IMPROVEMENTS IN THE MANUFACTURE OF SWASTY
Year: 1883

page_text: LETTERS PATENT to Sidney Gilchrist Thomas of 27 Tedworth Square Chelsea
London and Thomas Twynam of 22 Cromwell Houses Fellows Road South
Hampstead for an Invention of IMPROVEMENTS IN THE MANUFACTURE OF
SWASTY ING
PROVISIONAL SPECIFICATION left by the said Sidney Gilchrist Thomas
and Thomas Twynam at the Office of the Commissioners of Patents on the
26th January 1883.
SIDNEY GILCHRIST THOMAS of 27 Tedworth Square Chelsea London and
THOMAS TWYNAM of 22 Cromwell Houses Fellows Road South Hampstead
IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES
Our invention relates to the manufacture of phosphoric acid and pure phosphates
from metallurgical slags containing phosphoric acid. It is especially adapted to the
treatment of basic Bessemer and Siemens slags.
The slags are first dissolved in hydrochloric acid or treated with hydrochloric
acid gas. If sufficient oxide of iron and manganese be not present to combine
with the whole of the phosphoric acid in solution sufficient oxide of iron is added
for the purpose We prefer that the iron present should be in the state of peroxide.
Sufficient lime or limestone is added to the solution to precipitate the whole of the
phosphoric acid in combination with the metallic oxides.
The precipitate having been separated from the solution and washed, and
preferably partially dried, is then treated with sufficient strong sulphuric acid to
cause the decomposition of the metallic phosphates the decomposition may be
assisted by heat; if the sulphuric acid solution be not sufficiently strong to cause
the separation of the metallic sulphates as an insoluble precipitate the solution
must be evaporated until this takes place. It is sometimes convenient after partial
evaporation to add a further quantity of strong sulphuric acid.
It will be found that the precipitate which forms, will contain practically the
whole of the metallic oxides as sulphates, while the solution, which is carefully
separated will contain nearly the whole of the phosphoric acid.
The phosphoric acid which exists in the free state mixed with a certain amount
of sulphuric acid may be separated from this latter by the aid of heat. The
sulphuric acid may be recovered by decomposing the separated sulphates by heat.
The free phosphoric acid thus obtained may be utilised as such or may be
employed to decompose the chlorides or sulphates of the alkalies or in the
preparation of soluble phosphates or otherwise.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Sidney Gilchrist Thomas and Thomas Twynam in the Great Seal
Patent Office on the 26th July 1883.
SIDNEY GILCHRIST THOMAS, of 27 Tedworth Square, Chelsea, London, and
THOMAS TWYNAM of 22 Cromwell Houses, Fellows Road, South Hampstead
IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES
Our invention relates to the manufacture of phosphoric acid and pure phosphates
from metallurgical slags containing phosphoric acid. It is especially adapted for
the recovery of the phosphoric acid contained in the slags produced in the basic
Bessemer and Siemens processes The slag is first finely ground and any shots of
iron picked out with a magnet; the powdered slag is then treated with sufficient
hydrochloric acid either in aqueous solution or in the gaseous state to dissolve out
the phosphoric acid contained in it together with part of the oxides of iron. The
powdered slag may first be roasted in a rotary or other calciner so as to oxide the
ferrous oxide contained in it. If there be not sufficient ferric oxide present in the
solution to combine with all the phosphoric acid it will be necessary either to add
some ferric oxide or puddlers slag, which should preferably have been first roasted
or to oxidize part or the whole of any ferrous oxide there may be present either
by chlorine gas or by the addition of manganese binoxide (in which latter case
there must be sufficient free acid in the solution to cause the decomposition of the
manganese binoxide and set free chlorine) or the ferrous oxide may be oxidized by
injecting air into the solution or by other well known means. The solution is
then run off from any insoluble residue and a sufficient quantity of lime or
preferably chalk is added to it to cause the precipitation of ferric phosphate,
magnesian lime or limestone may be used in place of ordinary limestone for this
purpose; the magnesia dissolved being afterwards precipitated by lime. The
precipitation of the ferric phosphate may be effected in the cold, keeping the
solution well agitated, a gentle heat however causes the precipitate to settle down
better.
When the precipitation is complete the ferric phosphate is separated from the
solution by filtration and washed to free it from calcic chloride.
The precipitate is then dried so as to drive off all its water and digested with a
considerable excess of sulphuric acid so as to decompose it into phosphoric acid and
sulphate of iron, which latter is insoluble in the excess of sulphuric acid employed.
We have found that ordinary chamber acid is able to effect this decomposition but
we prefer to use a stronger acid; an acid such as is obtained when using a Glover
tower is very well adapted for the purpose. The ferric phosphate should be
kept well agitated in the liquid which may be gently heated to facilitate the
decomposition. When the ferric phosphate is considered to be completely
decomposed the insoluble ferric sulphate is separated from the solution containing
the phosphoric acid and excess of sulphuric acid by means of a filter press or
otherwise,
The filtrate will be found to contain nearly all the phosphoric acid in a free
state together with the excess of sulphuric acid, from which it may be separated
by the aid of heat, the sulphuric acid being driven off and condensed, leaving the
phosphoric acid practically pure, or the solution containing the mixed acids may be
used in place of ordinary sulphuric acid for making super-phosphate of lime.
The sulphate of iron precipitate after being washed with sulphuric acid may be
decomposed by heat into ferric oxide and fuming sulphuric acid, or it may be
mixed with salt and heated to form sodic sulphate.
In some cases when there is no lime in the slag employed (as when treating

page_text: puddlers' cinder) we throw down the phosphoric acid as a mixed ferrous and
ferric phosphate, by means of lime without any previous oxidation, it is then dried
and treated in the same way as the ferric phosphate.
Having thus described the nature of our invention we would observe in
conclusion that we do not claim the mere treatment of mineral phosphates with
strong sulphuric acid but what we claim and desire to secure by Letters
Patent is;
The treatment of metallurgical slags containing phosphoric acid by first dissolving
them in hydrochloric acid and precipitating the phosphoric acid in combination with
oxide of iron and then decomposing the iron phosphate by excess of sulphuric acid
substantially as hereinbefore described
In Witness whereof we the said Sidney Gilchrist Thomas and Thomas Twynam
have hereunto set our hands and seals this twenty fifth day of July in the year
of our Lord one thousand eight hundred and eighty-three.
TN בזדי
(10)