Tailings Disposal System Research Articles

Long-term evolution of heap surface of paste tailings under erosion / Evolução a longo prazo de pilha da pasta de rejeitos sujeita a erosão

Many mines are moving from conventional tailings storage facilities to filtered tailings disposal systems. The benefits of these systems include increased water recovery, reduced size of containment landfills, improved facility safety, and reduced environmental impact. In geotechnical terms, the challenges are to find the correct way of waste disposal: whether in piles of dry sandy tailings or co-disposal waste rock. The long-term evolution of the surface of fine and sandy tailings stockpiles is a matter of concern. The goal of this study was to quantitatively evaluate the temporal evolution of a paste tailings pile, using a computational model of landscape evolution. For this, SIBERIA, a simulator of the evolution of landscapes under the action of runoff and erosion, was used. The effect of erosion on a trunk-pyramidal tailings pile with about 21% of slope after long periods of decommissioning (100 and 250 years) was studied. The SIBERIA modelling data considered the surface roughness and the average diameter of the sediment particles and the typical properties of iron ore tailings. The results indicate that for a lower Manning roughness coefficient and larger average apparent diameter of the sediment particles (or clods), the lower the sediment transport will be and, therefore, in the long term, the greater will be the integrity of the tailings pile.

Estimating the escalation of mine tailings disaster risks by using a life cycle assessment approach

Mine tailings should be managed properly to avoid the tailings accident that recorded more than 230 tailings accident worldwide. These accidents caused human and environmental losses. This paper estimates the escalation of mine tailings dam failure using a life cycle assessment (LCA) approach. The LCA functional unit (FU) is defined as 1 tonne of fine coal concentrate slurry generated by flotation cells. SimaPro software was chosen to analyze the material flow data of a mine coal tailings disposal system and focused on impact categories associated with disaster issues including human toxicity, terrestrial eco-toxicity, freshwater eco-toxicity, and marine eco-toxicity. The results showed that the impact escalation of coal mine tailings during 20 years of operation for human toxicity, terrestrial eco-toxicity, freshwater eco-toxicity, and marine eco-toxicity were 13,740 DALY, 27.40 species year, 0.04 species year, and 0.001 species year respectively. These results indicated that a good mine tailings management should be applied by mine site to prevent a human and environmental disaster from mine tailings accident.

Laboratory Evaluation of Electrokinetic Dewatering of Bauxite Tailings

The mining tailings disposal system is often associated to the construction of large retaining systems, either for the great volume of materials generated by industrial plants or for the impossibility or difficulty of grants for new disposal areas. Due to increasing demand, these impoundments have become much more significant, triggering considerable increase of risk associated to them. In this context, new techniques must be developed aiming to decrease the volume of tailings produced and the optimization of disposal systems for these materials, particularly in terms of systems including tailings dewatering techniques. An alternative solution consists in dewater and consolidate mine tailings under current intermittence, technique called electroosmosis. This paper presents the development of an electroosmotic cell to measure the electrokinetic flow and the consolidation process of fine tailings under specified boundary conditions. The tailings are generated by the process of treatment of bauxite from BPM (Bauxita Paragominas Mining/Brazil), which consist of fine-grained materials, with initial solid content of 31%. The results of this experimental study are analyzed and discussed based on the principles of electrokinetic theory and has shown that the proposed technique would significantly accelerate the consolidation process of fine tailings (an average solid content of 58% was reached, within a 12-hour period), besides providing adequate design parameters for field applications.

Tailings Liquefaction Analysis Using Strength Ratios and SPT/CPT Results

Tailings dams constructed using the upstream method generally have relatively low- density materials with a high degree of saturation. Such conditions can generate the phenomena of liquefaction, which is potentially critical in slurry tailings disposal systems. Slope stability analyses involving liquefied soil require that the shear resistance of the softened soil be estimated and then, a good practical alternative is back-analyzed with field case studies involving slope failures, using commonly SPT and CPT results. The Olson (2001) and Olson & Stark (2003b) liquefaction analysis methodology based on strength ratios, included in this approach, is comprised of three stages: (i) liquefaction susceptibility analysis; (ii) triggering analysis; and (iii) post-triggering - flow failure stability analysis. In this paper, this approach was applied for stability assessments to verify liquefaction potential in an upstream tailings dam built by the hydraulic fill technique and located in the Quadrilátero Ferrífero (Iron Quadrangle) region, southeastern of Brazil. The results ratified the safety condition of the impoundment although they have demonstrated that the tailings tend to exhibit contractile behavior during shear, indicating liquefaction susceptibility.

Design, construction and management of tailings storage facilities for surface disposal in China: case studies of failures

Rapid development of China's economy demands for more mineral resources. At the same time, a vast quantity of mine tailings, as the waste byproduct of mining and mineral processing, is being produced in huge proportions. Tailings impoundments play an important role in the practical surface disposal of these large quantities of mining waste. Historically, tailings were relatively small in quantity and had no commercial value, thus little attention was paid to their disposal. The tailings were preferably discharged near the mines and few tailings storage facilities were constructed in mainland China. This situation has significantly changed since 2000, because the Chinese economy is growing rapidly and Chinese regulations and legislation require that tailings disposal systems must be ready before the mining operation begins. Consequently, data up to 2008 shows that more than 12 000 tailings storage facilities have been built in China. This paper reviews the history of tailings disposal in China, discusses three cases of tailings dam failures and explores failure mechanisms, and the procedures commonly used in China for planning, design, construction and management of tailings impoundments. This paper also discusses the current situation, shortcomings and key weaknesses, as well as future development trends for tailings storage facilities in China.

The origins of public concern with taconite and human health: Reserve Mining and the asbestos case

Asbestos first became an issue to Minnesota’s iron industry when it was revealed that mineral fibers similar to those in Reserve Mining’s tailings were being found in drinking water for several communities that used Lake Superior as their primary water source. This discovery turned what had largely been an environmental court battle into a case concerning public health. The courts listened to much conflicting and uncertain scientific testimony on the size and distribution of the mineral fibers and on the potential health effects imposed by them. In April 1974, the plant was ordered to shut down by a federal judge but the company quickly appealed the decision. The appeals court granted a stay and ultimately ruled that the plant’s closure could not be justified based on the unknown health effects of the mineral fibers since the consequences of such an action would have immediate and severe social and economic impacts. The plant was allowed to continue operation, but ordered to abate emissions to air around the plant and to switch to a land-based tailings disposal system. Much of the scientific uncertainty and public concern over mineral fibers in Minnesota’s taconite industry remain today.

High concentration suspension pumping

Environmental and economic considerations require that tailings disposal systems are performed using much higher solids content than was previously deemed acceptable. These new high concentration systems have many benefits, particularly lower water consumption, smaller impoundment areas and reduced solids’ mobility. These systems require that the solids are pumped out to the deposition sites as non-Newtonian suspensions which are generically, although nearly always erroneously, called pastes. This paper will present results gathered in recent years which demonstrate that such suspensions are almost invariably stratified, especially if the suspension’s size distribution is wide, a prerequisite for co-disposal systems. It will also show that the transport pressure gradients are substantially different from those predicted from simplistic paste theory for full size plant. These findings will be supported by experimental observations using both visual, MRI and ERT tomography data and from mathematical modelling results.

The reactivation of a landslide during the construction of the Ok Ma tailings dam, Papua New Guinea

The Ok Ma dam (Ok is a local word meaning river) was to form part of the permanent tailings disposal system designed for the Ok Tedi gold and copper opencast mine located at Mount Fubilan in the Star Mountains of Papua New Guinea. During the construction works a landslide involving approximately 35 million cubic metres of soil and rock moved downslope to partially fill the foundation excavations of the dam. The failure of this landslide was the start of an insurance litigation that finally reached the Supreme Court of Papua New Guinea in November 1989. The geotechnical, geomorphological and engineering geological data that were available at the time of the failure are presented together with an evaluation of the key deductions from the case study.

Geotechnical Aspects of Eroded Sediments Relevant to Tailings Disposal Design

Since 1975, Samarco Mineraco S.A. has been mining the iron ore deposits of the Germano Mine in the Quadrilatero Ferrifero (Iron Quadrangle) in Minas Gerais, Brazil. Presently, this mine is depleted, and a huge ultimate pit (approximately 1,300 m long, 800 m wide, and 220 m deep), known as the Germano Open Pit, was produced. Samarco Mineraco currently processes the iron ore from the adjacent Alegria Mine, having reserves that exceed 5 billion tons of itabirite. The iron ore is transported by a 1,500-m-long conveyor belt that crosses the eastern border of the Germano Pit. Design studies of the tailings disposal system to be implemented in this old pit area have generated several questions related to the geological complexity and geotechnical features of the pit and the engineering properties of the tailings. The proposed project will fill the abandoned pit with tailings using the upstream construction method and will reach up to 160 m high when completed. The paper discusses the geological and geotechnical concerns regarding instability of slopes and deposited sediments. These studies are essential for evaluation of the deposited sediments as a foundation material for future tailings pile structures.

Marine Tailings Disposal Simulation

The disposal of mine tailings in deep water body requires comprehensive assessment of the potential environmental impacts, and estimates of the effective storage capacity of the bottom bathymetry for accommodating the anticipated volume of disposed tailings over the life of a mine. A mathematical simulation model was developed for this purpose to predict the distribution and long-term deposition patterns of tailings in a fjord. The model describes the mechanics of the tailings slurry flow along the bottom of the receiving water body and the settling of suspended particles, as well as the redistribution of the deposited sediments due to slumping of unstable slopes. Specific processes simulated in the model also include entrainment at the top of the density current, entrainment associated with internal hydraulic jumps in areas of changing bottom slopes, hindered settling and coagulation of suspended particles, and sediment deposition and bathymetric changes resulting from the deposition of large quantities of tailings. Long-term tailings deposition patterns are predicted by analyzing the flow of the tailings slurry in a series of time increments, from a few months to a year. The bathymetry is assumed to remain unchanged within each time increment, and the model first simulates the steady-state flow field for the tailings slurry along the bottom and the resulting deposition rates for several sizes of suspended particles. Then the estimated tailings deposition rates are combined with slope stability considerations to predict the new bathymetry of the receiving water body. Data from several operating marine tailings disposal systems were reviewed to assess the applicability of specific relationships used in the model. The model was calibrated using data from one of the most extensively studied marine tailings disposal systems, the Island Copper mine in Rupert Inlet of Vancouver Island, British Columbia. Comparison of simulated tailings deposition patterns in Rupert Inlet with data from field observations and measurements suggests that calibration of the model is satisfactory and provides confidence in the capability of the model to predict deposition patterns and suspended sediment concentrations for proposed mines.

Review of 23 years of STD: Island Copper Mine, Canada : D. V. Ellis, T. F. Pedersen, G. W. Poling, C. Pelletier & I. Horne, Marine Georesources & Geotechnology, 13(1–2), 1995, pp 59–99

The submarine tailings disposal (STD) system at Island Copper Mine has been subjected to a comprehensive environmental monitoring program initiated in 1970, some 20 months before the mill started processing ore. The program has been extended and modified as new factors became relevant or it became clear that particular factors were not of concern at this site. The major environmental issues have concerned (1) tailings resuspension and upwelling, (2) smothering of benthos, and (3) trace metal contamination from acid rock drainage (ARD). A closure plan has been prepared for implementation in 1995. Tailings were resuspended and upwelled to surface close to the fiord sill due to unpredicted periodic high‐density tidal jets scouring the deposits at that point. The localized elevated turbidity has not affected biological productivity. Benthos have been smothered under rapid tailings deposition such that areas under thick tailings ( > about 20–30 cm) showed reduced biodiversity. At deposition rates of < l cm p.a...

Effects of changing environmental rules: Kitsault molybdenum mine, Canada

The Kitsault mine was reopened briefly in 1981–82, after prior operations in 1967–72. Initial oceanographic assessments showed that a submarine tailings disposal (STD) system similar to that at Island Copper Mine would function to produce a tailings density current that would deposit on the fjord bed. There was substantial community interest and action during the final years of the development at a time when new pollution controls were being developed in Canada. The STD system essentially met its design criteria, but new oceanographic instrumentation at the time showed some contribution of tailings at the outfall discharge point to a naturally present mid‐water turbidity layer. The first intensive postclosure monitoring of ecosystem rehabilitation following STD use anywhere in the world was undertaken between 1983 and 1989. Soon after closure in 1983, pore waters in the submerged deposited tailings were observed to be enriched in molybdenum, which must have supported an efflux of the metal to the overlying water. The indicated flux would have been too small to have had a measureable effect on the Mo inventory in the deep waters and, furthermore, was predicted to diminish with time. The only detected biological impact was on the fiord benthos in the deposition area. Although benthos were present in the tailings deposits by 1983, there were differences between the tailings and nontailings areas. Some differences remained in 1986 and 1989. Great variability of the benthos in the reference area paralleled that in the tailings area.

Tailings disposal at a marine placer mining operation by WestGold, Alaska

From 1985 to 1990 WestGold managed a marine placer mining operation with substantial documentation concerning its submarine tailings disposal (STD) system. For 5 years the operation involved the use of a floating bucket‐ladder dredge with an integrated, gravity‐based treatment plant to extract free particulate gold from the seabed gravels. Three‐quarters of the throughput was disposed of at 1.5 m below sea level through two pipes, each of 0.51‐m diameter. The system's design resulted from considerable trial and error and modeling studies to achieve regulated seawater conditions. The information is publicly available as a result of a very open permitting and operating process. The mining permit specified waste discharge controls and. environmental impact limits for topics of local concern: the dredge's effluents, the red king crab population (an important fishery resource), seawater turbidity, and bioaccumulation of trace metals, especially mercury (a remnant of prior beach mining). The impact on crab stoc...

Potential for retrofitting STD

Submarine tailings disposal (STD) systems have been retrofitted, designed, or appear to be possible at several existing or abandoned coastal and island mines. At Atlas Copper Mine, the Philippines, the system is somewhat different from the norm: a 500‐m pipe pier, with a discharge point just below the surface, extends offshore to 30‐m water depth. Little environmental information is in the public domain, but there appears to be some nearshore turbidity and deposition. A system was designed for the Toquepala and Cuajone mines, Peru, but was not implemented. The discharge depth was to have been at 20 m to a sloping offshore bank, with low‐oxygen water and sediments. The Marcopper Mine, the Philippines, elected for nearshore disposal, but extended this by causeway to surface discharge over deeper water. Reviews of potential STD sites showed at least three locations with apparently suitable depth and slope close to shore. At Bougainville Copper Mine, Papua New Guinea, the tailings disposal option was to a riv...

Review of 23 years of STD: Island copper mine, Canada

The submarine tailings disposal (STD) system at Island Copper Mine has been subjected to a comprehensive environmental monitoring program initiated in 1970, some 20 months before the mill started processing ore. The program has been extended and modified as new factors became relevant or it became clear that particular factors were not of concern at this site. The major environmental issues have concerned (1) tailings resuspension and upwelling, (2) smothering of benthos, and (3) trace metal contamination from acid rock drainage (ARD). A closure plan has been prepared for implementation in 1995. Tailings were resuspended and upwelled to surface close to the fiord sill due to unpredicted periodic high‐density tidal jets scouring the deposits at that point. The localized elevated turbidity has not affected biological productivity. Benthos have been smothered under rapid tailings deposition such that areas under thick tailings ( > about 20–30 cm) showed reduced biodiversity. At deposition rates of < l cm p.a...

Tailings disposal system for reserve mining company : Klohn, E J; Dingeman, D World Min, V31, N13, Dec 1978, P46–51

Tailings disposal system for reserve mining company : Klohn, E J; Dingeman, D World Min, V31, N13, Dec 1978, P46–51

Mineral flotation—a study of the re-use and disposal of aqueous solutions containing organic reagents

The fate of organic reagents added to a froth flotation process for the concentration of fluorite, barite and lead has been studied as an example of a unit process employing water as a transport medium. It has been shown that approximately half of the organic material added to the circuit was discarded in the mill tailings water—the other half being lost from solution within the circuit. Estimates have been made of the amounts removed in the different unit operations and of the amounts discarded in the final effluents from the tailings disposal system. The effluent from the operation studied has been shown to have a barely detectable effect on the organic levels in the river system into which it was discharged. BOD 5 and BOD 10 measurements have been made on fifteen of the commonest organic reagents used in the froth flotation process. A wide range of degradation behaviour is revealed. A survey has been made of the methods that have been adopted and proposed for the removal of residual organic reagents from froth flotation process waters and of the production of consistent supplies of water for re-use.