Tailings Impoundment Research Articles

The new expertise required for designing safe tailings storage facilities

The global mining community has seen a dangerous sequence of failures in tailings dams, beginning with Mount Polley mine, followed by the Samarco, Cadia Valley and Córrego do Feijão mines. This sequence of failures began on August 4, 2014, at the Mount Polley tailings storage facility in British Columbia, Canada. The initial failure in the embankment at the Mount Polley tailings storage facility had substantial impact on the global mining industry. The Independent Expert Engineering Investigation and Review Panel (IEEIRP) tasked with the investigation of the breach in the tailings dam at Mount Polley made major contributions for new guidelines. The incident has given rise to comprehensive recommendations for best available tailings technologies (BAT) based on principles such as the elimination of surface water from impoundments with the promotion of unsaturated conditions in the tailings through drainage provisions. The application of these BAT principles for the surface storage of tailings leads to the use of filtered tailings technology. Filtered tailings technology or “dry stack tailings” can satisfy each of the BAT components when the impoundment is properly designed and constructed. The implementation of the best available technologies for the physical stability (BAT-PS) of tailings impoundments competes directly with the best available technologies for the chemical stability (BAT-CS) of reactive tailings that may produce acid and metalliferous drainage. The new expertise in mine waste management required to achieve both BAT-PS and BAT-CS are discussed in the present paper.

Mine waste from carbonatite deposits as potential rare earth resource: Insight into the Phalaborwa (Palabora) Complex

The Phalaborwa (Palabora) Igneous Complex (PIC), South Africa, has been mined for the last six decades for copper and phosphate, among others commodities. As a result, more than 4500 Mt. of mining wastes have been deposited in waste rock dumps (WRDs) and tailing impoundments. This study aims to investigate the potential of the PIC wastes (WRDs and tailings) as a secondary resource of rare earth elements (REE) and its possible processing options, by means of both mineralogical and geochemical determinations, using X-ray diffraction (XRD), petrographic and scanning electron microscope with energy dispersive spectroscopy (SEM–EDS) and electron probe micro-analyzer (EPMA). The samples were also submitted to a REE leachability assay based in a sequential extraction procedure. Phoscorites and carbonatites are major lithologies in the WRDs and contain a notable concentration of REE, of which 0.2 and 0.1 wt%, respectively, would be easily extractable. The mineralogical results show monazite as the main REE-mineral (∑REE 60 wt%), while fluorapatite and calcite are the most important REE-bearing minerals (∑REE 1 and 0.5 wt%, respectively) for their abundance. On the other hand, the tailings are comprised mostly by monomineralic particles of calcite, dolomite, pyroxene, fluorapatite, magnetite and phlogopite. Based on the geochemical results, the extraction of REE from monazite, fluorapatite, calcite and dolomite, from tailings produced by both the Cu and the phosphate mines, might produce up to 5.65 and 1.75 kg of REE per ton, respectively. Therefore, tailings from PIC have the potential to become an asset. An approach to circular economy by re-processing mining wastes would extend the lifetime of the PIC mines and their benefits, while reducing the waste of resources and their environmental impact.

Linguistic and Discursive Features of Mining News Discourse in the Philippines

The Philippines is one of the mineral-rich countries in the world with an estimated US$840 billion worth of untapped mineral wealth, catapulting the mining industry as a significant economic player providing substantial contribution to the national revenue and generating employment opportunities for the Filipino people. However, the detrimental impact of mining to the country has also been heavily criticized as it causes massive potential destruction to environment and wildlife ecology such as acid mine drainage and contaminant leaching, soil erosion, and tailing impoundments among others. These conflicting interests are reflected in the mining discourses stoked or dimmed by media, which influence the readers’ construal of meanings in the mining texts, social actors’ roles in the mining industry, and the urderlying contexts of the mining reality. Drawing on critical discourse analysis, this study described the linguistic and discursive features of Philippine mining discourse in media texts. The study used 224 news articles published by three online portals within five years. Local news reports and peripheral discourses obtained through interviews with local “symbolic elites” in the identified mining communities and other archival documents supplemented the news texts. The UAM Corpus Tool, a software for linguistic tagging, complemented the manual analysis in identifying the social actor theme. Findings revealed that government actions, economic phenomenon, and political actors are the most prevalent themes in the mining news reports. Moreover, results showed that local news tends to focus more on the mining’s environmental impact, whereas the national news tends to put more premium on the mining’s economic impact. This means that the media allotted a much lesser spatio-temporal space for the environment and Indigenous Peoples’ cause. The findings further invalidate the assumptions that mining discourse is primarily concerned with environmental related issues. Keywords sociolinguistics; discourse studies; critical discourse analysis; discourse themes; Philippine mining discourse

A review on Pb-bearing nanoparticles, particulate matter and colloids released from mining and smelting activities

Lead (Pb) is one of the most paradoxical elements, both having diverse practical uses, as well as being extremely toxic to humans, and especially to children. The use of Pb records a steady growth with annual production currently exceeding 10 million metric tons. In spite of the environmental awareness of modern society, humans are still exposed to Pb through its emission by smelting and mining activities, and also by Pb-bearing mine wastes and soils. Here, we review the chemical and mineralogical forms of Pb generated from smelting and mining processes and subsequently altered in tailings, slag piles, and soils. In smelter plumes, Pb is emitted to the atmosphere either in the form of smaller nano-size particulate matter (PM) often associated with S, or larger micrometer Pb-bearing PM matter accompanied by oxide-silicate matrices. Pb-bearing phases in mine tailings and impacted soils depict a greater mineralogical and chemical complexity than those emitted from smelters and the larger particle size of this PM also leads to a lower Pb bioavailability. High resolution observations in aquatic system, soils and rock coatings impacted by smelting and mining activities show the presence of Pb-bearing phosphates, sulfides, sulfates, carbonates, and oxide nanoparticles. Larger micrometer size particles of Pb-bearing minerals form often through the aggregation of Pb-bearing nanoparticles, a process commonly referred to as crystallization through particle attachment. Mobilization of Pb within soil columns is strongly affected by the transport of colloids, especially those composed of organic matter and Fe-hydroxides because Pb is taken up efficiently by these two soil components. The extraordinary variability and complexities of all of these processes suggest that future reduction of Pb contamination in the environment and its impact on human health mainly depends on eliminating or greatly reducing Pb-release from smelting operations and tailings impoundments.

Reprocessing potential of pegmatite tailings for rare metal extraction and brick fabrication, Uis, Namibia

Abstract Historic tin mining and mineral processing of the Uis pegmatite deposit (Namibia) has resulted in a series of tailings impoundments. In this study, Uis tailings were characterised to establish their suitability for brick manufacturing and reprocessing potential for rare metals (Be, Li, Nb, Ta). Tailings occur on-site as two distinct types (a) fine- to medium-grained sand (d50 = 120 to 420 μm) in dune-like spoil dumps; and (b) fine- to medium-grained sand (Fraction A: d50 = 120 to 410 μm; ~25% of tailings type) and fine-grained silt (Fraction B: d50 = 18 to 83 μm; ~75% of tailings type) in four low-lying dried-out waste impoundment cells. The two tailings types have a similar and homogeneous mineralogical composition, comprising quartz, plagioclase, K-feldspar and mica as well as minor cassiterite, columbite-tantalite and petalite, reflecting the micaceous quartzo-feldspathic composition of the source rocks. The main clay mineral is illite with minor (ferroan) clinochlore, cookeite and kaolinite. Such a mineralogical composition allows contemporary brick fabrication due to illite as the main clay mineral, a large proportion of quartz as a stabilizer and only trace amounts of minerals that could have a detrimental effect (e.g. Fe oxides and pyrite). Consequently, the consistent particle size distribution and homogeneous mineralogical composition allow present-day production of high-quality fired bricks from tailings. To date, the use of Uis tailings for brick manufacturing supports the local economy, aids building development and removes silica-rich mine wastes prone to dust dispersion in a remote part of Namibia. In addition, geochemical analysis of the tailings reveals strongly elevated mean concentrations of rare metals (~2 760 mg/kg Li, ~140 mg/kg Be, ~41 mg/kg Ta, ~55 mg/kg Sn, ~74 mg/kg Nb). Resource estimates suggest the presence of ~25 200 t Li2O, ~1 600 t BeO and significant Nb-Ta-Sn in impoundment cell material and a total resource of ~365 000 t Li2O and ~27 900 t BeO in bulk tailings. Thus, Uis tailings also offer the opportunity for reprocessing and extraction of rare metals.

Stratigraphy and mineralogy of tailings at Macraes gold mine, southern New Zealand

ABSTRACT Processed tailings in the Mixed tailings impoundment at the Macraes gold mine built up a sedimentary pile up to 100 m thick between 1990 and 2013. The tailings consist of sand-dominated fluvio-lacustrine sediments with fine (cm scale) bedding and have a mineralogical stratigraphy that reflects changing mine processes. Most of the tailings (>90%) consist of silicate minerals discarded from the flotation system throughout that time. The deepest tailings (1990–1993) have the lowest contents of sulphides as these were extracted and deposited separately. Between 1993 and 1999, tailings with up to 0.5 wt% sulphide sulphur (as pyrite and arsenopyrite) were deposited. Introduction of a pressure oxidation system in 1999 caused a substantial decrease in sulphide minerals and a parallel increase in ferric oxyhydroxide, ferric sulphate, and ferric arsenate compounds in which trace metals are dispersed. Some primary scheelite reacted during pressure oxidation conditions to form ferric tungstate compounds. Processing of auriferous sulphide concentrate from Reefton, western South Island, from 2007 introduced stibnite to the ore stream, and this was readily oxidised to form insoluble As-bearing ferric antimonate.

An analytical solution to estimate the settlement of tailings or backfill slurry by considering the sedimentation and consolidation

A common and important task in mining industry is to estimate the settlement or final volume of the tailings or backfill associated with sedimentation and self-weight consolidation. Up to now however, most existing analytical solutions were developed by only considering the settlement induced by consolidation. In this paper, the process of shrinkage tests has been compared with those of sedimentation and consolidation. It was shown that the pore water and particles movement in the sedimentation are very similar to that in the normal shrinkage. The void ratio at the end of sedimentation is thus for the first time considered to be equal to the void ratio at desaturation onset of shrinkage tests. An analytical solution was then proposed to estimate the settlement of tailings or backfill by considering the sedimentation and consolidation. To validate the proposed analytical solution, tailing deposition tests were conducted in two molds to simulate the tailings impoundment and underground mine stope. The required parameters were obtained through shrinkage and consolidation tests. Good agreements were obtained between the measured settlements and those calculated by the proposed solution. The proposed solution can thus be considered as validated and used to evaluate the settlement of tailings or backfill slurry.

Formation and evolution characteristics of dam breach and tailings flow from dam failure: an experimental study

The safety of tailings impoundments has long been a concern of academic researchers globally. The tailings dam breaks are extremely likely to induce secondary disasters such as mudflows, landslides and water and soil pollution, thus further aggravating the risk of accidents. On the basis of practical engineering, this study performed a dam-break physical model experiment and theoretical analysis to examine tailings dam overtopping and dam body collapse processes. It also discussed the leaked tailings flow evolution characteristics after dam failure, based on important parameters such as the dam-breach variation rules after dam break, flow velocity of the leaked tailings flow, particle deposition characteristics and submerged depth. Our research discovered that dam-breach development was mainly constituted by water current erosion-induced longitudinal downcutting and dam-breach slope instability-caused horizontal expansion. A large sand inrush amount resulted in a high downstream flow rate and large sediment depth after dam failure. In addition, when the sampling site was > 100 cm (model scale) away from the dam site, the discharged tailings flow size grading phenomenon was obvious during dam breach, and the particle size gradually decreased with increasing distance between the sampling characteristic sites and dam site.

Laterite as a Potential Seepage Barrier From a Karst-Depression Tailings Impoundment

AbstractIn the absence of the necessary valley topography, karst depressions are sometimes used to construct conventional impoundments in order to contain tailings. Leakage is a primary concern for such impoundments. The purpose of the current study was to determine the characteristics and barrier performance of laterite mantling karst depressions, using, as an example, the Wujiwatang (WJWT) tailings impoundment, located in the Gejiu mining area, southwestern China. The geotechnical-hydrogeological properties, geochemistry, mineral compositions, and particle shapes of the laterite were investigated by geotechnical techniques, chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the laterite contained poorly sorted particles that covered a wide spectrum of grain sizes (<5 mm to <50 nm), and was unexpectedly categorized as silty clay or silt with a high liquid limit. The continuous gradation and small D90 value helped the laterite achieve saturated hydraulic conductivities in the range of <10–6 cm/s required for impoundment liners. The laterite beneath the tailings impoundment was finer-grained and had a lower permeability than that of the laterite on the depression walls within the same depression. Geochemically and mineralogically, the laterite was classified as true laterite and its major mineralogical constituents were gibbsite and goethite with chlorite occurring in trace amounts. The laterite was dominated by subspherolitic–spherolitic cohesionless grains (concretions) made up of Al, Fe, Ti, and Mn oxides and hydroxides. The laterite did not have plasticity indices in the clay range. Fortunately, slopewash prior to tailings containment selectively transported the finer oxide concretions to the depression floor, creating a natural low-permeability barrier for the WJWT tailings impoundment. This is undoubtedly important for the planning and design of future karst depression-type tailings impoundments around the world.

Prediction of Trace Metal Distribution in a Tailings Impoundment Using an Integrated Geophysical and Geochemical Approach (Raibl Mine, Pb-Zn Alpine District, Northern Italy).

When mines are decommissioned, tailings piles can act as sources of contamination for decades or even centuries. Tailings, which usually contain high concentrations of metals and trace elements, can be reprocessed for a secondary recovery of valuable elements with an innovative approach to a circular economy. This study offers new results for tailings ponds characterisation and chemical content prediction based on an integrated geophysical-geochemical approach. The study of the Raibl Pb-Zn tailings impoundment was done using bulk chemical analysis on borehole samples, Electrical Resistivity Tomography surveys, and Ground Penetrating Radar measurements. We found valuable and statistically significant correlations between the electrical resistivity of the mining impoundments and the metal distribution, thus providing a practical opportunity to characterise large volumes of metal-bearing tailings. In particular, these results can be useful to aid in the development of environmental monitoring programs for remediation purposes or to implement economic secondary recovery plans.

Comparing single‐phase, non‐Newtonian approaches with experimental results: Validating flume‐scale mud and debris flow in HEC‐RAS

AbstractPost‐fire debris flows and tailing impoundment failures destroy lives and property. These geologic hazards – and other similar processes – fall on a continuum between classic Newtonian flood analyses and geotechnical stability analyses. The US Army Corps of Engineers (USACE) is developing a non‐Newtonian library (DebrisLib) that includes a suite of rheological and clastic approaches to hyper‐concentrated, mudflow and debris flow dynamics. The Hydrologic Engineering Center (HEC) has implemented these non‐Newtonian methods into the widely used, public‐domain open‐channel hydraulics and morphodynamic software, HEC‐RAS (river analysis system). This work presents part of the verification and validation of these non‐Newtonian approaches, applying several rheological equations to published laboratory results high‐concentration flume experiments.This study tested the linear Bingham model as well as the turbulent and Bagnold quadratic terms of the O'Brien equation. HEC‐RAS also includes the non‐linear Herschel–Bulkley (HB) approach, which quantifies shear‐thickening or shear‐thinning processes. The study used these non‐Newtonian models in HEC‐RAS to simulate 10 of Parsons et al.’s (2001) flume experiments, which measured the snout and plug velocity of fluids with high solid concentrations (Cv = 68–74%) and a broad range of material gradations (d50 = 0.05–1 mm, d15 = 0.006–0.1 mm). The experiments also measured and back‐calculated Bingham and HB parameters of the materials, finding HB powers between 0.45 and 1.25 (i.e. fluids that are dilatant, pseudo‐plastic and visco‐plastic).The rheological models incorporated into DebrisLib and implemented in HEC‐RAS reproduce experimental data well for most experiments. The Bingham model generated a plug velocity root‐mean‐square error (RMSE) of 0.21 m/s using standard flow parameters and Parsons et al.’s calibrated parameters, a substantial improvement over the unmodified shallow water flow equations (RMSE 0.77 m/s). Experiments with strong snout effects tended to generate higher residuals, especially in the snout velocity. The RMSE associated with the O'Brien equation was larger with the Parsons et al. fit parameters, but similar (0.23 m/s) with measured parameters. The turbulent parameter was the largest (often the dominant) parameter in most O'Brien simulations, with the dispersive stress only proving significant for the coarsest material. DebrisLib had to use a modified version of the dispersive term to simulate these concentrations. Both the 2D depth‐averaged shallow water equation (SWE) and diffusion wave equation were used to simulate the experiments. The best results were obtained with the SWE with horizontal mixing.

Evaluation of mine site reclamation performance using physical models: Case of Ity mine (Ivory coast)

The exploitation of the Ity gold mine in Ivory Coast will generate tailings that can be considered as potential generators of acid mine drainage (AMD). Various materials such as marble and clay are available around the mine site that could be used as components of an engineered cover for the reclamation of the reactive tailings impoundment. However, it is important to assess the properties of these potential cover materials and test different reclamation scenarios in the laboratory to select the best scenario for mine site reclamation. For this purpose, physical modeling was performed using experimental instrumented column tests simulating covers with capillary barrier effects (CCBEs) and monolayer covers. The columns were instrumented with sensors for measurement of volumetric water content (VWC) and suction. Leaching tests were performed over many cycles and physical and chemical analyses were carried out on the leachates. The observed hydrogeological behavior shows that either a CCBE or a monolayer cover with clayey silt materials can be used for the Ity mine site reclamation. However, hydrochemical results allow confirming that the monolayer cover made with clayey silt material can be considered as the best scenario for the Ity mine site reclamation.

Physical Model Testing and Analysis of Hard Rock Tailings Consolidation Considering the Effect of a Drainage Inclusion

The use of waste rock inclusions (WRI) in tailings impoundments is a novel technique offering various advantages. It is however relatively new and not yet commonly used, so a few key technical issues must still be addressed to optimize the design of WRI. This paper presents an experimental investigation, conducted as a part of a major research program, aimed at assessing the consolidation behavior of tailings during and shortly after hydraulic deposition and the effects of placing a waste rock inclusion in contact with the tailings. The results of a first series of physical model tests performed in an instrumented column with hard rock tailings deposited in successive layers are presented and analyzed to investigate the evolution of pore water pressures, strains and related consolidation parameters at each stage of filling. The results of a second series of experimental tests on tailings with a cylindrical WRI placed at the center of the physical model are then presented and analysed to evaluate how the inclusion influences drainage and pore water pressure at different locations in the tailings. Numerical simulations are also conducted to further assess the consolidation behavior of tailings during sequential deposition and the influence of the WRI. Additional analyses and discussion of the results are also presented to address complementary aspects.

Uranium sorption from radioactive waste of uranium ore processing at Pridneprovsk Chemical Plant

Abstract. The research results were generalized regarding the possibility of uranium sorption from radioactive waste accumulated at Production Association “Pridneprovsky Chemical Plant” (PA PCP). The conceptual possibility was illustrated for sorption leaching of uranium from pulps produced by acidic leaching of radioactive waste dumped at Zapadnoye (Western) tailing impoundment using AMP anionite contained benzyl pyridinium functional groups (manufactured by Smoly State Enterprise). Uranium recovery was 70 % to 80 % during waste acidic leaching with the mixture of 15 % sulphuric and 1.5 % nitric acids. Application of sorption leaching allowed the recovery increase up to 15 %. Uranium recovery was assessed from upper ground and underground water of Centralny Yar tailing site using AM-p-2 strong base macroporous anionite (produced by Smoly SP) based on styrene-divinyl benzene copolymer with 2-hydroxyethyl-dimethylammonium functional groups. This tailing impoundment features acidic reaction of radioactive water since the pulp was almost not neutralized after ore processing. It poses an environmental hazard due to active uranium leaching from the tailing impoundment body and its ability to migrate into groundwater. It was found that the distribution factor may attain ~2 000 for uranium concentration 7 mg/l in interstitial water and 4 mg/l in underground water. Assessment results were given regarding uranium recovery from radioactively contaminated water accumulated in the basement of building No. 103 using phosphate cationite based on modified plant material. The building is extremely contaminated and of top-priority for treatment and further dismantling. Sorbent capacity by uranium achieved in static mode was ~20 mg/g with distribution factor ~4 800. The results obtained may be proposed as the reasoning for the method and technology intended to decontaminate polluted water before it would be pumped from underground rooms of building No. 103. The research performed has shown that application of sorption materials is the most expedient and promising method for selective uranium recovery when solving the problems of tailing site remediation and handling radioactive waste of the former Pridneprovsky Chemical Plant.

Status and Measures of Preventing and Controlling Environmental Risks in Tailing Impoundment

Nowadays, the situation of environmental pollution monitoring and emergency management of tailings impoundment is becoming more and more severe mainly due to the high incidence of environmental emergency in tailing impoundment. Based on which, this paper takes the environmental risk of tailing impoundment as the main research object, focusing on status and corresponding measures of its prevention and control. Hopefully, it will be helpful.

Research on radon exhalation characteristics of uranium tailings with cover materials under the coupling load of low-frequency vibration and seepage gradient

In this study, radon (222Rn) measurements were taken at compacted uranium tailings with cover materials by a self-developed coupling testing system under different low-frequency vibration loads and gas seepage rates. The maximum measured value appears at 0.723 Bq m−2 s−1, which is close to the upper limit value of national standard of China (0.74 Bq m−2 s−1). A vibration load significantly damages the compacted uranium tailings sample structure, resulting in a marked increase in the porosity of the porous media thus forming a channel for radon migration. The results presented here may provide a workable approach for simulating geological dynamic load conditions for radon exhalation studies on uranium tailings impoundment.

Assessment of the pollution potential of a special case of abandoned sulfide tailings impoundment in Riotinto mining district (SW Spain).

This work describes a special case of pollution potential assessment applied to an abandoned sulfide tailings impoundment located in the Riotinto mining district (Huelva), near the Tinto River. Three overlapping levels of discharged tailings were recognized in the impoundment, from deeper to upper: pale yellow to white, red, and brownish-yellow. Mineralogical, physical, and chemical characteristics of tailings, water leachates, water, and sulfate efflorescent salts were analyzed. The total toxic element content and the leachate concentration were respectively used to calculate two indices that support potential toxicity assessment: the Index of Contamination (IC) and the Hazard Average Ratio (HAQ). According to the IC values, all tailings samples showed a high potential for contaminating soils and sediments, especially the intermediate tailings with up to As (8.6 g kg-1), Pb (14.8 g kg-1), and Cu (1 g kg-1). Deeper tailings leachate was extremely saline and acidic, with a very high concentration of sulfates and toxic elements, exceeding the values: 2600, 980, 30, and 17 mg L-1 for SO4, Fe, Al, and Cu, respectively. For this reason, these deeper tailings were linked to the saline and acid seepage, and also to the sulfate acid efflorescences formed at the dike toe. In conclusion, the studied abandoned tailings impoundment is related with a high likelihood of polluting the environment, represented by very high IC and HAQ values. However, when the Tinto River is considered the receiving water body, the severity of the potential contamination must be judged as very low.

Assessment of Native and Endemic Chilean Plants for Removal of Cu, Mo and Pb from Mine Tailings

In Chile, 85% of tailings impoundments are inactive or abandoned and many of them do not have a program of treatment or afforestation. The phytoremediation of tailings with Oxalis gigantea, Cistanthe grandiflora, Puya berteroniana and Solidago chilensis have been tested in order to find plants with ornamental value and low water requirements, which enable reductions in molybdenum (Mo), copper (Cu) or lead (Pb) concentrations creating an environmentally friendly surrounding. Ex-situ phytoremediation experiments were carried out for seven months and Mo, Cu and Pb were measured at the beginning and at the end of the growth period. The capacity of these species to phyto-remedy was evaluated using the bioconcentration and translocation factors, along with assessing removal efficiency. Solidago chilensis showed the ability to phytoextract Mo while Puya berteroniana showed potential for Cu and Mo stabilization. The highest removal efficiencies were obtained for Mo, followed by Cu and Pb. The maximum values of removal efficiency for Mo, Cu and Pb were 28.7% with Solidago chilensis, 15.6% with Puya berteroniana and 8.8% with Cistanthe grandiflora, respectively. Therefore, the most noticeable results were obtained with Solidago chilensis for phytoextraction of Mo.

Natural rehabilitation of arsenic-rich historical tailings at the Alexander mine, Reefton, New Zealand

ABSTRACT Mine tailings resulting from orogenic gold processing commonly form arsenic (As)-enriched environments. A result of this is that they draw environmental attention in modern gold mining settings and significant effort in long-term rehabilitation. The Alexander River mine processing site in the Reefton area of Westland provides an opportunity to examine the natural rehabilitation of As-enriched tailings that have been left undisturbed for >70 years in a humid environment. These tailings comprise a ∼1 m thick package of finely laminated (mm-scale) sediments that were manually accumulated on a terrace downstream of the gold extraction plant. The tailings sediments are As-rich (up to 5000 mg/kg) due to relict arsenopyrite and As-bearing pyrite. Diagenetic Ca–Fe–arsenate (tentatively identified as yukonite) and As-bearing iron oxyhydroxide have formed during localised oxidation. There was sufficient calcite in the tailings to maintain circumneutral pH in the tailings despite sulphide oxidation. The historical tailing impoundment is now covered by grass, ferns and shrubs, with beech and rimu forest covering several metres at the margins. Leaf analyses indicate that the vegetation is absorbing only minor As. Therefore, the tailings substrate has not halted natural vegetation re-colonisation of this As-rich historical site.

Regional Hazard Degree Evaluation and Prediction for Disaster Induced by Discharged Tailings Flow from Dam Failure

Tailings impoundments are the important structures for the normal mine production, which are also the potential major hazard sources of mine safety. On the basis of the previous tailings dam break model experiment and numerical simulation results, the important characteristic parameters were selected to develop a hazard degree evaluation index system for the disasters induced by the discharged tailings flow from dam failure. The evaluation model was established further by using the uncertainty measurement theory. The results show that the hazard degrees of three characteristic regions (village locations) in the downstream of tailings impoundment were evaluated; it was determined that, the regional safety level of village I was “dangerous”, while those for villages II and III were “relatively safe”. Moreover, the evolution process of discharged tailings flow was divided into three characteristic stages on the whole, and a greater sand burst amount was associated with a greater risk to the downstream of the tailings impoundment. The results were highly consistent with the results of the laboratory dam break model experiments and numerical simulations.