Note: Descriptions are shown in the official language in which they were submitted.
rhis invention relates to a coal flotation reagent for use in froth
flotation cleaning of coal.
Proth flotation is a process commonly used for cleaning fine coal
in which the caal, with the aid of a reagent, becomes attached to alr bubbles
in a liquid medium and floats as a froth. When a coal mining slurry in water
containing a small amount of certain oils or reagents is agitated, the coal
particles are preferentially~wetted ay~the otl or the reagent and attach them-
s.elves to fine air bubBles which are introduced into the suspension. The
bubbles float the coal particles to the surface and form with them, usually with
the help of other reagents, a froth which is skimmed off. The mineral matter,
known as "slime", "tailings" or "refuse" is wetted by the water and remains
in the slurryD The separation is practlcally independent of the relative speciflc
gravltles of the coal and mlneral matter. The efEiclency of removal of mlneral
matter depends on such factors as partlcle size, interstratiflcatlon of mineral
matter with the coal, concentration of sllme, and proportions of coal, water
and oil. Roth flotation is adapted to cleanlng the Eine sizes of coal, par-
ticularly minus 48 mesh, although in some cases, coal up to 1/8-inch size has
been cleaned by froth flotation.
The process ls carried out ln a serles of water-fllled cells, lnto
the first of which are fed the coal and the proper volumes of reagents, usually
about 0.1 to 2.5 pounds per ton of coal. Alr is blown into the bottom through
a nozzle or dis;tributor which divides it lnto fine bubbles. The froth of coal
and oil overflows into a trough at one side, and the refuse from the bottom
is pumped to the second cell. Here the operation is repeated and continued
in each succeeding cell of the series. The slime from the last cell is
discarded The oils and reagents used to collect and wet the coal particles
include higher b.oilin~ petroleum fractions, city acids, and soaps. Cresylic
acid, pine oil or alcohols are commonly~added to the cells to produce frothing.
It has now Been discovered that an improved coal flotation reagent
is provided Br combining one or more fr~thers, such as blends of alcoholsJ
methylisobuty~l carainol or pine oil, with a hydrocarbon liquid such as fuel
oil as a collector and one or mqre hydrocarbon liquid disper$ants, i.c., a
material which will emulsify the hydrocarbon liquid when the dispersant or the
reagent is added to the aqueous slurry of coal. The use of this dispersant
results in an increase in coal recovery during the froth flotatian cleaning
of coal.
yarious hydrocarbon liquid dispersants may be used in the practice
of this invention. These materials are generally water-soluble surface active
materials; which have an IILB value greater than 7 and which will form oil-in-
water emulsions. materials such as ethoxylated alkylphenols, dialkylsulfosuc-
cinates and other ethoxylated alcohols, etc. may be used as the dispersants of
this invention. Preferred materials include IGEPAL D~-530*, a dialkylphen-
oxypolyethrleneoxy ethanol, ethoxylated nonylphenols and dioct~lsulfosuccinates.
The amounts of each ingredient included in the coal flotation reagent
may vary widely and will depend to some extent on the type of coal. Thus, the
presence of ashable minerals, especially clays and shales, in the coal reduce
the natural hydrophobicity of coal. Therefore, the increase in feed ash will
increase the collector (fuel oil) demand. The rank of coal may be defined as
the extent to which the organic material has matured during geological time
in going frQm peat to anthracite The maturing process is known variously as
coalif~cation, me*amorphism, or carbonification. one of the changes occuring
with the carbonification of the coal is the increase in its hydrophobicitr,
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Examining the relationship between the rank of the coal and the optimum ratio
of emulsified fuel awl to the frother it became obvious that the higher the
rank of the coal the more rother and the less Euel oil is required. Going
down in the rank (more precisely going up in the percent volatiles, as the
~tu content will not directly influence the hydrophobicity), the natural
flotability is lower and additional collector is needed. Generally, the
flotation reagent will comprise from about 95 to 20% by weight of frother,
preferably from about ~0 to 40% by weight; from about 5 to 80% by weight of
fuel oil, preferably rom about 5 to 60% by weight; and from about 2 to 20%
by weight of fuel oil dispersant, preferably about 3 to 9% by weight.
The coal flotation reagent of this invention is preferably added to
the water filled cells to which the coal is fed in an amount of from about
0.05 to S lbs. per ton of coal feed and more preferably Erom abo~lt 0.2 -to
2 lb. per ton of feed. Air is blown into the cell and the froth of coal recovered
in a conventional manner.
The following examples illustrate this invention:
Example 1
A coal flotation reagent was prepared by admixing 65% by weight of
fuel ail #l, 30% by weight of a commercially available frother which is a blend
of C6 to C8 alcohols, and 5% by weight of dioctylsulfosuccinate. The resultant
composition is referred to hereinafter as Product 1.
Exa
A coal flotation reagent was prepared by mlxing together 51% by weight
of #2 fuel oil, 36% by weight of a commercially available frother which is a
blend of C6 to C8 alcohols, ~.0% by welght of I~EPAL DM-530* and ~.0% by weight
of pine oil. This material is hereinafter referred to as Product 2.
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Example 3
Another coal flotation reagent was prepared by-mixing together
46.8% by weight of #2 fuel oil, 3804% by weight of a blend of C6 to C8 alcohols,
~.6% by weight of pine oil, 20G% by weight of IGEPAL D~-530 and 2.6% by weight
of IGEPAL DM-710*. This product is hereinafter referred to as Product 3.
xample 4
A coal flotation reagent useful in the flotation of low to medium
volatile type coals was prepared by mixing together the following ingredients:
80% by weight ox C6 - C8 alcohols, 3.0% by weight of dioctylsulfosuccinate,
and 17.~% by weight of #2 fuel oil. This material is hereinafter referred to
as Product 4.
Example 5
About 0.9 :I.bs. of the coal flotation reagent obta:in~d in example 1,
Product 1, per ton of coal feed was added to a coal flotat.ion cell. The
characteristics of the feed and the amount and characteristics of the recovered
product are set forth in Table I. For purposes of comparison, another run was
conducted with conventional flotation reagents added separately comprising 0.3
lb. per ton of coal feed of methylisobutylcarbinol (MIBC) and 1.3 lbs. per
ton of coal feed of fuel oil #2. The results for this run are also set forth
in Table I. It will be seen that the coal recovery increased from 49.05% for
the conventional flotation reagent to 76.41% with Product l. The yield of the
float product increased from 34.83% to 57.75%. This means that out of every
100 tons of coal processed, there would be obtained 22.92 more tons of coal of
the same quality using Product lu In spite of dewatering 22D92% more coal, the
moisture of the clean coal filter cake obtained with Product l dropped to
35.4% H20 from the value of ~0.1% H20 average of two samples) obtained with the
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conventional Elotation reagent. Part o:E the reason for the improved filtrationis the increased amount of +65 mesh particles floatlng when Product l was fed
to the flotation circuit. With the conventional flotation agent, the ~65 mesh
fraction was 10.2% and with Product 1, the +65 mesh fraction rose to 19.1%.
TABLE I
MIBC PLUS
ITEM PUEL OIL ~2 PRODUCT 1
.. ..
Ash Analysis
Feed 34.57% Ash 30.72% Ash
Float 7.85% Ash 8.33% Ash
Tails 48O85% Ash 61.32% Ash
C/C Filter* A - 8.09% Ash 9.30% Ash
C - 8.98% Ash
C/C Filter Cake* A - 38.7% H O 35.4% H O
I-- -- - 2 2
moisture C - 41.5% H O
Float Yield 34.83% 57.75%
Coal Recovery 49.05% 76.41%
~2a~2,~
SCREEN ANALYSIS_OF FLOUT PRODUCTS
SIZE DISTRIBUTlON ASH CONTENTASH DISTRIBUTION
Particle SizeMIBC * Product MI~C ~roductMIBC Product
Fuel Oil 1 Fuel Oil 1 Fuel Oil
+ 65 Mesh 10.2 l9.1 4.69 4.89 6.0 11.6
* 425-65 Mesh35.6 39O6 5.69 6.99 25.6 34.3
325 Mesh 5402 41.3 9.~8 10.56 68.4 54.1
Float Product100.0 100.0 7.91 80 06 100.0 100.0
* Sample A waken before Product l treatment. Sample C
was cut after Product 1 treatment was discontinued.
Example 6
The process of Example 5 was repeated at another coal plant. For
purposes of comparison, another run was conducted using an equivalent amount
of a conventional coal flotation reagent, CENTFROTII-R* which comprises a mixture
of fuel oll and alkoxypropylene glycol available in the United States from
Century ilulburt Co. The results are set forth in Table Il. It will be seen
that the coal recovery with CENTFROTH-R* reagent was only 16.09% whereas with
an equivalent amount of Product 1, the recovery increased more than five times
to 89.40%. The yield of the clean coal product increased from 9.40% with
CENTFROTH-R* to 54.07% with Product 1. This means that the plant would realize
an additional 44.67 tons of saleable coal from every 100 tons processed. Even
though the clean coal dewatering gird centrifuges were handling more than five
times the amount of coal as with the CENTFROTH-R* reagent, the moisture of the
final product decreased from 25.5% H2O with CENTFROTH-R to 22.2% moisture with
Product 1. The amount of ~65 mesh particles floated increased from 12.8%
with CENTFROTH-R* to 42,3% with Product 1.
.
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TABLE. I
ITEM CENTPROT~I R ;PRODUCT 1
Ash analysis
Feed 49.2Q% Ash 47.55% Ash
Float 13~06% Ash 13.28% Ash
Tails 52.~5% Ash 37.8~% Ash
Bird 9.90% Ash 11.85% Ash
Pond 56014% Ash 61.99% Ash
Dewatering Centri- 25.5% H2O 22.2% H O
fuge Cake Moisture 2
Float Yield 9.40% 54O07%
Coal Recovery 16.09% 89.40%
SCREEN ANALYSIS OF FLOAT PRODUCTS
SIZE DISTRIBUTION ASII CONTENT AS~II)ISTRIBUIION
Particle SizeCentri- Product Centri- Product Centri- Product
froth 1 froth 1 froth
65 Mesh 12.8 4203 5.09 7.20 5.0 23.6
325-65 Mesh42~5 3203 7.69 10.97 25.1 27.4
- 325 Mesh 44.7 25.5 20.40 24D80 69.1 49.0
Float Product100.0 100.0 13.04 12.91100.0 100.0
In the abo-ve table, the term "bird" refers to a bird or dewatering
centrifuge "feed" is the orig.inal material going through the flotation cell,
"float" is the clean coal recovered from the process, "tails" are the waste
materials recovered and:"p~nd" refers to a settling pond of tailings.
2~3
The material of Example 2 product 2) when tested at a level of
a pound per ton of coal gave a 79O5% by weight clean coal recovery in laboratory
studies. At a level of 0.8 pound per ton, an 84% by weight recovery was obtained.
In contrast, a frother material consisting of 0.3 pounds per ton of MIBC and
one pound per ton of #2 fuel oil gave only a 78% recovery.
Example 8
Rroduct 3 when tested on a coal feed at a level of 0.6 pound per
ton yielded an 84.7% by weight recovery. In contrast, 0.5 pound per ton of
~IBC along with 1.5 pounds per ton of #2 fuel oil gave the same recovery level.
Three tenths pound per ton of MIBC and 1.5 pounds per ton of #2 fuel oil gave
a recovery of only 81.2% by weight on the coal tested.
Example 9
Product 4 was tested at a feed rate of 4~ cc per minute to a coal
flotation cell. A recovery of 85.5% by weight was obtained. Using a com-
mercially available material as the frother, Aerofroth 76*, a material available
from the American Cyanimid Company and believed to be a C4 - C8 alcohol mixture,
in combination with an equal weight percent of #l fuel oil at the same feed
rate, only 74.6% by weight recovery was obtained.
Although the invention has been described in considerable detail
with specific reference to certain advantageous embodiments thereof, variations
and modifications can be made without departing from the scope of the invention
as described in the specification and defined in the appended claims.
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