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The rate at which certain non-ionic molecules can adsorb to bubble surface can be estimated by solving the Ward-Tordai equation. The enrichment and recovery depend on the hydrodynamic condition of the rising foam, which is a complex system dependent upon bubble size distribution, stress state at the
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in which hydrophobic particles attach to the surface of bubbles which rise to form a pneumatic (i.e. rising) foam. In this way, relatively hydrophobic particles can be separated from relatively hydrophilic particles. Froth flotation is typically used to separate coal particles from ash or particles
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As in many chemical processes, there are competing considerations of recovery (i.e. the percentage of target surfactant that reports to the overhead foamate stream) and enrichment (i.e. the ratio of surfactant concentration in the foamate to the concentration in the feed). A crude method of moving
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to characterise a model of adsorptive bubble separation processes, of which foam fractionation is one example. Until the mid-2000s, there was very little further development of foam fractionation or attempts to understand the underlying physics of the process. Many workers were satisfied with
87:, specifically into the prediction of liquid fraction and liquid flux in a pneumatic foam, that enabled a preliminary mechanistic description of foam fractionation. The synergies between foam fractionation and froth flotation have been explored in a 2009 special issue of the
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Just as in gas-liquid absorption, the adoption of reflux at the top of the column can engender multiple equilibrium stages within the column. However, if one can control the rate at which the bubble size changes with height in the column, either by coalescence or
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Robert
Lemlich showed how foam fractionation columns can be operated in stripping, enriching, or combined modes (depending on whether the feed is sent to the top, bottom or middle of the column), and can be operated with or without an external
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empirical descriptions of specific systems rather than attempt a mechanistic model of the process, and it is possibly for this reason that the adoption of the technology has been slow despite its enormous potential.
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upon the enrichment-recovery spectrum is to control the gas rate to the column. A higher gas rate will mean higher recovery but lower enrichment.
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Stripping of non-surface-active contaminants from streams of waste water (such as metal ions) with the help of one or more assistant surfactants.
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stream at the top of the column. It helps to think of the process as similar to a gas-liquid absorption column. The differences are that:
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have been common place in aquaria for many years, it was not until the 1960s that a concerted effort was made by Robert
Lemlich of the
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225:
Ward AFH & Tordai L 1946 Time-Dependence of boundary tension of solutions I. the role of diffusion in time-effects,
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The target molecules adsorb to a surface, rather than absorb by travelling into the bulk of one phase from another, and
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The bubbles form a foam which travels up a column and is discharged to the foamate stream of foam fractionation.
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263:
35:
50:". However it has much broader application in the chemical process industry and can be used for the
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Lemlich R 1968 Adsorptive bubble separation techniques: Foam fractionation and allied techniques,
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The removal of frother downstream of froth flotation operations (known as frother stripping).
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20:
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42:. It is commonly used, albeit on a small scale, for the removal of organic waste from
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143:. The hydrodynamic condition is described by the Hydrodynamic Theory of Rising Foam.
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Enrichment of the solutions of biomolecules in pharmaceutical and food technologies.
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material. It was research into the froth phase of froth flotation conducted at the
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Stevenson P, Jameson GJ 2007 Modeling continuous foam fractionation with reflux,
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from waste water streams in addition to the enrichment of bio-products.
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Stripping of surface-active contaminants from streams of waste water.
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120:, one can engineer an internal source of reflux within the column.
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Foam fractionation is closely related to the allied process of
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The foam autogenously provides the packing within the column.
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gas-liquid interface, rate of bubble coalescence, gas rate
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Lemlich R, Lavi E 1961 Foam fractionation with reflux,
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Stevenson P 2007 Hydrodynamic theory of rising foam,
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The target molecule adsorbs to a bubble surface, and
127:Foam fractionation proceeds via two mechanisms:
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89:Asia Pacific Journal of Chemical Engineering
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195:Industrial & Engineering Chemistry
52:removal of surface active contaminants
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211:Chemical Engineering and Processing
85:University of Newcastle, Australia
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1:
46:; these units are known as "
227:Journal of Chemical Physics
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79:of valuable minerals from
68:University of Cincinnati
38:using rising columns of
32:preferentially separated
95:Design considerations
243:Minerals Engineering
17:Foam fractionation
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118:Ostwald ripening
64:protein skimmers
48:protein skimmers
21:chemical process
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25:hydrophobic
141:inter alia
44:aquariums
28:molecules
23:in which
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232:, p.453
216:, p.590
184:, p.191
179:Science
62:Whilst
58:History
34:from a
102:reflux
81:gangue
166:Notes
19:is a
200:p.16
40:foam
30:are
182:134
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