Mn Hydroxides Research Articles

Dynamics of accumulation of heavy metals by subcolloidal fraction of bottom sediments is a result of biochemical processes in the marginal filter of the Razdol’naya River (the Amur Bay, the Sea of Japan)

Determined is the content of Fe, Mn, V, Cr, Cu, Zn, Pb, As, and Sc in the subcolloidal fraction of sediments of the Razdol’naya River marginal filter using the method of atomic emission spectroscopy. Proposed is one of the variants of separating biochemical zones with the increased content of Fe and Mn and other metals in the bottom sediments of the marginal filter: the river zone, the zone of flocculation and formation of Fe and Mn hydroxides, and the zone of biochemical metal accumulation (marine). In the sediments of the river zone and the zone of flocculation and formation of Fe and Mn hydroxides, two bottom areas are identified with the high content of the elements under study that is associated with long-term and seasonal variations of the river runoff.

Modeling the composition of mine (Waste Rock) water at the deposits of the Balkhach gold-bearing field

Modeling of hydrogeochemical processes in the rock-water system showed that the concentrations of Al, Fe, Sb, Sr, and W do not exceed the MAC levels even under conditions of prolonged interaction between water and rock minerals (R/W > 0.0001). The concentrations of As, Cd, Co, and Se are unlikely to significantly exceed the MAC even at decreasing rates of water exchange (at increasing R/W) owing to the low concentrations of these elements in the rocks of the deposit. The concentrations of Mn are likely to exceed the MAC level under reducing conditions, while they remain well within the MAC under weakly to moderately oxidizing conditions. A different situation is for Cr and S, which may be well above the MAC under oxidizing conditions and below the MAC under reducing conditions, when weakly oxidized species of S and Cr predominate. Model and measured concentrations of Cu, Mo, Ni, Pb, V, and Zn are generally similar to each other and to the MAC levels, but they may considerably exceed the MAC in the case of reduction in water exchange rates (longer duration of water-rock interaction and higher R/W). The concentrations of Cu, Mo, Ni, Pb, V, Zn, and Cr may exceed the MAC levels in the case of the prolonged exposure of strongly disintegrated rocks to moist air, whereas the wet environment is favorable for Mn hydroxide precipitation.

Storage and origin of metals in active stream sediments from mountainous rivers: A case study in the River Douro basin (North Portugal)

The study area is located in the transboundary River Douro basin (northern Portugal); it comprises the River Corgo fluvial network, which drains a meso-scale rural catchment with an area of 295km2, underlain by crystalline rocks, in a temperate climate. The results reported in this study derive from a geochemical survey of active fluvial sediments, with the aim of characterising the spatial and temporal distribution of the contents of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in a basin with mountainous features. To assess total contents of metals and their potential availability, as well as possible different origins of metals (natural vs. anthropogenic), a sequential chemical approach was used (modified BCR procedure). Multivariate data analysis (PCA) was used to assist the interpretation of datasets.The results show that, on the one hand, the metal contents distribute among all the geochemical phases studied. For the most relative labile fractions the reducible fraction is the most significant. The element-partitioning among geochemical phases indicates: (a) Co and Mn are transported in greater proportions in the most labile fraction, as exchangeable ions, as well as important proportions of Ni, Zn and Cu; (b) Cd and Pb associate preferentially with the hydroxides of Fe and Mn; (c) Cr and Cu are also transported by the organic phase; (d) the residual phase transport important proportions of Cr, Ni, Zn, Cu, Fe and Pb. The higher concentrations of Cu, Zn and, in particular, Pb, in the most labile fractions, which are higher where the total contents are also higher (and not concomitant with a correspondent increase in the residual fraction), suggest an important contribution of anthropogenic activities to the total contents of these elements in the sediments. Chromium and Ni are the main metals from a lithological source, with relatively higher contents in the residual fraction, and the lowest in the most mobile fractions. On the other hand, the spatial distribution pattern of metal contents in the mobile and semi-mobile fractions (available+reducible+oxidisable), shows that, in general, higher contents of metals in the most mobile fractions occur along the main courses of the major tributaries, in particular in the flatter reaches. The patterns of seasonal occurrence and distribution of metals show, in general, that the relative contents associated with the potentially available fraction increase during the period of low flow, which extends from April to September.

Specific chemical and mineral composition of ferromanganese nodules from the Chukchi Sea

The specific chemical and mineral composition of discoid, cake-shaped, and platy ferromanganese nodules (FMNs) from the Chukchi Sea are considered. The main ore components of these FMNs are Fe, Mn, and P. The contents of trace elements (except for Ba and Sr) do not exceed hundredths of percent. Maximum concentrations of most of these elements are specific for the cake-shaped nodules. In general, Mn accumulates most intensely in FMNs. Next (in order of decrease) are Ag(?), Co, and Pb; Sr, Fe, P, Y, and Ca; and Ni, La, Zn, and Cu. As for Ba, Cr, Mg, and K, they do not accumulate in the FMNs. “Dilution” is typical of Si, Al, Na, and Ti. The main ore phases are strengite and amorphous Mn hydroxides. It has been revealed for the first time for the Chukchi Sea that Cu, Zn, Sn, Ni, Pb, W, Bi, Cr, Fe, Ti, Ag, Au, Y, Zr, and La–Nd lanthanides form individual mineral microphases in FMNs: native elements, intermetallic compounds, oxides, and, much more seldom, tungstates, silicates, and phosphates. Accessory ore mineralization is the best pronounced and most diverse in the platy nodules. Though the FMNs from the Chukchi Sea are diagenetic, high-temperature fluids are, most likely, the source of microinclusions of various accessory ore minerals.

Modern sedimentation patterns in Lake El'gygytgyn, NE Russia, derived from surface sediment and inlet streams samples

Abstract. Lake El'gygytgyn/NE Russia holds a continuous 3.58 Ma sediment record, which is regarded as the most long-lasting climate archive of the terrestrial Arctic. Based on multi-proxy geochemical, mineralogical, and granulometric analyses of surface sediment, inlet stream and bedrock samples, supplemented by statistical methods, major processes influencing the modern sedimentation in the lake were investigated. Grain-size parameters and chemical elements linked to the input of feldspars from acidic bedrock indicate a wind-induced two-cell current system as major driver of sediment transport and accumulation processes in Lake El'gygytgyn. The distribution of mafic rock related elements in the sediment on the lake floor can be traced back to the input of weathering products of basaltic rocks in the catchment. Obvious similarities in the spatial variability of manganese and heavy metals indicate sorption or co-precipitation of these elements with Fe and Mn hydroxides and oxides. But the similar distribution of organic matter and clay contents might also point to a fixation to organic components and clay minerals. An enrichment of mercury in the inlet streams might be indicative of neotectonic activity around the lake. The results of this study add to the fundamental knowledge of the modern lake processes of Lake El'gygytgyn and its lake-catchment interactions, and thus, yield crucial insights for the interpretation of paleo-data from this unique archive.

Speciation of rare earth elements in surface sediments of Lagoon of Aveiro (N Portugal)

Martins, V.A., Dias, J.A., Laut, L.M., Sobrinho, F., Santos, J.F., Rodrigues, M. A., Frontalini, F., Miranda, P., Terroso, D., Fernandez-Fernandez, S., Bernardes, C., Figueira, R., Sousa, S., Amaral, P., Mahiques, M., Bernabeu, A., Rey, D., Rubio, B., and Rocha, F., 2013. Speciation of rare earth elements in surface sediments of Lagoon of Aveiro (N Portugal). In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 64-69, ISSN 0749-0208. The goal of this work is to determine the distribution of the rare earth elements in the surface sediments in the Ria de Aveiro (N Portugal) coastal lagoon. Concentrations of REE (La, Ce, Nd, Sm) and related elements (Th, Y and Sc) were evaluated by total digestion of sediments in the fine fraction of 33 grab-samples of surface sediments. The same method was followed for Al, Ca, S and Zr, related to terrigenous sources, but also, in the cases of Ca and S, to biogenic and quimiogenic processes. Concentrations of REE and related elements were additionally assessed by a three-step sequential chemical extraction (E1-3) procedure coupled with ICP–MS determination. The geochemical results were processed by statistical analysis combining textural and mineralogical data (XRD techniques). The results show that mobile La, Ce, Nd, Sm and Y are mostly adsorbed by amorphous Mn hydroxide (E3), secondly associate with organic matter (E2) and only in a very small extent are adsorbed on clay mineral structural sheets or associated with carbonates (E1). Thorium and Sc are almost exclusively linked with E2. Ytrium shows a very high percentage of availability, whilst Ce, La, Sc and Th are by far less mobile. Results of cluster analysis reveals that sediments are enriched in: i) quartz, feldspars and anhydrite in the most hydrodynamic areas with good connection with the ocean, where tidal currents are stronger and water is salty and welloxygenated; ii) mud, TOC, phyllosilicates, siderite, pyrite and S in low hydrodynamic areas. In these areas, pyrite and siderite can result from reducing bacterial activity in subsurface sediments. Early diagenetic changes in the sediments would also influence the elements adsorption to clay minerals and their co-precipitation with carbonates (E1). The highest values of REE, in E1, occur in distal locations in relation to the mouths of rivers and streams. The retention of the elements in this phase may occur mainly in the lagoon, depending on the availability of carbonates and clay minerals and their assemblage’s composition. Concentrations of REE and related elements adsorbed by organic matter (E2) and by amorphous Mn hydroxide (E3) tend to rise near the rivers mouths and may be related to geochemical processes that take place upstream in the course of the rivers before the entry of sediments into the lagoon. Elemental concentrations retained in the structure of mineral phases (R), also tend to reach high values near the rivers mouths but in low hydrodynamic areas. There is some fractionation between Th and the light REE which is more evident in the Murtosa channel that is fed mainly by the Antua river.

Mobility of Contaminated Heavy Metals and Metalloids in Sediments Caused by Recent Industrial Activities

Sequential leaches (sequential extractions) experiment of 62 elements were carried out for assessing the mobility of contaminated heavy metals and metalloids contaminated in natural sediments; river sediments of Oued El Harrach (Algeria) and lagoon sediments of Bizerte (Tunisia), North African Mediterranean coast. Applied extractants for the sequential leaches are: (A) distilled water for extracting water soluble components, (B) 1M sodium-acetate for extracting exchangeable cations by clay minerals and co-precipitations of carbonates, (C) 0.1M sodium-pyrophosphate for extracting the elements bound with organic matter, (D) 0.1M hydroxylamine for extracting the elements bound with amorphous Mn hydroxides, and (E) 0.25M hydroxylamine for extracting the elements bound with amorphous Fe hydroxides and more crystallized Mn hydroxides. According to the results of sequential leaches experiment, contaminated heavy metals, metalloids, and other potentially toxic element (PTEs) in the sediments are mostly presented as exchangeable cations by clay minerals, co-precipitations of carbonate compounds, binding complexes with organic matter, and/or amorphous manganese hydroxides. Mobility of contaminated heavy metal and metalloids is relatively larger in Algerian river sediment than in Tunisian lagoon sediments. However the mobility of the PTEs in the sediments can be easily changed if the depositional environment is altered by civil construction works.

Rare earth element sorption onto hydrous manganese oxide: A modeling study

Manganese oxides are important scavengers of rare earth elements (REE) in hydrosystems. However, it has been difficult to include Mn oxides in speciation models due to the lack of a comprehensive set of sorption reactions consistent with a given surface complexation model (SCM), as well as discrepancies between published sorption data and predictions using the available models. Surface complexation reactions for hydrous Mn oxide were described using a two surface site model and the diffuse double layer SCM. The specific surface area, surface side density, and pHzpc were fixed to 746m2/g, 2.1mmol/g, and 2.2, respectively. Two site types (XOH and YOH) were also used with pKa2 values of 2.35 (XOH) and 6.06 (YOH). The fraction of the high affinity sites was fixed at 0.36. Published REE sorption data were subsequently used to determine the equilibrium surface complexation constants, while considering the influence of pH, ionic strength, and metal loading. LogK increases from light REE to heavy REE and, more specifically, displays a convex tetrad effect. At low metal loading, the YOH site type strongly expresses its affinity toward REE, whereas at higher metal loading, the same is true for the XOH site type. This study thus provides evidence for heterogeneity in the distribution of the Mn oxide binding sites among REE.

Effects of salinity and humic acid on the sorption of Hg on Fe and Mn hydroxides

The objective of this study was to investigate the influence of humic acid (HA) and salinity on adsorption of Hg on the amorphous and crystalline of iron and manganese hydroxides. The results show that the adsorption of Hg2+ on Fe and Mn hydroxides was inhibited in marine system due to the formation of stable, nonsorbing aqueous HgCl2 complexes in solution. Moreover, Cl− inhibited the Hg2+ adsorption more severely on amorphous than crystalline hydroxides. The addition of HA inhibited Hg2+ adsorption on Fe and Mn hydroxides in freshwater system might be attributed to the competition between Hg2+ and HA on adsorption to Fe and Mn hydroxides. In contrast, the addition of HA promoted Hg2+ adsorption on Fe and Mn hydroxides in the marine system, which might be due to the addition of humic acid resulted in the reaction between Cl− and HA, and therefore the reducing of Cl− promoted more Hg2+ on Fe and Mn hydroxides. In addition, the influence of HA on Hg2+ adsorption on Fe and Mn hydroxides are more visible for crystalline than amorphous hydroxides.

The application of Fe–Mn hydrous oxides based adsorbent for removing selenium species from water

In this study, the adsorptive removal of selenium(IV) and selenium(VI) from water by a newly developed ion exchange adsorbent, based on Fe(III) and Mn(III) hydrous oxides, was examined. This study was conducted to determine the influence of various operating parameters, such as initial anion concentration, contact time, adsorbent dose, pH, solution temperature, and the presence of competitive anions, on the treatment performance. The high Se(IV) adsorptive capacity of the adsorbent (up to 41.02mg/g at pH 4) was due to its high affinity for selenite, as reflected in the fast rate of uptake (batch studies) and an efficient long-term removal (column experiments). Although adsorption of anions traditionally decreases as pH increases, the mixed adsorbent was capable of purifying large volumes of Se(IV)-containing water (at pH 7) to reach concentrations lower than 10μg/L, which meets the European Commission standards. The presence of sulphate and carbonate did not influence Se(IV) adsorption. However, high phosphate and silicate concentrations may have decreased the removal efficiency of Se(IV). Data from the batch and column adsorption experiments were fitted with a number of approved models, which revealed the adsorption mechanism and allowed for a comparison of the results.

Sedimentary records of metal deposition in Japanese alpine lakes for the last 250 years: Recent enrichment of airborne Sb and In in East Asia

Concentrations of 18 elements, including Sb, In, Sn, and Bi, were measured in sediment cores from two pristine alpine lakes on Mount Hachimantai, northern Japan, representing the past 250years. Vertical variations in concentrations are better explained by atmospheric metal deposition than by diagenetic redistribution of Fe and Mn hydroxide and organic matter. Anthropogenic metal fluxes were estimated from 210Pb-derived accumulation rates and metal concentrations in excess of the Al-normalized mean background concentration before 1850. Anthropogenic fluxes of Sb and In showed gradual increases starting around 1900 in both lakes, and marked increases after 1980. Comparison of Sb/Pb and Pb stable isotope ratios in sediments with those in aerosols of China or northern Japan and Japanese source materials (recent traffic- and incinerator-derived dust) suggest that the markedly elevated Sb flux after 1980 resulted primarily from enhanced long-range transport in aerosols containing Sb and Pb from coal combustion on the Asian continent. The fluxes of In, Sn, and Bi which are present in Chinese coal showed increasing trends similar to Sb for both study lakes. This suggests that the same source although incinerators in Japan may not be ruled out as sources of In. The sedimentary records for the last 250years indicate that atmospheric pollution of Sb and In in East Asia have intensified during recent decades.

REEs fractionation and sedimentary implication in surface sediments from eastern South China Sea

To get features of rare earth elements (REEs) fractionation, 106 surface sediment samples from eastern South China Sea were determined for REEs combined with major and trace elements by ICP-MS. The distribution pattern of REEs, strong correlation between REEs and Al, North American shale composite (NASC) normalization all suggest a dominant crustal source for REEs in the research area. However, distinct fractionation among REEs was observed in surface sediment from area with water depth over 2000 m, confirmed by the strong positive correlation among light rare earth elements (LREEs) and among heavy rare earth elements (HREEs) but weaker relationship between LREEs and HREEs. Eluviation by Cl− might be a key role on the fractionation of REEs, comparing with factors such as grain size, co-precipitation with Fe and Mn hydroxide, calcareous and siliceous biogenic precipitation. The fractionation among REEs could be used as index to illustrate the sedimentary environment in reverse.

Forms of some metals in the suspended sediments of the Northern Dvina River and their seasonal variations

The results of the analysis of samples of the Northern Dvina River’s suspended particulate matter obtained by the sedimentation method from large water volumes in the periods of the spring high water and summer low water are presented. By the method of sequential leaching using different reagents, four fractions have been separated: the F1 is the sorbed complex and carbonates, the F2 is the amorphous hydroxides of Fe and Mn, the F3 is the form connected with the organic matter, and the F4 is the residual or silicate-detrital (inert) form. The data have shown that all ten elements determined were grouped with respect to the ratio of the distinguished forms: F4 is the predominant form for Al and Fe (73–88% of all the forms; however, the summer sample contains only 38% of this form of iron, and F2 is the predominant form for this period with 46.6%). As to Mn, the F1, F2, and F4 are nearly equally distributed in the spring high water samples, and only the F3 form is less important (5.4%). In the summer sample, the manganese sorbed complex is predominant (53.5%); for Cu, Ni, Cr, and Co, the inert F4 form is predominant (60–70%) in the sample of the spring suspended matter. The summer low water suspended matter has a lower F4 contribution (25–45%); for Zn, Pb, and Cd, the equal distribution of the forms in the spring samples is typical, while the summer suspended matter differs by the F2 form’s predominance (53–61% for Zn and Pb). The main conclusion from the acquired data is that the geochemical mobility of all the studied elements, except for cadmium, in the summer low water suspended matter is higher than in the spring suspended matter. The more intensive biogeochemical processes in August, the high level of organic matter, and the higher contribution of phytoplankton lead to the intensification of the metals’ geochemical activity in the Northern Dvina suspended matter in the end of the summer compared to the spring high water period when the physical processes are predominant over the biogeochemical ones due to the high speeds of the freshened waters flow.

The impact of increased oxygen conditions on metal-contaminated sediments part I: Effects on redox status, sediment geochemistry and metal bioavailability

In order to evaluate the effect of improved oxygen concentrations in overlying surface water on the redox status, sediment geochemistry and metal bioavailability in metal-polluted sediments a 54 days lab experiment with two different experimental treatments was conducted (90% and 40% O2). Changes in redox potential (Eh) in the sediment were monitored over time. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) and at 4 sediment depths (0–1, 1–4, 4–8 and 8–15 cm), acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured and metal release to overlying surface water was determined. Labile metal species in both water and sediment were measured using Diffusive Gradients in Thin films (DGT). Our results showed that elevated oxygen levels in overlying surface water led to an Eh increase in the sediment of the 90% O2 treatment from 0 to ±200 mV while AVS concentrations in the upper sediment layer decreased by 70%. Following AVS oxidation metal availability in the pore water was highly elevated after 54 days. However, Cu remained strongly bound to the sediment during the whole experiment. Only a limited metal release to the overlying surface water was noticed, which was due to the fact that SEMtot concentrations in the sediment did not yet exceeded AVS levels ([SEMtot − AVS]/fOC = 0) after 54 days. Additionally, adsorption on Fe and Mn hydroxides and particulate organic carbon also slowed down any potential metal release. Our results indicated that increasing oxygen concentrations due to general water quality improvements can enhance the mobility of trace metals which may result in the leaching of sediment-bound metals to overlying surface water, even in undisturbed watercourses.

Heavy metals (Cr and Ni) distribution and fractionation in cropland soils from reclaimed tidal wetlands in Pearl River estuary, South China

Abstract Heavy metal contamination was compared for soils with different land use (cropland and wetland) in the reclaimed region of the Pearl River estuary. A sequential extraction technique was used to produce five chemical fractions (exchangeable (F1), carbonate (F2), Fe–Mn hydroxide (reducible) (F3), organic (F4) and residual (F5)) to study the effects of reclamation and tillage on the distribution and mobility of the heavy metals Cr and Ni. The results revealed that generally the contamination levels increased with a longer history of reclamation (100> 40> 30> 10 years) whilst an undisturbed reference wetland was least affected. The most substantial quantities of both Cr and Ni were observed in the residual fraction, which may be a consequence of the mixing effects of soil tillage and planting. With the exception of the 20-30 cm layers from the wetland and 10 year old cropland samples, the total concentration of Cr and Ni at all sites and all soil layers exceeded the moderately polluted level according to the SQGs of the US EPA.

Chemometric study on the trace metal accumulation in the sediments of the Cochin Estuary―Southwest coast of India

The distribution and accumulation of trace metals in the sediments of the Cochin estuary during the pre-monsoon, monsoon and post-monsoon periods were investigated. Sediment samples from 14 locations were collected and analysed for the metal contents (Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb), organic carbon, total nitrogen, total sulphur and grain size. The data were processed using statistical tools like correlation, factor and cluster analysis. The study revealed an enrichment of Cd and Zn in the study area particularly at station 2, which is confirmed by enrichment factor, contamination factor and geoaccumulation index. The factor analysis revealed that the source of Cd and Zn may be same. The study indicated that the spatial variation for the metals like Mg, Cr, Fe, Co, Ni, Cu, Zn, Cd and Pb were predominant unlike Mn which shows a temporal variation. The strong association of trace metals with Fe and Mn hydroxides and oxides are prominent along the Cochin estuary. The anthropogenic inputs of industrial effluents mainly control the trace metals enrichment in the Cochin estuary.

Adsorption of arsenite and selenite using an inorganic ion exchanger based on Fe–Mn hydrous oxide

The adsorption behaviour and mechanism of As(III) and Se(IV) oxyanion uptake using a mixed inorganic adsorbent were studied. The novel adsorbent, based on Fe(III)–Mn(III) hydrous oxides and manganese(II) carbonate, was synthesised using a hydrothermal precipitation approach in the presence of urea. The inorganic ion exchanger exhibited a high selectivity and adsorptive capacity towards As(III) (up to 47.6 mg/g) and Se(IV) (up to 29.0 mg/g), even at low equilibrium concentration. Although pH effects were typical for anionic species (i.e., the adsorption decreased upon pH increase), Se(IV) was more sensitive to pH changes than As(III). The rates of adsorption of both oxyanions were high. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) studies showed that the ion exchange adsorption of both anions took place via OH − groups, mainly from Fe(III) but also Mn(III) hydrous oxides. MnCO 3 did not contribute directly to As(III) and Se(IV) removal. A higher adsorptive capacity of the developed material towards As(III) was partly due to partial As(III) oxidation during adsorption.

Behavior of NiO–MnO 2/MWCNT composites for use in a supercapacitor

NiO–MnO 2/MWCNT composite was formed by a simple chemical precipitation method using a chelating agent and Ni and Mn hydroxides on MWCNT. The NiO–MnO 2/MWCNT was pretreated by ultrasonication, followed by thermal annealing at 300 °C. The material obtained was applied as an electrode in a supercapacitor. FT-IR, EDS, XRD, FE-SEM and FE-TEM were used to characterize the structural features. The results show that a nanosized NiO–MnO 2 layer covered the surface of the MWCNT, and the original structure of the MWCNT was retained during the coating process. The capacitive behavior of the NiO–MnO 2/MWCNT electrode was investigated by cyclic voltammetry and galvanostatic charge/discharge methods in a 6 M KOH aqueous solution. The cyclic voltammetry curves demonstrated that the maximum specific capacitance of the NiO–MnO 2/MWCNT electrode was 193.50 F g −1, which is significantly higher than that of an MWCNT electrode. The results show that both the MWCNT and NiO–MnO 2/MWCNT electrodes exhibited capacitive behaviors, and the NiO–MnO 2 layer increased the capacitance of the supercapacitor.

The Desorption of Antimony(V) from Sediments, Hydrous Oxides, and Clay Minerals by Carbonate, Phosphate, Sulfate, Nitrate, and Chloride

The desorption of antimony, Sb(V), from two sediment samples by phosphate, carbonate, sulfate, chloride, and nitrate at pH 8 was examined. One highly contaminated sediment sample was taken from an Sb mine (Goesdorf, Luxembourg); the other sample was the certified reference material PACS-2 (marine sediment). Phosphate was found to have a strong mobilizing ability, whereas that of carbonate was in general weaker. For comparison, and to understand better the possible importance of individual components of the sediments, desorption experiments were performed on pure phases (i.e., hydrous oxides of Fe, Mn, and Al) and the clay minerals kaolinite and montmorillonite. In the cases of hydrous metal oxides, Sb(V) was most effectively desorbed by phosphate, followed by carbonate. Phosphate also desorbed Sb(V) from the clay minerals, whereas carbonate had no effect. The pH dependence of adsorption of Sb(V) in the absence and presence of carbonate revealed that adsorption densities were higher (except in the case of montmorillonite) in the absence of carbonate, suggesting a competition between carbonate and [Sb(OH)] for surface sites generally and a lowering of surface charge in the case of hydrous aluminum oxide. The observations are unlikely to be due to ionic strength effects because activity coefficients in the blank and spiked solutions differ by <4%. Desorption experiments on sediments with varying concentrations of phosphate and carbonate demonstrated that at environmentally relevant concentrations, desorption by phosphate is negligible, whereas the effect of carbonate is not. Sulfate, chloride, and nitrate generally had little effect. The proportion of Sb desorbed in blank experiments coincides with that mobilized in the first fraction of the Bureau Communautaire de Référence (BCR) sequential extraction (easily exchangeable and carbonate-bound fraction).

A nickel availability study in serpentinised areas of Portugal

The factors that control Ni availability and adsorption in serpentine soils from the northeast of Portugal, which developed under temperate climacteric conditions, were investigated following characterisation of the soils' selected physicochemical properties. Ni bioavailability was assessed through complementary extractions. The results showed that surface-bound Ni in serpentine soils is primarily specifically adsorbed. The influence of the soils' physicochemical characteristics and of the Ni-bearing oxides on Ni bioavailability (EDTA-extractable Ni) was examined using correlation analysis. Our study revealed that most of the variability in Ni bioavailability in the Portuguese serpentine soils can be linked to hydrous manganese oxide. Surface affinity for exogenous Ni was evaluated by adsorption studies on soil suspensions followed by voltammetric titrations at pH 7.Sorption data was fitted to a Langmuir isotherm assuming the formation of one-to-one Ni complexes with the soil surface binding sites. Conditional surface formation constants and the concentration of surface groups for Ni binding were determined. The results showed that serpentine soils have potential available sites for further Ni adsorption. Hydrous Mn oxides existing in these serpentine soils determine the Ni sorption capacity.