Colloid flotation

Very finely divided minerals may be difficult to purify by flotation since the particles may a ere to larger, undesired minerals—or vice versa, the fines may be an impurity to be removed. The latter is the case with Ii02 (anatase) impurity in kaolin clay [87]. In carrier flotation, a coarser, separable mineral is added that will selectively pick up the fines [88,89]. The added mineral may be in the form of a floe (ferric hydroxide), and the process is called adsorbing colloid flotation [90]. The fines may be aggregated to reduce their loss, as in the addition of oil to agglomerate coal fines [91]. 

Haywood and Riley [14] have described a spectrophotometric method for the determination of arsenic in seawater. Adsorption colloid flotation has been employed to separate phosphate and arsenate from seawater [15]. These two anions, in 500 ml filtered seawater, are brought to the surface in less than 5 min, by use of ferric hydroxide (added as 0.1 M FeC 2 ml) as collector, at pH 4, in the presence of sodium dodecyl sulfate [added as 0.05% ethanolic solution (4 ml)] and a stream of nitrogen (15 ml/minutes). The foam is then removed and phosphate and arsenate are determined spectrophotometrically [16]. Recoveries of arsenate and arsenite exceeding 90% were obtained by this procedure. 

Voyce and Zeitlin [487] have used adsorption colloid flotation to determine mercury in seawater. The sample 500 ml is treated with concentrated hy-... 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

Murthy and Ryan [823] used colloid flotation as a means of preconcentration prior to neutron activation analysis for arsenic, molybdenum, uranium, and vanadium. Hydrous iron (III) oxide is floated in the presence of sodium decyl sulfate with small nitrogen bubbles from 1 litre of seawater at pH 5.7. Recoveries of arsenic, molybdenum, and vanadium were better than 95%, whilst that of uranium was about 75%. 

Selenium Adsorption colloid flotation Spectrophotometry of methylene blue complex - [517,546]... 

Adsorbing colloid flotation has been used to separate uranium from seawater [101]. 

Pacheco, A.C.C. and Torem, M.L. (2002) Influence of ionic strength on the removal of As5 + by adsorbing colloid flotation. Separation Science and Technology, 37(15), 3599-610. 

Electioultiafiltiation (EUF) combines forced-flow electrophoresis (see Electuoseparations, electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45-47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Flotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane facilitates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

The coprecipitation method combined with colloid flotation using stearylamine, sodium oleate, etc. has been used to preconcentrate analytes in seawater [49, 50],... 

Flotation is the term used to describe a process in which the species being separated from the bulk liquid media are insoluble particulates. Froth flotation is another one of the two foam separation processes. It also involves the production of foam in a heterogeneous aqueous system, and has a great deal of potential for the water and wastewater treatment. Froth flotation can be subdivided into at least seven categories (42,43,84), including precipitate flotation, ion flotation, molecular flotation, microflotafion, adsorption flotation, ore flotation, macroflotation, and adsorbing colloid flotation. They are described separately below. 

Type of flow pattern(s) involved in an adsorptive bubble separation system depends on the type of process used. For example, bubble fractionation involves two-phase (gas-phase and liquid-phase) bubble flow, while solvent sublation involves multiphase bubble flow in their vertical bubble cells. Foam fractionation involves a two-phase bubble flow in the bottom bubble cell, and a two-phase froth flow in the top foam cell. However, all froth flotation processes (i.e., precipitate flotation, ion flotation, molecular flotation, ore flotation, microflotation, adsorption flotation, macroflotation, and adsorbing colloid flotation) involve multiphase bubble flow and multiphase froth flow. 

Y. S. Kim and H. Zeitlin, The separation of zinc and copper from seawater by adsorption colloid flotation. Separation Science 7(1), 1-12 (1972). 

A sorption colloid flotation method has been developed for the separation of vanadium from sea water. The separation is based on a surfactant-collector inert gas system in which vanadate is sorbed on a positively charged colloidal iron(III) hydroxide collector. The vanadate enriched collector rises to the sea water surface and floats as a separable foam with aid of sodium dodecylsulfate as surfactant and nitrogen as inert gas. The major advantages of this method are the rapid attainment of flotation and the excellent recovery of 86 % vanadium based on spiked sea water samples. Flotation was found to be highly pH sensitive optimal values were found to be 5.00 + 0.02. In effect, at pH 4.90 a slight decline in recovery of vanadium could already be observed, whereas at pH 7 and above there was no vanadium float 53). 

Copper and zinc have been extracted from sea water by sorption colloid flotation. The metal ions are brought to the surface in less than 5 min. using a negatively charged ferric hydroxide collector, the cationic surfactant dodecylamine, and air. 95% copper and 94% zinc could be recovered. Maximum recovery is attained at pH 7.6 88). 

Methods suitable for the extraction of zinc from sea water have already been mentioned in the preceding chapters in context with other trace elements. Feasible methods are the sorption colloid flotation technique (chapter 2.3.9 88)), several column separation procedures with Chelex-100 (chapters 2.3.3 56), 2.3.4 61), 2.3.5 65), 2.3.9 86,87),... 

Molybdenum is rapidly extracted from sea water by a sorbing colloid flotation method. Optimum collection by ferric hydroxide takes place at pH 4.0, when the colloid has an apparent maximum positive charge density and is able to sorb molybdenum nearly quantitatively as molybdate anion. From a 500 ml sample of sea water molybdenum is accumulated in the foam on the water surface in 5 min. using sodium dodeeyl sulfate as surfactant and air bubbling through the solution 89,90). 

Sorption colloid flotation has been recommended to separate silver from spiked sea water by a collector-surfactant-inert gas system consisting of lead sulfide, stearyl amine, and nitrogen. When the sea water was adjusted to pH 2, separation was found to be nearly quantitative 94>. 

Sorption colloid flotation has shown to be capable of quantitatively separating ionic mercury from sea water at levels down to 0.02 gg/1 using a cadmium sulfide collector and octadecyltrimethylammonium chloride as a surfactant. The sea water samples need only to be acidified with hydrochloric acid. For flotation an adjustment to pH 1.0 is crucial. Mercury concentrations generally seemed to decrease with the depth of sea water 99). 

Natural surface ectivity In assoc ialion with surface-active agents Foam fractionation for example, dete[gents from aqueous solutions Ion flotation, molecular flotation, adsorbing colloid flotation for example, Sr1 +, PtiJ +, Hg2+, cyanides Fnam flotation for example, microurganisms, proteins Microflotation, colloid flotation, ultraflotation for example, particulates in wastewater, clay, microoiganisms Froth flotation of noapolar minerals for example, sulfur Froth flotation For example minerals such as silica Precipitate flotation (1st and 2nd kind) Tor example, ferric hydroxide... 

An analogous process is one called adsorbing colloid flotation in which the colligend is adsorbed on a colloid that can be floated using various mrcroflotaiion techniques.30... 

One flotation developed and grew in the three decades beginning in 19 l5.J-3 Our areas of interest—ion, molecular, precipitate, and adsorbing colloid flotation—are relatively new subjects, While Adamson s original text on surface chemisiiy provided an excellent introduction to basic principles, Sebha s book9 in 1962 first discussed ion flotation and solvent sublaiion in detail. Biketman s book6 provides detailed information on foam characteristics. 

Adsorbing colloid flotation (adsorption onto or coprecipitalion with a carrier floe which is floated)... 

When using precipitate or adsorbing colloid flotation techniques for the removal of metals, one finds thei many combinations will woik—some better than others. When removal efficiencies are comparable, other... 

Several other stadies were parformed using both precipitate and adsorbing colloid flotation which used various surfactants and pH valttes.7 It was found that a critical parameter was the pH at which the chromium was precipitated. If the pH were too high, the flotation resulted in poor removal. 

Copper also was removed by adsorbing colloid flotation using ferric hydroxide floe and SDS surfactant. Optirenm removal occurred in the pH range 6-8, depending on ionic strength. The 99.98% removal was achieved at pH 7.5 with an initial copper concentration of SO mg/L. ... 

Many industrial wastewaters contain copper ns wall as other heavy meials. Table 17.3-1 provides the results of the ndsorbing colloid flotation of such a mixture of metals.10 The floe was feme hydroxide aad tbe surfactant was SDS. Removals are generally good (based on initial concentrations of 20 mg/L for each metal). 

For pH valnes above 8, precipitate flotation was more efficient in removing zinc than foam separation of soluble zinc species.15 The optimum pH was 9.2. The surfactant was SDS. The adsorbing colloid flotation of zinc used aluminum hydroxide and NLS in the pH range 8.0-8.6 ferric hydroxide floes were not effective. Removal was 99.8% or higher.15 Table 17.3-1 shows the removal of ziec in association with other metals. 

Adsorbing colloid flotation is used to concentrate trace level components in seawater. Zeitlin and coworkers from the University of Hawaii Sieve studied seawater extensively in this manner. Tabla 17.3-2 summarizes heir results.2 Supplementing this work is a paper by Mnisuzaki and Zeitlin31 which stadies nine surfactants and their performance with six collectors [Fe(OH)j. Th(OH)i. AI(OH)j, HgS, CdS and MnOJ. 

The United Slates, the Soviet Union, and Japan lead in the study of flotation techniques to irent radioactive wastes.1,7 The metals of interest inclnde cobalt, strontium, zirconium, niobium, ruthenium, cesium, and cerium, as well as rhodium and yttrium. Tbe studies, all of which employed precipitate or adsorbing colloid flotation, indicated that an average of over 90% removal is achievable. Some removals approached 100%. 

TABLE 17,3-2 Summary of the Adsorbing Colloid Flotation of 5ea Water... 

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