by p. somosundaran
TRANSCRIPT
by P. Somosundaran
Flotation of minerals has usually been discussed in terms of solid-liquid interfacial phenomena. This paper discusses the relative importance of Jilenomena such as collectcx adsorption at other interfaces formed between the bubble, liquid and solid. Adsorp- tion of collector ions of various chain lengths at liquid-gas and solid-gas interfaces has been obtained. The data have been analyzed under conditions corre- sponding to those of flotation to show the significant role of collector adsorbed on the bubble surface in determining the bubble-mineral attachment required for flotation, and consequently to suggest coosider- ation of this role in the development of better flota- tion conditions.
ble surface. Collector ions or molecules are adsorbed both at the solid-liquid interface and the liquid-gas interface. Below the concentration for hemi-micelle association at the Stern plane adjacent to the surface, the bulk of the collector ions adsorbed at the solid- liquid interface are in the diffuse part of the dooble layer. If such systems, where there is a gas bubble coming in contact with the solid surface, are to achieve some degree of electroneutrali ty, those col. lector ions would have to migrate from the diffuse part of the double layer to the region directly adjacent to the surface during the induction period when the bubble is making contact with the solid. The time necessary for this migration would contribute to the induction period required for creation of the solid-gas interface. It seems reasonable that the induction period could be reduced sufficiently for flotation to occur if these collector ions were carried to the sur. face by the bubble.
In an attempt to ascertain whether or not the bubble could possibly have sufficient collector ions at its surface to meet the requirement mentioned above, the adsorption density of the collector ions at the liquid- air interface was determined. For this purpose, the surface tension of alkyl ammonium acetate solutions was determined as a function of concentration. Ad- sorption densities of the collector at the liquid-gas interface were calculated using the Gibbs adsorption equation:
dy --I., r,dll., [1:
V acuum flotation of quartz with alkyl ammonium acetate reported in the foregoing paper 1 showed
that the collector chain length has an effect on flota- tion even at concentrations below those necessary for hemi-micelle associatioJl of the hydrocarbon chains at a solid-liquid interface. This chain length effect might be explained by the following arguments: Hydrocarbon chains find it energetically favorable to be in a medium of low dielectric constant. Consider- ing the possibility of an iceberg structure at the solid-liquid interface,2 such a structure would pro- duce a region of lower dielectric constant at the solid-liquid interface than in the liquid phase, be- cause the dielectric constant of ice is 2 to 3,2 while that of water is 80. Depending on chain length, this difference will certainly cause even individual ions to adsorb in higher quantities at the solid-liquid interface. Another mechanism to consider is the pos- sible formation of dimers, trimers, etc.,3,4 and chain length would influence this formation.
Butl. above all, the chain length effect on flotation at concentrations of low adsorption at the solid-liquid interface could be due to the significant but of ten- neglected role of the collector adsorption at the bub-
P. SOMASUNDARAN, Member AIME, foltllerly with Inter- national Minerals and Chemical Corp., is now with the Research Department, Basic Science, R. J. Reynolds To- bacco Co., Winston-8alem, N.C. TP 67B159. Manuscript, July 12. 1967. This paper was presented at the AIME Annual Meeting, Los Angeles. Calif., February 19-23,1967. Discussion of this paper, submitted in duplicate prior to June IS, 1968. will appear in SME Transactions. September 1968, and AIME Transactions, 1968, vol. 241.
where 19 refers to liquid-gas interface and RA+ re- fers to the alkyl ammonium ions. For dilute solutions,
(tg) I.dYlc = - 2RT [' RA+ dlnCRA+ [3]
where C is the concentration of the collector ions in solution. ['~~ can now be evaluated using Eq. 3 and surface tension measurements.
MARCH 1968 - 105Society of Mining Engineers
where y is the interfacial tension and r I and III are the adsorption density and the chemical potential, respectively, of the chemical species, i. Using the convention that the adsorption density of water at the interface is zero, the following relationship is ob- tained for the liquid-gas interface
The particle-bubble adhesion was also studied as a function of collector chain length and of its concen- tration by measuring the adhesion tension of the solution on the mineral.
RESUL TS AND DISCU~ION
Fig. 1 gives the results of surface tension meas- urements of collectors of various chain lengths as a function of concentration. The slope of the curves at different concentrations, measured by drawing the tangents to the curves, is dyld log C. This, when substituted in Eq. 3, gives ['~A+' the adsorption density of collector ions at the liquid-gas interface, as a function of collector concentration. Fig. 2 shows ['~+ plotted against collector concentration.
These data can now be used to $tudy condition$ of flotation. For example, at 3 x 10-5 mole per liter dodecylammonium acetate solution which i$ below the hemi-micelle concentration, the ad$orption den- sity at the liquid-gas interface is 3 x 10 -11 mole per
sq cm. Under the same conditions, Li11 obtained a value of 10-12 mole per sq cm for the adsorption den- sity at the solid-liquid interface, and actually only a very small percentage of these ions would be an- chored to the surface in the Stem layer. Collector ions adsorbed on the liquid-gas interface would, however, be carried mostly on the surface of the
EXPERIMENTAL PROCEDURE
Surface tension measurements were carried out using a stalagmometer. To overcome the problem of local formation of drops from wetted regions of the undersurface of the tip at high collector concentra- tions, a syringe needle with its taper removed was attached to the stalagmometer. This stalagmometer technique was preferred to other techniques such as the ring method in which the film undergoes stretch- ing at the final stages thereby decreasing surface concentration of the collector and hence effectively increasing the surface tension. With the ring method, adsorption of the surfactant on the platinum ring is also a serious problem. Aging of the surface is an- other problem to be considered in the measurements of surface tension. To permit comparison with flota- tion data, a method where the bubbles would not be aged significantly was used in this study because during flotation a bubble remains within the solution for probably only one or two seconds.
Adhesion tension was measured by using the capil- lary rise method. Adhesion tension r, a measure of force required for dewetting the solid surface, is given by the equation
(4)y Cas 6 = 1/2 ,ria (pt - P2'
..
where () is the contact angle, g the gravitational constant, r the radius of the capillary, h the capillary rise, and PI - P2 the difference in density of the
liquid and gas medium. From Eq. 4, at constant r for liquids of ~imilar density, adhesion tension is pro- portional to the capillary rise. Thus, using water (w) as a standard, for dilute collector solution, the ad- hesion tension of the solution, r 801 is given by
"801
11. [5]r.ol w
For water on glass (J is zero, so Tw is 72 dynes per cm. With this value, and knowing the capillary rises for water and the dilute collector solution, the ad- hesion tension of the solution can be calculated using Eq. 5. The capillary tube used was made of glass. It has been assumed that the surfaces of glass and quartz behave in a similar manner in aqueous solutions, since the hydrolysis of either the pseudo- silicate groups on the glass surface or the silicate groups on the quartz surface would result in the for- mation of silanols. The experiments of Terminassian- Saraga 5,7 and others 8- to indicate this assumption to
be correct. The measurements made are for a receding capillary solution.
106 - MARCH 1968 TRANSACTIONS
bubble and do not occur in a diffuse layer as at the solid-liquid interface. Therefore, a bubble in the process of contacting a solid under the above condi- tions would carry enough collector ions to have a sufficiently low induction time for flotation to occur, even though the number of ions actually on the solid surface itself is very low. This shows the importance of considering the adsorption at the liquid-gas inter- face in addition to that at the solid-liquid interface when discussing flotation.
Fig. 3 gives adhesion tension as a function of pH at four different dodecylammonium acetate concen- trations. It can be seen that these curves exhibit a knee around pH 8 as the solution is made alkaline. Like the critical pH-concentration curves of vacuum flotation,. these curves also show the greater surface activity of neutral molecules in the presence of their ions. As the pH of the aminium acetate solution is increased, the neutral amine molecules that are formed adsorb in greater quantities than the aminium ions alone at the solid-liquid, the liquid-gas, and es- pecially at the solid-gas interface, as shown by the adhesion tension curves. The results of adhesion tension measurements as a function of the concentra-
tion of collectors of various chain lengths are shown in Fig. 4. The change in adhesion tension with con- centration seems to correspond to flotation conditions more than the change in the solid-liquid interfacial properties reported previously.12 Results obtained by Waksmundski and Maruszak 13 for dodecylammonium
chloride solution and quartz and those obtained by Ter-Minassian-SaragaS for dodecyl tri-methyl am- monium bromide solution and quartz compare well with those shown for dodecylammonium acetate solu- tion and glass in Fig. 4.
As shown earlier, the number of ions at the liquid- gas interface transferred to the solid surface and adsorbed' 'complementarily" 5,14 with those already adsorbed on the solid directly from the solutioo is important from the viewpoint of flotation. An estimate of this number can be obtained from the adhesion tension measurements and the use of Young's equation,
[6)}'.. - }'.1 = }'la COB 8
where Y and Y 1 are the interfacial tensions at the8. 8 solid-gas interface and the solid-liquid interface
respectively.
[8)r -r 1 =-- ~ 8E 8 ,,-- .. ...
1 dT
Using Eq. 8, the adhesion data shown in Fig. 4, and the adsorption data of Li 11 for dodecylammonium
acetate on quartz, the adsorption at the solid-gas interface was calculated. This is given in Fig. 5, together with the adsorption at the liquid-gas and solid-liquid interfaces for comparison. Fig. 5 shows that the collector that could be transferred to the solid-gas interface from the bubble surface upon con- tact is significantly higher than that which could be transferred from the solid-liquid interface. The neces- sity of greater adsorption at the solid-gas interface than at the solid-liquid interface has been shown by de Bruyn and others.15-17 Data similar to that in Fig. 5 were also obtained using the adsorption isotherm of de Bruyn.18 De Bruyn's adsorption data are higher than those obtained by Li. However, remembering that only a small percentage of [' .1 would actually be anchored to the solid surface, here also the collector adsorbed on the bubble would be higher than that anchored to the solid surface.
This treatment indicates that for better flotation conditions, one should look at the conditions of ad- sorption at the liquid-gas interface and solid-gas interface rather than just that at the solid-liquid interface, as is usually done. From Young's equation
Fig. 4 - Adhesion tension of alkyl ammonium acetate solutions on glass as a function of concentration.
Society of Mining Engineers MARCH 1968 - 107
..show the higher surface activity of the neutral col- lector molecule in the presence of I.(S ions.
Consideration of the role of collector molecules or ions adsorbed at the liquid-gas interface in flotation phenomena is very important and investigation of the role of bubble surface for introducing the collector to the mineral surface with its related problems may open an altogether new avenue in the flotation process.
ACKNOWLEDGMENT This work was done while the author was with the
International Minerals and Chemical Corp. Growth Sciences Center in Libertyville, Ill.
Fig. 5 - Comparison of adsorption of dodecylammmiuin acetate at different interfaces.
one obtains the following condition for solid-bubble attachment. For a large contact angle
[9]f.. - f.l < fl.
The maximum value of Yic is limited by the froth
stability requirement. Hence, to fulfill the condition given by Eq. 9, Y should be kept small and y'C .t should be made as large as possible. Since ~itive adsorption always decreases sudace tension, con- ventional conditioning of mineral particles with col- lector prior to flotation only reduces Y.t. Therefore, to keep Y.t as large as possible, and yet reduce Ysc' gas-phase adsorption can be used by techniques such as that used by Wada 19 where the collector was
passed into the flotation system in the fonn of aero- sols with the gas stream. Transfer of the collector to the solid-gas interface is energetically more favor- able in the gas-phase adsorption process than in the liquid-phase adsorption process and hence, even though the experiments of Wada are only preliminary, they have indicated optimum flotation at reagent con- centrations as low as 1/5 to 1/10 of those used in the conventional process.
REFERENCES Ip. Soma.und.ran and D.W. Fuer.tenau: On Incipient Flotation Condition., SAfE Trans., March 1968, vol. 241, pp. 102-104.
2J. T. Davie. and R.K. Rideal: Intedaclal Phenomena, Academic Pre.., New York, N.Y., 1963, p. 116; H.S. Frank. and M.W. Evan.,I. Chem. Phye., 1945, vol. 13, p. 507.
3F. Frank. and H. T. Smith, I. Phy.. Chern., 1964, vol. 68. p. 3581.
4L.B. Banc.: Sc.D. The.ie. Ma..achu.ett. In.titute of Tech-
nology.1964. 5L. Te...Mina..lan-S..aga: Contact ARcle. WeitabUlty, and
Adhe.ion, Advances 01 Chemistry Se"es 43, R.F. Gould, Ed., ACS Applied Publication., W..hincton, D.C., 1964, p. 233.
6L. Ter-Mina..ian-Saraca: Campi. Rend., 1959, vol. 249.
p.1952. 7L. Te...Minaealan-S..aca: Campi. Rend., 1961, vol. 252.
p.1596. 8M. Baruch - Well: Ann. Phye., 1959, vol. 4, p. 1159.
9F.E. Barteli and L.S. Barteli: I. Am. Chem. Soc., 1934, vol. 56, p. 2205. 1
10A.J. Rutcera, _d M. de Smet: Trans. Farsday Soc., 1945, vol. 4", p. 758.
II H.C. Li: Sc.D. The.I., Maa..chuaetta Inatitute of Technoiocy. 1958.
12P. Som..undaran, T.W. Healy and D.W. Fuer.tenau: J. Phys. Ch_., 1964, vol. 68, p. 3562.
13A. Wak.mundaki and E. Maru.z8k: Rocanlkl Cham., 1964, vol. 38, p. 835.
14L. T-ebre: Mem. Servo Chlm. Etat, 1955. vol. 40. p. 77, J. Chlm. Phys., 1956, vol. 53, p. 6.
15 .P.L. de Bruyn, J. Th. G. Overbeek, and R. Schuhmann. Jr.. Mlnln, Enllnee"nI, 1954. vol. 6, p. 519.
16C.A. Smolder.: Rec. Trav. Chlm., 1961, vol. 80.
17F.F. Aplan and P.L. de Bruyn: Trans. AlME, 1963. vol. 229.
p.235. 18P.L. de Bruyn: Trans. AlME, 1955, vol. 203, p. 291.
19M. Wada: Surface Energy and Ad.orption in Fine-Particle Flo- tation, pre.ented at the IV Intemstionale. Aufbereitunc.kol- 10qlum. For.chun..lntltut Fur Aufbereitunc, Freiberg (Sach.). May 1966.
CONCLUSIONS
The experiments show the significant role of col- lector adsorbed on the bubble surface in determining the bubble-mineral attachment required for flotation. Both adhesion tension and the flotation experiments
TRANSACTIONS108 - MARCH 1968
Flotation of minerals has usually been discussed in terms of solid-liquid interfacial phenomena. This paper discusses the relative importance of Jilenomena such as collectcx adsorption at other interfaces formed between the bubble, liquid and solid. Adsorp- tion of collector ions of various chain lengths at liquid-gas and solid-gas interfaces has been obtained. The data have been analyzed under conditions corre- sponding to those of flotation to show the significant role of collector adsorbed on the bubble surface in determining the bubble-mineral attachment required for flotation, and consequently to suggest coosider- ation of this role in the development of better flota- tion conditions.
ble surface. Collector ions or molecules are adsorbed both at the solid-liquid interface and the liquid-gas interface. Below the concentration for hemi-micelle association at the Stern plane adjacent to the surface, the bulk of the collector ions adsorbed at the solid- liquid interface are in the diffuse part of the dooble layer. If such systems, where there is a gas bubble coming in contact with the solid surface, are to achieve some degree of electroneutrali ty, those col. lector ions would have to migrate from the diffuse part of the double layer to the region directly adjacent to the surface during the induction period when the bubble is making contact with the solid. The time necessary for this migration would contribute to the induction period required for creation of the solid-gas interface. It seems reasonable that the induction period could be reduced sufficiently for flotation to occur if these collector ions were carried to the sur. face by the bubble.
In an attempt to ascertain whether or not the bubble could possibly have sufficient collector ions at its surface to meet the requirement mentioned above, the adsorption density of the collector ions at the liquid- air interface was determined. For this purpose, the surface tension of alkyl ammonium acetate solutions was determined as a function of concentration. Ad- sorption densities of the collector at the liquid-gas interface were calculated using the Gibbs adsorption equation:
dy --I., r,dll., [1:
V acuum flotation of quartz with alkyl ammonium acetate reported in the foregoing paper 1 showed
that the collector chain length has an effect on flota- tion even at concentrations below those necessary for hemi-micelle associatioJl of the hydrocarbon chains at a solid-liquid interface. This chain length effect might be explained by the following arguments: Hydrocarbon chains find it energetically favorable to be in a medium of low dielectric constant. Consider- ing the possibility of an iceberg structure at the solid-liquid interface,2 such a structure would pro- duce a region of lower dielectric constant at the solid-liquid interface than in the liquid phase, be- cause the dielectric constant of ice is 2 to 3,2 while that of water is 80. Depending on chain length, this difference will certainly cause even individual ions to adsorb in higher quantities at the solid-liquid interface. Another mechanism to consider is the pos- sible formation of dimers, trimers, etc.,3,4 and chain length would influence this formation.
Butl. above all, the chain length effect on flotation at concentrations of low adsorption at the solid-liquid interface could be due to the significant but of ten- neglected role of the collector adsorption at the bub-
P. SOMASUNDARAN, Member AIME, foltllerly with Inter- national Minerals and Chemical Corp., is now with the Research Department, Basic Science, R. J. Reynolds To- bacco Co., Winston-8alem, N.C. TP 67B159. Manuscript, July 12. 1967. This paper was presented at the AIME Annual Meeting, Los Angeles. Calif., February 19-23,1967. Discussion of this paper, submitted in duplicate prior to June IS, 1968. will appear in SME Transactions. September 1968, and AIME Transactions, 1968, vol. 241.
where 19 refers to liquid-gas interface and RA+ re- fers to the alkyl ammonium ions. For dilute solutions,
(tg) I.dYlc = - 2RT [' RA+ dlnCRA+ [3]
where C is the concentration of the collector ions in solution. ['~~ can now be evaluated using Eq. 3 and surface tension measurements.
MARCH 1968 - 105Society of Mining Engineers
where y is the interfacial tension and r I and III are the adsorption density and the chemical potential, respectively, of the chemical species, i. Using the convention that the adsorption density of water at the interface is zero, the following relationship is ob- tained for the liquid-gas interface
The particle-bubble adhesion was also studied as a function of collector chain length and of its concen- tration by measuring the adhesion tension of the solution on the mineral.
RESUL TS AND DISCU~ION
Fig. 1 gives the results of surface tension meas- urements of collectors of various chain lengths as a function of concentration. The slope of the curves at different concentrations, measured by drawing the tangents to the curves, is dyld log C. This, when substituted in Eq. 3, gives ['~A+' the adsorption density of collector ions at the liquid-gas interface, as a function of collector concentration. Fig. 2 shows ['~+ plotted against collector concentration.
These data can now be used to $tudy condition$ of flotation. For example, at 3 x 10-5 mole per liter dodecylammonium acetate solution which i$ below the hemi-micelle concentration, the ad$orption den- sity at the liquid-gas interface is 3 x 10 -11 mole per
sq cm. Under the same conditions, Li11 obtained a value of 10-12 mole per sq cm for the adsorption den- sity at the solid-liquid interface, and actually only a very small percentage of these ions would be an- chored to the surface in the Stem layer. Collector ions adsorbed on the liquid-gas interface would, however, be carried mostly on the surface of the
EXPERIMENTAL PROCEDURE
Surface tension measurements were carried out using a stalagmometer. To overcome the problem of local formation of drops from wetted regions of the undersurface of the tip at high collector concentra- tions, a syringe needle with its taper removed was attached to the stalagmometer. This stalagmometer technique was preferred to other techniques such as the ring method in which the film undergoes stretch- ing at the final stages thereby decreasing surface concentration of the collector and hence effectively increasing the surface tension. With the ring method, adsorption of the surfactant on the platinum ring is also a serious problem. Aging of the surface is an- other problem to be considered in the measurements of surface tension. To permit comparison with flota- tion data, a method where the bubbles would not be aged significantly was used in this study because during flotation a bubble remains within the solution for probably only one or two seconds.
Adhesion tension was measured by using the capil- lary rise method. Adhesion tension r, a measure of force required for dewetting the solid surface, is given by the equation
(4)y Cas 6 = 1/2 ,ria (pt - P2'
..
where () is the contact angle, g the gravitational constant, r the radius of the capillary, h the capillary rise, and PI - P2 the difference in density of the
liquid and gas medium. From Eq. 4, at constant r for liquids of ~imilar density, adhesion tension is pro- portional to the capillary rise. Thus, using water (w) as a standard, for dilute collector solution, the ad- hesion tension of the solution, r 801 is given by
"801
11. [5]r.ol w
For water on glass (J is zero, so Tw is 72 dynes per cm. With this value, and knowing the capillary rises for water and the dilute collector solution, the ad- hesion tension of the solution can be calculated using Eq. 5. The capillary tube used was made of glass. It has been assumed that the surfaces of glass and quartz behave in a similar manner in aqueous solutions, since the hydrolysis of either the pseudo- silicate groups on the glass surface or the silicate groups on the quartz surface would result in the for- mation of silanols. The experiments of Terminassian- Saraga 5,7 and others 8- to indicate this assumption to
be correct. The measurements made are for a receding capillary solution.
106 - MARCH 1968 TRANSACTIONS
bubble and do not occur in a diffuse layer as at the solid-liquid interface. Therefore, a bubble in the process of contacting a solid under the above condi- tions would carry enough collector ions to have a sufficiently low induction time for flotation to occur, even though the number of ions actually on the solid surface itself is very low. This shows the importance of considering the adsorption at the liquid-gas inter- face in addition to that at the solid-liquid interface when discussing flotation.
Fig. 3 gives adhesion tension as a function of pH at four different dodecylammonium acetate concen- trations. It can be seen that these curves exhibit a knee around pH 8 as the solution is made alkaline. Like the critical pH-concentration curves of vacuum flotation,. these curves also show the greater surface activity of neutral molecules in the presence of their ions. As the pH of the aminium acetate solution is increased, the neutral amine molecules that are formed adsorb in greater quantities than the aminium ions alone at the solid-liquid, the liquid-gas, and es- pecially at the solid-gas interface, as shown by the adhesion tension curves. The results of adhesion tension measurements as a function of the concentra-
tion of collectors of various chain lengths are shown in Fig. 4. The change in adhesion tension with con- centration seems to correspond to flotation conditions more than the change in the solid-liquid interfacial properties reported previously.12 Results obtained by Waksmundski and Maruszak 13 for dodecylammonium
chloride solution and quartz and those obtained by Ter-Minassian-SaragaS for dodecyl tri-methyl am- monium bromide solution and quartz compare well with those shown for dodecylammonium acetate solu- tion and glass in Fig. 4.
As shown earlier, the number of ions at the liquid- gas interface transferred to the solid surface and adsorbed' 'complementarily" 5,14 with those already adsorbed on the solid directly from the solutioo is important from the viewpoint of flotation. An estimate of this number can be obtained from the adhesion tension measurements and the use of Young's equation,
[6)}'.. - }'.1 = }'la COB 8
where Y and Y 1 are the interfacial tensions at the8. 8 solid-gas interface and the solid-liquid interface
respectively.
[8)r -r 1 =-- ~ 8E 8 ,,-- .. ...
1 dT
Using Eq. 8, the adhesion data shown in Fig. 4, and the adsorption data of Li 11 for dodecylammonium
acetate on quartz, the adsorption at the solid-gas interface was calculated. This is given in Fig. 5, together with the adsorption at the liquid-gas and solid-liquid interfaces for comparison. Fig. 5 shows that the collector that could be transferred to the solid-gas interface from the bubble surface upon con- tact is significantly higher than that which could be transferred from the solid-liquid interface. The neces- sity of greater adsorption at the solid-gas interface than at the solid-liquid interface has been shown by de Bruyn and others.15-17 Data similar to that in Fig. 5 were also obtained using the adsorption isotherm of de Bruyn.18 De Bruyn's adsorption data are higher than those obtained by Li. However, remembering that only a small percentage of [' .1 would actually be anchored to the solid surface, here also the collector adsorbed on the bubble would be higher than that anchored to the solid surface.
This treatment indicates that for better flotation conditions, one should look at the conditions of ad- sorption at the liquid-gas interface and solid-gas interface rather than just that at the solid-liquid interface, as is usually done. From Young's equation
Fig. 4 - Adhesion tension of alkyl ammonium acetate solutions on glass as a function of concentration.
Society of Mining Engineers MARCH 1968 - 107
..show the higher surface activity of the neutral col- lector molecule in the presence of I.(S ions.
Consideration of the role of collector molecules or ions adsorbed at the liquid-gas interface in flotation phenomena is very important and investigation of the role of bubble surface for introducing the collector to the mineral surface with its related problems may open an altogether new avenue in the flotation process.
ACKNOWLEDGMENT This work was done while the author was with the
International Minerals and Chemical Corp. Growth Sciences Center in Libertyville, Ill.
Fig. 5 - Comparison of adsorption of dodecylammmiuin acetate at different interfaces.
one obtains the following condition for solid-bubble attachment. For a large contact angle
[9]f.. - f.l < fl.
The maximum value of Yic is limited by the froth
stability requirement. Hence, to fulfill the condition given by Eq. 9, Y should be kept small and y'C .t should be made as large as possible. Since ~itive adsorption always decreases sudace tension, con- ventional conditioning of mineral particles with col- lector prior to flotation only reduces Y.t. Therefore, to keep Y.t as large as possible, and yet reduce Ysc' gas-phase adsorption can be used by techniques such as that used by Wada 19 where the collector was
passed into the flotation system in the fonn of aero- sols with the gas stream. Transfer of the collector to the solid-gas interface is energetically more favor- able in the gas-phase adsorption process than in the liquid-phase adsorption process and hence, even though the experiments of Wada are only preliminary, they have indicated optimum flotation at reagent con- centrations as low as 1/5 to 1/10 of those used in the conventional process.
REFERENCES Ip. Soma.und.ran and D.W. Fuer.tenau: On Incipient Flotation Condition., SAfE Trans., March 1968, vol. 241, pp. 102-104.
2J. T. Davie. and R.K. Rideal: Intedaclal Phenomena, Academic Pre.., New York, N.Y., 1963, p. 116; H.S. Frank. and M.W. Evan.,I. Chem. Phye., 1945, vol. 13, p. 507.
3F. Frank. and H. T. Smith, I. Phy.. Chern., 1964, vol. 68. p. 3581.
4L.B. Banc.: Sc.D. The.ie. Ma..achu.ett. In.titute of Tech-
nology.1964. 5L. Te...Mina..lan-S..aga: Contact ARcle. WeitabUlty, and
Adhe.ion, Advances 01 Chemistry Se"es 43, R.F. Gould, Ed., ACS Applied Publication., W..hincton, D.C., 1964, p. 233.
6L. Ter-Mina..ian-Saraca: Campi. Rend., 1959, vol. 249.
p.1952. 7L. Te...Minaealan-S..aca: Campi. Rend., 1961, vol. 252.
p.1596. 8M. Baruch - Well: Ann. Phye., 1959, vol. 4, p. 1159.
9F.E. Barteli and L.S. Barteli: I. Am. Chem. Soc., 1934, vol. 56, p. 2205. 1
10A.J. Rutcera, _d M. de Smet: Trans. Farsday Soc., 1945, vol. 4", p. 758.
II H.C. Li: Sc.D. The.I., Maa..chuaetta Inatitute of Technoiocy. 1958.
12P. Som..undaran, T.W. Healy and D.W. Fuer.tenau: J. Phys. Ch_., 1964, vol. 68, p. 3562.
13A. Wak.mundaki and E. Maru.z8k: Rocanlkl Cham., 1964, vol. 38, p. 835.
14L. T-ebre: Mem. Servo Chlm. Etat, 1955. vol. 40. p. 77, J. Chlm. Phys., 1956, vol. 53, p. 6.
15 .P.L. de Bruyn, J. Th. G. Overbeek, and R. Schuhmann. Jr.. Mlnln, Enllnee"nI, 1954. vol. 6, p. 519.
16C.A. Smolder.: Rec. Trav. Chlm., 1961, vol. 80.
17F.F. Aplan and P.L. de Bruyn: Trans. AlME, 1963. vol. 229.
p.235. 18P.L. de Bruyn: Trans. AlME, 1955, vol. 203, p. 291.
19M. Wada: Surface Energy and Ad.orption in Fine-Particle Flo- tation, pre.ented at the IV Intemstionale. Aufbereitunc.kol- 10qlum. For.chun..lntltut Fur Aufbereitunc, Freiberg (Sach.). May 1966.
CONCLUSIONS
The experiments show the significant role of col- lector adsorbed on the bubble surface in determining the bubble-mineral attachment required for flotation. Both adhesion tension and the flotation experiments
TRANSACTIONS108 - MARCH 1968