As explored further below, either the REEs are leached from multiple mineral sources, the mineral source is not represented in Fig. REE patterns of groundwater interacting with the sediments show a much greater variation between dif- ferent samples from the aquifer Fig. REE data for common minerals in a basalt data cited in Rollinson, , b secondary minerals from basalt Guy et al.
Dulski, , with the exception of sediments. Consistent with groundwater from the basalt aquifer, following section we apply a semi-quantitative com- and with work by Bau et al. The dissimilarity between most aquifers. All Therefore, it is unlikely that REE concentrations and groundwater samples are undersaturated with respect to patterns in groundwater from either the basalt or the amorphous silica SiO2 a Table 2 , and the major sedimentary aquifer predominantly reflect major min- silicate minerals, which indicates there is the potential eral dissolution reactions as indicated by the ground- for REE mobilisation during silicate dissolution.
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How- water major ion chemistry in Tweed et al. Co-precipitation and sorption REE concentrations and patterns. REE patterns of groundwater from the basalt aquifer Co-precipitation and sorption reactions can affect both are not identical to REE signatures of basalts throughout REE concentrations and patterns depending on the Victoria Fig. Saturation indices indicate REE, however the surface properties of sorption sites may that groundwater has the potential to precipitate iron also affect the extent of REE removal.
The permanent oxyhydroxides e. Therefore, montmorillonite clays different types of clays Table 1.
Therefore, the extent present in the basalt aquifer in the Dandenong Ranges of REE sorption may vary due to the variations in abun- Table 1 have the potential to sorb REEs. In comparison, dance of high cation exchange capacity CEC minerals.
Rare Earth Elements in Groundwater Flow Systems | SpringerLink
In Groundwater chemistry determines the REE aqueous general, sorption of REEs to kaolinite increases with species; therefore changes in groundwater chemistry along increasing pH Coppin et al. Sorption experiments flow paths can change REE behavior. For example, as by Coppin et al. Sorption of REEs to iron oxyhydroxide Sholkovitz et al. Individual elements can also behave diffe- Verplanck et al.
Rare Earth Elements in Groundwater Flow Systems
Drever, ; Fig. However, this may be offset by the decrease in specific ionic radii Bau, Other potential sorption sites sorption to iron oxyhydroxides e. Bau, or particulate matter e. Nozaki et al.
Gd and Lu surface complexes are also slightly less groups on clays e. Avena and De Pauli, Therefore, the positive 5. Groundwater flow paths Gd and Lu anomalies of groundwater in the basalt aquifer and some groundwater in the sedimentary aquifer Fig. These ratios indicate increased sorption of REEs in groundwater from discharge areas BHs 12 to 14 compared with groundwater from recharge areas BHs 9 to 11 in the sedimentary aquifer. The lack of local mine- ralogy data and no data for the type and number of sorption sites within the different aquifers inevitably limits interpretation of processes affecting groundwater REE concentrations.
However, interaction of ground- water with the different aquifers and mixing between these has been constrained using major ion chemistry Tweed et al. This interpretation of the history of groundwater flow at each location is used to highlight REE systematics at different stages of groundwater flow via the basalt and sedimentary aquifers. Recharge and flow via the basalt aquifer Fig. In these samples, groundwater flow through the sediments. HREEs given that both are present mostly as positively 3a are similar to those of other groundwater samples charged carbonate complexes Fig.
Therefore, REE patterns and sorb to kaolinite and montmorillonite to the same extent concentrations reflect early-stage interaction with the Coppin et al. Saturation indices for groundwater from the basalt aquifer at different indicate that co-precipitation of REEs with goethite has the stages along the flow paths suggest that REE steady potential to occur Table 2. Therefore, the REE pattern for state is achieved relatively quickly, perhaps during infil- groundwater from the basalt aquifer may have been tration of slightly acidic rainfall. The REE concentra- affected by co-precipitation with Fe oxides.
However, the tions decrease slightly with increasing pH Fig. These results are consistent with work state is maintained, so that there is limited net change to of Johannesson et al. In compari- concentrations and pH values. These complexes are ex- from the basalt aquifer have similar REE patterns Fig.
Also for BH 4, there may be limited ad- steady state results in no net change to patterns and sorption of REEs on goethite as the more crystalline concentrations. HREEs to clays only occurs in solutions of high ionic strengths. In addition to this, both light and heavy REEs 5. Recharge via the sedimentary aquifer are present as positively charged aqueous complexes Fig. REE patterns in groundwater from the sedimentary 4c , so sorption should result in little fractionation bet- flow paths show more variability than those from the ween these.
Verplanck et al. Therefore, differences in the REE pattern at the lowest pH values 4. Discharge via the sedimentary aquifer Groundwater from BHs 9—11 receives recent re- Groundwater at BHs 12—14 represents local dis- charge and has relatively short residence times Tweed charge Tweed et al. Therefore, although these et al. As noted previously, groundwater from BH bores are screened in the sedimentary aquifer, they are 11 has a REE pattern close to that of marine sediments down-gradient from recharge areas in both the sedi- Fig.
The REE pattern may also indicate an in- mentary and basalt flow systems Fig. Major ion fluence from rainfall, however local rainfall samples chemistry indicates there is some flow from the basalt during the time of groundwater sampling would be aquifer to this local discharge area Tweed et al. However, groundwater chemistry from BHs 12—14 Compared with groundwater at BH 11, although TDS represents groundwater with greater input from the contents are similar, groundwater from BHs 9 and 10 have regional flow system, dominated by reactions with the lower REE concentrations Fig.
Similar large screen interval 18— m , differences in major to groundwater from the basalt aquifer, the increase in Gd ion chemistry coupled with hydraulic heads between the anomalies may be due to sorption or co-precipitation. In the slightly acidic The increase in TDS contents in groundwater from groundwater, REEs are predominantly present as free ions this discharge area is not accompanied by an increase in Fig. REE concentrations Fig. Major ion chemistry in- Although groundwater at BH 10 has a lower pH 4.
The lower pH pared with recharge areas in the sediments, REE con- may be due to minor pyrite oxidation Tweed et al. Similar to the basalt aquifer, the steady state oxyhydroxides e. Worrall and Pearson, a. Du- behavior of REEs may be due to higher pH values 6. Saturation indices indicate that in the discharge cipitation.
However, SO4 concentrations are low Table area of the sedimentary aquifer, clays such as kaolinite 2 , therefore the amount of pyrite oxidation is likely to and illite may precipitate and therefore remove REEs be minor. Also, kaolinite do- distribution of source minerals.
Increased REE concentra- minant clay has a higher sorption potential with in- tions occur in groundwater where recharge is via sediments creased pH Coppin et al. Under these regional sedimentary aquifer has increased residence conditions, localised processes such as pyrite oxidation times Tweed et al.
Therefore, REEs may be and source heterogeneity affect REE patterns and derived primarily from interactions with the weathered concentrations. In contrast, where groundwater recharges sediments in lower pH environments and, as groundwa- via basalt, REE concentrations are lower and groundwater ter flows through the regional sedimentary aquifer, the pH values vary between 6.
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Increased water—rock contribution of REEs from dissolution is small relative to interaction with the basalt aquifer alters major ion the amount of sorption and co-precipitation occurring as chemistry but does not affect REE concentrations or pH values increase. This may be due to in groundwater with lower pH values is consistent with increased abundances of sorption sites in the shallower previous research e.