IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES.
Year: 1879

page_text: LETTERS PATENT to Sidney Gilchrist Thomas, of 3, Queen's Road Villas,
Wandsworth Road, London, for the Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF PHOSPHATES.'
"
'
Sealed the 30th January 1880, and dated the 9th August 1879.
PROVISIONAL SPECIFICATION left by the said Sidney Gilchrist Thomas at the
Office of the Commissioners of Patents on the 9th August 1879.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Wandsworth Road,
London. "IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES."
My Invention relates to the manufacture of phosphates from the calcareous slag
produced in treating phosphoretic pig-iron in basic lined converters or furnaces, this
slag containing from ten to twenty per cent. of phosphoric acid. I grind this slag
finely, and digest it in dilute hydrochloric acid. After some time the solution is
separated from the undissolved silica by filtration or syphoning off. The residue
is thoroughly washed, which I prefer to do with chlorine water. The whole of the
phosphoric acid, iron, &ct. of the slag will be found in solution; the iron exists
mainly as a ferrous salt. This I find should be converted in a ferric state, which
may be readily effected by treating the solution with chlorine or chlorine water till
a test shows no more ferrous salt to remain. Other means of oxidising may also
be employed. On adding chalk carefully to the solution till it is nearly neutralised,
and then boiling, the whole of the phosphoric acid will be precipitated as phosphate
of iron. The solution is filtered off or syphoned off, and may be treated for the
recovery of its manganese by the Weldon process. The precipitated phosphate of
iron (mixed with a little iron) is dried and mixed with sulphate of soda and coke-
dust, and then heated on the bed of a reverberatory furnace till no more sulphurous
acid is given off, and the whole mass is agglomerated. The resulting mixture of
phosphate of soda and oxide (with some sulphide) of iron is thrown into lixiviating
tanks after being broken up, the same liquor being used repeatedly till saturated.
The concentrated solution is then treated with just sufficient milk of lime to combine
ГДА

page_text: with the phosphoric acid. The phosphate of lime is precipitated, and after some
time the supernatant caustic soda solution is drawn off and evaporated. If chalk is
used to precipitate a bi-basic phosphate is obtained. The sulphurous acid given off
during the roasting of the sulphate of soda and phosphate of iron may be utilised
for the manufacture of sulphate of soda and hydrochloric acid by the Hargreaves
process. As an alternative I sometimes either heat the precipitated phosphate of
iron with caustic soda solution, or fuse it with carbonate of soda, and then take up
the phosphate of soda with water, afterwards precipitating with lime. It is some-
times desirable to remove any grains of metallic iron there may be in the ground
slag by magnets before dissolving it.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Sidney Gilchrist Thomas in the Great Seal Patent Office on the 9th
February 1880.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Wandsworth Road,
London. " IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES."
My Invention relates to the extraction of the phosphoric acid and other substances
from phosphoretic iron slags, particularly that produced in treating phosphoretic pig
iron in lime lined Bessemer converters or open hearth furnaces, which contain from
nine to twenty per cent. of phosphoric acid. I prefer to use slags in which this
phosphoric acid has been concentrated to 15 or 20 per cent. at least. I first grind
the slag to powder in any convenient way. To facilitate the grinding it is useful
to throw it while hot into water., If there is much iron in shots or globules in the
slag, I sometimes pick out this iron by magnets or by sorting. I then dissolve the
powdered slag in vats in common hydrochloric acid, and filter off the undissolved
silica (Si O,) preferably in a filter press or centrifugal filtering machine. I then
treat the solution (which I will call the solution A) in one of the following ways:-
I. When the slag contains much manganese, which it is desirable to recover, I treat
the solution A as follows:-I first add enough peroxide of manganese or chlorine
(Cl) to the acid liquor to oxidise all the iron in solution, or enough of the iron to
form phosphate of peroxide of iron, with the phosphoric acid (P, O,) present. The
oxidation may be conducted in any other known way, but I prefer the use of the
manganese oxide as the most simple. I then boil it, and add to the boiling liquid
enough powdered chalk (or preferably dolomite) to nearly neutralise the liquid, and
boil till the phosphate of iron is precipitated, leaving a solution I will call solution
B. The precipitate is dried, and intimately mixed with sulphate of soda in such
proportions as to give rather more than three equivalents of soda for each equiva-
lent of phosphoric acid. With these bodies I mix enough powdered coal, or coke,
or charcoal to reduce the sulphate of soda. I then throw the mass onto the bed of
the reverberatory furnace or calciner, or even into a cupola furnace, with an excess
of blast. The mass is then exposed for some hours to a high temperature, with
free access of air. I prefer to use a hollow rabble, through which I blow in air or
air and steam to stir up the mass directly it is melted. I continue the stirring till
no more action takes place, and only oxide of iron and phosphate of soda is left.
In order to assist the fusion I sometimes add some salt (Na Cl) to the mass so as
to form sulphate of soda as well. The SO,, or SO, and Cl, or SO₂, Cl and H Cl
may be collected and utilised by well known methods. The mass left in the
furnace is raked out and lixiviated in water till all the phosphate of soda is dis-
solved, leaving oxide of iron, which is fit for sale. The solution of phosphate of
soda may be either evaporated or precipitated by lime to obtain phosphate of lime
and caustic soda, the latter being in solution, while any sulphate of soda in the
solution may be crystallised out. Instead of fusing with sulphate of soda, as I
always prefer, the phosphate of iron may be either fused with carbonate of soda or
boiled with caustic soda solution (Na HO) to obtain phosphate of soda. II. If
there is not much manganese, or it is not desired to recover the manganese in the
slag, I add to the solution A, burnt lime (preferably magnesian lime) in powder or
small pieces to slight excess till all the phosphoric acid is precipitated as phosphate
of iron, with sometimes a little phosphate of manganese and some oxide of iron and
manganese, and I then filter or syphon off the solution, which solution I will call
solution D. I then treat the precipitate of phosphate of iron as before described.
The solution B from process I. should be boiled with either ordinary burnt lime or
burnt dolomitic lime, which latter I prefer. In the first case oxide of manganese
and a little oxide of iron only are precipitated; in the latter case they are mixed

page_text: with magnesia. This mixture of magnesia with oxides of iron and manganese I
use to precipitate a fresh quantity of oxide of manganese, the magnesia precipitating
the oxide of manganese, and leaving the oxide of iron and manganese undissolved.
I claim, the hereindescribed process for the manufacture of phosphates, consisting
of the separation of the phosphoric acid and other substances in phosphoric slags by
precipitating the phosphoric acid from a hydrochloric acid solution as phosphate of
iron, and then transforming into phosphate of soda or phosphate of lime, substan-
tially as herein described.
In witness whereof, I, the said Sidney Gilchrist Thomas, have hereunto set my
hand and seal, this 9th day of February, in the year of our Lord 1880.