Mansour Edraki

Understanding the salinity issue of coal mine spoils in the context of salt cycle

Coal mine spoils (CMSs), the solid wastes originated from the rock formations and soil cover overlying or interbedded with coal seams, are a worldwide environmental management challenge. Previous studies have shown that salinity is of most concern among the CMSs’ environmental impacts, especially in Australia. With increasing concerns from both the governments and communities, there is a real need for the coal mining industry to understand the source, dynamics and management options of CMS salinity. We reviewed the general properties of CMSs from coal mine sites worldwide and the current understanding of the CMS salinity, which are in a limited number of available published reports. Properties (e.g., pH, electrical conductivity and hydraulic conductivity) of studied CMSs varied largely due to its complex lithological origination. A conceptual model was proposed to illustrate the origin, dispersion paths and transformations dynamics of salts in spoils, taking the scenario of a coal mine in Australia as an example. The major factors governing the salt dynamics in CMSs are summarized as mineral weatherability and salt leachability of the spoils. Management of CMS salinity is still a vague area awaiting more extensive studies. Three topics related to the management were explored in the review, which are pre-mining planning, spatial variability of spoil properties and remediation including electrokinetics and phytoremediation. Particularly, based on the geological classification of CMSs and the leachate chemistry of spoils of various sources, a clear relationship between salinity and geounits was established. This association has a potential application in pre-mining planning for the management of salinity from coal mine spoils.

Heavy metal enrichment and ecological risk assessment of surface sediments in Khorramabad River, West Iran

The ecological health of rivers has often been threatened in urbanized catchments due to the expansion of industrial activities and the population growth. Khorramabad River which flows through Khorramabad city, west of Iran, is an example of such settings. The river water is used for agricultural purposes downstream. In this study, the effect of Khorramabad city on heavy metal and metalloid (Cu, Pb, Zn, Ni, Cr, and As) loads in Khorramabad River sediments was investigated. To evaluate sediment pollution and potential adverse biological effects, surface sediment samples were collected at selected locations along the river and were characterized for their geochemical properties. Contamination factor (CF), pollution load index (PLI), and ecological risk assessment (RI) were calculated. Also, sediment quality guidelines (SQGs) were used to screen contaminants of concern in the study area. The results showed that sediments were moderately polluted, with stations located in more densely populated areas showing higher pollution indicators. Copper, Zn, and Pb sources could be attributed to urban wastewater, whereas Ni, Cr, and As had both natural and anthropogenic sources. Moreover, ecological risk assessments showed that sediments could be classified in the category of low risk. The results of the present study showed the effect of anthropogenic activities on heavy metal loads of the river sediments and these findings can be used to mitigate potential impacts on the environment and human health.

Geochemical characteristics of rehabilitated tailings and associated seepages at Kidston gold mine, Queensland, Australia

Abstract This study investigated an uncapped tailings storage facility in a semi-arid subtropical climate, with the aim of understanding the hydro-geochemical processes controlling the seepage water quality and the dispersion/attenuation of metals and metalloids within the tailings and through a constructed wetland. While direct re-vegetation helped to stabilize the surface of tailings, development of an oxidation front in the tailings resulted in high sulphate and arsenic concentrations in the seepage. The findings of this study will assist maximizing the efficiency of any future passive treatment system on site and provide useful information for similar tailings closure strategies elsewhere.

Investigation of elemental enrichment and ecological risk assessment of surface soils in two industrial port cities, southwest Iran

In recent years, there has been a rapid growth in the two industrial port cities of Iran, the port of Mahshahr and the port of Imam Khomeini. In spite of their importance for the economy, the two cities require monitoring and assessment from an environmental and human health perspective. In this study, environmental quality and heavy metals pollution of soils influenced by human activities were investigated. A total of 30 soil samples were collected and subjected to detail physicochemical characterization. The results showed high levels of heavy metals in the urban soils of port of Mahshahr (POM) and elevated respective levels in surface soils of the port of Imam Khomeini (PIK) with Ni being significantly higher than those in POM. The integrated pollution index (IPI) values of metals ranged from 1.22 to 1.87 in POM and 1.52 to 3.31in PIK, 50% of soil samples in PIK were classified as highly polluted, and all of the soil samples in PM were classified as moderately polluted. These results are in accordance with Enrichment Factor (EF) values, which showed the role of anthropogenic activities in the soil heavy metal enrichment. Moreover, the highest potential ecological risk index (RI) was found in the sites of petrochemical industries in PIK indicating serious metal contamination. Statistical analysis showed that heavy metals were mainly controlled by human activities. The results showed more dense industrial activity in PIK is responsible for higher pollution. This study establishes a benchmark against which future monitoring and remediation programs can be based on. Because of proximity to the Persian Gulf, continued the release of contaminants into the region, could have adverse biological health effects.

The Effect of Particle Size and Mineral Liberation on the Acid Generating Potential of Sulphidic Waste Rock

Acid Rock Drainage (ARD) prediction is complicated by the number and complexity of influencing parameters. The objective of this study was to determine the effect of particle size and mineral liberation on the production of ARD. This information was used to classify waste rocks from an Australian mine site for their potential use as cover material. Samples were crushed and sieved into different particle size fractions, and were subjected to varying static and kinetic tests including paste-pH, Acid-Neutralization-Capacity tests, kinetic Net Acid Generation tests and Humidity Cell tests. The results showed a strong influence of particle size, which can be attributed to the widely different mineral liberation characteristics of acid generating and neutralizing minerals. Whereas standard Acid Base Accounting (ABA) resulted in an uncertain or Non Acid Forming classification of open-pit waste rocks, the application of modified ABA test procedures using different particle size fractions resulted in an uncertain or Potentially Acid Forming classification of the very same material. The study demonstrated that the standard ABA procedure may lead to erroneous classification with potentially costly environmental consequences by overlooking particle size specific mineral liberation effects. Testing different particle size classes proved to be a practicable method to investigate the ARD characteristics of waste rocks and to gain a clearer insight into the consequences of mineral liberation.

Chromium and nickel accumulation in the macrophytes of the Kawasi wetland on Obi Island, North Maluku Province, Indonesia

Five macrophytes, namely Crinum asiaticum L. (Amaryllidaceae), Lepironia articulata (Retz.) Domin (Cyperaceae), Machaerina rubiginosa (Spreng.) T. Koyama (Cyperaceae), Pandanus sp. (Pandanaceae) and Nepenthes mirabilis (Lour.) Druce (Nepenthaceae), were identified in the Kawasi wetland, a natural wetland on Obi Island, Indonesia, that overlies ultramafic rocks. The dominant species in this wetland was C. asiaticum, a native of the region. The surface runoff in the catchment of the Kawasi wetland was derived from serpentine soils, areas of which were being mined for nickel and, as a result, the water that flowed to the wetland typically contained dissolved chromium and nickel. In this study we investigated the accumulation of chromium and nickel in the macrophytes of the wetland. The five species of macrophytes under investigation accumulated greater quantities of chromium and nickel in their roots than in their shoots, with Pandanus sp. having the highest translocation factor (as evidenced by the highest shoot : root ratio) for both chromium and nickel. The species with the highest concentrations of the metals in both roots and shoots was C. asiaticum.

Removal of dissolved chromium from synthetic mine effluent: A mesocosm experiment

Dispersion of hexavalent chromium (Cr(VI)) in streams around nickel laterite mines, which are mostly located in the tropics, may pose serious risks for the environment and human health. In an earlier study, a local natural wetland effectively removed Cr from a nickel mine environment in Indonesia. In order to understand the processes and conditions that would facilitate the establishment of operational constructed wetlands that would remove Cr from mine water discharge, we used two native macrophyte species from the same wetland, Lepironia articulata and Machaerina rubiginosa, in a series of mesocosm experiments to follow the distribution of Cr species in water, substrate and plants. A 1 m3 mesocosm was charged with a sand/compost mixture to a depth of 0.5 m, filled to within 0.1 m from the top by water with Cr concentrations of about 1.0 mg L-1, similar to mine discharge water, and plants were introduced to part of the substrate surface. Stage 1 of the experiment supplied and removed fresh water continuously by surface flow, maintaining a residence time of 12 h. In stages, the water was recirculated (Stage 2), more plants were added (Stage 3) and outflow conditions were changed from totally surface to partially from beneath the substrate (Stage 4). All stages lowered Cr concentrations at the surface water outflow, but Cr concentrations were lower again close to the sediment/water interface. Due to the reduction of Cr(VI), the Cr concentrations in substrate pore water were higher near the surface compared to those at depth, and the pore water concentrations of Cr(VI) and total Cr were higher in the vegetated area compared to the non-vegetated area. Higher plant density and mixed species composition of the macrophytes did not increase the efficiency of Cr(VI) removal from the system. The hybrid system, comprising surface and below-substrate outflow (Stage 4), removed hexavalent chromium at a much higher rate than surface outflow only.

Indicators of metal pollution in prospective mining regions: a case study from Philippines

Understanding the baseline geochemistry of stream waters in a prospective mining area is the key to responsible life-of-mine planning and the protection of local rivers. This can be sometimes challenging due to the presence of abandoned mines, small scale mining, and geogenic sources of metals in the same area, particularly under a tropical humid climates with rivers carrying intermittently high solid loads. This study is focused on the Pula Bato, Danlag, Altayan, and Taplan Rivers in such a climatic setting in Philippines. The rivers are located in the vicinity of the Tampakan ore deposit. It was observed that elemental concentrations in water samples from Pula Bato were generally higher when compared to concentrations from Danlag, Taplan, and Altayan samples. In particular, SO42−, TDS, Al, Cu, Fe, Mn, Ni, and Zn present considerably higher concentrations in the water samples from Pula Bato. It was shown that water quality of Pula Bato is influenced by the natural weathering of sulphide minerals which is further enhanced by the small scale mining activities and old underground workings. The mining effects on the water of Pula Bato River were not apparent in the water of the Altayan due to the possible dilution of the uncontaminated water from Danlag River and sorption processes occurring during the course of contaminants transport. The geochemical indicators and water distinctions can be used in future for catchment-scale geochemical balance modelling.

Development of a textural acid rock drainage index for classifying acid formation

Textural analyses are largely absent from predictive ARD (acid rock drainage) assessments despite the direct control of texture on acid formation. The objective of this study was to develop a simple method for textural evaluation termed the ARD Index (ARDI) in order to categorise the acid-forming potential of intact samples. The ARDI is intended for use alongside routine predictive geochemical and mineralogical analyses as part of a geochemistry–mineralogy–texture (GMT) approach. The ARD Index (ARDI) assessed iron–sulphide minerals individually by five categories A–E, specifically chosen based on the direct influence on acid formation. Parameters A, B and C (ranked from 0 to 10) examined contents, degree of alteration and morphology of sulphides, while parameters D and E (ranked from –5 to 10) evaluated the neutralising mineral content and the spatial relationship between acid-forming and neutralising minerals. Scores from each category were totaled with values 50–41 considered as extremely acid forming (EAF); 40–31 as acid forming (AF); 30–21 as potentially acid forming (PAF); 20–10 as not acid forming (NAF); 10–0 as NAF/ANC and –1 to –10 as having acid-neutralising capacity (ANC). The ARDI was most efficiently performed on both a meso-scale and micro-scale. Eighty-one samples from an abandoned lode-gold operations and an operational iron-oxide copper gold mine (located in Queensland, Australia) were used to evaluate the ARDI. Samples were mesotexturally grouped (A–Q) and in addition to ARDI evaluations, geochemically and mineralogically analysed through static tests, elemental microanalysis (EA) and quantitative X-ray diffractometry (QXRD). ARDI classification identified lode-Au samples as the most acid forming, with group J (quartz–pyrite) classified as EAF, group H (quartz–arsenopyrite–pyrite) as AF and group G (quartz–galena–sphalerite) as PAF. When used in conjunction with paste-pH and sulphide-sulphur values, classifications were largely in agreement with traditionally used net acid-producing-potential/net acid generating (NAPP/NAG) geochemical methods. This indicates that the ARDI has the potential to be used as a simple textural screening method in predictive ARD studies.

Decision process for comparison of partial and complete XANES spectra

If the range of XANES spectra varies between sets of scans, it may be impossible to compare sets of spectra unless a restricted part of the spectra is used. The paper derives a decision process for comparison of partial and complete XANES spectra, taking lead as an example. Lead L3‐edge XANES spectra were collected at the Australian National Beamline Facility (BL‐20B) Photon Factory, Tsukuba, Japan over the energy range 13,000–13,150 eV (ring conditions: 2.5 GeV, 300–400 mA). The monochromator step size was reduced to 0.25 eV per step in the XANES region (13,000–13,100 eV and 13,040–13,100 eV) to collect high‐resolution spectra. XANES data for samples and model compounds were collected at ambient temperature and pressure in fluorescence, using simultaneous collection of a Pb metal reference foil for energy calibration (first derivative peak of elemental Pb was 13,050 eV). XANES spectra were fitted using spectral deconvolution and least‐squares linear combination fitting (LCF). Detailed XANES results with ...