Taryn L. Noble

North Atlantic Deep Water Production during the Last Glacial Maximum.

Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial–interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters.

Improved methodology for the microwave digestion of carbonate-rich environmental samples

ABSTRACT Microwave-assisted digestion permits a rapid and total dissolution of sediments and various other sample types, allowing easier and more accurate multi-element determinations. In this study, we present an optimised microwave digestion method for the complete digestion of 200 mg of carbonate-rich sediments. The optimised method prevents the formation of precipitates and assures a complete dissolution of the material. The optimised method involves treatment with concentrated hydrochloric acid (HCl) prior to microwave digestion, which prevents the formation of an insoluble calcium fluoride precipitate associated with the use of hydrofluoric acid (HF). Three different certified reference samples along with a pure calcium carbonate standard and a carbonate-rich in-house marine sediment sample were considered. Sediments were found to only be partially digested if insufficient HF was present, while a noticeable fluoride-based precipitate was found if excess HF was present. Twenty elements were analysed using sector field inductively coupled plasma mass spectrometry (ICP-MS) (Al, Ag, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Na, Ni, Sr, Th, Ti, U, V and Zn). A total sample digestion with average elemental recoveries above 90% was obtained by reacting carbonate-rich samples with HCl on a hotplate at 150°C for 2 h (time for the total release of generated CO2), prior to any microwave digestion step. This extra step prevented the accumulation of gas in the sealed vessels during digestion, which would otherwise influence the carbonate chemical equilibria and make insoluble calcium available for precipitation. After this initial treatment, the improved digestion method consisted of microwave attack employing a mix of concentrated HCl, nitric acid (HNO3) and HF (4 mL/10 mL/2 mL), followed by evaporation on a hotplate. The limits of detection (LOD) obtained using the optimised microwave protocol and ICP-MS measurements were below 0.1 µg/kg for the trace elements and below 0.2 mg/kg for major elements.

pH Testing Methods for Sulfidic Mine Wastes

pH tests are useful screening tools for assessing the characteristics of first flush waters draining sulfidic rocks and waste materials at mine sites. Rinse and paste pH tests are part of a suite of static tests used in acid-base accounting assessments. This study presents a comparison of eleven different pH tests (e.g., rinse and paste pH tests as well as soil tests of the International Organization for Standardization ISO 10390:2005, American Society for Testing and Materials ASTM D4972-01(2007) and Standards Australia AS4969.2-2008) using three different sulfidic rock samples and the acid-base accounting standard KZK-1. We show that different rinse and paste pH methodologies using different grain sizes and extraction solutions can result in different risk classification for ARD assessments. We suggest pH testing should be standardized in their grain size and solid to solution ratio. pH tests conducted using unweathered materials (e.g., drill core) should be carried out using a 0.01 M CaCl2 solution.

Modified Abrasion pH and NAGpH testing of minerals

The original abrasion pH test of Stevens and Carron (1948) is based on grinding and wetting of minerals and subsequent pH measurements of the minerals’ paste and suspensions. Such pH values allow insights into the behaviour of individual minerals upon fluid:mineral reactions in surface environments including mine sites and waste repositories. This study proposes a modified abrasion pH method which includes the use of 0.01 M CaCl2, an operationally defined grain size (<0.075 mm), and high precision pH measurements. Several mineral specimens (n = 20) were obtained from commercial suppliers for the modified abrasion pH testwork, with the acquired specimens having a range of purities and resultant pH values. The modified abrasion pH testwork demonstrates that small admixtures to monomineralic samples caused significant pH changes. Only pure monomineralic samples provide a true indication of the modified abrasion pH of that mineral type. The NAGpH method aims to oxidize sulfide minerals but the reliability of this method in waste classification can be compromised depending on the sample mineralogy. This study demonstrates that NAGpH measurements of some carbonate minerals led to very alkaline pH values that are possibly due to the formation of Ca and Mg hydroxides. Such reactions do not occur in waste environments and therefore, NAGpH measurements of carbonate-rich wastes may overestimate their acid buffering capacity .

Prediction of Mineral Dust Properties at Mine Sites

Predicting the properties of dust generated at mine sites is important for understanding the impact of dust dispersal to the surrounding environment. This chapter presents a new approach to predicting the mineralogical properties of the PM2.5 and PM10 dust fractions. A purpose-built dust resuspension machine was fitted with a size selective sampler to collect dust fractions. Dust particles were collected onto a polycarbonate filter, which was analyzed using a scanning electron microscope (SEM). Backscattered electron (BSE) maps of the polycarbonate surface were imaged and processed to determine dust properties. For a given population of particles, the BSE brightness distribution of the 2–5 and 5–10 µm size fractions were quantified. The mineralogical composition of the dust size fractions were inferred by the BSE brightness as biogenic particles and sulfates (30–50), silicates (60–100), iron silicates and oxides (110–190), and sulfides (>200). The method was validated by comparing laboratory-generated dust fractions with those collected from dust monitoring stations at a tailings repository site. Similar dust composition and size fractions were observed for both laboratory and field samples. Consequently, the purpose-built dust resuspension device and associated laboratory procedures allow the prediction of mineralogical properties of dust at mine sites.

Mineral Dust Emissions at Metalliferous Mine Sites

Mineral dusts produced from mining activities pose a risk to human health and the surrounding environment. The particle size distribution of dust is important for determining environmental, occupational health and physiological impacts. Dust is generally thought of as particulates with a diameter of between 1 and 60 μm, but it can be further divided into nuisance dust or total suspended particulates , fugitive dust, inhalable dust, thoracic dust, and respirable dust. This review considers aspects of mineral dust related to the mining of metalliferous ores including: (a) sources of mineral dust at mine sites (i.e. land clearing, drilling and blasting, transport operations, crushing, milling , screening, stockpiles); (b) control measures to reduce dust generation; (c) monitoring techniques; (d) mineral dust characterization to quantify particle concentration, size and morphology and chemical composition; and (e) prediction of mineral dust properties. Predicting the physical and mineralogical characteristics of dust is important for effective dust management and control strategies. At present, there are no appropriate testing procedures available to predict the chemical and mineralogical properties of mineral dust from mining operations. Further work is required to understand mineral fractionation according to grain size and to provide a rapid test methodology that would predict dust composition.

Prediction of Acid Rock Drainage from Automated Mineralogy

Automated mineralogy tools are now commonly used during mineral processing for particle characterization to help mine operators evaluate the efficiency of the selected mineral processing techniques. However, such tools have not been efficiently used to assist in acid rock drainage (ARD) prediction. To address this, the computed acid rock drainage (CARD) risk grade protocol was developed. The CARD risk grade tool involves: (1) appropriate selection of samples (i.e., following a geometallurgical sampling campaign); (2) careful preparation of a particle mount sample; (3) analysis on a mineral liberation analyser (MLA) using the X-ray modal analysis (XMOD) function; (4) processing of the XMOD data to produce a whole particle mount backscattered electron (BSE) image and a corresponding image of classified XMOD points; (5) fusion of both images to obtain particle area data; (6) calculation of the CARD risk ratio based on carbonate and sulfide particle areas, relative reactivities (\( {\text{pH}}_{{{\text{CaCl}}_{2} }} - {\text{pH}}_{{{\text{mineral}} + {\text{CaCl}}_{2} }} \)) and acid forming/neutralizing values (calculated based on mineral chemistry and stoichiometric factors, kg H2SO4/t); and (7) classification of CARD risk ratios ranging from extreme risk to very-low risk. Testing of the CARD risk grade tool was performed on materials selected from several mine sites representative of both run-of-mine ore and waste. This testing proved that CARD can be effectively used to map ARD risks on a deposit scale and forecast geoenvironmental risk domains at the earliest life-of-mine phases.

Assessing Mineral Dust Properties Using Passive Dust Samplers and Scanning Electron Microscopy

This study presents a novel method to characterize dust particles using a passive dust sampler (PDS). Six different PDS were deployed around six different metal mine sites (Tasmania, Australia) and left in the field for 1 month. Dust particles were analyzed directly on the PDS using a Field Emission Scanning Electron Microscope. Backscattered electron (BSE) images were collected with a resolution of 0.5 μm per pixel and used to characterize the size and composition of dust particles. Those particles >2 μm in diameter were classified according to the range of BSE brightness values, which correspond to mineralogical compositions. Particles were grouped according to BSE brightness and categorized as organic particles, silicates, Fe silicates and oxides, and sulfides. Dust sources with unique particle size:composition relationships were identified at particular mine site domains (e.g. rock crusher, concentrator plant, tailings dam). The documented method can be used to monitor the dispersal of mineral dust and provide information on the mineralogical composition of particle size fractions relevant to occupational health risks at metalliferous mine sites.

Mineral Dust Properties at the Mt Lyell Cu-Au Mine Site, Australia

Mine sites operating dust monitoring programs use a variety of techniques to comply with legislative constraints and maintain high standards of environmental and human health protection. One low cost option is the use of dust deposition gauges, which provide information on the total, soluble and insoluble dust fluxes. The aim of this study was to identify methods that could provide information on likely dust sources of samples, which were collected using dust deposition gauges at the Mt Lyell Cu-Au mine, Australia. Elemental analyses of archived dust samples combined with known dust deposition rates allowed quantification of annual metal fluxes. The highest annual metal fluxes were measured for Cu (1–33 g m−2 year−1) followed by Pb (8–343 mg m−2 year−1), Cr (3–59 mg m−2 year−1) and As (1–79 mg m−2 year−1). X-ray diffractometry and scanning electron microscopy permitted characterization of the mineralogical and morphological properties of dust samples. These analyses revealed that the analysed samples derived from at least four different dust sources. Consequently, geochemical and mineralogical characterization of mineral dust samples combined with a detailed site knowledge allows identification of dust sources at mine sites.

Mobility of arsenic and environmentally significant elements in mine tailings following liming

ABSTRACT Remediation of a legacy tin-tailings site in northeast Tasmania, Australia was carried out by statutory authorities. This study evaluated the fate of As and other deleterious trace metals Cd, Cu, Fe and Zn (among others) following the application of lime and fertiliser. Arsenic concentrations in the tailings ranged from 86 mg/kg to 0.26 wt%. Surface application of lime resulted in a 100-fold reduction in dissolved As concentrations in on-site surface waters; from an average of 196 µg/L prior to lime addition, to between 2.0 and 7.4 µg/L post-amendment. The concentration of other deleterious elements, however, varied between dry and wet cycles. The concentrations of Cd, Cu and Zn in surface waters were high and similar to pre-remediation levels during dry conditions (0.4, 13.5 and 6.1 mg/L, respectively), and only below freshwater ecosystem protection values during wet conditions. Bioaccumulation of Cd was observed in the naturally occurring coloniser, Juncus pallidus, with 4–5 times more Cd in the above-ground biomass relative to the tailings. Ferric arsenate (scorodite) was the dominant source of As identified in the tailings mineralogy. Hydrous ferric oxides and Fe-bearing cassiterite were also identified as hosting As. The pH increase in the surface lime-amended tailings was inferred to result in precipitation of observed hydrous ferric oxides, hematite and goethite, providing high-surface area for adsorption of arsenate onto positively charged surfaces. Jarosite was observed in both the surface lime-amended and subsurface non-amended tailings and suggests a continued supply of acidity to the pore waters despite the application of lime. Leaching experiments showed that As was more mobile in the lime-dosed tailings than in subsurface non-amended tailings, likely owing to desorption in alkaline pH conditions. By contrast, the mobility of Cd, Cu and Zn in the surface lime-amended tailings was reduced by at least two orders of magnitude compared with subsurface non-amended tailings. Evaluation of the applied rehabilitation strategy highlights the limits of a single chemical remediation approach to a polymetallic (including metalloids) waste with complex mineralogy and large seasonal fluctuations. Rehabilitation of metalliferous mine sites requires a complete understanding of all environmentally significant elements and their pathways into local receptors.