Sorption Of Organic Matter Research Articles

Simultaneous Cd2+ and organic matter sorption behavior on various microplastics: Modeling of influencing factors using the Taguchi method

In aquatic environments, microplastics (MPs) can serve as a vector for pollutants. Pollutants adsorbed on the surface of microplastics pose a potential risk to aquatic organisms. In this study, the effect of environmental conditions such as duration, pH and conductivity on the Cd+2 and organic matter adsorption capacity, qe,Cd and qe,COD of microplastic type was evaluated using the Taguchi experimental design method. ANOVA results showed that the most effective factor in adsorption capacity was the microplastic type. qe,Cd were listed as > 0.6–0.8 mg/gPP, >0.4 mg/gMDPE, 0.2 mg/gLDPE at 50 mS/cm. It was observed that conductivity had a positive effect on qe,Cd.,qe,Cd for PP in waters with conductivities of 50 mS/cm, 0.8 mS/cm, 0.02 mS/cm at pH 7.0 was found to be ≫ 0.6, >0.2, > 0.4, respectively. qe,Cd and qe,COD showed similar trends. It was determined that the qe,COD at 50 mS/cm was in the order of 15–22 mg COD/gPP, 5–10 mg COD/gMDPE, but not determined for LDPE. After MW and UV artificial aging, qe,COD of virgin PP increased by 31.5 % and 94.4 %, respectively, whereas the qe,Cd decreased by 1.2 % and 24 %.

Nano-Scale Secondary Ion Mass Spectrometry: A Paradigm Shift in Soil Science

Soils exhibit structural heterogeneity across diverse spatio-temporal scales, yielding myriad of microhabitats, highlighting the need for a nuanced understanding of the intricate interactions within the soil matrix. At the nanometer scale, the interplay among organic matter (OM), mineral particles, and microbiota intricately govern the long-term destiny of soil carbon (C), nutrient cycling, and the fate of both organic and inorganic pollutants. Notably, the sorption of soil organic matter (SOM) onto smaller clay particles and its entrapment in microaggregates further contribute to this complex dynamic. Understanding these processes depends on recognizing their scale-dependent nature, necessitating sophisticated techniques for investigation. Although various methods are employed across scales, the current set of techniques still lacks the requisite sensitivity and resolution for microscale data collection. To address this limitation, the adoption of novel microscopic and spectroscopic techniques capable of probing molecular, isotopic, and elemental patterns at the micro to nano scale becomes imperative. Among these cutting-edge methodologies, the nano-scale secondary ion mass spectrometer (NanoSIMS) emerges as a paradigm-shifting tool. Representing the latest evolution in ion microprobes, NanoSIMS seamlessly integrates high-resolution microscopy and isotopic analysis, maintaining unparalleled signal transmission and spatial resolution, reaching as fine as 50 nm. Its capabilities extend beyond conventional applications in science, as evidenced by recent breakthroughs in utilizing NanoSIMS to study biophysical interfaces in soils. This article underscores the pressing need to advance the incorporation of NanoSIMS as a pioneering instrumentation technique in soil studies. Furthering the implementation of this novel instrumentation technique in soil studies will pave avenues and aid in the advancement of future research.

Estimating Mineral-Associated Organic Carbon Deficits in Soils of the Okanagan Valley: A Regional Study With Broader Implications

To successfully reduce atmospheric CO2 by sequestering additional soil carbon, it is essential to understand the potential of a given soil to store carbon in a stable form. Carbon that has formed organo-mineral complexes with silt and clay particles is believed to be less susceptible to decay than non-complexed, or particulate, organic carbon. Using direct measurements of mineral associated organic matter (MAOC) on a subset of samples, and an approach developed previously for primarily allophanic soils, we took a modeling approach to estimate MAOC for 537 samples of much coarser and younger soils from 99 non-cultivated and agricultural sites in the Okanagan Valley, British Columbia, Canada. Using specific surface area (SSA) or soil texture as indicators of the mineral surface area available for sorption of organic matter, we used both Random Forest (RF) and Stepwise Multiple Regression with Akaike Information Criterion (SMR) to determine a best fit model for predicting MAOC. Random Forest modeling using SSA in addition to total SOC, exchangeable calcium, exchangeable potassium, and soil pH performed better than SMR for determining MAOC in these soils (R2: 0.790 for RF; R2: 0.713 for SMR). To determine if a MAOC deficit existed for these soils, we then applied a quantile regression approach wherein the predicted 90th quantile of MAOC represents the MAOC formation capacity. We determined that MAOC deficits were present in all soils and increased with depth. Moreover, clay rich soils had greater MAOC deficits (1.62 g kg−1 for 0–15 cm, 4.01 g kg−1 for 15–30 cm, and 5.80 g kg−1 for 30–60 cm), than sandier soils (1.01 g kg−1 for 0–15 cm, 2.72 g kg−1 for 15–30 cm, and 3.69 g kg−1 for 30–60 cm). Furthermore, the upper 30 cm of these soils have the potential to increase MAOC stocks by 29% (48.0 million kg of MAOC over 8,501 ha) before they reach formation capacity. This study highlights the variability in MAOC formation capacity of soils with different physicochemical properties and provides a framework for estimating MAOC concentrations and deficits for soils with a wide range of physicochemical properties.

Adsorption of Fulvic Acid and Water Extractable Soil Organic Matter on Kaolinite and Muscovite

The interaction of organic matter with mineral components of the solid phase of soils is the most important process that regulates the cycle and balance of carbon in the biosphere. The adsorption of humic acids on minerals is accompanied by their fractionation in size, composition, and amphiphilicity, thus decreasing their heterogeneity. Despite a strong interest in studying the regularities and mechanisms of the interaction between natural organic matter and layered aluminosilicates, it is necessary to take into account the natural diversity of soil organic matter, adsorption conditions, and mineral composition. This study was designed to investigate the adsorption regularities of fulvic acid (FA) and water-extractable organic matter (WEOM) isolated from horizon H of peaty-podzolic-gleyic soil on kaolinite and muscovite. Sorbates and sorbents were examined by the following methods: high-pressure size exclusion chromatography (HPSEC), high-performance liquid chromatography (HPLC), and potentiometric titration. The specific surface areas of the sorbents were determined by the sorption of N2 molecules. We found that hydrophobic components of FA and WEOM are mainly adsorbed on mineral surfaces. The adsorption of FA and WEOM on kaolinite and muscovite is followed by decreased hydrophobicity of organic matter and decreased heterogeneity of its amphiphilic properties in an equilibrium solution. At pH levels around 6, sorption of organic matter from FA solution containing 19% and 81% hydrophilic and hydrophobic components, respectively, onto kaolinite and muscovite occurs mainly due to hydrophobic components. Hydrophobic interactions on siloxane surfaces are the main mechanism to fix FA on both minerals. Kaolinite adsorbs slightly more organic carbon per unit area than muscovite. The adsorption of WEOM from a solution with 41% hydrophilic and 59% hydrophobic components results not only from hydrophobic and hydrophilic components but also from hydrophobic and electrostatic interactions and depends on pH. The most hydrophobic fractions of organic matter are adsorbed from the hydrophobic components on the surface of both minerals. Under conditions of the performed experiments at pH < 5, more WEOM is adsorbed on muscovite than on kaolinite.

Sorption and desorption of organic matter in soils as affected by phosphate

The contribution of different adsorption processes to soil organic matter (SOM) stabilization and the consequences of the intensification of land use on the adsorption of SOM are not yet fully understood. Therefore, this study aimed to explore the adsorption of dissolved organic carbon (DOC) in soils as well as desorption of organic carbon (OC) caused by phosphate addition. We conducted desorption and sorption experiments with DOC, phosphate (Na2HPO4), and chloride (KCl) in topsoil and subsoil samples from a Ferralsol, an Andosol, and a Podzol. Furthermore, we quantified the size of DOC by size-exclusion chromatography.We found that phosphate addition caused a strong increase in the DOC concentration in all soils. The DOC concentration was elevated by up to a factor of 4.5 compared to a control (water only) within five minutes after phosphate addition and kept increasing further with time, particularly in the Ferralsol. After 10 days, the DOC concentrations in the P addition treatment were between 5.5 and 18.0 times higher than in the control treatment. In contrast, chloride addition did not lead to increased DOC concentrations compared to the control (water only). Phosphate addition led mostly to desorption of organic matter of medium molecular size (10–100 and 100–1000 kDa) in the Ferralsol and the Andosol and of large molecular size (>1000 kDa) in the Podzol. In contrast, potassium chloride addition shifted the size distribution of DOC in the soil solution towards small compounds (<10 kDa), likely because KCl addition affected the aggregation of DOC compounds, in contrast to Na2HPO4 addition. Furthermore, phosphate addition also decreased subsequent sorption of DOC in the Ferralsol and the Andosol by a factor of up to 2.9 and 2.1, respectively.Our results have far-reaching implications because they show that phosphate addition can lead to desorption, and thus to destabilization of SOM, particularly in Ferralsols, and can also prevent further sorption of organic matter in soils. Our study provides a mechanistic explanation of why phosphate addition can decrease soil organic carbon sequestration and stabilization. This mechanism should be considered in the analysis of land-use and tillage effects on SOM sequestration in the future. Furthermore, our study indicates that also medium and large molecular size organic matter is stabilized through adsorption in soils.

Pore structure and sorption capacity investigations of Ediacaran and Lower Silurian gas shales from the Upper Yangtze platform, China

The shale gas potential of Ediacaran and Lower Silurian shales from the Upper Yangtze platform is assessed in this study with a focus on the contributions of clay minerals and organic matter to sorption capacity. For this purpose, a multidisciplinary assessment was carried out using petrophysical, mineralogical, petrographic and geochemical methods. In terms of TOC contents (4.2%), brittle mineral contents (68.6%) and maximum gas storage capacities (0.054–0.251 mmol/g) Ediacaran shales from this study show comparable properties to other producing shale gas systems although the thermal maturity is extremely high (VRr = 3.6%). When compared to lower Silurian shales from the same region, it is evident that (1) deeper maximum burial and (2) a lack of silica-associated preservation of the pores resulted in a relatively lower mesopore volume, higher micropore volume fraction and lower overall porosity (Ediacaran shales: 1.4–4.6%; Silurian shales: 6.2–7.4%). Gas production is therefore retarded by poor interconnectivity of the pore system, which was qualitatively demonstrated by comparing experimental gas uptake kinetics. TOC content exhibits a prominent control on sorption capacity and micropore volume for both shales. However, different contributions of clay minerals to sorption capacity were identified. This can partly be attributed to different clay types but is likely also related to burial-induced recrystallisation and different origins of illite. Additionally, it was shown that variations in sorption capacity due to incorrect estimates of clay mineral contribution are in the same range as variations due to differences in thermal maturity.Article highlightsPore structure and gas storage characteristics are evaluated for the first time for Ediacaran Shales from the Upper Yangtze platformDue to a lower free gas storage capacity and diffusivity, the Ediacaran shale can be regarded as a less favorable shale gas prospect when compared to the Silurian shaleClay mineral contribution to sorption capacity is evaluated taking clay mineralogy into considerationMaturity-related changes of organic matter sorption capacity have been discussed on the basis of a compiled data set

Petrophysical characterization of low-permeable carbonaceous rocks: Comparison of different experimental methods

Pore structure and gas transport properties of fourteen samples from the Jurassic Sargelu and the Cretaceous Garau formations in Lurestan province, southwest Iran, were studied under the aspect of shale gas exploration and production.Porosity was determined by helium pycnometry and water saturation (Archimedes principle). Low-pressure adsorption of N2 was used to determine total pore volumes, specific surface areas and microporosity. High-pressure mercury intrusion porosimetry (MIP) was applied to assess pore-size distributions. Permeability measurements were performed with helium and methane at confining pressures of 40 to 10 MPa using steady state and non-steady state methods.Permeability and porosity values determined by the different methods are in a good agreement. For low-permeable samples (less than 1 microdarcy ~ 10−18 m2) the “constant downstream pressure” technique is the most efficient method for slip flow evaluation (Klinkenberg plot), yielding apparent permeability coefficients over a wide range of reciprocal mean pressures (1/pmean) in one single run.A positive correlation was found between TOC content, porosity and permeability coefficients. Samples displaying clear signs of recrystallization tend to exhibit higher permeability. None of the parameters determined in this study, however, showed a correlation with mineralogy.The relationship between Klinkenberg-corrected permeability coefficients and confining pressure could be expressed by an exponential decay function. Stress sensitivity was typically higher for low-permeable samples. Samples containing highly recrystallized carbonates exhibited lower stress sensitivity, indicating an increase in rigidity due to recrystallization.No correlation was found between methane/helium permeability ratios, sorption capacity, and TOC contents. Thus, gas transport properties of this sample set were not affected by sorption and/or swelling of organic matter.

Effects of petroleum retention and migration within the Triassic Chang 7 Member of the Ordos Basin, China

The effects of petroleum retention within and expulsion from five intervals within the Triassic Chang 7 Member in the Ordos Basin in China have been demonstrated by deciphering a large suite of petrologic, organic petrographic, and organic geochemical analyses on 106 core samples.Organic properties and lithological heterogeneities control the amount and chemical composition of retained petroleum. Enrichment of aliphatic hydrocarbons in the silty, organic-lean intervals versus enrichment of aromatic fluids in the clayey, organic-rich units are probably caused by compositional fractionation occurred during primary and short-distance secondary migration. Migration of excess petroleum from organic-rich units to those organic-lean counterparts was further corroborated by the negative expulsion efficiencies calculated using a mass-balance model in the organic-lean intervals. Capillary pressure difference induced by the contrast in pore throat size of the clayey, organic-rich versus the silty, organic-lean intervals is postulated to be the major driver for the migration.A significant implication of this study is that the hydrocarbons in the first and fourth intervals constitute potential petroleum exploitation targets, given (i) improved oil quality caused by enriched aliphatic compounds versus viscous aromatic and polar compounds, (ii) lower organic matter sorption affinities, (iii) relatively high contents of brittle minerals in these two intervals. Despite its high content of retained hydrocarbons, the organic-rich fifth interval is not the best target, which is mainly due to the high sorption affinity of the organic matter structure, thereby causing low oil mobility and producibility.

Dissolved Organic Matter Sorption and Molecular Fractionation by Naturally Occurring Bacteriogenic Iron (Oxyhydr)oxides.

Iron (oxyhydr)oxides are highly reactive, environmentally ubiquitous organic matter (OM) sorbents that act as mediators of terrestrial and aqueous OM cycling. However, current understanding of environmental iron (oxyhydr)oxide affinity for OM is limited primarily to abiogenic oxides. Bacteriogenic iron (oxyhydr)oxides (BIOs), common to quiescent waterways and soil redox transitions, possess a high affinity for oxyanions (i.e., arsenate and chromate) and suggests that BIOs may be similarly reactive for OM. Using adsorption and desorption batch reactions, paired with Fourier transform infrared spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry, this work demonstrates that BIOs are capable of sorbing leaf litter-extracted DOM and Suwannee River Humic/Fulvic Acid (SRHA/SRFA) and have sorptive preference for distinct organic carbon compound classes at the biomineral interface. BIOs were found to sorb DOM and SRFA to half the extent of 2-line ferrihydrite per mass of sorbent and was resilient to desorption at high ionic strength and in the presence of a competitive ligand. We observed the preferential sorption of aromatic and carboxylic-containing species and concurrent solution enrichment of aliphatic groups unassociated with carboxylic acids. These findings suggest that DOM cycling may be significantly affected by BIOs, which may impact nutrient and contaminant transport in circumneutral environments.

Modeling Sorptive Fractionation of Organic Matter at the Mineral‐Water Interface

Core IdeasOM fractionation is studied for six minerals and more than 180 OM moieties.Mineral surface variability is explained by the pp‐LFER system parameters.OM functionality variability is quantified by the Abraham parameters.Factors governing fractionation are polarity, H‐bonding, dispersion, and cavitation.A link is developed between sorption and OM moiety molecular characteristics.Sorptive fractionation of organic matter (OM) at mineral–water interfaces alters the composition of OM and therefore affects the fate, transport, and bioavailability of nutrients and contaminants in terrestrial and aquatic environments. It is essential to identify the fractions of OM that are selectively sorbed on minerals and to elucidate the mechanisms of sorptive fractionation. In this study, the partition between mineral and water for a large set of organic molecules covering the most relevant OM functional groups and building blocks were predicted using the mechanistic Polyparameter Linear Free Energy Relationships (pp‐LFERs). The results were used to infer the sorptive fractionation tendency of OM moieties. It is found that for a OM moiety belonging to the chemical classes of alkanes, alkenes, or benzenes, its sorption to bentonite is the strongest, followed by kaolinite, talc or hematite, and Al2O3or quartz, relative to water. For a moiety with either double bond, or –OH, or –COOH, or R–COO–R′, or R–O–R′, or R–COH, or R–CO–R′, or –NH2, its partition to water is enhanced as compared to the respective alkane moiety. Opposite is found for thiols and sulfides. Meanwhile, a correlation is developed, that is, as the double bond equivalence decreases and the number of C atoms increases, the degree of sorption increases. Overall, the key factors controlling the sorptive fractionation are polarity, H‐bonding, van de Waals dispersion, and the energy for cavity formation. This work provides insights into the OM sorption at the mineral and water interface at the molecular level.

Is the adsorption of soil organic matter to haematite (α‐Fe2O3) temperature dependent?

SummarySoil organic matter interactions with minerals are a key determinant in the long‐term protection and sequestration of carbon in soils and sediments. Climate warming could potentially alter the dynamics of the Earth's largest carbon pools through processes controlling the formation of mineral–organic associations (MOAs). We studied the adsorption of Elliott soil humic acid (HA) and fulvic acid (FA) to the iron oxide mineral haematite (α‐Fe2O3) at temperatures from 15 to 35°C through batch sorption experiments. The ΔG°, ΔH° and ΔS° of sorption were derived for HA and FA and suggested that formation of MOAs was spontaneous and exothermic. The Langmuir sorption coefficients for HA and FA decreased with warming, but the maximum sorption capacities were not temperature dependent. The decrease in sorption coefficient was less when the temperature was increased from 30 to 35°C than from 15 to 30°C. Our infrared, ultraviolet and visible spectroscopy analysis of the bound and unbound HA and FA revealed preferential adsorption of oxygen‐ and hydrogen‐substituted aromatic and aliphatic carbon, which was independent of temperature. The adsorption of a hydrophobic probe molecule, Rose Bengal, to haematite increased with warming. Our results suggest that (i) MOAs in warmer climates might be less sensitive to temperature changes, (ii) the amount of iron oxide‐associated organic matter might remain unchanged with warming and (iii) hydrophobic interactions with iron oxides may be temperature dependent.Highlights How does temperature affect the formation of soil organic matter–iron oxide associations? Warming can change the sorption of organic matter on to minerals thus altering carbon dynamics Warming decreases sorption coefficients, but does not affect maximum sorption capacities The amount of iron oxide-associated organic matter might remain unchanged with warming

SIMULATED DAIRY WASTEWATER TREATMENT IN A PILOT PLANT SCALE MAGNETO-ACTIVE HYBRID ANAEROBIC BIOFILM REACTOR (MA-HABR)

The aim of this study was to determine the effects of magneto-active microporous packing media manufactured by extrusion technology and modified by the addition of relevant amounts of metal catalysts and magnetic activation on the effectiveness of simulated dairy wastewater (SDW) treatment and biogas productivity in a pilot plant scale hybrid anaerobic biofilm reactor with full mixing. The best performance was found at an organic loading rate (OLR) in the range 6.0 - 8.0 kg COD/m3·d, where the chemical oxygen demand (COD) removal was about 80%, the biogas yield ranged from 256.7 - 310.9 L/kg CODremoved, the methane production ranged from 420.6 - 557.1 L/d and total phosphorus removal ranged from 82.9 - 90.7%. The study demonstrated that the application of the innovative packing media in the biofilm-bed reactor enhanced the sorption of organic matter, biogas productivity and the binding of biogenic compounds.

Physical Processes Dictate Early Biogeochemical Dynamics of Soil Pyrogenic Organic Matter in a Subtropical Forest Ecosystem

Quantifying links between pyOM dynamics, environmental factors and processes is central to predicting ecosystem function and response to future perturbations. In this study, changes in carbon (TC), nitrogen (TN) , pH and relative recalcitrance (R50) for pine- and cordgrass-derived pyOM were measured at 3-6 weeks intervals throughout the first year of burial in the soil. Objectives were to 1) identify key environmental factors and processes driving early-stage pyOM dynamics, and 2) develop quantitative relationships between environmental factors and changes in pyOM properties. The study was conducted in sandy soils of a forested ecosystem in the Longleaf pine range, US with a focus on links between changes in pyOM properties, fire history (FH), cumulative precipitation (Pcum), average temperature (Tavg) and soil residence time (SRT). Pcum, SRT and Tavg were the main factors controlling TC and TN accounting for 77-91% and 64-96% of their respective variability. Fire history, along with Pcum, SRT and Tavg, exhibited significant controlling effects on pyOM, pH and R50 - accounting for 48-91% and 88-93% of respective variability. Volatilization of volatiles and leaching of water-soluble components (in summer) and the sorption of exogenous organic matter (fall through spring) were most plausibly controlling pyOM dynamics in this study. Overall, our results point to climatic and land management factors and physicochemical process as the main drivers of pyOM dynamics in the pine ecosystems of the Southeastern US.

Constructed Wetlands and their Role in Remediation of Industrial Effluents via Plant-Microbe Interaction – A Mini Review

Constructed Wetlands and their Role in Remediation of Industrial Effluents via Plant-Microbe Interaction – A Mini Review

Nitrogen Removal From Municipal Wastewater Using a Two‐Sludge Denitrification/Nitrification Batch Reactor: Performance and Mechanisms

Biosorption is a common phenomenon, in that organics in wastewater are trapped by sludge flocs. To achieve high nitrogen removal efficiency from the treatment of low chemical oxygen demand (COD) content wastewater, a two‐sludge denitrification/nitrification batch reactor (TDNBR) is successfully established based on the sorption of organic matter by anoxic activated sludge. During 123 days of operation, the TDNBR achieved high ammonia (&gt;99%) and total nitrogen (TN) (80%) removal efficiency. A higher C/N ratio and exchange frequency have no obvious effect on nitrification but effectively enhanced denitrification. The sorption assays indicated that anoxic sludge could take up a large amount of organic matter (23.79–55.62 mg COD g−1 TSS) but has a low sorption capacity of NH4+‐N. Nitrate utilization rate tests reveal that both the soluble and colloidal organics pre‐sorbed on the sludge can be utilized in denitrification with few organics stored as PHA in bacterial cells. Through cyclic study analysis, it was found that, by interchanging the supernatant in oxic and anoxic tanks alternately, nitrification and denitrification processes are successfully separated and high ammonia and TN removal efficiencies are achieved.

Dissolved organic matter retention in volcanic soils with contrasting mineralogy: a column sorption experiment

There is an increasing recognition that sorption and precipitation reactions between the dissolved phase of organic matter and reactive minerals and metals found in soils are an important carbon stabilization mechanism. We explored the relative importance of this sorption mechanism with pedological shifts in soil properties by conducting a dissolved organic matter leaching/sorption experiment using intact soil cores from a substrate/age gradient in Hawai’i. In the subsurface horizons, sorption of dissolved organic carbon was often positively correlated short-range ordered (SRO) mineral content, with sorption rates approaching 100% when SRO minerals dominated. Dissolved organic matter sorption in the presence of SRO minerals was highly selective towards aromatic compounds, consistent with prior nuclear magnetic resonance spectroscopy conducted on carbon found in SRO rich mineral soil. In subsurface horizons where SRO content was low (youngest and oldest sites in the chronosequence), sorption was also found to be high but much less selective, more reversible and more degradable indicating that different stabilization mechanisms are operative. These experimental results provide further evidence for a direct mechanism by which volcanic soils are able to store disproportionately high amount of soil organic matter via retention of aromatic acids.

Organic matter and clay interaction in a meromictic lake: Implications for source rock OM preservation (Lac Pavin, Puy-de-Dôme, France)

Investigation of organic matter (OM) preservation mechanisms is crucial for understanding organic accumulation in sedimentary environments. We focus here on the contribution of organo-clay interaction in such preservation. Most studies addressing this issue deal with organo-mineral complexes which have settled, omitting consideration of early aggregation within the water column. We therefore investigated the sorption of OM on montmorillonite (Na MMt) and kaolinite (Kaol) immersed in a permanently stratified water column (Lake Pavin, France). The two types of clay samples were kept immersed for different lengths of time and characterized via analytical methods suited for the organic phase [pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), GC-MS, Fourier transform infrared spectroscopy (FT-IR) and dissolved organic carbon (DOC) analysis], as well as for the mineral phase [X ray diffraction (XRD) and microprobe elementary cartography]. Results suggest that strong organo-clay interaction occurred within the water column to a varying extent depending on water physicochemical conditions and the mineral phase typology. A higher concentration of DOC was observed in the proximal environment of the clay traps, suggesting an attractive effect induced by the clay minerals. Lipid compounds sorbed during the immersion were essentially fatty acids and aromatic compounds. Their distributions were closer to a phytoplankton signature than allochtonous pedogenetic OM.The sorption was particularly efficient in the O2 transition zone, with a greater amount of OM on Na-MMt than Kaol. This was principally due to the high specific surface area and cationic exchange capacity (CEC) of the 2/1 clay mineral. Besides, XRD characterization revealed an increase in Na MMt interlayer spacing, which did not necessarily correspond to organic intercalation.The study confirms that the sorption of dissolved OM cannot alone explain the preservation of hydrocarbon-rich OM in such a lacustrine environment. Indeed, the sorbed OC was very low compared with the amount proposed by several authors as an expression of the monolayer equivalent principle.

Lower residue decomposition in historically charcoal-enriched soils is related to increased adsorption of organic matter

Previous field observations have shown increased soil carbon (C) sequestration in charcoal amended soils due to an accumulation of non-charcoal derived soil C. This study was set up to compare and analyse mineralization of non-charcoal derived C between soils that were either or not historically enriched in charcoal. Maize straw (13C-enriched) was added to samples of arable soil collected under historical charcoal kilns and corresponding adjacent control soil. The respiration was monitored in laboratory conditions for 227 days. Charcoal in soil significantly lowered total soil respiration (1905 vs. 1984 mg C kg−1). Mineralization of 13C-enriched added maize C (AMC) was unaffected by charcoal in the initial weeks after maize straw addition, however differences became significant at longer incubations yielding a markedly lower mineralized fraction in the charcoal enriched samples after 227 days (70 versus 62%, P < 0.05). A two fraction mineralization model revealed no charcoal effect on the labile fraction and its degradation but that the stable fraction of AMC was larger and degraded slower in the presence of charcoal. A soil drying-rewetting event (35 days) increased respiration to the same extent in charcoal-enriched as in adjacent soils. In contrast, the dissolved organic carbon (DOC) in pore water was significantly lower in charcoal-enriched than in adjacent soils. Microbial biomass-C (MBC) determined by fumigation-centrifugation was not significantly different between charcoal-enriched and adjacent soil (309 mg vs. 266 mg MBC kg−1). A soil adsorption experiment with DOC, extracted from a grassland soil, revealed larger DOC sorption with increasing soil charcoal concentration. This study shows that reduced C mineralization of non-charcoal C in charcoal-enriched soil is most likely related to enhanced sorption of more recalcitrant organic matter, rather than to lower MBC.

Sorptive removal of HgII by red mud (bauxite residue) in contaminated landfill leachate

ABSTRACTThe ability of red mud (RM) (bauxite residue) to remove HgII from landfill leachate (LL) was assessed. The studied aspects comprised the effects of time, pH, HgII concentration and the sorption isotherm, besides the influence of chloride and representative organic ligands. HgII removal by RM exhibited a complex kinetics where initial rapid sorption was followed by desorption at longer times. The sorption of HgII on RM was strongly pH-dependent. Outstanding maximum sorption was observed at pH∼4–5 (≥99.6%), while it abruptly dropped at higher pH values down to a minimum ∼28% at pH∼10.5. Chloride decreased HgII sorption at acid pH and shifted the pHmax towards higher pH∼9.4, which opposes to sorption in LL and suggests Cl− did not primarily control the process in LL. Amongst the organic ligands, acetate and salicylate slightly affected HgII sorption. Conversely, glycine affected sorption in a pH-dependent manner resembling that in LL, which suggests the relevant role of the organic nitrogenated compounds of LL. EDTA suppressed HgII sorption at any pH. HgII speciation modelling and dissolved organic matter (DOM) sorption support complexation of HgII by DOM as the primary factor governing the removal of HgII in LL. The sorption isotherm was better described by the Freundlich equation, which agrees with the heterogeneous composition of RM. The results indicate that HgII sorption on RM is favorable, but reveal differences in sorption and reduced efficiency, in LL media. Notwithstanding, RM possesses a notable capacity to remove HgII, even under the unhelpful complexing and competing conditions of LL.

The relation of structural mobility and water sorption of soil organic matter studied by 1H and 13C solid-state NMR

The impact of low water contents on the molecular mobility of soil organic matter (SOM) and its most frequent components was investigated. Combined 1H, 2H, and 13C solid-state nuclear magnetic resonance (NMR) techniques allow for an advanced insight into mechanisms of water uptake under defined atmospheres and its effect on SOM segment mobility. The major individual organic components of two peats, a gleyic podsol and a number of model substances (cutin, suberin, wood and cellulose) were distinguished with respect to their contribution to the 1H and 13C NMR spectra. Water molecules and mobile polymer constituents of SOM contribute to the mobile fraction in 1H NMR wide line spectra. Poly(methylene), being most probably part of amphiphilic molecules, have been identified as SOM components that are mobilized in the presence of water. Even though being of hydrophobic nature, water acts as a plasticizer on such long chain aliphatic soil components. Differential scanning calorimetry measurements of SOM samples support this insight in terms of a thermal step transition. Based on our findings, comparison of experimental results from different soils with varying water contents and soil composition should consider mobility effects of both, aliphatic moieties as well as polar moieties of SOM.