Discharge Of Mine Tailings Research Articles

Dynamic stochastic modeling for adaptive sampling of environmental variables using an AUV

Discharge of mine tailings significantly impacts the ecological status of the sea. Methods to efficiently monitor the extent of dispersion is essential to protect sensitive areas. By combining underwater robotic sampling with ocean models, we can choose informative sampling sites and adaptively change the robot’s path based on in situ measurements to optimally map the tailings distribution near a seafill. This paper creates a stochastic spatio-temporal proxy model of dispersal dynamics using training data from complex numerical models. The proxy model consists of a spatio-temporal Gaussian process model based on an advection–diffusion stochastic partial differential equation. Informative sampling sites are chosen based on predictions from the proxy model using an objective function favoring areas with high uncertainty and high expected tailings concentrations. A simulation study and data from real-life experiments are presented.

Impacts of climate change on metal leaching and partitioning for submarine mine tailings disposal.

At present, there are no standardised tests to assess metal leaching during submarine tailings discharge. In this study the influence of variables known to affect metal mobility and availability (dissolved organic carbon (DOC), pH, salinity, temperature, aerated/anoxic conditions) along with variables affected by the discharge conditions (flocculant concentration, suspension) were studied in bench-scale experiments. The leaching tests were developed based on the case of a copper mine by Repparfjorden, northern Norway, which is planned to re-open in 2022. The experiments, which had three week duration, revealed low (<6%) leaching of metals. Multivariate analysis showed that all variables, apart from DOC, highly influenced leaching and partitioning of at least one metal (Ba, Cr, Cu, and/or Mn). The high quantity of the planned annual discharge of mine tailings to the fjord (1-2milliontonnes) warranted estimation of the leached quantity of metals. Multivariate models, using present-day conditions in the fjord, estimated leaching of up to 124kg Ba, 154kg Cu and 2400kg Mn per year during discharge of tailings. Future changes in the fjord conditions caused by climate change (decreased pH, increased temperature) was predicted by the multivariate models to increase the leaching up to 55%, by the year 2065. The bench-scale experiments demonstrated the importance of including relevant variables (such as pH, salinity, and temperature) for metal leaching and -partitioning in leaching tests. The results showed that metal leaching during discharge is expected and will increase in the future due to the changed conditions caused by the foreseen climate change, and thereby underline the importance of monitoring metal concentrations in water during operations to determine the fate of metals in the fjord.

High-resolution numerical modelling of a marine mine tailings discharge in Western Norway

Waste from mining operations includes mine tailings, a slurry of fine-grained mineral particles and processing chemicals that remains after the desired compounds have been extracted from the ore. In some cases, the method of disposal is to place tailings into the marine environment; this is known as Submarine Tailings Placement (STP). To understanding the environmental impact of releasing large amounts of mine tailings into the marine system, multiple processes must be well characterised, including those relating to the transport and fate of the disposed material.We applied a set of high-resolution models for wind, hydrodynamics, and sediment transport to simulate a submarine mine tailings discharge in a Norwegian fjord. The transport model includes processes to account for the effect of flocculation on mine tailings transport and fate. We calculated the mean tailings sedimentation rate in the fjord, which is closely related to the environmental footprint of the STP. Comparisons with measurements of winds, currents, turbidity, and sedimentation rates were made to evaluate the model, and we found overall reasonable agreement. We investigated discharge scenarios during 2013 and identified a strong wind event around November 17, which caused increased particle dispersal. The increased mixing caused by the strong winds were seen in elevated turbidity measurements, as well as increased modelled suspended sediment concentration.

Impact of historical sulfide mine tailings discharge on meiofaunal assemblages (Portmán Bay, Mediterranean Sea)

Portmán Bay is one of the most contaminated and chronically impacted coastal marine areas of the world. Here, from the 1957 to 1990, about 60 million tons of mine tailings from the processing of sulfide ores were dumped directly at the shoreline. The resulting deposit provides a unique opportunity to assess the impact of mine tailings on coastal marine ecosystems after ca 30 years since the discharge has ceased. We investigated meiofaunal abundance, biomass and biodiversity along a gradient of metal concentration that overlaps with a bathymetric gradient from 30 to 60 m depth. Despite the localized presence of extremely high concentration of metals, the bay was not a biological desert, but, nevertheless, was characterized by evident signs of impact on benthic diversity. Meiofaunal variables increased significantly with decreasing metal contamination, eventually reaching values comparable to other uncontaminated coastal sediments. Our results show that mine tailings influenced the spatial distribution of meiofaunal taxa and nematode species composition. In particular, we report here that the bay was characterized by the dominance of nematode opportunistic species tolerant to high metal concentration. The effects of mine tailing discharge on meiofaunal biodiversity and composition were still evident ca 30 years after the end of the mining activities. Overall, this study provides new insights on the potential impact of mine tailings disposal and metal contamination in coastal sediments, and, can also contribute to predict the potential long-term consequences of ever-expanding deep-sea mining industry on benthic environments.

Lability of toxic elements in Submarine Tailings Disposal: The relationship between metal fractionation and metal uptake by sandworms (Alitta virens)

Mine tailings from the iron ore mine Sydvaranger Gruve have been deposited in Bøkfjorden, Northern Norway, for >40 years. This study investigates the environmental impacts of submarine tailings disposal one year after the cessation of the mine by combining analyses of total metal concentrations (nitric acid digestion) and metal fractionation patterns (sequential extraction procedure) of sediments with the metal uptake (bioassays) by sandworms (Alitta virens) exposed to Bøkfjorden sediment. The analyses focused on metals (As, Cd, Cr, Cu, Fe, Ni, Pb, Zn) in sediment cores retrieved from a horizontal transect of the fjord. High concentrations of the target metal iron was found in the fjord (>13,000 mg/kg). According to Norwegian sediment quality guidelines (SQG), cadmium (2.55 mg/kg) and lead (174 mg/kg) were the only metals to exceed good sediment quality at the source area of mine tailings discharge. Despite general low total metal concentrations, labile (summarized exchangeable, acid soluble, reducible fractions) and potentially labile (summarized labile and oxidisable fractions) pools of mine tailings-related metals of cadmium (10–82%), copper (25–88%) and lead (10–67%) were detected while iron were characterized as inert (residual fraction: 89–97%). Despite spatial trends in total metal concentrations presumed to originate from mine tailings (Cd, Cu, Fe, Pb), there were no correlations between total and labile fractions. This can be explained by the high concentrations of iron, which under oxidised forms are suggested to inhibit a high lability of other metals. The metal uptake of sandworms was generally high compared to similar studies and exceeded moderate contamination classes for all metals compared to Norwegian standard values. Both labile metal fractions (cadmium, copper and iron) and total metal concentrations (copper, iron) showed positive correlations (r > 0.6) with metal uptake. Thus, both the total and labile metal fractions can pose an environmental risk.

Using Ionic Liquid Modified Zeolite as a Permeable Reactive Wall to Limit Arsenic Contamination of a Freshwater Lake—Pilot Tests

Arsenic (As) contamination of surface water has long been a threat to human health. Extensive studies were made at the bench-scale for the removal of As from water. Commonly-used materials for the removal of As include Al and Fe hydroxides that will form complexes with As. Recently, modification of Earth materials to reverse their surface charge to positive to reduce the mobility of arsenite and arsenate also attracted great attention. In 2008, a severe As contamination was reported in the lake of Yangzonghai, Yunnan, China. Although the As concentration was maintained below 0.05 mg/L for the lake, after 28 months of restoration, the discharge of mine tailings from a nearby fertilizer plants was still one of the contributors to the As in the lake. In this study, zeolite was modified by ionic liquids and the modified materials were installed as a permeable reactive wall (PRW) to contain the As movement. Preliminary results showed more than an 80% reduction in As after surface water moved through the PWR over the six-month sampling period confirming the effectiveness of ionic liquid-modified Earth materials for environmental application.

심해저 망간단괴 생산규칙의 잠재적 환경보호 의무 범위에 관한 연구

International Seabed Authority (ISA) is currently developing rules with regard to exploitation of manganese nodules which will be contained in its first regulations governing the exploitation of deep seabed mineral resources. A stakeholder survey was conducted in the early 2014 by ISA with the aim of facilitating participation of interested entities in the development process of the rules. The stakeholders who had replied to the survey included existing contractors, sponsoring States, environmentalists, academics, and nongovernmental organizations. Opinions given by them largely reflect their own interests. This paper aims to clarify the scope of the obligations regarding the environmental protection which may be imposed on contractors under the new regulations for the exploitation of manganese nodules. To do so, it first analyses the express provisions on environmental protection applicable to deep seabed mining included in the Law of the Sea Convention, its agreement on implementation of Part XI, and the regulations on exploration for manganese nodules. Secondly, it categorizes these obligations based on the categories of international obligations suggested by Combacau and Alland. Based on the categorizations this paper concludes that, in addition to the existing duties to protect deep seabed environment within the Law of the Sea Convention system, the following new obligations could be added: conservation of exploitation sites for a limited time after the contract is ceased; taking all necessary measures for rehabilitation of destroyed ecosystems that occurredas a result of mining activities; monitoring exploitation sites for a limited period time after the contract is ceased; observing rules and standards on safety of ships and environmental protection adopted under IMO instruments; regulation on the discharge of mine tailings from the facilities used for exploitation of deep sea minerals. Lastly, this paper attempts to provide ways of reflecting national interests in terms of potential obligations which may be included in the new regulations.

Natural recovery rates of a river system impacted by mine tailing discharge: Shag River, East Otago, New Zealand

Gold mining in Deepdell Creek, a tributary of the Shag River, occurred between 1890 and 1946. At least 85,000 tonnes of mine tailings were discharged into the creek during this time. Arsenic is the best geochemical tracer of these tailings, and an estimated 850 tonnes of arsenic in the form of arsenopyrite was discharged. Chromium is also anomalous in source rocks, but As and Cr are decoupled in the sedimentary system. Copper, zinc, and nickel show no mining-related variations down the catchment. Tailings produced 100 times more sediment and 1000 times more arsenic per year than natural erosion of mineralised rocks. Minor dissolved arsenic also discharged from the mining area (ca. 0.024 mg/l at 10 l/s), but this was negligible compared to the tailings. The Shag catchment has little sediment storage capacity, allowing the tailings to pass rapidly through the catchment. Floods are sufficiently frequent and voluminous to remove all tailings within ca. 60 years. Nevertheless, small amounts of arsenic-bearing sediments remain, with concentrations up to 250 ppm 4 km downstream of the mining area in Deepdell Creek. Sediments in the main Shag valley below the Deepdell Creek confluence have low but anomalous As contents (15–25 ppm). Rare relict arsenopyrite grains are trapped in bedrock crevices 25 km from source. Significant tailing deposition is not detectable in the Shag estuary, and the tailings have presumably been discharged into the sea. Natural rehabilitation of the Shag catchment has been rapid and effective.

The concept of “sustainable ecological succession”; and its value in assessing the recovery of sediment seabed biodiversity from environmental impact

The problem of determining whether the biodiversity of an impacted muddy seabed is recovering can be resolved by drawing on a concept termed “sustainable ecological succession”. At a site impacted by discharge of mine tailings, a suite of ∼6 primary opportunist species (mostly polychaete worms) had started to sustain itself within 1–2 years after discharge ceased (1995), within the mix of 100+ other species which were not sustaining themselves. The start of a sustaining ecological succession is easily measurable by repeat surveys, and requires only the services of one taxonomic identifier to demonstrate the consistent presence and numbers of a limited range of species. At the assessed site, by 2000, some secondary opportunist species had entered the succession, and the species richness of the impacted area had come to equal that of the reference areas.

A one-dimensional reactive multi-component landfill leachate transport model

A one-dimensional reactive multi-component landfill leachate transport model coupled to three modules (geochemical equilibrium, kinetic biodegradation, and kinetic precipitation–dissolution) is presented to simulate the migration of contaminants in soils under landfills. A two-step sequential operator splitting method is applied to solve the coupled transport equations and the biogeochemical reaction equations. The geochemical module is based on the equilibrium speciation model (MINTEQA2), which uses ion-association equilibrium–constant approach to represent the various geochemical reactions. The biodegradation module describes the sequential biological degradation of organic compounds by multiple functional bacterial populations. Analytical equations based on macroscopic approach are used to model changes in porosity and permeability caused by biomass accumulation and mineral precipitation in soils. The model has been evaluated by comparing the model results with the widely used one-dimensional mixing-cell model PHREEQM for acidic mine tailings discharge in a carbonate aquifer. The composite leachate transport model is applied to a hypothetical landfill to simulate the effect of biological degradation of organic matter on the local inorganic geochemistry and also to demonstrate the effect of microbial activity on the evolution of porosity reduction of soils under the landfill.

Removal of dissolved copper and iron at the freshwater-saltwater interface of an acid mine stream

The King River, Tasmania, contains elevated levels of heavy metals, in particular copper, a result of the discharge of mine tailings and acid mine water from the Mt Lyell copper mine, which operated until late 1994. Samples were collected from the lower King River in July 1994, over a 48-h period, during which time the power station at the head of the river was off for the first 24 h. Saline water was observed in the delta region during this low flow period, and dissolved iron and copper were found to exhibit nonconservative behaviour with salinity. Removal of dissolved copper, as the river enters the harbour, was confirmed by laboratory experiments. The removal mechanism appears to be dependent on rapid pH increases and the formation of amorphous iron flocs which occur in the estuary, and results in a significant proportion of dissolved copper being removed from solution.

Arsenic bioaccumulation and toxicity in aquatic macrophytes exposed to gold-mine effluent: relationships with environmental partitioning, metal uptake and nutrients

Arsenic concentrations in freshwater macrophytes were examined in relation to arsenic loadings in sediments (solid phase and pore water) and surface waters for a group of lakes contaminated by the discharge of mine tailings near Yellowknife, N.W.T. Lakes closest to the current discharge were highly contaminated with arsenic (up to 18 650 μg g −1 in sediments) compared with other areas. Macrophytes tended to bioconcentrate arsenic relative to sediment concentrations (up to a factor of ten), with submerged species containing much higher levels of arsenic than emergents. Differences in levels between the most common submerged ( Potamogeton pectinatus L.) and emergent species ( Typha latifolia L.) were attributed to differences in growth form and possible differences in the ability to exclude arsenic with increasing sediment concentrations. High environmental arsenic concentrations appeared to have negative effects on Typha latifolia, as suggested by decreased stand height, necrosis of leaf tips and reduced micro-nutrient concentrations in root tissues of copper, managanese, and zinc. Phytotoxic symptoms in Typha were generally observed at sediment and water concentrations exceeding 300 μg g −1 and 400 μg l −1, respectively. The lack of relationships between tissue concentrations of arsenic and environmental concentrations of phosphorus (as pore water PO −3 4, particulate total extractable P, or As:P ratios) did not support the hypothesis that arsenic bioavailability (as arsenate) and toxicity is related to its competition for uptake with phosphate.

Modeling of multicomponent reactive transport in groundwater: 2. Metal mobility in aquifers impacted by acidic mine tailings discharge

The mobility of potentially toxic dissolved metals discharged from a mine tailings source into an aquifer is investigated by using the multicomponent reactive transport model MINTRAN. A generic aquifer resembling a site in northern Ontario is used as a basis, and a scenario analysis is performed to determine the effect of terminating the source input of acidity and dissolved metals after a finite time. It is found that for most metals the buffering reactions in the carbonate aquifer lower the dissolved metal concentrations substantially, often by several orders of magnitude. In the case of a 12‐year source duration, most metals are effectively immobilized by precipitation, and the concentrations of metals remaining in solution are well below drinking water limits. The risk of contamination of water resources by toxic metals can thus be controlled.

Benthos on tailings beds from an abandoned coastal mine

Abstract The marine benthos which had recolonized the site of a mine tailing discharge 12 years after mining activity had ceased was compared to an adjacent area in which no tailings were found. Test (tailings) and Reference (no tailings) sampling stations consistently separated in a series of 6 cluster analyses. They invariably provided the last linkages, thus demonstrating that biological differences between tailing and non-tailing areas remain after 12 years. Tailing station faunas were less diverse than those at non-tailing stations, and each had characteristic faunas. Shallow (25 m) and deep (100 m) stations clustered together for both Test and Reference transects, but were significantly different (P

Turbidity currents and submarine channel formation in Rupert Inlet, British Columbia: 1. Surge observations

Acoustic backscatter images obtained at 107 and 200 kHz of surge‐type turbidity currents resulting from mine tailing discharge are presented. Excess densities in the head of the order of 100 kg m−3 are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom‐reflected signal. These excess densities are comparable to estimates based on surge height and speed, the speed being determined by assuming a universal head shape. Unlike gravity current surges from an impulsively started steady source, the surge‐type turbidity flows consist of a high concentration slug of short duration followed by a longer‐lived wake in which sediment concentrations are lower by 2–3 orders of magnitude. The profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments. Discrete scatterers, probably fish, are observed to avoid the surges.

Turbidity currents and submarine channel formation in Rupert Inlet, British Columbia: 2. The roles of continuous and surge‐type flow

Acoustic backscatter images are presented of the continuous flow turbidity current resulting from mine tailing discharge into Rupert Inlet. The current flows partially within a submarine channel, which both hooks to the left and meanders. The images show the turbidity current spilling over the outer levees at channel bends. A model for continuous turbidity flow incorporating overspill is developed and applied to the left‐hooking section of the submarine channel. It is very likely that the observed overspill is primarily an inertial effect resulting from the outer bank being more sharply curved than the channel axis. The model results are combined with a sediment accumulation budget based on successive seismic profiling surveys and with results for surge‐type flows (taken from the companion paper (Hay, this issue)). It shows that surges are primarily responsible for the transport of tailing to large distances from the point of discharge and should recur at 1‐ to 2‐day intervals on average. This is consistent with the characteristics of coarse‐grained turbidites observed in cores from the levees. Relative to the intervening fine‐grained mud deposits the turbidites increase both in thickness and frequency in the downchannel direction. Furthermore, the surge recurrence interval obtained from the number of turbidites per core and the local accumulation rate is 2–5 days, essentially the same as that obtained from the model. Suspended tailing transport within the channel appears to be dominated by surge‐type turbidity currents except close to the outfall. It is concluded that the surge‐type flows are most responsible for the formation and morphology of much of the channel. It is not clear, however, that the meanders are formed principally by surges. Although the surges occur frequently and transport most of the sediment in the meander reach, the volume transport is dominated by continuous flow.

On the remote acoustic detection of suspended sediment at long wavelengths

Experimental results are presented which indicate a linear relation between the time‐averaged amplitude of the envelope of the backscattered acoustic pulse at 192 kHz and the square root of suspended sediment concentration in the 10 to 103 mg 1−1 range. Particle sizes ranged from 2 to 140 μm. The measurements were made in a negatively buoyant, mine‐tailing discharge plume in a submarine channel at depths of 60 to 90 m in Rupert Inlet, British Columbia. From the theory of acoustic backscatter from a solid elastic sphere in the Rayleigh region it is shown that if the pressure amplitude of the backscattered wave is Rayleigh distributed, then such a linear relation is to be expected. Expressions for the optimum acoustic frequency for the detection of dilute suspensions at a given range and for the minimum detectable concentration are obtained assuming a thermal noise background. The possibility that bubbles contribute to the backscatter is considered and found to be unlikely on the basis of probable bubble lifetimes.