Robert B. Grieves

Foam separations: A review

Abstract A review is presented of foam separations reported in the world literature in the period 1970–1974. Processes are included the objective of which is the removal and concentration from dilute aqueous solution of surface-active-agents; or of charged inorganic species (colligends) foam separated by surfactants. The 200 references which are cited encompass foam fractionations, ion flotations, precipitate flotations, and adsorbing colloid flotations, but do not include processes whose primary aim is the flotation of particulates. Four separations are described in some detail: cationic surfactant selectivity in the foam fractionation of inorganic anions; the foam fractionation of surfactants and of Cu (II) from seawater desalination brines; the ion flotation of Cr(VI) and precipitate flotation of Cr(III), with application to electroplating waste treatment; and the adsorbing colloid flotation of trace metallic and non-metallic species from seawater.

Separation of Toxic Heavy Metals by Sulfide Precipitation

Abstract Sulfide precipitation with Na2S is found to be highly effective to obtain a high degree of separation of heavy metal cations (Cd, Zn, Cu, and Pb) and of the oxyanions of arsenic and selenium from complex wastewaters. The metal separation characteristics are evaluated with a dilute synthetic mixture and with an actual copper smelting plant wastewater. The overall separation of arsenic and other heavy metals and precipitate settling rates are optimum at sulfide dosages about 60% of the theoretical values and at a final pH greater than 8.0. The removals of Cd, Zn, and Cu from the actual wastewaters are greater than 99%, and As and Se removals are 98 and >92%, respectively. Cd, Cu, and Zn concentrations in the range of 0.05 to 0.1 mg/1 can be achieved with sulfide precipitation. The metal separations and settling rates obtained with conventional hydroxide precipitation (lime) are considerably lower than those obtained with sulfide precipitation.

Ultrafiltration Characteristics of Oil-Detergent Water Systems: Membrane Fouling Mechanisms.

Abstract The ultrafiltration characteristics of oil (bilge oil and synthetic based lubricating oil)-nonionic detergent-water (river water and distilled water) systems are evaluated with noncellulosic, tubular membranes. The water flux behavior (membrane fouling) is dictated by the membrane resistance increase due to detergent-membrane interaction and due to surface fouling in the presence of oil-detergent emulsions and suspended solids. Membrane fouling and cleaning requirements depend on the type of oily water systems. Flux drop can be minimized by operating at temperatures above 35°C and/or with short-term membrane depressurization. In all cases the steady-state water flux is a function of the initial membrane water flux. Depending on the oil water systems, water fluxes of 8 to 52 ± 10−4 cm/sec are obtained. Excellent oil rejections are observed in all cases: even with oil-detergent systems, an ultrafiltrate oil concentration of less than 10 mg/1 can be achieved.

Foam fractionation of cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III)

Abstract An experimental investigation is presented of the batch foam fractionation of the cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III) from 1.0 × 10 −5 M (metal concentration) alkaline aqueous solutions, with the cationic surfactant hexadecyltrimethylammonium chloride. The effects are established of the presence of CN − over the concentration range 2.5 × 10 −5 M−1.0 M, of the presence of NO 3 − over the concentration range 0.05–0.75 M, and of interferences to metal foam fractionation provided by 0.50 M concentrations of NO 3 − , Br − , CN − , Cl − or SO 4 2− . Results are discussed in terms of the complex cyanide species of each metal that may have been present and in terms of the extent of hydration of the complex cyanide anions and of the potentially-interfering simple anions. The selectivity sequence, Au(CN) 4 − Hg(CN) 4 2− Cd(CN) 4 2− Zn(CN) 4 2− is established, both from data for single-metal solutions and for solutions containing equimolar concentrations of all four metals. A partial separation of the metals can be achieved in the presence of high concentrations of NO 3 − , which can be improved by taking maximum advantage of flotation rate differences.

Nomenclature Recommendations for Adsorptive Bubble Separation Methods

Abstract Recently several spearation techniques employing adsorption on bubbles have been introduced. As these methods must be added to the already well-established techniques using this general mechanism for separation, certain confusions have arisen in the literature in regard to the naming of these operations. In this note we should like to recommend nomenclature for these techniques. These recommendations have also been submitted to the I. U. P. A. C. subcommittee on nomenclature in the field of surface activity.

Foam Separation of Anions from Aqueous Solution: Selectivity of Cationic Surfactants

Abstract Anions are selectively separated and concentrated from dilute aqueous solution by foam fractionation. Selectivity coefficients are established from steady-state equilibrium data (solution concentrations 10−4 to 10−3 M) for SCN-, I-, ClO3-, NO3-, BrO3 −, and NO2 −, each vs Br−, with the quaternary ammonium surfactant modeled as a soluble anion exchanger. Studies are reviewed on the foam separation of Re(VII), Mo(VI), and V(V) oxyanions; Au(I), Ag(I), Ni(II), and Co(III) cyanide complexes; and Pt(IV), Pd(II), and Au(III) chloro complexes. In a five-component system, the oxyanions of Re(VII), Mo(VI), Cr(VI), W(VI), and V(V) are foam fractionated from 10−6 M solutions with the cationic surfactant, hexadecyldimethylbenzylammonium chloride. In the batch, time-dependent experiments, the metals are monitored by radiotracers and gamma radiation spectrometry. At pH 6.0 and a chloride (NaCl) concentration of 10−2 M, and at pH 2.0, adjusted with HCl, Re(VII) and Mo(VI) oxyanions can be separated completely f...

Anion exchange selectivity coefficients from the continuous foam fractionation of a quaternary ammonium surfactant

Abstract An experimental study is presented of the continuous-flow, foam fractionation of ClO3−, BrO3−, NO2−, and SCN−, each vs Br−, with a quaternary ammonium surfactant at concentrations of 10−4 → 10−3 M. Anion exchange selectivity coefficients are established from the steady-state and equilibrium data, with the surfactant adsorbed in the surface “phase” modelled as a soluble ion exchanger. The coefficients are 15·1, 5·85, 2·21, 1·56, 0·95 and 0·73, respectively for SCN−, I−, ClO3−, NO3−, BrO3−, and NO2− vs Br−. For each anion pair, the coefficient is rather independent of the fraction of the exchanger occupied by the preferred ion and of ionic strength. An increase in surfactant chain length decreases the selectivity coefficients for NO3−/Br−. The selectivity sequence is discussed in terms of the relative hydration of the anions.

Foam Separation of Anions: Stoichiometry

Abstract Experimental studies have been carried out on the foam separation of I−, HCrO4 −, S2O3 2−, and Ag(S2O3)2 3− using a cationic surfactant as the collector-frother. The object of the work is the establishment of the Stoichiometry of the foam-separated surfactant cation-anion product to gain some insight into the mode of interaction between the surfactant and the anion. The Stoichiometry, S, defined as the ratio of the rate of surfactant removal to the rate of anion (colligend) removal at the gas bubble interfaces, ranges from 2.2–2.8 mole/mole (average values) for S2O3 2−, being a function of foaming time for the only system which does not involve the formation of particulates between the surfactant and the colligend. For HCrO4 −, I−, and Ag(S2O3)2 3−, S is constant with foaming time and a participate product is formed in the bulk solution and/or the froth. For HCrO4-, S is close to unity and is almost independent of the feed surfactant/colligend ratio, indicating minimum free surfactant. For I-, S ...

Models for interactions between ionic surfactants and nonsurface-active ions in foam fractionation processes

Abstract Interactions are analyzed between an ionic surfactant and nonsurface-active ions (colligends) of opposite charge being separated in foam fractionations. Surfactant selectivity for competing colligends is determined in terms of models based on surfactant—colligend ion pair formation in the feed solution to a foam fractionation unit, based on colligend-surfactant counterion exchange at the gas-solution, bubble interfaces, and based on surface exchange coupled with ion pair formation in the bulk solution. Accurate, continuous-flow, single-equilibrium-stage foam fractionation data for NO− 3, BrO− 3, CIO− 3, and I−, each versus Br−, the counterion of the ethylhexadecyldimethylammonium cation, are used to discriminate among the models. Based on a detailed statistical analysis of the selectivity coefficients determined by two interaction models for each of the four colligends, the hypothesis of colligend-counterion exchange at the gas-solution interface is shown to be valid and that of solution ion pair...

Precipitate Flotation of Complexed Cyanide

Abstract Precipitated cyanide, complexed with Fe(II) at a molar Fe/CN ratio of 0.550, can be floated readily from aqueous suspension with a cationic surfactant, ethylhexadecyldimethylammonium bromide. The effects of three distinct mixing times of significance in preparing the precipitate and contacting it with surfactant, of pH, of initial cyanide concentration, of initial surfactant concentration, and of ionic strength have been established experimentally. Mixing times and the initial cyanide concentration have little influence on the flotation, while increases in pH and ionic strength have a most pronounced influence, part of which can be overcome with increased surfactant concentrations. At pH 6.0, 95% of the complexed cyanide can be foam separated from distilled water suspensions 1.5 to 3.1 mM in total cyanide. About 0.04 mole surfactant/mole complexed cyanide is required; about 0.08 mole/mole is required to increase the flotation to 99% or to overcome ionic strength effects.