Mine Water and the Environment

Kleinmann, Robert

doi: 10.1007/s10230-023-00940-8pmid: N/A

Earley, Drummond

doi: 10.1007/s10230-023-00931-9pmid: N/A

Natural and artificial sorption of arsenic on iron hydroxides is one of the most important reactions controlling arsenic mobility in mine water and other water resource systems. Thermodynamic equilibrium modeling can be used to design and optimize water treatment systems as arsenic sorption is a function of speciation, dose, pH, Eh, and water composition. However, the effects of temperature on arsenic treatment systems have not been extensively considered in mine water quality investigations and treatment designs. Laboratory and field studies have shown that adsorption of arsenic oxyanions onto iron hydroxide particles is endothermic and the equilibrium concentration of arsenic in water is lower at higher temperatures and higher at lower temperatures. Data from two field sites are presented to investigate the effect temperature has on arsenic treatment. At a site in Canada, ferric sulfate coagulation is used to treat arsenic in tailings contact water when not frozen. The dosage of ferric sulfate is held constant but is much less efficient during spring thaw than in the summer. Thermodynamic modeling shows that the dosage must be increased in the spring to meet discharge water quality standards because the sorption equilibrium constant is temperature dependent. At another site in the Rocky Mountains of the USA, the USGS studied and modeled passive treatment of arsenic and other contaminants in AMD-affected stream flows without including temperature dependent sorption. Thermodynamic modeling was used to reexamine the effect of temperature on arsenic sorption onto iron hydroxide precipitates.

Liu, Weitao; Han, Mengke

doi: 10.1007/s10230-023-00932-8pmid: N/A

Predicting floor water inrush has become increasingly challenging as coal is being mined at greater depths. We established a practical predictive method using a hybrid artificial intelligence (AI) model and geographic information system (GIS) techniques. The hybrid model is a classifier that mixes a back propagation neural network (BPNN) with an adaptive boosting algorithm (AdaBoost). To assess the effectiveness of the model, 33 borehole data points with known water inrush results in the Yangcheng coal mine were used as data samples to train and test the model. The outcomes demonstrated a predictive accuracy of 100%, far exceeding the accuracy and stability of the BPNN classifier alone using the same parameters. Then, GIS techniques were used to extend the approach throughout the mining region; the greatest risk was shown to be in the middle of the area. Given the limited data set, errors may exist in extending the risk predictions for the entire mining area, so more data needs to be collected to ensure the accuracy of subsequent predictions. Still, we believe that the methods and steps adopted in this study can be used to create practical predictive models in different mining regions.

Suliartini, Ni Made Sri; Joll, Cynthia A.; Douglas, Grant B.

doi: 10.1007/s10230-023-00934-6pmid: N/A

Uncontrolled release of acid mine drainage (AMD) causes widespread detrimental impacts on the receiving environment. Thus, effective treatment to neutralise AMD effluent pH and capture a suite of metals is required. In-situ hydrotalcite (HTC) precipitation is an emerging technology for AMD remediation. HTC has an inherent capacity to accommodate a range of cations and anions during in situ formation, offering a method of broad-spectrum contaminant removal. This study explored the feasibility of using seawater as an Mg source and synthetic AMD in HTC formation. The HTC was formed from a stoichiometric combination of synthetic AMD and seawater. While three initial stoichiometric M2+:M3+ ratios of 2:1, 3:1, and 4:1 were investigated, only HTC with an M2+:M3+ ratio of 2:1 was generated, as confirmed by both mineralogical and geochemical analyses. Importantly, the HTC was demonstrated to effectively remove a suite of metals present in AMD such as Cu, Zn, Al, and Mn with removal rates of between 99.97 to 99.99%. The HTC precipitate contained ≈6.6% Cu and 4.1% Zn, and thus shows the potential, if required, for future metal recovery. Since submarine placement is often used in metal mining and processing operations proximal to the coast, the stability of the HTC precipitate in seawater was also investigated. Importantly, only 0.2% of the Cu and 1.1% of the Zn within the HTC were subsequently leaching in decreasing increments into seawater over 30 days with decreasing increments after the initial seven days. This indicates robust element retention and confirms the potential of HTC for AMD remediation with direct submarine placement.

Wang, Yang; Wu, Yonghui; Ge, Qin; Pu, Zhiguo; Liu, Jinhui; Zhang, Yanhong; Xie, Xiangjian

doi: 10.1007/s10230-023-00930-wpmid: N/A

To solve various extraction-related problems existing in the deep Jurassic mines in the Inner Mongolia-Shaanxi (IM-S) mining area, this paper puts forward a method to control roof water hazards based on the sedimentary facies pattern of the aquifers. The problems we addressed are: high volumes of goaf water, mixing of coal-based water in the stope, the proximity of the upper coal seam to water-enriched aquifers, and the inability for safe excavation and stoping. We first investigated the spatial distribution patterns of the aquifers and their related storage properties. A zone model of water yield compatible with the hydrogeological characteristics of a deep Jurassic mine was evaluated for the aquifers in the roof of the 3–1 coal mine, and a “low-position and lateral interception” control method was proposed based on the water yield zonation. The results demonstrated that the depositional environment for the sandstone aquifer in the first member of the Zhiluo Formation had a channel bar paleoenvironment that was characterized by a varying water table. This proved to be the key layer for preventing and controlling the water hazards. The method described in this paper effectively mitigated the water hazards associated with that aquifer in the study area and thus provide a theoretical and practical basis for controlling mine water hazards in the IM-S mining area.

Yao, Qiangling; Yu, Liqiang; Shan, Changhao; Xia, Ze; Chen, Ning; Xie, Hongxin; Zhu, Liu

doi: 10.1007/s10230-023-00933-7pmid: N/A

The stability, design, and evaluation of coal-pillar dams are affected by how water and mining affect the mechanical performance and failure mode of coal. We analyzed the composition and water-absorption mechanisms of coal samples taken from the Chahasu coal mine in western China by x-ray diffraction and nondestructive water-soaking tests. Uniaxial compression tests were carried out on coal samples with different moisture contents and loading rates to investigate their mechanical properties and deformation damage characteristics while monitoring the acoustic emissions. The compressive strength and modulus of elasticity decreased with increased moisture content, with maximum attenuations of 50.3% and 42.4%, respectively. Increasing the loading rate caused the compressive strength and elastic modulus to first increase and then decrease; the maximum increases were 74.2% and 82.5%. With low moisture content and low loading rate, the coal samples become brittle; the main failure mode was tensile failure. Increasing the moisture content enhanced the plasticity of the coal samples, leading to more shear cracks and a switch in failure mode from tensile failure to shear failure. The increased loading rate reduces the effect of water on coal samples and increases the tensile effect. High loading rates tend to produce conical failure features. Acoustic emission characteristics were used as the basis for classifying the stress stages of coal samples, which further supplements the analysis of the failure process of coal samples. Finally, the reference of this study to field engineering practice and its own limitations were analyzed. These results should help guide the design of stable underground hydraulic systems and advance our understanding of rock-fracture-failure mechanisms in a water-rich environment.

Bedoya-Gonzalez, Diego; Kessler, Timo; Rinder, Thomas; Hilberg, Sylke; Szabó-Krausz, Zsuzsanna; Schafmeister, Maria-Theresia

doi: 10.1007/s10230-023-00938-2pmid: N/A

We tested the suitability of the multiple interactive continua approach (MINC) to simulate reactive mass transport in a disturbed post-mining coal zone. To the authors’ knowledge, this approach has not been employed in such mining settings despite its relative success in other environmental fields. To this end, TOUGHREACT software was used to set up a MINC model of the unsaturated overburden of the Ibbenbüren Westfield. With it, we examined and evaluated water–rock interactions in both the fractured and porous continua as the main driver of elevated hydrogen, iron, sulfate, and chloride concentrations in the coal mine groundwater. Long and seasonal geochemical signatures were obtained by formulating and applying a five-stage modelling process that depicts the mining history of the area. The simulation results agree well with the concentrations and discharge trends measured in the mine drainage. Oxygen and meteoric water flow through the fractured continuum, leading to a high and steady release of hydrogen, iron, and sulfate ions derived from pyrite oxidation in the matrix continua closest to the fractures. Likewise, high chloride concentrations resulted from the mixing and gradual release of relatively immobile solutes in the matrix as they interacted with percolating water in the fracture. In both cases, the use of a multiple continua approach was essential to resolve sharp gradients for advection and faster kinetic reactions, while reducing the model’s dependence on block size for diffusive transport at the fracture–matrix interface. The model further allows for the calculation and analysis of solute exchange and transport in the unsaturated overburden resulting from rebound and imbibition processes, something pioneering when compared to other models in the field.

Flatley, Alissa; Rutherfurd, Ian

doi: 10.1007/s10230-023-00937-3pmid: N/A

The poor condition of river diversion channels can prevent mining companies from relinquishing their mine to the government after mining has ceased. Many regions lack a locally derived template for integrating appropriate geomorphic and hydraulic conditions from unmodified river channels into river diversion designs to help guide post-mining closure activities. Establishing baseline geomorphic reference criteria for unmodified catchments can guide restoration efforts to allow recovery and stability of the fluvial system. Design-wise, channels should be built so that flow conditions are able to move sediment, but not high enough to accelerate erosion in the channel. We used natural headwater channels to inform a regional guide for geomorphic criteria for artificial channels constructed in the Pilbara, Western Australia. We provide guideline hydraulic criteria for specific channel types, including velocity, stream power, and bed shear stress values for five key channel types: alluvial single thread (≥ cobble) and single thread (sand), bedrock/confined channel sections, island-barform channels, and heavily vegetated channels.

Mei, Aoshuang; Wu, Qiang; Zeng, Yifan; Cui, Yashuai; Zhao, Di

doi: 10.1007/s10230-023-00939-1pmid: N/A

The shallow groundwater of the Quaternary Salawusu Formation in China is distributed widely in the arid and semi-arid areas of northern Shaanxi and is an essential component of water supply and ecosystem maintenance there. To safely exploit the coal resources and protect the water resources, it is important to understand the impact of local high-intensity coal mining on such shallow groundwater. We used the “three maps—two predictions” method, the theory of equivalent mining height, and numerical simulations to evaluate the water inrush conditions for the 3–1 coal seam and to analyze the feasibility of backfill mining under the Qingcaojiegou and Hezegou Rivers. The results for the Jinjie coal mine showed that: part of the Quaternary porous phreatic aquifer and most of the J2z weathered-bedrock pore–fissure confined aquifer are high-risk areas in the connectivity zoning map; there are large areas of strong or relatively strong water-abundant areas in the 3–1 coal seam roof, and; large areas in the southwest, northwest, and northeast parts of the coalfield are in high- and low-risk areas and face a serious threat of roof water inrush. Overall, it should be feasible to mine under these rivers, using backfill mining to effectively reduce the height of the water-flowing fractured zone and amount of surface subsidence.

Milesi, V.; Declercq, J.; Harding, W.; Jarman, T.; Baas, O.; Saukkoriipi, J.; van Wageningen, A.; Bowell, R.

doi: 10.1007/s10230-023-00935-5pmid: N/A

Assessing the environmental impacts of underground mines requires that the mine water sources and the geochemical processes that alter their chemical composition be determined. At the Kittilä underground mine, located near the village of Kiistala in Finnish Lapland, we used chemical and water isotope composition to investigate the contribution of surface and deep water to the mine complex and the source of mine water chlorinity. 39 water samples were collected from surface facilities, rivers, groundwater sources, seeps and drill holes. Four types of water were identified based on chemical composition: a surficial Ca–Mg–HCO3-type water with low total dissolved solid (TDS) concentrations represented by river and ground waters; a shallow Ca–SO4-type groundwater represented by seeps, also called ‘mine water’; a deep Na–Cl ± SO4-type groundwater sampled from drill holes; and a deep high-Cl brine with a high deuterium enrichment, also collected from drill holes. Water samples from ponds and underground pumping stations highlight three different mixing processes between the: surficial meteoric low-TDS Ca-Mg-HCO3-type water and the mine water; mine water and the deep Na–Cl ± SO4-type groundwater and, to a lesser extent; surficial Ca–Mg–HCO3-type water and the deep Na–Cl ± SO4-type groundwater. In contrast, no evidence of mixing involving the deep high-Cl brines was identified, suggesting that it remains mostly isolated from the other water types. The hydrogen and oxygen isotope composition of the surficial Ca–Mg–HCO3-type water and the deep Na–Cl ± SO4-type groundwater, together with chemical evidence of mixing, suggests a possible genetic link between the two endmembers. This is consistent with the presence of the Kiistala shear zone facilitating infiltration by shallow meteoric water into the underlying rock mass and mineralized zone. The negative deuterium excess of the mine water concurrent to sulfate enrichment indicates that it forms from the mixing of surficial Ca–Mg–HCO3-type water and deep Na–Cl ± SO4-type groundwater that evolved through evaporation and sulfide oxidation. A mixing ratio of 80% of the surficial Ca–Mg–HCO3-type water and 20% of the deep Na–Cl ± SO4-type groundwater best explains the Cl concentration of the mine water. The linear relationship between the sulfate concentrations of the mine waters and its isotopic deviation from the Global Meteoric Water Line suggests a correlation between evaporation and sulfide oxidation at Kittilä, which could represent a new tool for the assessment of water–rock reactions.