62 research outputs found
Uranium in Poland: Resources and Recovery from Low-Grade Ores
The presented studies deal with an assessment of the possibility of uranium recovery from the low-grade uranium resources in Poland. Uranium was leached from the ground uranium ores with efficiencies in 81â100% range that depend on the type of ore and leaching solution used. In the next step, the post-leaching solution was treated by the solvent extraction or ion exchange chromatography to separate uranium from other metals present in the ore. The novel routes of leaching by using membrane methods were examined. The final product, âyellow cake,â was obtained in precipitation step. The studies of precipitation of uranium as ammonium diuranate or uranium peroxide from diluted uranium solutions are presented in this chapter. The work was completed with tentative economic analysis and environmental impact assessment along with radiation protection issues connected to uranium production
Stability and deformation of oil droplets during microfiltration on a slotted pore membrane
This article was published in the Journal of Membrane Science [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/j.memsci.2012.01.034The effect of interfacial tension between two fluids, on the passage and rejection of oil droplets through slotted pore membranes is reported. A mathematical model was developed in order to predict conditions for 100% cut-off of oil droplets through the membrane as a function of permeate flux rate. Good agreement of theoretical predictions with experimental data shows that the model can be applied to the filtration of deformable droplets through slotted pore membranes. At high interfacial tension (40 mN/m) with lower flux (200 l mâ2 hrâ1)droplets of crude oil (27 API) were 100% rejected at droplet diameter 4.3 ÎŒm using a 4 ÎŒm slotted pore membrane. At lower interfacial tension (5 mN/m), with the same flux rate, 100% rejection occurred at 10 ÎŒm droplet diameter using the same membrane. It was also found that the droplet rejection efficiency below the 100% cut-off was roughly linear with drop size, down to zero rejection at zero drop diameter. Hence, the model, coupled with this approximate correlation, can be used to predict dispersed oil drop concentration from a known feed drop size distribution
Shear enhanced microfiltration and rejection of crude oil drops through a slotted pore membrane including migration velocities
This article was published in the Journal of Membrane Science [© Elsevier] and the definitive version is available at: http://www.sciencedirect.com/science/article/pii/S0376738812004991Shear enhanced microfiltration of crude oil/water emulsion is investigated and the effect of an applied shear rate on the rejection of droplets by the membrane is reported. Applying vibration provides shear rate at the membrane surface leading to shear-induced migration and an inertial lift of drops/particles. Both phenomena tend to move the droplets away from the membrane surface. The shear-induced migration and inertial lift increase with increasing of the shear rate. A mathematical model is presented to account for the presence of both phenomena. The developed model is used for theoretical prediction of 100% cut-off of crude oil droplets by the membrane with, and with-out, vibration applied. A satisfactory agreement of the model predictions with experimental data shows that the model can be successfully used for a theoretical prediction of 100% cut-off of droplets by slotted pore membranes. Rejection of droplets increased with applying shear rate: at 8000 s-1 shear rate and 200 l m-2 hr-1 flux rate 3 to 4 Όm radius droplets were almost completely rejected reducing 400 ppm of crude in the feed to 7 ppm in the permeate
OnâDemand Separation of OilâWater Mixtures
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92052/1/3666_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/92052/2/adma_201201364_sm_suppl.pd
A combined network model for membrane fouling
Membrane fouling during particle filtration occurs through a variety of mechanisms, including internal pore clogging by
contaminants, coverage of pore entrances, and deposition on the membrane surface. Each of these fouling mechanisms
results in a decline in the observed flow rate over time, and the decrease in filtration efficiency can be characterized
by a unique signature formed by plotting the volumetric flux, bQ
, as a function of the total volume of fluid processed,
bV . When membrane fouling takes place via any one of these mechanisms independently the bQ
bV signature is always
convex downwards for filtration under a constant transmembrane pressure. However, in many such filtration scenarios,
the fouling mechanisms are inherently coupled and the resulting signature is more difficult to interpret. For instance,
blocking of a pore entrance will be exacerbated by the internal clogging of a pore, while the deposition of a layer of
contaminants is more likely once the pores have been covered by particulates. As a result, the experimentally observed
bQ
bV signature can vary dramatically from the canonical convex-downwards graph, revealing features that are not captured
by existing continuum models. In a range of industrially relevant cases we observe a concave downwards bQ
bV signature,
indicative of a fouling rate that becomes more severe with time. We derive a network model for membrane fouling
that accounts for the inter-relation between fouling mechanisms and demonstrate the impact on the bQ
bV signature.
Our formulation recovers the behaviour of existing models when the mechanisms are treated independently, but also
elucidates the concave-downward bQ
bV signature for multiple interactive fouling mechanisms. The resulting model enables
post-experiment analysis to identify the dominant fouling modality at each stage, and is able to provide insight into
selecting appropriate operating regimes
APPLICATION OF A SURFACE-RENEWAL MODEL TO PERMEATE-FLUX DATA FOR CONSTANTPRESSURE CROSS-FLOW MICROFILTRATION WITH DEAN VORTICES
Tratamento de ågua produzida de petróleo para remoção de óleo por processos de separação por membranas: revisão
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