Mining Mitigation in Norway and Future Improvement Possibilities

arkisto.gtk.fi

Contaminative drainage from mine sites, and particularly from mine waste deposits, may pose risks to surface waters. Therefore, mine site risk assessment and management require knowledge of the whole series of processes from mine drainage formation to contaminant transport and the eventual ecological effects. This paper summarizes some of the recent studies by the Geological Survey of Finland covering these issues. The studies have included investigations of the mineralogical and geochemical changes in the tailings and variation in tailings effluent quality, the influence of sedimentation dynamics on contaminant distribution in lake sediments, and the use of sediment chemistry and biota to evaluate the environmental impact of the loading. The results demonstrate that even though sulphide oxidation in tailings may already start during the active disposal of tailings, the main impacts of mine drainage on surface waters are typically associated with the post-mining period of AMD generation. This underlines the importance of the proper design and after-care of tailings facilities. In addition, wind-driven bottom currents were observed to have a major influence on the sedimentation dynamics in shallow lakes, which are typical in Finland, and thus also on the contaminant distribution in lakes, further affecting the aquatic impacts of the mine site.

2007

2009

The Hornträsk open pit mine was originally reclaimed in 1995-1996. However, due to continued discharge of metals to nearby Lake Hornträsk additional amendments were found necessary. In 2005-2006 mesa lime, a calcite containing residue from production of wood pulp, was applied in the saturated zone of the soils within the industry area. Additional measures in 2007-2008 focused on reducing drainage of surface water from the local catchment's area and neutralisation of the acidity produced by sulphide oxidation. A saturated solution of mesa lime dissolved in water was infiltrated in the unsaturated zone at a 1:1 volume of solution to soil ratio. The infiltration of the mesa lime solution was terminated in September of 2007 and was continued during the snow free period in 2008. The discharge of water from the springs was reduced to about 50%. While the content of Cu, Zn and Cd in the discharge was reduced by about 85% respectively 50% in one of the springs only a minor increase in pH and varying concentrations of heavy metals was observed in another spring. The groundwater close to the lake showed a significant increase in pH and a decline of the metal concentrations.

Applied Geochemistry, 1999

A study of O 2 penetration and pore water geochemistry of the¯ooded tailings at Stekenjokk has been performed. The results show that there is a diusion of elements from the tailings pore water to the overlying water. The presence of elements such as Ca, Mg, S, Si, Ba and Sr are likely the result of diusion of older process water trapped in the tailings. Oxygen concentrations in the tailings measured with microelectrodes show that there is O 2 available down to 16 to 17 mm depth in the tailings. Pore water analyses show that there are subsurface maxima for the elements Cu, Zn, Ni, Co and Cd at depths of 0.25 to 2.75 cm. The highest concentrations of almost all elements were found where previously oxidised material was deposited before the¯ooding. Lower pH is measured in the uppermost part of the tailings compared with the pond water and the tailings pore water at depth. Oxidation of sulphides in the uppermost part of the tailings is probably occurring. A decrease in oxidation rate can be expected in the future due to deposition of organic material at the tailings surface. Flooding seems to be an ecient remediation method at Stekenjokk. #

Applied Geochemistry, 2015

Tailings generated during processing of sulfide ores represent a substantial risk to water resources. The oxidation of sulfide minerals within tailings deposits can generate low-quality water containing elevated concentrations of SO 4 , Fe, and associated metal(loid)s. Acid generated during the oxidation of pyrite [FeS 2 ], pyrrhotite [Fe (1Àx) S] and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate, (oxy)hydroxide, and silicate minerals. The extent of acid neutralization and, therefore, pore-water pH is a principal control on the mobility of sulfide-oxidation products within tailings deposits. Metals including Fe(III), Cu, Zn, and Ni often occur at high concentrations and exhibit greater mobility at low pH characteristic of acid mine drainage (AMD). In contrast, (hydr)oxyanion-forming elements including As, Sb, Se, and Mo commonly exhibit greater mobility at circumneutral pH associated with neutral mine drainage (NMD). These differences in mobility largely result from the pH-dependence of mineral precipitation-dissolution and sorption-desorption reactions. Cemented layers of secondary (oxy)hydroxide and (hydroxy)sulfate minerals, referred to as hardpans, may promote attenuation of sulfide-mineral oxidation products within and below the oxidation zone. Hardpans may also limit oxygen ingress and pore-water migration within sulfide tailings deposits. Reduction-oxidation (redox) processes are another important control on metal(loid) mobility within sulfide tailings deposits. Reductive dissolution or transformation of secondary (oxy)hydroxide phases can enhance Fe, Mn, and As mobility within sulfide tailings. Production of H 2 S via microbial sulfate reduction may promote attenuation of sulfideoxidation products, including Fe, Zn, Ni, and Tl, via metal-sulfide precipitation. Understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings.

Environmental Earth Sciences, 2006

Cemented layers (hardpans) are common in carbonate or sulphide-rich mine tailings and where pyrrhotite is the predominating Fe-sulphide. Laver, northern Sweden, is an abandoned Cu-mine where the tailings have low pyrrhotite content, almost no pyrite and no carbonates. Two cemented layers at different locations in the Laver tailings impoundment were investigated, with the aim to determine their effects on metal mobility. The cementing agents were mainly jarosite and Fe-oxyhydroxides in the layer formed where the tailings have a barren surface, whereas only Fe-oxyhydroxides were identified below grass-covered tailings surface. Arsenic was enriched in both layers which also exhibit high concentrations of Mo, V, Hg and Pb compared to unoxidised tailings. Sequential extraction indicates that these metals and As were mainly retained with crystalline Fe-oxides, and therefore potentially will be remobilised if the oxic conditions become more reducing, for instance as a result of remediation of the tailings impoundment.

Geochemistry [Working Title]

Spain has a long mining tradition dating from prehistoric times up to the present day. The cessation of mining activity has generated a large amount of mine wastes, most of which represent geochemical hazards. Mine tailings are watery sludge composed of medium-to-fine-grained material, resulting from grinding and mineral processing (e.g., galena, pyrite, sphalerite, and arsenopyrite). They entail both an accumulation and a potential subsequent emission source of trace elements (i.e. As, Cu, Fe, Pb, and Zn) with formation of acid mine drainage (AMD). Mineralogical and geochemical techniques (in combination with geophysical surveys and aerial photographs studies) have been jointly applied to selected mine areas. Seven mine deposits from the most important mine districts in Spain have been selected: Iberian Pyrite Belt, Cartagena-La Unión, Alcudia Valley, and Mazarrón. The main goal is focused on getting a geoenvironmental characterization as complete as possible by determining the geometry, evolution in time and composition of mine ponds, and the possible occurrence of AMD, for identifying related environmental hazards.

Applied Geochemistry, 2015

The long-term influence of a shallow water cover limiting sulfide-mineral oxidation was examined in tailings deposited near the end of operation in 1951 of the former Sherritt-Gordon Zn-Cu mine (Sherridon, Manitoba, Canada). Surface-water, pore-water and core samples were collected in 2001 and 2009 from above and within tailings deposited into a natural lake. Mineralogical and geochemical characterization focused on two contrasting areas of this deposit: (i) sub-aerial tailings with the water table positioned at a depth of approximately 50 cm; and (ii) sub-aqueous tailings stored under a 100 cm water cover. Mineralogical analyses of the sub-aerial tailings showed a zone of extensive sulfide-mineral alteration extending 40 cm below the tailings surface. Moderate alteration was observed at depths ranging from 40 to 60 cm and was limited to depths >60 cm. In contrast, sulfide-mineral alteration within the submerged tailings was confined to a <6 cm thick zone located immediately below the water-tailings interface. This narrow zone exhibited minimal sulfide-mineral alteration relative to the sub-aerial tailings. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy showed results that were consistent with the mineralogical investigation. Pore-water within the upper 40 cm of the sub-aerial tailings was characterized by low pH (1.9-4.2), depleted alkalinity, and elevated SO 4 and metal concentrations. Most-probable number (MPN) enumerations revealed abundant populations of acidophilic sulfur-oxidizing bacteria within these tailings. Conversely, pore-water in the sub-aqueous tailings was characterized by near-neutral pH, moderate alkalinity, and relatively low concentrations of dissolved SO 4 and metals. These tailings exhibited signs of dissimilatory sulfate reduction (DSR) including elevated populations of sulfate reducing bacteria (SRB), elevated pore-water H 2 S concentrations, and strong d 34 S-SO 4 and d 13 C-DIC fractionation. Additionally, mineralogical investigation revealed the presence of secondary coatings on primary sulfide minerals, which may serve as a control on metal mobility within the sub-aqueous tailings. Results from this study provide critical long-term information on the viability of sub-aqueous tailings disposal as a long-term approach for managing sulfide-mineral oxidation.

2015

The seepage water quality of old sulfide mine tailings was studied from eleven closed sulfide metal mines in Finland to assess the influence of ore type on the drainage quality of tailings in the longterm. The studied sites represent a wide variety of ore types and commodities (e.g. Mo; Cu and Zn; Ni and Cu; Cu, W, As, Ag; Fe). Also the operation periods of the mines vary, from the 1750s to 1990s. Mining operations had ceased at the sites some 15‒62 years ago (prior to sampling), but most of the facilities were left without any cover after mine closure. Only three of the tailings impoundments were covered with a thin layer of till or peat. The seepage quality varied largely between the different mine sites. The pH of the seepages was between 2.8‒7.3 and the total metal content (Zn + Cu + Cd + Pb + Co + Ni) between 0.004‒207 mg/L. Overall, the high-acid, high-metal waters were related to Cu mine tailings, whereas the seepages from the other tailings deposits (i.e. from Ni, Fe, Mo, an...

Applied Geochemistry, 2003

At the remediated tailings Impoundment 1 at Kristineberg, Northern Sweden, installations of tension lysimeters were performed in the protective cover (10, 50, and 100 cm), in the oxidised tailings (150 cm), in the unoxidised secondarily enriched tailings (200 cm) and in the unoxidised tailings (260 cm). The lysimeters in the till protective cover contained relatively low concentrations of most elements. After infiltration through the sealing layer, consisting of 0.3 m compacted clayey till, pH decreased and conductivity, together with the concentrations of several major and trace elements, increased significantly. In the lysimeters installed in the tailings at depths of 150 and 200 cm average pH decreased to 3.4 at 150 cm and 3.2 at 200 and average conductivity increased to 2.9 mS/cm. Elements such as Al, Cd, Co, Fe, Mn, Mo, Ni,Pb, S, Si and Zn had the highest concentrations in the lysimeter at 200 cm depth. Examples of concentration averages for this lysimeter are Cd 600 mg/L, Fe 1500 mg/L, Mn 11 mg/L, Ni 1.06 mg/L, S 1800 mg/L, and Zn 190 mg/L. Between the depths of 200 and 260 cm the concentration of most elements decreased. The increase between the lysimeters at the depths of 150 and 200 cm can be explained by remobilization of secondarily retained oxidation products as well as from the continued oxidation. The decrease between the second and the third lysimeters is interpreted as co-precipitation with different Fe oxyhydroxides as well as adsorption onto secondarily formed minerals and primary mineral surfaces. Calculations of saturation indices indicate that several different hydroxides might precipitate at this level. This retainment takes place mainly due to the increase in pH. The pH increases from 3.2 up to 4-4.4 in this depth interval. Between the deepest lysimeter and the groundwater table, the element concentrations probably decrease even further. pH increases to 5-6.5 in the groundwater. Most of the pre-remediation oxidation products that are secondarily retained above or below the oxidation front and are released by the small amount of infiltrating water together with the present oxidation products are retained again during continued transport downwards. If the depth to the groundwater table is large enough, most of the metals released by the infiltrating water and the diffusing O 2 do not reach the groundwater. #