Characterization of Nickel Speciation in Soils Near Kalgoorlie, Western Australia
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Characterization of nickel speciation in soils near Kalgoorlie, Western Australia ENSC 501 By: Mitchell Skuce Supervisor: Dr. Heather Jamieson Secondary Examiner: Dr. Ron Peterson April 15, 2011 Queen’s University 1 Abstract Nickel has been identified as an element of concern in soils surrounding the city of Kalgoorlie, Western Australia. The area’s geology is naturally nickel-enriched, and there is also a large nickel smelter near the city. Nickel is of interest because all Ni compounds are carcinogenic and many cause respiratory diseases. This study attempts to characterize the nickel-hosting minerals in the soil, as they may have significant impacts on the health risk posed by inhalation or ingestion. Previous work in the area had come to different conclusions regarding the nickel mineralogy, which this study will endeavour to resolve. Also, this study will assess the degree of anthropogenic influence on soil nickel; this is of interest mainly due to the proximity of the smelter. Scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and petrographic analysis of thin sections where used to accomplish these goals. Results suggest that nickel is mainly hosted by nickel iron oxides, of the trevorite- magnetite solid solution. Nickel sulphides, likely pentlandite and haezlewoodite, likely also represent significant forms of nickel. Nickel carbonates, elemental nickel, adsorbed nickel, and nickel substituted in into iron oxides such as hematite and goethite were determined to be minor phases. Anthropogenic influence on soil composition was found to be very important near the smelter, in the form of nickelliferous slag particles in the soil. However, no significant anthropogenic influence was detected in soils in the city and background locations. 2 Table of Contents 1.0 Introduction…………………………………………………………………………………………….…………. 4 1.1 Geology…………………………………………………………………………………………………………………….. 5-6 1.2 Soils…………………………………………………………………………………………………………………………… 6-7 1.3 Kalgoorlie Nickel Smelter…………………………………………………………………………………………… 7-8 1.4 Previous research and possible nickel hosts……………………………………………………….…... 8-11 1.5 Toxicological implications of nickel speciation……………………………………………..………… 12-14 2.0 Methodology….................................................................................................. 15-17 3.0 Results……………………………………………………………………………………………………………… 18 3.1 Scanning Electron Microscopy………………………………………………………………………..…….. 18-20 3.2 Petrography…………………………………………………………………………………………………………… 21-22 3.3 X-ray Diffraction (XRD)…………………………………………………………………………………………..…… 23 4.0 Discussion…………………………………………………………………………………………………….. 24-27 5.0 Conclusion……………………………………………………………………………………………………………….…………… 28 6.0 Summary of key findings……………………………………………………………………………………….…………. 29 7.0 Acknowledgements……………………………………………………………………………………………………………. 30 8.0 References……………………………………………………………………………………………………………………... 31-36 3 1.0 Introduction This study focuses on the town of Kalgoorlie, located in the Goldfields region of Western Australia. The town of about 28 000 people was founded in 1893 during a gold rush, and is still today in the heart of the region’s mining industry. It features a large open-pit gold mine and a nearby nickel smelter. Kalgoorlie is considered an asthma hotspot and has elevated levels of respiratory diseases and cancer (Lee et al, 2006; HDC, 2004). This has been attributed to the region’s history of mining activity as well as high airborne dust concentrations. The region has low precipitation and fine-grained red soils which are can easily become airborne. Although these soils contain various potentially toxic metals that could contribute to the health issues, nickel is of particular concern, as it is a well-documented carcinogen (Doll et al., 1970; Pederson et al., 1973). Nickel is naturally abundant in the bedrock of the region, and is also was released during the region’s long history of mining and smelting activity. Nickel occurs in a variety of mineral forms, some of which are more toxic than others (Grimsrud et al., 2002). While nickel has been studied before in this region, it has not been conclusively determined which mineral species host nickel in these soils (Drysdale, 2008; Segnit, 1976;-77). While it is expected that some of the nickel in the soil is of natural origin, the proximity of the smelter is also of concern and raises the possibility of significant levels of anthropogenically-introduced nickel, which may have important implications regarding mining and smelting regulations. The objectives of my research were to identify and assess the abundance of nickel- hosting minerals present in the soil, and also to evaluate the degree of natural versus anthropogenic nickel mineralization. Surface soil samples were collected in 2008 by my supervisor, Dr. Heather Jamieson, and one of her graduate students, Mallory Drysdale, who was researching nickel bioaccessibility in the area. The samples were collected from locations near the smelter, in the city, and outside the influence of both city and smelter. These samples were analysed via several techniques in order to get more accurate results, including Scanning Electron Microscope (SEM), reflective light petrography, and X-ray Diffraction (XRD). 4 1.1 Geology Kalgoorlie is located on the central eastern portion of the Yilgarn Craton, and overlies Archean-age rocks of the Southern Cross Domain and the Eastern Goldfields Superterrane. The craton covers most of Western Australia, and hosts a variety of ore deposits, including nickel, iron, gold, uranium, and Platinum Group Elements (PGEs). The basement rocks in the region consist of a mix of granite, gneiss and greenstone. The greenstone belts contain a mixture of metamorphosed mafic to ultramafic rocks, felsic volcanic rocks and metasedimentary rocks. This bedrock has been extensively weathered to thick layers of laterite (a type of Fe-rich, tropically-weathered soil), which in turn is overlain by recent alluvial, colluvial and aeolian deposits (Tille, 2006). The local geological unit, the Kalgoorlie Terrane, consists of felsic volcaniclastics overlying mafic lava sequences and intruded by mafic-ultramafic sills. These formations are found near surface 55km south of Kalgoorlie in the famous mining center of Kambalda, where they host large nickel deposits. In Kalgoorlie, the bedrock nearest the surface is the metasedimentary Black Flag sequence, which overlies the Paringa Basalt, an ultramafic basalt unit. These formations are intruded by a set of mafic sills, including the Golden Mile Dolerite, which hosts the majority of the area’s gold deposits (Phillips, 1986). The bedrock at Kalgoorlie is buried under 40-50m of relatively homogeneous overburden, developed both from weathering of the bedrock and from aeolian input (Sergeev & Gray, 2001). The local geology near Kalgoorlie is shown below in Figure 1. 5 Figure 1: Local geology of the Kalgoorlie area showing major rock types (Elias et al., 1981) 1.2 Soils The Kalgoorlie area consists of an extensive plateau, with flat to undulating plains and small valleys. Duricrust, claypans and playa lakes are common in the area. The soils in the area are very fine-grained and have a characteristic reddish colour, derived from their high iron oxide content. The soils are characterized by extensive areas of calcareous loamy earths, red loamy earths, red deep and shallow loamy duplexes (Tille, 2006). A typical profile of the regolith near the city consists of a thin gravel layer overlying a 1- 2m thick layer of calcareous clay-rich red soil with ferruginous granules. The soil transitions to a 6 sandy clay with sand lenses, and decreasing carbonate concentrations with depth (Drysdale, 2008). A thin mica-rich layer marks the unconformity between the sandy clay soil and the underlying clay-rich saprolite, which extends down to bedrock (Lintern, 2004). While the underlying bedrock affects the regolith mineralogy of Kalgoorlie to some degree, there is also very significant influence from aeolian transport at the surface. Common surface soil minerals include iron oxides such as hematite and goethite, as well as kaolinite, quartz, and carbonate minerals. The soil pH is generally above neutral, and can go above 9 in some areas due to high carbonate content (Anand & Paine, 2002; Drysdale, 2008). Evaporated lakes, or playas, are common in the area, and there are several near the city of Kalgoorlie. These differ somewhat from the surrounding soils; while the lake beds have similar mineralogy to the surrounding soils, evaporation of saline waters results in the precipitation of minerals like halite and gypsum, which can form large crystals near the surface and have a significant influence on soil chemistry (Clarke, 1994). 1.3 Kalgoorlie Nickel Smelter The Kalgoorlie Nickel Smelter, owned by BHP Billiton, is located 12km south of Kalgoorlie along the Goldfields Highway 94. The ore processed here is shipped by rail from surrounding nickel deposits, including Kambalda to the south, and Leinster and Mt Keith to the north. The ore consists of massive and disseminated nickel sulphides, hosted by komatiites or within olivine cumulates (Barnes, 2004). The primary ore minerals are pyrrhotite and pentlandite, with minor chalcopyrite and pyrite (Hill et al., 2004). The Kalgoorlie Smelter is an Outokumpu-type flash smelter, a design developed in Finland that is similar to the INCO smelter in Sudbury. The nickel sulphide ore is mixed with pre- heated oxygen-rich air, which causes the oxidation of iron and sulfur, separating the