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To mitigate climate change, it is of vital importance to increase the stocks of global soil organic carbon (SOC), which also improves soil resilience, soil fertility and thus food security. The preservation of SOC heavily depends on its vulnerability to microbial degradation. Two processes and their interplay strongly influence carbon protection: the formation of primary organo-mineral (O-M) complexes via the sorption of dissolved organic carbon (DOC) to fine-grained soil minerals, and the aggregation of these to form micro and macroaggregates. To date, research suggests that the chemistry of the SOC and the mineralogy of the soil matrix play a key role in the formation of O-M complexes and their stability against microbial degradation, but whether and to what extent these factors help control micro and macroaggregation are unknown. We focus our investigation on how the chemistry of the SOC source affects the stability and aggregation of iron (oxyhydr)oxide O-M complexes. Thus, we determine the sorption behaviour of different SOC sources chosen to represent different functional group chemistries, using sorption isotherm experiments and electrophoretic techniques. We also conduct long-term aggregation experiments to track aggregate particle size using a novel Particle Size and Shape Analyzer technique. Our findings suggest that the stability and aggregation modes of O-M complexes are a function of SOC chemistry, and that aggregation patterns are strongly influenced by the presence of microbial exudates and communities.

Phosphorus (P) is an essential element for biomass growth and is a major component of fertilizers applied to crops. Excessive application of P to agricultural soils may lead to P-leaching and increasing concentrations of this element in aqueous system. This may cause the degradation of water quality through eutrophication processes. Arsenic on the other hand is a very toxic element that may be present at high concentrations in soil and aqueous environments due to weathering processes or to anthropogenic sources as mining and agricultural activities.To design adequate remediation techniques for the mitigation of phosphorus (P) and arsenic (As) pollution it is key to understand the geochemical processes and the environmental drivers controlling their availability. In soil systems, the mobility of P and As is controlled by their interaction with soil minerals. Among these minerals, iron and aluminum oxyhydroxides are known to form especially strong surface complexes with both components, limiting its availability to the environment. On the other hand, the presence of soil organic matter may compete with these pollutants for the mineral surface sites, increasing the contamination risk in the soil system.In the present work, we have studied at laboratory scale the As and P adsorption process on iron mineral surfaces under variable conditions. This includes changes of pH, redox conditions, presence of major ions (i.e. calcium, sulfate) or other trace elements (i.e. chromate, copper), and the presence of natural organic matter (i.e. humic substances or simple organic acids). Also, surface complexation models were applied in order to simulate and predict the behavior of such systems. The obtained results reveal that the presence of organic matter or other anionic species are important factors capable of increasing the mobility of P and As contaminants, whereas changing the redox potential or the carbon content in the organo-mineral aggregates has little effect.The information obtained, allowed to design remediation solutions that could be applied at field scale. The soil characteristics and the biogeochemical processes can be improved by the application of amendments based on circular economy aspects, i.e. compost, biochar, Technosols. We have studied the effectiveness of the superficial application of these materials to immobilize both P and As, varying the main environmental drivers affecting to the sorption or desorption processes.

The potential of composts produced from different origin residues to be used in environmentally friendly agriculture is addressed in this work. Seven composts obtained from different raw materials and composting methodologies are compared using elemental, thermal and spectroscopic characterization data. Despite the stabilization of the organic matter in all composts being adequate for agricultural applications, they display distinct elemental and structural compositions. Likewise, the fertilisers have very different effects on lettuce growth. Despite the observed differences, some common features were found, namely a mass loss (TGA) of 25.2 g per mol C, association between groups of elements (Fe, Al, Ni, Co, Cr, Cu and S; Mg, Na, K and P, C, Coxi, N and Pb) and correlations between the amount of carbon nanostructures and the characteristic aromaticity parameters. These results suggest that the tuning of the compost features for specific cultures may be possible for sustainable food production., This work was financially supported by the Interreg VA Spain-Portugal Programme (EU) through the project Res2ValHum (0366_RES2VALHUM_1_P). A.C. Silva acknowledges receipt of a PhD grant (UMINHO/BD/40/2016) financed by the Operational Programme Norte 2020 (through the Project “NORTE-08-5369-FSE-000033”). A. Teixeira acknowledges the grant (Res2ValHum 01/2018) to develop experimental work for 11 months on the project. J. Antelo and S. Fiol are also grateful for the financial support provided by Xunta de Galicia—Consellería de Educación e Ordenación Universitaria de Galicia (Consolidation of Competitive Groups of Investigation; GI-1245, ED431C 2018/12 and CRETUS AGRUP2015/02, ref. 2018-PG10).

The iMirabilis2 expedition was conducted from the 23rd to the 30th of July 2021 (Leg 0, Vigo-Las Palmas de Gran Canaria) and from the 31st of July to the 30th of August 2021 (Leg 1, Las Palmas de Gran Canaria- Las Palmas de Gran Canaria). This report includes the activities conducted in Leg 1, as well as two specific activities conducted during Leg 0 and which were part of the iAtlantic project: capacity building in sea bird ecology, and ROV training and outreach.

The Olsen method is widely used to determine bioavailable phosphate (P) in upland soils. It is also used in flooded soils, although different estimates of extractable-P are obtained under anoxic and oxic conditions. In this study, variations in extractable-P in three soils under different redox conditions were evaluated as a function of solid to solution ratio (SSR) (1:5-1:200) and bicarbonate concentration (0.1-1 M). The parameterized CD-MUSIC model was used to describe the data, with optimization of reactive surface area (RSA) and reversibly adsorbed-P (R-PO

The solubility and bioavailability of arsenic in the environment are to a large extent governed by adsorption reactionswith iron (hydr)oxides, the extent of which is affected by competitive interactions with other ions, for example, phosphate. Here,batch experiments were performed with ferrihydrite suspensions to determine the adsorption of arsenate [As(V)] and phosphate(PO4)atdifferent As(V)-PO4ratios. A surface complexation model based on the Charge Distribution MUltisite Ion Complexation(CD-MUSIC) concept (the"Ferrihydrite CD-MUSIC model") was developed to describe these interactions in a way consistent withresults from spectroscopic studies. For this purpose, several previously published data sets on As(V) and PO4adsorption inferrihydrite suspensions were reviewed, including a number of systems containing other major ions (CO32-and Ca2+), and newsurface complexation constants were derived. During model development, it was found that the inclusion of ternary complexes wasnot needed to describe the observed Ca2+-PO4interactions. For both As(V) and PO4, the resulting model predicts the presence ofcorner-sharing bidentate complexes as well as monodentate complexes, with the latter being important particularly at low pH. Theexperimental results showed that As(V) and PO4displayed similar adsorption patterns in the single-ion systems studied, which wereconducted using a constant anion-to-Fe ratio of 0.2. Even so, As(V) was preferentially adsorbed over PO4in competitive systems,particularly at low As(V)-to-PO4ratios when theKdvalues for As(V) were up to 2.1 times as high as those for PO4. The model,which described these patterns very well, suggests that adsorbed As(V) consists of a larger fraction of bidentate complexes than inthe case of PO4. This causes aflatter adsorption isotherm for As(V), which leads to a stronger As(V) adsorption as the As(V)-to-Feratio decreases, compared to that for PO4

The chemical stabilization, or immobilization, of trace elements (metals and metalloids; TE) in contaminated soil has been studied for decades. A vast number of scientific publications are available on the method performance in laboratory settings, reporting that the application of various soil amendments to contaminated soil reduces TE mobility, bioavailability and toxicity. The most commonly used soil amendments include organic matter, iron oxides, phosphates, ashes, and lately biochar, alone or in combination with each other and/or lime. Most of the implemented field studies show a certain degree of improvement in soil and/or vegetation status following amendment. Regardless the positive performance of the technique in the laboratory, field validations and demonstrations remain scarce. The establishment of a field experiment often involves permits from authorities and agreements with site owners, both of which are considerably more time-consuming than laboratory tests. Due to conservative institutional structures, public authorities have been slow to adopt alternative remediation technologies, especially when the total TE concentration in soil remains the same and all of the associated risks are not yet convincingly described. For this reason, researchers should also focus on enhancing public knowledge of alternative remediation techniques so that future projects which aim to demonstrate the effectiveness of in situ immobilization techniques under natural conditions will be supported.

Soil and water characteristics and biogeochemical processes can be improved by the application of an integrated technology based on circular economy: designed Technosol. The evaluation of the effectiveness of the superficial application of a designed Technosol, with andic and eutrophic properties, on the rehabilitation of sulfide tailings of a uranium mine (Fé mining area, Spain) was the aim of this study. After 20 months of the Technosol application, the tailing rehabilitation status (Rehabilitated tailing) was compared to a non-rehabilitated tailing (Tailing). To assess the rehabilitation of these systems, several properties were analyzed: chemical characteristics of the materials and their leachates, soil enzymatic activities (dehydrogenase, β-glucosidase, acid phosphatase and urease), basal respiration and several plant endpoints from direct and indirect bioassays and pot experiment using Lolium perennse L. and Trifolium pratense L.. Potentially toxic concentrations of Co, Mn and Ni were identified in both available fraction and leachates, pointing out the serious environmental risk posed by the tailing. The improvement of overall physicochemical properties in the rehabilitated tailing materials (e.g., decrease of the hazardous element concentrations in leachates and available fraction, and improvement of the fertility and structure) allowed a quick plant cover with pasture species and provided a suitable habitat for active microbial community (evaluated by increasing dehydrogenase activity and basal respiration). This improvement in the rehabilitated tailing contributed to a significant decrease in the ecotoxicological risk and the spread of hazardous elements. The field application of this specific Technosol was a promising and lasting solution for rehabilitation of this type of tailings.

The availability of phosphorus (P) in estuarine ecosystems is ultimately controlled by the nature of interactions between dissolved P and the soil components (e.g., soil minerals), especially iron (Fe) oxyhydroxides. P retention on Fe oxyhydroxides and its subsequent availability depends on mineral crystallinity and susceptibility to dissolution. However, in estuarine soils, geochemical conditions (e.g., redox oscillation and high soil organic matter content) may alter the fate of P and decrease the environmental quality of estuarine waters. The large input of Fe-rich tailings into the Rio Doce Estuary in Brazil in 2015 after a rupture of a Fe ore tailings dam (i.e., "Mariana mine disaster") offers a unique framework to evaluate the Fe oxyhydroxides role in P availability in estuarine soils, their potential effects on the cycling of P and eutrophication. We observed a significant correlation between Fe minerals and the P content in the estuary soils, suggesting that P enrichment was promoted by the deposited Fe-rich tailings. Adsorption isotherm curves indicated that mine tailings had a strong affinity for P due to presence of crystalline Fe oxyhydroxides in the tailings. Significant losses of Fe (62%) and P (56%) from the estuarine soil was observed two years after the initial impact and in response to redox conditions oscillations. Additionally, the content of high crystallinity Fe oxyhydroxides decreased significantly, whereas that of low crystallinity Fe oxyhydroxides showed an increase over time. These changes were associated with the dissimilatory Fe reduction, which led an increase in the concentrations of readily available P (2015: 2.30 ± 0.41 mg kg-1; 2017: 3.83 ± 1.82 mg kg-1; p

Schwertmannite is a metastable mineral playing a crucial role in the immobilization of metal(oid)s in acid mine drainage (AMD) systems. High temperatures associated with wildfires could lead to a sudden schwertmannite transformation, changing the mobility of metal(oid)s. The objective of the present study was to examine the thermal transformation from schwertmannite to hematite, and the subsequent effect on the chromium partitioning. The immobilization of arsenate after thermal transformation and its implications on chromium mobility was also evaluated. Natural schwertmannite, with increasing contents of chromium, was thermally treated between 200 to 800 °C. Transformation products were characterized by solid-phase techniques and selective chemical extractions. Results indicated a transformation to hematite at temperatures above 400 °C. The presence of chromium barely affected the temperature at which the transformation occurred, although partitioning of chromium in the mineral changed with temperature. As the temperature increased from 25 °C to 400 °C, chromium was less mobile and less outcompeted by arsenic adsorption, suggesting a larger contribution of inner-sphere complexes with increasing temperature. At temperatures above 600 °C, non-mobile forms strongly associated with neo-formed hematite were found. Finally, neo-formation of hematite led to a decrease in arsenic adsorption, implying a potentially enhanced arsenic mobility in AMD systems upon wildfires.

The uranium mineralization from Fé mining area (Spain) contains sulfides, resulting mine wastes generators of acid mine drainage rich in potentially hazardous elements (PHE). The improvement of the physicochemical characteristics and biogeochemical processes of sulfide mine tailings as well as their socioeconomic valorisation can be achieved by the application of a green technology based on circular economy: Technosol. The efficiency of the application of a superficial layer of a designed Technosol with specific properties to the rehabilitation of the sulfide tailings from Fé mining area was tested. Also, the risk assessment of the land recovery by this technology to pasture was evaluated through a microcosm experiment.After 20 months of the Technosol application in the field, composite samples of Technosol, recovered tailing (bottom of the Technosol) and tailings without recuperation (control tailing) were collected. These samples were used for microcosm assay and characterized for pH, electric conductivity, fertility, PHEs concentration in total fraction and available fraction extracted with rhizosphere-based method. The substrate effect on development of Lollium perenne and Trifolium pratense (visual signs of phytotoxity, percentage of plant cover and dry shoots biomass) and multielemental composition in their of shoots was evaluated in microcosm assay under greenhouse conditions.Mine wastes from control tailing had pH ≈4 and high total concentrations of several PHEs (g/kg; Al: 46.2; As, Co and Pb: 0.02-0.03; Cu: 0.04; Fe: 63.2 Mn: 1.3; Ni and Zn: 0.1-0.2). Potentially toxic concentrations of Co, Mn and Ni were identified in the available fraction pointing out the serious environmental risk posed by the control tailing. These chemical characteristics together lack of structure iin mine wastes from control tailing contributed to total inhibition of Trifolium germination and a significant diminution of Lollium growth. Both species growing in Technosol and recovered tailing produced significant plant cover and quite similar amounts of shoot biomass.The improvement of the overall physicochemical properties in the recovered tailing materials (e.g. the decrease of the hazardous element concentrations in available fraction, and the improvement of the fertility and structure) allowed a quick and secure plant cover with pasture species. The results evidenced the efficiency of the designed Technosol in the sulfide mine tailing rehabilitation and potential land recovery to pastures.The authors thank ENUSA for technical cooperation and providing the study area and soil samples.

A generic hydrous Fe oxide surface is often used in surface complexation modeling for predicting metal behavior in aqueous and soil environments. However, this approach may lead to incorrect results because there are many different naturally-occurring Fe(III) (oxyhydr)oxide mineral phases in the environment, each exhibiting distinct adsorption characteristics. This work presents a consistent dataset of surface complexation model parameters valid at 25 °C and 1 bar that characterize the adsorption of selected divalent metals (Cd, Cu, Pb, Zn) onto environmentally relevant Fe(III) (oxyhydr)oxides, i.e., FeOOH and Fe2O3 polymorphs (goethite, hematite, lepidocrocite, maghemite), at varying metal concentrations and ionic strengths. The parameters were obtained using a simple and unified workflow and are readily implementable into widely used geochemical codes, such as Visual MINTEQ, MINEQL+, and ORCHESTRA, enabling quantification of metal adsorption onto a range of Fe(III) oxides in various aqueous environments.

Phosphorus is an essential element that at high concentrations generates eutrophication of aquatic systems. In this study, we used batch and continuous tests to evaluate the efficiency of a Technosol to retain the phosphorus present (as phosphate) in aqueous samples. Phosphate sorption on Technosol was studied through batch and continuous experiments. Sorption kinetics and isotherms were investigated at different phosphate loadings and pH. In batch tests, we have determined how the presence of different anions (bicarbonate, sulphate, chloride, chromate and molybdate) affected phosphate retention. In continuous flow systems, phosphate immobilization was assessed as a function of flow rate, pH and Technosol concentration. Finally, the potential reutilization of the column was evaluated using consecutive sorption-desorption cycles. Phosphate sorption follows a pseudo-second-order kinetics model and a Langmuir isotherm model. The maximum sorption capacity ranged from 7.1 to 18.5 mg g−1, with larger values obtained at the highest pH. The main mechanisms involved in the sorption process were precipitation (as Ca-P minerals) and surface adsorption. In the column experiments, we observed a sorption reduction from 6.19 ± 0.06 to 2.37 ± 0.06 mg g−1 as the flow rate increased from 1.5 to 5.0 mL min−1. In addition, the retention capacity decreased by 14% when the height of the reactive layer was halved. Finally, the retention capacity of the Technosol spolic silandic recovered well after several sorption-desorption cycles, reaching 40% of the original value after first and second cycles. The material effectively retained phosphate in batch and continuous flow systems. The Technosol spolic silandic is considered an efficient sorbent to remove the excess of phosphate from the soil solution and the aqueous system. This material may be a useful tool to mitigate or minimize two important environmental problems: eutrophication and the scarcity of natural sources of phosphate. The Technosol can thus be recycled as a phosphate-rich amendment and the leachates can be used to produce liquid fertilizer.

The development of three-dimensional (3D) patterned Cu-based composites with Al2O3 matrix has significant potential for an array of uses in industrial applications ranging from aerospace t...

Organo-mineral composites formed by the association of iron (hydr)oxides and organic matter are widespread in natural environments and play an important role as scavengers of bioessential elements and contaminants. To better understand the mobility and fate of Cu in natural soils and sediments we precipitated ferrihydrite and goethite organo-mineral composites using humic acid as an analogue for natural organic matter, with organic carbon content in the composites ranging from 2 to 16 wt% C. We then measured the adsorption of Cu to the end-member mineral and organic phases and the composites as a function of pH and Cu concentration. We determined the molecular mechanisms of Cu adsorption to the end-member phases and the composites, and used this information to develop molecularly constrained thermodynamic surface complexation models to quantify Cu adsorption. By combining our work here with previous work on the adsorption of Cu to ferrihydrite-bacteria composites, we provide insight into the predominance of Cu-carboxyl binding for Cu adsorption to iron (hydr)oxide organo-mineral composites, and the nature of Cu adsorption behaviour across a range of iron (hydr)oxide composites composed of different minerals and different types of organic matter. Taken as a whole our results show that Cu adsorption to the carboxyl group present in organic matter coatings on iron (hydr)oxides is likely common to most iron (hydr)oxide composites, such that Cu-carboxyl binding provides a key control on the fate and mobility of Cu in soils and sediments. Our work also suggests there is a universal adsorption behaviour for Cu adsorption to ferrihydrite organo-mineral composites, in which the mineral:organic mass ratio is a crucial parameter for determining Cu uptake. Overall we show that ferrihydrite composites composed of different types of organic matter and containing a wide range of organic mass ratios, but where the mineral is the dominant composite fraction, possess additive Cu adsorption behaviour which can be predicted using a component additivity surface complexation model.

Secondary iron minerals are important in mining areas as they are natural scavengers of many contaminants. Thus, aluminium and iron oxides derived from acid mine drainage determine the fate of trace metals commonly found in mining areas. They mainly do this via sorption processes, which prevent leaching of the metals and contamination of surface and groundwater. In the present study, abiotic precipitates were obtained from samples of acid drainage water collected from an abandoned copper mine. Characterization of the precipitates revealed that schwertmannite was the dominant iron mineral phase present. Retention of Cu, Cd, Ni and Pb by natural iron precipitates was compared with retention of the same elements by synthetic analogues. The study findings indicate that the natural abiotic precipitates have a higher retention capacity than their synthetic analogues. Thermodynamic modelling was used to predict the geochemical behaviour of the trace metals in the presence of iron precipitates. Inclusion of adsorption and precipitation reactions in the models yielded a good description of the degree of attenuation of adverse effects of the trace metals. Under acidic conditions, the schwertmannite-like particles initially present in the natural precipitates evolve towards more crystalline mineral phases. This transformation process is accompanied by the release of sulphate ions into the solution and by a decrease in trace metal sequestration.

Goethite is a common iron oxide present in the environment. It is used as a model system to represent the mineral fraction of the soil, whereas humic acid is used as a model system to represent natural organic matter (NOM). In this study, we tried to understand the behaviour of anionic and cationic pollutants in a model system, which could easily represent the organic-mineral interaction in the environment. Specifically, the retention of arsenate and copper over different organo-mineral systems was studied. The obtained results show an increase in the adsorption of copper as the pH and the C content in the organo-mineral composites was raised, whereas in the case of the arsenate, the opposite behaviour was observed. The adsorption behaviour was compared with that of the end-members goethite and humic acid. Furthermore, the NOM-CD model (natural organic matter-charge distribution model) was used to describe the reactivity of the pollutants in the solid/solution interphase and to predict the surface and aqueous speciation. To simulate the behaviour of the organo-mineral composites, a surface component was included to describe the chemical and electrostatic interactions of the NOM with the goethite in the modelling of the solid/solution interphase. This approximation allows the quantification of the effective organic matter, which can be used to describe the copper and arsenate reactivity in organo-mineral systems.

Secondary iron oxides formed in acid mine drainage, such as schwertmannite, are scavengers for metal(loid)s in mining environments. Increasing the understanding of the geochemical transformations of these minerals, as well as knowing how metal(loid)s affect these transformations, is crucial to ultimately predict the fate of these trace elements in acidic mine drainage and to minimize the potential environmental risk. In this study, transformation experiments have been conducted with a schwertmannite-rich sediment collected from a mining area and with synthesized schwertmannite as a reference material. The transformation of schwertmannite into goethite was studied as a function of the presence of arsenic, pH value, and redox conditions. Arsenic delayed the mineral transformation from pseudo-stable amorphous phases to more stable crystalline forms, especially at higher arsenic loadings and more acidic pH. Experiments in the presence of Fe(II) and ascorbic acid have proven that both components promote the mineral transformation or reductive dissolution of schwertmannite under anoxic conditions. The presence of arsenic reduced the catalytic effect of Fe(II), stabilizing the schwertmannite particles. On the other hand, arsenic had no effect on the reductive dissolution at these conditions when ascorbic acid was used as a reducing agent.

Biochar samples were generated by low temperature pyrolysis of different types of waste. The physicochemical characteristics of the different types of biochar affected the copper retention capacity, by determining the main mechanism involved. The capacity of the biochar to retain copper present in solution depended on the size of the inorganic fraction and varied in the following order: rice biochar>chicken manure biochar>olive mill waste biochar>acacia biochar>eucalyptus biochar>corn cob biochar. The distribution of copper between the forms bound to solid biochar, dissolved organic matter and free organic matter in solution also depended on the starting material. However, the effect of pH on the adsorption capacity was independent of the nature of the starting material, and the copper retention of all types of biochar increased with pH.

The kinetics of N-chlorination reaction of pyrrolidine, pyrrolidone, succinimide, 5,5,-dimethyloxazolidine-2,4-dione, 5,5-dimethylhydantoin and 1-hydroximethyl-5,5-dimethylhydantoin with HOCl in aqueous solution were studied at 25 °C, constant ionic strength and under isolation conditions in a wide pH range. The set of compounds studied in this paper is characterized by having different functional groups and the same cyclic structure, consisting of a five-member ring with a nitrogen atom in the ring, which is susceptible to be chlorinated. This series of compounds covers nine pKa units, and the kinetic studies allow us to know, like, the presence of an amino, amide or imide group modify the reactivity of nitrogenous compound. Experimental data were fitted to the first-order kinetic equation. All reactions were found to be of first order in both HOCl and nitrogenous compound concentration. Kinetics studies demonstrate that some of these compounds are hydrolyzed in alkaline medium. In each case, reaction mechanism in agreement with the experimental results is proposed. The results were compared with other compounds with similar cyclic structure (2-oxazolidinone and proline). Copyright © 2016 John Wiley & Sons, Ltd.

Low redox potential in flooded soils may affect phosphate bioavailability by reducing iron oxides or formation of new minerals. To investigate phosphate behavior in anoxic conditions, goethite was selected as a soil model and coated by humic acid (HA) and sodium borohydride was used as a reducing agent. Adsorption experiments were conducted in 0.1 M NaNO3 as a function of pH in oxic (Eh = +254 to +448 mV) and suboxic (Eh = −162 to +167 mV) conditions for four phosphate concentrations (0.05–0.8 mM). CD-MUSIC and NOM-CD models in combination with Extended Stern model were used to describe the experimental data. Results show that by increasing pH and carbon content in the organo-mineral composites, the released phosphate to the solution increases in both oxic and suboxic conditions. In suboxic conditions, as a result of sodium borohydride dissociation in water and consequently boron release to the solution, at high loading of boron and low loading of phosphate, boron can compete with phosphate for the surface reactive sites and decrease its adsorption. On the other hand, ferrous iron can attenuate boron effect and promote phosphate adsorption. The results indicated that goethite surface is resistant to the reductive transformation that may occur at relatively low redox potential due to its high crystalline character and thermodynamic stability. HA may, however, promote the formation of amorphous iron phases, which consequently might induce phosphate adsorption in OM-mineral composites. The derived affinity constants in oxic conditions described the experimental data of suboxic conditions reasonably well.

Pyrolysis of waste materials to produce biochar is an excellent and suitable alternative supporting a circular bio-based economy. One of the properties attributed to biochar is the capacity for sorbing organic contaminants, which is determined by its composition and physicochemical characteristics. In this study, the capacity of waste-derived biochar to retain volatile fuel organic compounds (benzene, toluene, ethylbenzene and xylene (BTEX) and fuel oxygenates (FO)) from artificially contaminated water was assessed using batch-based sorption experiments. Additionally, the sorption isotherms were established. The results showed significant differences between BTEX and FO sorption on biochar, being the most hydrophobic and non-polar contaminants those showing the highest retention. Furthermore, the sorption process reflected a multilayer behaviour and a relatively high sorption capacity of the biochar materials. Langmuir and Freundlich models were adequate to describe the experimental results and to detect general differences in the sorption behaviour of volatile fuel organic compounds. It was also observed that the feedstock material and biochar pyrolysis conditions had a significant influence in the sorption process. The highest sorption capacity was found in biochars produced at high temperature (> 400 °C) and thus rich in aromatic C, such as eucalyptus and corn cob biochars. Overall, waste-derived biochar offers a viable alternative to be used in the remediation of volatile fuel organic compounds from water due to its high sorption capacity.

The geochemical behaviour of phosphate and arsenate ions in soil and aquatic systems is determined by the presence of mineral surfaces and major ions. Information about the distribution of oxyanions over the solid and solution phases is essential for understanding the transport, bioavailability and toxicity of these compounds in the environment. Here, we studied the adsorption of both arsenate and phosphate on ferrihydrite nanoparticles in the presence of calcium ions. The presence of calcium ions enhanced the retention of these oxyanions on ferrihydrite and vice versa. The arsenate–calcium and phosphate–calcium multi-component systems were described using a mechanistic surface complexation model. Use of this type of model enables prediction of the solution and surface speciation, along with analysis of oxyanion mobility in relation to environmental conditions. We were able to calibrate the charge distribution model with the macroscopic data obtained for the single-component systems, thus obtaining surface complexation constants for later use to simulate multi-component systems. The mutual interactions between arsenate and calcium were successfully described with these parameters, indicating that changes in the electrostatic forces at the solid/solution interface caused the observed enhanced adsorption. However, adsorption in the phosphate–calcium system was underestimated with the parameters obtained for the single-component systems, indicating that additional mechanisms or processes should be considered. Formation of insoluble mineral phases was ruled out, but the inclusion of a phosphate–calcium ternary surface complex improved the modelling predictions.

The chlorination reactions of 2-oxazolidinone with hypochlorous acid (HOCl), tert-butyl hypochlorite (tBuOCl) and N-chlorosuccinimide (NCS) were studied at 25 °C, constant ionic strength, and under isolation conditions. The kinetic results obtained in the formation processes of the N-chloro-2-oxazolidinone are summarized in this paper. The kinetics studied showed a first order with respect to the concentration of the each reactant and a complex dependence of the pH on the rate constant. The reactivity order with respect to the chlorinating agent found is k(HOCl) > k(tBuOCl) > k(NCS). Copyright © 2015 John Wiley & Sons, Ltd.

Acid mine drainage (AMD) constitutes a serious environmental problem in mining areas due to the acidification of soils and aquatic systems, and the release of toxic metals. Many of the pollutants that occur in AMD display a high affinity for the surfaces of the aluminium and iron oxides that are typically present in systems affected by AMD. This binding affinity reduces the mobility of trace metals and metalloids, such as copper and arsenic, thus helping to mitigate contamination of aquatic systems. In the present study, water samples and iron-rich bed sediments were collected in areas affected by copper mining activities. A loose ochre-coloured precipitate occurring on the banks of a river close to an abandoned tungsten and tin mine was also sampled. The composition of the precipitate was established, and adsorption experiments were performed with copper and arsenate ions to determine the ability of natural iron precipitates to reduce the concentration of these ions in solution. Surface complexation models provided a good description of the behaviour of natural iron oxides in terms of copper and arsenate retention. Use of this type of model enables prediction of the distribution of pollutants between the solid and solution phases and analysis of their mobility in relation to environmental conditions (pH, ionic strength, presence of competing species, etc.).

The chlorination reactions of nitrogenous organic compounds (2,2,2-trifluoroethylamine, benzylamine, glycine, and dimethylamine) by tert-butyl hypochlorite (tBuOCl) were studied at 25 °C, ionic strength 0.5 M and under isolation conditions. The kinetic results obtained in the formation processes of the corresponding N-chloramines in acid medium (pH = 5–7) are summarized in this paper. Kinetic studies showed a first order with respect to tBuOCl concentration. The chlorination reactions involving benzylamine, glycine and dimethylamine were all first order with respect to nitrogenous compound concentration and approximately −1 order with respect to proton concentration. The reaction with 2,2,2-trifluoroethylamine was more complex, and the order of reaction with respect to the amine varied with pH. Copyright © 2014 John Wiley & Sons, Ltd.

Surface complexation models have proved to be valuable tools for predicting processes that occur at the solid-solution interface. Use of such models has become more widespread and nowadays more complex systems are studied, in an attempt to explain processes such as the competition between different species for mineral surfaces and the effect of the presence of organic matter. The aim of the present study was to analyze the mobility of phosphate in ferralic soils. The charge distribution model parameters for phosphate-goethite adsorption were used to predict phosphate mobility on samples from 2 horizons of a ferralic soil containing large amounts of iron oxides. The soil reactivity was attributed to the iron oxides, and some specific parameters were determined by means of phosphate adsorption-desorption experiments and included in the model. Adsorption of phosphate in the upper horizon, which contained more organic carbon and phosphate than the deeper one, was modeled by using the information obtained for the soil and the charge distribution model parameters derived for phosphate-goethite interaction with no need of further optimization. In contrast, some extra fitting parameters were required to improve the modeling of the phosphate adsorption in the deeper horizon.

High levels of oxyanions are found in the soil environment, often as a result of human activity. At high concentrations, oxyanions can be harmful to both humans and wildlife. Information about the interactions between oxyanions and natural samples is essential for understanding the bioavailability, toxicity, and transport of these compounds in the environment. In the present study, the authors investigated the reactivity of different oxyanions (AsO4 , MoO4 , SeO4 , and CrO4 ) at different pH values in 2 horizons of a ferralic soil. By combining available microscopic data on iron oxides with the macroscopic data obtained, the authors were able to use the charge distribution model to accurately describe the adsorption of these 4 oxyanions and thus to determine the surface speciation. The charge distribution model was previously calibrated and evaluated using phosphate adsorption/desorption data. The adsorption behavior on ferralic soil is controlled mainly by the natural iron oxides present, and it is qualitatively analogous to that exhibited by synthetic iron oxides. The highest adsorption was found for arsenate ions, whereas the lowest was found for selenate, with chromate and molybdate ions showing an intermediate behavior.

Second-order rate constants were determined for the chlorination reaction of 2,2,2-trifluoethylamine and benzylamine with N-chlorosuccinimide at 25 °C and an ionic strength of 0.5 M. These reactions were found to be of first order in both reagents. According to the experimental results, a mechanism reaction was proposed in which a chlorine atom is transferred between both nitrogenous compounds. Kinetics studies demonstrate that the hydrolysis process of the chlorinating agent does not interfere in the chlorination process, under the experimental conditions used in the present work. Free-energy relationships were established using the results obtained in the present work and others available in the literature for chlorination reactions with N-chlorosuccinimide, being the pK a range included between 5.7 and 11.22. Copyright © 2014 John Wiley & Sons, Ltd.

The formation, transformation and surface chemistry of iron oxides is geologically important in surface waters polluted by acid mine drainage (AMD). The geochemical behaviour of these oxides controls the availability and mobility of contaminants in such highly polluted systems. The low pH values, together with the presence of large amounts of sulphate, favour the formation of schwertmannite, which is a metastable iron oxide that is transformed to goethite under oxic conditions. However, in copper mining environments, co-precipitation of iron and copper ions is expected and therefore the surface chemistry of the iron oxides present in these systems may be different. Several schwertmannite samples were prepared in the presence of high concentrations of sulphate and different concentrations of copper to simulate copper-rich mining environments. Long-term transformation experiments were conducted to study the mineral oxide stability and variations in surface chemistry produced over a period of 15 months. Schwertmannite-like particles were initially formed, but sulphate release and the dissolution and re-precipitation of iron and copper ions occurred under more acidic conditions throughout the experiment, which led to the formation of goethite-like particles. The capacity for arsenate adsorption was highest in the initial schwertmannite-like particles, and arsenate mobility increased in the presence of more stable iron mineral phases that were formed throughout the transformation experiment.

The kinetics of the oxidation reaction of bromide by tert-butyl hypochlorite (tBuOCl) was studied at 25°C, ionic strength 0.5 M, and under isolation conditions. A stopped-flow spectrophotometer was employed for monitoring the reactions. Kinetic studies show that the reaction is first order with respect to [Br-] and [tBuOCl]. Linear dependences of the proton concentration, in perchloric acid medium, and the buffer solution concentration were found on the rate constant. The activation parameters were calculated using the Arrhenius and Eyring equations from the kinetic studies performed to analyze the influence of temperature on the rate constant. The results are consistent with a reaction mechanism of general acid catalysis. The catalytic constants were obtained for the oxidation of bromide by tert-butyl hypochlorite. The slope obtained for the Bronsted relationship was 0.36. © 2013 Wiley Periodicals, Inc.

Second-order rate constants (k2) were determined for the addition of ten nitrogenous organic compounds (benzylamine, 2,2,2-trifluoethylamine chlorhidrate, methylamine chlorhidrate, glycine ethyl ester chlorhidrate, glycine, glycylglycine chlorhidrate, morpholine, pyperidine, pyperazine and dimethylamine) to the N-chloro-N-methyl-p-toluenesulfonamide (NCNMPT) in the formation reaction of N-chloramines in aqueous solution at 25 °C and ionic strength 0.5 M. The series of nucleophiles considered is structurally very varied and covers five pKa units. The kinetic behaviour is similar for all compounds, being the elementary step the transfer of chlorine from the NCNMPT molecule to the nitrogen of the free amino group. These reactions were found first order in both reagents. The values of the rate constants indicate that the more basic amines produce N-chloramines more readily. Rate constants for the nucleophilic attack are shown to correlate with literature data for some of these nitrogenous organic compounds in their reaction with N-methyl-N-nitroso-p-toluenesulfonamide. Both reactions involve that the rate determining step is the attack of nitrogenous compounds upon electrophilic centre (Cl or else NO group). NCNMPT is a particularly interesting substrate, for which has not hitherto been published kinetic information, that allows us to assess the efficiency and the competitiveness of this reaction and compare it with other agents with a Cl+ atom. Copyright © 2013 John Wiley & Sons, Ltd.

The presence of iron oxides may play an important role in controlling the mobility and availability of contaminants in soils and waters affected by acid mine drainage. The present study describes the uptake of arsenate, chromate and molybdate from solution by synthetic schwertmannite. Batch experiments were performed at different pH values in order to obtain the adsorption isotherms for the three oxyanions. In addition to the formation of surface complexes between the oxyanions and the iron surface reactive groups, it is also expected that anion exchange will occur between sulphate anions from the schwertmannite structure and the oxyanions present in the solid/solution interface. Comparison of the experimental adsorption results for the different oxyanions showed large differences, not only the amount adsorbed, which was much higher for arsenate, but also in the sulphate exchange with the anions in solution. In case of chromate, the main mechanism of adsorption process is the exchange reaction with the sulphate groups present in the schwertmannite. The observed results suggest a different adsorption mechanisms for each of the three oxyanions, with important implications for the mobility of these anions in acid mine drainage systems.

A sample of an ombrotrophic peat was washed thoroughly with nitric acid to release bound cations, and potentiometric titrations were carried out with the untreated peat and the acid-washed peat at five different ionic strengths of between 0.01 and 0.3. M. The experimental titration curves were used to obtain the absolute charge-pH curves for the acid-washed peat and relative charge-pH curves for the untreated peat (i.e. for the latter only the surface charge due to ionization of acid groups, as the value of the initial charge was not known because of the presence of exchangeable cations). The effect of ionic strength on proton binding was the same for the acid-washed peat and the untreated peat, as indicated by the similar spacing between the charge curves for both types of samples. The charge curves for the acid-washed and untreated peat corresponded after correction of the charge of the untreated peat, considering that the initial charge is equal to the charge on the exchangeable cations. The NICA-Donnan model, in which the Donnan volume varied with ionic strength, provided an excellent fit to the experimental data for the acid-washed peat and enabled the values of the intrinsic proton binding parameters to be obtained. Good simulation of the experimental charge curves for the untreated peat was obtained from the parameters of the acid-washed peat, by use of the same values of the Donnan volume, and including the charge due to the exchangeable cations. The parameters of the acid-washed peat therefore provide a realistic representation of the observed behavior of the untreated peat, and enable prediction of the behavior of peat in the natural environment. © 2011 Elsevier B.V.

Adsorption of cationic pesticides in soils is generally attributed to mineral clays and organic matter components. However, iron oxides may also contribute to such adsorption or affect it by associating with other components. Using goethite and humic acid as models for iron oxides and organic matter respectively, we studied the adsorption of the cationic pesticide paraquat on goethite and humic acid-coated goethite. At pH 4.0 the adsorption on goethite was not significant, and at pH 10.0, although the surface of the oxide was negatively charged, much less pesticide was adsorbed than on mineral clays. At this pH the adsorption of paraquat decreased as the ionic strength increased, and application of the charge distribution multisite complexation model (CD-MUSIC model) enabled interpretation of the results. At pH 4, the adsorption of paraquat on the humic acid-coated goethite was similar to the adsorption on mineral clays, but was considerably less than the adsorption on humic acid in solution. The lower adsorption on solid organic matter is attributed to a decrease in the number of "active" binding sites on the humic acid as a result of the binding to iron oxide.

The kinetics of disproportionation of N-Cl-methylamine and N-Cl-ethylamine in water were studied at acid pH. Its disproportionation and protonation constants and the coefficients of absorption of N,N-dichloramines are calculated and the mechanism of its disproportionation is discussed.

Spectrophotometric determinations of the pK of six secondary N-chloramines have been used to obtain an empirical equation relating the pK of secondary N-chloramines to those of the corresponding amines.

Studying the kinetic behaviour of the system 2-ethylaminoethanol+hypochlorite under various experimental conditions shows that the rapid formation of N-chloro-2-ethylaminoethanol (t1/2

Information on the particle size and reactive surface area of natural samples and its interaction with natural organic matter (NOM) is essential for the understanding bioavailability, toxicity, and transport of elements in the natural environment. In part I of this series (Hiemstra et al., 2010), a method is presented that allows the determination of the effective reactive surface area (A, m2/g soil) of the oxide particles of natural samples which uses a native probe ion (phosphate) and a model oxide (goethite) as proxy. In soils, the natural oxide particles are generally embedded in a matrix of natural organic matter (NOM) and this will affect the ion binding properties of the oxide fraction. A remarkably high variation in the natural phosphate loading of the oxide surfaces (Γ, μmol/m2) is observed in our soils and the present paper shows that it is due to surface complexation of NOM, acting as a competitor via site competition and electrostatic interaction. The competitive interaction of NOM can be described with the charge distribution (CD) model by defining a ≡NOM surface species. The interfacial charge distribution of this ≡NOM surface species can be rationalized based on calculations done with an evolved surface complexation model, known as the ligand and charge distribution (LCD) model. An adequate choice is the presence of a charge of −1 v.u. at the 1-plane and −0.5 v.u. at the 2-plane of the electrical double layer used (Extended Stern layer model). The effective interfacial NOM adsorption can be quantified by comparing the experimental phosphate concentration, measured under standardized field conditions (e.g. 0.01 M CaCl2), with a prediction that uses the experimentally derived surface area (A) and the reversibly bound phosphate loading (Γ, μmol/m2) of the sample (part I) as input in the CD model. Ignoring the competitive action of adsorbed NOM leads to a severe under-prediction of the phosphate concentration by a factor ∼10 to 1000. The calculated effective loading of NOM is low at a high phosphate loading (Γ) and vice versa, showing the mutual competition of both constituents. Both constituents in combination usually dominate the surface loading of natural oxide fraction of samples and form the backbone in modeling the fate of other (minor) ions in the natural environment. Empirically, the effective NOM adsorption is found to correlate well to the organic carbon content (OC) of the samples. The effective NOM adsorption can also be linked to DOC. For this, a Non-Ideal Competitive adsorption (NICA) model is used. DOC is found to be a major explaining factor for the interfacial loading of NOM as well as phosphate. The empirical NOM–OC relation or the parameterized NICA model can be used as an alternative for estimating the effective NOM adsorption to be implemented in the CD model for calculation of the surface complexation of field samples. The biogeochemical impact of the NOM–PO4 interaction is discussed.

Information on the particle size and reactive surface area of natural samples is essential for the application of surface complexation models (SCM) to predict bioavailability, toxicity, and transport of elements in the natural environment. In addition, this information will be of great help to enlighten views on the formation, stability, and structure of nanoparticle associations of natural organic matter (NOM) and natural oxide particles. Phosphate is proposed as a natively present probe ion to derive the effective reactive surface area of natural samples. In the suggested method, natural samples are equilibrated (⩾10 days) with 0.5 M NaHCO3 (pH = 8.5) at various solid–solution ratios. This matrix fixes the pH and ionic strength, suppresses the influence of Ca2+ and Mg2+ ions by precipitation these in solid carbonates, and removes NOM due to the addition of activated carbon in excess, collectively leading to the dominance of the PO4–CO3 interaction in the system. The data have been interpreted with the charge distribution (CD) model, calibrated for goethite, and the analysis results in an effective reactive surface area (SA) and a reversibly bound phosphate loading Γ for a series of top soils. The oxidic SA varies between about 3–30 m2/g sample for a large series of representative agricultural top soils. Scaling of our data to the total iron and aluminum oxide content (dithionite–citrate–bicarbonate extractable), results in the specific surface area between about 200–1200 m2/g oxide for most soils, i.e. the oxide particles are nano-sized with an equivalent diameter in the order of ∼1–10 nm if considered as non-porous spheres. For the top soils, the effective surface area and the soil organic carbon fraction are strongly correlated. The oxide particles are embedded in a matrix of organic carbon (OC), equivalent to ∼1.4 ± 0.2 mg OC/m2 oxide for many soils of the collection, forming a NOM–mineral nanoparticle association with an average NOM volume fraction of ∼80%. The average mass density of such a NOM–mineral association is ∼1700 ± 100 kg/m3 (i.e. high-density NOM). The amount of reversibly bound phosphate is rather close to the amount of phosphate that is extractable with oxalate. The phosphate loading varies remarkably (Γ ≈ 1–3 μmol/m2 oxide) in the samples. As discussed in part II of this paper series ( Hiemstra et al., 2010 ), the phosphate loading (Γ) of field samples is suppressed by surface complexation of NOM, where hydrophilic, fulvic, and humic acids act as a competitor for (an)ions via site competition and electrostatic interaction.

In this kinetic study of the reaction between the iodide ion and the N-chlorosuccinimide, we have found that the reaction is first order in N-chlorosuccinimide: namely, first order with respect to the iodide ion and first order with respect to the proton concentration. Based on the experimental results, we propose a mechanism consistent in Cl+ transfer from the N-chlorosuccinimide to the iodide ion. We have found that the reaction presents general acid catalysis with a Bronsted exponent value of 0.10. In addition, given that the N-chlorocompounds are not stable in aqueous solution, we have carried out a study on the influence of bases in the presence of N-chlorosuccinimide. We have found that the reaction is first order in hydroxide ion, as well as in the 1,1,1,3,3,3-hexafluoroisopropanoxide ion and the 2,2,2-trifluorethoxide ion, which shows that the reaction is general-base catalyzed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 243–252, 2005

The kinetics of N-bromination of 2-oxazolidinone by transferor Br from sodium hypobromite, N-bromosuccinimide (NBS), or N-bromoacetamide (NBA) were determined spectrophotometrically, at pH between 4.6 and 12.45 (depending on the brominating agent). The reaction with hypobromite was of first order with respect to both the hypobromite and the substrate. The bromination of oxazolidinone with NBS (or NBA) has been found to be a reversible process of order one with respect to both NBA (or NBA) and oxazolidinone in the forward direction, and order one with respect to SI (or ACAM) and the resulting N-bromo-oxazolidinone in the other. The pH dependence of the reaction rate was in keeping with a mechanism in which all the brominating agents (HOBr, BrO -, NBS and NBA) react predominantly with the anion of the substrate. Bimolecular bromination rate constants increased in the order BrO- < NBA < NBS < HOBr. © 2004 Wiley Periodicals. Inc.

We studied the effect of pH on the binding of Cu2+ to a soil fulvic acid in solutions containing dissolved organic carbon at concentrations within ranges typical of freshwaters and soil solutions. ...

Potentiometric titrations of a sample of soil extracted fulvic acid (FA) were carried out using different concentrations (20 mg l−1

The acid-base properties of two fulvic acids (FA) extracted from senescent leaves of eucalyptus and oak were characterized by carrying out potentiometric titrations at two FA concentrations and four ionic strengths (0.005 M[KNO(3)]1.0 M). Experimental data were analyzed by means of the master curve approach, which includes an electrostatic spherical double layer model, and the Langmuir-Freundlich isotherm was used to fit the data. The contribution of the electrostatic effect to the proton binding reaction was lower than that observed for soil fulvic acids. The chemical heterogeneity of both samples was described by two acid sites with p Ks of about 4 and 7.5, the most abundant being the carboxylic site of p K = 4.

A simple electrostatic model was used to study the effect of pH on the binding of Cu2+ to fulvic acid in solutions containing similar amounts of dissolved organic carbon (DOC) as natural media, such as aquatic environments and soil solutions. Complexation behavior was affected by increased pH because of changes in the electrostatic interaction resulting from an increase in the negative charge on the fulvic acid molecule. Solutions of soil-extracted fulvic acid (FA), at concentrations of 25 and 35 mg L(-1), ionic strength 0.005 M, and pH 5.0, 5.5, 6.0, 6.5, 7.0, and 7.5, conditions that simulate those of natural freshwaters, were titrated with copper ion using differential pulse anodic stripping voltammetry. Assuming the formation of 1:1 complexes, the conditional binding parameters (stability constant and binding capacity) were calculated for each pH value. Use of a 1:1 electrostatic model allowed estimation of the contribution of the electrostatic effect to the ion binding reaction, at each pH value, as well as calculation of a binding constant that was not dependent on pH and which thus represented the contribution of the chemical heterogeneity. Furthermore, it was found that only a small proportion of the FA acid functional binding sites are involved in the formation of copper complexes.

Surface complexation models have proved to be valuable tools for predicting processes that occur at the solid-solution interface. Use of such models has become more widespread and nowadays more complex systems are studied, in an attempt to explain processes such as the competition between different species for mineral surfaces and the effect of the presence of organic matter. The aim of the present study was to analyze the mobility of phosphate in ferralic soils. The charge distribution model parameters for phosphate-goethite adsorption were used to predict phosphate mobility on samples from 2 horizons of a ferralic soil containing large amounts of iron oxides. The soil reactivity was attributed to the iron oxides, and some specific parameters were determined by means of phosphate adsorption-desorption experiments and included in the model. Adsorption of phosphate in the upper horizon, which contained more organic carbon and phosphate than the deeper one, was modeled by using the information obtained for the soil and the charge distribution model parameters derived for phosphate-goethite interaction with no need of further optimization. In contrast, some extra fitting parameters were required to improve the modeling of the phosphate adsorption in the deeper horizon.