legaltranslations.biz
`
` (Division of Nelles Translations)
`
` 20 N. Wacker Drive - Suite 1408 - Chicago, IL 60606 - 312-977-9772 Fax-866-615-8606
`
`Certification
`
`This is to certify that the foregoing translation of the document entitled Size of gas bubbles forming
`during electroflotation was made from Russian to English from the document by a competent
`translator well acquainted with both languages. I further declare that all statements made herein of my
`own knowledge are true, and that all statements made on information and belief are believed to be
`true; and further that these statements were made with the knowledge that willful false statements and
`the like so made are punishable by fine or imprisonment, under Section 1001 of Title 19 of the United
`States Code.
`
`Date: February 23, 2021
`
`Donald W. Hanley, CEO
`
`Tennant Company
`Exhibit 1124
`
`

`

`ACADEMY OF SCIENCES OF MOLDAVIAN SSR
`
`INSTITUTE OF APPLIED PHYSICS
`
`ELECTRONIC
`PROCESSING OF MATERIALS
`
`ELECTRONIC
`
`

`

`V.A. Glembotsky, A.А. Mamakov,
`V.N. Sorokina
`Chisinau
`
`Size of gas bubbles forming
`during electroflotation
`
`Dispersity and type of gaseous medium are of great importance in
`the course of flotation of minerals. Available techniques of air dispersion
`can produce 0.8-0.9 mm air bubbles (impeller flotation machines), 0.1-
`0.2 mm (vacuum flotation), and in certain cases – 0.06-0.08 mm
`(compression type units). Producing fine dispersed gas bubbles is
`important, since these bubbles penetrate the hydrate layer of the surface
`of mineral particles more actively. Smaller bubbles attach to mineral
`particles much faster than larger ones.
`Electrolytic technique is one of the methods for producing fine
`dispersed gas bubbles. Electrolytic water decomposition process
`produces very fine bubbles of hydrogen and oxygen. In alkaline solutions,
`hydrogen bubbles formed near the cathode are so fine that the solution
`becomes milk-white. Bubbles forming near the anode are much larger.
`The situation is reverse in acid conditions.
`B.N. Kabanov, A.N. Frumkin [1] studied the conditions causing a
`gas bubble to break away from the electrode it was attached to. They
`determined that the size of a bubble attached to an electrode in
`equilibrium is defined by contact angle of wetting. Bubbles with larger
`contact angle are attached to the electrode more tightly, therefore growing
`larger in size.
`Electrode potential is an important factor affecting the contact angle
`
`[1].
`
`Maximum contact angle is observed at the electrode potential close
`to the point of zero charge. Shift of potential to either side (both + and -)
`results in change (reduction) of contact angle. Gas bubbles are therefore
`decreasing in size as well.
`Electrochemical polarization, both cathodic and anodic, caused by
`shift of potential, may produce significant effect on the size of bubbles
`breaking away from the electrode.
`The amount of shift of cathodic polarization is greatly affected by
`current density [2], pH value of the medium, cathode material, [2--9],
`temperature [10], etc.
`Current density dependence of overvoltage is described by Tafel equation
`
`η = a + b ln i,
`where η is hydrogen overvoltage; і is current density; а is a coefficient
`
`defined by cathode material, ion composition of slurry, temperature; 𝑏=
`(cid:3019)(cid:3021)(cid:3080)(cid:3007),𝛼≈0,5.
`
`For most metals, as pH value increases, cathodic polarization
`initially increases and then decreases. Maximum overvoltage occurs in
`neutral or mild alkaline conditions [3-6]. Anodic polarization [7]
`decreases as pH value increases.
`
`66
`
`

`

`Amount of bubbles, %
`
`Diameter of bubbles, μm
`
`Fig. 1. Effect of electrode material on the size of electrolytic bubbles.
`Current density 25 ma/cm2, electrode diameter 0.4 mm, temperature 20°. pH 2 (a),
`7 (b) and 12 (c)
`
`Order of metals in this area in terms of bubble size corresponds to
`their order in terms of overvoltage [8, 11]. In alkaline conditions (Fig.
`1, c) the size of hydrogen bubbles is to a lesser extent affected by the
`cathode material, average diameter of bubbles varies from 15 to 30 μm.
`In neutral conditions (Fig. 1, b) the size of produced hydrogen bubbles
`is virtually not affected by the cathode material. Average diameter of
`bubbles varies from 15 to 20 μm.
`The minimum size of oxygen bubbles formed on the platinum
`electrode (other materials were not used for anodes) is observed in acid
`conditions (25 μm). The size of bubbles increases when shifting to
`neutral and then to alkaline conditions (30 and 55 μm respectively).
`
`Fig. 2. Variation of the size of bubbles with respect to the diameter of
`electrode.
`Material – platinum, current density 25 ma/cm2, temperature 20°, pH 12..
`Electrode diameter, mm: 0.2 (1), 0.5 (2) and 1(3)
`
`Diameter of bubbles, μm
`
`Amount of bubbles, %
`
`67
`
`Dependence of size of electrolytic gas bubbles on the factors affecting
`the overvoltage of oxygen and hydrogen release was studied by high speed
`shooting method, using SKS-16 movie camera (800 -1200 fps).
`Size of bubbles was measured using MPS-1 microscope. The
`electrodes used included platinum, copper, tin, silver, stainless steel wire
`and graphite bar, dia. 0.2 to 1.0 mm. Current density varied from 10 to 40
`ma/cm2, temperature varied from 5 to 75°. The required pH was achieved
`by using H2SO4, NaOH and Na2SO4 solutions. In the course of analysis of
`the effect produced by a single variable, all other variables remained
`unchanged. The electrodes were prepared as follows: thorough mechanical
`polishing, chemical degreasing with strong organic solvents, rinsing in
`distilled water, 1.5-2 h electrochemical cleaning.
`Fig. 1 shows variation of the size of bubbles with respect to pH value
`and electrode material. Variation of the size of bubbles is inversely related
`to the overvoltage variation, i.e. hydrogen bubbles are larger in acid
`conditions (Fig. 1, а) compared to neutral (b) and alkali (c) conditions. The
`smallest bubbles are observed in neutral conditions (for all cathode
`materials) and alkali conditions (for copper and tin), i.e. pH values
`corresponding to the maximum hydrogen overvoltage.
`The effect of cathode material on the size of produced bubbles is
`especially pronounced in acid conditions. Average diameter of bubbles
`varies from 20 to 70 μm.
`
`5*
`
`

`

`Amount of bubbles, %
`
`Amount of bubbles, %
`
`Diameter of bubbles, μm
`
`Diameter of bubbles, μm
`
`Fig. 3. Effect of current density on the size of bubbles
`Material – platinum, electrode diameter 0.2 mm, рН 12, temperature 20°. Current
`density, ma/cm2: 12 (1), 25 (2) and 40 (3)
`
`Fig. 4. Effect of temperature on the size of hydrogen bubbles.
`Material – platinum, electrode diameter 0.5 mm, current density 25 ma/cm2, рН 7.
`Temperature °С. 5 (1), 25 (2), 55 (3) and 75 (4)
`
`Fig. 2 shows the variation of size of the produced bubbles with
`respect to the electrode surface curvature at pH 12. As electrode diameter
`increases, average diameter of the hydrogen and oxygen bubbles
`increases only slightly. Noticeable increase of variation of diameters of
`bubbles is also observed. With 0.2 mm dia. electrode, at pH12, diameter
`of the major portion of bubbles ranges from 15 to 40 μm, whereas with 1
`mm dia. electrode the variation of diameter extends to 60 μm. Diameter
`of oxygen bubbles ranges from 40 to 60 μm (with 0.2 mm dia. electrode)
`and from 30 to 90 μm (1 mm dia. electrode).
`Fig. 3 shows the effect of current density on the average diameter of
`bubbles. Within the specified shift of current density (10 to 40 ma/cm2),
`average diameter of bubbles demonstrates only slight change in acid and
`neutral conditions. In alkaline conditions, average diameter of bubbles
`varies from 15 to 30 μm; as current density increases, the variation of
`diameter of bubbles increases as well, especially for oxygen in alkaline
`conditions*.
`Fig. 4 shows the distribution of diameter of bubbles against
`temperature. Within the temperature interval under consideration, it was
`found that as the temperature increases, average diameter of hydrogen
`bubbles shifts towards increasing as well. Thus, the minimum diameter
`of bubbles (30 μm) is observed at 5°, while the maximum diameter (50
`μm) is observed at 75°.
`
`* The effect of current density and electrode surface curvature is not
`significant in neutral and acid conditions; therefore the corresponding
`data is not provided.
`
`Compared with the nature of variation of overvoltage with respect
`to temperature in neutral conditions [10], it was found that though
`temperature only slightly affects the overvoltage, the effect of
`temperature on the size of produced bubbles within this interval is quite
`significant.
`Therefore, electrode diameter and current density only slightly affect
`the size of hydrogen and oxygen bubbles within the interval under
`consideration. Temperature dependence is more significant, but рН value
`of media and electrode material produce the maximum effect on the size
`of bubbles forming in the course of electrolytic decomposition of water.
`
`References
`1. B.N. Kabanov, A.N. Frumkin. Journal of Physical Chemistry,
`4, 1933, 539
`2. A.N. Frumkin. Kinetics of Electrode Processes. Moscow, 1952
`3. I. E. Bagotsky, I. E. Yablochkova. Journal of Physical
`Chemistry, 23, 1949, 413.
`4. K. Sabo, I. A. Bagotskaya. Proceedings of the USSR Academy
`of Sciences, No.2, 1964, 156.
`5. O. L. Kabanova, L.A. Doronin, O. O. Semetyunenko.
`Electrical Chemistry, 7, No. 9, 1971, 1390.
`6. P. P. Lukovtsev, S.D. Levina, A.N. Frumkin. Journal of
`Physical Chemistry, 13, 1939, 916.
`7. N. T. Bardina, L.I. Krishtalik. Electrical Chemistry, 2, No. 2,
`1966, 216.
`8. N. E. Khomutov. Journal of Physical Chemistry, 39, 2, 1965.
`9. I. Nenov. Proceedings of the Academy of Sciences of Bulgaria,
`18, No. 5, 1965, 465.
`10. V.F. Vladimirova, O. A. Tataev, G. G. Dadasheva. Collection
`of papers: Scientific Reports, published by the University of
`Dagestan, issue No.7, 1971.
`11. Yu. Yu. Lurye. Analytical Chemistry Reference Book.
`Moscow, 1971, p. 412.
`68
`
`