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A simplified analysis of the effect of nano-asperities on particle-bubble interactions

Drelich J. W.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 1

10--18

EN

The interactions of gas bubbles with particles having rough and heterogeneous surfaces are much more complex than the commonly used DLVO – based models predict. The effects of surface roughness on flotation and particle – bubble interactions have been reported many times in the past, although a clear understanding of their origins has been lacking. To explain differences in interactions for spherical hydrophobic particles, a theoretical analysis of the interaction potential was carried out for a model rough particle interacting with a bubble surface in an electrolyte solution in this study. The attractive hydrophobic interaction potential was added to repulsive retarded van der Waals and repulsive electrical double layer interaction potentials. The rough microscopic particles were modeled as spheres decorated with nano-sized asperities. Parameters that reflect common flotation separation systems were selected for testing this theoretical model and computation of the energy barrier applicable to particle – flat bubble surface interactions. It was found that hydrophobic asperities with a height of only several nanometers can reduce the repulsive interaction energy by an order of magnitude. Theoretical analysis also reveals that surface coverage of microscopic particles by nano-sized asperities is important as well.

2

Hollow fibre membrane oscillations against fouling process – a numerical study

Gac J.M., Gradoń L.

Chemical and Process Engineering

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2014

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Vol. 35, nr 1

149--158

EN

The modelling of colloidal fouling and defouling of hollow fibre membranes in the presence of membrane oscillations is analysed by means of numerical simulations as an effect of complex coupling between hydrodynamic and surface forces. To describe the latter the Derjaguin-Landau-Vervey-Overbeek (DLVO) model has been employed. We have investigated the influence of various parameters of the process like flow rate, mean particle diameter, amplitude and frequency of the oscillations, and others, on the efficiency of the defouling process. The investigated parameters is close to that of a silica suspension in , a typical system modelling used to investigate membranę separation. On the basis of numerical simulation resu lts e have defined an optimal set of parameters preventing membrane fouling.

3

O przewidywaniu hydrofobowej koagulacji w oparciu o rozszerzoną teorię DLVO

Skvarla J.

Inżynieria Mineralna

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2002

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R. 3, nr 1

1-10

PL

Parshley i Israelachvili [Colloids Surfaces, 2, 169, 1981] zastosowali proste wyrażenie wykładnicze krótkiego zasięgu do przybliżonego opisu energii potencjalnej oddziaływań hydrofobowych pomiędzy dwoma płytkami miki. Mika użyta do badań była hydrofobizowana poprzez adsorpcję in situ kationowego surfaktanta. Wyeliminowali oni współczynnik przed wyrażeniem wykładniczym dzięki użyciu prostego równania Li i Neumanna [J. Colloid and Interface Sci., 137, 304 (1990)] pozwalającego na obliczania napięcia międzyfazowego. Dla zweryfikowania modelu rozszerzonej teorii DLVO dla hydrofobowej koagulacji przeprowadzono serię eksperymentów z wodną zawiesiną drobnych ziaren syderytu, które stopniowo hydrofobizowano poprzez adsorpcję oleinianu sodu przy dwóch siłach jonowych. Dodatkowo, wyznaczono eksperymentalnie takie parametry modelu jak potencjał dzeta oraz kąt zwilżania wodą. Uzyskano zadawalającą korelację (R≈0.99) pomiędzy napięciem elektrycznym na fotodiodzie, będącym względną eksperymentalną miarą stopnia koagulacji hydrofobowej, które rejestrowano po zadanym czasie sedymentacji suspensji syderytu, oraz teoretycznie obliczonym maksimum całkowitej energii potencjalnej koagulacji. Przetestowano również dwa inne, dostępne w literaturze, wyrażenia na oddziaływania hydrofobowe dalekiego zasięgu, które wykazały słabą korelację z danymi ksperymentalnymi.

EN

A single short-range exponental, obtained for two mica sheets hydrophobized by in situ adsorption of cationic surfactants [Pashley and Israelachvili, Colloids Surfaces, 2, 169 (1981)], was used to approximate the hydrophobic interaction potential energy. The prefactor of the exponential was estimated by using a simple equation of state for interfacial tensions [Li and Neumann, J. Colloid Interface Sci., 137, 304 (1990)]. To verify the simple extended DLVO model of hydrophobic coagulation, a series of experimental tests on a fine siderite suspension with particles gradually hydrophobized by adsorption of sodium oleate surfactant was performed at two ionic strengths. The model parameters (ζ potential and water contact angle) of the siderite particles were determined experimentally. A satisfactory (R≈0.99) correlation between the photodiode voltage, detected after a selected period of time of the siderite suspension sedimentation being an experimental measure of the extent of hydrophobic coagulation, and the theoretically calculated total potential energy maximum was obtained. Two other long-range exponential expressions of the hydrophobic interaction available in the literature were also tested, which provided a poor correlation with the presented experimental results.