce its carbon structure. Montmorillonite-biochar composite owned more CC functional groups and porous structure than kaolinite-biochar composite. The addition of clay minerals could promote electrostatic attraction of ionic formed norfloxacin (NOR) on clay-pine wood biochar. However, the sorption capacity of nonionic diethyl phthalate (DEP) adsorption on clay-corn straw biochar decreased, owing to that clay increased the compactness of the biochar carbon structure, thus inhabited hydrophobic partition of nonionic organic compounds on disordered carbon fraction. The results from this study provide insights into the suitable contaminated site remediation by clay-biochar composite.

The development of efficient, recyclable, and environment-friendly adsorbent for wastewater remediation is considered a challenge. In this study, a hierarchical porous kaolinite microsphere (HPKS) with three-dimensional (3D) structure was fabricated based on natural-layered kaolinite mineral via an environmentally friendly direct hydrothermal strategy. Characterization results revealed that HPKS microsphere with 3D hierarchical porous structure was constructed with numerous nanospheres which are assembled by ultrafine aluminosilicate flakes. HPKS exhibited negative charge feature ranging from strong acid to high alkaline solution. The influence of contact time, solution pH, initial dye concentration, adsorbent dosage, and foreign ions on methylene blue (MB) adsorption capability was systematically investigated. The synthesized HPKS with higher specific surface area (250.6 m²/g) shows an outstanding adsorption capacity towards MB (411.8 mg/g) and excellent selectivity for cationic MB dyes over anionic methyl orange and competitive metal ions. The adsorption kinetic experiment results fit very well with the pseudo-second-order model and reflect the fast adsorption rate of MB on HPKS. The sorption isotherm study reveals the chemisorption of electrostatic attraction between the cationic MB molecules and the negative charged surfaces of HPKS. More importantly, the MB removal efficiency is more than 99% in a broad range of solution pH value. The adsorption capacities of HPKS can be easily recovered by calcination at 600 °C to remove the adsorbed dyes and without obvious diminishment even after six successive cycles. Therefore, the HPKS is a cost-effective and environmentally friendly adsorbent which has is promising to use in practical applications.

The water quality of mine water is obviously improved after being stored in underground reservoir, but the process of water–rock interaction and the purification mechanism of mine water quality are not clear. In this study, the water samples and rock samples collected in the underground reservoir of Daliuta coal mine were taken as the research object. Based on the analysis of the hydrochemical characteristics of the reservoir water samples and the characterization of the rock samples, combined with PHREEQC analysis, the mechanism of water quality purification of mine water was discussed. The results showed that the rocks in the underground reservoir had layered silicate structure and flaky kaolinite structure, with some irregular edges and microcracks, and higher specific surface area and total pore volume. These characteristics made the rocks have a certain adsorption and removal capacity for heavy metal ions and other pollutants in the mine water. The water–rock interaction, such as the dissolution of albite and halite, the precipitation of gypsum and kaolinite, and the cation exchange, resulted in the increase of the concentration of Na⁺ and the decrease of the concentration of Ca²⁺, Mg²⁺, and TDS in the outlet water, and the hydrochemical type changed from SO₄²⁻-Cl⁻/Ca²⁺ type to SO₄²⁻-Cl⁻/Na⁺ type. Moreover, this study shows that PHREEQC analysis can be used to analyze the water–rock interaction of coal mine underground reservoir and can obtain more detailed information; therefore, it may have the potential ability to help assess the migration and transformation of pollutants during the storage process of mine water in underground reservoirs.

The idea of reusing municipal incinerator bottom ash (MIBA), the residue from incinerating municipal solid wastes, fits nicely in a circular economy scheme, which leads to an avoided impact of landfill disposal, and at the same time reduces the demand of natural resources. Past studies have attempted to add 20 to 60% MIBA for ceramic production, and resulted in some inspiring success. Focused on delivering quality interior and exterior floor tiles meeting industrial standards, this study investigated the operative conditions and the optimum amount of MIBA in the mix. In this study, only the kaolinite clay and MIBA were used. Before making specimens, raw materials of clay and MIBA underwent SEM, EDS, and TCLP tests to determine their chemical contents. Six sets of specimens with different replacement levels of MIBA (0%, 5%, 10%, 15%, 20%, and 30%) were then prepared. These specimens were fired at 1000°C, 1050°C,1100°C, and 1150°C and the products underwent a series of mechanical tests to verify their performance. NMR (nuclear magnetic resonance spectroscopy) were also used to determining the organic compound structure after each specimens’ crystallization. Research results showed that proper mix of MIBA up to 20% could result in quality tiles complying with specifications for interior and exterior flooring applications at certain kiln temperatures, while the specimens with 30% MIBA failed to meet either bending strength or size shrinkage requirement at all four kiln temperatures, and could not deliver a satisfactory result.

The sediments were studied according to the granulometric characteristics, the geochemical analyses of the sediments (organic matter (OM), carbonate, and pH), the analyses of heavy metals (HM) characteristics, and their contamination status in the ecological system and the mineralogical analysis of the sediments at 8 sites spread over the Marchica lagoon (NE-Morocco). Our results showed that the opening of the new wide and deep pass affected the spatial distributions of the metals, which were closely related to fine fraction and sediment OM concentration. In the north and southeast lagoon zones presented low concentrations of the HM, fine particles (clay), OM, whereas the south and the center of the lagoon were heavily loaded with HM and OM, corresponding to the trapping zones by fine particles. The results of mineralogy analyses have revealed the predominance of non-clay minerals such as quartz and calcite, and for the clay fractions of sediments showed that they are formed of illite, kaolinite, smectite, and chlorite in highly variable proportions; illite was the most dominant clay in the north-western Marchica lagoon sediments. Therefore, the HMs are fixed by clay colloids having a high cation exchange capacity with smectite-chlorite-kaolinite assembly.

Antibiotic toxicity and antibiotic resistance have become significant challenges to human health. However, the potential ecotoxicity of sediment-associated antibiotics remains unknown. In this study, biochemical responses, histological changes, and behavioral responses of Corbicula fluminea exposed to sediment-associated ciprofloxacin (CIP) were systemically investigated. Special attention was paid to the influence of different substrate types. Biochemical analyses revealed that the balance of the antioxidant system was disrupted, eventually leading to oxidative damage to the gills and digestive gland with increasing CIP concentration. Severe histopathological changes appeared along with the oxidative damage. An enlargement of the tubule lumen and thinning of the epithelium in the digestive gland were observed under exposure to high CIP concentrations (0.5 and 2.5 μg/g CIP). In a behavioral assay, the filtration rate of C. fluminea in high concentration exposure groups was clearly inhibited. Moreover, from the integrated biomarker response (IBR) index, the toxicity response gradients of the digestive gland (no substrate--NOS > Sand > Sand and kaolinite clay-- SKC > Sand, kaolinite clay, and organic matter--SCO) and gills (NOS > SCO > SKC > Sand) were different among substrate exposure groups. The most serious histopathological damage and highest siphoning inhibition were observed in the NOS group. The changes in the morphological structure of digestive gland cells in C. fluminea were similar in the other three substrate groups. The inhibition of the filtration rate in the higher concentration groups decreased in the order Sand > SKC > SCO.

The high alkalinity of bauxite residue and its sustained release impose major limitation on its reuse and ecological disposal. It has been confirmed from sustained rehabilitation that gypsum can effectively reduce the alkalinity of bauxite residue by continuously releasing Ca²⁺ to react with carbonate and hydroxide. However, the combined bauxite residue with high calcium content exhibits stubborn alkalinity for most alkaline reduction methods employing cations to consume carbonate. In this study, we have aimed to address this knowledge gap by investigating the dose–response relationship in the alkaline reduction induced by ferrous sulfate (FS) neutralization. The pH, exchangeable sodium percentage (ESP), and CO₃²⁻/HCO₃⁻ of bauxite residue decreased from 10.6, 44.1%, and 42.7/24.5 mg/kg to 8.1, 27.7%, and 0.7/18.0 mg/kg, respectively. Approximately 20–55 days were required for the neutralization reaction to reach equilibrium. The FS induced an increase in free iron oxide (Fed) and amorphous iron oxide (Feₒ), and partial dissolution of alkaline minerals including calcite, cancrinite, and kaolinite in bauxite residue. Further, addition of FS also affected the kinetic dissolution process of bauxite residue; the acid neutralization capacity of bauxite residue to pH 7 decreased from 0.21 mol H⁺/kg solid to 0.02 mol H⁺/kg solid. The results showed FS to be a potential candidate for improving the characteristics of the combined bauxite residue, and guide the FS application for the disposal of the combined bauxite residue.

This paper presents a study on orange II sodium salt (OII) degradation based on iron nanoparticles supported by kaolinite clays. The effects of nanoscale iron and initial dye concentration, as well as hydrogen peroxide dosage in a Fenton process, on the degradation of OII were studied. These nanoparticles were synthesized by green methods using coffee bean extract as a natural antioxidant for this process. Aqueous iron chloride was mixed with coffee extract, which is rich in antioxidants, and these antioxidants are responsible for the reduction of metal compounds into nanoparticles. The composite iron nanoparticle-kaolinite composite was synthesized from an aqueous FeCl₃ and kaolinite solution with the added coffee bean extract. The results showed that OII removal efficiency increased with the amount of iron nanoparticles (n-Fe) alone and with the amount iron-supported-kaolinite composite. By increasing the amount of composite, the adsorptive surface area increases as well as the number of active sites, which determine the higher removal efficiency. Regarding H₂O₂ dosage, dye removal was more efficient at lower quantities: 62% removal efficiency with addition of 10 mL H₂O₂, while for the test conducted with 20 mL H₂O₂, removal efficiency was 47%. A possible reason for this behavior can be the n-Fe/ H₂O₂ ratio, which influences the production of degradation products and hinders the degradation. HIGHLIGHTS: • Green synthesized metallic iron nanoparticles (n-Fe) using coffee bean extract as a natural oxidant were used for the removal of Orange II • In order to improve the degradation process, a clay-nanoscale iron composite was used, as well as Fenton oxidation using added H₂O₂. As a support material for the composite, kaolinite was used. The results showed that both reduction and adsorption processes are involved in the dye removal process. Applying Langmuir and Freundlich isothermal models shows monolayer coverage • By comparing the efficiency of the composite alone with the efficiency of the composite with the Fenton process, better results were obtained for the second case which shows the importance of the H₂O₂/Fe system in the degradation process. Also, we may state that the best results were obtained by using n-Fe only • Since the amount of n-Fe present in the composite is low (0.01 g), further experiments should be held concerning the ratios between n-Fe and clay in the composite. Experiments using wastewater containing dyes from a real industrial process should also be done as well, to confirm the activity of this material containing nanoscale iron made using green synthesis in a real wastewater environment, with all the associated ions and compounds.

Xylene is a typical petrochemical industry pollutant. The fate of xylene spilled into soil was investigated in laboratory-scale batch and column experiments. The results show that free xylene in the soil evaporated quickly (7.2–10.4 mg h⁻¹), but any fraction adsorbed onto the soil particles evaporated much more slowly (2.3–2.4 mg h⁻¹). The retention of xylene in the soil was mainly controlled by its adsorption onto the soil minerals. The adsorption was best described using a pseudo-second-order kinetic model and Langmuir model. Adsorption up to 530 mg kg⁻¹ was observed, and minerals such as quartz and kaolinite were the key adsorbents. Adsorption of xylene was promoted by the presence of dissolved organics up to about 50 mg L⁻¹, but it was significantly inhibited by cobalt-bearing compounds which are often used as catalysts in the petrochemical industry. The release of xylene from soil would be facilitated by intense rainfall and cobalt-bearing compounds but would be inhibited with the increase of rainwater acidity. This study reveals the environmental behavior of xylene in soil and provides scientific guidance for pollution control and risk assessment of BTEX contaminated sites.