Concentration Of Alkaline-earth Ions Research Articles

Electrocoagulation for the purification of highly concentrated brine produced from reverse osmosis desalination of coal seam gas associated water

The ability of electrocoagulation (EC) at facilitating salt recovery from brine resultant from reverse osmosis (RO) desalination of coal seam gas (CSG) associated water is described. The aim was to reduce the presence of high concentrations of dissolved silicate which inhibit salt recrystallization by forming precipitates on equipment. The hypothesis was that EC could operate effectively in brine solutions and provide high silicate removal; thus facilitating a zero liquid discharge strategy. A benchtop EC unit equipped with either aluminium, iron or mixed iron-aluminium electrodes was used to treat simulated brine from a high recovery RO process. Up to 98.9% of silica was removed when aluminium or aluminium-iron electrodes were used. Significant reduction in concentrations of alkaline earth ions were also recorded (Ba > Sr > Ca > Mg) especially with iron electrodes. It appeared that silicate removal was via aluminosilicate formation. Hydraulic retention time was a key variable with 20 s recommended on the basis of performance/cost trade-off. Polarity reversal did not substantially change removal performance but impacted power consumption. For iron and iron-aluminium electrodes 1 min polarity reversal was preferred whereas for aluminium electrode 5 min was optimal. However, a thick coating was formed on the electrode surface and this may inhibit performance if longer tests are conducted. All flocs formed settled relatively rapidly (<20 min) which was in a time frame suitable for industrial application.

Stream water quality affected by interacting hydrological and biogeochemical processes in a riparian wetland

Riparian wetlands as both hydrological and biogeochemical hot spots often have a major impact on the release of solutes from headwater catchments. Numerous studies give some evidence of a rather complex interplay of hydrological and biogeochemical processes that is still poorly understood. This study seeks to address this challenge using a multivariate solute concentration data set from a small riparian headwater wetland. First, a non-linear variant of the Principal Component Analysis (Isomap) was performed in a preceding study to identify prevailing biogeochemical processes controlling water chemistry. Second, the scores of the components of the stream draining the wetland were subjected to a cluster analysis to identify typical biogeochemical patterns for different biogeochemical and hydrological boundary conditions.Four different clusters could be identified, which roughly followed a seasonal pattern, although modified by hydrological boundary conditions in the short-term. During the first three months of the year, Cluster 3 prevailed, indicating a discharge of rather unaltered shallow to mean depth groundwater. Cluster 3 was increasingly replaced by Cluster 2 and then subsequently by Cluster 1, indicating increasingly anoxic conditions, increasing denitrification and desulphurization, and increasing decomposition of organic carbon reflecting increasing biological activity and increasing water residence time within the wetland. However, stream water during stormflow after extended periods of low groundwater level in the second half of the growth season exhibited a very distinct pattern, represented by the fourth cluster. It indicated strong oxic conditions causing enhanced oxidation of sulphides, a corresponding decrease in pH values, and a substantial increase in the concentration of alkaline earth ions, manganese and in electric conductivity during the dry period.It is concluded that temporal variations in stream water chemistry clearly reflected the intensity of biological activity in the wetland, interacting with water table dynamics. Our results provide strong evidence for major effects of single extreme events like drought periods which are expected to become more frequent because of climate change.

Softening of coal seam gas associated water with aluminium exchanged resins

This study concerned aluminium exchanged strong acid cation resin for the removal of alkaline earth ions from simulated coal seam gas (coal bed methane) associated water samples which comprised of significant bicarbonate concentrations. The hypothesis was that use of aluminium exchanged resins for water softening would require only one regenerant stage, thus avoiding health and safety issues associated with strong acids and alkali on a coal seam gas water treatment site. Equilibrium exchange tests revealed that the selectivity of the aluminium exchanged resin was in the order Ba>Sr>Ca>Mg, albeit the exchange was unfavourable unless a stoichiometric excess of bicarbonate ions was present in solution. Equilibrium studies of multi-component solutions of alkaline earth ions indicated that at low loadings the alkaline earth ions co-sorbed on the resin surface, but the more preferred ion displaced ions of lesser affinity as monolayer exchange was approached. The presence of sodium ions not only reduced alkaline earth ion loading when in concentrations relevant to coal seam gas associated water application but also appeared to be incorporated into flocs in the form of salts. Column studies revealed significant loading of alkaline earth ions (0.787eq/kg resin) but regeneration with AlCl3 (aq) did not recover all these species (0.67eq/kg resin). Partial restriction of the flow was noted during column tests due to floc formation. A subsequent loading/regeneration cycle resulted in further diminishment in alkaline earth ion uptake and an inability to achieve low effluent concentrations of alkaline earth ions.

Co-L3 X-ray absorption near-edge structure analysis of Pr1−xCaxCoO3−δ and Pr1−xSrxCoO3−δ

Abstract The valence state of Co ions in Pr 1− x Ca x CoO 3− δ and Pr 1− x Sr x CoO 3− δ has been investigated by an analysis of the Co-L 3 X-ray absorption near-edge structure (XANES) profile. The observed intensity distributions of Co-L 3 XANES change continuously with increasing concentration of alkaline-earth ions. To investigate the origin of this change in the XANES profile, charge transfer multiplet calculations were carried out, which could successfully explain the change in the spectral profile; they also suggest that the valence state of Co ions in Pr 1− x Ca x CoO 3− δ and Pr 1− x Sr x CoO 3− δ is between 3+ and 4+ and increases gradually with the concentration of alkaline-earth ions.

The solvent extraction of radium using sym-Di[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid

The extraction of radium using sym-Di[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid (DTBDB16C5-OAcH) in toluene is excellent. The reaction is reversible without counterions at pH higher than 9. The distribution ratio decreases as the dissolved concentration of alkaline earth ions increases. Probed factors involved in this solvent extraction system include pH values, solvents, metal ions, and the concentration of DTBDB16C5-OAcH. Liquid scintillation cocktails including Ultima Gold and Hionic Fluor were also evaluated in liquid scintillation counting.

Characterisation and activity of sol–gel-prepared TiO2 photocatalysts modified with Ca, Sr or Ba ion additives

TiO2 (anatase)-based photocatalyst powders containing up to 20 mol% calcium, strontium or barium ions were prepared from α-titanic acid by calcining gels prepared from triethanolamine-based sols at 600°C. The powders were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance ultraviolet spectrophotometry, nitrogen sorption porosimetry and in situ infrared spectroscopy to examine surface adsorbed species. Compositions containing greater than 15 mol% alkaline earth ions resulted in largely amorphous materials. The residual anatase showed decreased crystallite sizes and increased crystallographic cell volumes with increasing concentration of alkaline earth ions, while the BET surface areas of the materials increased from around 80 m2 g−1 (no additive) to 160 m2 g−1 at higher levels of additive. Electronic spectroscopy showed that the band gaps of the materials increased with increasing Ca2+ content, due to the decreasing particle sizes. Under the synthesis conditions used, no other crystalline phase was observed, except rutile (< 1% w.r.t. anatase). The photocatalytic decomposition of oxalic acid was used as a model system to determine the relative influences of the additives on the photocatalytic activities. Titania containing 20 mol% alkaline earth ions showed approximately double the photocatalytic activity of similarly prepared anatase without additive. Half of the enhancement occurred for titania samples containing only 2 mol% alkaline earth ions. Comparisons of the physico-chemical properties of the photocatalysts with oxalic acid decomposition rates were carried out to determine the factors influencing the photocatalytic activity.

The influence of the size and concentration of alkaline earth ions on the structural and sorption properties of faujasites

The structural and sorption properties of type X and Y zeolites, ion-exchanged with Mg 2+, Ca 2+, Sr 2+, and Ba 2+ ions have been studied by X rays, IR, and adsorption. The nitrogen sorption in the zeolites was found to decrease with increased alkaline earth content in both X and Y zeolites and followed a general sequence Na + > Mg 2+ > Ca 2+ > Sr 2+ > Ba 2+. A similar trend was shown for the sorption of water, ethanol, and benzene vapors. Equilibrium sorption capacity and diffusion coefficient decreases with increase in cation radius. The sorption behavior of 1:3:5 trimethylbenzene (TMB) was specific: in X-type zeolites the substitution of Ca 2+ or Ba 2+ ions revealed a sharp fall in the sorption of 1:3:5 TMB, which is attributed to a blocking effect caused by Ca 2+ or Ba 2+ cations in the windows (SI site) large cavities.