Leaching Of Minerals Research Articles

Using Single-Species and Whole Community Stream Mesocosm Exposures for Identifying Major Ion Effects in Doses Mimicking Resource Extraction Wastewaters.

Wastewaters and leachates from various inland resource extraction activities contain high ionic concentrations and differ in ionic composition, which complicates the understanding and effective management of their relative risks to stream ecosystems. To this end, we conducted a stream mesocosm dose-response experiment using two dosing recipes prepared from industrial salts. One recipe was designed to generally reflect the major ion composition of deep well brines (DWB) produced from gas wells (primarily Na+, Ca2+, and Cl-) and the other, the major ion composition of mountaintop mining (MTM) leachates from coal extraction operations (using salts dissociating to Ca2+, Mg2+, Na+, SO42- and HCO3-)-both sources being extensive in the Central Appalachians of the USA. The recipes were dosed at environmentally relevant nominal concentrations of total dissolved solids (TDS) spanning 100 to 2000 mg/L for 43 d under continuous flow-through conditions. The colonizing native algal periphyton and benthic invertebrates comprising the mesocosm ecology were assessed with response sensitivity distributions (RSDs) and hazard concentrations (HCs) at the taxa, community (as assemblages), and system (as primary and secondary production) levels. Single-species toxicity tests were run with the same recipes. Dosing the MTM recipe resulted in a significant loss of secondary production and invertebrate taxa assemblages that diverged from the control at all concentrations tested. Comparatively, intermediate doses of the DWB recipe had little consequence or increased secondary production (for emergence only) and had assemblages less different from the control. Only the highest dose of the DWB recipe had a negative impact on certain ecologies. The MTM recipe appeared more toxic, but overall, for both types of resource extraction wastewaters, the mesocosm responses suggested significant changes in stream ecology would not be expected for specific conductivity below 300 µS/cm, a published aquatic life benchmark suggested for the region.

Preparation of carboxy methyl cellulose stabilized nano-sized zero-valent iron and its properties for in situ remediation of groundwater in areas after acid in situ leach uranium mining

In this study, a highly dispersed carboxy methyl cellulose stabilized nZVI was synthesized and characterized, showing excellent uranium removal efficiency in acid in situ leach mine water.

Heavy Metal Estimation and Quality Assurance Parameters for Water Resources in the Northern Region of Pakistan

The current study investigates the water quality parameters of drinking water resources in District Neelam (DNLM), Azad Jammu & Kashmir (AJK), Northwestern Pakistan. The studied area has been recently reported with many waterborne diseases, which probed this analytical study. The samples were aseptically collected from springs, taps, and surface water bodies. The water quality parameters, such as physical, microbiological, anions, and heavy metals, were tested. Results showed that the electrical conductance (EC) and total dissolved solids (TDS), were 974.60 µS/cm and 912.10 mg/L, respectively, exacerbating the quality of drinking water in DNLM. For microbial water testing, we used 3M-Petrifilms as a detection source, which could separate coliform bacteria from E. coli by creating unique surface chromophores. Out of sixty collected samples, 76% had bacterial contamination. Nitrite, nitrate, and phosphate (9.8, 15.0, and 15.1 mg/L), were also surpassing the safe limits of the World Health Organization (WHO) standards for water quality measurement. The heavy metals, i.e., As, Cr, Cu, and Pb were also tested in current analysis. Pb and Cr (0.04 mg/L and 0.06 mg/L) exceeded from safe drinking water guidelines of the WHO and more than 50% of the collected samples had Pb as a major water pollutant in DNLM. Poor waste management, open sludge discharge, lack of municipality measures, and mineral leaching into the freshwaters of DNLM due to mining and metal extraction processes were the main sources of water pollution in the region. The inorganic pollutants were responsible for the sudden rise of different malignancies and other fatal diseases (vital organ failures and reproductive disorders) in the region, which has not been reported in the past. The current investigation yielded useful baseline data of the drinking water reserves of NW Pakistan that could help to develop techniques for the mitigation of water pollutants present in the region.

Hydrodynamic Hysteresis and Solute Transport in Agglomerated Heaps under Irrigation, Stacking, and Bioleaching Controlling

Hydrodynamic hysteresis exists widely in agglomerated heaps with well-developed intra-pores, and it directly affects solute transports and bioleaching reaction. In this paper, the dynamic liquid retention behavior under different heap porosity and irrigation condition is quantified via a novel real-time, in-situ liquid retention characterizing system (RILRCS), and the potential effects of initial liquid retention on solute transport and leaching reaction are carefully discussed. The results show that the immobile liquid is dominant in agglomerated heaps. The ratio of immobile and mobile liquid (η) dynamically changes due to mineral dissolution and new flow path appearances. The η normally increases and mobile liquid occupies a higher proportion due to acidic leaching reactions, especially at a smaller Rg (10.32 mm) and a larger u (0.10 mm/s). The dynamic liquid retention is more sensitive to the diameter of packed feeds (Rg) and superficial flow rate (u) instead of leaching reactions. This might be because the damage of leaching reaction on minerals pores/voids is limited and cannot extensively change the potential pore channels or fluid flow paths. Based on pulse tracing and conductivity tests, we reveal that the solute resides longer under a slower u and smaller packed Rg condition, which corresponds well with desirable copper leaching efficiency. Specifically, the liquid hysteresis behavior is more obvious at a lower u (0.01 mm/s) and smaller Rg (10.32 mm). This paper gives a good reference to ascertain the liquid retention and hydrodynamic hysteresis and promote mineral leaching performance.

Application of Machine Learning in a Mineral Leaching Process-Taking Pyrolusite Leaching as an Example.

In this study, several machine learning models were used to analyze the process variables of electric-field-enhanced pyrolusite leaching and predict the leaching rate of manganese, and the applicability of those models in the leaching process of hydrometallurgy was compared. It showed that there was no correlation between the six leaching conditions; in addition to the leaching time, the concentrations of sulfuric acid and ferrous sulfate had great influences on the leaching of pyrolusite. The results of the prediction models showed that the support vector regression model has the best prediction performance, with regression index (R 2) = 0.92 and mean square error = 25.04, followed by the gradient boosting regression model (R 2 > 0.85). In this research, machine learning models were applied to the optimization of the manganese leaching process, and the research process and methods were also applicable to other hydrometallurgical processes for majorization and result prediction.

Artificial macropores and water management effects on reduction of greenhouse gas emissions from rice paddy fields

Rice production is an important sector of global agriculture, sustaining more than half of the world's population. However, rice production contributes significantly to global warming through increased emission of greenhouse gasses (GHGs), primarily CH4, into the atmosphere. Therefore, this study examined countermeasures to reduce GHG emissions from paddy fields without affecting rice production. A column experiment was conducted to investigate the effects of soil macroporous structure and water management on GHG emissions from flooded alluvial clay soil (paddy soil). The soils were subjected to different management regimes: with and without artificial macropores, compost, and drainage treatment. Drainage was maintained at 6.5 mm d − 1 to ensure infiltration yet prevent excessive leakage from the paddy field. The measured parameters included GHG emissions, soil water content, redox potential, soil temperature, soil swelling, total carbon, total nitrogen, iron, and manganese. The results showed that the soil column with macropores and drainage had significantly lower CO2 and CH4 emissions than that without macropores and drainage. In addition, the soil level increment, and thus, the amount of gas (CH4) produced in the soil column with drainage were lower than that without drainage. The combination of drainage treatment and macropores might have effectively acted as a hydrodynamic gradient and a structure that promotes freshwater intrusion into deeper soil profiles, inhibiting absolute anaerobic methanogenic activity. The redox potential of the column with drainage and macropores was the highest. Moreover, CO2 and CH4 emissions were reduced at a relatively small drainage rate of 6.5 mm d − 1 by adding macropores to the soil. The findings confirmed that GHG emissions were effectively reduced by a porous soil structure at a low drainage rate. Macropore application also exhibited effectiveness at mitigating nutrient loss (TOC and TN) through the drainage. Therefore, low tillage before flooding would be preferable to conserve the macroporous structure. However, the results also highlight an adverse effect on mineral leaching (particularly Mn) through the column with macropores.

Comparative Characterization of Trends and Patterns of Physical and Chemical Attributes of Optimal and Traditional Processed Cowpea Leaves

Seasonality in the availability of cowpea leaves has often limited their utilization and thus the promotion of preservation techniques that convert the vegetables into storable and stable forms. The recommendations for the use of highly mechanized techniques in preservation are brought into question due to limited affordability among resource-constrained households that prefer less costly approaches. Therefore, this study used statistical techniques of principal component analysis to comparatively evaluate the trends of physicochemical quality of the two diverse approaches of processing cowpea leaves. The study evaluated dehydrated cowpea leaves of different processing techniques from farmer groups and optimally processed using modern techniques for nutritional composition, phytochemical compounds, and colour changes. Sun drying techniques that excluded blanching had the least content of beta-carotene and ascorbic acid, 2.65 ± 0.95 and 21.80 ± 1.24 mg/100 g dry weight basis (dwb), respectively, accompanied by the most significant ( p < 0.001 ) deterioration of colour (7.74 ± 3.49) than techniques that included. Whereas the antinutrients declined, the difference did not significantly differ ( p > 0.05 ) based on preservation techniques. With factor analysis determining optimal nutritional quality for cowpea leaves at 8 weeks after emergence, sun drying had the highest loss of beta-carotene and ascorbic acid, 66.7–80.1% and 53.7%–58.3%, respectively ( p < 0.001 ), whereas mineral leaching, reduction of antinutrients, and colour changes were more pronounced in dehydration techniques incorporating fermentation as pretreatment. For the traditional preservation techniques, increasing retention of minerals resulted in aggravated losses of beta-carotene and ascorbic acid, whereas in the mechanized techniques, this was not the case. In concluding that the mechanized techniques have a better combination of attenuating losses of micronutrients, the study recommends that in promoting the utilization of traditional preservation techniques, low-cost processes like steam blanching can help improve the nutritional quality of the product.

Optimizing fertigation schemes based on root distribution

When fertigation is applied, fertilizer is often injected into drip irrigation systems according to a single-pulse application method (SPAM) where a single dose is given either in the early, middle, or late stage of an irrigation event. To improve the consistency of distributions between nutrients and roots and thus promote root nutrient uptake, a root distribution-based multistage application method (RMAM) was proposed, where fertilizer was injected in stages during each irrigation event and proportionally according to the distribution of normalized root length density. A case study to verify the potential of RMAM and to test it against other fertigation scheduling strategies was conducted in a two-year field experiment with drip-irrigated cotton under film mulch in Xinjiang, China. Results indicated fertilizer application strategies significantly impacted soil nutrient dynamics. Generally, SPAM caused nutrient accumulation in certain soil layers, while uniform multistage application method (UMAM) resulted in a more even nutrient profile. Optimal nutrient profile for root uptake was obtained by RMAM, where more nutrients were located in the upper soil layers containing more roots. Compared to late-stage SPAM, the best among all the schemes of UMAM and SPAM, RMAM did not influence deep leaching of mineral N and available P, but did reduce leachate of available K by an average of 3.5% during the fertigation periods over the two seasons. Furthermore, at the late boll-opening stage, due to 25.8%, 35.7% and 35.3% increases of average aboveground accumulation (representing root nutrient uptake) for N, P and K, average soil residual respectively decreased 23.8%, 6.2% and 3.1%, and average cotton yield enhanced 5.5%. Besides root length density, crop nutrient uptake is also affected by many other complicated factors such as soil water/nutrient dynamics and root uptake activity, and thus RMAM should be further investigated to consider these factors comprehensively.

Precise determination of dolomite content in marine sediments

AbstractDolomite (CaMg[CO3]2) is a common rock‐forming mineral. Nevertheless, its mechanisms of formation and the factors that cause dolomite concentration variations within the sedimentary records constitute long‐standing geochemical questions. In addition, the flux of Mg2+leaving the ocean by the formation of dolomite is a controversial question, with some studies arguing that dolomite formation is a negligible Mg2+sink in the modern ocean, while others show that it constitutes more than 50% of the total Mg2+removal rate. An important factor that impedes the resolution of the dolomite Mg2+flux is the lack of analytical methods with adequate precision and detection limit to directly measure minute quantities of authigenic dolomite in marine sediments. Here, we present a new analytical method for direct, precise measurement of dolomite content in marine sediments. The method is based on sequential leaching of carbonate minerals in acid and tracks the CO2emitted by the dissolution. Based on the measurement of gravimetric standards of calcite and dolomite, the method's detection limit and precision were determined as better than 0.2 and ± 0.2 dry wt% of dolomite, respectively. The method out‐performed dolomite quantification made by x‐ray diffraction and by inductive coupled plasma mass‐spectrometry, which provided precision of ± 2 and ± 1 dry wt%, respectively. Measurements of the dolomite content in modern sediments from the seafloor below the oligotrophic Eastern Mediterranean and the eutrophic Mississippi plume, and in clayey‐silty alluvial soil from south‐eastern Israel, demonstrated that the aforementioned precisions are also valid for natural samples.

SEASONAL VARIATIONS IN TURAG RIVER WATER ALKALINITY

Rivers in Bangladesh play a very important role in the life and economy of the country. Eventhough several key parameters of rivers are usually measured to adjudge the quality of rivers,alkalinity has been neglected in the routine measurement of river parameters. Alkalinity levels areimportant because they buffer acidic rain and acidic wastes and high alkalinity in river water cancause the change in the dynamics of chemical processes in the rivers. This paper reports theseasonal changes in the alkalinity of Turag, a commercially important river in Bangladesh on thebanks of the capital Dhaka. The results shows that overall alkalinity in the river is high due to thehigher level of bicarbonate contaminations and the discharge from industries including untreatedwastewater. There is no carbonate in water, but bicarbonate is very high specially at locations nearthe concrete and cement factories which opens up the possibility that the chemistry of urbanstreams is modified by the leaching of minerals from concrete infrastructure. This has far reachingconsequences for the amount of alkalinity in rivers and its potential impact on the environment.

Combining geophysical methods (DC, IP, TDEM and GPR) to characterise mining waste in the Linares-La Carolina district (southern Spain)

The accumulation of waste materials in old, abandoned mining districts without prior sealing of the substrate currently poses a significant risk of contamination to soils and surrounding waters. Some of these mining dams have undergone a reclamation and sealing process in recent years to alleviate this problem. The current study is an analysis of the effectiveness of using different geophysical techniques for characterising these structures and monitoring the isolation performed. This study was carried out in the old mining district of Linares-La Carolina (southern Spain). The following techniques were investigated in this study: direct current (DC) resistivity, induced polarization (IP), ground-penetrating radar (GPR) and the time domain electromagnetic method (TDEM).Combining DC and IP made it possible to characterise the internal structure of the abandoned mining dams, whereby the geometry of these deposits was determined and the corresponding potential risks were assessed. In addition, percolation zones of mining leachates were detected that indicate defects in the sealing stage.TDEM was a good complementary technique for calculating the depth of the bedrock on which the mining dam is located. GPR could only be used to investigate shallow depths at all of the antenna frequencies used (100, 250 and 500 MHz) but was useful for obtained detailed information about the last stages of filling and characterising the encapsulation performed during sealing.

Autogenous acid production using a regulated bio-oxidation method for economical recovery of REEs and critical metals from coal-based resources

Acid is a necessary component for the successful leaching of minerals containing REEs (rare earth elements) and other sources. Pyrite (FeS2), which is present in REE containing minerals, can be used to produce acid. Pyrite is utilized as a source to create ferric sulfate and sulfuric acid in the presence of A. Ferroxidans. Such microorganism-based bio-oxidation necessitates the establishment of optimal conditions for continual acid production. For efficient acid generation, additional optimization was done by varying residence time, solid percentage, and airflow rate. A step-by-step analysis and associated details are offered in this work, which used pyrite to create acid for leaching. For the bio-oxidation of pyrite with varying purity, an automated bioreactor was used. Scanning electron microscopy with energy-dispersive X-ray spectroscopy was used to examine the morphology and elemental content of bioleaching sediments. Eh and pH measurements were continuously done to ensure healthy operation of the bioreactors. The analysis suggested that, the Eh value in the range of ∼ 640–680 mV, pH range of ∼ 1.3–1.5 and residence time of 4–6 days with 6% solid feed are favorable conditions of operation.

Multiple fluid flow events and diversity of hydrothermal minerals in Neoproterozoic to lower Paleozoic carbonate reservoirs, Tarim Basin, NW China

• Two stages of hydrothermal events account for carbonate-hosted mineralization . • Quartz precipitated from silica-rich fluids from the Precambrian sandstone layers. • Saddle dolomite, fluorite and calcite formed in the Cambrian shale-derived fluids. • The same parent fluid could precipitate different minerals in differing host rocks. • Basal sandstones do not always act as lateral conduits for hydrothermal fluids . Contrasting mineral assemblages have been frequently found in Neoproterozoic-lower Paleozoic carbonate reservoirs along high-angle faults in the Tarim Basin. However, the reason for the change in mineral types over time is poorly constrained. Field and petrographic observations, fluid inclusion microthermometry, rare earth element (REE) and C, O and Sr isotope analyses are used to constrain the changes in water chemistry and fluid flow during the development of the mineral assemblages. During the Middle Devonian-early Carboniferous, the flux of hydrothermal fluids from Neoproterozoic sandstone layers, linked to the activity of NE–SW-trending strike-slip faults, resulted in extensive silicification. The silica-bearing fluids were hot (128.1–209.4 °C), saline (17.1–21 wt% NaCl eq.) and enriched in radiogenic strontium and showed no link to large-scale petroleum migration. During the Permian, a regional thermal anomaly induced the expulsion of hydrocarbon-bearing hydrothermal fluids from lower Cambrian shales, where Mg 2+ , 87 Sr and F − were derived via the transformation and leaching of clay minerals. A more significant in situ source of Mg 2+ was the dolostone interval, as the migrating fluids contributed to the precipitation of saddle dolomite with high T h values (82–176.4 °C) and salinities (15–21.4 wt% NaCl eq.), negative δ 18 O values and radiogenic Sr compositions. The succession of saddle dolomite followed by fluorite with similar T h values, salinities and 87 Sr/ 86 Sr ratios indicates a Mg 2+ deficit and increased dissolved calcium activity in the same parent fluid system, which facilitated the breakdown of MgF − and combination of Ca 2+ and F − . Subsequently, cooling and desalination of the hydrothermal fluids occurred, which was induced by the infiltration and mixing of meteoric water related to the compression and uplift of the north-western flank of the Tarim block. These processes resulted in the precipitation of milky white calcite (Cal 1) with similar oxygen and strontium isotope compositions but wider ranges of T h (82.1–154 °C) and salinity (3.4–16.9 wt% NaCl eq.) than those of the saddle dolomite and fluorite. The lateral flow of hydrothermal fluids through suitable layers, such as bed interfaces, permeable aquifers and karstic units, facilitated the formation of stratabound mineral deposits away from the feeding faults. The termination of hydrothermal mineralization was marked by the precipitation of brown calcite (Cal 2), whose meteoric origin has been proven by the combination of its reddish staining, oscillatory luminescent zonation and low δ 18 O values. This integrated study approach improves the understanding of the diversity of exotic mineral assemblages in carbonate hosts and the evolution and migration of hydrothermal fluids connected to late Paleozoic tectonism.

A review of the influence of blast fragmentation on downstream processing of metal ores

Rock fragmentation is one of the most commonly optimized blasting outcomes due to its significant influence on the efficiency of downstream operations. This paper reviews the influence of blast fragmentation on processing of metal ores. Two aspects of rock fragmentation that influence downstream mineral processing operations include the particle size of the run-of-mine ore and the degree of internal microfracturing in the fragments induced by blasting. The main influences identified include productivity of comminution equipment, energy consumption in comminution equipment and mineral recovery. An increase in blasting energy results in higher throughput and energy reduction in comminution circuits. Increase in blasting energy results in energy savings in the overall mining operations. However, when increasing the blasting energy, the environmental and safety impacts must be taken into consideration. Blast-induced microfractures increase the permeability of the fragments, therefore enhancing mineral exposure to leaching reagents and consequently may lead to higher mineral recoveries, particularly in heap and dump leaching operations which employ-one-stage comminution. However, the textural characteristics of the ore also influence the mineral recovery. Further research should focus on establishing the relationship between blast intensity and mineral leaching recovery for metal ores of different textural properties.

Enhancement of the photoelectrochemical production of hydrogen peroxide under intermittent light supply in the presence of an optimized biochar supercapacitor

A photocatalytic fuel cell has been used to convert light into electricity and photoelectrochemically produce hydrogen peroxide by reduction of atmospheric oxygen. An energy storage functionality was added to this cell by introducing a supercapacitor electrode functioning with the cell electrolyte. When the cell was operated with intermittent light supply, hydrogen peroxide production was much smaller than under continuous illumination; however in the presence of the supercapacitor, hydrogen peroxide production was substantially larger demonstrating the energy storage functionality and its importance in practical applications. The supercapacitor electrode was loaded with a biochar obtained by pyrolysis of spent malt rootlets under limited oxygen supply. The biochar was further subjected into mild treatment by boiling a biochar suspension in pure or alkaline water. Both untreated and mild-treated biochar was extensively characterized by several techniques. It was shown that even mild treatment can lead to substantial leaching of minerals and part of the organic residues giving materials with much larger specific surface resulting in higher supercapacitance values.

Glycine leaching kinetics of chalcocite in alkaline medium in the presence of hydrogen peroxide

The leaching of copper-containing raw materials with environmentally friendly reagents under near-environmental conditions is an important problem of modern hydrometallurgy. In this regard this article presents kinetic regularities of leaching of sulfide mineral – chalcocite (Cu2S) using the simplest amino acid – glycine (Gly) in alkaline medium at 25 ºС. It is assumed that the leaching is mainly due to complexation of copper (II) glycinates. The influence of different parameters on the amino acid leaching process such as concentrations of glycine, sodium hydroxide, hydrogen peroxide, reagent ratio and duration of the experiment were studied. The results of atomic absorption analysis indicated a significant increasing of copper recovery efficiency from chalcocite when the oxidant hydrogen peroxide was added to the alkaline glycine solution system. After 30 minutes the degree of copper recovery has reached 30.79 % in the system «Cu2S-0.1M Gly-0.1M NaOH-0.1M H2O2» while without hydrogen peroxide about 4 % of copper has been leached. The research results allow to recommend glycine as a promising reagent for hydrometallurgical copper production process.

Simulation of Simultaneous Leaching of Copper and Cobalt Minerals in Acid-Reductive Media: Sensitivity Analysis and Optimization

Simulation of Simultaneous Leaching of Copper and Cobalt Minerals in Acid-Reductive Media: Sensitivity Analysis and Optimization

Interaction of ferric ions with europium metal organic framework and application to mineral processing sensing

ABSTRACT Metal organic frameworks (MOFs) have numerous practical applications including hydrogen storage, drug delivery, separation processes and sensing. Sensing is particularly important in the mineral processing sector, where the success of mineral leaching processes depends upon the development of reliable and efficient methods for the detection of ferric ions (Fe). Here, we examine the atomic interactions between a hydrated ferric ion and an europium-based MOF with a view to the development of a sensing device capable of determining the ferric ion concentration in an analyte solution. Using a continuum approach together with the Lennard-Jones potential, we determine the Lennard-Jones (van der Waals) interaction energy and force between a hydrated ferric ion and a MOF pore. The hydrated ferric ion is modelled as a point at the centre of two concentric spheres, while the MOF pore is modelled by a semi-infinite cylinder. The model predicts that it is energetically more favourable for the hydrated ferric ion to reside inside the MOF pore and that the greatest attractive force is experienced at the entrance of the MOF pore. However, the hydrated ferric ion is unlikely to enter the MOF pore because it is geometrically larger than the free space inside. This means that in practice the hydrated ferric ion will remain on the surface of the MOF crystal, considerably simplifying ion removal. This property will be useful for washing and reusing the sensor.

Lithium isotope behavior under extreme tropical weathering: A case study of basalts from the Hainan Island, South China

Chemical weathering of silicate rocks (especially basalt) is an important sink of atmospheric carbon dioxide, and has an important impact on long-term carbon cycle and storage. Lithium (Li) isotopes have been regarded as a good tracer of chemical weathering, however, the behavior of Li isotopes in tropical settings is poorly understood. In this study, we studied the Li elemental and isotopic variation in the solid weathering products (soil and saprolite) from a highly-weathered (CIA ∼100%) basalt weathering profile (>15 m thick, including soil, saprolite, semi-weathered rock and fresh basalt) on the tropical Hainan Island in South China. The weathering products have 1.99–58.1 ppm Li, mostly below the average fresh basalt value (4.6 ppm, n = 5). The δ7Li values (−14.3 to 8.9‰) of the solid weathering products exhibit complex stratigraphic variation across the weathering profile. The Li and Mn enrichments coincide spatially, with the Mn-rich samples having the highest Li content and lowest δ7Li value. Lithium is enriched in the semi-weathered basalt sample, but its δ7Li value (−2.7‰) is close to that of fresh basalts (0.7–5.3‰, avg. 3.0‰, n = 5). Strontium isotope data show that the weathering profile is affected by marine aerosol input, and the marine strontium may have been leached to the profile bottom or out of it under extreme weathering. Sequential extraction results indicate that Li in the soil, saprolites (lower part), and semi-weathered basalt occurs mainly in the residual phase, while Li in the saprolites (middle part) occurs largely in Fe–Mn oxides. We suggest that Li isotope fractionation in the upper, middle and lower parts of the profile was controlled by, respectively, marine aerosol input and secondary mineral leaching, dissolution/re-precipitation of Fe–Mn oxides, and neoformation of secondary minerals from heavy pore water. Our results show that the preferential light Li isotope uptake by Fe–Mn oxides may have been the main cause for the major Li isotope fractionation in the Wenchang weathering profile.

Imaging acidic contaminants in a confined aquifer using electromagnetic geophysical method constrained by hydrochemical data

Acid in-situ uranium leach mining is an effective, popular technology for extracting uranium without large uranium mill tailings. However, acid in-situ leaching causes extremely high concentrations of acidic contaminants in aquifers. To represent the migration and range of acidic contaminant pollutants in confined aquifers, this study applied the controlled source audio-frequency magnetotellurics (CSAMT) method to a uranium mining area located in the Yili Basin, Xinjiang, northwest China. We collected ten CSAMT profiles from 364 sites with an average site interval of 20 m. The electrical resistivity model of the uranium mining area was obtained via two-dimensional inversion using CSAMT data, with 23 frequencies, ranging from 8192 Hz to 4 Hz. Combined with geological, geochemical, and well log data, this resistivity model was successfully used to identify the scale and position of acid contaminant plumes beneath the uranium mining area, which appear as electrically well-defined features that closely coincide with the distribution of sulfate and uranium ions in groundwater. With uranium mining activities ceasing, the scale of acid contaminant plumes has been reduced, owing to the natural attenuation of the aquifer or the contaminants well confined in the mining site. The low-permeability sandstone surrounding the aquifer was imaged as a resistive feature, which confines the contaminant plumes to the uranium mining area and slows the downstream migration of contaminants. According to the modified Archie's law, the porosity of the sandstone bearing uranium beneath the injection well zone increases, owing to acidification, while the porosity of the sandstone beneath the production well zone decreases, owing to pore plugging.