Impact Of Sulfate Research Articles

Impact of sulfation and desulfation on NOx reduction using Cu-chabazite SCR catalysts

This bench reactor study investigates the impact of gaseous sulfur on the NOx reduction activity of Cu-chabazite SCR (Cu-CHA) catalysts at SO2 concentrations representative of marine diesel engine exhaust. After 2h of 500ppm SO2 exposure at 250 and 400°C in the simulated diesel exhaust gases, the NOx reduction activity of the sulfated Cu-CHA SCR catalysts is severely degraded at evaluation temperatures below 250°C; however, above 250°C the impact of sulfur exposure is minimal. EPMA shows that sulfur is located throughout the washcoat and along the entire length of the sulfated samples. Interestingly, BET measurements reveal that the sulfated samples have a 20% decrease in surface area. Furthermore, the sulfated samples show a decrease in NOx/nitrate absorption during NO exposure in a DRIFTS reactor which suggests that Cu sites in the catalyst are blocked by the presence of sulfur. SO2 exposure also results in an increase in NH3 storage capacity, possibly due to the formation of ammonium sulfate species in the sulfated samples. In all cases, lean thermal treatments as low as 500°C reverse the effects of sulfur exposure and restore the NOx reduction activity of the Cu-CHA catalyst to that of the fresh condition.

The impact of sulphate and magnesium on chloride binding in Portland cement paste

The effect of magnesium and sulphate present in sea water on chloride binding in Portland cement paste was investigated. Ground well hydrated cement paste was exposed to MgCl2, NaCl, NaCl+MgCl2, MgSO4+MgCl2 and artificial sea water solutions with a range of concentrations at 20°C. Chloride binding isotherms are determined and pH of the solutions were measured. A selection of samples was examined by SEM-EDS to identify phase changes upon exposure. The experimental data were compared with calculations of a thermodynamic model. Chloride binding from sea water was similar to chloride binding for NaCl solutions. The magnesium content in the sea water lead to a slight decrease in pH, but this did not result in a notable increase in chloride binding. The sulphate present in sea water reduces both chloride binding in C–S–H and AFm phases, as the C–S–H incorporates more sulphates instead of chlorides, and part of the AFm phases converts to ettringite.

Effect of Sulfate and Redox Mediator on Reduction of AO7 in Upflow Anaerobic Filter (UAF)

Azo compounds constitute the largest and the most diverse group of synthetic dyes and are widely used. The release of coloured wastewaters represents a serious environmental problem and a public health concern. The aim of this study was to investigate the impact of sulfate and redox mediator on the reduction of an azo dye (Acid orange 7, AO7) by anaerobic sludge. The kinetics showed the AO7 reduction rate can be greatly improved by the addition of sulfate and RF, thus it is possible to speed up the start-up of AO7 reduction system under appropriate condition.

Impact of sulfate and chloride on sediment phosphorus release in the Yangtze Estuary Reservoir, China

The impact of sulfate (SO4(2-)) and chloride (Cl(-)) on phosphorus (P) release from sediment in the drinking water reservoir of Yangtze River Estuary was studied systematically. A significant correlation between sodium (Na(+)), Cl(-), SO4(2-) and total P was found, suggesting that P was directly or indirectly associated with these ions. SO4(2-) and Cl(-) were important factors that had an impact on P release from the sediment. The results showed that both sulfate and chloride enhanced phosphorus release from sediment. In the sulfate treatment, the decrease of organic phosphorus (OP) suggested that the mineralization of OP enhanced P release from sediment. Phosphonate was the main factor affecting the P release under sulfate condition. In chloride treatment, the sediment composition of iron (Fe), aluminum (Al), calcium (Ca) and magnesium (Mg) increased. The P fractions of Fe/Al-P, Ca-P and OP in sediment also increased. However, the increase of P was unstable after chloride treatment and was easy to release under disturbance. In this study, it was observed that sulfate and chloride could increase the risk of eutrophication in the Yangtze River Estuary drinking water reservoir.

Sources and impact of sulphate on groundwaters of Triassic carbonate aquifers, Upper Silesia, Poland

Summary Groundwater within the unconfined or semi-confined parts of Triassic carbonate aquifers in Upper Silesia (Poland) contains high concentrations of sulphate (up to 290 mg/L), sometimes in excess of drinking water limits (>250 mg/L). To assess the influence of different possible sulphate sources, isotopic analyses of S and O were performed on groundwater sulphate and potential sulphate sources and combined with literature data. Three dominant sources of sulphate were delineated, based on the geological and literature study and supported by the mixing relations between inverse concentration of sulphate and its isotopic compositions. These sources are: (i) sulphate from rainfall; (ii) weathering of sulphide minerals in ore deposits in the aquifer-forming carbonate rocks; (iii) dissolution of sulphate evaporites in the Triassic sequence. Fortunately these three sources have distinctive S and O isotope compositions and thus their contributions to the total dissolved sulphate could be estimated. The application of linear mixing models for three sources in the dual isotope system allowed the impact of the three different sulphate sources on particular parts of the aquifers to be calculated. The average isotopic composition of sulphate in abstracted groundwater indicates that the most important source of sulphate is sulphide weathering, contributing about 50% of total sulphate. The second most significant source of sulphate input is rainfall and it is characterised by a mean contribution of 30%. Application of Monte Carlo analysis that incorporates the full variability in distributions of isotopic compositions for the three sources and all mixing fractions between them gave the most probable ranges of the dissolved in groundwater sulphate. This analysis indicated that the proportion of sulphate derived by sulphide oxidation is comparable with the estimations based on linear models. This study has shown that the water quality of these important groundwater resources is under threat from both natural sources, i.e. metal sulphide oxidation and gypsum dissolution. Analysis of the mathematical models analysis shows that the first process is the predominant source of sulphate in groundwater. However, the highest concentrations of dissolved sulphate are positively correlated with the increasing proportion of sulphate derived from gypsum dissolution. Moreover, one should keep in mind that natural processes might be anthropogenically accelerated due to variable water demands and groundwater abstraction. Eventually, the statistically second-order source of sulphate – rainfall might contain surface-derived contaminants, and its contribution to the total load of sulphate might indirectly indicate the vulnerability of aquifers for the pollution.

Impact of sulfate and nitrate incorporation on potassium- and sodium-based geopolymers: geopolymerization and materials properties

One of the most promising applications of geopolymers is their use as a waste encapsulating matrix. These binders are indeed compatible with aqueous waste streams and capable of activating several chemical and physical immobilization mechanisms for a wide range of inorganic waste species. Several works have investigated the immobilization of cations, mainly heavy metals or radioactive wastes, but very few studies have taken counterions, namely anions, into account. This work is an experimental investigation of the impact of anions with different valences on the material properties in regard to the requirements of an industrial process at ambient or slightly elevated temperature, including the setting time, maximum achievable compressive strength, or resistance to leaching. The modifications caused by the introduction of monovalent and divalent anions, such as sulfate and nitrate, are also evaluated in term of mineralogy, porosity, and microstructure. Their immobilization appears to be related to the progress of the geopolymerization reaction. Moreover, depending on the alkali ions used in the activation solution, the anionic species considered may also enhance the precipitation of some zeolites.

Sulphate reduction and the suppression of peatland methane emissions following summer drought

Peatland methane emissions have been proposed to decrease during summer drought as the onset of more aerobic conditions causes enhanced methane oxidation and suppressed methane production. However, emissions often fail to return to pre-drought levels for a year or more after the water table has returned to the peat surface and conditions favourable for methane production have been restored. Droughts release sulphate into the soil solution, and such increases in sulphate abundance could stimulate sulphate-reducing bacteria. These microbes are known to compete with methanogens for access to organic substrates. To examine whether this effect could continue to cause suppression of methanogenesis even after a drought, peat cores from a gully mire were incubated with either (a) the water table held at the surface of the peat, or (b) with a lowered water table for 4 weeks, followed by a period of rewetting. After a brief pulse of high methane release, methane emissions were confirmed to decrease during the drought, and to remain lower than the control emission rates throughout the rewetting period. Addition of an inhibitor of sulphate-reducing bacteria (molybdate) to the peat core slurries confirmed that sulphate reduction was significantly impairing methanogenesis and that this effect can persist longer than the end of a drought. However, low primary production during drought may be more important than the impact of sulphate in suppressing peatland methane emissions following drought.