Symposium report

International Journal of Mineral Processing, 3 (1976) 375--384

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@ Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

Symposium Report* ADVANCES IN INTERFACIAL PHENOMENA AT PARTICULATE/ SOLUTION/GAS INTERFACE This symposium was held on August 20--21, 1974 in Salt Lake City as part of the 78 th National AIChE Meeting. The proceedings of this symposium have been published as No. 150, Vol. 71 (1975) of the American Institute of Chemical Engineers Symposium Series (P. Somasundaran and R.B. Grieves, Editors). A list of titles, authors and most of the abstracts is given below

INTERFACIAL CHEMISTRY OF PARTICULATE FLOTATION P. S O M A S U N D A R A N

Henry Krumb School of Mines, Columbia University, New York, N. Y. 10027 Flotation, a technique widely used for the concentration or purification of particulates, is dictated mainly by the interfacial properties of the solid/liquid/gas system and changes in those properties due to adsorption of various inorganic and organic reagents. Basic principles governing the adsorption process(as) and the resulting flotation are reviewed in this introductory paper. Examples are discussed to show the effects of relevant controllable variables such as solution pH; collector structure and concentration; ionic strength; concentrations of flocculants, depressants, and activators; and conditioning temperature.

ROLE OF METAL ION HYDROLYSIS IN OXIDE AND SILICATE FLOTATION SYSTEMS M.C. F U E R S T E N A U

Department of Metallurgical Engineering, South Dakota School of Mines and Technology, Rapid City, S.D. Flotation of insoluble oxides and silicatesoccurs in the presence of anionic collectors that form relatively insoluble metal collector salts after slight mineral dissolution has occurred and after metal ions comprising the mineral have hydrolyzed to hydroxy complexes and have adsorbed on the mineral surface. The role and adsorption of bulk precipitates are also discussed.

*Compiler: P.M. Gy, 97 Boulevard Carnot, 06 Cannes, France.

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ELECTROCHEMICAL PROPERTIES OF THE OXIDE-SOLUTION FACE IN RELATION TO FLOTATION

INTER-

SYED M. AHMED

Mineral Sciences Division, Mines Branch, Department of Energy, Mines and Resources, Ottawa, Canada The adsorption and flotation properties of oxides are influenced to a large extent by the electrochemical nature of the oxide-solution interface. The hydrogen and hydroxyl ions, when adsorbed on oxide surfaces, together constitute a polarizable hydration layer with a hydrogen-bonded structure. Three types of surface behavior are distinguished: (1) acidic, (2) basic and (3) amphoteric dissociation. In type-1 oxides, in the pH range above the zpc where there is little or no dissociation, the activities of H ÷ and OH- in the hydration layer are greatly altered due to ion-surface interactions. The corresponding potential drop is attributed to the re-orientation of water dipoles (x potential) and to the rearrangement of the hydrogen-bonded structure (~C.H.potential). In this pH range the surfacecharge densities are low, but the adsorption of neutral organic molecules, such as starches and alcohols, that can interact with hydrogen bonds and of chelating agents could be high. As the pH is increased further, the double layer becomes strongly ionic due to acidic dissociation of the surface hydroxyl groups, and a further potential drop occurs in the compact layer due to specific adsorption of cations. A converse behavior is found for oxides showing type-2 dissociation. Type-3 dissociation can be considered as a composite of types 1 and 2 with or without the specific adsorption of anions. Specific adsorption of anions on oxides can affect the flotation properties significantly.

ION AND PRECIPITATE

FLOTATION

OF METAL IONS FROM SOLUTION

J.W. PEREZ and F.F. APLAN

Mineral Processing Section, Pennsylvania State University, University Park, Penn. 16802 PRECIPITATE FLOTATION OF CALCIUM SULFITE FROM DILUTE AQUEOUS SOLUTION WITH AN ANIONIC SURFACTANT ROBERT B. GRIEVES, DIBAKAR B H A T T A CH A RY Y A and W. T E R R Y STRA N G E

Department of Chemical Engineering, University of Kentucky, Lexington, Kentucky 40506 Sulfite is precipitated from 2.5 to 10.5.10 -3 M aqueous solutions as calcium sulfite, and the precipitate is floated with the strongly basic anionic surfactant, sodium dodecylbenzenesulfonate (NaDBS) over pH 6.5 to 10.0. Precipitation results in terms of total soluble sulfite and total soluble calcium are compared with values calculated from the calcium sulfite--calcium sulfate equilibria, taking into account the conversion of about 20% of the feed sulfite concentration into sulfate. Optimum precipitation conditions are pH 8.6 and a feed calcium to sulfite ratio of 1.0 to 2.0. Of the four surfactants evaluated, NaDBS provides the best flotation, and pH 8.6 is the most satisfactory value. The effects on the flotation of precipitated sulfite and on the removal of total sulflte are established of NaDBS concentration and of the feed calcium to sulfite ratio. A relative minimum in

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the concentration of precipitated sulfite in the residual suspension (after flotation) is found at a NaDBS to precipitated sulfite ratio in the range 0.02 to 0.03 mole/mole. For initial suspensions containing 5.1 and 10.5 mM sulfite, precipitation and flotation at the o p t i m u m conditions of a feed calcium to sulfite ratio of 2.0 mole/mole and a feed NaDBS to sulfite ratio of 0.011 mole/mole yield 93% flotation of the precipitated sulfite and 85% removal of total sulfite. The foam is approximately 20 times more concentrated in sulfite compared to the initial suspension.

DETERMINATION OF SURFACE EOUILIBRIA AND MASS TRANSFER RATES IN A CONCURRENT-FLOW BUBBLE COLUMN ERNESTO VALDES-KRIEG, C. JUDSON KING and HUGO H. SEPHTON

Dgpartment of Chemical Engineering and Sea Water Conversion Laboratory, University of California, Berkeley, Calif. 94720 A technique which allows measurement of surface equilibria in a straightforward fashion in concurrent-flow gas--liquid bubble columns is described. The method appears to offer advantages over other procedures currently in use and is also adaptable to situations involving very low collector concentrations incapable of supporting a foam. The technique also enables simultaneous determination of effective axial dispersivities and mass transfer coefficients to the surface on the basis of an axial dispersion model.

HIGH-EXPANSION FOAM FLOW ANALYSES R. M A H A L I N G A M ,

H.S. S U R A T I and J.A. BRINK, Jr.

Department of Chemical Engineering, Washington State University, Pullman, Wash. 99163 Flow of foam in a column at low shear rates is characteristically non-Newtonian, with the viscosity increasing with decreasing shear rate, and with the observed yield stress depending primarily on the bubble diameter. In the present analyses, the Casson and HerschelBulkley models have each been coupled with available literature data to predict the thickness of the skimming layer close to the wall, the velocity at the edge of the skimming layer, the velocity profile for the region between the plug and the skimming layer, and the core yelocity. The analyses indicate that, although the thickness of the skimming layer is extremely small, its presence gives rise to a slip velocity at the wall. At low average velocities, the flow is almost as a plug. As the average velocity increases, the plug radius decreases, as does the thickness of the skimming layer. Additionally, core velocities as calculated by two different expressions are in very good agreement, implying that the assumptions concerning the relationship between skimming layer thickness and wall shear stress are valid. Comparison of the computed average velocity with that obtained experimentally shows that the predicted values are slightly lower due to the presence of the wall slip in t h e experimental case. It should be noted that interstitial draining has not been accounted for in the above analyses.

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ON THE WETTABILITY AND FLOTATION CONCENTRATION OF SUBMICRON HEMATITE PARTICLES WITH OCTYLHYDROXAMATE AS COLLECTOR S. R A G H A V A N and D.W. F U E R S T E N A U

Department o f Materials Science and Engineering, University o f California, Berkeley, Calif. 94720 Contact angles of air bubbles and iso-octane droplets have been measured on hematite in the presence of octylhydroxamate at different concentrations and pH values. Contact angles, which correlate well with the adsorption data, exhibit a maximum at pH 8, the PZC of the hematite used. Using iso-octane as the nonpolar phase, the feasibility of extracting submicron hematite particles from an aqueous phase into the nonpolar phase has been studied, and the results obtained correlate well with the contact angle behavior. Experiments conducted to determine the relative efficiency of oil extraction and froth flotation on the recovery of fine hematite particles from synthetic quartz--hematite mixtures show that the oil extraction technique is superior to froth flotation. DEWETTING

REACTION

AND FLOTATION

L. TER-MINASSIAN-SARAGA

C.N.R.S. and U.E.R. Biom~dicale 81, 75270 Paris Cedex 06, France A quasi crystalline model is used for an ideal solid-fluid interface which is assumed to be comprised of one monolayer of solid and one monolayer of fluid. The chemical composition of this interface is expressed in terms of the number of solid-fluid molecular contacts. These contacts determine the interfacial free energy or surface tension which is minimum at equilibrium of adsorption. Reversible wetting of a solid by a solution is related to the displacement of this equilibrium when the solid is transferred from the liquid phase to the vapor. Nonreversible wetting depends on the adsorption equilibrium at the solid-liquid interface only. The results obtained for the systems of silica or glass slides/aqueous solutions of several cationic soaps are discussed. It is concluded that, for these systems, wetting is reversible. The cationic soaps studied are the bromides of dodecyltrimethylammonium, tetradecyltrimethylammonium, hexadecyltrimethylammonium, and hexadecylpyridinium chloride at various temperatures and pH of solution.

EFFECTS OF DISSOLVED HYDROCARBON GASES ON FROTH FLOTATION I.J. LIN and A. METZER

Department o f Mineral Engineering, Technion, and Institute o f Technology, Haifa, Israel, A. Metzer is with IMI, Institute for Research and Development, Haifa, Israel Most of the research work in flotati.~n has been concerned with the solid and liquid phases, the gas phase having received relati~-ely little attention. As a digest of our previous efforts to study the effects of gases other than air, this paper briefly describes the co-adsorption

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of paraffinic gases in the solid/liquid/gas system and its effect on flotation recovery. The latter increased when using ethane, propane, or butane for flotation of quartz with dodecylammonium chloride (DACI). The adsorption of these gases and the interfacial phenomena associated with it are interpreted in terms of effective chain length of DAC1. BEHAVIOR OF HYDROGEN WATER INTERFACE

AND HYDROXYL IONS AT THE OXIDE--

TAKAHIDE WAKAMATSU and SHIGERU MUKAI

Department of Mineral Science and Technology, Kyoto University, Kyoto, Japan Adsorption isotherms of hydrogen and hydroxyl ions on alumina, and also a value of pH, defined here as the equi-adsorption point, at which hydrogen and hydroxyl ions are equally adsorbed onto the alumina, are determined by means of the acid titration method for alumina suspension. The equi-adsorption point for the alumina is pH 7.4, while the isoelectric point for the same material is pH 9.0 by electrophoresis measurement. The equiabsorption point of alumina does not change even with the addition of dodecylsulfonate. Further, it is recognized that the adsorption density of hydrogen ion as well as hydroxyl ion on alumina increases with an increase in the sulfonate concentration. QUANTITATIVE CHARACTERIZATION FLOTATION AND ADSORPTION

OF pH-DEPENDENCE OF

S.G. DIXIT and A.K. BISWAS

Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur-16, India. S.G. Dixit is at present with the University of Bombay, India Adsorption of collectors on minerals and mineral flotation is highly sensitive to changes in the pH of the mineral pulp. Quantitative characterization of adsorption and collection as a function of pH has been studied in case of the zircon-sodium oleate system. It has been possible to use the adsorption isotherm equations to characterize pH-dependence of adsorption. For flotation recovery curves, a semi-empirical approach was found to be more fruitful. It is believed that the approach developed for the system studied may be extended and adapted to any nonmetallic mineral-anionic collector system. AMPHOTERIC COLLECTOR--MINERAL FLOTATION

CHARGE INTERACTION

AND

S U B H A S H C. G U P T A and R O S S W. S M I T H

Department of Chemical and Metallurgical Engineering, University of Nevada, Reno, Nevada. S.C. Gupta is with Cities Service Company, Cranbury, N.J. The use of sodium N-coco ~ aminopropionate and ~-~ dipalmitoyl L-~ lecithin'as flotation collectors for quartz and alumina has been investigated. A study of the relationship between collector species present and charge on the minerals and flotation was made. For these two collectors and the minerals studied, a positive-negative charge interaction was necessary for flotation although the primary collector specie in most cases was the Zwitter ion rather than the anion or cation.

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ADSORPTION OF N-ALKYLAMINE CHLORIDES ON HETEROGENEOUS SURFACES J.M. CASES, G. G O U J O N a n d S. SMANI

lnstitut National Polytechnique de Lorraine, Centre de Recherches sur la Valorisation des Minerais de I'E.N.S.G. et E.R.A. 219 B.P. 452-54001 Nancy Ctdex France, and Laboratoires des Mecanismes de la Croissance Cristalline, Marseille, France A d s o r p t i o n i s o t h e r m s are p r e s e n t e d for t e t r a d e c y l a n d d o d e c y l a m i n e c h l o r i d e s o n n a t n r a l a n d s y n t h e t i c calcite, b e f o r e a n d a f t e r grinding, a n d o n p h o s p h a t e oolites. T h e shape o f t h e i s o t h e r m s seems t o b e due t o a b i d i m e n s i o n a l c o n d e n s a t i o n o n a n h e t e r o g e n e ous surface w h e n t h e n u m b e r of CH~ groups in t h e alkyl c h a i n is greater t h a n 8. Lateral b i n d i n g energies in t h e a d s o r b e d layers are calculated. T h e a t t r a c t i v e e n e r g y p e r CH 2 g r o u p is f o u n d t o lie b e t w e e n 0.8 a n d 1.17 kT.

USE OF ELECTROPHORESIS IN DETERMINING THE CHEMISORPTION OF SURFACTANTS ON MINERAL SURFACES S A L I M A K H T A R a n d E O N G - L I P LAI

Mackay School o f Mines, University o f Nevada, Reno, Nev. 89507 A m e t h o d b a s e d o n t h e isoelectric p o i n t (i.e.p.) a n d t h e p o i n t o f zero c h a r g e (p.z.c.) o f solids for t h e i n t e r p r e t a t i o n o f c h e m i s o r p t i o n at m i n e r a l - w a t e r i n t e r f a c e s is p r o p o s e d . The p.z.c, a n d i.e.p, o f h e m a t i t e in s o l u t i o n s o f d o d e c y l a m i n e h y d r o c h l o r i d e a n d N a o l e a t e were m e a s u r e d w i t h electrophoresis. T h e v a r i a t i o n s in p H o f i.e.p, o f h e m a t i t e in dodecyla m i n e h y d r o c h l o r i d e s o l u t i o n s are a t t r i b u t e d to t h e c h e m i s o r p t i o n o f R N H : o n M O - sites, a n d t h e e q u i l i b r i u m c o n s t a n t o f t h e c h e m i s o r p t i o n r e a c t i o n is c a l c u l a t e d t o b e log K = 12.71 ± 0.14. T h e v a r i a t i o n s in t h e p H o f i.e.p, of h e m a t i t e in N a o l e a t e s o l u t i o n s are a t t r i b u t e d t o t h e c h e m i s o r p t i o n o f R C O O H o n M O - sites, a n d t h e e q u i l i b r i u m c o n s t a n t o f t h e c h e m i s o r p t i o n r e a c t i o n is e s t i m a t e d t o be greater t h a n 10 ~5. T y p e s o f c h e m i s o r p t i o n w h i c h d o n o t e f f e c t t h e i.e.p, o f solids are discussed.

PERMEABILITY AND ELECTROKINETIC FLUCTUATIONS IN TIME EUGENE A. THIERS, C O L I N C. H A R R I S a n d P A U L DUBY

Henry Krumb School o f Mines, Columbia University, New York, N. Y. 10027. E.A. Thiers is with Stanford Research Institute, Menlo Park, Calif. F l u c t u a t i o n s in t h e p e r m e a b i l i t y o f p o r o u s b e d s t o t h e flow o f liquids have b e e n r e p o r t e d in t h e l i t e r a t u r e f r o m t i m e t o time. Earlier studies h a v e e x c l u d e d c e r t a i n m e c h a n i c a l , chemical, a n d biological f a c t o r s as a cause o f t h e o b s e r v e d p h e n o m e n a . This investigation, cond u c t e d o n p a c k i n g s o f fine q u a r t z particles, has e x a m i n e d e l e c t r o k i n e t i c e f f e c t s as a possible cause. A c o r r e l a t i o n b e t w e e n p e l m e a b i l i t y a n d e l e c t r o k i n e t i c changes in t i m e has b e e n f o u n d a n d a c o m m o n m e c h a n i s m is suggested.

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KINETICS OF OLEATE ADSORPTION AT THE LIQUID/AIR AND ITS ROLE IN HEMATITE FLOTATION R.D. K U L K A R N I

INTERFACE

and P. S O M A S U N D A R A N

Henry Krumb School o f Mines, Columbia University, New York, N. Y. 10027 Dynamic surface tension properties of potassium oleate solutions have been investigated as a function of pH, surfactant concentration, ionic strength, and temperature in order to establish the role of these properties in determining the flotation response of hematite using oleate. Correlation of the results suggests a major role of the collector adsorption on the bubble and the related kinetics in determining the flotation response. Also, the role of oleate solution chemistry is examined as a function of pH. Maximum flotation response is found to occur under conditions of acid-soap formation.

CHARACTERIZATION INTERFACE

OF ADSORBED

COBALT AT THE OXIDE-WATER

PARAM H. TEWARI and NORMAN S. McINTYRE A t o m i c Energy o f Canada Limited, Whiteshell Nuclear Research Establishment, Pinawa, Manit., R O E ILO, Canada. AECL No. 5150 Adsorption of cobalt at the oxide-water interface has been studied and the adsorbed cobalt characterized by electrophoretic mobility (EM) and X-ray photoelectron spectroscopy. The photoelectron line-binding energies for the adsorbed species have been compared with those for a number of cobalt oxides and hydroxides to identify the cobalt species adsorbed on the surface. For the cobalt adsorbed from solutions at 30 ° C, the presence of electronic shake-up associated with the Co(2p) photoelectron lines indicates that the species is paramagnetic and is probably Co(II). The Co(2p 3/2) line position for the cobalt adsorbed on Al~O 3 and ZrO 2 is 780.7 +- 0.2 eV and is in excellent agreement with the binding energies observed for Co(OH)2. At 200 ° C, the adsorbed surface cobalt forms CoAl204 with the substrate as shown by the similarity between the X-ray photoelectron spectrum of CoA1204 and that of Al~O3 with adsorbed cobalt. CHARACTERIZATION OF SULFIDE MINERAL SURFACES IN FROTH FLOTATION SYSTEMS USING ELECTRON SPECTROSCOPY FOR CHEMICAL ANALYSIS ROGER K. CLIFFORD, KEVIN L. PURDY and JAN D. MILLER Department o f Metallurgical and Nuclear Engineering, University o f Missouri-Rolla, Rolla, Miss. 65401. K.L. Purdy is also with St. Joe Mineral Corporation, Bunker, Miss. 63629. J.D. Miller is with the University o f Utah, Salt Lake City, Utah 84112 Electron spectroscopy for chemical analysis (ESCA) was used to characterize the surfaces of ten natural sulfide minerals: galena, sphalerite, chalcopyrite, chalcocite, covellite, bornite, pyrite, pyrrhotite, molybdenite, and millerite. ESCA surface analyses were made

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on high-quality specimens after: (1) comminution in air, (2) comminution in a nitrogen atmosphere, (3) adsorption of xanthate collector, and (4) adsorption of dithiophosphate collector. Analyses were also made after modifiers such as Na 2 Cr20~, S02, starch, NaCN, and CuSO 4 and the collector had been adsorbed onto the surfaces of the sulfide minerals. The objective of the investigation was to characterize the sulfidemineral surfaces both before and after the adsorption of activators, depressants, and collectors in an effort to gain insight into their actions and the flotation process. ESCA has been most useful for following the action of modifiers rather than collectors due to the large amounts of sulfur and background carbon already present on the sulfide surfaces. ESCA has the potential of yielding semiquantitative chemical analyses of the oxidation states of many elements (excluding hydrogen and helium) on a mineral surface (the outer 25 A ). Normalization constants for semiquantitative analysis based on relative elemental sensitivity have been calculated for the minerals studied.

ADSORPTION MECHANISM OF SULFIDES AT A PLATINUM-SOLUTION INTERFACE K.A. NATARAJAN and I. IWASAKI

Mineral Resources Research Center, University of Minnesota, Minneapolis, Minn. 55455. K.A. Natarajan is with the Karnataka Regional Engineering College, Srinivasnagar 574157, India. The behavior of platinum electrodes in redox potential measurements in the presence of hydrogen sulfide and sulfide ions was studied. In acidic solutions, hydrogen sulfide was a severe poisoning agent and the electrode behavior became erratic in its presence. In neutral to alkaline solutions, the presence of sulfide ions in low concentrations did not seriously hamper the electrode response. The mechanism of the adsorption of sulfides is discussed and related to the potential measurements.

ADSORPTION OF ZINC(II) AT THE CINNABAR (HgS)/H20 INTERFACE ROBERT O. JAMES and GEORGE A. PARKS

Department of Applied Earth Sciences, Stanford University, Stanford, Calif. 94305. R.O. James is with the University of Melbourne, Parkville, Vict. 3052, Australia In previous studies the uptake of aqueous metal species by sulfide minerals has been considered to be controlled by the relative solubilities of the sulfide minerals. This study reports results in which the uptake cannot be described by this criterion and shows that models using adsorption of hydrolysis products in the electrical double layer of the sulfideH20 interface or ion exchange of free aquo metal ions for surface protons can describe this uptake when the solubility of the host sulfide is greater than that of the sulfide of the adsorbing metal ion.

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NATURAL AND INDUCED HYDROPHOBICITY IN SULFIDE MINERAL SYSTEMS N.P. FINKELSTEIN, S.A. ALLISON, V.M. L O V E L L and B.V. S T E W A R T

National Institute for Metallurgy, Johannesburg, South Africa Microflotation tests were conducted on a number of samples of sulfide minerals, both before and after they had been treated with xanthate and other reagents, on metal xanthates, and on elemental sulfur. The concentrations of sulfur and xanthate at the surface of the minerals were determined. Because detectable amounts of sulfur were not formed at the surfaces of the minerals during their reaction with xanthates and because all the metal xanthates proved to be highly floatable, it is concluded that the hydrophobic entity responsible for the collecting action of xanthates can equally well be dixanthogen or a metal xanthate and that sulfur plays no part. The floatabilities of the mineral samples in their as-ground state differed, as did the concentrations of sulfur at their surfaces. The concentration of sulfur could be increased by various chemical treatments. However, although elemental sulfur is extremely floatable, no correlation was found between floatability and the concentration of sulfur at the surface of the mineral. It is concluded that, in general, the sulfide minerals cannot be classified as either naturally floatable or nonfloatable and that their floatability is markedly influenced by relatively minor changes at their surfaces. These findings are used to show that the inability of sulfide minerals to form hydrogen bonds is the principal reason why they, unlike oxygen-containing minerals, are not strongly hydrophilic.

SURFACE PROPERTIES OF HYDROPHOBIC SOLIDS N. ARBITER, Y. FUJII, B. H A N S E N and A. R A J A

Henry Krumb School of Mines, Columbia University, New York, N. Y. N. Arbiter is with the Anaconda Company, Tucson, Ariz. Y. Fujii is with Yamaguchi University, Ube City, Japan. B. Hansen is with Hanna Mining Company, Hibbing, Minn. A. Raja is with Shyam Sadan, Bombay, India

ON THE NATIVE FLOATABILITY AND SURFACE PROPERTIES OF NATURALLY HYDROPHOBIC SOLIDS S. CHANDER, J.M. WIE and D.W. FUERSTENAU

Department of Materials Science and Engineering, University of California, Berkeley, Calif. 94720 The zeta potential, contact angle, and flotation data for a number of naturally floatable materials, namely, graphite, molybdenite, pyrophyllite, stibnite, sulfur, talc, and paraffin wax have been compared and contrasted. On the basis of the available data, it is concluded that the crystal structure of the solid, the nature of charged hydrophilic sites present on the mineral surface, and the anisotropic behavior of the mineral surface play an important role in determining the properties of inherently hydrophobic materials.

384 G E N E R A L DISCUSSION OF PAPERS ON T H E F L O T A T I O N CHEMISTRY OF SULFIDES AND HYDROPHOBIC SOLIDS S. CHANDER Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, India 208016