Introduction

Mine waste is a multifaceted and major environmental problem that is well recognized as having tremendous impact globally (e.g., Monjezi et al. 2009; Antunes et al. 2008; Krekeler et al. 2008; Marescotti et al. 2008; Pereira et al. 2008; Hancock and Turley 2006; Brown 2005; Younger et al. 2005; Hamilton 2000; Pain et al. 1998). One approach to lessen the environmental impact of mine waste is to recycle the waste (e.g., Driussi and Jansz 2006; Brunori et al. 2005; Jung et al. 2005; Ritcey 2005; Yoo et al. 2005; Siriwardane et al. 2003; Marabini et al. 1998; Smith and Williams 1996a, b). Major challenges exist however. For example, mine waste that is or has been generated from sulfide ores and some types of gold mines clearly may have no environmentally sound use owing to heavy metal and sulfur anion content. The nature of the mineralogy is clearly a control in the environmental impact of mine waste (e.g., Dold and Fontbote 2001; Hudson-Edwards et al. 1999; Foster et al. 1998; Cotterhowells et al. 1994; Davis et al. 1993; Ruby et al. 1993).

Mine waste from some industrial minerals operations may be less environmentally damaging. Mine operations extracting feldspars, quartz, aluminosilicates and certain clay minerals may produce recyclable mine waste, because commonly there are lesser amounts of heavy metals and toxic anions occurring in these types of ores. Many silicate minerals also have lower solubilities than sulfides (e.g., Langmuir 1997). Many industrial mineral products require a high degree of purity and the separation processes required enable waste materials to be sorted and potentially reused.

Kyanite Mining Corporation, located in Dillwyn, Virginia has been in operation for approximately 50 years and is the sole producer of kyanite in North America. This facility is the largest kyanite mine in the world and has 40 million tons of proven reserves. The ore body is a kyanite quartzite with approximately 20–30% kyanite and is mined at Willis Mountain. According to the company’s information the final refined suite of products are typically 90–92% kyanite. The company has a strong environmental management program in place and has won a United States national mine reclamation award.

Aspects of the geology of the region have been most notably described by Owens and Pasek (2007), Owens and Dickerson (2001) and references therein. The ore body is located in the Piedmont physiographic province of central Virginia and is part of the Ordovician Chopawamsic Formation of the central Virginia volcanic-plutonic belt. The kyanite quartzites were long believed to represent simple prograde metamorphism of aluminous sandstones. However, Owens and Pasek (2007) have refined the geologic model of kyanite quartzites in the region and interpret the protoliths as being igneous rocks subjected to severe leaching in a high sulfur alteration environment.

As part of the processing of kyanite quartzite ore, quartz, K-feldspar, muscovite, pyrite, hematite and magnetic minerals (magnetite and pyrrhotite) are separated. Three waste streams result. Several tens of tons daily of quartz, muscovite and feldspar are separated into sand which is sold to aggregate companies and occasionally to other industrial mineral companies. A second waste stream is the pyrite which may be negligible to several tons per week. The pyrite is sold as a mineral commodity or stored in sealed silos depending on market demand. Several tons to tens of tons per day of magnetic separate, the third waste stream, are generated. Currently no use for the magnetic separate has been identified. Possible uses for the magnetic waste stream, may include ore for iron or potentially an ore for titanium.

Kyanite Mining Corporation permitted the collection of eight representative samples from recent dump piles of the magnetic waste stream to be investigated in detail to determine if there were any components which may pose an environmental risk for recycling applications. An investigation of the variability of mineralogical and bulk physical properties of the mine waste was conducted to determine possible uses for the material. An unusual blue mineral coating that has recently developed in a specific region of the mine was also included in the investigation to determine the nature of the mineralogy and assess potential environmental impacts.

Materials and methods

X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence (XRF) were used for materials investigation. XRD analysis was done with a Philips θ − 2θ X-ray diffractometer using CuKα radiation under conditions of 40 kV and 30 mA. Scanning conditions were at 0.02° 2θ with dwell times of 0.3 s per step. Samples were finely powdered and packed into back pack well mounts. Search/match phase identification, as well as diffraction pattern presentation was done with “JADE” software. SEM investigation was conducted using a LEO 1430VP scanning electron microscope using a standard tungsten filament. Energy dispersive spectroscopy (EDS) analyses were obtained using an Oxford, Inc., light element energy dispersive spectrometer in conjunction with the SEM. Element analyses and presentation utilized “INCA” software, a product of Oxford, Inc. XRF investigations were obtained using a Rigaku XRF spectrometer and samples were prepared using pressed powder pellet method. Grain size analysis was done using mechanical sieves. Coefficients of permeability were determined using a Geotest permeameter. Twenty-five replicate determinations were made from each sample.

Diffuse reflectance spectra for the 350–2,500 nm region were gathered using an Applied Spectral Devices Far Range Spectroradiometer (ASD-FR2). The band sample interval for the instrument was 1.5 nm in the 350–1,050 nm region and 10–12 nm in the 1,050–2,500 region. All spectra were resampled at a 1 nm band interval during the data reduction process, using vendor-supplied RS3™ software. The instrument was used in two configurations. First, it was outfitted with an 8° field of view (FOV) fore-optic attachment. The optical head was positioned 0.5 m above each sample at a nadir-viewing angle, resulting in a spot size of 7.0 cm. This configuration was used to collect spectra of the blue mineral coating and the magnetic waste stream samples. A contact probe was attached to the fiber optic to gather spectra of the kyanite samples, which were all smaller than the instrument’s FOV at 0.5 m and for spectrally heterogeneous sub-sections of the hydrous copper sulfate and the kyanite ore samples.

The system’s dark current adjustment used the mean of 60 co-added dark current spectra. The white reference spectrum was the mean of 60 co-added spectra taken of a Spectralon™ panel (model SRT-99-120, SNI4440-D), manufactured by Labsphere, Inc., Nashua, NH, USA. Five mean spectra, each determined from 30 co-added spectra, were taken for each sample condition. The five mean spectra were averaged to obtain the mean spectrum for each sample condition. Each of the five samples’ spectra were then averaged; this spectrum is used in the data analysis. The spectrometer’s fiber optic cable inherently limits the spectra in the 2,450–2,500 nm region. Each sample was illuminated from one side using a 250 W, quartz–tungsten–halogen (QTH) lamp positioned at a 30° angle from a height of 0.36 m.

Sample containers were plastic petri dishes, 10 cm in diameter and 1.2 cm deep. Each container had two coatings of a flat, black-colored paint. The painted sample containers have flat, featureless, 5% reflectance spectra over the 400–2,500 nm region, which made them ideal backgrounds. Each container was larger than the spectroradiometer’s 7.0 cm instantaneous field-of-view (IFOV) at the 0.5 m viewing height.

Results

The magnetic separate has accumulated in a waste pile that is approximately 150 m wide, 350 m long and has an average height of approximately 20 m. The estimated volume is 1.05 million m3 and the estimated tonnage using a non-weighted average of common minerals present of 3.4 g/cm3 is 3.57 million metric tons. Field inspection of the magnetic waste pile indicates that it consists of mixed wastes including occasional quartz and kyanite-rich sands. Approximately 95% of the pile appears to be magnetic waste. An inspection of the perimeter of the pile indicates that there is no secondary mineralization or iron staining associated with it.

Mineralogy

Pyrrhotite occurs as smooth grains with a velvety surface luster and are moderately magnetic. Most grains are black with a minority of grains having a faint bronze coloration. X-ray diffraction on selected individual grains shows that pyrite occurs at the core of many pyrrhotite grains or as an intergrowth with pyrrhotite.

Oxide minerals are very common in the magnetic waste stream and include magnetite, hematite and titanium oxides (Figs. 1, 2). Magnetite composes approximately 1–80% of the mine waste. The mineral occurs as euhedral to anhedral grains and are commonly 50 μm–0.5 mm in diameter. EDS analyses indicate that there are no impurities above detection limit (~0.10 wt%). Magnetite is intimately associated with kyanite grains and occurs as inclusions, which are commonly 10–50 μm in diameter and also as coatings on kyanite and other grains. Hematite composes approximately 1–10% of the mine waste. Hematite is found in two modes, as thin smooth dull red coatings on pyrrhotite/pyrite grains and as botryoidal coatings on kyanite and feldspar grains. Hematite can be found on approximately 10–20% of kyanite and feldspar grains and 20–30% of pyrrhotite grains. Titanium oxides are rare in sample material and are observed only as coatings on silicate grains.

Fig. 1
figure 1

Powder XRD patterns with major minerals listed

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Fig. 2
figure 2

SEM images of particles in the magnetic waste. a Magnetite overgrowths on kyanite. b Charcoal grain with kyanite. c Ti-oxide coating on K-feldspar with muscovite grain. d Botryoidal hematite. e Ti–V alloy in charcoal interpreted as saw blade residue. f Botryoidal hematite on K-feldspar. g Several representative magnetite grains. h Spherical magnetite. i Titanium oxide coating on muscovite grain

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Several silicate minerals occur in the magnetic waste stream including kyanite, quartz, K-feldspar, and muscovite. Kyanite is a major component of most of the magnetic waste separate and composes approximately 1–95% of the material. Sample MT 1 is very rich in kyanite. Kyanite in the magnetic mine waste is commonly a light yellow and gives bulk material a tan color. Kyanite in the magnetic separate commonly has fine grained inclusions of magnetite, composing an estimated 5% to as much as 60% of the grain volume. These inclusions are commonly subhedral to euhedral and commonly are 10–50 μm in diameter. Quartz composes approximately up to 20% in some samples and occurs as conchoidal, anhedral to subhedral grains, commonly with small magnetite inclusions similar to those found in the kyanite. Muscovite grains were rarely observed and were found to contain approximately 1–2 wt% BaO using EDS analysis. K-feldspars were common and often had 0.1–0.5 wt% BaO using EDS analysis.

Charcoal is a major non-mineral component of the waste and found in all samples of the waste but typically compose approximately 1–3% by volume of the magnetic separate. Fragments are commonly 50 μm to a few centimeters in diameter. SEM data show that charcoal has a high surface area with many micropores. Rarely fragments of titanium–vanadium alloy are present.

A blue mineral coating is pervasive on approximately 5% of ore boulders on the Willis Mountain mining area. The coating is very faint to 2 mm thick. XRD analyses of the blue crust did not conclusively identify the mineral. SEM investigation however does identify the material as a copper sulfate with no other impurities (Fig. 3). Images indicate particles are between 5 and 60 μm in diameter with anhedral interlocking textures. Some particles are well rounded or partially well rounded.

Fig. 3
figure 3

SEM data for blue mineral coating. a Small rounded particle of Cu sulfate. b BSE image of Cu sulfate on mica flake. c Irregular shaped particles of Cu sulfate. d Higher magnification of upper left portion of c. e EDS data showing histogram of wt% elements

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Bulk properties

Grain size analysis indicates particle size distribution in four samples is unimodal and in four samples is multimodal (Fig. 4). The >0.710 mm fraction is commonly dominated by charcoal fragments and the <0.710 mm size fraction is dominated by mineral grains. The uniformity coefficient (d 60/d 10) varies from 1.97 to 4.72.

Fig. 4
figure 4

Grain size distributions for magnetic waste stream

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Observed K values vary between 0.0036 and 0.0077 cm/s and are broadly consistent with values expected of sands with similar grain size distributions (Table 1). Average values obtained for K were compared to estimates based on grain size analysis using the method of Sheperd (1989) and Alyamani and Sen (1993). Both methods overestimated the hydraulic conductivity with that of Sheperd (1989) producing values of approximately two orders of magnitude above the observed and that of Alyamani and Sen (1993) producing values approximately one order of magnitude above observed.

Table 1 Comparison of observed hydraulic conductivity values with grain estimate methods
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XRF

The chemical compositions of the magnetic waste stream samples show some variation with respect to major and trace elements (Table 2). Major element contents varied with P2O5 (0.06–0.30 wt%), SiO2 (1.86–57.71 wt%), TiO2 (0.81–1.49 wt%), Al2O3 (19.27–33.85 wt%), Fe2O3 (36.70–56.76 wt%), MgO (0.47–1.09 wt%), CaO (3.07–3.48 wt%), MnO2 (0.01–0.03 wt%), Na2O (3.79–8.17 wt%), K2O (1.17–3.02 wt%), and S (0.03–1.73 wt%). Some elements showed correlations (Fig. 5). Concentrations of Al2O3 and SiO2 systematically varied showing a linear correlation (r 2 = 0.97). Concentrations of Al2O3 and Fe2O3 also showed a very strong linear correlation (r 2 = 0.94). Bulk minor and trace element XRF data show that Ba, Mo, Nb, Zr, Y, Sr, U, Rb, Th, Pb, Zn, Cu, Ni, Co, Cr, and V are present. Elements which are of potential environmental concern are Mo (10–32 ppm), Pb (21–77 ppm), Zn (17–48 ppm), Cu (33–276 ppm), Ni (<1–8 ppm), Co (22–187 ppm), and Cr (82–137 ppm). A strong correlation (r 2 = 0.91) exists between Mo and Pb and a weak linear correlation (r 2 = 0.63) exists between V and Cr concentrations. Moderate correlations between phosphorous and V (r 2 = 0.82), Cr (r 2 = 0.56), and Cu (r 2 = 0.91) occur. No discernable correlation between concentrations of Pb, Zn, Cu and S occur.

Table 2 XRF data for major and trace elements for magnetic waste samples
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Fig. 5
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Examples of correlation of element concentrations determined by XRF for bulk samples of the magnetic waste stream. a V and Cr showing moderate correlation. b Mo and Pb showing moderate to high correlation suggesting occurrence in the same phase. c Correlation of Al2O3 and SiO2 and d Fe2O3 and Al2O3 suggesting linear mixing of waste

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Remote sensing

Contact-probe spectra of the kyanite samples are displayed in Fig. 6a. The ore sample demonstrates 3–4% absorption maxima from 2,190 to 2,210 nm—indicative of aluminum-hydroxyl (Al–OH) stretching at the surface of aluminum-rich minerals—and a gradual decrease in reflectance from 1,500 to 2,500 nm. Both of these features are consistent with previously collected data (Salisbury et al. 1991; Hunt et al. 1971, 1973; Hunt and Salisbury 1970) and the spectra of three kyanite specimens included in the figure (Kyanite A, B, and C). In addition, the kyanite A, B, and C samples also mildly fluoresce at 688–689 nm (0.2–0.5%) and 705–706 nm (0.3–0.8%) (Lakshminarasappa et al. 2006). When these samples are illuminated by the lamp instead of the contact probe, they do not fluoresce.

Fig. 6
figure 6

Reflectance spectra of mine samples and exemplars. a Shows several remote sensing spectra for kyanite and kyanite ore. Kyanite exemplar samples are from Minas Gerais, Brazil. Kyanite A and C show fluorescence peaks under contact probe whereas Kyanite B and the kyanite ore do not show fluorescence. All kyanite material spectra show 3–4% absorption maxima between 2,190 and 2,210 nm that is indicative of Al–OH stretching. b Remote sensing spectra for magnetic waste stream samples showing flat featureless spectra. The exception is that of MT-1 which has a distinct linear reflectance increase from 6 to 12% over the 400–900 nm range. This feature is attributed to the appreciable kyanite content of the sample. This particular spectral feature may be useful for optical signature automated separation for reprocessing. c Remote sensing spectra for Cu sulfate and related materials which may permit areal mapping of these materials in the mine from airborne platforms. The offset present in the spectra at 1000 nm is an artifact of the ASD instrument. Blank areas in all spectra are regions of atmospheric water vapor adsorption

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The mine waste samples produced largely featureless spectra from 400 to 2,500 nm (Fig. 6b). Seven of eight kyanite mine waste samples (MT-2–MT-7) are flat, featureless spectra ranging from 3 to 7% reflectance, consistent with typical magnetite spectra in the near and shortwave infrared (700–2,500 nm) (Clark et al. 2007; Grove et al. 1992; Hunt et al. 1971). For these samples, very slight increases in reflectance (~1%) in the visible region (400–700 nm) are likely caused by impurities in the waste stream mentioned above (e.g., kyanite, quartz, titanium dioxide) that contribute to a higher overall reflectance in the samples. Sample MT-1 presents a linear reflectance increase from 6 to 12% over the 400–900 nm range and then assumes a gradual upward reflectance trend similar to, but stronger (3.5%) than, samples MT-2–MT-7 from 900 to 2,400 nm. The higher reflectance is likely a function of greater kyanite impurities in this waste stream sample than the others considered here.

The amorphous hydrous copper sulfate and substrate spectra are displayed in Fig. 6c. The copper sulfate crust is a vivid blue-green color, confirmed by a strong reflectance peak at 530 nm in the visible spectrum combined with overlapping copper and possible iron absorptions at wavelengths <530 nm (5%) and a strong copper absorption at 760 nm (>20%) (Hunt et al. 1971, 1972, 1973). The sample also presents an aluminum-hydroxyl (Al–OH) absorption at 2,190 nm (2%), and subtle features at 1,520 nm (1%) and 1,695 nm (2%); the latter two may be subtle ferrous iron absorptions (Hunt et al. 1971, 1973). The offset present in the spectra at 1,000 nm is an artifact of the transition between spectrometers in the ASD-FR2 instrument. As expected, the white-colored kyanite ore substrate for the copper sulfate crust possesses a strong aluminum-hydroxyl (Al–OH) absorption feature at 2,190 nm (>20%). The substrate also has Al–OH absorption features at 2,345 nm (11%) and 2,440 nm (5%). The ore substrate also has a minor copper-induced absorption feature (1%) centered at 750 nm. Like the copper sulfate crust, the ore substrate also possesses weak absorptions at 1,520 and 1,695 nm, although they are weaker in this sample (<1%) (Hunt et al. 1971, 1973).

The whole sample spectra were gathered with the lamp instead of the contact probe and demonstrate the mixing of the two constituents in the sample—the blue-green copper sulfate crust and the kyanite ore substrate. This spectrum has a visible reflectance maximum at 555 nm, 25 nm longer than the blue crust, the strong copper-induced absorption feature at 770 nm (15%), and subtle incarnations of the possible ferrous iron features at 1,520 nm (<1%) and 1,695 nm (<1.5%). The Al–OH absorption feature at 2,190 nm (9%) remains prominent. Although noise begins to dominate the spectra ~2,350 nm, the Al–OH absorption feature at 2,345 nm is also apparent in this sample.

Discussion

Materials

Discussions with mine staff indicate that the nature of the heterogeneity of the magnetic waste pile has changed over time with the core consisting more of a mix of silicate-rich sand and magnetic-rich waste. Accordingly, estimates of the total percentage of minerals and the total reserves of metals in the pile may be high.

Wood cuttings from the local forestry industry are used in processing kyanite product and result in the charcoal observed. Titanium–vanadium alloy fragments observed in charcoal are interpreted as saw blade fragments and therefore these materials may complicate the interpretation of bulk chemical data.

The blue coating is X-ray amorphous and cannot be identified as a mineral most likely owing to the hygroscopic nature causing a state of constant re-equilibrium with changing humidity. The rounded nature of the Cu-sulfate masses in the SEM images is interpreted as a dissolution–solidification texture. Only Cu, S, and O were observed in EDS analysis. The material is identified as an amorphous copper sulfate. The origin of the copper sulfate is likely related to the hydrothermal history of the rock as suggested by Owens and Pasek (2007).

Broadly similar minerals have been identified from other mine waste settings. Peterson et al. (2006) described efflorescent alpersite, (Mg,Cu)SO4·7H2O, from the Big Mike Mine in central Nevada and efflorescent alpersite and cuprian pentahydrate (Mg0.49,Cu0.41,Mn0.08,Zn0.02) SO4·5H2O from Miami, Arizona, from sulfide mine waste. They point out that these minerals may commonly be misidentified as chalcanthite.

Several minerals in the magnetic waste stream such as magnetite, K-feldspar, quartz, muscovite are stable in aqueous solutions whereas the pyrite and pyrrhotite are more reactive in aqueous solutions. Pyrites have a low abundance (<1–2 wt%) in the samples investigated. Pyrites are commonly enveloped in oxide coatings and this may explain the lack of acid mine drainage features such as staining at the base of the waste pile.

Charcoal is well recognized as a strongly absorptive material. Organic molecule pollutants such as pyrene (Wang et al. 2006), benzene (Braida et al. 2003), other aromatics (Sander and Pignatello 2005; Zhu and Pignatello 2005) are known to be absorbed by charcoal. Charcoal is also recognized as a media that absorbs heavy metals from aqueous solutions (Amuda et al. 2007; Aziz et al. 2005; Ndiokwere 1984). Therefore the charcoal may also act as an absorptive buffer for aqueous components dissolved from pyrites and this may explain the lack of acid mine drainage indications near the perimeter of the pile. The continued use of wood cuttings in the production process is recommended as this approach recycles waste but also plays a role in waste management.

The strong linear correlations of Al2O3 and SiO2 and of Al2O3 and Fe2O3 are attributed to simple mechanical mixing of quartz, kyanite and magnetite. From bulk XRF data alone it is not possible to elucidate a specific relationship between kyanite and magnetite content owing to the presence of feldspar and mica.

The mineralogical control on the distribution of heavy metals is somewhat unclear; however, linear correlations of bulk analyses provide some insight. The strong to modest correlations of P2O5 content to concentrations of V, Cr, and Cu suggest that some of the distribution of these transition metals is controlled by phosphate minerals, presumably apatite but other phosphates are possible. SEM investigation shows that no apatite, occurs as distinct grains, however, apatite is common as inclusions in quartz. The correlation of V and Cr suggest they occur in a single mineral phase. Vanadium and chromium commonly substitute in apatites (Pan and Fleet 2002; Dai and Hughes 1989; Sudarsanan et al. 1977; Banks et al. 1971; Banks and Jaunarajs 1965). The lack of a more pronounced correlation may be explained by a number of factors. V and Cr have solid substitution in oxides and solid solution between hematite (Fe2O3), eskolaite (Cr2O3), and karelianite (V2O3) can occur. Cr exhibits solid solution with magnetite and is a major constituent of chromite. Vanadium occurs in magnetite at minor concentrations and is a major constituent of coulsonite. The strong correlation between Mo and Pb suggests these elements occur in the same mineral phase. These elements have a strong affinity for S and their occurrence and distribution may be controlled by the sulfide phases.

The now non-operational Graves Mountain kyanite mine, located in Georgia, has significant amounts of titanium oxide in the form of rutile. Titanium oxides are a very minor mineral in the waste investigated from Dillwyn. Bulk concentrations of Ti in the waste are not sufficient to warrant reprocessing of the material for titanium. TiO2 concentrations are likely controlled by a minor amount of Ti in solid solution with magnetite which has well-known extensive Ti substitution (e.g., Anderson and Lindsley 1988; Ghiorso and Sack 1991). TiO2 concentrations do not correlate well with V or Cr. Complicating this interpretation is the presence of minor saw blade fragments composed of Ti–V metal that is associated with some charcoal fragments.

The multimodal grain size distribution and the comparatively low K values for these grain sizes must be accounted for in any reprocessing or reuse. Because there is a range of grain size it should be possible to select a size distribution as needed and possibly tune the permeability for reactive bed media in a given recycling process.

Remote sensing

The spectra in Fig. 6 provide useful library references for airborne/spaceborne imaging spectrometer data. It is reasonable to expect that features ≥2% in strength are detectable via remote sensing, although this is highly subject to atmospheric conditions, flying height/orbit constraints, the quality of atmospheric compensation, sensor signal to noise ratios, and pixel phasing by the target materials (Jensen 2005). Features such as the copper/iron absorptions at wavelengths <530 nm in the blue-green crust and kyanite ore, the copper absorption at 760 nm in the blue-green crust, and the aluminum-hydroxyl (Al–OH) features at 2,190 and 2,345 nm in both kyanite ore samples should all be readily detectable from an airborne sensor, such as AVIRIS or a spaceborne sensor, such as Hyperion. The fluorescence features in the kyanite ore samples are not present when sample spectra are gathered with the lamp (not shown) and thus, would be unlikely to appear in data gathered from a remote passive sensor. Signal to noise ratios in imaging spectrometers are generally poor beyond 2,400 nm. Hence, the amorphous copper sulfate substrate’s absorption feature at 2,440 nm would be difficult to extract from noisy remotely sensed data in this wavelength range.

Data from 940–980, 1,120–1,180, 1,300–1,450, and 1,800–1,950 nm were removed from the plots because atmospheric water vapor renders these portions of the electromagnetic spectrum opaque or highly attenuated and thus, difficult to work with when using airborne and especially spaceborne data sets.

Environmental impacts

Kyanite has been shown to have a comparatively low solubility (Oelkers and Schott 1999) and thus should not contribute appreciable dissolved Al species to waters interacting with the mine waste. This is important as aqueous Al species are commonly regarded as toxic to freshwater fauna (e.g., Borgmann et al. 2005; Lyderson et al. 2002; Schmidt et al. 2002; Soucek et al. 2002).

Cu is a well-recognized heavy metal pollutant having toxic effects on invertebrates (Rainbow 2002; Di Toro et al. 2001; Santore et al. 2001; Langmuir 1997; Korthals et al. 1996), fish species (Santore et al. 2001; Meyer et al. 1999; Farag et al. 1995; Ryan and Hightower 1994; Playle et al. 1993; Wilson and Taylor 1993), vegetation (Ebbs and Kochian 1997; Gallego et al. 1996; Fernandes and Henriques 1991; Devos et al. 1992) and bacteria (Cevik and Karaca 2006; Hattori 1992). Cu toxicity is particularly pronounced in freshwater invertebrates, including crabs (Ferrer et al. 2003, 2006) and amphipods (Gale et al. 2006; King et al. 2006). Although negative impacts of Cu pollution have also been observed in soil bacteria, some investigations have shown that bacteria can adapt to increases in Cu (e.g., Rodrigues-Montelongo et al. 2006; Niklinska et al. 2006). Detrimental effects of aqueous Cu cation species have been shown to be complex and species dependent in bacteria in some estuaries (Boyd et al. 2005). The copper sulfate is of concern for water quality management and impact would be most expected for invertebrates, fish and vegetation in nearby streams.

Suggested environmental practices

The presence of minor amounts of sulfides indicates that the waste is not suitable for applications involving surface or groundwaters such as use as media in constructed wetlands or as a sand filter. Recycling the waste as fill is also not recommended. A more realistic use may be as iron ore. The United States Geological Survey (USGS) Mineral Commodity Summaries (2008) reports the 2007 price per metric ton is $63.00 US. Assuming that the 3.57 million metric tons is ore, the upper limit of value of the magnetic mine waste as ore is $225 million US. Using the minimum value for Fe-rich samples of 36.70 wt% Fe2O3, which is the approximate concentrations of some iron ores (Liu et al. 2006), as a multiplier of likely concentration, the mine waste value estimate becomes $82.5 million US. The annual market of iron ore in 2007 estimated by the USGS is $3.1 billion US, thus the mine waste would represent 2.6% of the annual US market. Although this is a small fraction of the US market, if a demand could be identified or created locally, modest production could take place. Kyanite separation from the magnetic waste may enable Fe2O3 concentrations to be more in agreement with traditional ores. Kyanite is used in specialized castings and if an integrated product could be identified and produced at the waste site, then transportation costs could be reduced. Estimates are at best approximate but illustrate that under value-added conditions a reprocessing of the waste stream may be feasible.

Remote sensing techniques provide several management options. The remote sensing results indicate that it may be possible to differentiate very kyanite-rich waste from more magnetite-rich waste based on reflectance. Samples with reflectance values of ≥0.08 in the 800–2,200 nm range may be considered for reprocessing in some fashion. An ASD or similar system could be placed in an automated system to sort waste stream materials. Fluorescence may indicate high grade kyanite ore, but this feature is expected to be observed only in field ASD contact probe conditions or possibly process conditions. Cu-sulfate may be able to be detected using remote sensing and periodic imaging is recommended.

The occurrence of Cu sulfate at the mine is minor but likely has some impact on the local environment. Precautions should be taken to minimize the dissolution or migration of Cu and sulfate. It may be possible to capture aqueous Cu species using exchangeable mineral materials. Zeolites and sepiolite have been shown to absorb aqueous Cu cations. Cui et al. (2006) showed clinoptilolite functions well as a sorbent for Cu and Zn in a slurry bubble column. Fungaro and Izidoro (2006) demonstrated efficacy of zeolites for improving the quality of acid mine drainage waters through cation exchange and precipitation reactions. Zamzow et al. (1990) investigated clinoptilolite, mordenite, chabazaite, erionite, and phillipsite for removal of heavy metals from mine waste waters. Clinoptilolite was challenged with waste water from a Cu mine and all metals including Cu were reduced in concentration to below drinking water standards. Using wastewater from an abandoned mine, Zamzow and Murphy (1992) found that phillipsite was most effective at removing heavy metals including Cu. Cu and Zn were shown to be removed to concentrations below drinking water standards.

The absorption of heavy metals in sepiolite has been investigated (Kara et al. 2003; Brigatti et al. 1996; Garcia-Sanchez et al. 1999). Brigatti et al. (2000) showed that sepiolite has the highest affinity for removing Cu2+ and that the removal of Cu2+, Zn2+, Cd2+ and Pb2+ is functionally independent of competitive cation interactions. Sanchez et al. (1999) also investigated sepiolite and found a high affinity for Cu2+ sorption although they found Cd2+ was more strongly absorbed than Cu2+. Brigatti et al. (1999) compared the sorption of Cu2+, Co2+, Zn2+, Cd2+ and Pb2+ on sepiolite and zeolite-rich tuff and found that Cu2+ was most strongly absorbed by sepiolite but least strongly absorbed by the zeolite. Zeolites are also granular and thus have a high hydraulic conductivity compared to sepiolite. It is recommended that a reactive media being comprised of a mixture of sepiolite and clinoptilolite or phillipsite be placed at the base of slopes where the copper sulfate is present.

Conclusion

Investigations of the mine waste provide explanations of the variability of properties of waste materials and can provide insight into environmental management strategies. Potential reprocessing of the material as an iron ore may be an option if economic requirements can be met. Managing copper sulfate pollution in the mine could be accomplished with simple sorption media.