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Two-Liquid Flotation for the Recovery of Ultrafine Particles
Mohit Gupta, Kaiwu Huang, Nathan, Youmans, Biao Li, Aaron Noble and Roe-Hoan Yoon
Center for Advanced Separation Technologies, Virginia Tech, Blacksburg, VA
ABSTRACT: Lai and Fuesternau (1968) used an oil (dodecane) rather than air bubbles to recover submicronic
particles in a laboratory flotation cell. The process, known as two-liquid flotation (TLF), is more efficient than
flotation, as oil drops form nearly twice as large contact angles as air bubbles can on hydrophobic mineral
surfaces. In the present work, we used low-boiling oils to recover spent oils for recycling purposes. The process
has no lower particle size limit and produces high-grade concentrates due to the special provisions to eliminate
the entrainment and entrapment problems, Also, TLF products practically dry due to the dewatering-by-
displacement (DbD) mechanism (US patent No. 5,458,786, 1995). The modified TLF process has been tested
successfully to produce ultraclean coal with 1% ash from coal waste and high-grade copper concentrates from
cleaner-scavenger tails (CSTs). The benefits of using the new TLF process have been determined by simulating
a porphyry copper flotation plant using a flotation model that can predict both recovery and grade.
INTRODUCTION
In 1905, Sulman and Picard were awarded a U.S. patent
(No. 793,808), which described a method of using air bub-
bles for flotation. This simple method was the forefather
of the modern froth flotation technology, which contrib-
uted so much to the minerals industry. Practically all metals
humans use today are being produced by flotation, and it
is still recognized as the best available method of separating
mineral fines. In flotation, air bubbles are used to selectively
collect hydrophobic particles on the surface, while previous
inventors used oil drops (Haynes, 1860 Everson 1885) and
CO2 bubbles (Bessel, 1886 Potter, 1902) for flotation.
Despite its successes and continued use in industry, flo-
tation has two serious limitations: i) a narrow particle size
range of ~20–150 µm for effective flotation, and ii) poor
selectivity with fine particles due to entrainment. To address
the latter issue, column flotation is widely used to wash the
froth with fresh water to remove entrained particles. Fine
particles below ~20 µm have low collision frequencies and
hence give rise to slow kinetics, resulting in low recoveries.
In a flotation circuit, much of the ultrafine particles report
to the cleaner scavenger tails (CSTs). Therefore, they are
circulated back to the rougher flotation banks as circulat-
ing loads (CLs) to give the slow-floating particles additional
retention times for recovery. However, a CL can substan-
tially reduce throughput as the particles in a CST suffer
from low flotation rates due to small particle size and poor
liberation characteristics despite the small particle sizes. On
the other hand, an open circuit configuration entails loss of
recovery (Gupta, et al., 2023).
Sivamohan (1990) reviewed various methods of recov-
ering very fine particles in mineral processing in general,
which include i) surface-based methods, ii) magnetic and
electrostatic methods, and iii) gravity concentration. Of
these, the first group is considered most promising, sim-
ply because surface property gains its importance with
decreasing particle size (dp) as dp–2, while gravity loses
its importance as dp–3. In these regards, it is not surpris-
ing that flotation has been used in the minerals industry
as the primary method of separating fine particles. With
Two-Liquid Flotation for the Recovery of Ultrafine Particles
Mohit Gupta, Kaiwu Huang, Nathan, Youmans, Biao Li, Aaron Noble and Roe-Hoan Yoon
Center for Advanced Separation Technologies, Virginia Tech, Blacksburg, VA
ABSTRACT: Lai and Fuesternau (1968) used an oil (dodecane) rather than air bubbles to recover submicronic
particles in a laboratory flotation cell. The process, known as two-liquid flotation (TLF), is more efficient than
flotation, as oil drops form nearly twice as large contact angles as air bubbles can on hydrophobic mineral
surfaces. In the present work, we used low-boiling oils to recover spent oils for recycling purposes. The process
has no lower particle size limit and produces high-grade concentrates due to the special provisions to eliminate
the entrainment and entrapment problems, Also, TLF products practically dry due to the dewatering-by-
displacement (DbD) mechanism (US patent No. 5,458,786, 1995). The modified TLF process has been tested
successfully to produce ultraclean coal with 1% ash from coal waste and high-grade copper concentrates from
cleaner-scavenger tails (CSTs). The benefits of using the new TLF process have been determined by simulating
a porphyry copper flotation plant using a flotation model that can predict both recovery and grade.
INTRODUCTION
In 1905, Sulman and Picard were awarded a U.S. patent
(No. 793,808), which described a method of using air bub-
bles for flotation. This simple method was the forefather
of the modern froth flotation technology, which contrib-
uted so much to the minerals industry. Practically all metals
humans use today are being produced by flotation, and it
is still recognized as the best available method of separating
mineral fines. In flotation, air bubbles are used to selectively
collect hydrophobic particles on the surface, while previous
inventors used oil drops (Haynes, 1860 Everson 1885) and
CO2 bubbles (Bessel, 1886 Potter, 1902) for flotation.
Despite its successes and continued use in industry, flo-
tation has two serious limitations: i) a narrow particle size
range of ~20–150 µm for effective flotation, and ii) poor
selectivity with fine particles due to entrainment. To address
the latter issue, column flotation is widely used to wash the
froth with fresh water to remove entrained particles. Fine
particles below ~20 µm have low collision frequencies and
hence give rise to slow kinetics, resulting in low recoveries.
In a flotation circuit, much of the ultrafine particles report
to the cleaner scavenger tails (CSTs). Therefore, they are
circulated back to the rougher flotation banks as circulat-
ing loads (CLs) to give the slow-floating particles additional
retention times for recovery. However, a CL can substan-
tially reduce throughput as the particles in a CST suffer
from low flotation rates due to small particle size and poor
liberation characteristics despite the small particle sizes. On
the other hand, an open circuit configuration entails loss of
recovery (Gupta, et al., 2023).
Sivamohan (1990) reviewed various methods of recov-
ering very fine particles in mineral processing in general,
which include i) surface-based methods, ii) magnetic and
electrostatic methods, and iii) gravity concentration. Of
these, the first group is considered most promising, sim-
ply because surface property gains its importance with
decreasing particle size (dp) as dp–2, while gravity loses
its importance as dp–3. In these regards, it is not surpris-
ing that flotation has been used in the minerals industry
as the primary method of separating fine particles. With