Year: 1886

page_text: I ALEXANDER BOBROWNICKI of 05 Gracechurch Street in the City of London,
Chemist do hereby declare the nature of this invention to be as follows:-
The object of this invention is to reduce phosphoretic slag, such as that obtained
from the Gilchrist-Thomas process of purifying iron, to a state that will admit of
its being used as a fertilizer.
To this end I reduce the slag to powder, and subject it to the action of a
re-agent in the presence of heat, whereby it is brought into a state assimilable by
plants. I have found that this result is obtainable by the use of one or other of
several re-agenta. Thus, I take the powdered slag, moisten it with water, and
treat the same with concentrated sulphuric acid, stirring the materials to produce
an intimate admixture, while at the same time water or steam is added in the
proper proportion for supplying the requisite water of combination. The addition
of this water also creates the requisite heat for setting up the required re-action.
Or, in place of the concentrated sulphuric acid, I may use soluble bi-sulphates,
or soluble acid sulphates, which may readily be obtained as residual or waste
products.
Again, the conversion of the slag may be economically effected by mixing it
with chloride of sodium in a dry state, or as a saturated solution, and adding
thereto sulphuric, nitric, or other acid, capable of decomposing the chloride of
sodium and generating the nascent chlorine.
It should be remarked, that when the reaction is proceeding satisfactorily, the
silicate contained in the slag is brought to a gelatinous state, and that ultimately
the whole product is reduced to powder, when the proper proportion of water has
been employed.
The conversion of the slag may be carried out in wooden or other vessels, either
open or closed, and the heat required for effecting the reaction, when not derivable
from the reaction, may be obtained by the use of steam or hot air.
In the several examples above given, the sulphur contained in the slag is
oxidized, and rendered useful, instead of being driven off, as in previous modes of
treating the slag, and the phosphoretic elements are converted into phosphoric acid.

page_text: I, ALEXANDER BOBROWNICKI of 65 Gracechurch Street in the City of London,
Chemist do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
$
.
The object of this invention is to reduce "Phosphoretic " (phosphorous) slag, such
as that obtained in the Gilchrist-Thomas process of purifying iron, to a state
which will admit of its being used as a fertilizer, that is to say, its reduction from
a strongly alkaline condition into a neutral product, in which various phosphates
will be produced, sulphurous impurities destroyed or separated, and from which
metallic salts will also be eliminated."
The reasons for this treatment are :-
(1) That the slag, in its raw state (phosphorous slag), is not fertilizing, as
it contains many noxious substances, such as sulphide of iron and calcium, but
does not contain tri-basio phosphoric acid in the condition in which the latter
exists in plants, although the presence of such phosphoric acid may be manifested
by analysis, being formed by such analytical process.
(2) That the phosphorous slag, being strongly alkaline, acts upon cultivated soil
like any other fixed base, driving therefrom the stored ammonia, thus stimulating
the vegetation at first, but ultimately driving out from the soil this most essential
substance, and also rendering the soil. sterile through impurities contained in
the slag.
(3) That the phosphorous slag has a remarkable reductive power, similar to that
of hydrogen, upon sulphuric acid.
According to my invention, I pulverize the slag, and subject it to the reaction of
a re-agent in the presence of atmospheric air and water, whereby phosphorous
matter is transformed into corresponding phosphates.. This conversion destroys
the alkalinity of the slag, and converts it into a neutral, or but slightly alkaline
product.
I have found that the transformation of phosphorous into neutral phosphatio
slag is effected by the use of one or other of several re-agents, the choice of which
is determined more from commercial than scientific reasons.
The re-agents which I employ are (1) sulphuric acid, (2) soluble bi-sulphates
(soluble acid sulphates) of soda, potash, or ammonia. It should, however, be
remarked, that when employing sulphuric acid as the re-agent, I avoid the use of
an excess of that acid, which would form sulphate of lime, a comparatively useless
product, and would dissolve out, together, all the phosphates and other metallic
salts contained in the slag, the phosphoric acid remaining in combination with the
metals, and being therefore wasted.
Of the re-agents above mentioned, I prefer, in general, any one of the soluble
bi-sulphates (soluble acid sulphates) of soda, potash, or ammonia, which may be
made for the purpose, or readily obtained as waste products, either in a dry or
liquid state. I give such materials a preference, for the following reasons:-
1st. That soluble bi-sulphates, (soluble acid sulphates) bring the raw slag into a
better state of disaggregation than could be obtained by subjecting it to the action
of mineral acids,

page_text: 2nd. That the raw alkaline slag, in becoming neutral, transforms the bi-sulphate
employed into a mono-sulphate, a valuable substance for use in the arts, such as
the manufacture of carbonate of soda, glass, etc.
3rd. That the mono-sulphate thus formed can be washed out economically from
such neutral product, and valuable salts may be recovered from the wash water by
crystallization.
4th. That the soluble bi-sulphates (such as the bi-sulphate of soda) dissolve, at
ordinary temperatures, certain phosphates obtained from phosphorous slag, and
that such phosphates are insoluble at a higher temperature (at about boiling
point), or will be precipitated, on standing, at ordinary temperatures.―This
provides a simple mode of separating and of purifying the product.
When using sulphuric acid as the re-agent, I mix water sparingly with the
phosphorous slag to be operated upon, say 30 parts of water with 100 parts, by
weight, of the slag, and then introduce thereto, from below, the air and commercial
sulphuric acid gradually, continuing the supply until sulphurous vapours cease to
be evolved. The proportion of sulphuric acid used will vary according to the
quality of the slag, and the air admitted must be sufficient to oxidize the
phosphorous matter and to drive off sulphurous fumes in a more or less oxidized
state. In general, the amount of acid will vary between 10 and 30 per cent., by
weight, of the slag treated.-The action of the sulphuric acid is to disaggregate the
constituents of the slag, and bring the same to a gelatinous state. This treatment
I carry on in a closed vessel, and the vapours driven off from the closed vessel
I collect for direct use, or to be further oxidized, so as to recover a portion of the
sulphuric acid used in the treatment of the slag.
By limiting the proportion of acid employed as above indicated, I avoid the
formation of an excess of sulphate of lime, and also avoid dissolving the metallic
compounds, all the phosphorous matter being now converted into phosphates, and
the phosphorous slag becoming a neutral phosphatic slag, without requiring the
addition of alkali, such as lime or soda or their carbonates-Some of these
phosphates are useless, or even detrimental, as fertilizers, but may be removed by
lixiation or other well known means. Thus, for example, I may mix and burn the
neutral product with lime, and by subjecting the same to a red heat, effect the
conversion of heavy metallic phosphates into phosphate of lime.
When employing a bi-sulphate as re-agent, I mix it intimately with powdered
slag, adding, at the same time, water or steam until sulphurous vapours cease to be
evolved. By this means I obtain a neutral product containing both the neutral
phosphatic slag and the re-agent in modified and useful conditions, which product,
if obtained from a slag rich in phosphorous matter, and containing no excess of
metallic impurities, may be used as a fertilizer, without further treatment, other
than the grinding and oxidizing hereafter mentioned. Or the neutral product may
be, when desired, separated into its chief constituent parts, by well known dry or
wet methods.
A crystalline bi-sulphate of soda (acid sulphate of soda), in a dry state, may be
intimately mixed with powdered slag in such proportion as to produce a neutral
compound. The dry mixture thus obtained should be immediately conveyed into
a tank supplied from below with about 25-30 parts of water to each 100 parts of
raw slag, the mixture being well aerated and stirred.-The contact of the water
with this powder excites a powerful reaction, which is manifested by a rise in
temperature and the emission of sulphurous vapours, and the necessary temperature
of about 200° F. is thereby maintained without difficulty during the time of
reaction.
When treating slag which contains much sulphur or other impurities capable of
producing noxious gases, it should be operated upon in a closed vessel or apparatus,
in order that the escaping vapours may be led off to a condenser, and ultimately
oxidized, or otherwise utilized.-Atmospheric air may be supplied to the vessel
containing the slag under treatment, from below, by means of a steam injector or
otherwise, in order to assist the oxidation and agitation of the semi-fluid mass, as

page_text: well as to clear it from gaseous matters.-The supply of water should be so
regulated, in the case of continuous work, that the mixture, which should be of
pale colour, and in a gelatinous condition, should flow readily out of the vessel, but
the mixture, when run off, should settle into a firm and uniform mass within a
few hours.
This mass, when dried either naturally or artifically, may be readily disintegrated
into a fine white or pale brown powder.-A slow or natural drying improves the
product. The colour of the product depends on the quality of the slag, of the
water, and of the re-agent employed; the amount of water in combination with
the phosphates of iron also affects the colour.-This will however indicate a
sufficient oxidation of the product.
It should be remarked that by this process the oxidation is uniform throughout
the mass, which is rendered porous by the crystallization therein of mono sulphate
with other salts, and by drying.
The grinding of the friable cake, with or without heated air, is sufficient to
complete the process of oxidation or formation of neutral phosphates. The same
effect is produced by separating the mono-sulphate from the neutral product, by
lixiviation, so that, in many instances, the washing may follow as soon as the
reaction of the bi-sulphate is accomplished.-This will be distinctly manifested by
the gelatinous condition of the wet mass, which should also be free from smell.
The washing of the neutral product, when obtained from a slag poor in phos-
phorous matter, may be advantageously effected by the addition of bi-sulphate of
soda, the action of which will be to remove, from the neutral product, salts of the
magnesia series (iron, manganese, copper, etc.), which are more or less detrimental
to the action of the manure. When the slag contains but little metallic impurity,
bi-sulphate of potash, or bi-sulphate of ammonia, is used as the re-agent, and then
no washing out of the mono-sulphate is necessary, but the neutral product may be
used, without any separation of its constituents, as a fertilizer.
Soluble bi-sulphates occurring as waste products, from various sources, and of
variable strength, may be used in making the neutral product. Or the acid
sulphate of soda formed by the action of sulphuric acid upon chloride of sodium, in
the first stage of the ordinary process of making sulphate of soda, may be used.---
Their strength, if deficient, I increase by the addition of sulphuric acid, and where
excess of acidity occurs, I neutralize that excess by the addition thereto of alkaline
raw slag. In this way, the neutral state of the mixture will be maintained, and
the deterioration of the closed vessels or other apparatus used in the preparation of
the neutral product, would be minimized.
Liquid re-agents I prefer to use in the form of a saturated solution, as I thereby
avoid an unnecessary excess of water in the neutral product.-The quantity of
water necessary for the production of the neutral product can also be regulated
much more easily by addition than by subtraction.
I may here remark that in using a liquid re-agent, I supply it to the mixing
vessel through a lead pipe from below, causing it to meet a descending shower of
the raw powdered slag, as otherwise the slag, being much heavier in its raw state
than when oxidized, would, in falling down quickly, have a tendency to escape the
action of the re-agent, and form a deposit at the bottom of the vessel. The same
remark is also applicable to lixiviators.-Should a heavy deposit be formed, it may
be re-submitted to the action of the re-agent.
The satisfactory condition of the re-action may easily be recognised by the
gelatinous appearance of the mass flowing out of the apparatus, especially when
the neutral product, washed with water and with bi-sulphate, dries into a light
and friable gray or white material that can be readily reduced by the fingers into
fine dust. The fine dust (the neutral product) should contain a phosphate of lime
soluble in carbonic acid, and should also be soluble in dilute nitric acid, leaving
only, an insoluble residuum of about 10%-By the comparative test with bi-
sulphate, the proportion of slag remaining untreated by the first process may be
Lestimated. L

page_text: It should be remarked that the nitric acid contained in the soil acts but slowly
upon the raw, or even burnt, slag applied thereto, taking from the slag only a small
proportion of phosphorous matter, and leaving a residuum, which, like ordinary
silica, resists the action of the strongest acids. Sulphate of lime is also but little
soluble in the weak nitric acid of the soil-But, when phosphate of lime is
chemically combined with sulphate of lime, the double compound is integrally
soluble in dilute nitric acid, and it is known as a highly fertilizing manure.
Chemically hard slag, or heavy deposits; when worth treatment, I prefer to mix
with chloride of sodium, either in a dry state, or as a saturated solution, adding
thereto sulphuric, nitric, or other acid, capable of decomposing the chloride of
sodium and liberating the nascent chlorine.
Thus, for example, when sulphuric acid is employed, the formation of bi-sulphate
of soda results, and chlorine will be liberated.-The hard slag, by this powerful
reaction, is brought quickly into a gelatinous state, and becomes soluble, to a great
extent, in dilute nitric acid.
As the quantity of the raw slag varies in a residual deposit, so will the proportion
of re-agents employed vary, but generally, I find that 25 parts of chloride of
sodium, with a corresponding quantity of sulphuric acid to forin the bi-sulphate, or
the mono-sulphate of soda, will suffice for the treatment of 100 parts of raw slag.
This operation must be performed in a closed vessel, in order to prevent the escape
into the atmosphere of the hydrochloric acid vapours.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that I do
not claim the making of acid super-phosphates from this material, but what
I claim is:-
1. Subjecting phosphorous slag to the action of sulphuric acid in the presence of
air in the manner above described, whereby I obtain a neutral phosphatic product
free of sulphurous impurities.
2. Subjecting phosphorous slag to the action of the acid sulphates of soda, potash,
or ammonia, in the manner above described, for the purpose of converting it into a
neutral phosphatic product.
3. Subjecting phosphorous slag to the combined action of chloride of sodium and
sulphuric or equivalent acid, for the purpose of converting it into a neutral
phosphatic product.
4. The removal from the neutral phosphatic product obtained by the use of acid
sulphate of soda as above explained, of mono-sulphate, by lixiviation.