Dissertations / Theses on the topic 'Copper mine tailings'

Geopolymerization is a chemical reaction process, reacting SiO₂ and Al₂O₃ with alkaline solutions, which can transform aluminosilicate solids or particles to polymer materials. Geopolymers have many engineering applications such as cementation binders for construction and solidification or encapsulation of hazardous heavy metals. Mine tailings mainly consist of SiO₂ and Al₂O₃. Theoretically, mine tailings can be used as source materials for geopolymerization. However, for most researchers, they use fly ash, metakaolin or furnace slag as source minerals, because these minerals are much more reactive with alkaline solutions. Mine tailings are naturally-forming minerals and are considered to be inert in geopolymerization. How are mine tailings to be activated through different reaction conditions? We conducted several tentative or preliminary experiments to study the geopolymerization process step by step. We tried different methods to react mine tailings with alkaline solutions. Mine tailings were submerged into alkaline solutions in a plastic bucket for 6 days in room temperature (20-25 °C). We wanted mine tailings to be activated by soaking. The results were not satisfying. Then we tried to react mine tailings with alkaline solutions at 60 °C and 90 °C. After analyzing, we found that the results were not satisfying either. So, we conducted simplified geopolymerization experiments in order to better understand the chemical reaction mechanism. Pure SiO2 and Al2O3, which were two major reactants, were employed to simplify and simulate the geopolymerization process. We drew some useful conclusions such as that geopolymerization took place at elevated temperatures; Al₂O₃ almost did not react with alkaline solutions at low temperatures, etc. We conducted experiments at elevated temperatures (150 °C, 180 °C, 210 °C). Different levels of pressure (5 MPa, 10 MPa, 20 MPa) were applied to make compact specimens. After many attempts, the results were successful. The highest mechanical strength was about 20 MPa. Most importantly, we obtained polymers produced from geopolymerzation, which could be seen by naked eyes. The experiment techniques such as scanning electron microstructure (SEM) imaging and X-ray diffraction (XRD), inductively-coupled plasma mass spectrometry (ICP-MS), and unconfined compression tests (UCS) were applied to study the geopolymerization reaction mechanism and the feasibility of using mine tailing-based geopolymers as construction materials.

In mining industry, waste storage is a very prominent issue
in this respect, safety of storage structures is one of the leading problems in the industry. Most of the tailings dams require remedial measures, throughout their lifespan to increase their reliability. The objective of the study is to investigate stability problems of formerly constructed but newly raised Eti Copper Mine tailings dam and alternative dam geometries for future raises. Plenty of methods were developed to analyze the reliability of structures
limit equilibrium methods, finite element methods and finite difference methods are among them. In this case, stability of the dam was analyzed with finite element method under static loading conditions. In order to determine input parameters properly, disturbed samples obtained at the field investigations were used. For this purpose, several laboratory experiments were conducted to determine natural moisture content, grain size distribution, specific gravity, Atterberg limits, maximum dry density and shear strength parameters of tailings and embankment material.

Phytostabilization is a remediation technology that uses plants for in-situ stabilization of contamination in soils and mine tailings. The objective of this study was to identify native plant species with potential for phytostabilization of the abandoned mine tailings in Nacozari, Sonora in northern Mexico. A flora of 42 species in 16 families of angiosperms was recorded on the tailings site and the abundance of the most common perennial species was estimated. Four of the five abundant perennial species showed evidence of regeneration: the ability to reproduce and establish new seedlings. A comparison of selected physicochemical properties of the tailings in vegetated patches with adjacent barren areas suggests that pH, electrical conductivity, texture, and concentration of potentially toxic elements do not limit plant distribution. For the most abundant species, the accumulation factor for most metals was <1, with the exception of Zn in two species. A short-term experiment on adaptation revealed limited evidence for the formation of local ecotypes in Prosopis velutina and Amaranthus watsonii . Overall, the results of this study indicate that five native plant species might have potential for phytostabilization of the Nacozari tailings and that seed could be collected locally to revegetate the site. More broadly, this study provides a methodology that can be used to identify native plants and evaluate their phytostabilization potential for similar mine tailings.

Mercury is a well known environmental pollutant. Anthropogenic sources include coal combustion, waste incineration and metal processing. In base metal mines, Hg is often left in the mining wastes (i.e., mine tailings). Once disposed of in open-air impoundments, these Hg-containing tailings can undergo various biogeochemical transformations, including Hg methylation. It is the methylated form of mercury (MeHg) that poses a threat to the environment, because it bio-accumulates at each level of the food chain. The present study was undertaken to assess the biogeochemical factors affecting Hg methylation in Cu-Zn and Au mine tailings. The study focused on the role of sulfate-reducing bacteria (SRB) because they are suspected to be associated with Hg methylation. Temperature, sulfate and organic carbon availability, along with SRB activity were tested as potential factors affecting Hg methylation in column experiments containing old Au tailings and fresh Cu-Zn tailings. The results first showed that SRB activity did not enhance Hg methylation in Cu-Zn tailings and Au tailings, indicating that iron reducing bacteria, and not SRB, along with abiotic methylation reactions played an important role. Cold temperatures did not slow down SRB activity and MeHg production, but the accidental freezing and thawing of the Cu-Zn tailings promoted the production of soluble MeHg. The mechanism responsible for this unexpected Hg methylation is however unknown. Elevated organic carbon and sulfate concentrations did enhance SRB activity, but not MeHg formation in the tailings, because increased sulfide production hindered Hg methylation. Tailings mineralogy played a significant role in the production of methyl mercury, Au tailings contained more soluble and solid-bound MeHg than Cu-Zn tailings. These results add to the increasing amount of information on Hg cycling in the environment, and indicate that SRB might not be the dominant Hg methylators in mining environments.

Establishing plant communities is essential for the restoration of contaminated land. As potential cover materials, fly ash and sewage sludge can prevent formation of acid mine drainage from sulfidic mine waste. The aim of the thesis was to i) screen for plants that can be established in, and prevent leakage of metals and nutrients from sludge on top of ash and tailings, and ii) investigate root growth into sealing layers of ash and sludge. Analyses were performed under laboratory, greenhouse and field conditions using selected plant species to examine the release of Cd, Cu, Zn, N, and P from the materials. Plant physiological responses and interactions with fly ash were also investigated. The data show that plants can decrease metal and nutrient leakage from the materials, and lower the elemental levels in the leachate, but with varying efficiencies among plant species. Plants capable of taking up both nitrate and ammonium were more efficient in preventing N leakage compared with those taking up primarily ammonium. Fast growing plants could raise the pH in acidic sludge leachate, but the initial pH decrease and N leakage was not counteracted by plants. Germination in fresh sludge was problematic, but enhanced by aeration of the sludge. In general, the accumulation of metals in plant shoots was low, especially if ash was located below the sludge. Fresh ash was phytotoxic (e.g., high alkalinity, salinity and metal levels) and induced the activity of stress-related enzymes in shoots. In sealing layers of aged and cured ash, roots could grow if the penetration resistance was low, or into the surface of stronger layers if the surface had become pulverized. The roots caused dissolution of calcium-rich minerals, possibly by exudation of saccharides. Addition of sludge to an ash layer increased root growth, likely due to decreased bulk density and pH, and nutrient addition. In conclusion, with selected plant species and a properly constructed cover, metal and nutrient leaching from the materials and root growth into the sealing layer can be restricted.

The current manufacturing of clay-fired and cement bricks has contributed greatly to anthropogenic global emissions and environmental damages. A possible solution that could be used to alleviate such environmental pressures is through the adoption of carbon neutral, microbial induced calcium carbonate precipitation (MICP) bio-bricks as a replacement for traditional bricks. MICP produced bio-bricks are formed by exploiting the ability of the microorganism, Sporosarcina pasteurii, to produce a biocement capable of binding sand particles (or any aggregate) together into a solid. Furthermore, such bio-bricks can be grown from otherwise ‘waste' resources such as human urine. This significantly reduces energy inputs whilst creating value by ‘upcycling' waste streams, resulting in a product which is sustainable whilst promoting the modern ethos of implementing environmentally friendly circular economies. However, the environmental benefits of MICP bio-bricks are hindered by the use of sand in their production. Sand, after water, is by volume the worlds most exploited and traded raw material and as such the supply of sand is being rapidly depleted globally. Added to this, sand extraction processes are known to cause extensive environmental damages. A possible solution to this issue is to replace the sand aggregate used to grow bio-bricks with mine tailings. The increasing global demand for metal products has resulted in the concurrent production of vast volumes of waste mine tailings which, if left untreated, pose a potential risk of leaching toxins into surrounding populations and biota. As such it was postulated that this risk to surrounding populations and the environment could be mitigated by repurposing mine tailings, as a replacement for sand, into MICP bio-bricks. Both a technical and economic study was conducted to determine the feasibility of repurposing copper mine tailings into bio-bricks. As bio-bricks were resource intensive to produce (reagents, chemicals etc.), bio-columns were used as a proxy in studying the technical feasibility of such a process. The technical aspect of this study involved characterising copper mine tailings received from Columbia in terms of physiochemical make-up, particle size distribution and the development of a MICP submergent technique used in growing the bio-columns. This was necessitated by the fact that it was noted during the characterisation of the mine tailings that the cementation media could not be pumped through the columns filled with mine tailings aggregate, resulting in the traditional pumping method used to grow MICP bio-solids being impractical. The submergent technique was used to compare the MICP efficiency of growing biocolumns from either beach sand or copper mine tailings. In addition, the toxicity of copper to S. pasteurii was investigated and an attempt was made to acclimate a culture of S. pasteurii to the copper concentration found within copper mine tailings. Furthermore, the copper mine tailings were screened to determine if there were any indigenous, anaerobic and copper tolerant ureolytic extremophiles contained within, which had the potential to grow more robust bio-columns.

Samples of agronomic grasses and legumes grown on copper mine tailings under two surficial amendment regimes and two fertilizer treatments were analyzed for Ca, Cu, Fe, K, Mg, Mn, Mo, N, Ni, P, and Zn. These values were compared to National Research Council and Agriculture Canada diet recommendations for beef cattle. Foliar Ca, Fe, Mn, Ni and P concentrations were satisfactory. Zn levels in most species were in the deficient range. Some samples contained excessive K or Mg, although overall foliar concentrations for these minerals were satisfactory. Copper and molybdenum concentrations were well above normal levels. Copper concentrations in the legumes and grasses averaged 63 and 44 mg/kg, respectively. Mean molybdenum concentrations were found to be 52 mg/kg in the grasses and 237 mg/kg in the legumes. Cu:Mo ratios in all species violated recommended dietary guidelines for beef cattle. Fluctuations in Cu:Mo ratios were attributable mainly to variations in foliar Cu. Most species were subjected to severe grazing by rodents, producing abnormal growth habits. As a result, assessment of relative species success was difficult. Grazing stress may also have affected foliar elemental levels. Tailings material was artificially weathered by leaching with 0.3 N acetic acid for seven weeks in a Soxhlet extraction chamber. Leached and unleached samples were analyzed for pH, 0.1 N HCl available Cu, Fe, Mn, Ni, and Zn, acid ammonium oxalate extractable Mo, total elemental levels and mineralogical composition. As a result of leaching, the pH of the tailings was reduced from 6.6 to 3.5. Declines in available Cu, Fe, Mn, Zn, and Mo were noted after leaching. No qualitative changes in tailings mineralogy were detected after artificial weathering. During leaching, three general elemental release patterns were observed. These were attributed to the sequential dissolution of readily soluble salts and carbonates, followed by the degradation of micas, pyroxenes, amphiboles and host ore minerals. The relatively inert minerals, such as, quartz, some alumino-silicates and oxyhydroxides of Fe and Al represented the third group. At present, the tailings are unsuitable as a forage production area for beef cattle as a result of toxic Cu:Mo ratios in the foliage. Based on chemical changes induced by artificial weathering, it is probable that forage grown on the tailings will become less toxic over time. Various management practices may be employed to accelerate improvement in growth medium parameters.
Land and Food Systems, Faculty of
Graduate

Previous studies have shown that sulfate-reducing bacteria (SRB) are present and possibly active in gold and copper-zinc mine tailings. Sulfate-reducing bacteria can play an important role in the geochemistry of the mine tailings as they are responsible for the precipitation of diagenetic iron monosulfides and pyrite, a potential source for the generation of acid mine drainage. On the other hand, the formation of iron monosulfides can also serve to immobilize trace metals, and therefore has potential benefits to the tailing water systems. In addition, microbial sulfate reduction generates alkalinity which can be used to neutralize some of the acidity generated by the oxidation of metal sulfides. To better understand the role that sulfate-reducing bacteria play on the geochemistry of mine tailings, this present study was designed to identify some of the factors controlling the growth of sulfate-reducing bacteria in the tailings. The main goal was to determine the influence of organic electron donors (specifically lactate, acetate, formate and pyruvate) on microbial sulfate reduction in closed batch systems possessing physico-chemical conditions (pH, redox potential) matching the in situ conditions of the tailings in order to identify the preferred electron donor. (Abstract shortened by UMI.)

Organic matter amendments have long been known to improve native organic matter content, aggregation and structure of soils. In the laboratory, however, organic matter amendments to autoclaved soils have no such effect. This may explain the failure of many reclamation attempts on mine tailing wastes, which often proceed without regard for the microbiological processes necessary for soil formation and cycling of plant nutrients. In this study, incubation of tailing waste with soil microbes and a simple carbon source proved sufficient to increase the formation of water stable aggregates from tailing particles. Autoclaved control samples showed no change in aggregation. The incorporation of microbial cell mass into the mineral matrix of the tailing was observed using scanning electron microscopy. These results suggest that microbial activity is necessary in order to incorporate organic matter into the abiotic matrix of tailing, promoting aggregation and ultimately soil formation from this material.

Anaerobically digested biosolids (treated sewage sludge) were applied to Copper mine tailings (pH 8.0) in Princeton, B.C. to determine how well biosolids could achieve land reclamation on a site prone to wind erosion in a semi-arid climate (350 mm mean annual precipitation). In October 1992, biosolids at 62, 77 (two plots), and 179 Mg/ha were applied to four 0.5 ha plots with manure spreaders. In 1993, vegetation established on all sites without irrigation which reduced wind erosion. The 77 Mg/ha treatment led to the best vegetation quality and yield in the first growing season. Yield increased from 300 kg/ha (Control) to 5500 kg/ha (77 Mg/ha). In October 1993, additional biosolids were applied to the 62 and one of the 77 Mg/ha plots to test if it is beneficial to apply biosolids in two applications rather than one larger application. Yields in 1994 were generally lower than in 1993 reflecting lower precipitation. Alfalfa established well on all sites and was the dominant legume while brome and fescue were dominant grasses. Vegetation samples showed no micronutrient or metal toxicity problems. Notable trends in both growing seasons included: foliar Mo concentrations were lower; foliar Cu:Mo ratios were higher; cattle and deer grazing did not hamper growth; soil pH decreased whereas concentrations of Total P, Bray-P, TKN-N, NH₃-N, NO₃-N, Fe, and Hg increased with increasing application rates. Nitrate below 60 cm was negligible for all plots except the 179 Mg/ha and split application plots in 1994. N leaching losses were below 4-8% of applied TKN-N. Metal concentrations were below the CCME criteria for agricultural and residential soils except for Cu. Well water samples met the Canadian Drinking Water Guidelines.

MENVSC
Department of Ecology and Resource Management
Mine tailings (MT) have been a global problem due to the environmental impacts the waste generates such as air, soil and water pollution. The detrimental impacts include a global problem such as acid mine drainage (AMD) which has been difficult to cleanup. Several studies have been conducted to find alternative measures in reducing or mitigating impacts such as AMD and air pollution. Several studies have revealed how alumino-silicate mineral waste can be used as raw material to produce construction materials. This study aimed at evaluating the potential of synthesizing a geopolymer material from Musina copper mine tailings. Tailings were characterized for their physicochemical and mineralogical compositions using standard laboratory techniques in order to evaluate suitability in geopolymerization. First section of the results presented physicochemical and mineralogical characterization of the Musina copper tailings together with the bioavailability of the chemical species. It was observed that the tailings are mainly composed of SiO2 and Al2O3 as the major oxides indicating that they are aluminosilicate material. Mineralogical analysis revealed dominance of quartz, epidote and chlorite as the major minerals. The bioavailability assessment showed that largely Cu and Ca are bioavailable and highly soluble in an aqueous solution while Al, Mg, Ni, Co, Cr and Fe have a high proportion in non-labile phase. Second section presented the preliminary results wherein the potential application of Musina copper tailings in geopolymerization was evaluated. The results showed that Musina copper tailings can be used to synthesize a geopolymer material. However, it was recommended that several parameters influencing geopolymerization need to be evaluated. The third section presented the evaluation of optimum parameters that influence the geopolymerization process, which include type of alkali activators, alkali activator concentration, curing temperature, liquid-solid (L/S) ratio and curing regime. It was observed that a mixture of NaOH:Na2SiO3.5H20 at a ratio of 70:30 yields a better geopolymer material. The concentration of 10 M NaOH:Na2SiO3.5H20 at a ratio of 70:30 was observed to be the best that yielded the UCS that is acceptable according to SANS1215 standards. When evaluating curing regime, it was found that the material cured using greenhouse has lower UCS as compared to the material cured using oven. The v effect of temperature showed that the UCS decreases with increasing curing temperature. An admixture of river sand and cement was introduced which resulted in a high UCS of 21.16 MPa when using an admixture of cement. The mineralogical composition of the geopolymer bricks showed formation of secondary minerals such as phlogopite, fluorapatite, diopside and actinolite. Batch leaching conducted on the geopolymer bricks detected high leaching of Na from the bricks. Based on the findings of the study of the raw MT potential to produce geopolymer bricks, it was concluded that the material can be used to produce bricks that are within the SANS 1215 requirements. The study further recommended that the study a focus on using cylindrical moulds, other alkali activators and a mechanical mixer. It was also recommended that the greenhouse be restructured to contain heat within the greenhouse during the evening so as to allow constant temperature within
NRF

Revegetation and sustainable cattle grazing are major objectives in the program for the reclamation of mine tailings at the Highland Valley Copper mine in British Columbia, Canada. Residual molybdenum (Mo) in the tailings is imbibed by vegetation and can accumulate to extremely high levels (> 25 ppm Mo on a dry matter basis). Accordingly, grazing studies were initiated with cattle to determine the feasibility of utilizing the Bethlehem and Highmont tailings sites for livestock production. Molybdenum levels in forages were at least ten times higher at Highmont than at Bethlehem. A total of 262 cow-calf pairs grazed the Bethlehem site for four consecutive years (1994 - 1997) and the Highmont site for five consecutive years (1998 - 2002). Cattle at Bethlehem did not show clinical signs of Mo toxicity or copper deficiency. In contrast, cattle at Highmont showed clinical signs including lameness, diarrhea and haircoat depigmentation. The onset and severity of the affliction appeared to be related, in part, to prevailing moisture conditions, which affected Mo availability in forage. The cattle recovered by the end of each trial and haircoat problems were resolved by the next spring. Preventive measures were attempted using copper supplements that can alleviate Mo toxicity. Copper boluses did not provide adequate protection in 2001 but copper sulphate supplementation in loose salt prevented the onset of clinical signs in 2002.

Anaerobically digested biosolids (treated sewage sludge) were applied to copper mine tailings (pH 8.0) in Princeton, B.C. to determine how well biosolids could achieve land reclamation on a site prone to wind erosion in a semi-arid climate (350 mm mean annual precipitation). In October 1992, biosolids at 62, 77 (two plots), and 179 dry tonnes/ha (dt/ha) were applied to 0.5 ha plots. In the first growing season, vegetation established on all plots without irrigation, and the 77 dt/ha treatment led to the best vegetation quality and yield (5500 kg/ha). Trends in the first growing season included: lower foliar Mo concentrations, higher foliar Cu:Mo ratios, decreased soil pH, and increased concentrations of TKN, NH4-N, NO3-N, Total P, Bray P-1, Total Fe, and Total Hg with increasing application rates. Nitrate in the tailings below 60 cm was negligible. Metal concentrations were below the CCME criteria (1991) for agricultural and residential soils except for Cu. Associated with the field trial were laboratory leaching experiments consisting of two runs of 26 columns and one run of 10 pots testing application rates of 0, 30, 100, and 300 dt/ha biosolids. Leaching experiments primarily estimated the magnitude of nitrate leaching, the mineralization rate of biosolids, and the behaviour of metals. The first column run was conducted under wetter conditions than the other trials. Under wetter conditions, the leaching of nitrate, TKN, and TP was minimal. Under dryer conditions, TKN leaching was below 0.6 kg/ha for all columns except col. H (103 kg/ha), and nitrate leaching was less than 0.4 kg/ha for all columns except col. G (123 kg/ha) and col. H (79 kg/ha). The high nitrate concentrations were probably due to a preferential flow. Mineralization rates ranged from 17 to 31 % for the wetter run (10 weeks) and from 29 to 43% for the dryer run (13 weeks). Mineralization was highest for 30 dt/ha treatments. For the 300 dt/ha treatments, soil mineral N ranged from 200 to 745 kg/ha under wetter conditions and from 1200 to 3000 kg N/ha under dryer conditions. Nitrogen losses increased with application rate (30-34% of added N was lost for 300 dt/ha biosolids). Metal concentrations were below the CCME criterion for residential use except for Cu.

Oxidation of sulphide minerals contained in the mine tailings impoundments at Copper Cliff, Ontario generates acidic conditions and elevated concentrations of dissolved constituents in the pore water. The tailings groundwater migrates radially outwards and might pose an environmental hazard if reaches the nearby water systems. There is a need to estimate the dimension of the current problem and assess future prospects. That need prompted a combined DC resistivity and Induced Polarization (IP) survey along one of the major flowpaths in the tailings. The DC resistivity and IP data were inverted to produce the detailed electric conductivity and chargeability structures of the cross section below the survey Une. Problems, generic of the inversion methodology and specific to the inversion of data from the tailings, are discussed and solutions are elaborated and demonstrated. The conductivity structure can be directly translated, through theoretical or empirical relations, to a map of the concentration of dissolved solids along the cross section and thereby provide insight about the current pore water quality. The sulphide minerals are the source of the IP response and thus the chargeability model can be used to estimate the amount and distribution of the sulphides. A new methodology to construct and invert IP decay curve information was developed. Assuming Cole-Cole relaxation to model the IP phenomenon, data sets constructed through the inversion of IP data of different time windows were inverted using a damped least squares algorithm. Values of the resultant Cole-Cole parameters might contribute additional insight about the sulphides in the tailings. Lack of time and laboratory verifications prevented full development and comprehensive conclusions. The research in this thesis concentrated along one line of the survey data with the intention of showing the capability of the DC resistivity and IP methods and their potential contribution to estimation of location and concentrations of the sulphide minerals and their oxidation products. The conclusions should assist designers of a large scale survey and prompt investigations of the relations between the physical properties mapped by these methods and the chemical parameters which are considered while assessing the damage and contemplating solutions.

Samples of agronomic grasses and legumes grown on copper mine tailings under two surficial amendment regimes and two fertilizer treatments were analyzed for Ca, Cu, Fe, K, Mg, Mn, Mo, N, Ni, P, and Zn. These values were compared to National Research Council and Agriculture Canada diet recommendations for beef cattle. Foliar Ca, Fe, Mn, Ni and P concentrations were satisfactory. Copper and molybdenum concentrations were well above normal levels. Copper concentrations in the legumes and grasses averaged 63 and 44 mg/kg, respectively. Mean molybdenum concentrations were found to be 52 mg/kg in the grasses and 237 mg/kg in the legumes. Cu:Mo ratios in all species violated recommended dietary guidelines for beef cattle. Fluctuations in Cu:Mo ratios were attributable mainly to variations in foliar Cu. Most species were subjected to severe grazing by rodents, producing abnormal growth habits. As a result, assessment of relative species success was difficult. Grazing stress may also have affected foliar elemental levels. Tailings material was artificially weathered by leaching with 0.3 N acetic acid for seven weeks in a Soxhlet extraction chamber. Leached and unleached samples were analyzed for pH, 0.1 N HCl available Cu, Fe, Mn, Ni, and Zn, acid ammonium oxalate extractable Mo, total elemental levels and mineralogical composition. As a result of leaching, the pH of the tailings was reduced from 6.6 to 3.5. Declines in available Cu, Fe, Mn, Zn, and Mo were noted after leaching. No qualitative changes in tailings mineralogy were detected after artificial weathering. During leaching, three general elemental release patterns were observed. These were attributed to the sequential dissolution of readily soluble salts and carbonates, followed by the degradation of micas, pyroxenes, amphiboles and host ore minerals. The relatively inert minerals, such as quartz, some aluminosilicates and oxyhydroxides of Fe and Al represented the third group. At present, the tailings are unsuitable as a forage production area for beef cattle as a result of toxic Cu:Mo ratios in the foliage. Based on chemical changes induced by artificial weathering, it is probable that forage grown on the tailings will become less toxic over time. Various management practices may be employed to accelerate improvement in growth medium parameters.

MENVSC
Department of Ecology and Resource Management
Historically, mining activities have generated vast quantities of abandoned tailings dumps in several regions of South Africa and throughout the world. The management and disposal of huge volumes of tailings dumps has constituted a major challenge to the environment. The current study aims to establish the physicochemical properties and mineralogical characterization of the old copper tailings dump in Musina, to reveal the mobility patterns and attenuation dynamics of potentially toxic or heavy metal species as a function of depth, with a view of assessing their potential environmental impact with respect to surface and ground water systems. This information is crucial in the beneficial utilization of copper tailings in the development of sustainable construction materials as part of reuse approach management system. About twelve tailings samples were collected into polyethylene plastic bags from three established tailings profiles drilled by a hand auger. The collected tailings samples were characterized using standard analytical procedures i.e., X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS). The transfer of potentially toxic or heavy metal species from tailings to water was evaluated using the standardized batch leaching test (EN 12457) and speciation-equilibrium calculations on the aqueous extracts performed by MINTEQA2. The leachate concentration of cations in the collected tailings samples was determined by inductively coupled mass spectrometry (ICP-MS) and the leachate concentration of anions was determined by ion chromatography (IC). A modified sequential extraction scheme was applied on the selected tailings samples of the drilled tailings profiles to further understand the mode of occurrence, the geochemical partitioning and distribution, real mobility, and environmental bioavailability of potentially toxic or heavy metal species in the tailings and tailings-soil interface. The extracted fractions or phases from sequential scheme were as follows: (F1) water-soluble fraction, (F2) exchangeable fraction, (F3) carbonate fraction, (F4) iron and manganese hydroxide associated fraction, (F5) organic matter and secondary sulphide associated fraction, (F6) primary sulphide bound fraction, and (F7) residual or silicate fraction. The results obtained from the seven steps sequential extraction scheme were validated by the determination vi of percentage recoveries from pseudo-total digestion or total metal content of the original sample. The distribution of major elements and potentially toxic or heavy metal species in different leachate fractions obtained after each step of sequential extraction of the selected tailings samples was determined by inductively coupled plasma mass spectrometry (ICP-MS). The appraised data was used to reveal the impact of atmospheric oxygen and infiltrating rain-water on the chemistry of copper tailings dump by depth profiles. Macroscopic properties revealed that the abandoned Musina copper tailings are fine to medium coarse grained, and range in color from light/dark gray at the upper or shallow depth of the tailings, to dark reddish-brown at the deeper zone where the tailings are mixed with the underlying soil or soil-interface. The drilled respective tailings profiles were uniform and slightly varied in both mineralogical and bulk chemical compositions with tailings depth. Mineralogical analysis showed the following order of mineralogical composition within the respective tailings profiles: quartz> epidote> chlorite> muscovite> calcite> hematite. Chalcopyrite was the only sulphide mineral observed by optical microscopy, although not identified or quantified by XRD and SEM-EDS analysis. The observed discrete chalcopyrite grains were attributed to the primary mined ore (i.e., chalcopyrite, chalcocite and bornite) during past copper mining activities in Musina. The tailings profiles were characterized by a medium alkaline pH (7.97-8.37) that corresponds very well with the tailings leachates or pore-water pH (8.36-8.46). This pH was constant and slightly varied with tailings depth in the respective tailings profiles. The high abundance of alumino-silicate minerals and traces of carbonates as calcite coupled with low sulphide mineral content, suggested a high neutralization capacity of the tailings which was in common agreement with an alkaline nature of the copper tailings dump. The chemical composition of major elements within the respective tailings profiles followed the order: Si>Al>Fe>Ca>Mg>K>Na, and corresponds very well with the mineralogical composition of the tailings, whereby alumino-silicates were the most abundant minerals in the tailings samples. Nevertheless, the solid-phase concentration of metals decreases with increasing tailings depth as Cu>Sr>Zr>Ni>Zn and was incongruent with the mineralogical composition within the respective tailings profiles. The main secondary minerals were calcite and hematite, and their proportion increased with increasing tailings vii depth. In addition, hematite formed coatings on the rims and corners of chlorite as observed from optical microscopy, and retained relatively high amounts of potentially toxic or heavy metals (up to 862 ppm of Cu, up to 36 ppm of Ni, and up to 25 ppm of Zn) at the upper and shallow depth of the respective tailings profiles, where bulk density was high and low porosity. Based on batch leaching tests, the amounts of potentially toxic or heavy metal species released into solution were low (0.27-0.34 μg/L Pb, 0.54-0.72 μg/L Ni, 0.88-1.80 μg/L Zn, and 20.21-47.9 μg/L Cu) and decreases with increasing tailings depth, indicating that, presently, the tailings have a minor impact on heavy metals load transported to the receiving surface and groundwater systems. The low concentration of potentially toxic or heavy metal species in solution is primarily due to their retention by secondary Fe oxide phases (i.e., hematite) and the prevailing medium alkaline pH condition of the tailings leachate or pore-water. The observations are consistent with MINTEQA2 speciation calculations, which predicted the precipitation of secondary phase cuprite (Cu2O) as the main solubility-controlling mineral phase for Cu, Zn, and Ni. Primary factors influencing aqueous chemistry at the site are neutralization and dissolution reactions as a function of pH, precipitation, and sorption into hydrous oxides (hematite and cuprite). Based on sequential extraction results, the leachable concentration of potentially toxic or heavy metal species in the water-soluble, exchangeable and carbonate fractions of the respective tailings profiles was relatively low, except for Cu and Mn. For instance, the leachable concentration of Cu and Mn reached 10.84 mg/kg and 321.7 mg/kg at the tailings-soil interface (3 m) in tailings profile C, respectively. The low concentration of potentially toxic or heavy metal species (Cr, Co, Ni, Zn, Cd, and Pb) in these fractions could be due to the low solubility of minerals bearing these trace elements caused by variations in pore-water pH in the respective tailings profiles. The high concentration of Cu and Mn in these fractions suggests their high mobility and therefore most available for uptake in the environment. Except for Cu>Mn>Cr, the contents of potentially toxic or heavy metal species in the Fe and Mn oxides and organic matter or sulphides bound fractions was low, due to the low viii quantity of these fractions in the tailings, despite their high affinity and sorption capacity for potentially toxic or heavy metal species. Likewise, the residual fraction of the respective tailings profiles contained the highest proportion of potentially toxic or heavy metal species. Although the highest potentially toxic or heavy metal species content was in fractions with limited mobility, care must be taken since any geochemical change or shift in the tailings pH or acidic conditions may cause them to be displaced to more mobile fractions, thereby increasing their mobility and environmental bioavailability. Therefore, physicochemical properties of the tailings including pH and mineralogical composition of the tailings samples were the main substrate controlling the geochemical partitioning and distribution, potential mobility, and environmental bioavailability of potentially toxic or heavy metal species by tailings depth. The knowledge of mobility and eco-toxicological significance of tailings is needed when considering tailings dump disposal or reuse in the environment. The addition of copper tailings at 3 and 28 days successfully improved the compressive strength of cement mortar mixtures incorporating tailings at C5 (5%) and C10 (10%) respectively, although with small margin relative to the control mixture (C0). The maximum strength was 31.15 Mpa attained after 28 curing days, and slightly varied when compared with other compressive strength on copper blended cement mortars mixtures in other countries, used for the development of sustainable construction materials. The chemical composition, physical properties and improved compressive strength on cement mortars mixtures incorporating copper tailings, implies that copper tailings are suitable for the development of sustainable construction materials, thereby ensuring job creation, availability of land for development usage, and the reduction of environmental pollution induced by the abandoned copper tailings dumps.

Since 1993, Inco Ltd. has been investigating the possiblity of using a flotation-derived low-sulfide tailings as a means of providing a potentially inactive cover and dam construction material for their Copper Cliff tailings area. The investigation involves open-air field lysimeter and laboratory oxidation column tests of a low-sulfide tailings product produced by the Clarabelle mill; as well as, the evaluation of the concurrent alteration of two tailings products, a main tailings (1.0 wt. % S), and a total tailings product (2.5 wt. % S), to provide comparisons of oxidation rates and the geochemical evolutions that accompany the sulfide-mineral oxidation in the different sulfide-bearing tailings. A pyrrhotite-rich tailings (approximately 14 wt. % S) was also subjected to oxidation in the laboratory columns for the same period of time and was also examined for comparison. This project was undertaken to identify the solid phases that are the primary sources of potential or known contaminants, and solid phases that provide potentially acid-neutralizing capacity to the tailings, as well as to identify secondary precipitates that serve to control the pore-water concentrations of dissolved ions in the various tailings types. The analytical methods employed to achieve these objectives include powder x-ray diffractometry, optical and scanning electron microscopy, energy dispersion spectroscopy and multi-element x-ray mapping techniques, electron probe microanalysis, and Debye-Scherrer x-ray film methods. In these tailings, the sulfide mineral of primary concern with respect to acid generation is pyrrhotite. The oxidation of pyrrhotite is marked by replacement with iron oxyhydroxides, including goethite and lepidocrocite, native sulfur, ferric iron sulfates, and covellite. Nickeliferous pyrrhotite is the primary source of pore-water nickel, with minor contributions from the oxidation of pentlandite and nickeliferous slag particles. Secondary goethite detected in the saturated zone of the tailings contains more nickel than the goethite from the unsaturated zone of the tailings and is the primary "sink" for dissolved nickel. Pentlandite has oxidized to various degrees in the tailings and is demarcated by replacement with iron oxyhydroxides. The oxidation of chalcopyrite is also evident contributing to pore-water concentrations of dissolved copper. Alteration is most commonly seen as dissolution and subsequent precipitation of secondary covellite, as well as replacement by iron oxyhydroxides. Slag particles, although volumetrically of less importance than the sulfides, may be a source of metal contamination including Ni, Cu, Co, and Cr. The oxidation of slag particles in the tailings is evident and is most intense in the total tailings resulting in the formation of secondary covellite and iron oxyhydroxides. Other secondary phases detected in the tailings include gypsum, jarosite, a venniculite-type clay mineral, and montmorillonite. The venniculite, and most likely the montmorillonite, are products of biotite alteration which poses the greatest potential for acid neutralization. Plagioclase is another source of neutralization potential in the tailings and shows some evidence of dissolution. The different tailings types show varying and progressive degrees of oxidation correlative with their specific sulfur contents. The degree of oxidation is determined by the relative extent to which the sulfides have reacted as well as the maximum depth to which oxidation is evident in the tailings. The low sulfur tailings (0.4 wt. % S), show the least degree of oxidation, the main tailings (1.0 wt. % S), show alteration intermediate between the low sulfur tailings and the total tailings (2.5 wt. % S), which have reacted the most. Goethite, gypsum, and jarosite, which are present in abundance in the pyrrhotite-rich tailings (14 wt. % S), have formed as secondary cements which, to all appearances, have impeded the oxidation occuring in the pyrrhotite-rich tailings column. The column tests indicate much higher degrees of oxidation and sharper demarcation boundaries between the oxidized and the unoxidized tailings. More pronounced differences among the three chemically different tailings are seen in the column samples than in the field lysimeters, and pyrrhotite in the tailings from the columns also show "leached" textures not seen in the field lysimeters.