A Parbhakar-Fox

A new test for plant bioaccessibility in sulphidic wastes and soils: A case study from the Wheal Maid historic tailings repository in Cornwall, UK

Currently, bioaccessibility testing at contaminated sites is dominated by techniques designed to assess oral bioaccessibility to humans. Determining the plant bioaccessibility of toxic trace elements is also important. In mining landscapes, sulphides are an important source of potentially toxic elements. Simple tests to evaluate readily leachable metals and metalloids exist but do not extract elements temporarily constrained within the sulphide fraction. Sequential extractions describe the association of trace elements with different geochemical fractions but are time consuming, costly and provide excessive detail. This paper proposes a new test for plant bioaccessibility in sulphidic mine wastes and soils that uses hydrogen peroxide to simulate environmental oxidation. The bioaccessible fraction determined is operationally defined and does not predict actual plant uptake. The test targets a) the portion of an element that is currently available in the pore water for uptake by plant roots and also b) the fraction that is temporarily constrained in sulphide minerals but may become available upon oxidation of the substrate. A case study was conducted at a historic mine waste repository site in Cornwall, U.K. where near total As concentrations were extremely elevated and Cd, Cu, Pb, Sb and Zn were also high. Our test determined that bioaccessible concentrations of As, Cd, Cu and Zn and to a lesser extent Sb and Pb were highest in samples of pyritic grey tailings. This is attributed to sulphide mineral oxidation and, particularly for Cd and Zn, the dissolution of soluble secondary minerals. High As concentrations in the marbled tailings were not bioaccessible. Results from the case study show that this new test provides useful information on the future bioaccessibility of contaminants, allowing for classification of mineralised sulphidic waste materials which otherwise cannot be obtained using established geochemical and mineralogical techniques. Furthermore, the test is rapid, repeatable and cost effective.

Predictive Waste Classification Using Field-Based and Environmental Geometallurgy Indicators, Mount Lyell, Tasmania

Best practice for acid rock drainage (ARD) risk assessment predominately relies on the geochemical properties of sulfidic rocks. Consequently, a plethora of geochemical tests are routinely utilised by the mining industry to predict ARD formation. Due to limitations associated with these tests and their relatively high costs, analysis of recommended best practice sample numbers is rarely achieved, thus reducing the accuracy of waste management plans. This research aimed to address this through identifying potential geometallurgy indicators using drill core samples (n = 70) obtained from the Comstock Chert, a new prospect proximal to Mount Lyell, western Tasmania, Australia. Samples were subjected to a range of mineralogical analyses, routine ARD geochemical tests (i.e., paste pH; acid-base accounting, ABA; net acid generation, NAG), field-based techniques (e.g., portable X-ray fluorescence, pXRF; short-wave infrared spectrometry, SWIR), and geometallurgical analyses (i.e., HyLogger, Equotip). This study demonstrated: (1) HyLogger data allows identification of acid-neutralizing carbonate minerals; (2) Equotip hardness data provide a conservative indication of lag-time to acid formation; (3) CARD risk grading accurately identifies high and low risk ARD domains; and (4) pXRF data provides a sound indication of the abundance of environmentally significant elements. Consequently, the application of geometallurgical techniques to drill core allows the prediction of ARD characteristics that inform waste characterization and management plans.

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.

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.

Prediction of Metal Mobility from Sulfidic Waste Rocks Using Micro-Analytical Tools, Spray, Tasmania

The Zeehan Pb-Zn field in western Tasmania (Australia) contains over one hundred abandoned and historical mine sites. Combined with a temperate rainforest climate and abundant waste rock material, many sites are affected by acid rock drainage (ARD). The Spray mine, located southwest of the town of Zeehan, was one of the field’s largest historical producers of Pb and Ag. Abandoned in the early 1900s, the site contains numerous adits and waste rock piles which contribute to ARD in the region. The aim of this study was to predict the likely ARD surface water quality, using the major and trace element chemistry of sulfide minerals present within waste materials on site. Major ore sulfides are galena and sphalerite with associated Sb-rich sulfosalt minerals including boulangerite and geocrocite. These minerals contain minor concentrations of Ag, Bi, Cd , In and Sn. Minor arsenopyrite and abundant pyrite (average 7500 ppm As) represent the main repository for As. Siderite is a major gangue mineral, containing slightly elevated In, Pb, Sb and Zn (250–50 ppm). Metals and metalloids (Ag, As, Bi, Cd, Cu, In, Pb, Zn) contained within sulfides and siderite may be mobilized upon mineral dissolution into ARD waters. Consequently, micro-analytical analyses of sulfides and associated gangue minerals can assist in the prediction of aqueous metal and metalloid mobility from sulfidic waste rock piles.

Prediction of Leachate Quality for a Gossan Dump, Angostura, Spain

The Iberian Pyrite Belt (IPB) is one of the largest of the world’s massive sulfide provinces. Since the Chalcolithic era, gossans formed from massive sulfide mineralization have been worked for copper, silver and gold. Consequently many historical mine sites have abandoned dumps of gossanous material. One such example is located at Angostura, a historical copper mine which operated from 1906 to 1931. The aims of this study are to determine the mineralogical hosts of environmentally significant elements (As, Ba, Bi, Co, Cu, Hg, Mo, Sb, Se, Ni, Pb, Zn) in gossanous waste rocks dumped adjacent to the Angostura open cut, using geochemical, optical, SEM-MLA and laser ablation techniques. Our findings demonstrate that the gossan materials are enriched in environmentally significant elements with several hosted by iron oxides and iron-oxyhydroxides. Leaching of these gossan materials was performed using three extractants to represent different conditions which may be experienced in a surficial environment (i.e., deionized water, hydrogen peroxide and sulfuric acid). Results from these experiments indicated that under ambient surface conditions all analyzed elements will not be released from their goethite and hematite hosts. However, under ARD conditions, elements such Co, Cu, Pb and Zn will be mobilized.

Prediction of Acid Rock Drainage Using Field-Based Testing Tools

Tests currently used by the industry for acid rock drainage (ARD) prediction heavily utilize static geochemical tests. Instead, effective tools which allow for early domaining should be utilized as they can be performed on a greater number of samples, allowing for deposit-wide environmental characterization. These must be simple enough to perform in the core shed or field-laboratory to keep cost and turn-around time to a minimum. Simple field-based pH tests and chemical staining should be performed. In addition, mineralogical characterization methods for drill core materials i.e., an ARD focused logging code and the use of portable instruments (i.e., pXRF, Equotip) should be pursued. This chapter presents several field tools appropriate for ARD prediction. These tools were developed, tested and validated using drill core and waste rock materials obtained from several Australian mines with differing geology, mineralogy and mineralization style. This chapter demonstrates that by utilizing these field based tests, industry has the opportunity to achieve: (i) effective ARD prediction testwork; (ii) detailed deposit-wide characterization, (iii) development of best practice waste management plans; and (iv) identification of the most suitable rehabilitation options.

Micro-analytical Technologies for Mineral Mapping and Trace Element Deportment

Quantifying the texture, mineralogy and mineral chemistry of rocks in the mine environment is required to predict the value of a deposit and maximize extraction efficiency. Scanning electron microscopy supported by recognition of minerals by characteristic X-ray emissions is the preferred mineral mapping method in the mining industry at present. This system is fully mature and supported by highly optimized software. Laser Raman mapping may compete for some of this space in the future. Very coarse scale mineral maps are possible from drill core images but these cannot be used to measure the key parameters required for most mine planning. Trace elements can be highly concentrated in rare minerals so that they are easy to detect but very difficult to accurately measure due to sampling problems, or they may be very dispersed and difficult to detect at all. There are a range of tools available to support trace element deportment and most studies will need to use more than one methodology. The key new development of the last decade is the emergence of laser ablation inductively coupled plasma mass spectrometry for the measurement of most elements at sub-ppm level. There are still many trace and minor elements for which accurate models of deportment are extremely difficult.

Prediction of Metal Mobility from Sulfidic Waste Rocks Using Micro-analytical Tools, Baal Gammon, Northern Australia

Predictions on the behavior of environmentally significant elements at mine sites requires the use of advanced laboratory techniques. The aim of this contribution is to demonstrate the use of electron microprobe analysis (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to gain an understanding of likely element behaviour. Sulfidic boulders sampled from an acid rock drainage (ARD) impacted ephemeral stream adjacent to the historical Baal Gammon workings are dominated by chalcopyrite, arsenopyrite, pyrrhotite and lesser pyrite. Micro-analytical investigations using EMPA and LA-ICPMS reveal that chalcopyrite contains significant quantities of Ag, Cd, Sn, In and Zn either substituted directly into the crystal lattice or occurring as discrete sphalerite and stannite inclusions. Arsenopyrite, comprising more than 50 % of some boulders, is most notably rich in Co, Ni, Sb and Se, but it also contains inclusions of sphalerite, chalcopyrite and stannite. By contrast, pyrrhotite contains relatively few trace elements, but it may be a significant contributor to ARD development. The trace element composition of Fe-oxides in the oxidized rinds of these boulders is likely directly influenced by the mineralogy of the sulfidic boulders on which they precipitate. Although significant quantities of As, Bi, Cu, In, Pb and Zn occur in Fe-oxides at Baal Gammon, these elements may be liberated during acid flushing of the ephemeral stream. Consequently, EMPA and LA-ICPMS represent valuable tools for evaluating the source and potential mobility of environmentally significant elements at mine sites.