Applied Geochemistry (v.16, #13)

This study examines the rare earth element (REE) pattern of acidic mine discharges in the Durham basin (NE England) as a means of fingerprinting their sources and understanding the water-rock interactions Although whole rock compositions proved to be unhelpful, mimicking acid mine water generation in a series of selective leachates of the coal and coal-bearing strata gave REE patterns similar to those measured in the emergent waters. REE ratios and anomalies were used as indicators of specific interactions in the development of acidic groundwater. The implications of the findings for the classification and evolution of acid mine discharges are discussed.

Recovery of trace metals in formation waters using acid gases from natural gas by Brian Hitchon; E.H Perkins; W.D Gunter (1481-1497).
The maximum contents of Pb (360 mg l−1), Zn (360 mg l−1) and Ag (7.9 mg l−1) in formation waters from the Alberta basin were high enough to suggest that it would be of interest to test the concept of recovering these metals by passing natural gas through the water, thereby precipitating the metal sulphides as the result of contact with hydrogen sulphide. The idea was to see if these metals could be recovered from formation water co-produced with crude oil prior to disposal of the water in deep formations, with the possibility of the sale of the metals partially offsetting the cost of disposal. It was proposed to use natural gas with a relatively small amount of hydrogen sulphide (insufficient for sulphur recovery) that must be removed by flaring before the gas is utilized. Accordingly, a database of 694 formation waters with major, minor and trace components was searched for appropriate analyses for detailed study. Of the nine analyses selected the majority were from Devonian and Granite Wash aquifers in the Peace River Arch area of northern Alberta, Canada. Modelling with PATH.ARC showed that there is a consistent set and order of precipitation reactions, in spite of the differences among the formation waters. As would be expected intuitively, acid gas addition makes the formation water more acidic, and metallic sulphide minerals are precipitated. Depending on the initial composition, the end minerals are any of galena, sphalerite, acanthite, covellite and pyrite. These are the minerals that must be beneficiated to recover the metals. A preliminary evaluation of the dollar value of the recovered metals shows that although the absolute values are low, there may be an advantage to recovering the metals if the waters are already being handled at the surface.

Oxidative dissolution of metacinnabar (β-HgS) by dissolved oxygen by Mark O Barnett; Ralph R Turner; Philip C Singer (1499-1512).
The oxidative dissolution rate of metacinnabar by dissolved O2 was measured at pH ∼5 in batch and column reactors. In the batch reactors, the dissolution rate varied from 3.15 (±0.40) to 5.87 (±0.39) × 10−2 μmol/m2/day (I=0.01 M, 23°C) and increased with stirring speed, a characteristic normally associated with a transport-controlled reaction. However, theoretical calculations, a measured activation energy of 77 (±8) kJ/mol (I=0.01 M), and the mineral dissolution literature indicate reaction rates this slow are unlikely to be transport controlled. This phenomenon was attributed to the tendency of the hydrophobic source powder to aggregate and minimize the effective outer surface area. However, in a column experiment, the steady-state dissolution rate ranged from 1.34 (±0.11) to 2.27 (±0.11) x 10−2 μmol/m2/day (I=0.01 M, 23°C) and was also influenced by flow rate, suggesting hydrodynamic conditions may influence weathering rates observed in the field. The rate of Hg release to solution, under a range of hydrogeochemical conditions that more closely approximated those in the subsurface, was 1 to 3 orders of magnitude lower than the dissolution rate due to the adsorption of released Hg(II) to the metacinnabar surface. The measured dissolution rates under all conditions were slow compared to the dissolution rates of minerals typically considered stable in the environment, and the adsorption of Hg(II) to the metacinnabar surface further lowered the Hg release rate.

Smoke particulate matter from conifers subjected to controlled burning, both under smoldering and flaming conditions, was sampled by high volume air filtration on precleaned quartz fiber filters. The filtered particles were extracted with dichloromethane and the crude extracts were methylated for separation by thin layer chromatography into hydrocarbon, carbonyl, carboxylic acid ester and polar fractions. Then, the total extract and individual fractions were analyzed by gas chromatography and gas chromatography–mass spectrometry. The major organic components directly emitted in smoke particles were straight chain aliphatic compounds from vegetation wax and diterpenoid acids (biomarkers) from resin. The major natural products altered by combustion included derivatives from phenolic (lignin) and monosaccharide (cellulose) biopolymers and oxygenated and aromatic products from diterpenoids. Other biomarkers present as minor components included phytosterols, both the natural and altered products, and unaltered high molecular weight wax esters. Polycyclic aromatic hydrocarbons (PAH) were also present, however, only as minor constituents. Although the concentrations of organic compounds in smoke aerosols are highly variable and dependent on combustion temperature, the biomarkers and their combustion alteration products are source specific. The major components are adsorbed or trapped on particulate matter and thus may be utilized as molecular tracers in the atmosphere for determining fuel type and source contributions from biomass burning.

Smoke particulate matter from deciduous trees (angiosperms) subjected to controlled burning, both under smoldering and flaming conditions, was sampled by high volume air filtration on precleaned quartz fiber filters. The filtered particles were extracted with dichloromethane and the crude extracts were methylated for separation by thin layer chromatography into hydrocarbon, carbonyl, carboxylic acid ester and polar fractions. Then, the total extract and individual fractions were analyzed by gas chromatography and gas chromatography–mass spectrometry. The major organic components directly emitted in smoke particles were straight chain aliphatic compounds from vegetation wax and triterpenoid acids (biomarkers) from gums and mucilages. The major natural products altered by combustion included derivatives from phenolic (lignin) and monosaccharide (cellulose) biopolymers and oxygenated and aromatic products from triterpenoids. Steroid biomarkers and polycyclic aromatic hydrocarbons (PAH) were also present, however, as minor constituents. Although the concentrations of organic compounds in smoke aerosols are highly variable and dependent on combustion temperature, the biomarkers and their combustion alteration products are in these cases source specific. The major components are adsorbed or trapped on particulate matter and thus may be utilized as molecular tracers in the atmosphere for determining fuel type and source contributions from biomass burning.