Pyritic Tailings Research Articles

Bioremediation of an industrial acid mine water by metal-tolerant sulphate-reducing bacteria

The microbiological diversity associated with mining environments is a very well proven fact. One of the communities appearing in these environments is that formed by anaerobic sulphate-reducing bacteria (SRB) which can be used for the decontamination of acid mine drainage waters. In this work, the potential of a mixed population of SRB, isolated from the bottom of a pyritic tailing pond situated in the Spanish pyritic Belt, has been investigated with the main objective of treating the effluent generated in the same disposal site. The efficiency of the system is based on the presence of an important amount of reducing agents contained in the acid mine drainage received in the pond. Results showed that this option is effective for the precipitation of the dissolved metals (copper and iron), for the reduction and removal of sulphates and even for the alkalising of the waters. SRB were able to remove up to 9,000 ppm of sulphate ion efficiently, to grow in the presence of up to 100 ppm of copper and 30 ppm of iron, and alkalise the medium, provided that this was not extremely acidic (pH>4). Finally, according to the results obtained, the possibility of applying this method to the treatment of a real effluent is discussed.

Microbial succession during weathering of pyritic tailings: column model

Mining residues (tailings) undergo major transformations when they are subjected to changing environmental conditions. This weathering of the residues causes serious environmental problems which affect all mining companies around the world. In the present work the microbiological evolution of pyritic tailings was studied under both laboratory and real environment conditions. A column model was designed for this purpose. The microbiological selection and succession were determined for the real system and then these conditions were reproduced by means of the column model selected. The microbiological implications of transformation of the mining residues were demonstrated.

The Aznalcóllar Tailings Dam Accident - A Case Study

The Aznalcollar tailings dam owned by Boliden Apirsa failed on April 25, 1998, releasing approximately 1.3 million cubic metres of fine pyrite tailings and 5.5 million cubic metres of tailings water into the nearby river systems. Approximately 2,600 hectares of river banks and agricultural land were affected by tailings deposition and an additional 2,000 hectares were affected by tailings water. Apirsa closed the breach in the dam within one day and within a week commenced tailings removal. Responsibility for the clean-up was divided between Apirsa and the Spanish authorities. By the end of November 1998, Apirsa had completed the clean-up in its sector, an area containing 80% of the discharged tailings. A consultant engaged by Apirsa, Eptisa, concluded that the failure occurred as a result of a 60 metre lateral displacement along a bedding plane in a blue marl clay formation some 14 metres below the dam. Another Apirsa consultant, Principia-EQE, concluded that several deficiencies in the work carried out by the designers of the dam in 1978 and by the independent consultants who studied the stability of the dam in 1996 contributed to the failure. In responding to the accident, Apirsa positioned itself as part of the solution, taking an open and proactive posture in its dealings with the media, the general public and the Spanish authorities. Apirsa built support for its environmental assessment and remediation activities by subjecting its plans to external scientific peer review and applying principles of continuous improvement to their implementation. Apirsa's response to the accident can usefully serve as a model for others faced with adverse circumstances of the magnitude of the failure of the Aznalcollar tailings dam.

Characterization of organic compounds in soil and water affected by pyrite tailing spillage

A variety of mono- and di-chlorinated and brominated triphenylamines were identified in the sludge and contaminated soils affected by a toxic waste spill that occurred in the Los Frailes pyrite mine (SW Spain). A negative gradient of aromatic amine concentrations from 29 μg g −1 in the vicinity of the broken dam to 0.14 μg g −1 in contaminated soils collected 30 km to the south in the Guadiamar River valley was observed. Substituted carbazoles (e.g. 9-phenylcarbazole) were also identified as contaminating sludge, soils and the temporarily dammed water at Entremuros and the Guadalquivir River and its tributary, the Guadiamar River. Our results demonstrate that contaminated waters from the pyrite sludge spill reached the Guadalquivir Estuary. However, the more lipophilic compounds, such as the halogenated triphenylamines, were not recorded in water bodies because of their strong adsorption by soils during the weathering process. Conversely, the more hydrophilic benzothiazoles were widespread in surface waters, a finding attributable to their higher solubility than chlorinated aromatic amines. Although the source of the nitrogen organic compounds (NOCs) has not yet been identified, it would seem to be related to the pyrite tail spillage. For example, degradation of technical products used in ore processing or industrial waste dumped in the mine waste collection dam could be the source of these compounds. Given the widespread occurrence of 9-phenylcarbazole in the affected area, this compound is proposed as a specific molecular marker of the Aznalcóllar spill. Furthermore, some of the NOCs were identified in the contaminated waters of the Guadiamar and Guadalquivir Rivers, providing evidence that these rivers were affected by the mining spill. Taking into account the field concentrations (water, sludge) and the spill volume, it can be concluded that the budget of aromatic amines is in the range of 27 t — of this, 32.6% was in the aqueous phase and the remaining 67.4% was in the soil.

Progress in Establishing Wetland Plants in Permanently Flooded UraniumTailings

Trials are taking place on flooded pyritic uranium tailings near the city of Elliot Lake, Ontario to establish deep water aquatic plants. It is anticipated that the wetland eventually formed will produce organic matter that will hinder oxygen penetration into the tailings and help to keep acid production to a minimum. In 1993, plots and vegetation islands of cattail, common reed, beaked sedge and wool rush were transplanted into water less than 0.75 m deep. By 1995, these plants had overcome any transplant shock and islands of several species were expanding. In 1995, a large scale transplant was undertaken to establish vegetation in deeper water. A total of 50 sites of varying depths were established within Rio Algom Limited's Quirke Waste Management Area (WMA). These sites were planted during the month of August with 10 units of plant material with substrate from their source wetland. The term ‘unit‘ represents 2 different planting methods. One method involved placing plant roots/rhizomes and substrate in a biodegradable burlap bag and the other being direct planting, into the tailings substrate. White water lily, pickerel weed, pondweed, watershield, hardstem bulrush and bladderwort were planted in 50 locations ranging in depth from 0.34-4.53 m. Each planting unit received approximately 70 g of bonemeal (2- 11 -0) at the time of planting. Survival rates near 40% were recorded for fragrant water lily, and 80% for bath pickerel weed and hardstem bulrush. Watershield survival was minimal at 10%. Pondweed and bladderwort transplants were not successfully transplanted. Transplants were relocated and survived in Cell 14 only as turbidity levels were extremely high in Cell 15 the year of and the year following transplant. Analytical results with respect to elemental, nutrient and radionuclide concentrations in plants, substrate and water are presented for source sites and the large scale transplant in the WMA cells.

Chemical and microbiological transformations in a pyritic tailing pond

A common practice in mines and metallurgical plants around the world is to deposit tailings in decantation ponds. The chemical and microbiological transformations which occur in these ponds can severely affect the quality of the water. Furthermore, if these plants use S02 as a flotation conditioner, the effluents become contaminated with sulphite ions. The present work was based on the study of a pond for pyritic tailings from the flotation of a complex polymetallic sulphide concentrate from the southwest of Spain. The chemical characterization of the pond waters was carried out by controlling pH, redox potential, conductivity and metals in solution. From a microbiological point of view, the study focused on. screening those microorganisms directly related with oxidation and reduction processes: iron and sulphur oxidizing bacteria and sulphate reducing bacteria. The chemical oxidation of the sulphite ion and its influence on effluent quality was also studied. This ion produces reducing conditions in the system, which influence the chemical characteristics of the waters: pH, metals in solution, etc. In the absence of sulphite ions, different oxidative processes take over and microbial growth is greater.

Bioleaching of gold pyrite tailings with adapted bacteria

Auriferous sulfide ores often contain very finely disseminated gold and other precious metal particles inside the sulfide crystals. The encapsulation of precious metal particles gives rise to the refractory nature of such ores to current extraction methods. As a result, these fractions are frequently lost in the tailings. This work investigates the feasibility of pre-treating these refractory tailings with bioleaching before using standard extraction techniques such as cyanidation. Leadville gold ore tailings containing auriferous pyrite were first concentrated by froth flotation. The pyrite concentrate was treated for different periods of time with 12-weeks-adapted Thiobacillus ferrooxidans before cyanide leaching. The bioleaching of the concentrate before cyanide leaching increased the gold extraction from 32 to 95% and that of silver from 48 to > 98%.

Geochemical evolution of inactive pyritic tailings in the Elliot Lake uranium district

Geochemical data obtained between 1979 and 1983 from a network of piezometer nests and cores from three inactive uranium tailings impoundments in the Elliot Lake district indicate that oxidation of pyrite taking place in the shallow part of the zone above the water table is causing the chemistry of the pore water above and below the water table to change. A two-layer hydrochemical zonation has developed in which infiltration water from rain and snow has resulted in an upper zone of low-pH water with high concentrations of SO4, Fe, and heavy metals. This zone is gradually expanding downward at rates generally between 0.2 and 2 m/year, causing displacement of the original mill process water, which has neutral pH and low concentrations of heavy metals. High concentrations of Fe(III) at shallow depth in the zone above the water table indicate that ferric iron is an important oxidizer of pyrite in the presence of free oxygen.The pe of the groundwaters is controlled by the ferric–ferrous redox couple, and trends in the data indicate iron solubility control by siderite at high pH, by ferric hydroxide at moderate to slightly acid pH values, and possibly by jarosite at low pH. Aluminum solubility controls are complex, and precipitation of amorphous aluminum hydroxide, allophane, and basic aluminum sulfates may occur over different pH ranges. Transport of low-pH conditions is retarded relative to the rate of groundwater flow in the tailings, because of the buffering effect of small amounts of carbonate minerals added during tailings neutralization; primary aluminosilicates such as sericite; and secondary aluminum hydroxides.Field data show that the flux of dissolved iron from the vadose zone to the groundwater zone in the Nordic Main tailings has been decreasing in recent years. However, mass-balance calculations indicate a potential for the generation of high-Fe groundwater for several decades to several hundred years. A long-term potential for acid and iron production is also shown by data from two tailings impoundments that have been inactive 8–10 years longer than the Nordic Main area. Presently only a small portion of the Nordic Main and West Arm tailings areas has become acidic through the entire tailings thickness; however, under existing infiltration conditions more extensive acidification will occur in future decades.

Laboratory Simulation of Fly Ash as an Amendment to Pyrite‐Rich Tailings

AbstractColumn leaching experiments show that fly ash Interlayered with sulfide‐rich tailings can reduce the vertical permeability of tailings by at least three orders of magnitude. Chemical reactions between the fluid, alkaline fly ash from Western coal and pyritic tailings result in a one to three order of magnitude reduction in the dissolved metals content of the effluent solution. Metal precipitation, which produces the dissolved metals reduction, is a significant element in the permeability reduction. The combined factors reduce the metals flux from the tailings by four to six orders of magnitude. We believe that tailings ponds with fly ash layers as amendments can greatiy reduce ground water contamination from pyritic tailings. In addition, concentrated application of fly ash layers near the end of mining should act to restrict infiltration and access of oxygen, thereby enhancing reclamation. Similar results maybe obtainable using other amendments with lower base capacity (lime, crushed limestone, trona).