As a result of the collapse of a mine tailing dam, a large extension of the Guadiamar valley was covered with a layer of pyritic sludge. Despite the removal of most of the sludge, a small amount remained in the soil, constituting a potential risk of water contamination. The kinetics of the sludge oxidation was studied by means of laboratory flow-through experiments at different pH and oxygen pressures. The sludge is composed mainly of pyrite (76%), together with quartz, gypsum, clays, and sulphides of zinc, copper, and lead. Trace elements, such as arsenic and cadmium, also constitute a potential source of pollution. The sludge is fine grained (median of 12 μm) and exhibits a large surface (BET area of 1.4±0.2 m2 g−1).
The dissolution rate law of sludge obtained is r=10−6.1(±0.3) [O2(aq)]0.41(±0.04)aH+0.09(±0.06) gsludge m−2 s−1 (22 °C, pH=2.5–4.7). The dissolution rate law of pyrite obtained is r=10−7.8(±0.3) [O2(aq)]0.50(±0.04)aH+0.10(±0.08) mol m−2 s−1 (22 °C, pH=2.5–4.7). Under the same experimental conditions, sphalerite dissolved faster than pyrite but chalcopyrite dissolves at a rate similar to that of pyrite. No clear dependence on pH or oxygen pressure was observed. Only galena dissolution seemed to be promoted by proton activity. Arsenic and antimony were released consistently with sulphate, except at low pH conditions under which they were released faster, suggesting that additional sources other than pyrite such as arsenopyrite could be present in the sludge. Cobalt dissolved congruently with pyrite, but Tl and Cd seemed to be related to galena and sphalerite, respectively.
A mechanism for pyrite dissolution where the rate-limiting step is the surface oxidation of sulphide to sulphate after the adsorption of O2 onto pyrite surface is proposed. 相似文献
In this study, the removal of free cyanide from aqueous solutions by activated carbon was investigated. Effects of metal impregnation (Cu and Ag), aeration, and concentrations of adsorbent and cyanide on the rate and extent of the removal of cyanide were studied. The results have shown that the capacity of activated carbon for the removal of cyanide can be significantly improved (up to 6.3-fold) via impregnation of activated carbon with metals such as copper and silver. Silver-impregnated activated carbon was found to be the most effective at the reduction of cyanide level in solution. This appeared to be coupled with its comparatively high metal content after impregnation process where silver (5.07%) could be more readily loaded on activated carbon than copper (0.43%). Kinetics and equilibrium data for cyanide removal by plain and metal-impregnated activated carbons were determined to be consistent with the pseudo second-order kinetics and the Langmuir adsorption isotherms, respectively. Aeration (0.27 l/min) was found to exert a profound effect on the process leading to a 5.5–49.1% enhancement in the performances of plain and metal-impregnated activated carbons. This enhancement could be attributed to the increase in the availability of active sites on activated carbon for adsorption and the catalytic oxidising activity of activated carbon in the presence of oxygen. Practical limiting capacity of plain, copper- and silver-impregnated activated carbons for the removal of cyanide were experimentally determined to be 19.7, 22.4 and 29.6 mg/g, respectively. 相似文献
The geotechnical properties of municipal sewage sludge, in particular those pertinent to the handling and landfilling of the
material, are presented. Index, drying, compaction, shear strength and consolidation tests were conducted on the material
at different states of biodegradation. The organic content and specific gravity of solids were found to be inversely related,
with typical organic contents of 50–70% and specific gravity of solids values of 1.55–1.80. The density of the compacted material
was low in comparison with mineral soils. Standard Proctor compaction yielded a maximum dry density of 0.56 tonne/m3 at 85% water content. Laboratory vane-shear and triaxial compression tests indicated that, below about 180% water content,
the shear strength of the sludge material increased exponentially with reducing water content. Consolidated-undrained triaxial
compression tests on the pasteurised sludge material indicated an effective angle of shearing resistance of 32° for the moderately
degraded material and 37° for the strongly degraded material. Biogas was produced at rates of up to 0.33 L/day/kg slurry due
to ongoing biodegradation and the resulting pore pressure response must be taken into account in any stress analysis. Consolidation
tests using the hydraulic consolidation cell, oedometer and triaxial apparatus indicated that the sludge material was highly
compressible although practically impermeable, for example the coefficient of permeability for the moderately degraded slurry
was of the order of 10−9m/s. However, creep deformation was significant with typical coefficient of secondary compression values of 0.02–0.08 for
the compacted material. A more free-draining material was produced at higher states of biodegradation. 相似文献