IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES
Year: 1884

page_text: I FRANK WILLIAM HARBORD of 5 Cleveland Road, Wolverhampton Chemist and
Metallurgist do hereby declare the nature of said invention for "IMPROVEMENTS IN
THE MANUFACTURE OF PHOSPHATES" to be as follows:-
This invention relates to a process for obtaining phosphates free from iron from
Thomas-Gilchrist slags or other phosphatic materials containing iron. I dissolve
the phosphatic material in acid, taking precautions while dissolving out all the
phosphoric acid, to leave behind as much of the iron associated with it as possible.
This may be effected by using weak acids, and sometimes by previously roasting
the material To the solution preferably nearly neutral I add an alkaline or
alkaline earth ferrocyanide in sufficient quantity to precipitate the whole or great
part of the iron The phosphoric acid remaining in solution may be then
precipitated with chalk or lime, and is thus obtained free from iron. The blue
precipitate may be either sold or regenerated by treatment with lime or baryta or
soda salts solution and used over again.

page_text: I FRANK WILLIAM HARBORD of 5 Cleveland Road Wolverhampton Chemist and
Metallurgist do hereby declare the nature of my said invention for IMPROVEMENTS
IN THE MANUFACTURE OF PHOSPHATES 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 obtain phosphates practically free from Iron,
from the slags resulting from the Thomas-Gilchrist process or from other Phosphatic
materiels containing iron.
The Phosphatic material finely ground and either raw or calcined and freed as
far as possible from shots. of metallic iron is treated in suitable vats with acid
preferably very dilute, care being taken to dissolve out as much phosphoric acid
as possible, and to leave behind in the residue as much of the iron as possible.
This residue is reserved.
The solution is separated from the residue by decantation or otherwise and steam
and air are blown through to peroxide the iron; the iron in a given bulk of the
solution is then estimated and a solution of any alkaline or alkaline earth ferro-
cyanide of known strength added in just sufficient quantity to precipitate the.
iron in form of Prussian Blue; the Phosphatic solution should be as nearly neutral
as possible and preferably hot.
Each pound weight of metallic iron in solution will require 4.07 lbs of Sodic
ferrocyanide, or its equivalent of any other ferrocyanide. As it is important not to
add excess of the ferrocyanide I prefer to precipitate the bulk of the iron by a
strong solution of ferrocyanide (about 1 pint of Ferrocyanide to 3 pints by weight
of water) and to complete the precipitation by a solution about one twentieth this
strength The precipitate of Prussian Blue formed is separated from solution by
decantation or otherwise and may be either sold or reserved for further treatment
to recover the ferrocyanide as hereinafter described.
The solution which contains the whole of the Phosphoric Acid free from iron
may be evaporated to dryness, when; if Sulphuric Acid has been used to treat the
slag and an alkaline ferrocyanide (such as Potassic Ferrocyanide or Yellow
Prussiate of Potash) to precipitate the iron, the phosphoric acid is obtained in a
soluble form; or the phosphoric acid may be precipitated from the solution by
chalk.or lime.
The Precipitate of Prussian Blue may be reconverted into ferrocyanide of Soda
or lime or other ferrocyanide by treatment with solutions, preferably hot, of
hydrates or Carbonates of the alkalios or alkaline earths, the resulting solution
being a ferrocyanide of the alkali or alkaline earth used, which may then be used
to precipitate the iron from a fresh quantity of phosphatic solution. On thus
decomposing the prussian blue, the greater portion of iron present is precipitated as
Hydrate or Carbonate of Iron which can be mixed with the residue left on first
treating the slag with acid (if Hydrochloric acid has been used) and made into

page_text: bricks for smelting in Blast Furnaces or may be made into bricks alone and sold as
pure ore.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed I declare that what
I claim is
1st Effecting the separation in a phosphatic compound of the iron from phosphoric
acid in the form of Prussian Blue by means of a ferrocyanide substantially as and
for the purpose above described.
2nd The method of recovering the ferrocyanide which consists in treating the
Prussian Blue with hydrates or Carbonates of alkalies or alkaline earths sub-
stantially as and for the purpose herein described.
3rd The described method of obtaining soluble phosphates which consists in
treating the phosphoretic and iron bearing substances with sulphuric acid, freeing
the solution from iron, and evaporating in the presence of a soluble alkaline salt
substantially for the purposes set forth.
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A
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