Characteristics of isothermal adsorption and desorption of aluminum ion to/from humic acids

The adsorption and desorption characteristics of Al^3＋ to/from humic acids at different pH, ionic strength, and temperature were studied by the C-25 glucosan-gel chromatography method. The results showed that the maximum adsorption amount （Qmax） and adsorption constant （k） increased, whereas, the absolute value of standard thermodynamic molar free energy change （ΔGm^0） decreased with the increase of pH at constant ionic strength and temperature. With ionic strength increasing from 0 to 0.15 mol/L, Qmax, and k increased and the absolute value of ΔGm^0 decreased at constant pH and temperature. High temperature was unfavorable for the adsorption reaction, as indicated by the dramatic decrease of Qmax and the absolute value of ΔGm^0 with an increase in temperature. The standard thermodynamic molar free energy change （ΔGm^0） and the standard thermodynamic enthalpy change （ΔHm^0） of the adsorption reaction were both negative, suggesting that adsorption reaction was spontaneous and exothermic. The desorption rate of HA-Al^3＋ complex accelerated with the decrease of pH, and a significant linear relationship could be obtained between pH and the desorption rates of Al^3＋ from humic acids. These results demonstrated that the Al^3＋ adsorption reaction was a ＂biphase＂ reaction, and adsorption occurred at both the interior and exterior adsorption sites of humic acids.

Optimization of Methylene Blue Dye Adsorption onto Coconut Husk Cellulose Using Response Surface Methodology: Adsorption Kinetics, Isotherms and Reusability Studies

In this study, coconut husk cellulose was employed as a cost-effective and environmentally friendly adsorbent to eliminate methylene blue (MB) dye from aqueous solutions. The successful development of response surface methodology paired with a central composite design (RSM-CCD) enabled the optimization and modelling of the adsorption process. The study investigated the individual and combined effects of three variables (pH, contact time, and initial MB dye concentration) on the adsorption of MB dye onto coconut husk cellulose. The developed RSM-CCD model exhibited a remarkable degree of precision in predicting the removal efficiency of MB dye within the specified experimental parameters. This was demonstrated by the strong regression parameters, with an R2 value of 99.79% and an adjusted R2 value of 99.6%. The study depicted that the optimal parameters for attaining a 98.8827% removal of MB dye using coconut husk cellulose were as follows: an initial MB dye concentration of 30 mg∙L−1, contact time of 120 minutes, and pH 7 at a fixed adsorbent dose of 0.5 g. The Freundlich isotherm model provided the most satisfactory description of the equilibrium adsorption isotherms, suggesting that MB dye adsorption onto coconut husk cellulose occurs on a heterogeneous surface. The experimental results demonstrated a strong agreement with the pseudo-second-order kinetics model, indicating that the number of active sites present on the cellulose adsorbent predominantly influences the adsorption process of MB dye. Additionally, the adsorbent made from coconut husk cellulose exhibited the potential to be reused, as it retained its efficiency for a maximum of three cycles of adsorption of MB dye. The results of this study show that coconut husk cellulose has the potential to be an effective and sustainable adsorbent for removing MB dye from aqueous solutions.

Isothermal Adsorption and Desorption Properties of Marine Shales on Longmaxi Shale in South China

The investigation of adsorption and desorption properties of shale are important for estimating reserves and exploitation. The shale samples used in this paper were from the marine shale on Longmaxi shale in Sichuan and Hubei province, China. A series of analyses, such as organic carbon content test, vitrinite reflectance test, rock pyrolysis, X-ray diffraction, and N2/CO2 adsorption were performed. Gravimetric method with magnetic suspension balance was used to conduct isothermal adsorption and desorption experiments. The Langmuir, Freundlich, Langmuir-Freundlich, D-R, semi-pore, and Tothequations were used to fit the isothermal adsorption and desorption curves. And adsorption potential theory was used to explain the adsorption and desorption process. According to the results, the shale samples have a high level of organic carbon content with the same organic matter type II1 and high degree of maturation. The volume of adsorption increases rapidly and slows down to stable with the pressure increasing. Desorption is the inverse process of adsorption and 10 MPa - 0.5 MPa is the main period of shale gas desorption. The fitting results show that three-parameter isotherm equations are better than the two-parameter ones. The adsorption temperature has a great influence on adsorption volume, little effect on potential energy. Adsorption potential varies under different TOC to affect adsorption properties. Moreover, a large adsorption potential means that the gas molecule is easy to adsorb but difficult to desorb.

Pore structure of low‑permeability coal and its deformation characteristics during the adsorption–desorption of CH4/N2

The pore structure of coal plays a key role in controlling the storage and migration of CH4/N2.The pore structure of coal is an important indicator to measure the gas extraction capability and the gas displacement efect of N2 injection.The deformation characteristic of coal during adsorption–desorption of CH4/N2 is an important factor afecting CH4 pumpability and N2 injectability.The pore structure characteristics of low-permeability coal were obtained by fuid intrusion method and photoelectric radiation technology.The multistage and connectivity of coal pores were analyzed.Subsequently,a simultaneous test experiment of CH4/N2 adsorption–desorption and coal deformation was carried out.The deformation characteristics of coal were clarifed and a coal strain model was constructed.Finally,the applicability of low-permeability coal to N2 injection for CH4 displacement technology was investigated.The results show that the micropores and transition pores of coal samples are relatively developed.The pore morphology of coal is dominated by semi-open pores.The pore structure of coal is highly complex and heterogeneous.Transition pores,mesopores and macropores of coal have good connectivity,while micropores have poor connectivity.Under constant triaxial stress,the adsorption capacity of the coal for CH4 is greater than that for N2,and the deformation capacity of the coal for CH4 adsorption is greater than that for N2 adsorption.The axial strain,circumferential strain,and volumetric strain during the entire process of CH4 and N2 adsorption/desorption in the coal can be divided into three stages.Coal adsorption–desorption deformation has the characteristics of anisotropy and gas-diference.A strain model for the adsorption–desorption of CH4/N2 from coal was established by considering the expansion stress of adsorbed gas on the coal matrix,the compression stress of free gas on the coal matrix,and the expansion stress of free gas on micropore fractures.N2 has good injectability in low-permeability coal seams and has the dual functions of improving coal seam permeability and enhancing gas fow,which can signifcantly improve the efectiveness of low-permeability coal seam gas control and promote the efcient utilization of gas resources.

Experimental and Numerical Research on Water Transport during Adsorption and Desorption in Cement-Based Materials

The durability of cement-based materials is related to water transport and storage in their pore network under different humidity conditions.To understand the mechanism and characteristics of water adsorption and desorption processes from the microscopic scale,this study introduces different points of view for the pore space model generation and numerical simulation of water transport by considering the“ink-bottle”effect.On the basis of the pore structure parameters(i.e.,pore size distribution and porosity)of cement paste and mortar with water-binder ratios of 0.3,0.4 and 0.5 obtained via mercury intrusion porosimetry,randomly formed 3D pore space models are generated using two-phase transformation on Gaussian random fields and verified via image analysis method of mathematical morphology.Considering the Kelvin-Laplace equation and the influence of“ink-bottle”pores,two numerical calculation scenarios based on mathematical morphology are proposed and applied to the generated model to simulate the adsorption-desorption process.The simulated adsorption and desorption curves are close to those of the experiment,verifying the effectiveness of the developed model and methods.The obtained results characterize water transport in cement-based materials during the variation of relative humidity and further explain the hysteresis effect due to“ink-bottle”pores from the microscopic scale.

Determination of Competitive Adsorption and Desorption of Heavy Metals by Isotherm and Sequential Extraction Methods in Different Soil Orders in Erzurum Plain

The objective of this study was to DTPA （complexion agent） and a sequential extraction procedure, and adsorption-desorption isotherm （competitive） evaluate the mobility and distribution of Fe, Zn, Mn, Cu, Cd, Ni, and Pb using the in surface samples of five soil great groups differing in their physicochemical properties. For determining heavy metal adsorption and desorption capacities of soil samples, six different concentrations （0, 2.5, 5, 10, 15 and 20 mg Lt） were used in a laboratory experiment with tree replications. An analytical procedure involving sequential chemical extractions has been used for partitioning of heavy metals into five fractions. Sorption isotherms were characterized using linear, Frendlich and Langmuir equations. The results indicated that the selective sequences of the metal adsorption based on the distribution coefficient was Pb〉Cu〉Ni〉Cd〉Zn〉Mn〉Fe and Pb, Cu, and Ni are the most strongly sorbed metals by these soils, whereas Cd, Zn and Mn are the least sorbed ones. The total adsorbed amount of these metals on the studied soils was well described by Langmuir equation. Calciorthid had the highset Pb, Cu, Ni, Cd, Zn, Mn, and Fe adsorption, and the sequences followed order Fluvaquent〉Argiustoll〉Pellustert〉Haplustept of the studied soil.

Study on the Effects of Polyacrylamide on Phosphorus Adsorption and Desorption Characteristics of Soil Aggregates

[Objective]The research aimed to provide scientific reference for reasonable utilization of polyacrylamide(PAM).[Method]After PAM treatment,the soil aggregates were classified through dry sieve analysis and the adsorption capacity and desorption capacity of all soil aggregates to phosphorus at different phosphorus concentrations were analyzed.[Result] The phosphorus adsorption and desorption of soil sample treated by PAM declined. The amount of phosphorus adsorption increased with the increase of phosphorus concentration and this increase was fast in low phosphorus concentration area but slow in high phosphorus concentration area.At different phosphorus concentrations,adsorption showed a へ shape changing trend.The phosphorus adsorption was related to phosphorus concentration and the 2-3 mm aggregate had the highest desorption rate while 0.1-0.25 mm aggregate and 0.45-1 mm aggregate had lowest desorption rate.[Conclusion]The PAM treatment generated significant influence on phosphorus adsorption and analytic features of aggregate in all size fractions.

Hydrogen desorption kinetics mechanism of Mg-Ni hydride under isothermal and non-isothermal conditions

The Mg-Ni hydride was prepared by hydriding combustion synthesis under a high magnetic field. The dehydriding kinetics of the hydrides was measured under the isothermal and non-isothermal conditions. A model was applied to analyzing the kinetics behavior of Mg-Ni hydride. The calculation results show that the theoretical value and the experimental data can reach a good agreement, especially in the case of non-isothermal dehydriding. The rate-controlling step is the diffusion of hydrogen atoms in the solid solution. The sample prepared under magnetic field of 6 T under the isothermal condition can reach the best performance. The similar tendency was observed under the non-isothermal condition and the reason was discussed.

Adsorption and Desorption Characteristics of Cadmium and Lead in Typical Paddy Soils of Jiangxi Province and Its Environmental Risk Assessment

[Objective] This study aimed to investigate the adsorption and desorption characteristics of cadmium and lead in typical paddy soils of Jiangxi Province. [Method] Gleyed paddy soil and waterloggogenic paddy soil were collected from Jiangxi Province and used as experimental materials to investigate single and com- petitive adsorption and desorption behaviors of cadmium and lead by batch equilib- rium method. The environmental risk of the presence of cadmium and lead in paddy soils was assessed using distribution coefficients. [Result] Under equal ratio condi- tions, the adsorption capacity of lead by two types of paddy soils was higher than that of cadmium, and the adsorption rate in waterloggogenic paddy soil was higher than that in gleyed paddy soil. The desorption capacity of cadmium by two types of paddy soils was higher than that of lead, and the desorption rate in gleyed paddy soil was higher than that in waterloggogenic paddy soil. Under competitive condi- tions, the adsorption capacity of cadmium and lead by paddy soils was significantly reduced compared with single ion system, while the desorption rate was remarkably improved. The potential environmental risk of cadmium contamination was greater than that of lead in paddy soils. Moreover, environmental risks of cadmium and lead were reduced with the increase of pH, which increased significantly under the coex- istence state. [Conclusion] In the coexistence of cadmium and lead, cadmium con- tamination should be controlled and avoided compared with lead contamination in paddy soils.

Adsorption and Desorption of Natural Zeolite on NH_4^+

The adsorption and desorption kinetic of natural zeolite on NH4＋ was stud-ied by lab analysis. The results showed that the adsorption and desorption kinetic of natural zeolite on NH4＋ coincided with the first-order kinetics, modified Freundlich equation, parabolic diffusion model, and heterogeneous diffusion model. The desorp-tion of the adsorbed NH4＋ was far rapider than the adsorption, which can be fin-ished within 60 min.

Insights into carbon dioxide sequestration into coal seams through coupled gas flow-adsorption-deformation modelling

Injecting carbon dioxide(CO_(2))into coal seams may unlock substantial carbon sequestration potential.Since the coal acts like a carbon filter,it can preferentially absorb significant amounts of CO_(2).To explore this further,desorption of the adsorbed gas due to pressure drop is investigated in this paper,to achieve an improved understanding of the long-term fate of injected CO_(2) during post-injection period.This paper presents a dual porosity model coupling gas flow,adsorption and geomechanics for studying coupled processes and effectiveness of CO_(2) sequestration in coals.A new adsorption?desorption model derived based on thermodynamics is incorporated,particularly,the desorption hysteresis is considered.The reliability of the proposed adsorption-desorption isotherm is examined via validation tests.It is indicated that occurrence of desorption hysteresis is attributed to the adsorption-induced pore deformation.After injection ceases,the injected gas continues to propagate further from the injection well,while the pressure in the vicinity of the injection well experiences a significant drop.Although the adsorbed gas near the well also decreases,this decrease is less compared to that in pressure because of desorption hysteresis.The unceasing spread of CO_(2) and drops of pressure and adsorbed gas depend on the degree of desorption hysteresis and heterogeneity of coals,which should be considered when designing CO_(2) sequestration into coal seams.

Adsorption/desorption behavior between a novel amphoteric granular lignin adsorbent and reactive red K-3B in aqueous solutions

A novel amphoteric granular lignin adsorbent(AGLA) was prepared using magnesium lignosulfonate as a raw material which was provided by a straw sulfite pulp mill in Guangdong Province, China. A reactive dye(red K-3B) was used as an adsorbate to investigate the adsorption behavior by static and mobile ways. The removal of reactive red K-3B was found to be initially pH and concentration dependent. Moreover, an increase of solution temperature ranging from 5℃ to 60℃ helped to enhance the rate of intraparticle diffusion of adsorbate and changes in the size of the pores of the adsorbent and thus to reduce the adsorption time. The total breakthrough adsorption capacity was 531 mg/g, and the saturated adsorption capacity was 560 mg/g, which prevailed over the activated carbons evidently. The reactive red K-3B adsorbed on AGLA could be recovered with a mixture of alcohol, NaCl and HCl aqueous solutions. The recovery percentage could reach 92.4%.

Effect of dissolved organic matter on adsorption and desorption of mercury by soils

Effects of dissolved organic matter (DOM) on adsorption and desorption of Hg were investigated in two kinds of soils, Xanthi-Udic Ferralosols (XUF) and Typic Purpli-Udic Cambosols (TPUC). The DOM was obtained from humus soil (DOMH), rice straw (DOMR), and pig manure (DOMP). The presence of DOM obviously reduced Hg maximum adsorption capacity with up to 40% decreases over the control, being an order of DOMH (250.00 mg/kg)< DOMR (303.03 mg/kg) < DOMP (322.58 mg/kg) < CK (control 416.67 mg/kg) for the...

Adsorption and desorption of Cu(Ⅱ) and Pb(Ⅱ) in paddy soils cultivated for various years in the subtropical China

The adsorption and desorption of Cu（Ⅱ） and Pb（Ⅱ） on upland red soil,and paddy soils which were originated from the upland soil and cultivated for 8,15,35 and 85 years,were investigated using the batch method.The study showed that the organic matter content and cation exchange capacity （CEC） of the soils are important factors controlling the adsorption and desorption of Cu（Ⅱ） and Pb（Ⅱ）.The 15-Year paddy soil had the highest adsorption capacity for Pb（Ⅱ）,followed by the 35-Year paddy soil.Both the 35-Year paddy soil and 15-Year paddy soil adsorbed more Cu（Ⅱ） than the upland soil and other paddy soils.The 15-Year paddy soils exhibited the highest desorption percentage for both Cu（Ⅱ） and Pb（Ⅱ）.These results are consistent with the trend for the CEC of the soils tested.The high soil CEC contributes not only to the adsorption of Cu（Ⅱ） and Pb（Ⅱ） but also to the electrostatic adsorption of the two heavy metals by the soils.Lower desorption percentages for Cu（Ⅱ） （36.7% to 42.2%） and Pb（Ⅱ） （50.4% to 57.9%） were observed for the 85-Year paddy soil.The highest content of organic matter in the soil was responsible for the low desorption percentages for the two metals because the formation of the complexes between the organic matter and the metals could increase the stability of the heavy metals in the soils.

Adsorption-desorption behavior of acetochlor to soils in the presence of some environmental substances

The behavior of herbicide acetochlor adsorption desorption to soil in the presence of humic acid (HA), anionic surfactant sodium dodecylbenzene sulfonate (SDBS), cationic surfactant hexadecyltrimethyl ammonium bromide (HDAB) and NH 4NO 3 as a chemical fertilizer was studied. Observed acetochlor adsorption isotherm were well described using Freundlich isotherm equation, from which the desorption isotherm equation has been deduced. The deduced equation can more directly describe acetochlor desorption process. The results showed that the enhance of acetochlor adsorption capacity by solid HA was greater than by soluble HA. The presence of NH 4NO 3 can slightly enhance acetochlor adsorption to soil by comparison with that measured in NH 4NO 3 free solution. In soil water system, surfactant acetochlor interaction is very complex, and the surfactant adsorptions as well as acetochlor adsorption need to be considered. When acetochlor soil suspensions contained lower concentration SDBS or HDAB (40 mg/L), K f for acetochlor adsorption was decreased in comparison to that measured in SDBS or HDAB free solution. When acetochlor soil suspensions contained higher concentration SDBS or HDAB (corresponding 1400 mg/L or 200 mg/L), K f for acetochlor adsorption was increased in comparison to that measured in SDBS or HDAB free solution.

Coalbed methane adsorption and desorption characteristics related to coal particle size

Effects of particle size on CH4 and CO2adsorption and desorption characteristics of coals are investigated at 308 K and pressures up to 5.0 MPa.The gas adsorption and desorption isotherms of coals with particle sizes ranging from 250 μm to 840 μm are measured via the volumetric method,and the Langmuir model is used to analyse the experimental results.Coal particle size is found to have an obvious effect on the coal pore structure.With the decrease of coal particle size in the process of grinding,the pore accessibility of the coal,including the specific surface area and pore volume,increases.Hence,coal with smaller particle size has higher specific surface area and higher pore volume.The ability of adsorption was highly related to the pore structure of coal,and coal particle size has a significant influence on coal adsorption/desorption characteristics,including adsorption capacity and desorption hysteresis for CH4 and CO2,i.e.,coal with a smaller particle size achieves higher adsorption capacity,while the sample with a larger particle size has lower adsorption capacity.Further,coal with larger particle size is also found to have relatively large desorption hysteresis.In addition,dynamic adsorption performances of the samples are carried out at 298 K and at pressures of 0.1 MPa and 0.5 MPa,respectively,and the results indicate that with the increase of particle size,the difference between CO2 and CH4adsorption capacities of the samples decreases.

Adsorption/desorption of toluene on a hypercrosslinked polymeric resin in a highly humid gas stream

In many sources of volatile organic compounds (VOCs), large amounts of water vapor come from the air and the reactors. The relative humidity (RH) of exhaust gas is normally >60% and is supersaturated. Maintaining the property of adsorbent on VOCs in a highly humid gas stream is a serious industrial problem. In this study, the adsorption/desorption behavior of toluene in a micro-mesoporous polymeric resin was investigated in a highly humid environment to explore the influence of abound water vapor on resin adsorption and regeneration. This resin could selectively adsorb toluene at an RH of 80%, and its adsorption property was unaffected by the presence of water vapor. In the case of humidity saturation, the resin displayed a high adsorption capacity at a moisture content of <30%. Therefore, the polymer resin is an excellent water-resistant adsorbent of VOCs. In the regenerative experiment, the resin maintained its original adsorption capability after four adsorption/ desorption cycles of toluene purging with nitrogen gas at 120℃. The resin exhibited excellent regeneration performance at high humidity.

Adsorption and desorption behaviors of ssDNA molecules on mica surface by surface forces apparatus

An approach for studying the adsorption and desorption behaviors of single-stranded DNA（ ssDNA） molecules on the mica surface by the surface forces apparatus（ SFA） is reported,which can be used to characterize the precise thickness,configuration and mechanical properties of ssDNA layers on the mica surface at a certain buffer solution. The formation of ss DNA layers is first studied by tuning the ssDNA concentrations, and the experimental results indicate that the ss DNA concentration of 100 ng / μL is ideal for forming a ssDNA monolayer structure on the mica surface, and the hardwall value measured to be 1.04 nm under this circumstance is regarded as the thickness of the ssDNA monolayer confined on mica. The desorption behavior of ssDNA molecules from the mica surface is further studied by observing and comparing different shapes of the force-distance curves under certain conditions. It is found that the desorption of ss DNA molecules from the mica surface occurs as the monovalent salts are added into the gap buffer. It is inferred that the competition effect between monovalent and divalent salts can induce the release of ssDNA from substrate.The results also reveal that 10 mmol / L monovalent salts（ Na~＋）is sufficient for the desorption of ssDNA from mica. This work provides an applicable method to study the binding mechanism of ss DNA molecules on inorganic substrates.

Oxygen adsorption/desorption behavior of YBaCo4O7+δ and its application to oxygen removal from nitrogen

A new medium-temperature (200-400 °C) adsorbent material for oxygen removal and air separation, YBaCo4O7+δ, was prepared by the solid-state reaction method. This new adsorbent could adsorb a large quantity of oxygen in the temperature range of 200-370 °C. Adsorbed oxygen could be released by raising temperature over 400 °C or by switching the atmosphere from oxygen to nitrogen. This oxygen adsorption and desorption process had good reproducibility. Taking advantage of this unique oxygen intake/release behavior, a nitrogen purification process was investigated. The results showed that YBaCo4O7+δ material was a promising candidate for the oxygen sorption process and could be used to produce high-purity nitrogen or to remove trace oxygen from other gases.

CO_2 isothermal adsorption models of coal in the Haishiwan Coalfield

Since the capacity of CO2 adsorption of coal is a key factor in coal and CO2 outbursts,an experimental study was carried out on CO2 isothermal adsorption with high-pressure volumetry with dry coal samples from the No.2 coal seam in the Haishiwan Coalfield.Four different equations(Langmuir,BET,D-R and D-A) were used to fit the experimental data.We discuss adsorption mechanisms.The results show that the amount of CO2 adsorption increases rapidly under low relative pressure,i.e.,the ratio of equilibrium pressure and saturated vapor pressure,which indicates that molecular layer adsorption or micropore filling may occur in coal.No clear equilibrium state was observed on the isothermal adsorption curves under relative pressure(P /P0 ) ranging from 0 to 0.8.The fitted results show that the accuracy of the D-A equation is highest with n=1.Micropores are more developed in coal by comparing the BET equation with a pressure mercury injection method on the surface area.The D-A equation(n=1) provides the best fit.By comparing the calculated specific surface area of the BET equation and the mercury intrusion method,it is found that micropore adsorption of CO2 occupies a dominant position.