M A R C H 1 9 4 0 ^ ^ ^ V O L U M E 30 No. 3 - Mines Magazine

112 The Mines Magazine
for March, 1940
and are also used in the mining operations,
where open cuts are used.^
Occasionally, one or more of the raw
materials are produced from underground
mines, hut generally at a
higher cost than hy open cut."
Quarrying or underground operations
depend on the dip of the beds,
thickness of the beds, daily tonnage
to be mined, drainage, and a multitude
of other factors. Each particular
deposit has its own characteristics
which present problems which
probably are not exactly duplicated in
another locality.
The individual raw materials are
crushed and sampled then sent to
storage bins from which they are
drawn in the amounts necessary for
correctly proportioning the mix. This
crushing and storage is generally a
part of the cement plant proper but
may be an individual and separate
operation if the cement plant purchases
a portion of its raw materials.
The plant proper should be located
as near the quarry as is feasible to cut
down transportation costs on the raw
materials. Fuel, a major item of expense
should be easily available.
Natural gas can be piped to any location
but transportation costs on coal
may be a deciding factor in the location
of the plant if natural gas is not
obtainable at reasonable cost.
The manufacture of cement in the
United States is a huge industry. The
value of the cement produced annually
leads all other non-metallic products
and about equals the combined value
of gold and zinc. In 1938, the United
States produced 105,357,000 barrels
of cement with a value of about
$154,000,000."'
Beneficiation
Cement is such a low priced product
that any beneficiation process must be
correspondingly low in cost and in
addition must offer advantages which
will offset the added cost of the
process.
Grinding the raw materials before
clinkering represents one of the major
cost items in any cement plant and
this cost is also one of the chief items
of any concentrating plant. Since the
raw materials must be ground in either
case the concentration can be effected
without any appreciable increase in
the cost of this item.
In general, limestone is the material
constituting the greatest tonnage so if
the analysis of the limestone can be
controlled by concentration it is much
easier to control the analysis of the
final mix than if one of the minor
constituents of the mix was concentrated.
Thus, we find that flotation
of limestone is coming into fairly wide
use in localities where suitable raw
limestone is becoming exhausted.
Limestone is being treated by flotation
at the plant of the Valley Forge
Cement Company, W^est Conshohocken,
Pennsylvania at the rate of
700 tons per day.^
The limestone containing mica,
quartz and iron oxides as impurities
is ground wet to 85%—200 mesh and
sent to a hydroseparator which makes
a separation between the very fine and
the coarser material. In addition, the
hydroseparator controls the tonnage
of feed to the flotation cells.
Oleic Acid is added to the cell feed
and is thoroughly conditioned in a
turbo-mixer ahead of the cells. Cresylic
Acid is added to the cells,to produce
frothing. Concentrates high in
calcium and low in silica, mica and
iron, join the fines from the hydroseparator
and the combined product
goes to a final thickener for dewatering.
The flow sheet permits great
flexibility in the control of the calcium
content of the final mixture of concentrates
and fines. Recovery of the
Calcium Carbonate is around 98%
based on concentrates plus hydroseparator
fines.
Several advantages to be derived
from the flotation of limestone:-for
cement manufacture are:^ A reduction
in the cost of mining because
selective mining is unnecessary. Dirty
or lean spots in the limestone beds can
be mined and sent to the milling plant
where the impurities are rejected.
Lower grade limestone in proximity
to marketing centers now becomes
available for cement manufacture
when treated by flotation, whereas,
such limestone was heretofore unsuitable.
This also increases the
available reserves of limestone for cement
manufacture at locations near
the marketing centers.
Costs of grinding the raw materials
are reduced because the quartz is rejected
at relatively coarser sizes. Since
quartz is much harder to grind than
limestone, hence more expensive, any
rejection of coarse quartz is bound to
result in lower grinding costs.
Saving in fuel results from the
elimination of coarse quartz, and mica
because lower temperatures may be
used to produce the desired chemical
reaction when these impurities are
absent.
Costs of grinding the clinker are
reduced because it commonly happens
that coarse quartz particles pass
through the kiln unchanged. The
elimination of these coarse quartz
particles results in lower grinding
costs on the burned clinker.
By producing a high-grade limestone
concentrate, a cement plant will
find it unnecessary to buy high-grade
limestone for their mix. These purchases
of high-grade limestone have
become almost prohibitive in cost at
many plants. The cement is improved
in quality because a mix is obtained
which permits an optimum proportion
of elements for combination in
the kiln at normal temperatures. This
results in better properties in the
finished product. Various types of cement
may be produced from a single
bed of limestone where a high-grade
limestone is produced which permits
blending with other materials to give
any desired cement depending on the
market.
By-products from the flotation of
the limestone may be recovered and
sold if the market warrants. As far
as is known this has not been done,
yet, but the possibility remains.
A few of the disadvantages inherent
to any concentration process give the
other side of the picture and may have
such weight as to negitate the advantages
to be derived from the process
:
The cost of the concentrating plant
represents a considerable investment
which may mean additional financing
in order to permit construction.
Amortization of this plant cost means
that every barrel of cement produced
must hear its part of the cost of the
installation.
Operating costs of the concentrating
plant must be absorbed into the
selling of the finished product.
Tailing losses of limestone must be
charged against the concentration process
and this is reflected in increased
mining costs per unit of limestone
produced as a finished product by the
concentrator.
Whether limestone processing by
flotation or other means of beneficiation
would be economically advantageous
is a problem which will vary with
every cement manufacturer. Careful
study of the individual problem and
the balancing of advantages against
disadvantages is necessary to arrive at
any conclusion.
Other plants where limestone is
processed by flotation are reported in
Argentina, South Africa, France and
Finland.^
The trend in the cement industry
is beginning to turn toward the concentration
of limestone and as far as
can be predicted the trend is becoming
stronger and more widespread year by
year.
(Continued on page 140)
N B C
presents
MINES MEN
i n
"MAN AND MINERALS"
Over the Air - Feb. 18, 1940
T y p e of Gasoline for Automobiles
Announcer: The Colorado School of
Mines presents "Man and Minerals."
Announcer: Hei'e we are again,
comfortably seated in the office of
Doctor Arthur S. Adams, in
Golden, Colorado, for another
fifteen minutes with Doctor Adams,
Professor Robert Baxter of the
Chemistrj' Department, and Coach
John Mason, an athletic director
who is also interested in the scientific
and technical development of
his school. These programs are
written and presented by the faculty
and student body of the school in
co-operation with the Rocky Mountain
Radio Council. The discussion
is on the subject of tj^pes of
gasoline for automobiles. Here
they are:
Coach: You know, Doc, that car of
mine is certainly running smoother
these days.
Adams: Weil, that's fine. What
caused the improvement?
Coach: You remember I was telling
you that Professor Baxter was talking
to me about getting the right
type of fuel—
Adains: And you followed his suggestion
?
Coach: I thought I would try him
out, and he certainly was right.
Adams: Well, Baxter was coming
over this afternoon for a visit. I
would like to hear what he has to
say—
Adams: Here he is now.
Baxter.
Come in,
Baxter: Hello, Doc. Hello, Coach.
Coach: Hello, Baxter, glad to see j'ou.
Adams: We were just talking about
3'ou. John says that your suggestions
helped him a lot in buying
gasoline.
Baxter: I'm glad to hear that I did
help you to buj'' the right gasoline.
Adams: Well, what are the factors involved
in buying gasoline? I read
and hear lots of advertising, but,
frankly, I am confused by the
various terms—high-octane rating,
high-test, etc. What do they each
mean?
Baxter: The best way to explain that
is to consider for a minute the operation
of your automobile engine.
Coach & Adams: Yes—?
Baxter: As you know, the gasoline is
drawn into a carburetor where it
is mixed with many times its
volume of air.
Coach: And the result is a mixture
that will burn.
Baxter: That's right. This mixture
is drawn into the cylinder and compressed.
Coach: How much is it compressed?
Baxter: Oh—to about a sixth or a
seventh of its original volume.
Adams: That makes the pressure
about ninety pounds to the square
inch, doesn't it?
Baxter: Yes, more or less, depending
on the original atmospheric pressure
and on the compression ratio.
Coach: Does the compression ratio
have anything to do with the engine
efficiency ?
Baxter: Yes, the engine is more
efl!icient the greater the compression,
so modern design has gone to greater
and greater compression ratio.
Coach: The spark explodes the
compressed fuel mixture, doesn't it?
Baxter: Yes, and it's a peculiar thing
that the greater compression has the
disadvantage of causing the fuel to
burn so fast that it causes a distinct
knock.
Ada?ns: What are the disadvantages
of this knock?
Baxter: It puts a shock on the engine
parts, and equally important, it
makes the driver think that something
is wrong with his car.
Adams: Nobody likes to feel that he
is driving a wreck, huh ?
Baxter: No, indeed.
Coach: What was the stuif in the
gasoline you told me to buy that
made ray car quit knocking?
Baxter: Ethyl fluid and a generally
superior original gasoline, which together
gave it a higher octane number.