The interstitial location of selenium and arsenic in rocks associated with coal mining using ultrasound extractions and principal component analysis (PCA).

The release of selenium and arsenic from coal mine wastes into main waterways is an environmental cause for concern in the mining industry due to a myriad of subsequent ecotoxicological problems associated with the two metalloids. In a 2002 USEPA study undertaken in a mountaintop removal/valley fill (MTR/VF) mining area in southern West Virginia, measured Se concentrations were higher than the stipulated 5 ng/mL in 66 out of the 213 water samples collected. We studied the chemical composition of forty seven randomly selected pulverized core rock samples collected from depths of 25 ft to 881 ft from MTR/VF sites to determine the amounts of bioaccessible (ultrasound leachable) As and Se concentrations and their tentative locations within the rock matrix. The application of principal component analysis (PCA) to the chemical data, suggested that ultrasound leachable selenium concentrations were associated with 14 Å d-spacing phyllosilicate clays (chlorite, montmorillonite and vermiculite all 2:1 layered clays) whilst ultrasound leachable arsenic concentrations were closely related to the concentration of illite, another 2:1 phyllosilicate clay. Negative correlations between leachable arsenic and selenium with kaolinite a 1:1 layered clay, were also observed. We used the observed negative correlations to rule out the presence of selenium or arsenic in 1:1 kaolinite. Hence mining waste from MTR/VF sites containing substantial amounts of illite and 14 Å d-spacing clays may require to be placed in priority landfills or valley fills.

Ultrasonic extraction of arsenic and selenium from rocks associated with mountaintop removal/valley fills coal mining: Estimation of bioaccessible concentrations.

Ultrasonic extraction (UE) was used to estimate the total bioaccessible fractions of arsenic and selenium released from rocks associated with mountaintop removal/valley fill coal mining. The combined readily bioaccessible amounts of arsenic and selenium in water soluble, exchangeable and NaOH fractions can be extracted from the solid phase within a 20 or 25 min application of 200 W cm(-2) ultrasound energy in nanopure water for selenium and arsenic, respectively. Application of a two-way ANOVA predicted that there are no significant differences (p0.001, n=12) in the extracted arsenic and selenium concentrations between the combined bioaccessible and ultrasonic extracts. The mechanisms for the UE of arsenic and selenium are thought to involve the formation of secondary minerals on the particle surfaces which eventually dissolve with continued sonication. This is supported by the presence of transient Si-O stretching and OH absorption and bending ATR-FTIR peaks at 795.33 cm(-1), 696.61 cm(-1) and 910.81 cm(-1). The subsequent dissolution of secondary minerals is followed by the release of chemical species that include selenium and arsenic. Release rates decrease after the ultrasound energy elastic limit for the particles is reached. Selenium and arsenic are bound differently within the rock lattice because no selenium was detected in the acid soluble fraction and no arsenic was found in the exchangeable fraction. However, selenium was found in the exchangeable fraction and arsenic was found in the acid soluble fraction. The characterization of coal associated rocks is essential to the design of methodologies and procedures that can be used to control the release of arsenic and selenium from valley fills.

Characterisation of particulate matter emissions from the Zimbabwe Mining and Smelting Company (ZIMASCO) Kwekwe Division (Zimbabwe): a ferrochrome smelter.

Particulate matter emissions from stack number 2 of a major ferrochrome smelter, Zimbabwe Mining and Smelting Company (ZIMASCO) were characterized and the rates at which the elements Cr, Fe, Cu and Zn and total ferrochrome dust are emitted into the atmosphere were determined. The extent of soil contamination by the dust deposited around the smelter in the generally prevailing southeasterly wind direction around the smelter was carried out. The highest concentrations of Cr and Fe occurred in the fine particulates of sizes less than 59 microm whilst that of Cu and Zn occurred in the coarse particulates of size range 70-100 microm. The emission rates from stack 2 were; total ferrochrome particulates 62.17 kg h(-1), Cr 6.217 kg h(-1), Fe 2.423 kg h(-1), Zn 42 mg h(-1) and 6 mg h(-1) for Cu. Particulate matter was emitted at a rate of 289 mg m(-3) from stack number 2. This value exceeds the legal limit of 200 mg m(-3). Chromium and iron are the metals in the largest amounts. The particles that constitute the largest proportion of the dust were in the range of 58-107.5 microm. This is a characteristic feature of the particulate matter emissions from ZIMASCO. Soils in the downwind direction from the smelter were polluted with Cr up to a distance of about 700 m outward from the perimeter of the boundary of the smelter.