Predictions of mine-related water pollution are often based on laboratory assays of mine-site material. However, many of the factors that control the rate of element release from a site, such as pH, water-rock ratio, the presence of secondary minerals, particle size, and the relative roles of surface-kinetic and mineral equilibria processes can exhibit considerable variation between small-scale laboratory experiments and large-scale field sites.Monthly monitoring of mine effluent and analysis of natural geological material from 4 very different mine sites have been used to determine the factors that control the rate of element release and mineral sources and sinks for major elements and for the contaminant metals Zn, Pb and Cu. The sites are: a coal spoil tip; a limestone-hosted Pb mine, abandoned for the last 200 a; a coal mine; and a slatehosted Cu mine that was abandoned 150 a ago. Hydrogeological analysis of these sites has been performed to allow field fluxes of elements suitable for comparison with laboratory results to be calculated. Hydrogeological and mineral equilibrium control of element fluxes are common at the field sites, far more so than in laboratory studies. This is attributed to long residence times and low water-rock ratios at the field sites. The high water storativity at many mine sites, and the formation of soluble secondary minerals that can efficiently adsorb metals onto their surfaces provides a large potential source of pollution. This can be released rapidly if conditions change significantly, as in, for example, the case of flooding or disturbance. 3 4 sample for contamination, but do not provide information on the rate at which contamination is produced, and are thus of limited use (e.g. Jambor, 2000). Batch and column experiments have also been used (van Grinsven and van Riemsdijk, 1992;Stromberg and Banwart, 1999;Banwart et al., 2002), to measure rates and to distinguish rate-controlling mechanisms of mineral dissolution. Column experiments can be more useful than batch experiments because they involve water:rock ratios and hydrological solute transport processes similar to those found in the field. Regardless of method, however, it is difficult to extrapolate laboratory results to field situations.Laboratory-derived mineral dissolution rates are often 2 to 4 orders of magnitude faster than those measured for minerals in the field (e.g. Schnoor, 1990;White et al., 1996).A number of factors have been proposed to account for this discrepancy.These include differing pH, grainsize, temperature, hydrology, cation exchange characteristics, availability of reactants such as O 2 , degree of physical and chemical heterogeneity, secondary mineral behaviour, mineral surface characteristics and proximity to chemical saturation with respect to the dissolving minerals, between weathering environments (e.g. Sverdrup and Warfvinge, 1995;Malmstrom et al., 2000;White and Brantley, 2003). Algorithms that quantitatively account for some of these factors have been devised (e.g. Sverdrup and Warfvinge, 1...
Quartz-type MOF (Me2NH2)2[Cd(NO2BDC)2] (SHF-81) exhibits anisotropic breathing behaviour as single crystals in response to multiple stimuli.
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