- Title
- Insight of arsenic behavior (mineralogy, fractionation and bioaccessibility), dissolution and remediation of abandoned mine site soils in New South Wales, Australia
- Creator
- Bari, A. S. M. Fazle
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Arsenic (As) is extremely toxic and a carcinogen that has attracted significant attention worldwide due to its detrimental effect on human health and the environment. Similarly, trace elements such as lead (Pb), antimony (Sb) and zinc (Zn) are also of concern due to their toxicity, persistence and non-biodegradable nature in the soil environment. Environmental contamination of As and other trace elements is caused by both natural and anthropogenic activities. Anthropogenic As contamination in soils originates from multiple sources such as mining, smelting, wastewater irrigation, and extensive usage of insecticides and pesticides. Among the anthropogenic sources, mining is one of the major sources, especially in Australia where approximately 50,000 abandoned mine sites are present. The aim of the proposed research was to undertake a geochemical and mineralogical characterization of abandoned mine soil and attempt remediation of As by soil washing with eco-friendly reagents. For this purpose, soils were collected from three abandoned mine sites including Webbs Consols mine (WC), Halls Peak mine (HP), and Mole River mine (MR) which are located in New South Wales (NSW), Australia to conduct the following experiments: firstly, to investigate the geochemical distribution of trace element enrichment and mineralogical composition in various particle size fractions from contrasting abandoned mine sites (WC, HP and MR); secondly, As bioaccessibility and the potential health risk of As linked to incidental As-contaminated soil ingestion; thirdly, to determine the leaching potential of As and Sb using different leaching tests; fourthly, to assess dissolution behaviour of As minerals (tooeleite and beudantite) in relation to As release and transformation of minerals and finally to achieve remediation of As and other co-contaminants by soil washing. Geochemical distribution of trace element enrichment and mineralogical composition in various particle size fractions from contrasting abandoned mine sites (WC, HP and MR, Australia) were investigated. Results showed that As and other trace element concentrations increased with decreasing particle size fractions for samples from Webbs Consols and Halls Peak and the highest As (3.05%), Pb (3.23%) and Zn (1110 mg/kg) were recorded in the finest fraction (<0.053 mm). However, the highest concentration of As (10.8 %), Pb (209 mg/kg) and Zn (351 mg/kg) were observed in coarse fractions in MR soil. Arsenic fractionation by sequential extraction revealed that As was strongly associated with the amorphous and crystalline iron phases. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies revealed that tooeleite (a ferric arsenite mineral, which was also confirmed by Transmission electron microscopy (TEM)), arsenopyrite, scorodite and arsenolite were the dominant As minerals. In a bioaccessibility study, As bioaccessibility in relation to As fractionation and particle size fractions of abandoned mine soils was determined using different extraction assays. In addition, potential health risk due to incidental ingestion was also determined. Bioaccessibility of As ranged from 0.24 to 32% for Solubility Bioaccessibility Research Consortium (SBRC) and Physiologically Based Extraction Test (PBET) methods, with extractable As (using 0.43M HNO3) being 1.3-24.9%. The highest As bioaccessibility (19-32%) was consistently observed in the fine particle size fraction (<53 μm) of all three extractions. The bioaccessibility of As in the gastric phase of SBRC and PBET methods highlighted a positive correlation (R2=0.83-0.88, p<0.01) with exchangeable, surface and amorphous- bound As fractions, while the intestinal phase showed a strong positive correlation (R2=0.85-0.89, p <0.01) with exchangeable and surface bound fractions. Our results showed that As bioaccessibility in soils can potentially be determined using the 0.43M HNO3 extraction procedure. In the leaching study, As and Sb leaching potential in abandoned mine soil was examined with Toxicity Characteristic Leaching procedure (TCLP), Waste Extraction Test (WET) and Waste Extraction Test –Extended (WET-EXT) (modified). Results revealed that leaching concentrations of As regularly exceeded the USEPA criteria (5 mg/L). Highest leaching concentrations of As and Sb were observed in the finest particle size (<0.053 mm) by WET-EXT (As = 1040 and Sb = 21.10 mg/L) followed by WET (800 mg/L for As and 20.90 mg/L for Sb). TCLP resulted in the lowest concentration of leached As (0.0009 mg/L) and Sb (0.0003 mg/L). However, the best correlation of TCLP (0.832), WET (0.944), and WET-EXT (0.961) was found with the non-specifically sorbed (NS1) As fraction. Leachability of As and Sb is controlled by Fe geochemistry. The TCLP method is unlikely to be suitable for assessing leachability as this procedure exhibited a lack of relationship with leachable Fe, and the substantially lower leached As and Sb. Most of the soil samples would not be recommended for placing in capping works, old shaft or reducing systems (e.g. collection in drainage basins) due to high to extremely high leachable As and Sb concentrations. Dissolution of tooeleite was conducted to investigate the dissolution mechanism and secondary mineralogical transformation of tooeleite during oxidative dissolution. A batch study was conducted at wide range of pH levels (2, 4, 6 and 8). The congruent dissolution reaction occurred at pH 2 while incongruent reaction was observed at higher pH levels (4, 6, and 8) during the dissolution of tooeleite. The highest As and Fe were released during the dissolution tooeleite at pH 2 compared to other pH levels while the highest SO4- was released at pH 8. The residual solids were also examined using XRD, SEM, and XAS to identify any secondary mineralogical transformation. The XRD pattern of residual solid after dissolution of tooeleite shows little to no transformation over the 56 days of dissolution of tooeleite. However, specifically, at pH 6, two dominant new peaks were observed corresponding to scorodite. Iron K-edge extended x-ray absorption fine structure (EXAFS) spectroscopy further demonstrated transformation to ferrihydrite and scorodite at pH 6. In addition, the Linear combination fitting (LCF) of As k-edge EXAFS spectra showed that little oxidation of As (III) to As (V) at 7 d for pH 2 and 56 day for pH 4, and 8. At 56 d dissolution, the LCF of As K-edge and Fe K-edge EXAFS spectra revealed the transformation of tooeleite to ferrihydrite at all pH levels while transformation to scorodite and goethite was occurred at pH 6 and 8, respectively. To investigate the dissolution mechanism and secondary mineralogical transformation during oxidative dissolution of synthetic beudantite a batch dissolution experiments were conducted at wide range of pH levels (2, 4, 6 and 8). Incongruent reactions occurred during the dissolution of beudantite. Higher As, Fe, and Pb were released during the dissolution of beudantite at pH 2. However, the higher SO4- was released at pH 8 compared to other pH levels. The components were dissolved in solution preferentially in the order of SO4 > Fe > As > Pb in the early phases of 2 h dissolution and after 2 h in the order of Pb > SO4 > Fe > As, suggesting the incongruent dissolution of synthetic beudantite. The residential solid was also examined using XRD, SEM, TEM, XPS, and XAS to identify any secondary mineralogical transformation. However, no new peak or morphology was observed by these techniques indicating the stability of beudantite during dissolution. Arsenic contamination in abandoned mine site soil is a global concern which warrants an effective way of remediation. Initially, we planned to use combination of physical separation by sieving and chemical extraction washing technique to remove As from soil where physical separation is mainly used to separate less contaminated coarse particle size fraction from highly contaminated fine particle size fraction to reduce volume of contaminated soil. However, we found that both coarse and fine fractions of soils contain significant concentrations of As. Hence, we used bulk soil sample (< 2 mm) for the soil washing study. In this study, two organic acids (oxalic acid and citric acid) and one biodegradable chelating agent (EDDS) were used to treat As contaminated abandoned mine soils. The concentration of As was 19,100 and 75,350 (mg/kg) for WC and MR samples, respectively. XRD and SEM confirmed that tooeleite, arsenopyrite, scorodite and quartz are the major minerals in these soils. A major portion of the As is composed of amorphous and crystalline oxides of Fe and Al determined by sequential extraction. Among the three washing reagents, oxalic acid showed the best performance to extract As. Based on the batch experiment, 0.5 M oxalic acid and 3 h of washing was the most efficient treatment to extract As and other trace elements. Extraction of As, Fe, and Pb was 69.5, 55, and 48% respectively for WC, while 68, 45 and 63%, respectively, for MR soil. Oxalic acid extracted 75 and 83 % of As and Fe, respectively from tooeleite. Leachability and bioaccessibility of As and Fe in the treated soil was reduced due to washing. However, bioaccessibility and leachability of Pb in soil and Fe and As in tooeleite were increased in washed samples. Though the leachability and bioaccessibility of As and Fe in soil was reduced in the treated soil, As still exceeded the USEPA criteria (5 mg/L) which is needed to successfully remediate abandoned soil by washing. Soil washing and subsequent solidification/stabilization could be an alternative option to remediate extremely contaminated abandoned mine soil. Based on the experimental results found in this thesis we concluded that mineral composition, particle size fraction, bioaccessibility and dissolution behaviour of minerals are crucial for the remediation of abandoned mine site soils.
- Subject
- arsenic; mine sites; New South Wales; dissolution and remediation
- Identifier
- http://hdl.handle.net/1959.13/1512025
- Identifier
- uon:56579
- Rights
- Copyright 2022 A. S. M. Fazle Bari
- Language
- eng
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