Sorption Of Anions Research Articles

Low-Molecular-Weight Organic Acids in Soils: Sources, Composition, Concentrations, and Functions: A Review

The main sources of the low-molecular-weight aliphatic and aromatic organic acids (LMWOAs) in soils are plant residues, root exudates, and microbial metabolites. In the solutions of upper soil layers of forest ecosystems, citric, oxalic, and malic acids predominate among aliphatic LMWOAs, while substituted and unsubstituted benzoic and cinnamic acids predominate among aromatic LMWOAs. The LMWOA concentrations in plant tissues, root exudates, and microbial metabolites vary from several to some tens of millimoles per liter. In soil solutions, these values decrease by one–two orders of magnitude because of LMWOA sorption and biodegradation, their migration downward the profile, and dilution effect. The sorption of LMWOA anions increases with a decrease in pH and an increase in the concentrations of iron oxides/hydroxides and amorphous aluminosilicate clays. Polybasic acids are more tightly bound to solid phase as compared with monobasic acids. The sorption mechanisms vary depending on pH and LMWOA molecular structure and include formation of innersphere and outersphere surface complexes, ligand exchange, and cation bridge bond. Aromatic LMWOAs can be involved in a hydrophobic interaction. LMWOAs are very rapidly decomposed in the upper horizons, their lifespan amounting to several hours. Some important functions of LMWOAs in soils and landscapes are discussed, including their involvement in the global carbon cycle, mineral weathering, Al and Fe mobilization and translocation, mobilization of Fe and P compounds in the soils deficient in these elements, formation of acid–base buffering of natural waters, and detoxication of soils with increased contents of aluminum, heavy metals, and organic pollutants in soil solutions.

Layered Rare-Earth Hydroxide Unilameller Nanosheets: Synthesis, Characterization, and Adsorption

Unilameller nanosheets with a lateral dimension of one nanometer have been isolated from a colloidal solution of europium-containing layered rare-earth hydroxide (LRH) material by the flocculation method. The nanosheets were achieved by changing pH of the colloidal solution from 6.7 to 11.5. The resultant flocculated nanosheets show high efficiency in sorption of fluoride anions from aqueous media (40 mmol/g), providing a potentially useful sorbent material for water purification technology. The sorbent material is demonstrated to be reusable for at least ten times without a significant loss of adsorption efficiency. And the results fit the Langmuir adsorption curve, indicating the chemisorption nature of the nanosheets. Most importantly, the isolated nanosheets are expected to widen the applicability and flexibility in material synthesis using two-dimensional nanomaterials.

Sorption of pertechnetate anion by cation modified bentonites

Pertechnetate anion sorption was investigated on modified bentonites. Mn-, Cr-, Sn-bentonites were prepared by ion exchange process to sorb radioactive pertechnetate ions. In the case of Mn-, Cr-bentonite the sorb amount of metal ion was 70–90% of the cation exchange capacity of the bentonite which is expected. Interestingly in the case of Sn-bentonite this amount was 1.42 times higher than the cation exchange capacity. On Mn-bentonite the sorption was 35% at pH 5. The removal of pertechnetate ions was 100% on Cr-, Sn-bentonites and the significant sorption was achieved below 650 mV/SHE.

Sorption of d-metal cations by keratin from aqueous solutions

The Cu2+, Cd2+, Ni2+ and Zn2+ metal ions sorption by wool keratin was evaluated from the thermodynamic and kinetic points of view. The experimental data had a very good fit with Langmuir, Freundlich and Dubinin-Radushkevich isotherm models, and the best coefficient of determination was deduced by Langmuir isotherm having value 0.99. The process kinetics was evaluated by intraparticle diffusion model, pseudo-first and pseudo-second order kinetic models, the latter showing the highest correlation with the experimental data. The temperature effect on sorption of Cu2+, Ni2+, Cd2+ and Zn2+ ions from aqueous solutions was determined within a range of adsorption temperatures (283–353 K). The endothermic effect of heavy metal ions sorption by zwitter-ionic form of wool keratin (+H3N-)W(−COO−) indicates that there is a superposition of the sorption process which runs with participation of amino- and carboxyl groups. Acidic keratin groups in the anionic form are involved in the sorption of metal cations, and the amino groups being in the cationic H-form are participated in the sorption of anions to form salt structures [SO42−(+H3N-)2]W[(−COO)2M]. A competitive sorption between doubly- and singly-charged metal cations (M2+/2M+) according to the ion exchange mechanism on the same acid sorption centers of the sorbent was observed. FTIR analysis demonstrated the formation of complexes between Cu2+ and keratin sorption centers that involve terminal free carboxyl groups of amino acids of wool. The chelate structures with metal complexes on acidic sorption sites were computed with the methods of quantum chemistry on modeled compounds, by adhering to chemistry’s best practices.

New highly-percolating alginate-PEI membranes for efficient recovery of chromium from aqueous solutions

Highly percolating membranes are prepared by the interaction of polyethylenimine and alginate (with glutaraldehyde crosslinking). SEM illustrates the macroporous structure of the material. The material is characterized by FTIR before and after chromate anions sorption. Batch-simulated continuous sorption experiments revealed that the maximum sorption occurred at pH 2 and the flow rate has limited effect on sorption efficiency. Uptake kinetics and sorption isotherms are well fitted by the pseudo-second-order rate and Sips equations, respectively. Maximum sorption is found close to 314 mg g−1. Competition effects from Ca(II), Cu(II), Cl−, NO3−, and SO42− are investigated to evaluate sorbent selectivity. The membranes are applied to remediate a simulate of Cr(VI) contaminated electroplating wastewater. Successive cycles of sorption and desorption show that the membranes maintain sorption capacity higher than 200 mg Cr g−1 for both Cr(VI) and total chromium for the first two cycles. These new highly percolating membranes have promising performances for Cr(VI) removal.

Enthalpies of Anion Exchange of Chloride by Pyridinecarboxylate in AV-17-8 Anionite

Enthalpies of Cl– anion exchange for anions of nicotinic, isonicotinic, dipicolinic, and cinchomeronic acids on the strongly basic anionite AV-17-8 are measured at 298 K by means of microcalorimetry. Partial and standard enthalpies of sorption of pyridinecarboxylic acid anions on the Cl-form of AV-17-8 anionite from aqueous solutions are determined. The values of standard enthalpies lie in the range 3–14 kJ/mol, increasing in the order nicotinate, isonicotinate, dipicolinic acid anions, and cinchomeronic acid anions.

Heats of exchange of chloride with pyridinecarboxylate ions in Dowex-1 anion exchanger

The heats of exchange of chloride with pyridinecarboxylic acids anions in Dowex-1 strongly basic anion exchanger was obtained by the microcalorimetric method at 298 K. Nicotinic acid, isonicotinic acid, dipicolinic and cinchomeronic acids as pyridinecarboxylic acids were selected. It has been revealed that the sorption of pyridinecarboxylic acid anions by Cl form of Dowex-1 anion exchanger from aqueous solutions is the endothermic process. The standard enthalpy values of the exchange of chloride by pyridinecarboxylate ions in Dowex-1 anion exchanger calculated via microcalorimetric experimental data are in the range of 3–14 kJ mol−1. The standard enthalpies of model reaction that simulated the anion exchange process were determined via quantum chemical calculations of the reagent formation enthalpies in vacuum in the framework of the MOPAC2016 program. The enthalpies of both ion exchange of chloride by pyridinecarboxylate and the model reaction increase in the sequence: nicotinate, isonicotinate, anion of dipicolinic acid, anion of cinchomeronic acid.

Effects of pyrolysis temperature on nitrate-nitrogen (NO3−-N) and bromate (BrO3−) adsorption onto date palm biochar

Biochars (BCs) produced through biomass pyrolysis are highly efficient adsorbents for retaining dissolved cations in soil and water. However, their anionic sorption characteristics are unclear and depend on the feedstock used and the pyrolysis temperature. Herein, the adsorption of nitrate-nitrogen (NO3−-N) and bromate (BrO3−) anions onto date palm biochar was evaluated by considering the pyrolysis temperature in relation with the initial concentrations, initial pH, and adsorbent dose. Biochars from date palm rachis were produced at 300 °C (BC300) and 700 °C (BC700). The latter exhibited the highest adsorption efficiency of NO3−-N from aqueous solutions at an initial pH of 2, which was 25.8%–44.3% (at an adsorbent dose of 4 g L−1) and 47.0%–73.0% (at an adsorbent dose of 10 g L−1). In contrast, BC300 adsorbed BrO3− with an adsorption efficiency of 19.3%, 14.5%, 14.9%, and 13.6% at initial added concentrations of 5, 10, 15, and 20 μg L−1, respectively. However, BC700 showed zero adsorption for BrO3−. The results also showed that the non-linear models of Langmuir and/or Freundlich for NO3−-N and BrO3− adsorption described the adsorption data better in most cases. It could be concluded that high pyrolysis temperature BC are suitable for adsorbing NO3−-N, and low pyrolysis temperature BC may be used to adsorb BrO3−.

О полифункциональности высокоосновных анионитов

Методом потенциометрического титрования в высокоосновном анионите АВ-17-8 установлено наличие трех типов функциональных групп. Определены константы их ионизации: pKb1=1.72÷1.78; pKb2=4.32÷4.38; pKb3=7.72÷7.82. В ионный обмен с кремниевыми кислотами вступают две функциональные группы с меньшими величинами pKb. Доля слабоосновных групп (с pKb3=7.72÷7.82) в разных партиях анионита достигает 12-34 % от полной обменной емкости. Полифункциональность анионита АВ-17-8 нужно учитывать при обсуждении различных закономерностей ионообменных процессов, а также при прогнозировании сорбции анионов слабых органических и минеральных кислот.

Razvoj i karakterizacija raznih katjonskih sorbenata na bazi lignocelulozne kore tikvice

The aim of this study is to develop miscellaneous cationic sorbents based on the lignocellulosic biomass of Lagenaria vulgaris fruit, with the property of efficient sorption of anionic pollutants from aqueous solutions. The lignocellulosic gourd shell (LGS biomass), as a potentially valuable agro-waste, was examined and used for the synthesis of sorbents. The preparation of synthesis precursor (LVAT) was performed by alkaline pretreatment of LGS biomass. Pretreatment under weak alkaline conditions with green carbonate solution was carried out for partial delignification and extraction of depolymerized hemicellulose, thereby achieving higher material porosity and activation of cellulose microfibrils. This activation involves the translation of available -OH functional groups into -ONa form (alkali-cellulose), while maintaining the initial biomass composition. Synthesis of the cationic sorbents was performed in three ways. Different N-reagents, such as tertiary amino and quaternary ammonium compounds, were used in the cation modification of LGS biomass and LVAT precursor, to determine the effects of reagent structure and hydrophobicity on the synthesis outcome, and primarily on the sorption properties of the resulting sorbents. The synthesized cationic sorbents were characterized by physico-chemical methods and tested for the removal of anionic pollutants from water, especially phosphates and nitrates. The various chemical modifications of lignocellulosic biomass provide a scientific contribution to a better understanding of the mechanism of anions sorption on the sorbent surface.

Insights into phosphate adsorption behavior on structurally modified ZnAl layered double hydroxides

Abstract The present study focuses on the phosphate uptake by synthetic ZnAl-layered double hydroxides having different charge density due to the modification of the cationic ratio (Zn2+/Al3+) within the brucite-like sheets. The structure of the as-synthesized ZnAl-LDH was confirmed by X-ray diffraction and 27Al NMR and micro-Raman spectroscopy characterization techniques. The materials were applied for sorption of phosphate anions in aqueous media under relevant conditions. Parameters affecting the sorption process were thoroughly investigated, such as the layer cationic ratio, the exchangeable interlayer anion, thermal treatment and competitive sorption in the presence of co-existing anions. The sorption data provided information regarding the relationship between the phosphate uptake and the physical-chemical properties of these materials. The phosphate adsorption onto the non-calcined LDH occurred via the anionic exchange mechanism while both structural reconstruction and precipitation mechanisms were observed for the calcined materials. The obtained results suggest that the Zn containing LDH are suitable candidates for the phosphate recovery or removal from aqueous media in wastewater treatment processes.

Role of macrocyclic effect in complex formation of palladium(II) with ligands anchored on a solid support

The method for grafting dithiacrown ether and its linear analogue to the silica surface using preliminary prepared organosilicon derivative is developed. The importance of the acylation step in the process of grafting is underlined. The acylation is required to prevent sorption of platinum metals complex anions by the anion exchange mechanism, the probability of which increases due to protonation of the spacer in an acidic medium. The interaction of palladium(II) with anchored ligands in hydrochloric acid media was studied in details. The comparative study of two sorbents revealed that the macrocyclic effect plays a negligible role in binding of palladi um(II) ions. Therefore, linear ligands are preferred for the development of sorbents for molecular recognition of platinum metals ions.

Zinc Presence during Mineral Formation Affects the Sorptive Reactivity of Manganese Oxide

The sorptive reactivity of layered manganese (Mn) oxides is controlled by their layer and interlayer structure, which can be affected by processes such as metal coprecipitation. This study investigated the effects of Zn coprecipitation on the sorptive reactivity of δ-MnO2, a common layered Mn oxide mineral. Selected cation (i.e., Cd) and anion (i.e., phosphate and arsenate) species were used to probe the changes in δ-MnO2 sorptive reactivity. Cd uptake by δ-MnO2 was suppressed by Zn coprecipitation but total metal uptake (Cd and Zn) was enhanced, indicating more available vacancy sites (e.g., smaller particle size and higher vacancy site density) in Zn-coprecipitated δ-MnO2. Phosphate and arsenate sorption on δ-MnO2 was significantly enhanced by Zn-coprecipitation, and the enhancement was more effective compared to Zn sorption on pure δ-MnO2. X-ray diffraction and X-ray adsorption spectroscopy analysis did not detect the formation of surface precipitations and/or ternary complexes. The enhanced anion sorption on Zn-coprecipitated δ-MnO2 was likely due to the compensation of negative surface charge by sorbed Zn, as well as the structural modifications introduced by Zn coprecipitation. Results from this study can provide a better understanding on the interactions between metal-coprecipitated Mn oxides and other species in natural environments.

Characterization of Sn-Apatites and 99mTcO4 – anions removal from aqueous solutions

Abstract Apatite is a natural mineral from the group of phosphate minerals. It originates primarily in rocks and converted limestones. It is also one of the few minerals produced and used by microeconomic systems. Due to its low solubility in water and high sorption capacity, apatite is a suitable sorbent for heavy metals and radionuclides removal from aqueous radioactive waste. Increasing amount of radioactive waste (RAW) has a negative impact on human health as well as on the environment. Production of RAW is constantly increasing because of the use of nuclear energy as well as by the development of nuclear medicine. The aim of this work was to study the effect of pH and various anions on the sorption of pertechnetate anions from aqueous solution to Sn-Apatite. Sn-Apatite samples used in the experiment were prepared by the wet precipitation method and adsorption of 99mTc was monitored by the radioisotope indication method. Sorption experiments were performed using the batch method. It was found that the sorption percentage was higher than 90 % in all Sn-Apatite samples and the dissociation constant, KD, indicated high affinity of pertechnetate anions to the solid Sn-Apatite particles. The presence of competing anions did not significantly influence the ability of Sn-Apatite materials to adsorb 99mTcO4 - from aqueous solutions.

Sodium hexametaphosphate (SHMP)-amended calcium bentonite for slurry trench cutoff walls: workability and microstructure characteristics

This study aims to investigate workability and microstructural characteristics of sodium hexametaphosphate (SHMP)-treated calcium bentonite (Ca-bentonite) as a potential material for soil–bentonite slurry trench cutoff walls. First, a series of Marsh viscosity, filtrate loss, density, and pH experiments are performed on bentonite – tap water slurries containing Ca-bentonite amended with 0%–8% SHMP dosages. Subsequently, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and zeta potential tests are conducted to explore microstructural characteristics that control the mechanisms of SHMP treatment. The results indicate that the workability of the slurry is significantly improved with SHMP addition. The SEM, XRD, and zeta potential analyses show that SHMP-amended Ca-bentonite possesses a more dispersed structure and higher negative zeta potential relative to the unamended Ca-bentonite. The mechanisms of SHMP amendment are identified to be exchange of bivalent calcium cations in Ca-bentonite by monovalent sodium cations in the SHMP, sorption of the SHMP anions that give the clay system a steric stabilization and increased negative surface charge density, and sequestration of the bivalent calcium cations on the Ca-bentonite. Overall, the SHMP treatment is effective in making the Ca-bentonite slurry amenable for use in the soil–bentonite slurry trench wall construction.

The influence of accompanying components on the sorption of molybdate anions from aqueous solutions on dispersed ice surface.

The influence of accompanying components on the sorption of molybdate anions from aqueous solutions on dispersed ice surface.

Влияние cопутствующих компонентов на сорбцию молибдат-анионов из водных растворов поверхностью дисперсного льда

Влияние cопутствующих компонентов на сорбцию молибдат-анионов из водных растворов поверхностью дисперсного льда

Polyethyleneimine cryogels for metal ions sorption

Polyethyleneimine (PEI) cryogels have been fabricated using poly(ethylene glycol) diglycidyl ether (DGE-PEG), 1,4-butanediol diglycidyl ether (DGE-1,4-BD), and glutaric aldehyde (GA) as cross-linking agents. The rate of PEI cross-linking changes in the order GA > DGE-1,4-BD > DGE-PEG. The established correlations between the modification degree, swelling, and static ion-exchange capacity revealed a tendency of diglycidyl ethers, especially DGE-1,4-BD, to graft as a side chain to PEI in alkaline media. Low reactivity of cross-linkers at temperatures below zero resulted in lower modification degree and higher sorption capacities of PEI cryogels in comparison with PEI cross-linked at room temperature. Due to the difference in mechanisms of sorption of metal cations and anions, PEI cryogels cross-linked with DGE-1,4-BD and DGE-PEG were the most efficient for sorption of Hg(II) as [HgCl4]2− complex and Cu(II) ions, respectively. The morphology of PEI cryogels depends on the type of the cross-linking agent, cross-linker/PEI molar ratio, and concentration of PEI solution; the pore volume of cryogels obtained under the same conditions decreased in the order GA > DGE-1,4-BD > DGE-PEG.

May humic acids or mineral fertilisation mitigate arsenic mobility and availability to carrot plants (Daucus carota L.) in a volcanic soil polluted by As from irrigation water?

Carrot (Daucus carota L.) is a widely consumed root vegetable, whose growth and safety might be threatened by growing-medium arsenic (As) contamination. By this work, we evaluated the effects of humic acids from Leonardite and NPK mineral fertilisation on As mobility and availability to carrot plants grown for 60 days in a volcanic soil irrigated with As-contaminated water – representing the most common scenario occurring in As-affected Italian areas. As expected, the irrigation with As-contaminated water caused a serious toxic effect on plant growth and photosynthetic rate; the highest rate of As also inhibited soil enzymatic activity. In contrast, the organic and mineral fertilisation alleviated, at least partially, the toxicity of As, essentially by stimulating plant growth and promoting nutrient uptake. The mobility of As in the volcanic soil and thus its phytoavailability were differently affected by the organic and mineral fertilisers; the application of humic acids mitigated the availability of the contaminant, likely by its partial immobilisation on humic acid sorption sites – thus raising up the intrinsic anionic sorption capacity of the volcanic soil; the mineral fertilisation enhanced the mobility of As in soil, probably due to competition of P for the anionic sorption sites of the soil variable-charge minerals, very affine to available P. These findings hence suggest that a proper soil management of As-polluted volcanic soils and amendment by stable organic matter might mitigate the environmental risk of these soils, thus minimising the availability of As to biota.

The role of bilberry and Alpine lady-fern in soil formation within the Carpathian subalpine spruce forest stands

The effect of the understory vegetation in the spruce forests of the upper montane belt on soil properties was investigated. Three types of understory vegetation were included: dominant Alpine lady fern, dominant bilberry or a mix of the two species. All studied soils were derived from sandstone, had acidic soil reactions, were located under similar physiographic conditions and have been populated by coniferous forests with similar to today's understory species for more than thousand years. The effect of Alpine lady fern on soil organic matter accumulation and quality as well as the amount of total Fe and Al and the share of different forms of these elements (linked to humus, amorphous inorganic, silicate and non-silicate crystalline) in the total Fe and Al were compared to the effect of bilberry on the aforementioned soil features. This work aimed to assess if the understory vegetation effect was strong enough to influence pedogenic processes taking place in the soils. The main differences between the studied soil properties were related to organic matter transformation and Fe and Al mobility. They were caused by a different susceptibility of Alpine fern lady and bilberry plant residues to the decomposition. In the soils with bilberry dominance, there were greater amounts of less decomposed organic matter accumulated than in soils with Alpine lady fern dominance in which organic matter was characterised by a high humification degree, large CH/CF ratios and significantly lower C/N ratios. Bilberry in the understory caused the increased Fe and Al mobility. Therefore in soils under bilberry podsolization processes and spodic horizon formation occurred that was indicated by the values of Fe and Al mobility indices. In soils under Alpine lady fern influence, these indices values were lower and the podzolisation processes were not intensive enough to form spodic horizons. In these soils, regardless of the condition favouring podsolization (low pH, spruce forest), the mobility of Fe and Al was slowed. The presence of Alpine lady fern as a dominant understory species resulted in a decrease in solubility of metallo-organic complexes, probably because of the quicker oxidisation of litter then in soils under bilberry. The sites with a mix of Alpine lady fern and bilberry turned out to be in a transitional phase, which with time would probably change to bilberry or fern understory. The ecological role of the studied soils resulting from accumulation of inorganic amorphous Fe, which takes part in anion sorption, thus limiting leaching, was also emphasized.