Adsorption-desorption characteristics of coal-bearing shale gas under three-dimensional stress state studied by low field nuclear magnetic resonance spectrum experiments

The micro-scale gas adsorption-desorption characteristics determine the macro-scale gas transport and production behavior. To reveal the three-dimensional stress state-induced gas adsorption-desorption characteristics in coal-bearing shale reservoirs from a micro-scale perspective, the coal-bearing shale samples from the Dongbaowei Coal Mine in the Shuangyashan Basin were chosen as the research subject. Isothermal adsorption-desorption experiments under three-dimensional stress state were conducted using the low field nuclear magnetic resonance (L-NMR) T2 spectrum method to simulate the in-situ coal-bearing shale gas adsorption-desorption process. The average effective stress was used as the equivalent stress indicator for coal-bearing shale, and the integral of nuclear magnetic resonance T2 spectrum amplitude was employed as the gas characterization indicator for coal-bearing shale. A quantitative analysis was performed to examine the relationship between gas adsorption in coal-bearing shale and the average effective stress. And a quantitative analysis was performed to examine the relationship between the macroscopic and microscopic gas quantities of coal-bearing shale. Experimental findings: (1) The adsorption-desorption process of coal-bearing shale gas follows the L-F function model and the D-A-d function model respectively with respect to the amount of gas and the average effective stress. (2) There is a logarithmic relationship between the macroscopic and microscopic gas quantities of coal-bearing shale during the adsorption-desorption process. This quantitatively characterizes the differences in the curves, which may be related to the elastic-plastic deformation, damage and fracture of the micropores in coal-bearing shale, as well as the hysteresis of gas desorption and the stress field of the gas occurrence state.

Adsorption-desorption characteristics of typical heavy metal pollutants in submerged zone sediments: a case study of the Jialu section in Zhengzhou, China

In recent years, the accumulation ability of heavy metals in sediment has become a key indicator for sediment pollution prevention and control. The adsorption-desorption processes of typical heavy metal pollutants in sediments under different conditions were explored and relied in this article. In addition, different binary competitive adsorption systems were designed to study the competitive adsorption properties of heavy metal contaminants, The quasi-secondary kinetic model simulated the adsorption kinetic process. The sediment adsorption rates for heavy metals were (in descending order) Cu, Pb, Cd, Zn. The Elovich equation simulated the desorption kinetics process better, and the sediment desorption rates for heavy metals were (in descending order) Cd, Cu, Zn, Pb. The average free adsorption energy E of heavy metals was within the range of 8-16 kJ∙mol-1. After the removal of organic matter, the ability of the sediment to sequester heavy metals decreases, The binary competitive adsorption results showed that the presence of interfering ions had the greatest effect on Cd and the least effect on Pb. The adsorption and desorption of the four heavy metals by the sediments in the submerged zone increased with the increase of temperature, and the ratio of desorption to adsorption also increased therewith: the adsorptions of heavy metals by the sediments were all spontaneous processes (under heat absorption reactions). The presence of organic matter can increase the ability of the sediment to sequester Cd, Pb, Cu, and Zn. Additionally, heavy metals exhibited significant selective adsorption properties.

Empirical model to assess leaching of pesticides in soil under a steady-state flow and tropical conditions

Abstract

An empirical model of leaching of pesticides was developed to simulate the concentration of fungicides throughout unsaturated soil. The model was based on chemical reactions and the travel time of a conservative tracer to represent the travel time required for water to flow between soil layers. The model's performance was then tested using experimental data from dimethomorph and pyrimethanil applied to the soil under field and laboratory conditions. The empirical model simulated fungicide concentration on soil solids and in soil solution at different depths over time (mean square error between 2.9 mg2 kg-2 and 61mg2 kg-2) using sorption percentages and degradation rates under laboratory conditions. The sorption process was affected by the organic carbon, clay, and the effective cation exchange capacity of the soil. The degradation rate values of dimethomorph (0.039 d-1-0.009 d-1) and pyrimethanil (0.053 d-1-0.004 d-1) decreased from 0 to 40 cm and then remained constant in deeper soil layers (60-80 cm). Fungicide degradation was a critical input in the model at subsurface layers. The model was determined to be a reliable mathematical tool to estimate the leachability of pesticides in tropical soil under a steady-state flow. It may be extended to other substances and soils for environmental risk assessment projects.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13762-023-05038-w.

Adsorption and Desorption Study of Reusable Magnetic Iron Oxide Nanoparticles Modified with Justicia adhatoda Leaf Extract for the Removal of Textile Dye and Antibiotic

The release of tetracycline hydrochloride (TCH) and methylene blue (MB) dye into the aquatic system uncontrollably caused major environmental and health problems; hence, their prevention required serious attention. Adsorption process is now being researched in order to increase adsorption efficiency and reprocess to alleviate environmental issues. The use of magnetic nanoparticle as an adsorbent for wastewater treatment has a lot of prospective. A magnetic iron oxide nanoparticle surface modified by Vasaka (Justicia adhatoda) leaf extract (JA-MIONs) is used to give a fast removal approach for MB dye and TCH antibiotics. Dynamic light scattering, UV-Vis and band gap measurement, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and transmission electron microscopy were operated to analyse the formation and size of these magnetic nanoparticles. The impacts of different factors such as contact time (30-150 min), adsorbate concentration (10-50 mg/L), pH (4-10), and adsorbent dose (2-10 mg) were explored. Adsorption kinetics and isotherms show that it follows the pseudo-first-order kinetic and the Freundlich isotherm, with maximum adsorption capacities of 76.92 mg/g for MB and 200 mg/g for TCH at 298 K. The reusability of the JA-MIONs eventually exhibited a decline in the adsorption percentage of MB and TCH after five and four times respectively. After the desorption-adsorption cycles, this adsorbent continued to exhibit significant adsorption capacity. This investigation furnished the significant reference data for the synthesis of JA-MIONs as a novel and auspicious adsorbent for the industrial clean-up of toxic dyes and heavily used antibiotics from water.

Simple adsorptive removal of crystal violet, a triarylmethane dye, from synthetic wastewater using Fe (III)-treated pine needle biochar

Untreated and Fe (III)-treated pine needle biochar (PNB) were evaluated at different pH for the removal of toxic crystal violet (CV) dye from synthetic wastewaters. Adsorption kinetics followed the pseudo-first-order kinetics involving intra-particle diffusion process. The adsorption rate constant increased with Fe treatment of PNB especially at pH 7.0. Adsorption data of CV conformed well to Freundlich adsorption isotherms and both adsorption capacity (ln K) and order of adsorption (1/n) of CV were nearly doubled with Fe (III) treatment of PNB at pH 7.0. Desorption of adsorbed CV from both untreated and Fe (III)-treated PNB could be accounted satisfactorily by third-degree polynomial equations. An increase in ionic strength and temperature enhanced dye adsorption onto untreated and Fe (III)-treated PNB. Adsorption of CV was an endothermic and spontaneous reaction with an increase in entropy of the system. FTIR spectra revealed that C = O of carboxylic acid aryls and C = O and C-O-C in lignin residues of PNB reacted with Fe (III) besides the formation of some iron oxyhydroxide minerals. The changes in FTIR confirmed the possible bonding of positively charged moiety of CV with the untreated and Fe-treated PNB. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed the porous surfaces of PNB with clear accumulation of Fe (III) after treatment and deposition of CV dye on surfaces and pores of PNB. Iron (III)-treated PNB at pH 7.0 can serve as an ecofriendly and cost-effective adsorbent for the efficient removal of CV dye from wastewaters.

Se(IV)/Se(VI) adsorption mechanisms on natural and on Ca-modified zeolite for Mediterranean soils amended with the modified zeolite: prospects for agronomic applications

In the present study, the ability of a modified CaCl₂ zeolite (Ca-Z) to both increase Se(IV) availability and restrict Se(VI) mobility in soils is examined. As it was resulted from batch experiments and verified by X-ray absorption fine structure (XAFS) and X-ray fluorescence (XRF) spectroscopies, higher amounts of both Se species adsorbed on Ca-Z compared to natural zeolite (Z-N) forming outer-sphere complexes while the oxidation state did not alter during agitation of samples. Thereafter, Ca-Z was incorporated in six Greek soils, divided into acid and alkaline, at a 20% (w/w) rate and a series of equilibrium batch experiments were performed with soils alone and soils-Ca-Z mixtures to investigate sorption and desorption processes and mechanisms. The acid soils, either treated with Ca-Z or not, adsorbed higher amounts of Se(IV) than alkaline ones, whereas soils alone did not adsorb Se(VI) but impressively high adsorption of Se(VI) occurred in the Ca-Z-treated soils. Desorption of Se(IV) was higher from the Ca-Z-treated soils and especially from the acid soils. Higher distribution coefficients of desorption than the distribution coefficients of sorption were observed, clearly pointing to a hysteresis mechanism. The experimental data fitted with Langmuir and Freundlich isotherms. In the presence of Ca-Z, the Langmuir q_m values increased indicating higher Se(IV) retention while Langmuir b_L values decreased suggesting lower bonding strength and higher Se(IV) mobility. Overall, treating the soils with Ca-Z increased Se(IV) adsorption and mobility whereas it provided sites for Se(VI) adsorption that did not exist in the studied soils.

Adsorption-Desorption and Leaching Behaviors of Tetraniliprole in Three Typical Soils of China

Tetraniliprole (TTP) is a new bisimide-based insecticide. Three typical surface soil samples were collected in farmland across China, including Jiangxi red soil (RS), Shandong yellow brown soil (YBS), and Heilongjiang black soil (BS). Adsorption, desorption and leaching experiments were conducted by using equilibrium oscillation and soil column leaching methods at 25°C ± 1°C. The isothermal adsorption and desorption curves of TTP in the above three soils were in accordance with the Freundlich model. The adsorption/desorption constants (K_ads-f/K_des-f) were 41.96-64.48 and 3.62-43.65, respectively. There is a certain hysteresis in the desorption curve, and the hysteresis coefficient (H) was between 0.14 and 0.89. Besides, the leaching properties of TTP in three soils were different. The leaching of TTP in RS and YBS was easy, while difficult for BS. It is concluded that the different adsorption-desorption ability and leaching ability of TTP in the above three soils was attributed to the distinct contents of organic matter (OM) and cation exchange capacity (CEC) in soil.

Regeneration of 4-chlorophenol from spent powdered activated carbon by ultrasound

Ultrasound-assisted regeneration of powdered activated carbon (PAC) saturated with 4-chlorophenol (4-CP) was investigated in this work. The variables, i.e., acoustic frequency, density levels, regenerating solution species, spent PAC mass, and the number of repeated cycle, were optimized. The UV-Vis spectra, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and pore structure analysis were used to characterize the regenerated PAC as compared to the virgin and spent PAC. The adsorption experiments indicated that the adsorption kinetics of 4-CP fitted well with the pseudo-second-order model, and the main chemisorption process was nonlinear and heterogeneous. The desorption results showed that the optimized regenerated conditions were identified as 40 kHz of frequency, 0.18 W/mL of sonication intensity, 0.1 M NaOH and 50% (v/v) ethyl alcohol mixture of regeneration solution, and 1 g/L of saturated PAC mass. Under this condition, the regeneration efficiency reached up to 86.81%. Hydroxylated oxidation products especially benzoquinone and hydroquinone were formed during ultrasound regeneration. Ultrasound mainly acted on surface functionalities, mesopores, and macropores of PAC through the hydroxyl radical oxidization resulted from the cavitation effect.

Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon

This study investigated the effects of surface functional groups, cation exchange capacity (CEC), surface charge, sesquioxides and specific surface area (SSA) of three soil clay fractions (SCFs) (kaolinite-illite, smectite and allophane) on the retention of dissolved organic carbon (DOC) in soils. Physico-chemical properties of the SCFs before and after removing native carbon and/or sesquioxides were characterised, and the DOC adsorption-desorption tests were conducted by a batch method. Native organic carbon (OC)/sesquioxide removal treatments led to a small change in the CEC values of kaolinite-illite, but significant changes in those of smectite and allophane. The net negative surface charge increased in all samples with an increase in pH indicating their variable charge characteristics. The removal of native OC resulted in a slight increase in the net positive charge on soil clay surfaces, while sesquioxide removal increased the negative charge. Changes in the functional groups on the SCF surfaces contributed to the changes in CEC and zeta potential values. There was a strong relationship (R ² = 0.93, p < 0.05) between the Langmuir maximum DOC adsorption capacity (Q _max) and SSA. The Q _max value also showed a moderately strong relationship (R ² = 0.55, p < 0.05) with zeta potential (at pH 7). Q _max was only poorly correlated with CEC and native OC content. Therefore, along with SSA, the surface charge and functional groups of SCFs played the key role in determining the adsorption affinity and hence retention of DOC in soils.

Biochar: A review of its impact on pesticide behavior in soil environments and its potential applications

Biochar is produced from the pyrolysis of carbon-rich plant- and animal-residues under low oxygen and high temperature conditions and has been increasingly used for its positive role in soil compartmentalization through activities such as carbon sequestration and improving soil quality. Biochar is also considered a unique adsorbent due to its high specific surface area and highly carbonaceous nature. Therefore, soil amendments with small amounts of biochar could result in higher adsorption and, consequently, decrease the bioavailability of contaminants to microbial communities, plants, earthworms, and other organisms in the soil. However, the mechanisms affecting the environmental fate and behavior of organic contaminants, especially pesticides in biochar-amended soil, are not well understood. The purpose of this work is to review the role of biochar in primary processes, such as adsorption-desorption and leaching of pesticides. Biochar has demonstrable effects on the fate and effects of pesticides and has been shown to affect the degradation and bioavailability of pesticides for living organisms. Moreover, some key aspects of agricultural and environmental applications of biochar are highlighted.

Kinetic modeling of pH-dependent antimony (V) sorption and transport in iron oxide-coated sand

Understanding the mechanisms and kinetics controlling the retention and transport of antimony (Sb) is prerequisite for evaluating the risk of groundwater contamination by the toxic element. In this study, kinetic batch and saturated miscible displacement experiments were performed to investigate effects of protonation-deprotonation reactions on sorption-desorption and transport of Sb(V) in iron oxide-coated sand (IOCS). Results clearly demonstrated that Sb(V) sorption was highly nonlinear and time dependent, where both sorption capacity and kinetic rates decreased with increasing solution pH. Breakthrough curves (BTCs) obtained at different solution pH exhibited that mobility of Sb(V) were higher under neutral to alkaline condition than under acidic condition. Because of the nonlinear and non-equilibrium nature of Sb(V) retention and transport, multi-reaction models (MRM) with equilibrium and kinetic sorption expressions were utilized successfully to simulate the experiment data. Equilibrium distribution coefficient (Ke) and reversible kinetic retention parameters (k1 and k2) of both kinetic sorption and transport experiment showed marked decrease as pH increased from 4.0 to 7.5. Surface complexation is suggested as the dominant mechanism for the observed pH-dependent phenomena, which need to be incorporated into the kinetic models to accurately simulate the reactive transport of Sb(V) in vadose zone and aquifers.

Kinetic modeling of antimony(V) adsorption-desorption and transport in soils

Antimonate [Sb(V)] adsorption-desorption and transport in an acidic red soil (Yingtan) and a calcareous soil (Huanjiang) was investigated using kinetic batch and miscible displacement experiments. Different formulations of a multi-reaction model (MRM) were evaluated for their capabilities of describing the retention and transport mechanisms of Sb(V) in soils. The experimental results showed that adsorption of Sb(V) by two soils was kinetically controlled and largely irreversible. The Sb(V) adsorption capacity and kinetic rate of the acidic red soil was much higher than that of the calcareous soil. The asymmetrical breakthrough curves indicated the strong dominance of non-equilibrium retention of Sb(V). A four step sequential extraction procedure provided evidence that majority of applied Sb(V) was irreversibly retained. A formulation of MRM with two kinetic sorption sites (reversible and irreversible) successfully described Sb(V) adsorption-desorption data. The use of kinetic batch rate coefficients for predictions of breakthrough curves (BTCs) underestimated Sb(V) retention and overestimated its mobility. In an inverse mode with optimized rate coefficients, the MRM formulation was capable of simulating Sb(V) transport in soil columns.

Effect of organic matter and calcium carbonate on behaviors of cadmium adsorption-desorption on/from purple paddy soils

Batch experiments and sequential extraction analysis were employed to investigate the effects of soil organic matter and CaCO3 on the adsorption and desorption of cadmium (Cd(2+)) onto and from two purple paddy soils, an acidic purple paddy soil (APPS) and a calcareous purple paddy soil (CPPS). The Cd(2+) adsorption isotherms on both soils could be well-described by the Langmuir and Freundlich equations. CPPS had a higher capacity and a stronger affinity for Cd(2+) adsorption compared with APPS. The adsorption process of Cd(2+) on APPS was dominated by electrostatic attractions, whereas the adsorption mechanism varied depending on the Cd(2+) concentrations in equilibrium solutions on CPPS. At low equilibrium concentrations, the adsorption process was primarily specific adsorption, but nonspecific adsorption dominated at high equilibrium concentrations. Removal of organic matter decreased the amount of Cd(2+) adsorption on both of the soils, slightly affected the Cd(2+) desorption rate and exchangeable Cd (EXC-Cd) in APPS and increased the desorption rate and EXC-Cd in CPPS, suggesting that the effect of organic matter on Cd(2+) adsorption-desorption depends on the soils. CPPS and APPS containing CaCO3 exhibited higher adsorption amounts but lower desorption rates and lower proportions of EXC-Cd than those of their corresponding soils without CaCO3, demonstrating that CaCO3 played an important role in Cd(2+) specific adsorption on soil. The changes in the thermodynamic parameters, including free energy (ΔG(0)), enthalpy (ΔH(0)) and entropy (ΔS(0)), as evaluated by the Van't Hoff equations, indicated that the adsorption was a spontaneous and endothermic process with the primary interaction forces of dipole interactions and hydrogen bonds on APPS, whereas both physical and chemical interactions dominated the adsorption on CPPS.

Uranium behaviour in an estuary polluted by mining and industrial effluents: the Ría of Huelva (SW of Spain)

This paper describes a comprehensive study of the behaviour of U in the Ría of Huelva estuary, formed by the Tinto and Odiel rivers. This ecosystem is conditioned by two hydrochemical facts: one connected with the acid mining drainage (AMD) generated in the first section of the river basins, and another one related to the fertilizer industry located at the estuary. AMD gives a singular character to these rivers; low pH and high redox potential that keep high amounts of toxic elements and radionuclides in dissolution. Most of the data for dissolved U in estuaries indicate conservative mixing, but there are examples of non-conservative behaviour attributed to oxidation/reduction processes or solubility variations. In the Ría of Huelva estuary the U shows a non-conservative behaviour due to solubility changes produced by variations in the pH. A complete removal of riverine dissolved U is observed in a pH range of 4-6. At higher pH values, U release from suspended matter, and probably also from sediments into the dissolved phase is found.