Tailings Water Research Articles

Performance and microstructural characterization of fiber-reinforced cement-based grout incorporating waste tailing sand and fly ash

A fiber-reinforced cement and tailing sand-based grout (FRCTG) was proposed to improve the utilization of solid waste in construction. Different grout specimens were prepared using various proportions of ordinary Portland cement, iron tailing sand (ITS), fly ash (FA), basalt fibers (BFs), and water as raw materials. Used single-factor test, orthogonal test and artificial neural network model that provided a comparative analysis of the change in the rheological and mechanical properties of different grout mixes according to their component ratios. Furthermore, microscopic characterization techniques were used to reveal the intrinsic physicochemical mechanisms underlying the structural evolution of the considered grouting materials. The results indicate that ITS significantly increases the rheological properties of the grouting material. The maximum strength of the grouting material is achieved when the length of BF is 6 mm and the dosage is 0.2 %. An 8 % dosage of FA can effectively improve the rheological properties of the grouting material and enhance its flexural strength. Microscopic tests reveal that SiO2 in ITS exists in the form of quartz with low reactivity, thereby inhibiting the hydration reaction of the binder material. Different distribution patterns allow BF to serve both as reinforcement for the matrix and as a framework for hydration products, effectively enhancing the density between the BF and the surrounding matrix. The surface of FA is covered in layers by hydration products, forming a chain-like structure that improves bonding strength with the material. The results of this research offer a high-performance, low-cost, and environmentally friendly grouting material for construction grouting projects, which is of significant importance for promoting innovation in comprehensive utilization of solid waste.

Effect of surfactant and PAM on the settlement of kaolinite particles and its mechanism analysis

High concentrations of fine-grained clay minerals in tailings water are highly detrimental to environmental protection and water recycling. Using kaolinite as the study subject, this research investigates the effects of various cationic surfactants (DDA, DTAB, TTAB, CTAB) and flocculants (APAM, NPAM, CPAM) on the sedimentation of kaolinite particles. The study explores the impact of single agents, combined agents, and the sequence of their addition on kaolinite particle sedimentation. The results indicate that when using individual agents at low concentrations, CTAB outperforms TTAB, DTAB, and DDA, while APAM is more effective than NPAM and CPAM. The optimal performance is achieved with a CTAB concentration of 2×10<sup>-4</sup> mol/L and an APAM dosage of 20 mg/L. When combining agents, the best results are observed when CTAB is added before APAM. By fixing the APAM dosage at 20 mg/L and varying the CTAB concentration, the highest sedimentation rate and lowest turbidity are obtained at a CTAB concentration of 1.5×10<sup>-4</sup> mol/L. Mechanistic insights were obtained through aggregate imaging, area measurement, zeta potential testing, and contact angle testing. Cationic surfactants alter the surface properties of particles, reducing surface electronegativity and increasing hydrophobicity, which diminishes inter-particle repulsion and promotes aggregation, thereby reducing turbidity. Flocculants form larger flocs through adsorption and bridging, accelerating the sedimentation process. When flocculants and cationic surfactants are used together, the resulting flocs are more stable and larger, with an average floc area reaching 5017.6079 µm<sup>2</sup>, indicating a significant reduction in fine particles within the solution.

Experimental study on fiber-reinforced cement tailings sand-based grouting material preparation and factors influencing the grouting effect

To address the problem of permeation of tailings pond initial dams rockfill dams, fiber-reinforced cement tailings sand-based grouting (FRCTG) material, which can be used for rockfill dam reinforcement, was prepared by selecting ordinary portland cement (OPC), iron tailings sand (ITS), basalt fiber (BF), fly ash (FA) and water as the raw materials. Orthogonal tests were used to investigate the effects of the water-binder ratio (w/b) and material mass fraction on the rheological and mechanical properties of FRCTG and determine the optimum mixing ratio. Comparative analyses were performed of the grouting effect of FRCTG and pure OPC grouting materials based on concrete self-compacting tests and COMSOL simulations. Combined X-ray diffraction (XRD) and scanning electron microscopy-energy spectroscopy (SEM-EDS) microstructural characterization were used to reveal the factors influencing FRCTG mechanical properties. The results showed that when the water-binder ratio (w/b) was 0.5, ITS substitution percentage for OPC was 10 %, BF dosage was 0.2 %, BF length was 6 mm, and FA substitution percentage for OPC was 8 %, FRCTG had better rheological properties and flexural strength than pure OPC grouting materials. In addition, FRCTG self-compacting concrete also had stronger compressive strength and splitting strength. FRCTG showed a better filling capacity and diffusion effect, which preliminarily verified the feasibility of rockfill dam grouting. ITS inhibited the hydration reaction of the cementitious material and prolonged the setting time of the slurry. The interlocking structure formed by FA and hydration products indirectly enhanced the flexural strength of the grouting material. BF not only provided FRCTG reinforcement but also acted as the hydration product skeleton. FRCTG demonstrated better economic and environmental performance than traditional cement material while effectively utilizing ITS and FA solid waste.

Influence of filling materials on mechanical properties of fissured sandstone treated by tailings water

Fissured rocks deteriorate with increasing water content, and the mechanical behavior is significantly influenced by the filling materials within their fissures. Understanding the effects of tailings water on the mechanical properties and failure modes of rocks under different filling conditions is crucial for assessing the stability of tailings ponds. In this study, uniaxial compression tests were conducted on single-fissured sandstone filled with gypsum, cement, and epoxy resin at various immersion heights, and acoustic emission signals were monitored. The results indicate that the mechanical properties of sandstone deteriorate significantly upon immersion, but the rate of deterioration decreases with increasing immersion height. The use of stronger and more cohesive filling materials can improve the mechanical properties of fissured sandstone, but there remains a gap compared to intact samples. Differences in physical properties and uneven stress distribution between immersed and dry portions lead to the formation of complex crack networks in partially immersed samples. The strong bonding between epoxy resin and sandstone results in local stress exceeding the sandstone's bearing limit, leading to increased fragmentation. The acoustic emission activity generally exhibits a pattern of gradual increase, quiescence, and then activation. As the immersion height increases, the number of acoustic emission events and energy release decrease. The average frequency and rise angle analysis reveals that tensile cracks dominate the failure process. Near failure, the b-value drops sharply and exhibits intense fluctuations, accompanied by the emergence of numerous high-frequency signals. These phenomena provide a basis for predicting rock instability and failure.

Mechanical and acoustic characteristics of sandstone failure at different immersion heights under tailings water erosion conditions

To investigate the influence of tailings water immersion height on the failure process of rocks, intact yellow sandstone samples and yellow sandstone samples with prefabricated fissures were prepared. Uniaxial compression tests were conducted on these sandstone samples with varying immersion heights, and the failure processes were simultaneously monitored using a camera and an acoustic emission monitoring system. Based on the test results, the crack propagation and failure characteristics of the yellow sandstone samples under uniaxial loading at different immersion heights were determined. The relationships between the immersion height and peak strength and between the immersion height and elastic modulus were characterized. Additionally, the intrinsic connection between sandstone damage and acoustic emission signal parameters was revealed. The experimental results indicate that the uniaxial compressive strength and elastic modulus of the sandstone samples decrease continuously with increasing immersion height, but the rate of decrease gradually slows. The presence of water is the primary reason for the deterioration of mechanical properties, and the chemical components in the tailings water are significant factors that cannot be ignored. The initiation location and propagation of cracks in intact samples depend on the immersion height, while the fracture behaviour of fissured samples after immersion is mainly influenced by the prefabricated fissures. As the immersion height increases, the longitudinal wave velocity increases, while the number of acoustic emission events, peak frequency, and amplitude exhibit a decreasing trend that is initially rapid and then slows. A damage evolution model based on acoustic emission ringing counts at different immersion heights was established. It was also found that the acoustic emission signals of these yellow sandstone samples mainly show the characteristics of abrupt signals under any immersion water height.

Parameters of back filling material prepared from mine tailing, fly ash, and mine water

The article investigates the influence of mine tailing, fly ash, and mine water on strength parameters as mine paste filling material performing the strength tests on different recipes of mortar mixes with individual types of fillers and wastewater from extraction of mine tailings. Recipe is prepared in proportions corresponding to the standard mortar and compared with a reference recipe according to the fresh mortar consistency test using a shaking table according to ČSN EN 1015-3. Resulting measured values on 40 × 40 × 160 mm solids samples for which the evaluation of the volume weight was carried out in the range of 2, 7, 14, 28, 56 and 90 days according to EN 1015-10 (722400). The results showed that that it is possible to prepare relatively fluid mixtures with extremely low binder dosage. And not only the water coefficient but also the granulometry of the raw material plays an important role in the long-term strengths of samples.

Effects of Ca<sup>2+</sup>/Mg<sup>2+</sup> ions in recycled water on the reverse flotation properties of iron oxides

Water quality, particularly hardness, plays an important role in affecting the floatability of minerals as it interferes with the chemical/electro-chemical characteristics of mineral surfaces and their interactions with flotation reagents. It could become unpredictable when water sources characterized by different calcium or magnesium ion distributions were involved. This study aimed to identify the role of Ca<sup>2+</sup>/Mg<sup>2+</sup> ions in the recycled water on the cationic reverse flotation selectivity of iron oxides through a series of bench/micro flotation tests, zeta potential, powder contact angle, and Fourier Transform Infrared (FTIR), etc. The results pointed out that the use of recycled tailing water deteriorates the flotation selectivity and dilutes the concentrates. This can be largely attributed to the presence of Ca<sup>2+</sup> ions at higher concentrations as they induce a drop in the Fe recovery and an increase in SiO2 content while an increase in the content of Mg<sup>2+</sup> ions seems to have little effect on the quality of concentrate. As evidenced by the data from micro-flotation, powder contact angle, zeta potentials, and FTIR, a hydrophilic colloidal layer formed by Ca-based hydrolyzed compounds, such as Ca(OH)<sup>+</sup> or, CaCO<sub>3(s)</sub>, etc., on quartz could change its zeta potentials and disturb its interactions with a cationic collector. They also play a role in weakening the flocculation of starch on hematite probably by pre-locking the acidic groups on the starch remnants and contracting their configurations, thus preventing their adsorption on mineral surfaces. However, magnesium ions seem to be beneficial to in strengthening the flocculation of starch on hematite as magnesium-based species could act as adsorption bridges of between starch and mineral surfaces.

Molecular and microbial insights towards anaerobic biodegradation of anionic polyacrylamide in oil sands tailings

Anionic polyacrylamide (A-PAM) is widely used as a flocculant in the management of oil sands tailings. Nevertheless, apprehensions arise regarding its potential biodegradation and environmental consequences within the context of oil sands tailings. Consequently, it is imperative to delve into the anaerobic biodegradation of A-PAM in oil sands tailings to gain a comprehensive understanding of its influence on tailings water quality. This work explored the dynamics of A-PAM biodegradation across concentrations: 50, 100, 250, 500, 1000, and 2000 mg/kg TS. The results showed a significant decrease in A-PAM concentration and molecular weight at lower concentrations (50 and 100 mg/kg TS) compared to higher ones, suggesting enhanced degradation efficiency. Likewise, the organic transformation and methane production exhibited dependency on A-PAM concentrations. The peak concentrations observed were 20.0 mg/L for volatile fatty acids (VFAs), 0.07 mg/L for acrylamide (AMD), and 8.9 mL for methane yield, with these maxima being recorded at 50 mg/kg TS. The biodegradation efficiency diminishes at higher concentrations of A-PAM, potentially due to the inhibitory effects of polyacrylic acid accumulation. A-PAM biodegradation under anaerobic condition did not contribute to acute toxicity or genotoxicity. SEM-EDS, FT-IR and XRD analyses further revealed that higher concentrations of A-PAM inhibited the biodegradation by altering floc structure and composition, thereby restricting the microbial activity. Major microorganisms, including Smithella, Candidatus_Cloacimonas, W5, XBB1006, and DMER64 were identified, highlighting A-PAM's dual role as a source of carbon and nitrogen under anaerobic conditions. The above findings from this research not only significantly advance understanding of A-PAM's environmental behavior but also contribute to the effective management practices in oil sands tailings.

Development of an integrated approach to the analysis and forecast of hydrographic and bathymetric data of water bodies and tailings ponds

There is a need for an effective monitoring solution for water quality control in tailings dumps and adjacent water bodies in order to prevent environmental pollution. This article highlights the importance of water quality monitoring and surveillance to prevent pollution. It is proposed to develop a mobile robotic complex equipped with sensors for monitoring water bodies and tailings, which is also capable of measuring underwater topographic data. The objects of study were a tailings pond and water bodies. The authors analyzed existing technical monitoring solutions, designed and developed a robotic complex, echolocation device, tested them on specific sites (the tailings dump of the Zhayrem Mining and Processing Plant and the Ishim River), conducted laboratory analysis of water samples, classified the results. Additionally, they obtained 2D and 3D maps of the bottom, and entered all collected data into a developed database and software. The developed complex demonstrated high accuracy of movement (an error of about 0.2 m on the x axis and 0.1 m on the y axis) and the ability to register environmental parameters such as temperature, humidity, PH. Data analysis for 2021–2023 showed a significant excess of recycled water discharged into the evaporator pond, which emphasizes the importance of monitoring and management of water resources. The research applies ARIMA models, neural networks to predict water body parameters. The results obtained indicate the high efficiency of the developed robotic complex and methods for analyzing data on water resources. These methods can be used in industry, scientific research and environmental projects to regularly monitor water quality and take measures to protect it

Electrochemical activation of peroxydisulfate by Ti/IrTaO2 anode for quick degradation of xanthate

High concentrations of residual xanthate in mineral processing wastewater often limit the reuse of tailing water. Targeted removal of xanthate is an effective strategy for improving the tailing water recycling rate. In this study, the degradation efficiency and mechanism of sodium ethyl xanthate (SEX) in an electroactivated peroxydisulfate (EAPDS) system were investigated systematically. To avoid the influence of co-existing organic and inorganic matters in real flotation wastewater, we used simulated SEX wastewater to conduct the efficiency and mechanism investigation. A significant synergistic effect between electrocatalysis and peroxydisulfate was observed during the SEX decomposition. When the initial concentration of SEX was 200 mg/L, it achieved 100% removal rate only in 30 min with PDS dosage of 5 mM at current density of 10 mA/cm2. The introduction of peroxydisulfate boosted the removal efficiency six-fold compared to electrocatalysis alone. UV-Vis spectroscopy and GC-MS analyses revealed that the intermediate products of SEX were C2H5OH and CS2. The reactive oxygen species induced in the EAPDS were identified using a series of detection methods. •OH, 1O2, h+, O2•− and electron transportation process (ETP) all contributed to SEX removal. The degradation mechanism in the EAPDS system was proposed based on the analysis of the reactive oxygen species and products. Application to real flotation wastewater was attempted as well. The effects of different operating conditions were also evaluated, including pH, coexisting anions, PDS dosage, and current density. This study provides a new approach for the rapid removal of residual xanthates from mineral processing wastewater.

Metagenomic analysis revealed the evolution of microbial communities, metabolic pathways, and functional genes in the heterotrophic nitrification-aerobic denitrification process under La3+ stress

Trivalent lanthanum (La3+) exists widely in ammonia nitrogen (NH4+-N) tailing water from ionic rare earth mines; however, its effect on heterotrophic nitrification-aerobic denitrification (HN-AD) is unknown, thereby limiting the application of the HN-AD process in this field. In this study, we conducted an HN-AD process using a sequencing batch reactor (5 L) that was continuously operated to directly treat acidic (NH4)2SO4 wastewater (influent NH4+-N concentration of approximately 110 mg/L and influent pH of 5) containing different La3+ concentrations (0–100 mg/L). The NH4+-N removal efficiency of the reactor reached 98.25 % at a La3+ concentration of 100 mg/L. The reactor was in a neutral-to-alkaline environment, which favored La3+ precipitation and complexation. Metagenomic analysis revealed that the relative abundance of Thauera in the reactor remained high (88.62–92.27 %) under La3+ stress. The relative abundances of Pannonobacter and Hyphomonas significantly increased, whereas that of Azoarcus significantly decreased. Metabolic functions in the reactor were mainly contributed by Thauera, and the abundance of metabolic functions under low La3+ stress (≤5 mg/L) significantly differed from that under high La3+ stress (≥10 mg/L). The relative abundance of ammonia assimilation-related genes in the reactor was high and significantly correlated with ammonia removal. However, traditional ammonia oxidation genes were not annotated, and unknown ammonia oxidation pathways may have been present in the reactor. Moreover, La3+ stimulated amino acid biosynthesis and translocation, the citrate cycle, sulfur metabolism, and oxidative phosphorylation and promoted the overproduction of extracellular polymeric substances, which underwent complexation and adsorbed La3+ to reduce its toxicity. Our results showed that the HN-AD process had a strong tolerance to La3+, stable NH4+-N removal efficiency, the potential to recover La3+, and considerable application prospects in treating NH4+-N tailing water from ionic rare earth mines.

The effects of indigenous microorganisms and water treatment with ion exchange resin on Cu-Ni flotation performance

Mineral processing utilizes large amounts of water and aims to reduce water consumption by recirculation and closing the water loops. This results in accumulation of chemical and biological contaminants in process water that may have adverse outcomes on the process performance. To optimize water quality suitable for each process step and plant, knowledge of both chemical and biological effects are needed as well as techniques to best remove the contaminants. This study focused on the consequences of microorganisms, enriched from the actual process earlier, on the flotation performance in the multi-metal Kevitsa mine in Northern Finland and the applicability of ion exchange for the removal of dissolved sulfur species and microorganisms from water. The increase of microbial load from the original 106 to added 107 16S rRNA copies mL−1 affected positively the flotation selectivity, especially in the case of nickel. Two tested water types, process water (PW) and final tailings water (FT), behaved slightly differently. In the Cu flotation phase added microorganisms did not affect the Cu recovery of FT but decreased significantly the recovery of Cu in PW. With equal Cu grade, the recovery was as high as approximately 25 percentage points lower. However, added microorganisms in both water types decreased notably the recovery of Ni in Cu concentrate (18 to 37 %-points). At the same time the amount of Ni recovered in the Ni concentrate increased by 18 to 33 %-points with added microorganisms. Visually the froth layer was higher and more stable in the Ni flotation in experiments with added microorganisms compared to experiments without added microorganisms. The concentrations of dissolved sulfate and thiosulfate ions were low in the studied waters compared to operations treating massive sulfide ores and did not significantly affect the flotation performance. For this reason, the IX water treatment was not required for these ions. However, the IX treatment proved to be effective in removing both sulfur species and microorganisms. The use of dissolved air flotation (DAF) was a successful pretreatment for ion exchange in removal of microorganisms. However, microorganisms are not usually taken into consideration when process performance or water cleaning techniques are designed and optimization could result generally in even better outcome.

Is the use of a geotextile a necessary rehabilitation strategy to mitigate tailings contamination in soil cover materials? A 7-year field study

The potential pollution risk associated with poor management of mine tailings includes metal pollution of the surrounding environment from dusting and runoff. Thus, the establishment of a vegetation cover (rehabilitation) is viewed as an effective management strategy. Mine tailings can be inhibitory to plant growth due to their physico-chemical characteristics such as extreme pH, high salinity and potential high metal(loid) content, and the provision of a cover soil (≥ 30 cm) is usually recommended. This requires significant volumes of topsoil, which are often in limited supply at mine sites. An alternative may be the use of engineered soil (using organic and/or inorganic additives to improve physico-chemical properties) and placement of a barrier layer to prevent migration of tailings water or fines into the soil cover medium.Metal(loid)s content in soil cover treatments and vegetation uptake were evaluated after 7 years of rehabilitation in 1 m3 plots on a Pb/ Zn TSF. Final 30 cm covers included unamended tailings, subsoil material and subsoil amended with organic wastes (Spent Mushroom Compost (SMC) and Compost like output (CLO)). Treatments were divided into with/without geotextile inclusion. Soil samples were taken at 0–10 cm and 10–20 cm and analysed for pH, salinity (EC), and metal(loid)s/elements (As, Pb, Zn, Ca, Mg, Mn and, K) content. Vegetation was sampled after 1 yrs. growth (2015) and again after 7 years (2021) and analysed for their metal(loid)s/element content.Unamended tailings showed high metal(loid)s content at both depths, but concentrations were much lower in soil treatments. Herbage samples analysed in 2015 showed a higher concentration of metals than for 2021, highlighting the effectiveness and sustainability of amendments over a long period. Vegetation grown in unamended tailings showed the highest content of metal(loid)s, with significantly lower content in soil treatments. No significant difference was found for soil or vegetation metal(loid) content between geotextile inclusion/ exclusion. Results, highlight the relatively shallow soil covers without geotextile provide long term success with no evidence of metal(loid) contamination from underlying tailings.

Research on Legal Risk Identification, Causes and Remedies for Prevention and Control in China’s Aquaculture Industry

Aquatic products fulfill the protein needs of people and play an important role in food safety. And aquaculture is prized for its high productivity, sustainability and environmental friendliness. Considering the importance of aquaculture, the legal risks exposed during the aquaculture process deserve attention in order to prevent them from hindering the development of the aquaculture industry. Through online research, literature analysis and practical communication, it is shown that the current legal risks with commonalities include land use violations, lack of legal documents, failure to meet tailing water criteria, unquarantined fry and misuse of prohibited agricultural pharmaceuticals through online research, literature analysis and practical communication. By analyzing the reasons for the formation of legal risks and combining the experiences in sustainable development of three major aquaculture countries, which are Korea, Norway and Chile, this paper provides targeted preventive remedies and suggestions for aquaculture operators, administrative parties, legislators and other parties on legal risks. It includes promoting the improvement of the rule of law in multiple aspects, clarifying the positioning of the aquatic breeding certificates, improving and propagating the standards for wastewater discharge, increasing the self-sufficiency rate of aquatic fry and fingerlings, as well as making use of the synergy of soft law and hard law.

Phytoplankton Ecology in an Oilsands End Pit Lake

Alberta oilsands mining and extraction have produced over 1 trillion litres of tailings wastewater (AER 2021) containing several compounds of concern (Cossey et al. 2021). End-pit lakes are a low-cost, long-term proposed strategy of tailings reclamation that sequester tailings in a mined-out pit under a freshwater cap. Through dilution and biogeochemical processes, the water cap should over time develop into a functional ecosystem integrable with the local watershed (Cossey et al. 2021, Saborimanesh 2021). Established in 2012, Base Mine Lake is currently the only full-scale pilot end pit lake developed by the Alberta oilsands industry and requires further investigation to validate end pit lakes as a tailings reclamation technology (Cossey et al. 2021). The first stage of reclamation requires the development of a phytoplankton community, which serves as the base of the aquatic food web (CEMA 2012). The primary objective of this study was to characterize the phytoplanktxon community over time in BML from 2016 to 2021 to determine how community composition and abundances shift over seasons and years. Characterization used Illumina gene sequencing targeting 16S rRNA, 18S rRNA, and 23S rRNA gene amplicons, giving relative abundance data over time for phytoplankton. Cell count data was used to verify gene sequencing results. The phytoplankton community composition and diversity in Base Mine Lake was compared to those of a freshwater reservoir and a tailings pond. Analysis of gene sequencing data revealed that major genera of phytoplankton included Cryptomonas (Cryptophyceae), Choricystis (Trebouxiophyceae), Euglena (Euglenales), and Synechococcus (Synechococcales), all of which appear to exhibit seasonal blooms during 2016-2021 (Fig. 1). Sequencing analysis also indicated that Base Mine Lake and its freshwater input source Beaver Creek Reservoir shared many of the same genera but different strains/species of those genera. This suggested that the distinct conditions in each aquatic site may have selected for distinct strains. Diversity analyses of gene sequencing data revealed that phytoplankton diversity in Base Mine Lake was intermediate between that of its freshwater input reservoir and a tailings pond. There currently exists no low-cost, large-scale treatment method that fully reclaims tailings water (Cossey et al. 2021, Saborimanesh 2021). End-pit lakes retain tailings until recalcitrant compounds are degraded to near-environmental levels (Saborimanesh 2021, CEMA 2012), but further research is required before end-pit lakes can be approved as a viable reclamation technology (Cossey et al. 2021). Although research is available now on native microbial communities in tailings waters, knowledge on their contributions to an aquatic microbial food web is limited (Saborimanesh 2021). This proposed research is the first of its kind to examine the contribution of phytoplankton to end pit lake food web ecology. This will advance knowledge of end-pit lakes as a reclamation strategy in effort to reduce the environmental footprint of tailings water.

Exploring the effects of different process water sources on xanthate adsorption and flotation performance

Driven by environmental concerns and restrictions arising from them, the mining industry has instituted an initiative to recycle process waters within plant operations. This has the two-fold advantage of using minimal freshwater for mining, thus freeing the water for other applications, and limiting the release of potentially toxic discharge to the environment. However, in recycling their process water, plant operations alter the chemistries of these waters; and since reagents such as collectors are active at the solid–liquid interface, changes in the aqueous phase are expected to affect the flotation responses of ores. A polymetallic ore was floated in synthetic plant waters of varying ionic strengths and actual onsite plant waters, with aerophine and sodium isopropyl xanthate (SIPX) as collectors. The study showed that water quality has a quantifiable effect on SIPX adsorption. The respective effects of water quality and collector adsorption on ore flotation could not be irrefutably decoupled. However, increased adsorption did not necessarily result in improved grades and recoveries. This study specifically showed that Cu recoveries are reduced in recycled water owing to the presence of residual SIPX. The presence of residual SIPX in recycled water increased Ni recoveries and grades. Tailings water at the end of flotation may be more suited to Ni flotation owing to the presence of residual SIPX. The use of recycled water containing residual SIPX was therefore beneficial for pentlandite flotation but not for chalcopyrite, thus suggesting the importance of the consideration of components in recycled process water and points of addition in circuit configuration and design where closed water circuits are implemented. Retrieving tailings water directly after Cu flotation for recycling to Cu flotation circuit would therefore allow a more suitable water type.

Predicting beach profiles for thickened tailings surface deposition

Thickened tailings deposition technology can form a stack with a certain slope by depositing high-concentration tailings slurries to reduce the footprint of tailings storage facilities and water consumption. Thickened tailings slurries exhibit complex non-Newtonian behaviors. Predicting the beach profile evolution of thickened tailings is important for the tailings storage facility design and management. A novel governing differential equation (GDE) derived from the lubrication theory is proposed in this work to capture laws of beach profile formation. Experimental data from three-dimensional laboratory-scale flume tests are analyzed using the proposed GDE. The GDE avoids the discrepancy from an inappropriate coordinate system, which exists in some state-of-the-art models and exhibits higher accuracy when predicting the beach shape near the toe of a preexisted layer. Compared with the Herschel–Bulkley (H–B) model, the Zhang’s equilibrium rheological model is preferred to determine the static yield stress, which leads to the accurate estimation of the stack profile in single- and multilayer thickened tailings depositions. The in-situ beach profile of thickened tailings is predicted using a numerical technique. A case study is included to demonstrate that the prediction based on the proposed GDE is consistent with the field measurement. The beach profile prediction of thickened tailings considering thixotropy is also discussed in this study. Results indicated that the decrease of yield stress along the flow path due to thixotropy leads to the concave beach shape of thickened tailings.

Strength enhancement of cement-based stabilized clays via vacuum-assisted filtration

The performance of the cement-based stabilized clay (CBSC), a kind of typical composite, is controlled by the homogeneity and interactions among the hydration products of the cementitious agents, clay minerals and water. For the shallow lowland ground by hydraulic filling or natural deposition with very high-water content, more cementitious agent was required to realize the designed strength when block solidification, where a higher water content should improve the feasibility and homogeneity but decrease its strength. To overcome this contradiction, a vacuum-assisted filtration technique used in sludge and concrete treatment was extended to remove excessive water within the CBSC for strength enhancement. Experiments including the laboratory and pilot project were conducted to study the efficiency of the filtration method by investigating tailing water volume, strength and microstructure of the CBSC. Results reveal that applying the filtration method can effectively discharge the free water from the CBSC within the initial 12 hrs’ hydration of the cementitious additives, with a reduction in water content by 5.8–24.7 %, accompanied by an increase in the 28-day’s strength by more than 1.7 and 1.6 times in the laboratory and field respectively. Microstructural and chemical analyses also reveal that the strength improvement originates from the enhanced mixing homogeneity facilitated by higher water content and subsequent filtration for cementation development. After the auxiliary filtration process, both the total porosity and water content decrease, and the large pores are transformed into smaller ones.

Structure, Stability, and Acidity of the Uranyl Arsenate Dimer in Aqueous Solution.

The migration of uranium (U) in the surficial environment has received considerable attention. Due to their high natural abundance and low solubility, autunite-group minerals play a key role in controlling the mobility of U. However, the formation mechanism for these minerals has yet to be understood. In this work, we took the uranyl arsenate dimer ([UO2(HAsO4)(H2AsO4)(H2O)]22-) as a model molecule and carried out a series of first-principles molecular dynamics (FPMD) simulations to explore the early stage of the formation of trögerite (UO2HAsO4·4H2O), a representative autunite-group mineral. By using the potential-of-mean-force (PMF) method and vertical energy gap method, the dissociation free energies and the acidity constants (pKa's) of the dimer were calculated. Our results show that the U in the dimer holds a 4-coordinate structure, which is consistent with the coordination environment observed in trögerite mineralogy, in contrast to the 5-coordinate U in the monomer. Furthermore, the dimerization is thermodynamically favorable in solution. The FPMD results also suggest that tetramerization and even polyreactions would occur at pH > 2, as observed experimentally. Additionally, it is found that trögerite and the dimer have very similar local structural parameters. These findings imply that the dimer could serve as an important link between the U-As complexes in solution and the autunite-type sheet of trögerite. Given the nearly identical physicochemical properties of arsenate and phosphate, our findings suggest that uranyl phosphate minerals with the autunite-type sheet may form in a similar manner. This study therefore fills a critical gap in atomic-scale knowledge of the formation of autunite-group minerals and provides a theoretical basis for regulating uranium mobilization in P/As-bearing tailing water.

Quantifying the potential seepage from porphyry copper tailing impoundments using a multi-isotopic approach

Porphyry-style copper deposits are characterized by low Cu grades and high tonnages, resulting in large mine tailing volumes disposed in impoundments. Due to the mining tailing sizes, waterproofing techniques cannot be applied along the dam base. Therefore, to minimize seepage towards the aquifers, pumping wells are usually installed as hydraulic barriers. Currently, there is a controversy over whether or not the water extracted from hydraulic barriers should be counted as the use of new water rights. Consequently, a growing interest to develop tools to trace and quantify the tailing impacts in groundwater and to determine the water pumped amount subjected to water rights exist. In the present study, isotope data (δ2H-H2O, δ18O-H2O, δ34S-SO42− and δ18O-SO42−) are proposed as a tool to quantify tailings seepage towards groundwater and to assess hydraulic barriers effectiveness. To illustrate this approach usefulness, the Quillayes porphyry Cu tailing impoundment (Chile) case study is presented. The multi-isotopic approach revealed that tailing waters are highly evaporated showing high SO42− content (~1900 mg L−1) derived from primary sulfate ore dissolution, whereas freshwaters, derived from recharge water, have low SO42− contents (10–400 mg L−1) resulting from the interaction with geogenic sulfides from barren host rock. The δ2H and δ18O values of groundwater samples collected downstream from the impoundment suggest a mixing at different proportions of highly evaporated water from the mine tailing waters and non-evaporated regional fresh groundwater. Cl−/SO42−, δ34S-SO42−/δ18O-SO42−, δ34S-SO42−/ln(SO42−) and δ2H-H2O/δ18O-H2O mixing models allowed to determine that groundwater located closer to the impoundment had a mine tailing water contribution from 45 to 90 %, whereas those located farther away had lower contribution (5–25 %). Results confirmed the stable isotope usefulness to determine the water origin and to calculate the hydraulic barrier efficiencies and the pumped water proportions unrelated to the mining tailing subject to the water rights.