February 9, 1917.

THE COLLIERY GUARDIAN.

291

THE USE OF COAL ASH IN SAND
STOWAGE/

By C. Toombs.

Some time ago it was decided to extend underground
sand-filling operations at the East Band Proprietary
Mines, by utilising the sand from one of the dumps for
that purpose. A trial run was made by the ordinary
water-borne methods, but troubles due to its extreme
acidity arose, which would be too costly to deal
with by means of ordinary neutralising agents, such
as lime or crude soda carbonate.

One sample of the water carrying this sand under-
ground gave a total available acidity of 1’71 per cent,
sulphuric acid, requiring 160 lb. air-slaked lime
containing 60 per cent, calcium oxide per 1,000 gallons.
(By total available acidity is meant sulphuric acid +
ferrous and ferric sulphates.)

To overcome this difficulty and large expense, a novel
scheme was suggested, which was to mix ordinary ash
from the ash dumps, with the acid sand, and send both
underground as filler.

Most Transvaal coals when burnt give an ash con-
taining lime, the amount of which varies with the ash
percentage. When the ash is fresh from the furnaces,
the lime is present in the form of calcium oxide, samples
giving from 25 lb. to 40 lb. calcium oxide per ton of ash,
by sugar solution test, being found at one of the boiler
plants. At another plant where mechanical stokers are
installed and combustion of the coal is almost complete,
the lime was found to have combined with silica, forming a
clinker which had practically no acid-neutralising powers.

After the ash has been exposed to the weather on the
dump for a short time, the calcium oxide is all converted
into carbonate, and tests by the sugar method on com-
paratively new ash, give very little calcium oxide.

A short account of the experimental work carried out
before the scheme was put into operation may be of
interest.

Ash.

Several samples of ash from the various ash dumps
were obtained and their acid-neutralising powers tested
as follows 1,000 gm. of ash was stirred up for a couple
of minutes with 2,u00 cc. semi-normal acid, when some
of the acid was drawn off and tested, the loss in
strength of the acid being calculated into pounds of
calcium oxide per ton of ash.

The test was rough, but sufficiently accurate for the
purpose required. The following yields of CaO per ton
were obtained:—A, 48 lb.; B, 58 lb.; C, 33 lb.; D, 13 lb.;
E, 2 lb.; F, 12 lb. Sample D was a badly burnt coal.
Sample E, new ash from mechanical stokers. Sample
F from ash dump from same mechanical stokers as E.
The higher result compared with E may be due to
disintegration of calcium silicate on exposure to weather.

Sand.

Several samples of sand were taken from a cutting in
the dump, and their lime-consuming powers determined.
The lime-consuming substances in the old dump sand
are sulphuric acid, ferric and ferrous sulphates, varying
in proportion and in relation to one another according
to whether the sample was taken deep or near the
surface. An average of several samples, calculating the
iron salts as sulphuric acid, gave a total acidity of about
IT per cent., requiring about 20 lb. air-slaked lime
containing 60 per cent. CaO per ton of sand On a
basis of 1,000 tons of sand per day, 10 tons air-slaked
lime, costing £25, would be required to give a neutral
overflow and drainage water.

Sand and Ash.

From the above determinations, calculations for a
neutral mixture of sand and ash were made, and a few
experiments carried out with 50 lb. lots of sand. The
quantities of sand and ash were weighed and thoroughly
mixed with water in a small tank, the water was drawn
off and leached through several times, then tested. It
was found to be neutral, or slightly alkaline to methyl
orange, pointing to the elimination of free sulphuric
acid. It had an acid reaction with phenolptbalein, and
on examination was found to be free from ferric
sulphate, but contained ferrous sulphate in abundance.
Further experiments were made with an increasing ratio
of ash to sand, but the ferrous sulphate was found to
remain unprecipitated. A further couple of experiments
with fresh ash from the furnaces proved more successful,
giving a water free from acid and salts of iron.
Knowing that the difference between the fresh ash and
that from the dump was, that in the new ash the lime
existed as oxide, but as carbonate in that from the
dump, the only theory one could establish was that
ferrous sulphate in solution was not precipitated by
calcium carbonate.

To prove if this theory was correct, further experi-
ments with made-up solutions containing sulphuric
acid, ferric and ferrous sulphates were done. Various
forms of calcium carbonate were tried—powdered lime-
stone, powdered calcite, and precipitated calcium
carbonate—the result in each case being the same,
sulphuric acid and ferric sulphate eliminated, ferrous
sulphate remaining. A long tube was filled with
granular pieces of very soft limestone, and the solution
passed through it repeatedly, the ferrous sulphate
remaining at the end of a considerable period. These
ferrous sulphate determinations were not quantitative,
but were made qualitatively to obtain sufficient knowledge
for the successful carrying out of the work in hand.

The conclusion that one must come to from these
experiments is that ferrous sulphate in solution does
not react with calcium carbonate, and that the use of
calcium carbonate for neutralising acid underground
waters will not achieve all that should be desired—
viz., the elimination of all acid and acid-producing
substances.

* The Journal of the Chemical, Metallurgical and Mining
Society of South Africa.

It may be mentioned that, some time ago, a sample
of very finely powdered limestone was submitted for
examination, with a view to use on underground waters.
The results obtained with it were excellent, but analysis
showed that it was not limestone, as it contained about
30 per cent, calcium oxide. A mixture of calcium
oxide and calcium carbonate would not be economical,
as the former, being soluble and more chemically active,
would react at once with the sulphuric acid and ferric
sulphare, leaving a large proportion of the carbonate
unused.

The fact that ferrous sulphate in solution does not
react with calcium carbonate was new to me, and several
chemists to whom the matter was referred said that
they would expect these substances to react, giving a
precipitate of ferrous carbonate. Dr. Moir explained
their non-reaction by saying that FeO as the base in
FeS04 was stronger than CaO as the base in CaCO3.

Following are the details of some of the experiments
made with mixtures of sand and ash :—

A.

San-1 requiring 21 ]b. lime per ton.

Ash from dump containing40 lb. CaC03 per ton, and CaO
0'7lb. per ton.

Mixture.

(a) 100 sand
20 ash

(0 100 sand
40 ash

(c)	100 sand

60 ash

(d)	100 sand

80 ash

(e)	100 s and
100 ash

Result.

C Free acid and ferric sulphate gone. Ferrous

1 sulphate left requiring 11 lb. lime per ton
j of sand.

L Saving in lime 101b. per ton of sand.

r Ferrous sulphate left requires 7flb. per
j ton sand.

(. Saving in lime 134 lb. per ton sand.

C Ferrous sulphate requires 5 lb. lime per ton
j of sand

L S wing in lime, 16 lb. per ton sand.

1 Further lime required is 2^ lb. per ton of
j sand.

(. Saving in lime, 184 lb. per t<m.

C Further lime required is 2? lb. per ton of
s sand.

t Saving in lime, 18^lb. per ton.

B.

Sand requiring 20 lb. lime per t<n.

Fresh ash containing 38 lb. CaO (by sugar test) per ton.
Mixture.	Result.

(a)	100 sand ( Drainings strongly alkaline. No iron left
100 ash ( in solution.

(b)	100 sand ( Drainings neutral, but contain ferrous

50 ash I sulphate.

(c)	100 sand ( Drainings just alkaline, no ferrous sul-

75 ash I phate.

^60 ash^ } Draining neutral, no ferrous sulphate.

Theoretically, 3 of ash should neutralise 9 of sand.

Actually, 3 of ash neutralised 5 of sand.

As a result of these experiments, and to obtain the
full value of the calcium carbonate in the ash, it was
suggested that the sand and ash be given as long a
contact with the water as possible, before the addition
of fresh lime for the neutralisation of the ferrous
sulphate.

The sand and ash mixture has been going underground,
however, for about six months, and has proved very
successful; much more successful than the laboratory
work would have led one to expect. The mixture makes
excellent filling, and the ash has a binding effect on the
sand, causing it to set very hard.

Following are the details of sand-filling with this
scheme in October :—

Old dump sand..........................

Ash from dump..........................

Lime...................................

Cost of lime .......j.......................

22,000 tons

2,200 „

13 „
<£32 10 0

From the utilitarian aspect we have achieved, in this
instance, the objective to which we should all aspire,
z.e., the development of a new and and more economical
method of working than the more obvious and costly
one. From the aesthetic standpoint we can credit our-
selves with the gradual removal of two of those
unsightly blemishes with which we are all too familiar—
sand dumps and ash dumps. The ash serves the
purpose of filling and binding, and the sand drains
very much more quickly when mixed with the ash:
settlement and subsequent reclamation of the pillars
taking place much more quickly. These are the principal
advantages from the practical point of view.

The British Electrical and Allied Manufacturers’ Associa-
tion.—-The annual report of the association states that it has
not been possible to supply the demands of established over-
seas trade connections, a considerable volume of trade in our
overseas dominions, ais well -as in neutral markets, being
diverted into the. hands of American, Japanese, and other
competing manufacturers. It is believed this lost ground
will be speedily regained when British manufacturers are
again in a position to re-enter it. The Australia Overseas
Committee has been successful not only in drawing up
general conditions of contract for electrical and engineering
work, but in obtaining for them the official, approval of the
Electrical Association of Australia. As that association
comprises in its membership many -of the important buying
engineers in the Commonwealth, including the engineers of
Government departments -and municipalities, there, is little
doubt that the conditions will in time become the recognised
standard for all public contracts. They have already been
adopted by several important public bodies. Progress is
being made in the same direction in India and South. Africa.
An energetic Overseas Committee, recently formed in Buenos
Ayres (Argentina), keeps in touch with representatives, in
Rio de Janeiro (Brazil). A small committee has -also just
been formed in Moscow (Russia), from which useful work is
anticipated. The experience gained with the overseas com-
mittees has shown the desirability of broadening the basis
of their constitution ; and steps are being taken to enlarge
their scope, and to make it possible to establish committees
in other countries. In -addition to. the work of the overseas
committees, useful reports have been received (and circu-
lated to members) from correspondents in Rio de Janeiro
(Brazil), Rosario (Argentina), China, France, various parts
of Australia and South Africa, etc. The number of members
on the register at December 31 was 144; 30 firms were
admitted to membership during the year, and one resigned.

MINE RESCUE APPARATUS AND
TRAINING.*

By James M. Stewart.

The writer is instructor at the Brazeau Station, and
having had training with the Draeger apparatus, is in a
position to make comparisons of this type and the
Fleuss Proto. A beginner is much impressed by the
helmet type, because of the ability to speak and
breathe naturally, but, being a practical man, he soon
realises, when working in the smoke chamber, that it is
impossible to fit tbe face mask tight enough to keep
out the smell and taste of smoke. This was the
experience of the writer and others in, training with
him at the time. In an attempt to keep out the taste
and smell of smoke when wearing the helmet, members
of the team used to inflate the pneumatic face cushion
so tightly that it frequently [resulted in giving them
severe headaches.

The dead space in tbe helmet accumulates CO2. The
percentage of the gas present in the helmet increases
during the time it is worn and no doubt accounts for
the difficulties members of teams found themselves
in at the end of the practice. For these reasons the
helmet type is now generally discarded. The introduc-
tion of the mouthpiece was a great improvement from
a safety point of a view. Whilst it necessitates the use
of goggles in the smoke chamber, which do not fit
very well, yet in an atmosphere of smoke the small
percentage that reaches the eyes is not sufficient to
injuriously affect the latter. There is no essential
difference in the type of the mouthpiece of the Draeger
and Fleuss Proto apparatus. A mouthpiece is less
comfortable to breathe through than a face mask,
which allows of breathing through the nose; and it is
impossible to speak distinctly through a mouthpiece,
but with a little practice and the aid of signs men can
make themselves understood. The mouthpiece at first
causes an uncomfortable flow of saliva and a dryness
in the throat. With usage the writer finds that this
discomfort becomes less as the wearer gets into the
habit of swallowing the saliva and so moistens the back
of the throat.

Both the Draeger and Fleuss Proto apparatus are
well constructed mechanically, and both types have their
strong advocates. The writer admits the advantages of
the good distribution of the caustic soda on the trays
of the Draeger, as this presents a large surface for
absorption of the CO2, and gives little or no resistance
to the passage of the air. He cannot see, however, any
advantage to be derived in changing the oxygen
cylinders and soda tins in the mine, as, in his opinion,
no man should be allowed to over-exert himself, but
should be withdrawn before his oxygen and soda supply
is exhausted.

Actual practice shows that there is a great deal of
difference in the quantity of oxygen required by different
persons when wearing the apparatus and doing similar
work. At the Brazeau Station, the Fleuss is set to
give 1'75 litres of oxygen per minute. Almost invariably
this has been found to be too much, and the relief valve
has to be repeatedly used; otherwise the men in training
suffer discomfort from the back pressure. If they are
not comfortable when training, men lose faith in the
apparatus, and would be nervous in the event of having
to use it under actual rescue conditions, becoming a
danger to themselves and their fellows in the mine.

The writer suggests that 14 litresof oxygen be supplied
to the men while in training, in order to do away with
the back pressure, prevent discomfort, and give the
wearer confidence in the apparatus. The apparatus
should be adjusted to two litres per minute for actual
rescue w?ork, this having been accepted as a standard in
most types of apparatus. Since, however, a man wearing
the apparatus can employ his energies so much as to
consume far more than two litres per minute, it is
absolutely necessary for the captain of a team to
see that a man is not called upon to over-exert himself.
The amount of muscular energy expended must be
made to correspond to the output of oxygen of the
apparatus, since the oxygen supply cannot be regulated
to suit calls on muscular energy as they may arise in
the mine. Cool, calculated work is what is likely to
make a man wearing the apparatus a success as a
member of a rescue party.

The caustic soda in stick form in the Fleuss type is
the most likely to give satisfaction. The sticks become
coated with carbonate and bi-carbonate of soda, which
prevent the proper absorption of C02. To prevent
this, the bag should be well shaken every five or ten
minutes. The shaking rubs the sticks against one
another and scrapes off the carbonate and bi-carbonate
of soda and presents a new surface for absorption of
CO2 ; at tbe same time this shaking opens up the mass
to the easy passage of air.

The writer advocates, even in practice, the use of
plugs of cotton wrool in the nostrils, in conjunction
with the nose clip ; and, in his opinion, there is room
for improvement on the type of nose clip used.

Can. Min. Inst. Bull.

By-Products from Lignite.—The possibilities of applying
the by-product principle of coke making to lignite hats
impressed the Geological Survey (U.S.A.), especially with
reference to. the brown lignites of North Dakota and Eastern
Montana, as well as to ,the.black lignites of Colorado. The
larger sizes of the residue are being sold in direct competition
with anthracite. The dust and fine sizes are being briquetted.
One of the oils, which is a by-product of the process, is
becoming increasingly popular for use in connection with
flotation.