Adsorbing colloid flotation

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... 

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]. 

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. 

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. 

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)... 

The information resulting from tbe maihematical modeling helps address some practical problems on flotation. For example, two practical problems in precipitate and adsorbing colloids are ... 

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. ... 

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... 

Two methods of arsenate removal are reported which reduce initial concentrations in (he range of 10-20 mg/L to 0.1-0.2 mg/L. Adsorbing colloid flotation uses eithat Fe(OH)3 with sodium dodecyl sulfate (SDS) at pH 4-5 or Mn02 with SDS at pH 8.5.2-51... 

Thare ate two mejor stadies in the removal of cyanides. First, Grieves and Bhattacheryya used ethyl-hexadecyIdimelhylammonlum bromide to float colloidal or precipitated foams with iron at acidic pH values.22"2 Clarke used precipitate and adsorbing colloid flotations to remove free cyanide as Ferric fenro-cyanide on ferric hydroxide Hoc with SDS at pH 5. Performance was good (over 90% removal from 50 mg/L solution) for chromium, cobalt, copper, and nickel cyanides but not for zinc. 

Clarke and coworkers15 demonstrated fluoride removal was performed easily at neutral pH 7,3-7,8 using adsorbing colloid flotation with Al(OH)3 and SDS. Residual fluoride was less than detection limits with an Ai F ratio of 2.54 or more. 

Both adsorbing colloid and precipitate flotation have been studied in larger columns. Results for lned, copper, chromium, and magensium indicate drinking level residuals are possible after treatment at optimum conditions. The operating coed it ions and results for several studies are provided in Table 17,5-1. 

Peng F. F. and Dl P. (1994) Removal of arsenic from aqueous solution by adsorbing colloid flotation with hydrogen peroxide addition. Ind. Eng. Chem. Res. 33, 922-928. 

As discussed earlier, the flotation techniques most promising for adaptation to full scale are precipitate and adsorbing colloid flotation. To assist in this development, there has been considerable effort expended in modeling these techniques at the molecular level. techniques are sensitive to interfering factors at the molecuiar level these include pH, ionic strength, surfactant concentration, and specifically imerfering ions. However, before going into a discussion of the molecular level mathenuitical models, we wish to address the role of fluid dynamics in particle flotation. 

Precipitate flotation was shown to remove cadmium (as the sulfide) using hexadecyltrimethylammonium bromide (HTA) at a pH of S-9. The residual cadmium concentration was approximately 0.5 mg/L. Using adsorbing colloid flotation with ferrous sulfide and HTA at pH 9 resulted in residual cadmium concentrations of 0.003 mg/L. In an effort to eliminate the use of sulfide, cadmium hydroxide was floated with ferric hydroxide and HTA. The lowest residual was 0.010 mg/L at pH 12. This system, however, was very sensitive to ionic strength variations. Other studies removed cadmium precipitates with various systems over large ranges of pH by varying the coprecipitates and surfactants. ... 

Many industrial wastewaters contain copper as well as other heavy metals. Table 17.3-1 provides the results of the adsorbing colloid flotation of such a mixture of metals. The floe was ferric hydroxide and the surfactant was SDS. Removals are generally good (based on initial concentrations of 20 mg/L for each metal). 

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