IMPROVEMENTS IN THE MANUFacture of PHOSPHATES
Year: 1884

page_text: I SIDNEY GILCHRIST THOMAS of 9 Palace Chambers Westminster Bridge London
temporarily residing at the Hotel Kirsch, Algiers, Africa Metallurgist do hereby
declare the nature of said Invention for IMPROVEMENTS IN THE MANUFacture of
PHOSPHATES to be as follows:-
My invention consists in an improved process for the manufacture of phosphates
of soda or potash from their carbonates or hydrates by means of the phosphoric
acid produced by oxidising phosphoric iron in the presence of these bodies.
I conduct the operation in a lime or magnesia lined Bessemer converter or gas
furnace the metal (which I prefer to be run in very hot and may have been first
blown in another Bessemer converter to deprive it of its silicon) being treated in
the manner usual in the Siemens and Bessemer processes.
The carbonate or hydrate may be spread on the bottom of the furnace or
converter in which case I prefer it to be protected by a casing or cover of cast iron
or lime which prevents it being wasted, or it is blown in through twyers which
I prefer. The action of the phosphoric acid on the hydrate or carbonate produces
a slag consisting in great part of alkaline phosphate which is run off and lixiviated
and so separated from oxide of iron. Alkaline hydrate and phosphate of lime
may be obtained by treating the solution with milk of lime.

page_text: I SIDNEY GILCHRIST THOMAS of 9 Palace Chambers Westminster Bridge,
London temporarily residing at the Hotel Kirsch Algiers, Africa, Metallurgist do
hereby declare the nature of my invention for IMPROVEMENTS IN THE MANU-
FACTURE OF PHOSPHATES and in what manner the same is to be performed to be
particularly described and ascertained in and by the following stateinent :—
My invention consists in an improved process by which phosphate of soda or
potash are manufactured from their carbonates or hydrates by means of the
phosphoric acid produced by oxidising highly phosphoric molten iron in the
presence of these bodies. I find it best to use carbonates in preference to the
hydrates. The phosphoric iron employed to effect the decomposition should be
very high in phosphorus and should be first decarburised and desiliconised in a
silicious lined Bessemer vessel before running it into the vessel which contains the
carbonate. The highly phosphoric iron made by smelting calcareous phosphoric slag
with silicious phosphoric iron ore, or puddling cinder, is the material I find best
adapted for my process. The phosphorus content of iron made in this way may
be made to range between six and thirty per cent, and an iron phosphide or ferro.
phosphorus containing very little carbon or silicon may be produced. The carbon
in this phosphorus-iron will as a rule be lower in inverse proportion to the content
of phosphorus. When the carbon and silicon have been thus reduced very low by
increasing the phosphorus, the metal may be run direct into the decomposing
furnace without prior decarburation. I prefer to effect the decomposition of the
alkali in a Siemens gas furnace (though à converter may be used). This must have
a basic or neutral lined hearth. If it is desired to convert the whole or nearly the
whole of the phosphorus in the iron into sodic phosphate (it being assumed that
sodic carbonate as the cheapest salt will be generally used) about six times the
weight of carbonate of the weight of phosphorus in the molten iron used to effect
the decomposition, is employed as a charge. To make the process commercially
and technically successful, it is absolutely necessary to provide against the very
considerable volatilisation and loss of the alkali which under ordinary circumstances
would be so excessive as to be prohibitive. Thus if soda is thrown without
precaution into a highly carburised ordinary Bessemer or Siemens bath, the waste
of alkali is extremely high. I find carbon and carbonic oxide greatly retard and
impede the formation of phosphate of soda so that while they are prescut in any
quantity the loss of alkali is very considerable. Before the molten metal is run in
I place on the furnace hearth, previously brought to a high temperature, a part of
the carbonate of soda, and cover it with oxide of iron or limestone or lime or a
rough cast iron plate to retard its volatilisation, and then immediately run in the
molten metal, when a brisk reaction at once takes place. If it is for any reason
specially convenient to use in the decomposing furnace a phosphoric iron with a
considerable content of carbon, say over one, per cent (which I do not recommend)
it is best to defer the addition of even the first part of the soda charge till the
carbon is nearly removed. I prefer to add the further quantity of soda making up
the total charge by blowing it in through twyers regulating this so as not to cause
a too violent reaction. If the layer of slag grows too thick so as to prevent the
heat reaching the metal so as to cool the metal, a part should be run off, care being
taken so to adjust the addition and tapping of slag as always to keep the iron
quite fluid.
When the reaction appears to be at an end and the metal to be
deprived of its phosphorus, the slag is tapped off into bogeys and the metal finished
in the usual way. The removal of phosphorus from the iron employed in my

page_text: process, particularly when the initial content of phosphorus is not very high,
will be found remarkably complete. If a Bessemer converter has been employed,
which is only permissible when treating metal with a very great initial heat, the
greater part of the soda should be blown in through the twyers with a blast
preferably superheated to at least 300° C, and the greatest care must be taken to
stop the introduction of soda directly the metal blows cold. If all the phosphorus
has not at this point been removed, it is best to finish the removal with lime. In
this case also the soda should only be introduced when the metal is entirely or
nearly free from carbon. The slag obtained by either of the methods above
described consists essentially of phosphate of soda or potash, it may be used
directly as as manure or lixiviated in tanks to free it from oxide of iron and other
bases.
Phosphate of soda may be obtained by evaporation of the solution or it may be
otherwise utilised by well known means.
I do not claim generally the use of alkaline carbonates or hydrates as fluxes or
purifiers in metallurgical operations.
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 :-
1. The improvements in the manufacture of Phosphates consisting in treating
sodic or potassic carbonates or hydrates with molten phosphoric decarburised and
desiliconised iron in a basic or neutral lined furnace or converter under oxidising
influences substantially as herein described.
2. When treating alkaline carbonates or hydrates with molten phosphoric iron to
produce phosphates, preventing the premature volatilisation of the alkalies by
covering them or mixing them with lime iron ore or similar bodies, or by covering
them with an iron plate and by introducing a part of such alkalies through blast
twyers substantially as herein described.
Dated this eighth day of October 1884.
SIDNEY GILCHRIST THOMAS.