Arsenite and chromate sequestration onto ferrihydrite, siderite and goethite nanostructured minerals: Isotherms from flow-through reactor experiments and XAS measurements

Sorption isotherms remain a major tool to describe and predict the mobility of pollutants in natural and anthropogenic environments, but they are typically determined by independent batch experiments. In the present study, the sequestration of As(III), Cr(VI) and competitive As(III)-Cr(VI) on/in 6L-ferrihydrite, siderite and goethite nanostructured minerals was reinvestigated using stirred flow-through reactor experiments. Herein, sorption isotherms were particularly determined from breakthrough curves for inert and reactive tracers monitored simultaneously in a single percolation experiment. In complement, X-ray absorption spectroscopy (XAS) was used to identify As sorption sites on 6L-ferrihydrite and goethite. As expected, the minerals have high potential to remove As and Cr from water (siderite = ferrihydrite (about 60 mg/g) > goethite (20 mg/g)). As and Cr sorption isotherms were modelled with a Langmuir model, and with a sigmoidal Hill model in the case of the competitive sorption. XAS measurements have revealed that As(III) was partially oxidized (up to 22%) in the competitive system with chromate oxyanion Cr(VI). As(III) sorbed on ferrihydrite and goethite adopted edge-sharing and corner sharing complex geometries. Nowadays, a new class of adsorbing phases is being developed for wastewater treatment, including engineered nanostructured materials and nanocomposites. The use of flow through reactor experiments as a high throughput method, combined with XAS, should be considered as efficient screening methods to test their sorbing properties on various contaminants.

Phosphate sorption and desorption by two contrasting volcanic soils of equatorial Africa

Volcanic soils cover 1% of the Earth's surface but support 10% of the world's population. They are among the most fertile soils in the world, due to their excellent physical properties and richness in available nutrients. The major limiting factor for plant growth in volcanic soils is phosphate fixation, which is mainly attributable to active species of aluminium and iron. The sorption and desorption of phosphate is studied on the surface horizons of two African agricultural soils, a silandic Andosol (Rwanda) and a vitric Andosol (São Tomé and Principe). Both soils are slightly acid. The silandic Andosol is rich in active aluminium forms, while the vitric Andosol has high amounts of crystalline iron and aluminium oxides. Sorption isotherms were determined by equilibrating at 293K soil samples with phosphate solutions of concentrations between 0 and 100 mg P L^-1 in NaNO₃; phosphate was determined by visible spectrophotometry in the equilibrium solution. To study desorption, the soil samples from the sorption experiment were equilibrated with 0.02 M NaNO₃. The isotherms were adjusted to mathematical models. In almost all the concentration range, the adsorption of phosphate by the silandic Andosol was greater than 90% of the amount added, being lower in the vitric Andosol but always higher than 65%. The high sorption by the silandic Andosol is attributed to its richness in non-crystalline Fe and Al, while in the vitric Andosol crystalline iron species seem to play a relevant role in the adsorption. The sorption isotherms of both soils fitted to the Temkin model, the adjustment to the Langmuir or Freundlich models being unsatisfactory; throughout the range studied, the sorption increases with increasing phosphorus concentration, a maximum sorption is not predictable (as occurs when the sorption is adjusted to the Langmuir model). For an added P concentration of 100 mg L^-1 (3.2 mmol L^-1), the sorption is 47.7 µmol P g^-1 in the silandic Andosol and 41.6 µmol P g^-1 in the vitric Andosol. The desorption is low and the comparison of the sorption and desorption isotherms reveals a pronounced hysteresis, that is, the irreversibility of the sorption. The high phosphate sorption and its irreversibility are comparable to those published for other volcanic soils with high contents of allophane, active aluminium and free iron. The strong phosphate adsorption is a serious limiting factor for plant growth, which requires a careful management of phosphorus fertilization.

Ultra-sonication assisted cross-linking of cellulose polymers

Cross-linked cellulose-epichlorohydrin polymers were synthesized by a conventional heating with stirring (C-EP heating) and a parallel process using ultra-sonication (C-EP sonication) in the presence of aqueous ammonia. Structural characterization of modified cellulose was carried out using FTIR/¹³C solid state NMR spectroscopy and thermal methods (DSC and TGA). Evidence of products with variable textural properties and morphology was supported by nitrogen gas adsorption, solvent swelling, and microscopy (SEM, TEM) results. C-EP sonication possess greater cross-linker content judging by the loss of the cellulose fibril structure which was facilitated by acoustic cavitation effects due to ultra-sonication. Equilibrium sorption studies in aqueous solution with 2-naphthoxy acetic acid (NAA) revealed that C-EP heating had slightly greater sorption capacity than C-EP sonication at alkaline pH. By contrast, C-EP sonication had greater uptake of NAA at acidic pH. Kinetic uptake studies at pH 3 is described by the pseudo-second order model, where the surface sites of C-EP heating became saturated within ca. 75 min; whereas, ca. 350 min occurred for C-EP sonication. This study demonstrates that the yield of sonication assisted cross-linking of cellulose is greater with improved adsorption properties. The study also reveals the utility of sonication assisted synthesis for the valorization and utilization of cellulose modified materials.

Arsenic adsorption and plant availability in an agricultural soil irrigated with As-rich water: Effects of Fe-rich amendments and organic and inorganic fertilisers

The use of As-rich water for irrigation in agricultural soils may result in As accumulation in soil and crops, with the consequent risk of its entry into the food chain. The effectiveness of three different Fe-based materials (a commercial iron oxide (Bayoxide^®), lamination slag (a by-product of the hot rolling of steel) and a commercial red mud derivative (ViroBind™)) used as soil amendments to minimise the impact of irrigation with As-rich water in an agricultural soil-plant system was evaluated in a pot experiment. Simultaneously, the influence of organic and inorganic fertilisation (olive oil mill waste compost versus NPK fertiliser) on the effectiveness of iron oxide in As adsorption processes was also assessed. The As adsorption capacity of the amendments was determined in a preliminary batch experiment using sorption isotherms. Then, a pot experiment was carried out in a growth chamber using an agricultural soil (arenosol) from Segovia province (central Spain), amended with the different materials, in which Lactuca sativa (lettuce) was grown for two months. The As adsorption capacity was higher in the commercial iron oxide and in the red mud derivative, which fitted the Freundlich model (no saturation), than in the lamination slag, which fitted the Langmuir model (limited adsorption). All the materials decreased the pore water As concentration compared to the control (by 29-80%), but only iron oxide reduced As availability in the soil, and none of the amendments decreased the As concentration in plant leaves. The combination of iron oxide and compost did not significantly improve plant growth, but increased nutrients (N, K, Ca, Na and Mg) concentrations and availability in the soil and their concentration in the plants, relative to the other treatments and the control. Therefore, this seems to be a viable option to prevent As leaching and improve the plant nutritional status.

Municipal solid waste compost as a novel sorbent for antimony(V): adsorption and release trials at acidic pH

The ability of two municipal solid waste composts (MSW-Cs) to sorb antimony(V) in acidic conditions (pH 4.5) was investigated. Sorption isotherms and kinetics showed that both MSW-Cs could sorb antimony(V), even if in different amounts (~ 0.18 and 0.24 mmol g^-1 of Sb(V) by MSW-C1 and MSW-C2, respectively). These differences were ascribed to the chemical composition of composts, as well as to the total acidity of their humic substances. The Sb(V) sorption by both MSW-Cs followed a pseudo-second-order kinetic model, while the sorption isotherms data fitted the Freundlich model better than the Langmuir one. The humic acids extracted from composts contributed to 4.26 and 8.24% of Sb(V) sorption by MSW-C1 and MSW-C2 respectively. SEM-EDX spectra of the MSW-C+Sb(V) systems showed a certain association of Ca(II) with Sb(V), while sequential extraction procedures indicated that more than 80% of the Sb(V) sorbed was strongly retained by MSW-Cs. On the other hand, treatment with oxalic acid at pH 4.5 favored the release of more than 98 and 65% of the Sb(V) sorbed by MSW-C1 and MSW-C2 respectively, supporting a possible role of calcium in Sb(V) retention. The results from this study suggest that MSW-Cs could be used as amendments for the in-situ immobilization of Sb(V) in acidic-polluted soils.

Gas Transport Properties of Polybenzimidazole and Poly(Phenylene Oxide) Mixed Matrix Membranes Incorporated with PDA-Functionalised Titanate Nanotubes

Functionalised titanate nanotubes (TiNTs) were incorporated to poly(5,5-bisbenzimidazole-2,2-diyl-1,3-phenylene) (PBI) or poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) for improving the interfacial compatibility between the polymer matrix and inorganic material and for altering the gas separation performance of the neat polymer membranes. Functionalisation consisted in oxidative polymerisation of dopamine-hydrochloride on the surface of non-functionalised TiNTs. Transmission electron microscopy (TEM) confirmed that a thin polydopamine (PDA) layer was created on the surface of TiNTs. 1.5, 3, 6, and 9 wt.% of PDA-functionalised TiNTs (PDA-TiNTs) were dispersed to each type of polymer matrix to create so-called mixed matrix membranes (MMMs). Infrared spectroscopy confirmed that -OH and -NH groups exist on the surface of PDA-TiNTs and that the nanotubes interact via H-bonding with PBI but not with PPO. The distribution of PDA-TiNTs in the MMMs was to some extent uniform as scanning electron microscope (SEM) studies showed. Beyond, PDA-TiNTs exhibit positive effect on gas transport properties, resulting in increased selectivities of MMMs. The addition of nanotubes caused a decrease in permeabilities but an increase in selectivities. It is shown that 9 wt.% of PDA-TiNTs in PBI gave a rise to CO₂/N₂ and CO₂/CH₄ selectivities of 112 and 63 %, respectively. In case of PPO-PDA-TiNT MMMs, CO₂/N₂ and CO₂/CH₄ selectivity increased about 25 and 17 %, respectively. Sorption measurement showed that the presence of PDA-TiNTs in PBI caused an increase in CO₂ sorption, whereas the influence on other gases is less noticeable.

Glyphosate binding in soil as revealed by sorption experiments and quantum-chemical modeling

The herbicide glyphosate (GLP) is supposed to be rapidly degraded or adsorbed strongly by soil solids but findings in soil years after application and concentrations in waters above legal limits question a harmless disappearance. Therefore, we conducted batch sorption experiments with 23 thoroughly characterized arable surface soils, correlated isotherm coefficients with numerous inorganic and organic soil parameters, and investigated GLP-SOM-complexes by quantum-chemical modeling. The Freundlich sorption model yielded the best fits, and coefficients K_f and n_f were correlated positively with the contents of clay/silt. The contents of organic C (C_org) and of the mass-spectrometrically determined SOM-compound classes carbohydrates, phenols/lignin monomers, lignin dimers, lipids, alkylaromatics, non-amide N and amides and sterols all were strongly positively correlated with the Freundlich coefficients. Quantum-chemical modeling showed that both GLP phosphonic and carboxylic functional groups interact similarly with the polar SOM functional groups via H-bond formation but the GLP phosphonic moiety is most important in the GLP-SOM-interaction. Moreover, the interaction mechanism between GLP and every modeled SOM-compound class was explored indicating the importance of the polarity, electron density, and site of attack of the SOM fragments in the GLP-SOM-interaction. Partial binding energies were combined to a total binding energy (E_B,tot) of GLP to the SOM, considering the mass spectrometrically quantified compound classes for each individual soil sample. The resulting strongly positive correlation between the E_B,tot and the C_org provided compelling new experimental-theoretical evidence for the importance of SOM on the GLP binding and its behavior in the environment. In conclusion, the multitude of binding mechanisms to clay minerals and organic colloids make the occurrence of free GLP rather unlikely but a leaching of GLP complexes via preferential flow path through soil and transfer to waterways rather likely.

Influence of lead in the sorption of arsenate by municipal solid waste composts: metal(loid) retention, desorption and phytotoxicity

The ability of two municipal solid waste composts (MSW-C) to sorb As(V) in the presence of Pb(II) and in acidic conditions was investigated. Sorption isotherms and kinetics showed that both MSW-C were able to sorb As(V) in a similar way (∼0.24mmolg^-1 MSW-C), but only when Pb(II) was present (0.45mmolL^-1). The concomitant sorption of Pb(II) by both MSW-C (∼0.40mmolg^-1) suggested that the metal cation was likely acting as bridging element between the negatively charged functional groups of composts and As(V). SEM-EDX analysis of the MSW-C+Pb(II)+As(V) systems supported the association between Pb(II) and As(V), while sequential extraction procedures and organic acids treatment showed that As(V) was strongly retained by MSW-C+Pb(II) and suggested the presence of different interaction types between As(V) and Pb(II). Plant growth experiments highlighted the key role of Pb(II) in the reduction of As(V)-phytotoxicity for triticale plants (×Triticosecale Wittm.) in the presence of MSW-C.

Iron-impregnated biochars as effective phosphate sorption materials

A new post-treatment method was applied for improving the sorption efficiency of biochar-based sorbents for anionic forms of phosphorus. The Fe-impregnation through direct hydrolysis of Fe(NO₃)₃ was used to produce impregnated corn cob- (IBC A), garden wood waste- (IBC B), and wood chip-derived biochars (IBC C). The qualitative and quantitative effects of impregnation process on biochars were confirmed by SEM-EDX, FTIR, and ICP-MS. The analyses revealed increased concentrations of N and thus potential NO₃^- participation in the phosphate sorption process. Biochar surface area showed a significant decrease after the impregnation process due to the filling of micro- and mesopores with Fe maximum sorption capacity (Q _max) increased by a factor of 12-50. The sorption processes of phosphates by IBC A, IBC B, and IBC C were dependent on pH, initial concentration, and time. Speciation analysis and pH-study confirmed the range of pH 4.5-5.5 as optimum values at which most of phosphorus is present in form of mononuclear H₂PO₄^-. Batch sorption experiments showed a significant increase in the sorption capacity for phosphates by Fe impregnation of biochar as well as effectiveness and stability of this treatment. These findings indicate an option for utilizing engineered biochars as tools for the recovery of phosphorus from the aquatic environment.

Synthesis and characterization of poly(carboxymethyl)-cellulose for enhanced La(III) sorption

The grafting of amino and carboxylic acid groups on cellulose increased La(III) sorption efficiency of cellulose: maximum sorption capacity increased from 38mgLag^-1 for cellulose to 101 and 170mgLag^-1 for amino derivative (PAC) and amino-carboxylic derivative (PCMC). Langmuir equation successfully fits sorption isotherms while uptake kinetics are effectively modeled using the pseudo-first order rate equation (though resistance to intraparticle diffusion plays a significant role in the control of metal recovery). Uptake equilibrium occurred within 150-180min. The thermodynamic study shows that the reaction is spontaneous, endothermic and entropic. Nitric acid solutions (0.5M concentration) can be efficiently used for metal recovery and sorbent can be recycled for at least 5 cycles with limited decrease in sorption performance for the three sorbents. The materials were characterized by elemental analysis, acid-base titration, FTIR spectrometry, x-ray diffraction analysis, X-ray photoelectron spectroscopy, SEM-EDX analysis and also by TGA.

Impacts of compound properties and sediment characteristics on the sorption behaviour of pharmaceuticals in aquatic systems

Sorption is a key factor in determining the persistence, attenuation and bioavailability of sediment-associated contaminants. However, our understanding of the sorption behaviour of pharmaceuticals in sediments is poor. In this study, we investigated the sorption behaviour of a diverse set of pharmaceuticals in a range sediment types. Sorption affinity of pharmaceuticals for all sediments was found to increase in the order mefenamic acid<cimetidine<atenolol<amitriptyline<diltiazem. Comparison of the experimental observations with predictions from an existing model for estimating sorption revealed the model worked poorly for the study pharmaceuticals. Multiple linear regression analysis was therefore used to develop new models for estimating sorption of individual pharmaceuticals based on sediment properties. The analyses indicated that sorption is related to properties such as Log Dow of a compound in the sediment (lipophilicity corrected for the sediment pH), cation exchange capacity, clay%, organic carbon content and exchangeable Ca(2+), although, with the exception of atenolol, robust relationships between sediment properties and sorption were not obtained. Overall, the results demonstrate how complex the processes are that drive the sorption of pharmaceuticals in sediments and highlight the need for generation of further experimental data and further model development work.

The interactions of UV and/or H2O2 treated CNTOH and CNTCOOH with environmental fulvic acids

The fate of carbon nanotubes (CNT) in the environment will be governed by the presence of natural dissolved organic matter (DOM). Many studies indicate that CNT create stabilized suspensions in the presence of DOM. Easier transport in the environment may indicate their greater hazard. However these studies describe the interactions of DOM with as produced CNT. In the present studies the interactions of UV and/or H2O2 treated wastewater containing CNTOH or CNTCOOH with the naturally occurred fulvic acids (FA) were presented. FA sorption, both kinetics and mechanism, were described using batch regime. The sorption of FA followed a pseudo-second order kinetics and was described with the highest accuracy by Langmuir or Dubinin-Radushkevich model for CNTOHs and Langmuir, Temkin or Dubinin-Radushkevich - for CNTCOOHs. The mechanism of FA sorption onto CNTOHs was ascribed to π-π, heterogeneous and electrostatic interactions. The π-π and electrostatic interactions can the mostly defined FA adsorption onto CNTCOOHs. The parameters affecting FA sorption were combination of porosity and dispersity.

Arsenic(V) adsorption-desorption in agricultural and mine soils: Effects of organic matter addition and phosphate competition

High total and bioavailable concentrations of As in soils represent a potential risk for groundwater contamination and entry in the food chain. The use of organic amendments in the remediation of As-contaminated soils has been found to produce distinct effects on the solubility of As in the soil. Therefore, knowledge about As adsorption-desorption processes that govern its solubility in soil is of relevance in order to predict the behaviour of this element during these processes. In this paper, the objective was to determine As adsorption and desorption in four different soils, with and without compost addition, and also in competition with phosphate, through the determination of sorption isotherms. Batch experiments were carried out using three soils affected differently by previous mining activity of the Sierra Minera of La Unión-Cartagena (SE Spain) and an agricultural soil from Segovia province (central Spain). Adsorption was higher in the mining soils (and highest in the acidic one) than in the agricultural soils, although the latter were not affected negatively by organic matter or phosphate competition for sorption sites. The results show that As adsorption in most soils, both with and without compost, fitted better a multimolecular layer model (Freundlich), whereas As adsorption in competition with P fitted a monolayer model (Langmuir). Moreover, the use of compost and phosphate reduced the adsorption of As in the mining soils, while in the agricultural soils compost increased their low adsorption capacity. Therefore, the use of compost can be a good option to favour As immobilisation in soils of low adsorption, but knowledge of the soil composition will be crucial to predict the effects of organic amendments on As solubility in soils and its associated environmental risk.

Soft computing modelling of moisture sorption isotherms of milk-foxtail millet powder and determination of thermodynamic properties

Moisture sorption isotherms of spray-dried milk-foxtail millet powder were determined at 10, 25 and 40 °C. Sorption data was fitted using classical and soft-computing approaches. The isotherms were of type II, and equilibrium moisture content (EMC) was temperature dependent. The BET monolayer moisture content decreased from 3.30 to 2.67 % as temperature increased from 10 to 40 °C. Amongst the classical models, Ferro-Fontan gave the best fit of EMC-aw data. However, the Sugeno-type adaptive neuro-fuzzy inference system (ANFIS) with generalized bell-shaped membership function performed better than artificial neural network and classical models with RMSE as low as 0.0099. The isosteric heat of sorption decreased from 150.32 kJ mol(-1) at 1 % moisture content to 44.11 kJ mol(-1) at 15 % moisture. The enthalpy-entropy compensation theory was validated, and the isokinetic and harmonic mean temperatures were determined as 333.1 and 297.5 K, respectively.

Progress in the preparation and application of modified biochar for improved contaminant removal from water and wastewater

Modified biochar (BC) is reviewed in its preparation, functionality, applications and regeneration. The nature of precursor materials, preparatory conditions and modification methods are key factors influencing BC properties. Steam activation is unsuitable for improving BC surface functionality compared with chemical modifications. Alkali-treated BC possesses the highest surface functionality. Both alkali modified BC and nanomaterial impregnated BC composites are highly favorable for enhancing the adsorption of different contaminants from wastewater. Acidic treatment provides more oxygenated functional groups on BC surfaces. The Langmuir isotherm model provides the best fit for sorption equilibria of heavy metals and anionic contaminants, while the Freundlich isotherm model is the best fit for emerging contaminants. The pseudo 2(nd) order is the most appropriate model of sorption kinetics for all contaminants. Future research should focus on industry-scale applications and hybrid systems for contaminant removal due to scarcity of data.

Towards a molecular level understanding of the sulfanilamide-soil organic matter-interaction

Sorption experiments of sulfanilamide (SAA) on well-characterized samples of soil size-fractions were combined with the modeling of SAA-soil-interaction via quantum chemical calculations. Freundlich unit capacities were determined in batch experiments and it was found that they increase with the soil organic matter (SOM) content according to the order fine silt > medium silt > clay > whole soil > coarse silt > sand. The calculated binding energies for mass-spectrometrically quantified sorption sites followed the order ionic species > peptides > carbohydrates > phenols and lignin monomers > lignin dimers > heterocyclic compounds > fatty acids > sterols > aromatic compounds > lipids, alkanes, and alkenes. SAA forms H-bonds through its polar centers with the polar SOM sorption sites. In contrast dispersion and π-π-interactions predominate the interaction of the SAA aromatic ring with the non-polar moieties of SOM. Moreover, the dipole moment, partial atomic charges, and molecular volume of the SOM sorption sites are the main physical properties controlling the SAA-SOM-interaction. Further, reasonable estimates of the Freundlich unit capacities from the calculated binding energies have been established. Consequently, we suggest using this approach in forthcoming studies to disclose the interactions of a wide range of organic pollutants with SOM.

Moisture adsorption behaviour of biscuit during storage investigated by using a new Dynamic Dewpoint method

The changes in moisture adsorption isotherms of commercial biscuits during storage were investigated by means of a rapid Dynamic Dewpoint Isotherms (DDIs) method. Moreover, the relationships between the changes in moisture content and some quality characteristics of biscuits (moisture, aw, peroxide value - PV and texture) were studied during 92 days of storage at 35 °C. GAB model was used to fit the experimental sorption behaviours. During storage, moisture content and aw of biscuits increased and the obtained isotherms showed modifications in behaviour and shape. Significant changes were observed in PV values and texture, particularly during the first 40 days of storage. The monolayer moisture content, obtained by the BET equation, significantly increased during storage from 1.473 to 2.080 g water 100 g db(-1), probably because of the increase in the active sites for water binding due to the chemical and physical changes of the main components, induced by product ageing.

Lithium sorption properties of HMnO in seawater and wastewater

The lithium concentration in seawater is 0.17 mg/L, which is very low, but the overall quantity is approximately 2.5 × 10(14) kg. Therefore, seawater, which contains a vast amount of lithium, could be a major alternative source that might supply the rising demand for lithium. This research was undertaken to evaluate the feasibility of a manganese oxide (HMnO) adsorbent, which was produced after leaching lithium from lithium manganese oxide, for lithium collection from seawater. The HMnO was synthesized and deformed to a plastic after wet blending of manganese oxide and lithium hydroxide, and subsequently, the influence of pH, sorption isotherms, sorption rates, sorption energies, and effects of the co-ions were measured. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° indicated that the nature of the lithium sorption was both spontaneous and endothermic. The used HMnO could be regenerated by washing it with an HCl solution. The results demonstrated that HMnO could be effectively used for the collection of lithium from seawater with good selectivity.

Thermodynamic sorption of red cabbage extract (Brassica oleracea L. var. capitata L. f. rubra) encapsulated by spray drying

Red cabbage aqueous extract acidified with 2 % citric acid was spray-dried using gum Arabic as encapsulating agent. The concentration of anthocyanin in the powder was 253.45 ± 10.82 mg/100 g of dry basis and antioxidant activity of 4.6 ± 0.2 mmol trolox/kg of dry basis. The sorption isotherms were determined at 15, 25 and 35 °C, and the GAB model was the one that best adjusted to the experimental data. The differential enthalpy and entropy for moisture levels up to 2 g of water/g of dry basis decreased to a minimum value of -4.36 kJ/mol and -0.019 kJ/molK respectively, and then increased in magnitude with the rise in moisture content to levels close to the free moisture with a spontaneous process, governed by the entropy. The spreading pressure increased with the rise in water activity for all temperatures, while net integral enthalpy and entropy decreased with the rise in moisture content reaching levels close to 10 kJ/mol and 0.025 kJ/molK, respectively.

Pharmaceuticals' sorptions relative to properties of thirteen different soils

Transport of human and veterinary pharmaceuticals in soils and consequent ground-water contamination are influenced by many factors, including compound sorption on soil particles. Here we evaluate the sorption isotherms for 7 pharmaceuticals on 13 soils, described by Freundlich equations, and assess the impact of soil properties on various pharmaceuticals' sorption on soils. Sorption of ionizable pharmaceuticals was, in many cases, highly affected by soil pH. The sorption coefficient of sulfamethoxazole was negatively correlated to soil pH, and thus positively related to hydrolytic acidity and exchangeable acidity. Sorption coefficients for clindamycin and clarithromycin were positively related to soil pH and thus negatively related to hydrolytic acidity and exchangeable acidity, and positively related to base cation saturation. The sorption coefficients for the remaining pharmaceuticals (trimethoprim, metoprolol, atenolol, and carbamazepine) were also positively correlated with the base cation saturation and cation exchange capacity. Positive correlations between sorption coefficients and clay content were found for clindamycin, clarithromycin, atenolol, and metoprolol. Positive correlations between sorption coefficients and organic carbon content were obtained for trimethoprim and carbamazepine. Pedotransfer rules for predicting sorption coefficients of various pharmaceuticals included hydrolytic acidity (sulfamethoxazole), organic carbon content (trimethoprimand carbamazepine), base cation saturation (atenolol and metoprolol), exchangeable acidity and clay content (clindamycin), and soil active pH and clay content (clarithromycin). Pedotransfer rules, predicting the Freundlich sorption coefficients, could be applied for prediction of pharmaceutical mobility in soils with similar soil properties. Predicted sorption coefficients together with pharmaceutical half-lives and other imputes (e.g., soil-hydraulic, geological, hydro-geological, climatic) may be used for assessing potential ground-water contamination.

Interaction of polar and nonpolar organic pollutants with soil organic matter: sorption experiments and molecular dynamics simulation

The fate of organic pollutants in the environment is influenced by several factors including the type and strength of their interactions with soil components especially SOM. However, a molecular level answer to the question "How organic pollutants interact with SOM?" is still lacking. In order to explore mechanisms of this interaction, we have developed a new SOM model and carried out molecular dynamics (MD) simulations in parallel with sorption experiments. The new SOM model comprises free SOM functional groups (carboxylic acid and naphthalene) as well as SOM cavities (with two different sizes), simulating the soil voids, containing the same SOM functional groups. To examine the effect of the hydrophobicity on the interaction, the organic pollutants hexachlorobenzene (HCB, non-polar) and sulfanilamide (SAA, polar) were considered. The experimental and theoretical investigations explored four major points regarding sorption of SAA and HCB on soil, yielding the following results. 1--The interaction depends on the SOM chemical composition more than the SOM content. 2--The interaction causes a site-specific adsorption on the soil surfaces. 3--Sorption hysteresis occurs, which can be explained by inclusion of these pollutants inside soil voids. 4--The hydrophobic HCB is adsorbed on soil stronger than the hydrophilic SAA. Moreover, the theoretical results showed that HCB forms stable complexes with all SOM models in the aqueous solution, while most of SAA-SOM complexes are accompanied by dissociation into SAA and the free SOM models. The SOM-cavity modeling had a significant effect on binding of organic pollutants to SOM. Both HCB and SAA bind to the SOM models in the order of models with a small cavity>a large cavity>no cavity. Although HCB binds to all SOM models stronger than SAA, the latter is more affected by the presence of the cavity. Finally, HCB and SAA bind to the hydrophobic functional group (naphthalene) stronger than to the hydrophilic one (carboxylic acid) for all SOM models containing a cavity. For models without a cavity, SAA binds to carboxylic acid stronger than to naphthalene.

Viability of organic wastes and biochars as amendments for the remediation of heavy metal-contaminated soils

Composts derived from municipal (MOW and MSW) and domestic wastes (DOM), wastes from the olive oil industry (OWH and OP), green waste (GW), and biochars (BF and BS) were investigated to test their viability for remediating metal-contaminated soils. In addition to common analyses, the characterisation included structural analyses (FTIR and (13)C NMR), determination of the acid neutralisation capacity (ANC) and the construction of sorption isotherms for target metals (Pb, Zn, Cd, Ni and Cu). MOW and GW had the highest ANC values (4280 and 7100 meq kg(-1), respectively), and MOW, GW, DOM, BF and BS exhibited the highest solid-liquid distribution coefficients (Kd) with maximum values in the 10(4) L kg(-1) range. Sorption isotherms were fitted using linear and Freundlich models for better comparison of the sorption capacities of the materials. Based on their basic pH, high ANC and high sorption capacity, MOW, GW and biochars are the most promising materials.

Hygroscopic behavior and degree of caking of grugru palm (Acrocomia aculeata) powder

This work aims to investigate the hygroscopic behavior of grugru palm powder through adsorption isotherms and its degree of caking. The powders of grugru palm (T1 - without maltodextrin, T2 - with 8 % of maltodextrin) were obtained by oven drying at 65 °C for 25 h. The experimental data was obtained through static gravimetric method at temperatures of 25, 30, 35 and 40 °C with different saturated salt solutions. The models of GAB, BET, Henderson, and Oswin were fitted to experimental data. The values of hygroscopicity were 6.39 and 5.17 % and degrees of caking were 3.11 and 0.03 % for T1 and T2, respectively. The adsorption isotherms from mathematical models can be classified as Type III. The GAB and Oswin models were the best representing the behavior of the powder isotherms, T1 and T2, respectively. The grugru palm powder proved to be non-hygroscopic and non-agglomerating. The T2 with 8 % of maltodextrin presented the lowest hygroscopicity.

Sorption isotherms and isosteric heats of sorption of Malaysian paddy

Understanding the water sorption characteristics of cereal is extremely essential for optimizing the drying process and ensuring storage stability. Water relation of rough rice was studied at 20, 30, 40 and 50 °C over relative humidity (RH.) between 0.113 and 0.976 using the gravimetric technique. The isotherms displayed the general sigmoid, Type II pattern and exhibited the phenomenon of hysteresis where it was more pronounced at lower temperatures. The sorption characteristics were temperature dependence where the sorption capacity of the paddy increased as the temperature was decreased at fixed (RH). Among the models assessed for their ability to fit the sorption data, Oswin equation was the best followed by the third order polynomial, GAB, Smith, Chung-Pfost, and Henderson models. The monolayer moisture content was higher for desorption than adsorption and tend to decrease with the increase in temperature. Given the temperature dependence of the sorption isotherms the isosteric heats of sorption were calculated using Claussius-Clapeyron equation. The net isosteric heats decreased as the moisture content was increased and heats of desorption were greater than that of adsorption.

Copper(II) and lead(II) removal from aqueous solution by water treatment residues

In this study, we investigated the ability of Fe- and Al-based water treatment residues (Fe- and Al-WTR) to accumulate Pb(II) and Cu(II) at pH 4.5. The role of the inorganic and organic fractions of WTRs in metals sorption was also assessed. Sorption isotherms showed a higher sorption of Pb(II) by both WTRs with respect to Cu(II) (e.g. 0.105 and 0.089 mmol g(-1) of Pb(II) and Cu(II) respectively sorbed by Fe-WTR). Fe-WTR revealed a stronger sorbent for both metals than Al-WTR. The amount of Pb(II) and Cu(II) sorbed by Fe-WTR was about the 69% and 63% higher than that sorbed by the Al-WTR. The organic matter of Fe- and Al-WTR contributed to about 26% and 8.5% respectively in the sorption of both metals. The sequential extraction procedure showed that the greatest amount of metals sorbed by both WTRs were tightly bound and not extractable, and this was particularly apparent for Cu(II). The FT-IR spectra indicated the formation of inner-sphere complexes between the Fe(Al)-O nucleus and Pb(II) and Cu(II). Moreover, the FT-IR spectra also suggested that the humic fraction of WTRs interacted, through the carboxylate groups, with Cu(II) and Pb(II) by forming mainly monodentate and bidentate complexes, respectively.