Geochemistry of REEs and trace elements in Diz alteration area, NW Iran

<p>Diz alteration area is situated in the southern part of Ardabil province in the northwest of Iran. This alteration area is a limited part of Tarom-Hashtjin volcanic zone. The hydrothermal alteration process has been mostly taken place in pyroclastic and volcanic units such as tuff, ignimbrite, and trachyandesites. The alterations of this area are related to Eocene volcanism which has considerably developed in the northwest of Iran. The argillic alterations in Diz area are mainly seen in ignimbrite unit and the precursor rock has been intensely altered such that many parts of the parent rock has been fully leached and all of the mobile elements have been removed from the parent rock while the resistant elements such as Al, Si, and some other immobile elements have remained in the context. Considering to the special behavior of REEs in the weathering and alteration profiles, depending on the REE bearing mineral’s resistivity against weathering and alteration processes, REEs can be removed or fixed in the environment. In the studied samples different concentrations of REEs are observable.            </p><p>The drawn REE diagrams show unique patterns for the studied samples where Ce group elements (LREEs) show a slight enrichment comparing to Y group (HREEs). The comparison of LREEs with HREEs represents that LREEs have been enriched 4 times more than HREEs.</p><p>The positive correlation coefficient between ΣREE and TiO<sub>2 </sub>(R<sup>2</sup>=0.70) represents the role of Ti bearing minerals such as ilmenite, pyroxene, rutile, and anatase in the fixation of REEs. On the other side the presence of considerable amounts of P<sub>2</sub>O<sub>5 </sub>in the studied samples and also the positive correlation coefficients between P<sub>2</sub>O<sub>5 </sub>and LREEs (R<sup>2</sup>=0.90), and P<sub>2</sub>O<sub>5</sub> and ΣREE (R<sup>2</sup>=0.74) suggest that some minor minerals such as monazite (Ce,La,Nd,Th)(PO<sub>4</sub>,SiO<sub>4</sub>) must be considered. The positive correlation coefficient between Al<sub>2</sub>O<sub>3 </sub>and ΣREE shows the influence of clay minerals in the adsorption of REEs.         </p><p>The evaluation of REE patterns normalized to chondrite show a remarkable peak for Gd. Geochemically, Gd shows similarities with Ca<sup>2+</sup>. The Gd complexes may decompose in the presence of some elements such as Cu, Y, and REEs and Gd<sup>3+ ­­</sup>can be released. Hence, CaO is a main component in the parent rock of the studied altered samples, the positive Gd anomaly is most likely related to the primary composition of the parent rock. Furthermore, the decomposition of Gd complexes in the presence of competitor elements and also the high Gd content of altering fluids can be thought as the main reasons of Gd positive anomaly in the studied samples.</p>

Substantial gadolinium enrichments in lake and river near metrocities in Korea

<p>We measured dissolved rare earth elements (REEs) in the water samples from Shihwa Lake (SL), which was assumed to be highly polluted, as well as in the downstream portion of the Han River (HR), which runs through, Seoul, Korea. Among the investigated REEs, only Gadolinium (Gd) was found to be significantly enhanced after REE concentrations were shale-normalized (SN). The calculated Gd anomaly (Gd/Gd* = 3×Gd<sub>SN</sub>/(Sm<sub>SN</sub> + 2×Tb<sub>SN</sub>)) was about 1.5±0.1 (n=16) in SL and 1.6±0.3 in HR (n=26) water relative to other types of natural water such as groundwater, seawater, and river water in uncontaminated areas (Gd/Gd*~1.2, n>400). These significant Gd anomalies seem to be due to the inputs of anthropogenic Gd (Gd<sub>anth</sub>), especially by the use of Gd-based contrast agents for magnetic resonance imaging (MRI) tests from a number of hospitals and medical institutes surrounding our study areas. The Gd<sub>anth</sub> inventory was estimated to be 190±80 g and 680±360 kg Gd in SL and the HR (watersheds in our study area), respectively. The Gd<sub>anth</sub> flux to the Yellow Sea from the HR is estimated to be 530±330 g Gd day<sup>-1</sup>. Overall, these results suggest that quantitative evaluation of man-made REEs for associated human risk assessments are needed, because considerable amounts of REEs are now used by modern high-tech industries.</p>

Anthropogenic Rare Earth Elements: Gadolinium in a Small Catchment in Guizhou Province, Southwest China

Rare earth elements (REEs), known as “industrial vitamins”, are widely used in medical treatment, industry, agriculture, etc. However, with the increasing demand for REEs, excess REEs, such as gadolinium (Gd), are considered micropollutants in the environment. In this paper, the distributions of dissolved REEs were analyzed in three small streams, in order to determine the extent and occurrence of Gd anomalies. The shale-normalized REE patterns in the three streams were less smooth with heavy REEs higher than light REEs, for a weak reaction of the heavy REE complexes. A negative Ce (cerium) anomaly and positive samarium (Sm) and europium (Eu) anomalies were observed in the three streams and the negative Ce anomaly was affected by the pH of the alkaline rivers. However, a positive Gd anomaly was found in only a typical urban small stream, Jinzhong. With a population of approximately 60,000, Jinzhong runs by a hospital and through wastewater treatment plants (WWTPs). The concentrations of Gd in Jinzhong ranged from 1.54 to 86.65 ng/L with high anthropogenic Gd proportions (63.64%–98.07%). Anthropogenic Gd showed significant seasonal variations and distinct spatial disparities from upstream to downstream, and it was associated with certain ions such as Cl−. Anthropogenic Gd could be attributed to gadopentetic acid (Gd-DTPA), which is used in magnetic resonance imaging (MRI) in hospitals. This type of Gd was shown to be correlated with municipal wastewater. Due to the high stability and low particulate reactivity in water, anthropogenic Gd has great potential to serve as a tracer to prove the presence of medical wastewater.

Controls on the distribution of arsenic and rare earth elements in groundwaters of the Bafgh city area, central Iran

High arsenic (As) contents in groundwater were found in the Bafgh area in central Iran and chosen for hydrogeochemical study. A total of 20 groundwater samples were collected from existing tube wells in the study areas in 2013 and analyzed. The water chemistry is predominantly of Na–Cl type, with concentrations of dissolved As in the range between 0.9 and 74.7 μg/L. The chondrite-normalized rare earth elements patterns exhibited a flat profile, positive Gd anomaly with a predominance of light rare earth elements (LREEs) over heavy rare earth elements (HREEs), suggest that they originated from the same source. The metals in the groundwater of the region have a geological origin.

Authigenic phase formation and microbial activity control Zr, Hf, and rare earth element distributions in deep-sea brine sediments

Sediments collected from hypersaline and anoxic deep-sea basins in the eastern Mediterranean (Thetis, Kryos, Medee, and Tyro) were characterised in terms of their mineralogical composition, the distributions of rare earth elements (REE), Zr, and Hf and their content of microbial DNA. We identified two major mineralogical fractions: one fraction of detritic origin was composed of quartz, gypsum, and low-Mg calcite bioclasts (with 0 < Mg < 0.07%) and another fraction of authigenic origin constituted of halite, dolomite, high-Mg calcite (with a Mg content of up to 22%) and rare bischofite and showed a textural evidence of microbial assemblages. We found that in the Medee and Tyro sediments, the shale-normalised REE pattern of these sediments is strongly enriched in middle REE (MREE), whereas in the Thetis and Tyro basins, a positive Gd anomaly in the residue was obtained after the removal of the water-soluble fraction. In all investigated basins, Y / Ho ratio clustered around chondritic values, whereas Zr / Hf ratio ranged from slightly subchondritic to superchondritic values. Subchondritic Y / Ho and Zr / Hf values were mainly found in the high-Mg carbonate having a microbial origin. The observed preferential removal of Zr with respect to Hf without significant partitioning of Y with respect to Ho indicates that the Zr / Hf ratio and Y–Ho fractionations are influenced by the microbial activity in the sediments. We propose that the concurrent Y-Ho and Zr–Hf fractionations are a suitable tracer of microbial activity in marine sediments.

Tracing the spatial propagation of river inlet water into an agricultural polder area using anthropogenic gadolinium

The inlet of diverted river water into agricultural areas or nature reserves is a frequently applied management strategy to prevent fresh water shortage. However, the inlet water might have negative consequences for water quality in the receiving water bodies. This study aimed to obtain a spatial image of the inlet water propagation into a hydrological complex polder area. We used anthropogenic gadolinium (Gd-anomaly) as a tracer for diverted river water. A clear reduction in the river water contribution was found from very dry conditions on 5 August 2010 to very wet conditions on 22 October. Despite the large inlet water impact on 5 August, the diverted river water did not propagate up into the small agricultural headwater ditches. Gadolinium proved to be an effective tracer for diverted river water in a polder system. We applied our results to upgrade the interpretation of water quality monitoring data and to validate our integrated nutrient transport models.

Aquatic geochemistry of the rare earth elements and yttrium in the Pioneer River catchment, Australia

The rare earth elements are strong provenance indicators in geological materials, yet the potential for tracing provinciality in surface freshwater samples has not been adequately tested. Rare earth element and yttrium concentrations were measured at 33 locations in the Pioneer River catchment, Mackay, central Queensland, Australia. The rare earth element patterns were compared on the basis of geological, topographical and land-use features in order to investigate the provenancing potential of these elements in a small freshwater system. The rare earth element patterns of streams draining single lithological units with minor land modification show strongly coherent normalised behaviour, with a loss of coherence in agricultural locations. Evidence is reported for an anthropogenic Gd anomaly that may provide a useful hydrological tracer in this region since the introduction of magnetic resonance imaging in 2003. Several samples display a superchondritic Y/Ho mass ratio (up to 44), which is not explainable within the constraints imposed by local geology. Instead, it is suggested that the additional Y is derived from a marine source, specifically marine phosphorites, which are a typical source of fertiliser phosphorus. The data indicate that, under some circumstances, scaled and normalised freshwater rare earth patterns behave conservatively.