Acid Mine Drainage Research Articles

Predicting mine water inflow volumes using a decomposition-optimization algorithm-machine learning approach

Disasters caused by mine water inflows significantly threaten the safety of coal mining operations. Deep mining complicates the acquisition of hydrogeological parameters, the mechanics of water inrush, and the prediction of sudden changes in mine water inflow. Traditional models and singular machine learning approaches often fail to accurately forecast abrupt shifts in mine water inflows. This study introduces a novel coupled decomposition-optimization-deep learning model that integrates Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), Northern Goshawk Optimization (NGO), and Long Short-Term Memory (LSTM) networks. We evaluate three types of mine water inflow forecasting methods: a singular time series prediction model, a decomposition-prediction coupled model, and a decomposition-optimization-prediction coupled model, assessing their ability to capture sudden changes in data trends and their prediction accuracy. Results show that the singular prediction model is optimal with a sliding input step of 3 and a maximum of 400 epochs. Compared to the CEEMDAN-LSTM model, the CEEMDAN-NGO-LSTM model demonstrates superior performance in predicting local extreme shifts in mine water inflow volumes. Specifically, the CEEMDAN-NGO-LSTM model achieves scores of 96.578 in MAE, 1.471% in MAPE, 122.143 in RMSE, and 0.958 in NSE, representing average performance improvements of 44.950% and 19.400% over the LSTM model and CEEMDAN-LSTM model, respectively. Additionally, this model provides the most accurate predictions of mine water inflow volumes over the next five days. Therefore, the decomposition-optimization-prediction coupled model presents a novel technical solution for the safety monitoring of smart mines, offering significant theoretical and practical value for ensuring safe mining operations.

PENGARUH REVEGETASI TERHADAP SIFAT-SIFAT TANAH PADA LAHAN BEKAS TAMBANG TEMBAGA DI NUSA TENGGARA BARAT

Copper mining activities mainly using open-pit techniques, lead to environmental issues such as overburden waste in waste dump areas that have potential to generate acid mine drainage (AMD), which can decrease soil pH and increase heavy metal toxicity. Reclamation efforts, including revegetation using pioneer plants and cover crops are necessary to restore degraded land in waste dump areas. The aim of this research is to analyze soil physical and chemical properties improvement after revegetation on copper post-mining land as an evaluation and to provide recommendations for future reclamation. The research was carried out by analyzing and interpreting laboratory data from soil observations in revegetation areas for the 2016, 2018, 2019 and 2020 planting years, as well as natural forests belonging to PT. Amman Mineral Nusa Tenggara. Revegetation of copper post-mining land does not show a significant improvement in soil physical properties because improving physical properties takes quite a long time, especially in post-mining areas with heavy structural damage. Soil chemical properties analysis shows that revegetation can increase base saturation (BS), cation exchange capacity (CEC), exch-Ca, exch-Mg, and reduce soil Al saturation. In contrast, soil pH, organic-C, total-N, and soil available-P in the revegetation area did not increase as the revegetation age increased. The effect of revegetation appears to be more significant at the age of 2 to 3 years. However, based on the Tukey test, the age of revegetation mostly does not have a significant effect on enhancing soil chemical properties.

Characterization, potential valuable metals recovery and remediation of historic wolframite mining waste

The understanding of tungsten (W) mineral weathering and mobilization in nature remains limited due to W being a transition element with a wide range of oxidation states, which enables it to form a variety of complex chemical compounds. This study examined W mining waste at the abandoned Wolfram Camp mine in North Queensland, Australia, to address this gap. The mineralogical analysis showed the W tailings primarily consisted of silicates, including quartz, illite/mica, plagioclase, and K-Feldspar, with low WO3 content. Static acid mine drainage (AMD) tests indicated most tailings were non-acid forming, while groundwater samples exhibited acidification, with pH ranging from 3.8 to 5.2. The reprocessing trials using gravity separation and bioleaching demonstrated promising results, suggesting both techniques could effectively recover resource and decontaminate the mining waste. The gravity separation reprocessing test has successfully recovered 48.4% W from the tailings, with the resulting W concentrate achieving a 21.6% WO3 grade. On the other hand, the bioleaching reprocessing exhibited a remarkable 44-fold enrichment of W from the tailings, with 2.2% W in the AMD sediment. Synchrotron-based XFM/μ-XANES imaging analysis revealed significant wolframite weathering in reprocessed W concentrates. This study proposed a comprehensive approach, integrating environmental remediation and resource recovery technologies, to repurpose abandoned W mining waste. Passive treatment appears to be an economical option for remediating abandoned W mine sites. The findings provide valuable insights for sustainable W mining waste management and the rehabilitation of the abandoned Wolfram Camp W mine site.

Prediction technology of mine water inflow based on entropy weight method and multiple nonlinear regression theory and its application

Mine water inflow is an important basis for the formulation of mining plans and the utilization of groundwater resources. The mine water inflow is the result of the combined influence of many factors. The weight value of the influencing factors is calculated by the entropy method, and the order of importance of the factors is: precipitation > mining depth > cumulative mined-out area > aquifer thickness > mining area > mining height. The optimal univariate nonlinear regression model of mine water inflow to each influencing factor is obtained by factor scatter analysis and Matlab function programming. On this basis, combined with the weight values of factors, a multivariate nonlinear regression prediction model of mine water inflow based on weighting is innovatively established, which overcomes the defect that the traditional water inflow prediction method that cannot reflect the relative importance differences of various influencing factors. The multivariate weighted nonlinear regression model is used to predict the mine water inflow of typical coal mines, and the prediction results are compared with the linear regression model and the measured value. The results show that the prediction model of mine water inflow based on weighted multivariate nonlinear regression is accurate higher, with higher practical application value.

Green Transformation of Mining towards Energy Self-Sufficiency in a Circular Economy—A Case Study

This article presents the concept of green transformation of the coal mining sector. Pump stations that belong to Spółka Restrukturyzacji Kopalń S.A. (SRK S.A., Bytom, Poland) pump out approximately 100 million m3 of mine water annually. These pump stations protect neighboring mines and lower-lying areas from flooding and protect subsurface aquifers from contamination. The largest cost component of maintaining a pumping station is the expenditure for purchasing electricity. Investment towards renewable energy sources will reduce the environmental footprint of pumping station operation by reducing greenhouse gas emissions. The concept of liquidation of an exemplary mining site in the context of a circular economy by proposing the development/revitalization of a coal mine site is presented. This concept involves the construction of a complex consisting of photovoltaic farms combined with efficient energy storage in the form of green hydrogen produced by water electrolysis. For this purpose, the potential of liquidated mining sites will be utilized, including the use of pumped mine wastewater. This article is conceptual. In order to reach the stated objective, a body of literature and legal regulations was analyzed, and an empirical study was conducted. Various scenarios for the operation of mine pumping stations have been proposed. The options presented provide full or nearly full energy self-sufficiency of the proposed pumping station operation concept. The effect of applying any option for upgrading the pumping station could result in the creation of jobs that are alternatives to mining jobs and a guarantee of efficient asset management.

Harnessing phosphate limestone waste as a cost-effective solution for acid mine drainage treatment

Mining mineral ores like pyrrhotite often generates positive and negative outcomes for the community. On the one hand these valuable minerals are explored to provide economic opportunities. On the other, mining pyrrhotite presents adverse environmental and health effects that relates to acid mine drainage (AMD) formation in abandoned mines. This suggest that the sustainable mining of valuable minerals in Pyrrhotite requires cost and environmentally friendly approaches. In this research, we simulate in-situ neutralisation effect of phosphate limestone waste (PLW) on AMD from two mining sites in Morocco under continuous oxic conditions. To this end, we conducted batch tests to assess the effectiveness of PLW in mitigating AMD and releasing contaminants. These tests involved reacting limestone particles (at two sizes: <2 cm and < 4 cm) with AMD leachates over a five-day period The results indicated that the AMD is characterised by a pH of 2.5 and an electrical conductivity of 11.8 mS/cm. The inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses showed a high sulfate concentration of 3668.83 mg/L and the presence of some metals, notably copper, aluminium, and iron. The neutralisation process of the AMD using PLW under oxic conditions was highlighted by the variation in pH while the water was in contact with the PLW. The pH rose from 2.5 to 5.25 while the electrical conductivity decreased from 11.8 to 7.03 mS/cm. During the treatment of the AMD with PLW, the percentage of sulfate removal from the effluent was 35 %. In addition, iron and aluminium were significantly removed from the AMD with a percentage of 99 % in the leachate. Therefore, these results indicate that neutralising AMD using this passive treatment approach is effective and may serve as a cost-effective mitigation for AMD, since no excessive grinding is required for the PLW.

Integration of layer-by-layer hollow-fibre nanofiltration membranes and crystallization for water reclamation and resource recovery from acidic mine waters

Water pollution remains a critical issue in the global mining industry. Moreover, the access to a reliable source of raw materials such as Cu, Zn, Mg and Rare Earth Elements has become a challenge for the European Union. In this context, the treatment of Acidic Mine Waters (AMW) with a circular perspective can be a solution to both challenges. This study focused on the integration of crystallization processes and nanofiltration (NF) to selectively recover Mg(OH)2(s) and reclaim AMW for irrigation purposes from the Aznalcóllar open-pit (1629 mg/L Mg2+, 360 mg/L Ca2+ and 10,962 mg/L SO42−). The pre-treatment, involving selective precipitation, attained removals higher than 95 % of transitions elements. Different concentrations of NaOH (0.16 M, 0.25 M, 0.5 M) were used for the crystallization of Mg(OH)2(s), affecting the morphology and content of the final product. The removal of Ca2+ was performed by the addition of NaHCO3 at constant pH, achieving Ca removals of 99 %. The remaining salinity removal was achieved using a layer-by-layer hollow-fibre NF membrane, resulting to rejections higher than 80 % for Ca2+, SO42−, and Na+. The obtained results demonstrate that the combined crystallization and NF stages is a feasible approach for the efficient treatment and water reclamation of AMW.

GIS analysis for the selection of optimal sites for mine water geothermal energy application: a case study of Scotland's mining regions

Water within flooded coal mines can be abstracted via boreholes or shafts, where heat can be extracted from (or rejected to) it to satisfy surface heating (or cooling) demands. Following use, water can be reinjected into the mine workings or discharged to a surface water receptor. Four criteria have been applied, using ArcGIS, to datasets describing mine workings and mine water below the Midland Valley of Scotland to provide an initial screening tool for suitability for mine water geothermal energy exploitation. The criteria are: (i) the presence of two or more worked coal seams below site; (ii) the absence of potentially unstable shallow (&lt;30 m) workings; (iii) a depth to mine water piezometric head of less than 60 m; and (iv) a depth of coal mine workings of less than 250 m. The result is the Mine Water Geothermal Resource Atlas for Scotland (MiRAS). MiRAS suggests that a total area of 370 km 2 is ‘optimal’ for mine water geothermal development across 19 local authority areas, with greatest coverage in North Lanarkshire. This result should not be taken to suggest that mine water geothermal potential does not exist at locations outside the identified ‘optimal’ footprint. The MiRAS does not preclude the necessity for specialist engineering and geological input during a full feasibility study.

Research on the influence of major ions in weakly alkaline mine water on anchor cable corrosion and protection technique

Anchor cables in water-rich roadways frequently experience severe corrosion and resultant fractures due to the combined effects of mine water and high stress. However, the precise factors influencing corrosion on these cables remain ambiguous, presenting challenges to roadway support safety. This study investigated the impact of major ions present in weakly alkaline mine water on anchor cable corrosion using salt spray corrosion experiments. The results indicated that major anions such as Cl- notably influence anchor cable corrosion, which primarily manifested as pitting corrosion. The nominal yield strength decreased by 95.68–156.01 MPa, and the nominal tensile strength decreased by 133.44–202.77 MPa because of a decrease in the cross-sectional area. During the corrosion process, major anions such as Cl- continuously degraded the passivation film on the surface of the anchor cable, exposing its internal metal structure and exacerbating corrosion until eventual fracture failure occurred. Therefore, this paper proposes a corrosion protection technique for mine anchor cables to realize superior protective effects compared to conventional anchor cables used concurrently in field applications.

Efficient Copper Extraction from Industrial Dilute Solutions Using Air-Assisted Solvent Extraction

ABSTRACT The growing demand for valuable metals in recent decades has heightened the economic significance of extracting them from dilute solutions. This research carefully assesses the extraction efficiency of the air-assisted solvent extraction (AASX) process for effectively recovering copper from industrial dilute solutions, such as the raffinate of the solvent extraction (SX) plant and heap leach solutions. The results clearly showed that increasing the frother dosage to 50 mg/L improved the Cu extraction from 83.5% to 90.2%, but increasing the frother dosage beyond 50 mg/L did not change this response significantly. Although varying the extractant concentration and silicone oil dosage in the studied range did not affect Cu extraction, it noticeably led to an increase in the barrier metals recovery. Furthermore, a nine-step AASX system was applied to comprehensively evaluate the extraction efficiency of Cu from dilute heap leach solution. Moreover, an impressive 95.1% of Cu recovery (from a solution containing 890 mg/L Cu, 12.32 g/L Fe, 2.64 g/L Zn, and 4.1 g/L Mn) was achieved with selectivity ratios of 149.6, 153.0, and 93.5, for Cu/Fe, Cu/Zn, Cu/Mn, respectively. It could be concluded that the AASX process is an efficient and promising method for extracting Cu from industrial dilute solutions derived from secondary resources, low-grade ores, and acid mine drainages.

Characterization and stable isotopic fingerprinting of mine seepage in hyperarid environments: An example of the Namib Lead & Zinc mine, Namibia

Mine drainage at the Namib Lead & Zinc mine in the hyperarid environment of the Namib Desert close to Swakopmund, Namibia, has been investigated using mineralogical, hydrochemical, and isotopic methods. The principal ore minerals are galena and sphalerite. Mine drainage is neutral due to the reactions with the marble gangue rock. Mine water seepage is of the Na-Ca-Cl-SO4 type and sources of dissolved ions are likely halite and gypsum in the unsaturated zone above the mine. Concentrations of dissolved metals are relatively low, and the principal attenuation mechanism of metals is probably their adsorption on ferric minerals because equilibrium of the seepage water with secondary minerals that host the metals is not attained. Based on strongly enriched δ2H (up to 13.27 ‰) and δ18O (up to 4.5 ‰) values, seepage water originates from advective fog and is strongly evaporated after the fog deposition. The high δ13C(DIC) values indicate equilibrium with carbonates and CO2 de-gassing. The δ34S(SO4) values are enriched in shallower depths, probably because of pedogenic gypsum dissolution and then the δ34S values decrease with depth, probably due to the increasing input of sulfur from sulfides. Mine drainage at the Namib Lead & Zinc mine does not represent any risk for the environment due to its neutral character and relatively low seepage water volumes caused by high degree of aridity.

Acid Mine Drainage Precipitates from Mining Effluents as Adsorbents of Organic Pollutants for Water Treatment.

Acid mine drainage (AMD) is one of the main environmental problems associated with mining activity, whether the mine is operational or abandoned. In this work, several precipitates from this mine drainage generated by the oxidation of sulfide minerals, when exposed to weathering, were used as adsorbents. Such AMD precipitates from abandoned Portuguese mines (AGO, AGO-1, CF, and V9) were compared with two raw materials from Morocco (ClayMA and pyrophyllite) in terms of their efficiency in wastewater treatment. Different analytical techniques, such as XRD diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), N2 adsorption isotherms, and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) were used to characterize these natural materials. The adsorption properties were studied by optimizing different experimental factors, such as type of adsorbent, adsorbent mass, and dye concentration by the Box-Behnken Design model, using methylene blue (MB) and crystal violet (CV) compounds as organic pollutants. The obtained kinetic data were examined using the pseudo-first and pseudo-second order equations, and the equilibrium adsorption data were studied using the Freundlich and Langmuir models. The adsorption behavior of the different adsorbents was perfectly fitted by the pseudo-second order kinetic model and the Langmuir isotherm. The most efficient adsorbent for both dyes was AGO-1 due to the presence of the cellulose molecules, with qm equal to 40.5 and 16.0 mg/g for CV and MB, respectively. This study confirms the possibility of employing AMD precipitates to adsorb organic pollutants in water, providing valuable information for developing future affordable solutions to reduce the wastes associated with mining activity.

Sensitivity of ordinary rock weathering tests to acid rock drainage

Sensitivity of ordinary rock weathering tests to acid rock drainage

Effect of acid mine drainage on the mechanical properties of AISI 1020 carbon steel and AW6060 aluminium

Acid mine drainage severely affects metallic materials due to the high acidity and oxidising capacity of these lixiviates. A study was carried out to evaluate the time evolution of the mechanical properties of AISI 1020 carbon steel and AW6060 aluminium in contact with acid mine drainage. Weight loss, fatigue and tensile strength were evaluated in two different scenarios, one involving erosion corrosion (dynamic scenario) and the other involving chemical corrosion only (static scenario). Over 80 days of exposure in a static scenario, weight loss is almost 2% for aluminium and 0.5% for steel, fatigue strength is reduced by 28% for steel and ultimate tensile strength is reduced by almost 5% for aluminium and by 2.5% for steel. In a dynamic scenario, the weight loss after 4 days of exposure is 30–35% for both materials, the fatigue strength is reduced by almost 50% for steel, the ultimate tensile strength is reduced by 33% for aluminium and by almost 5% for steel. Acid drainage causes an increase in brittleness and a decrease in stiffness of these materials, much more rapidly in a dynamic environment favoured by the effects of erosion corrosion.

Interplay between denitrifying and sulfate-reducing bacterial communities under acid mine drainage stress

Acid mine drainage (AMD) pollution leads to the enrichment of sulfate in paddy soil. The interplay between denitrifying and sulfate-reducing bacteria across varying soil depths, and their response to AMD pollution is not yet fully understood. The responses of denitrifying and sulfate-reducing bacteria(SRB) to AMD pollution were analyzed by collecting soil samples at four depths (0–10 cm, 10–20 cm, 20–40 cm, 40–60 cm) under two treatments (AMD-polluted and control soil). AMD pollution resulted in a significant decrease in pH value, elevated SO42- and metal concentrations. Compared to the control soil, denitrifying and sulfate-reducing bacteria in AMD-polluted soils were more sensitive to environmental fluctuations. Co-occurrence analysis revealed that there were more microbiological linkages and nodes in control soil than in polluted soil. Denitrifying and sulfate-reducing bacteria can maintain part of N and S cycle under long-term AMD pollution by increasing the negative correlation in ecological network. Desulfobacca exhibited a positive correlation with nitrate and held a significant position in the symbiotic network, suggesting its potential important role in inhibiting nitrogen loss. This study revealed the intricate ecological network of functional communities, which could have important implications for environmental management and the development of sustainable agricultural practices in areas affected by AMD pollution.

The influence of exploration activities of a potential lithium mine to the environment in Western Serbia

The proposed exploitation of the Jadar Valley lithium/borate deposit in Serbia, by the Rio Tinto Corporation, indicates that it would become large-scale processing of boron- and lithium-containing ore. It would be one of the world’s very first lithium mines in populated and agricultural area. The company claims that the envisioned mining will be in accordance with environmental protection requirements. The Jadar Valley deposits have been claimed to cover 90% of Europe’s current lithium needs. Yet, local opposition to the mining has arisen due to potential devastating impacts on groundwater, soil, water usage, biodiversity loss, and waste accumulation. Research drilling by the mining company has already produced environmental damage, with mine water containing high levels of boron leaking from exploratory wells and causing crops to dry out. Furthermore, our investigations reveal substantially elevated downstream concentrations of boron, arsenic, and lithium in nearby rivers as compared to upstream regions. Additionally, here we show that soil samples exhibit repeated breaches of remediation limit values with environmental consequences on both surface and underground waters. With the opening of the mine, problems will be multiplied by the tailings pond, mine wastewater, noise, air pollution, and light pollution, endangering the lives of numerous local communities and destroying their freshwater sources, agricultural land, livestock, and assets.

Optimalisasi Penggunaan Fly Ash Untuk Reduksi Kadar Besi (Fe) Dan Mangan (Mn) Serta Peningkatan pH Dalam Air Asam Tambang

Coal mining activities often result in acid mine drainage (AMD), which can cause environmental pollution if not properly managed. This study aims to evaluate the potential use of fly ash from the Stream Power Plant (PLTU) Tenggarong to mitigate the impacts of AMD, specifically targeting iron (Fe), manganese (Mn), and pH parameters. Acid Mine drainage is formed when sulfide minerals oxidize, producing acidic compounds that can harm the environment. This research focuses on analyzing the ability of fly ash to adsorb iron and manganese from AMD solutions, as well its capability to increase solution pH. Based on the conducted research, the optimum pH value was achieved when using 10 grams and 15 grams of fly ash in the adsorption process. The optimum concentration of iron (Fe) was attained using 10 grams to 15 grams of fly ash, while for manganese (Mn), it was achieved with 20 grams to 25 grams of fly ash. The adsorption process using 25 grams of fly ash showed the highest efficiency in reducing iron (Fe) concentration by 93.78 % and manganese (Mn) concentration by 75.47 %.

How environmentally friendly are electric cars? The relationship between lithium usage and water resources, Chile example

AbstractThe extraction of minerals such as lithium, widely used in the battery technologies of electric vehicles, is a process that necessitates consideration of its environmental impacts. This study aims to examine the environmental impacts of electric vehicles and the effects of lithium mining on water resources, particularly in regions abundant in lithium reserves like Chile. The analyses indicate a long‐term relationship between lithium mining and irrigation water sources. This study establishes a foundation for understanding the relationship between the environmental sustainability of electric vehicles and the environmental impacts of lithium mining.

Principles and Optimization of China’s Unconventional Water Management: From a Brand-New Perspective of Responsibility Allocation

Unconventional water includes reclaimed water, harvested rainwater, desalinated seawater, and mine water. Unconventional water use is considered more of a “mandatory responsibility” in China. The initial allocation of unconventional water emphasizes quantity-centered responsibility allocation while the minimum utilization reflects this responsibility. The unconventional water use responsibility (UWUR) should be tailored to the characteristics of each area, moving away from a ‘more is better’ mindset. However, there is a large research gap in this field. This paper first presented six fundamental principles for unconventional water allocation. Ensuring fairness in allocation involves aligning the allocated amount with urban water usage characteristics. Hence, based on four key features, this paper integrated various socioeconomic and environmental factors to build an initial allocation model. To enhance efficiency, an optimal allocation model was constructed using the zero-sum gains–data envelopment analysis (ZSG-DEA) method. The models were then applied to Jiangsu Province, China, to verify their applicability. The results showed that the projected minimum UWUR allocation (unit: 100 million m3) for each city in 2025 is 1.482 (Nanjing), 1.501 (Wuxi), 0.919 (Xuzhou), 1.029 (Changzhou), 2.977 (Suzhou), 1.497 (Nantong), 0.818 (Lianyungang), 0.766 (Huai’an), 0.875 (Yancheng), 0.920 (Yangzhou), 0.790 (Zhenjiang), 0.858 (Taizhou), and 0.766 (Suqian). The rational and feasible results indicated that the allocation framework proposed in this paper has a certain practicability. Lastly, this paper considered the differences in unconventional water utilization conditions across 13 cities and proposed corresponding measures to improve the utilization. This paper represents a tentative exploration of unconventional water allocation in China and offers theoretical and practical insights for policy-makers to improve territorial spatial planning and sustainable water management.

Association of rare earth elements with secondary mineral phases formed during alkalinization of acid mine drainage

Rare Earth Elements (REE) are present in acid mine drainage (AMD) in micromolar concentrations and AMD discharge may lead to an environmental risk. Alkaline Passive Treatment Systems (PTS) are often used to treat AMD and trap toxic trace elements. This study was set up to identify mechanisms by which REE are trapped in or on secondary phases formed in a PTS. Batch alkalinization experiments were performed to simulate PTS by sequentially increasing the pH of AMD collected from the Tharsis mining area inside the Iberian Pyrite Belt and synthetic AMD water samples via CaCO3 addition. The solids that precipitated up to pH ~4 and between pH 4–6 were collected and characterized by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) in combination with Scanning Electron Microscope/Energy Dispersive X-ray spectroscopy (SEM/EDX) and synchrotron-based X-ray Absorption Spectroscopy (XAS) and synchrotron-based Micro-X-ray Fluorescence (μ-XRF). Results reveal that REE are mostly scavenged between pH 4–6 in association with Al and Fe phases, whereas a smaller fraction is scavenged at pH ~4 by association with gypsum. Synchrotron-based analysis evidences the incorporation of La3+ into the gypsum structure by substituting Ca2+, indicating a co-precipitation mechanism with gypsum occurring mainly at low pH. Results from parallel adsorption and co-precipitation tests suggest that the REE scavenging between pH 4–6 could be due to a combination of adsorption and co-precipitation on Al(OH)3 and ferrihydrite. This implies that in PTS, REE would be mainly found in Al- (and Fe-) oxyhydroxides occurring in deeper layers of the PTS, i.e., where higher pH-values occur, though a small fraction, especially the light REE, could also be found incorporated into gypsum in the upper layers.