Electrical Aspects of Adsorbing Colloid Flotation. VIII. Specific Adsorption of Ions by Flocs

Abstract

A Gouy-Chapman model of the solid-water interface with specific adsorption of ions is used to calculate surface and zeta potentials. The effects of sign and magnitude of ionic charge and surface charge density, ionic strength, specific binding energy, and temperature are examined. Experimental data on foam flotation of ferric hydroxide with sodium lauryl sulfate in the presence of a variety of anions support the model.     

Electrical Aspects of Adsorbing Colloid Flotation

Abstract

The Gouy-Chapman theory of the electric double layer is applied to the calculation of the interaction energy of a charged surface film and a solid surface of opposite charge immersed in a solution of electrolyte. This model is found to account for the decrease in efficiency of precipitate flotation and adsorbing colloid flotation which is observed when ionic strength is increased. The Gouy-Chapman theory is also used to predict the existence of analogs to the phenomena of electroosmotic flow and streaming potential in foams and surface films.     

Electrical Aspects of Adsorbing Colloid Flotation. XV. Adsorption Isotherms of Mixed Surfactants

Abstract

A theory is developed for the calculation of absorption isotherms of binary mixtures of surfactants A and B on solid-water interfaces. The effects of the relative magnitudes of the interaction energies of A-A, A-B, and B-B nearest neighbor pairs are explored. The theory makes use of the random approximation in order to overcome mathematical difficulties which arise in the general case. The possibility of reducing surfactant costs in precipitate and adsorbing colloid flotation by the use of mixed surfactants is suggested.     

Electrical Aspects of Adsorbing Colloid Flotation. XVI. Double-Layer Relaxation

Abstract

A mathematical model for studying relaxation processes in the electric double layer adjacent to a plane charged surface is developed and analyzed. The model is nonlinear and nonideal. A time constant of roughly 7 × 10^?8 s qualitatively describes the relaxation processes. Increased applied potentials yield nonlinear responses, which are investigated by Fourier analysis. The effects of ionic size are determined. The relaxation rate is fast enough so that the local equilibrium assumption in foam flotation is amply justified.     

Electrical Aspects of Adsorbing Colloid Flotation. XVII. Quasi-Chemical Method for Adsorption of Mixed Surfactants

Abstract

The quasi-chemical approximation is applied to the calculation of adsorption isotherms for two-component surfactant systems. No further approximations are necessary. The effects of the relative sizes of the interaction energies of the various nearest neighbor pairs are investigated, and plots of representative adsorption isotherms are given. Some possible applications of the theory to foam flotation and other surface chemical separation techniques are suggested.     

Electrical Aspects of Adsorbing Colloid Flotation. IV. Stripping Column Operation

Abstract

The operation of a continuous flow foam flotation column in the stripping mode is analyzed under steady-state conditions. The effects of diffusive mixing, nonlinear adsorption isotherms, and finite rate of mass transport between the surface and bulk phases are taken into account in the differential equations from which column efficiencies are calculated. Adsorption isotherms are calculated by means of statistical mechanics for systems having coulombic interactions.     

Electrical Aspects of Adsorbing Colloid Flotation. XIII. Adsorption onto Surfaces with Positive and Negative Sites

Abstract

The adsorption of anions and cations, including amphipathic ions, onto floes having both positive and negative adsorption sites was examined theoretically. The effects of ionic strength, substrate concentration, site lattice spacing, adsorption energy, and (in the case of amphipaths) hydrocarbon chain length were examined. An approximate thermodynamic approach was used.     

Electrical Aspects of Adsorbing Colloid Flotation. Y. Nonideal Flocs and Salts

Abstract

Three methods are developed for the calculation of adsorption isotherms in precipitate and adsorbing colloid flotation. The Gouy-Chapman model is used in all three, with corrections for the effective volumes of the ions in the ionic atmosphere and of the floc particles. The theories all predict a weak dependence of adsorption isotherm on temperature and a stronger dependence on ionic strength; increasing either variable decreases the surface adsorption. The effects of film surface potential, floc zeta potential, ion and floc effective volumes, and floc-floc screening are examined.     

Electrical Aspects of Adsorbing Colloid Flotation. VI. Electrical Repulsion between Floc Particles

Abstract

Adsorption isotherms are calculated for precipitate and floc foam flotation within the framework of a Gouy-Chapman model which includes both the electrical attractions of the floc particles to the surface and their electrical repulsions for each other. The canonical ensemble is used, and algebraic expressions are found for approximating the sum of products of cluster integrals. Algebraic expressions for the surface excess of adsorbed floc are obtained which involve three reasonably simple integrals. The dependence of the adsorption isotherms on temperature, ionic strength, surface potentials of the floc and the air-water interface, ionic charge, and floc particle size is investigated.     

Electrical Aspects of Adsorbing Colloid Flotation II. Theory of Rate Processes

Abstract

The kinetic and equilibrium factors affecting the rate of precipitate flotation are analyzed by means of the Gouy-Chapman model. Kinetic effects are found to be extremely rapid, and the rate of precipitate flotation is due to equilibrium considerations. Removal efficiency as a function of inert salt concentration goes through a maximum at about 10^?5 M for films 300 Å thick. Removal efficiency increases with increasing zeta potential of the film surface and with increasing charge on the precipitate particles.     

Electrical Aspects of Adsorbing Colloid Flotation. XXI. Flotation with Dodecylphosphate/n-Hexanol Mixtures

Abstract

The adsorbing colloid flotation of Pb(II), Cd(II), and Cu(II) with ferric hydroxide floc and the mixed surfactant system sodium dodecylphosphate (SDP)/n-hexanol was investigated. Good removals of Pb and Cu were obtained; removal of Cd was less satisfactory. The effects of interfering anions (sulfate, oxalate, silicate, phosphate) were studied; higher concentrations of these ions could be tolerated with SDP/n-hexanol than with sodium dodecylsulfate. Measurements of the cmc of SDP were made; low solubility prevented determinations in the pH range ^4–8.5.     

Electrical Aspects of Adsorbing Colloid Flotation. XX. NMR Studies of Laurie Acid Solubilization

Abstract

Mixed micelles of dodecanoic acid with sodium dodecylsulfate, Triton X-100 (TX-100, an alkylphenylpolyethoxy alcohol), and dodecyltrimethylammonium chloride were studied. T₁ and nuclear Overhauser enhancement (NOE) measurements were made using dodecanoic acid C-13 labeled at the carboxyl group. Viscosity measurements were made and titration curves run of dodecanoic acid in these mixed micelles. The pK_a of dodecanoic acid increases, as one goes, from cationic to neutral to anionic micelles. Generally the mixed micelles are apparently small and roughly spherical; in acidic solution, however, dodecanoic acid-TX-100 micelles are large with an extended structure. NOE measurements indicate that the carboxyl group is relatively close to the protons in the micelle core, and that the carboxyl group moves out slightly into the aqueous phase on becoming ionized. The NOE of dodecanoic acid-TX-100 micelles indicates interaction between the carboxyl carbon and the protons in the ethoxy chain of TX-100.     

Electrical Aspects of Adsorbing Colloid Flotation. XII. Floc Diffusion Rates in Nonideal Systems

Abstract

The dynamics of the diffusion of charged floc particles to charged air-water interfaces is examined within the framework of a modified Gouy-Chapman model in which the finite volumes of floc particles and inert electrolytes were taken into account. The methods of Verwey and Overbeek were used to calculate the electrical free energy of the floc-interface interaction. For the cases considered, diffusion was found to be quite rapid. Fluid mechanical considerations were used to calculate the capture cross-sections of rising bubbles for suspended floc particles; bubbles in the creeping and inviscid flow regimes were considered. These results were used to calculate removal rates from batch and continuous-flow pool-type foam flotation devices.     

Electrical Aspects of Adsorbing Colloid Flotation. XIX. Viscosity and the Structures of Mixed Micelles

Abstract

Viscosity measurements on mixed surfactant solutions containing the nonionic surfactant Triton X-100 and a number of other cosurfactants (dodecanoic acid, dodecyl amine, sodium dodecylsulfate, dodecyltrimethylammonium chloride, dodecyl alcohol, and sodium dodecylphosphate) indicate the presence of two quite different ‘types of micelles’. Solutions containing an electrically neutral cosurfactant exhibit very large viscosities, indicating the presence of extended micellar structures. Solutions containing a charged cosurfactant exhibit much lower viscosities, indicating that the micelles in these solutions are small spherical or ellipsoidal structures. Evidently coulombic repulsions destabilize the extended structures when charged surfactants are present in the micelles. The effects of pH and ionic strength are consistent with this interpretation.     

Electrical Aspects of Adsorbing Colloid Flotation. XXII. Relaxation Times of Micellized and Adsorbed Surfactants

Abstract

Proton longitudinal relaxation times (T ₁ s) were measured for dodecyltri-methylammonium chloride (DTAC), dodecylammonium chloride, and sodium dodecylsulfate solutions in D₂O. Effects of added paramagnetic and diamagnetic salts on the various relaxation times were determined and interpreted in terms of the structures of the micelles. Relaxation times of DTAC adsorbed on A1(OD)₃-FeS floc were also determined and interpreted.     

Electrical Aspects of Adsorbing Colloid Flotation. XVIII. NMR Studies of Sodium Dodecyl Sulfate Sorbed on Al(OD)3

Abstract

Adsorption of dodecyl sulfate on Al(OD)₃ flocs has been studied by means of proton and ¹³C-NMR. Spin-lattice relaxation times (T ₁) of α-CH₂ and the unresolved methylene proton signals were measured in monomer, micellar, and adsorbed forms of the surfactant. These results, together with the spin-spin relaxation times (T ₂) estimated from the line-widths of ¹³C signals, indicate that dodecyl sulfate ions adsorbed on Al(OD)₃ flocs are more constrained in their motions than are micellar dodecyl sulfate ions, and that the binding to the floc is through the sulfate group.     

Solvent Sublation and Adsorbing Colloid Flotation of Magenta

Abstract

Magneta was removed from aqueous solution into paraffin oil by solvent sublation of a magenta-lauryl sulfate complex. Over 96% of magenta was removed in 25 min. A stoichiometric amount of surfactant was found to be most effective for magenta removal (1 mol of surfactant to 1 mol of dye). First-order kinetics was not followed. It is proposed that some kinds of aggregate of the dye-surfactant complex may exist in the solution. Magenta was also removed by adsorbing colloid flotation techniques using either ferric hydroxide or aluminum hydroxide as the coagulant. Sodium lauryl sulfate was used as the collector. Over 99.6% of magenta was removed from the solution in as little as 3 min. However, the amount of surfactant needed appears to be high.     

Recovery of Dodecylbenzene Sulfonate from Adsorbing Colloid Flotation Foamates

Abstract

Dodecyl benzene sulfonate, used in the foam separation of Fe(OH)₃ floc, can be recovered from the collapsed foamate by treating the foamate with various salts (such as NaOH, Na₂CO₃, or Na₂SO₄), thereby displacing the surfactant from the floc. Both NaOH and Na₂CO₃ are very effective in surfactant recovery; Na₂SO₄ is much less effective.     

Separation of Metals from Sulfated Deep-Sea Ferromanganese Nodules by Adsorbing Colloid Flotation

Abstract

Adsorbing colloid flotation (ACF) is applied to aqueous leach solutions of sulfated deep-sea ferromanganese nodules and their process tailings. Metal cations of Cu, Co, Ni, Mn, Al, and Zn are separated simultaneously by flotation with hydroxide collectors and cationic surfactants from the leach liquors of sulfated ferromanganese nodules. Applications of ACF to the nodule tailings also makes possible the recovery of residual Cu, Co, Ni, Ti, Zn, Al, Fe, Mn, and the separation of Pb and V, the most abundant toxic species in the nodules and tailings.     

Adsorbing Colloid Flotation of Cu(II) with a Chelating Surfactant

Abstract

Cu(II) is effectively removed from synthetic mixtures by dodecylamine-N,N-diacetic acid with Fe(OH)₃ and a carrier foam. The effects of pH and ionic strength on the separation are ascertained. Cu(II) is effectively floated at much higher ionic strengths with dodecylamine-N,N-diacetic acid than with nonchelating surfactants such as sodium lauryl sulfate.