Rare Earth Elements In Waters Research Articles

Determination of rare earth elements in waters by inductively coupled plasma optical emission spectrometry after preconcentration with 6-(2-thienyl)-2-pyridinecarboxaldehyde functionalized Amberlite XAD-4 resin

A new method has been developed for the determination of rare earth elements (REEs) (Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in water samples based on preconcentration with a mini-column packed with 6-(2-thienyl)-2-pyridinecarboxaldehyde functionalized Amberlite XAD-4 resin prior to their determination using inductively coupled plasma optical emission spectrometry (ICP-OES). The optimum experimental parameters for preconcentration of REEs, such as pH of the sample, sample and eluent flow rates and sample volume, were investigated. The optimum pH values for quantitative (90-110%) sorption of the REE ions were between 6.0 and 8.0. The elution process was carried out using 2 mL of 1.0 mol L(-1) HNO3 solution. Under the optimum conditions, detection limits between 0.032 and 0.963 μg L(-1) for a 10 mL sample volume and 0.006 and 0.193 μg L(-1) for a 50 mL sample volume were determined. The proposed method was successfully applied to the determination of REEs in water samples with recoveries in the range of 90.1-110.5%.

State of rare earth elements in different environmental components in mining areas of China

China has relatively abundant rare earth elements (REEs) reserves and will continue to be one of the major producers of REEs for the world market in the foreseeable future. However, due to the large scale of mining and refining activities, large amounts of REEs have been released to the surrounding environment and caused harmful effects on local residents. This paper summarizes the data about the contents and translocation of REEs in soils, waters, atmosphere, and plants in REE mining areas of China and discusses the characteristics of their forms, distribution, fractionation, and influencing factors. Obviously high concentrations of REEs with active and bioavailable forms are observed in all environmental media. The mobility and bioavailability of REEs are enhanced. The distribution patterns of REEs in soils and water bodies are all in line with their parent rocks. Significant fractionation phenomenon among individual members of REEs was found in soil-plant systems. However, limited knowledge was available for REEs in atmosphere. More studies focusing on the behavior of REEs in ambient air of REE mining areas in China are highly suggested. In addition, systematic study on the translocation and circulation of REEs in various media in REEs mining areas and their health risk assessment should be carried out. Standard analytical methods of REEs in environments need to be established, and more specific guideline values of REEs in foods should also be developed.

Geochemistry of rare earth elements in water and solid materials at abandoned mines in SW Sardinia (Italy)

This study investigates the behavior of rare earth elements (REE) in near-neutral waters that drain abandoned mines in SW Sardinia (Italy). The REE, together with other major and minor components, were determined in waters (146 samples) and solid materials (13 samples). Research was performed to evaluate the main factors that control the geochemical behavior of REE in non-acidic mining environments. Zinc, cadmium and lead are the main contaminants in the study area, either in the processing residues or in the waters that drain the mine site. Contamination of stream waters extends several km downstream of the mine, till the Mediterranean Sea.The mine tailing (MT) materials are the main REE source, with peak concentrations of 300mg/kg ΣREE. PAAS-normalized patterns of MT are characterized by light REE (LREE) enrichment with respect to heavy REE (HREE). The waters flowing out of the MT heaps are near-neutral (6.2 to 7.0 pH), with Zn-sulfate dominant composition, and a mean concentration of 53μg/l ΣREE. Drainages from MT and an adit flow in the Naracauli stream headwaters (mean 1.4μg/l ΣREE). Concentrations of REE in the Naracauli stream decrease dramatically about 400m downstream of source. The REE decrease matches Fe and Zn decrease in waters, probably because the REE are sorbed on freshly precipitated solid phases.Sorption processes, and/or co-precipitation with secondary phases, appear to control the REE geochemistry in the studied waters under near-neutral conditions. Also, despite the non-acidic environment, it is worth to observe that small changes in pH seem to affect the mobility of REE at Naracauli.The PAAS-normalized REE patterns in the waters generally reflect the PAAS-normalized REE patterns in the solid materials with which the water interacts, either MT or secondary phases such as Fe-hydroxide and bio-hydrozincite. As it is expected in waters under oxidizing conditions, patterns with negative Ce anomalies are developed due to the poor solubility of Ce+4 species, and its consequent scavenging in solid phases. However, there is an exception: Ce shows a poor affinity for the bio-hydrozincite mineral, probably reflecting the role of bacteria in the precipitation of the Naracauli hydrozincite.

Rare earth element (REE)–silicic acid complexes in seawater to explain the incorporation of REEs in opal and the “leftover” REEs in surface water: New interpretation of dissolved REE distribution profiles

In light of a new finding that diatom opal carries rare earth elements (REEs) at an amount exceeding that which would explain the REEs/Si ratio in open ocean columns, the complex formation of REEs with silicic acid and subsequent incorporation of the complex into diatom opal has been explored. Reported complex formation constants of EuH3SiO42+ and an empirical linear relationship of the constants with hydrolysis constants were employed in the species calculation. The calculation reveals that REE–silicic acid complex is the dominant species of dissolved REEs especially in deep layers of the Pacific and the Atlantic Oceans. The degree of complex formation varies depending on dissolved silica concentration, pH, and pCO2. Assuming that only REEs in the form of REEH3SiO42+, which is diffused/advected from deep water to surface water together with dissolved silica, are incorporated into diatom opal, a REE incorporation theory has been developed. The theory links the intake of REEs and silica by diatoms in surface water and their concentrations in deep water and presents two distribution coefficients (Ds) of REEs in diatom opal, conventional D against surface water and columnar D against deep water as functions of pH and dissolved silica concentration. The theory successfully explains the significant REE concentration level (“leftover REEs”) in the surface water of the oceans and reproduces a concentration of REEs in diatom opal that is consistent with that observed in diatom opal in the North Pacific Ocean. The REE composition of oceanic deep water is largely explained by two fractionation processes: REE incorporation into opal and carbonate/oxide scavenging of REEs.

Geochemical behavior and speciation modeling of rare earth elements in acid drainages at Sarcheshmeh porphyry copper deposit, Kerman Province, Iran

Acid mine drainage is a major source of water pollution in the Sarcheshmeh porphyry copper mine area. The concentrations of heavy metals and rare earth elements (REEs) in the host rocks, natural waters and acid mine drainage (AMD) associated with mining and tailing impoundments are determined. Contrary to the solid samples, AMDs and impacted stream waters are enriched in middle rare earth elements (MREEs) and heavy rare earth elements (HREEs) relative to light rare earth elements (LREEs). This behavior suggests that REE probably fractionate during sulfide oxidation and acid generation and subsequent transport, so that MREE and HREE are preferentially enriched. Speciation modeling predict that the dominant dissolved REE inorganic species are Ln3+, Ln(SO4)2−, LnSO4+, LnHCO32+, Ln(CO3)2− and LnCO3+. Compared to natural waters, Sarcheshmeh AMD is enriched in REEs and SO42−. High concentrations of SO42− lead to the formation of stable LnSO4+, thereby resulting in higher concentrations of REEs in AMD samples. The model indicates that LnSO4+ is the dissolved form of REE in acid waters, while carbonate and dicarbonate complexes are the most abundant dissolved REE species in alkaline waters. The speciation calculations indicate that other factors besides complexation of the REE's, such as release of MREE from dissolution and/or desorption processes in soluble salts and poorly crystalline iron oxyhydroxy sulfates as well as dissolution of host rock MREE-bearing minerals control the dissolved REE concentrations and, hence, the MREE-enriched patterns of acid mine waters.

Normalized Rare Earth Elements in Water, Sediments, and Wine: Identifying Sources and Environmental Redox Conditions

The concentrations of the rare earth elements (REE) in surface waters and sediments, when normalized on an element-by-element basis to one of several rock standards and plotted versus atomic number, yield curves that reveal their partitioning between different sediment fractions and the sources of those fractions, for example, between terrestrial-derived lithogenous debris and seawater-derived biogenous detritus and hydrogenous metal oxides. The REE of ancient sediments support their partitioning into these same fractions and further contribute to the identification of the redox geochemistry of the sea water in which the sediments accumulated. The normalized curves of the REE that have been examined in several South American wine varietals can be interpreted to reflect the lithology of the bedrock on which the vines may have been grown, suggesting limited fractionation during soil development.

Geochemical Behaviour of Rare Earth Elements in Mining Environments under Non-Acidic Conditions

The rare earth elements (REE) were determined in water and solid samples at the abandoned mine of Ingurtosu (Sardinia, Italy). Research was performed to evaluate the main factors that control the geochemical behaviour of REE in near-neutral pH mining environments. REE show the highest concentrations (13-100μg/l) in drainages from mine tailings, especially when water sampling was carried out under high flow conditions. Positive correlations between ΣREE and Zn and Pb were observed, possibly indicating REE sorption on Zn- and Pb-rich fine particles (<0.4μm). Fractionation processes were observed normalizing REE in waters with respect to REE in mining-related residues. The Naracauli waters show an enrichment in HREE, probably due to the high stability of dissolved HREE(CO3)2− complexes in the studied waters. REE fractionation was not observed during hydrozincite bioprecipitation.

Anthropogenic dissolved and colloid/nanoparticle-bound samarium, lanthanum and gadolinium in the Rhine River and the impending destruction of the natural rare earth element distribution in rivers

The strong increase in the consumption of rare earth elements (REE) in high-tech products and processes is accompanied by increasing amounts of REE released into the environment. Following the first report of Gd contamination of the hydrosphere in 1996, anthropogenic Gd originating from contrast agents has now been reported worldwide from river and estuarine waters, coastal seawater, groundwater and tap water. Recently, microcontamination with La, that is derived from a point source where catalysts for petroleum refining are produced, has been detected in the Rhine River in Germany and the Netherlands. Here we report the occurrence of yet another REE microcontamination of river water: in addition to anthropogenic Gd and La, the Rhine River now also shows significant amounts of anthropogenic Sm. The anthropogenic Sm, which enters the Rhine River north of Worms, Germany, with the same industrial wastewater that carries the anthropogenic La, can be traced through the Middle and Lower Rhine to the Netherlands. At Leverkusen, Germany, some 250km downstream from the point source at Worms, anthropogenic Sm still contributes up to 87% of the total dissolved Sm concentration of the Rhine River. Results from ultrafiltration suggest that while the anthropogenic Gd is not particle-reactive and hence exclusively present in the truly dissolved REE pool (<10kDa), the anthropogenic La and Sm are also present in the colloidal/nanoparticulate REE pool (between 10kDa and 0.2μm). Though difficult to quantify, our data suggest that the Rhine River may carry up to 5700kg of anthropogenic La, up to 584kg of anthropogenic Sm, and up to 730kg of anthropogenic Gd per year toward the North Sea. There exist no regulatory limits for dissolved REE in natural waters, but total REE and Y (∑REY) concentrations of up to 0.14mg/kg in the plume downstream of and 52.2mg/kg at the head of an effluent pipe at Rhine-km 447.3 at Worms get close to and well-above, respectively, the levels at which ecotoxicological effects have been documented. Because of the increasing use of REE and other formerly “exotic” trace elements in high-tech applications, these critical metals have now become emerging contaminants that should be monitored, and it appears that studies of their biogeochemical behavior in natural freshwaters might soon no longer be possible.

Dynamics of rare earth elements in water–soil systems: The case study of the Pineta San Vitale (Ravenna, Italy)

The European Union Site of Community Importance Pineta San Vitale (Ravenna, Italy) is located in a complex lagoon system nearby the Adriatic Sea. This area is affected by relevant environmental pressures related to subsidence, groundwater salinization and industrial contamination. The occurrence of rare earth elements (REE), and the characterization of processes that control their migration in the water–soil system were performed for implementing the knowledge of the present environmental status in the area.Nine soil profiles were opened in the Pineta San Vitale and each horizon was characterized. In the parent material, dominant quartz, followed by plagioclase, mica, chlorite and calcite were recognized by XRD. Topsoil samples were characterized by neutral or sub-acid pH, relatively high organic carbon content (LOI up to 43wt.%; TOC: 38÷61g/kg), and low carbonate (11÷20g/kg CaCO3). Subsoil horizons were sub-alkaline or moderately alkaline, rich in carbonate (up to 114g/kg CaCO3), and depleted in organic matter. The electrical conductivity (EC: 0.2÷4.2 mS/cm) values along the soil profiles did depend on the water table fluctuations and the salinity of groundwater. Sequential extraction tests on two soil profiles showed the highest Y and ΣREE occurrence in the residual fraction of soils, with values generally increasing at depth, and total amounts similar to values estimated in the upper continental crust (UCC). Poor fractionation of REE was observed when the bulk soil horizon was considered, but different REE patterns occurred in the organic, oxide, and carbonate soil fractions, suggesting REE fractionation during weathering and pedogenic processes.Physical–chemical parameters and concentrations of total and dissolved elements were determined in 44 water samples. Waters showed near-neutral or slightly alkaline pH (6.8÷8.0) and total dissolved solids mostly in the range of 2 to 24g/L, with values increasing with increasing seawater influence. Concentrations of ΣREE determined in waters filtered through 0.4μm pore size filters varied from 0.1 to 189μg/L (0.7·10−9÷1.3·10−6mol/L ΣREE), with the highest values observed in soil waters. REE values were not related to salinity, nor to major ions, while were positively correlated to Al concentrations. Further filtration through 0.015μm pore size filters removed about 90% of REE compared to the 0.4μm filtered samples, i.e. the studied waters showed a small quantity of truly dissolved REE species. Speciation modeling results by Visual MINTEQ indicated that truly dissolved REE species are dominated by bi-dentate organic complexes in the soil waters rich in dissolved organic carbon (up to 74mg/L DOC); aqueous complex with the carbonate and bicarbonate ligands increased in waters having low DOC. UCC-normalized patterns of REE in the colloidal fraction of soil waters showed slight enrichments in the middle REE (MREE), likely due to preferential adsorption of the MREE onto <0.4μm particles. UCC-normalized patterns of REE truly dissolved in soil waters showed slight enrichments in the heavy REE (HREE), probably due to dominant low molecular weight DOC in the truly dissolved fraction.For evaluating the potential REE contribution from the atmosphere, 12 vegetation samples (ivy leaves) were submitted to leaching tests using acidulated water as a proxy of rain water. The REE leached from leaves were in the range of 0.5 to 10μg/kg ΣREE, suggesting a significant atmospheric contribution to the water–soil system. UCC-normalized patterns of REE leached from leaves were nearly flat, possibly indicating a dominant geogenic source of atmospheric REE.

Study of the Influence of Rear Earth Elements on Microstructure of Pearl Surface Observed by SEM

We investigated the influence of rare earth element (REE) Ce on the surface microstructure of bivalves pearl in the scaled of micro and nanometer range by means of scanning electronic microscopy (SEM). And we discussed the relevant of surface microstructure and lustrous of pearls to the concentration of REE in culture water by analyzing the influence of additive REE on the surface microstructure. We found that pseudo-hexagonal relatively grow slowly when REE Ce was absent in the culturing water, and the pearls surface were mainly build up by spindly aragonite blocks. On the contrary, the pearls grow quickly when REE was added in the culturing water, and the pearls surface were chiefly composed of regular hexagonal aragonite blocks that is the most idea blocks in crystallography. The results show that an appropriate quantity of Ce will promote the development and growth of pearls, and enhanced the lustrous of pearls significantly. However, as the REE concentration is large, the blocks composed of pearls became to around, and oval dics, thus leading the roughness increasing of pearls surface and the lustrous decrease.

The Surface Micro-Morphology Transition of Pearls Induced by Cerium

The surface microstructure transition of pearl induced by rare earth element (REE) cerium (Ce) was investigated in micrometer scale range by means of scanning electronic microscopy (SEM). We found that pearls cultured in the control group (no REE Ce added) relatively grow slowly when there is in the culturing water, but the pearls grow quickly when REE Ce was added in the culturing water. At the same time, the former pearls were built up by aragonite blocks with spindly shape, but the latter pearls sampled in the REE test group are made of aragonite blocks with regular hexagonal shape. Moreover, the luster of the pearls free of REE Ce is relatively low because their surface were mainly build up by spindly aragonite blocks. On the contrary, the pearls with REE Ce have high luster since their surface were chiefly composed of regular hexagonal aragonite blocks that is the most idea blocks in crystallography. The results show that a quantity of Ce will promote the development and growth of pearls, and enhanced the lustrous of pearls significantly. Finally, we discussed the relevant of surface microstructure and lustrous of pearls to the concentration of REE in culture water by analyzing the influence of additive REE Ce on the surface microstructure

A magnesium hydroxide preconcentration/matrix reduction method for the analysis of rare earth elements in water samples using laser ablation inductively coupled plasma mass spectrometry

This paper describes a simple method for simultaneous preconcentration and matrix reduction during the analysis of rare earth elements (REEs) in water samples through laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS). From a systematic investigation of the co-precipitation of REEs using magnesium hydroxide, we optimized the effects of several parameters – the pH, the amount of magnesium, the shaking time, the efficiency of Ba removal, and the sample matrix – to ensure quantitative recoveries. We employed repetitive laser ablation to remove the dried-droplet samples from the filter medium and introduce them into the ICP–MS system for determinations of REEs. The enrichment factors ranged from 8 to 88. The detection limit, at an enrichment factor of 32, ranged from 0.03 to 0.20 pg mL −1. The relative standard deviations for the determination of REEs at a concentration of 1 ng mL −1 when processing 40 mL sample solution were 2.0–4.8%. We applied this method to the satisfactory determination of REEs in lake water and synthetic seawater samples.

Assessment of the Uvod Reservoir pollution with heavy metals

Concentrations of heavy metals (Cu, Ni, Cd, Pb, Cr, and Zn) in bottom sediments, water, snow, and biota of the Uvod Reservoir, as well as of rare-earth elements (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Y, and Yb) in its water are assessed. Geochemical studies of concentrations of Cu, Ni, Cd, Pb, Cr, and Zn in soils, water, and snow allow us to state that the metals enter the reservoir mostly from natural sources; however, some part of them are of anthropogenic origin. The sum of concentrations of light rare-earth elements (La, Ce, and Nd) make almost the total of all rare-earth elements in the reservoir—from 70 to 97%, depending on the sampling site. The highest concentrations of metals (and the highest percentage of their labile forms) are recorded in the Priplotinnyi and Kolbaskinskii (in macrophite deposits) pools and at the site of water inflow from the Volga-Uvod canal. There is also reason to suppose a secondary entry of the elements under study into the water mass. The largest variations in metals’ concentrations are observed during the periods of spring and autumn floods, when a great quantity of terrigenous suspended matter enters the water body. The distribution of the above metals and rare-earth elements in water is uneven; their highest concentrations are observed in the site of water inflow from the canal and in the Uvod River (the latter is likely to be due to the effect of the settlement of Pistsovo). The analysis of biota (fennel-leaved pondweed and zooplankton) has shown that the Uvod Reservoir is polluted with heavy metals.

Determination of REEs in natural water by ICP-MS with the aid of an automatic column changing system

An automatic column changing system was developed for preconcentration and measurement of rare earth elements (REEs) in natural water samples, where syringe driven chelating columns (SDCCs) were applied to the hybrid (off-line operation and on-line operation) solid phase extraction of REEs. The sample loading was carried out off-line prior to the measurement. After that, the SDCCs were set into the column holder of the automatic column changing system and REEs were on-line eluted and measured by an inductively coupled plasma mass spectrometer (ICP-MS). The present automatic column changing system permitted continuously automatic measurement of 30 samples, while 3 min was enough for measuring one sample. The reproducibilities of REEs' signals obtained with two kinds of SDCCs showed that both of them are fit for the hybrid solid phase extraction method for preconcentration of REEs. The analytical detection limits (ADL) of REEs were in the range from 0.013 pg mL−1 for Tm to 0.15 pg mL−1 for Ce when 10 mL of water sample was loaded to each SDCC. The usefulness of the present method was confirmed by analysing NMIJ CRM 7201-a. After that, REEs in Lake Baikal water samples from depth of 50, 100, 150, 200, 250 m were determined. The results showed that dissolved REEs in the sample of 50 m depth were significantly lower than other samples, while the total REEs in the sample of each depth were close to one another. The distribution of REEs in Lake Baikal water samples was also discussed using shale normalized REEs distribution pattern.

On-line elution of iron hydroxide coprecipitate carrier for determination of REEs in natural water by mix-gas ICP-MS

A new coprecipitation method using iron hydroxide was developed to preconcentrate rare earth elements (REEs) in natural water prior to determination by inductively coupled plasma mass spectrometry (ICP-MS). The precipitate was collected in a syringe filter, which was connected into an ultrasound-assisted on-line elution and ICP-MS measurement system for REEs. Nitrogen (120 mL min−1) was mixed in auxiliary gas of ICP-MS to get rid of the oxide spectral interference with the REEs' measurements. When 10 mL of water sample was used, the blanks of REEs were from 0.001 pg mL−1 of Tm and Lu to 0.22 pg mL−1 of La and Ce. Detection limits calculated from 3-fold standard deviation of blanks were from 0.0006 pg mL−1 of Tm to 0.21 pg mL−1 of Ce. Recoveries of all REEs were from 97.1% to 103.1% with good reproducibility (standard deviation less than 3.3%). The usefulness of the method was confirmed by comparing the analytical results of NMIJ CRM 7201-a obtained with the present method and those obtained with an established solid-phase extraction method.

Identifying Controls on Water Chemistry of Tropical Cloud Forest Catchments: Combining Descriptive Approaches and Multivariate Analysis

We investigated controls on the water chemistry of a South Ecuadorian cloud forest catchment which is partly pristine, and partly converted to extensive pasture. From April 2007 to May 2008 water samples were taken weekly to biweekly at nine different subcatchments, and were screened for differences in electric conductivity, pH, anion, as well as element composition. A principal component analysis was conducted to reduce dimensionality of the data set and define major factors explaining variation in the data. Three main factors were isolated by a subset of 10 elements (Ca2+, Ce, Gd, K+, Mg2+, Na+, Nd, Rb, Sr, Y), explaining around 90% of the data variation. Land-use was the major factor controlling and changing water chemistry of the subcatchments. A second factor was associated with the concentration of rare earth elements in water, presumably highlighting other anthropogenic influences such as gravel excavation or road construction. Around 12% of the variation was explained by the third component, which was defined by the occurrence of Rb and K and represents the influence of vegetation dynamics on element accumulation and wash-out. Comparison of base- and fast flow concentrations led to the assumption that a significant portion of soil water from around 30 cm depth contributes to storm flow, as revealed by increased rare earth element concentrations in fast flow samples. Our findings demonstrate the utility of multi-tracer principal component analysis to study tropical headwater streams, and emphasize the need for effective land management in cloud forest catchments.

Rare earth elements in seawater during an iron-induced phytoplankton bloom of the western subarctic Pacific (SEEDS-II)

During an iron-enrichment experiment in the western subarctic Pacific (SEEDS-II), concentrations of dissolved and acid-soluble rare earth elements (REEs) were determined in shallow waters. Detailed vertical profiles of dissolved REEs were compared with those of nutrients in a preliminary survey. The results showed good correlation, except for Ce and Y. Along with phytoplankton growth within the iron-enriched patch, dissolved REEs were decreased in surface waters. The changes in REE concentrations were small but systematic: light REEs were adsorbed preferentially over heavy REEs. This systematic trend is consistent with results of earlier studies of REE adsorption onto biogenic particle surfaces. However, we were unable to detect a decrease of acid-soluble REEs in surface waters. During the phytoplankton bloom decline phase, dissolved REEs were elevated to concentration levels at the preliminary survey, although nutrients were decreased. The liberation of REEs from the suspended particles might be related to disaggregation from large particles to colloid particles, desorption from the particulate phase, and remineralization from organic matter. Outside the Fe-patch, time variations of REEs were also observed during SEEDS-II, indicating that both artificially induced phytoplankton blooms and natural variation of biogenic particles can affect the biogeochemical cycles of REEs in shallow waters within a short time.

Mineralogy and geochemistry of trace metals and REE in volcanic massive sulfide host rocks, stream sediments, stream waters and acid mine drainage from the Lousal mine area (Iberian Pyrite Belt, Portugal)

Acid mine drainage represents a major source of water pollution in the Lousal area. The concentrations of trace metals and the rare earth elements (REE) in the host rocks, stream sediment, surface waters and acid mine drainage (AMD) associated with abandoned mine adits and tailings impoundments were determined, in order to fingerprint their sources and to understand their mobility and water–rock interaction. The results show that the Fe–SO4-rich acid waters vary substantially in composition both spatially and seasonally. These waters include very low pH (mostly in the range 1.9–3.0), extreme SO4 concentrations (4635–20,070 mg L−1 SO42-), high metal contents (Fe, Al, Cu, Zn and Mn) and very high REE contents. The trace metal concentrations decrease downstream from the discharge points either due to precipitation of neoformed phases or to dilution. The North-American shale composite (NASC)-normalized patterns corresponding to sediment from one stream (Corona stream) show a flat tendency or are slightly enriched in light-REE (LREE). The NASC-normalized patterns corresponding to acidic mine waters show enrichment in the middle REE (MREE) with respect to the LREE and heavy REE (HREE). Moreover, the REE concentrations in acidic mine waters are 2 or 3 orders of magnitude higher than those of the surface waters. Changes of REE concentrations and variation of Eu anomaly show two spatially distinct patterns: (a) pond and spring waters with higher REE concentrations (ranging from 375 to 2870 μg L−1), that records conspicuous negative Eu anomaly, and (b) seeps from tailings impoundments corresponding to lower REE concentrations than the first pattern (ranging from 350 to 1139 μg L−1) with typically negative Eu anomaly. The stream water samples collected from the impacted stream during the spring show a low pH (2.8–3.1) and contain high concentrations of Fe and trace elements (up to 61 mg L−1). Also, temporal variations of the REE concentrations were observed in the Corona waters. The results obtained show that the REE concentrations increase during the winter–spring transition. Stream waters draining the Lousal mine area show high REE concentrations, reaching a maximum value of about 2846 μg L−1 (spring). The MREE concentrations are usually enriched with respect to both the LREE and HREE. A decrease in REE concentrations and a pH increase from 3 to 6 was observed downstream of the confluence of a tributary stream. The geochemistry of the waters strongly influenced the mineralogy and geochemistry of efflorescent sulfates precipitated on the banks of the streams polluted by AMD. The mineralogy is dominated by hexahydrite, rozenite, szomolnokite, alunite, gypsum, halotrychite, coquimbite, copiapite and schwertmannite. The REE concentrations determined in the efflorescent sulfates suggest a selective partitioning of the HREE onto Mg–Al-oxyhydroxides.

Rare earth elements (REE) and yttrium in stream waters, stream sediments, and Fe–Mn oxyhydroxides: Fractionation, speciation, and controls over REE + Y patterns in the surface environment

We have collected ∼500 stream waters and associated bed-load sediments over an ∼400 km 2 region of Eastern Canada and analyzed these samples for Fe, Mn, and the rare earth elements (REE + Y). In addition to analyzing the stream sediments by total digestion (multi-acid dissolution with metaborate fusion), we also leached the sediments with 0.25 M hydroxylamine hydrochloride (in 0.05 M HCl), to determine the REE + Y associated with amorphous Fe- and Mn-oxyhydroxide phases. We are thus able to partition the REE into “dissolved” (<0.45 μm), labile (hydroxylamine) and detrital sediment fractions to investigate REE fractionation, and in particular, with respect to the development of Ce and Eu anomalies in oxygenated surface environments. Surface waters are typically LREE depleted ([La/Sm] NASC ranges from 0.16 to 5.84, average = 0.604, n = 410; where the REE are normalized to the North America Shale Composite), have strongly negative Ce anomalies ([Ce/Ce ∗] NASC ranges from 0.02 to 1.25, average = 0.277, n = 354), and commonly have positive Eu anomalies ([Eu/Eu ∗] NASC ranges from 0.295 to 1.77, average = 0.764, n = 84). In contrast, the total sediment have flatter REE + Y patterns relative to NASC ([La/Sm] NASC ranges from 0.352 to 1.12, average = 0.778, n = 451) and are slightly middle REE enriched ([Gd/Yb] NASC ranges from 0.55 to 3.75, average = 1.42). Most total sediments have negative Ce and Eu anomalies ([Ce/Ce ∗] NASC ranges from 0.097 to 2.12, average = 0.799 and [Eu/Eu ∗] NASC ranges from 0.39 to 1.43, average = 0.802). The partial extraction sediments are commonly less LREE depleted than the total sediments ([La/Sm] NASC ranges from 0.24 to 3.31, average = 0.901, n = 4537), more MREE enriched ([Gd/Yb] NASC ranges from 0.765 to 6.28, average = 1.97) and Ce and Eu anomalies (negative and positive) are more pronounced. The partial extraction recovered, on average ∼20% of the Fe in the total sediment, ∼80% of the Mn, and 21–29% of the REEs (Ce = 19% and Y = 32%). Comparison between REEs in water, partial extraction and total sediment analyses indicates that REEs + Y in the stream sediments have two primary sources, the host lithologies (i.e., mechanical dispersion) and hydromorphically transported (the labile fraction). Furthermore, Eu appears to be more mobile than the other REE, whereas Ce is preferentially removed from solution and accumulates in the stream sediments in a less labile form than the other REEs + Y. Despite poor statistical correlations between the REEs + Y and Mn in either the total sediment or partial extractions, based on apparent distribution coefficients and the pH of the stream waters, we suggest that either sediment organic matter and/or possibly δ-MnO 2/FeOOH are likely the predominant sinks for Ce, and to a lesser extent the other REE, in the stream sediments.

Controls on transport and fractionation of the rare earth elements in stream water of a mixed basaltic–granitic catchment basin (Massif Central, France)

We present rare earth element (REE) patterns of small streams from a catchment basin in the Massif Central (France) in order to characterize the individual fractionation stages for the dissolved REE from the source to the catchment outlet. The upper part of the catchment is located on a basalt plateau, followed downstream by deep and narrow valleys within granitic and orthogneissic bedrock. Basalt-normalized 0.45 μm filtered stream water has REE patterns slightly depleted in the light REE (La–Sm, LREE) on the basalt plateau close to the source, followed by a continuous amplification of this LREE depletion downstream. At the same time also a negative Ce anomaly develops in the adsorbed fraction of > 0.45 μm particles, which has been isolated by leaching with 1 M HCl. Strontium and Neodymium isotope ratios of stream water demonstrate that the dissolved REE are essentially of basaltic origin, even in the lower, granitic and gneissic part of the catchment. Mixing with gneiss or granite derived REE thus cannot explain the observed evolution of the REE patterns. Our data suggest that the REE of the < 0.45 μm fraction are associated to Fe colloids, which grow during transport downstream to Fe oxyhydroxide particles exceeding 0.45 μm in size. Precipitation of these oxyhydroxide particles leads to selective removal of LREE from 0.45 μm filtered stream water, and of Ce adsorbed on > 0.45 μm particles. In contrast to earlier studies, we found no link between REE behavior and organic colloids or organic complexes. This scenario is confirmed by a detailed analysis of the REE patterns at 3 stream confluences. The results show that the REE do not behave conservatively during mixing at stream confluences, but that the LREE and Ce are preferentially removed similarly to what has been observed at catchment scale. Our study thus underlines the importance of Fe colloids for the transport and fractionation of the REE in stream water.