IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES AND MANURES
Year: 1878

page_text: LETTERS PATENT to Sidney Gilchrist Thomas, of 3, Queen's Road Villas,
Queen's Road, Battersea, in the County of Surrey, for the Invention of
"IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES AND MANURES."
PROVISIONAL SPECIFICATION left by the said Sidney Gilchrist Thomas
at the Office of the Commissioners of Patents on the 4th November 1878.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea,
in the County of Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES
AND MANURES."
By my Invention I effect the utilisation of the phosphoric acid contained in the
calcareous highly phosphoretic basic cinder or slag produced in treating phosphoretic
pig iron in converters or furnaces lined with lime or magnesian lime compounds.
In the Bessemer and open hearth furnace cinder produced in carrying out my
patent process for the removal of phosphorus in the Bessemer converter and open
hearth processes, when operating on phosphoretic pig I find from seven to thirteen
per cent., and sometimes more, phosphoric acid is generally present in the calcareous
In order to sepa-
slag produced, the greater part being in combination with lime.
rate the phosphates from the oxide of iron silica, &ct., with which they are mixed, I
proceed as follows:-
The slag is first roasted with free access of air, sometimes after a preliminary
moistening with sulphuric acid, so as to peroxidise and render insoluble the protoxide
of iron.
The ground calcined slag is then treated and agitated with cold acid, so as to
dissolve out the phosphates, leaving the bulk of the iron, silica, &ct., undissolved.
The solution is drawn off and evaporated, and either dried up with the ordinary
driers of the manure maker, precipitated with lime, or still further evaporated and
sold as phosphate of lime for the use of manure makers or phosphorus makers.'

page_text: The roasting may be conducted without preliminary grinding in clamps or in kilns
similar to brick-kilns, or the slag may be first ground to powder (the grinding is facili-
-tated-by-the-hot-slag being thrown into water), and either with or without a pre-
liminary moistening with sulphuric acid, which facilitates the peroxidation of the iron,
and renders the sesquioxide more easily separable by levigation, is calcined on the bed
of a reverberatory furnace or a revolving calciner. A free access of air is indispensable.
A red heat (not sufficient to melt the slag) should be used for calcining. After
calcination the slag should be ground fine, and is preferably treated with cold
sulphuric acid or a cold solution of sulphurous acid, though cold hydrochloric acid
or acetic acid may be used. In case of sulphuric or hydrochloric acid being used
the-slag-may be first moistened with strong acid, water being gradually added, or a
dilute acid may be used at once. The solution, after settling, is drawn off from the
residue (which will contain all or nearly all the iron) and evaporated. If the
solution be in sulphurous acid the phosphate will on heating be almost at once
precipitated as a phosphate mixed with sulphite of lime. The sulphurous acid given
off may be recovered in condensing towers in the ordinary way. The solution in
acetic acid may be treated with sulphuric acid, and the acetic acid recovered. The
solution in hydrochloric or sulphuric acid may be completely evaporated, and the
phosphate sold in a concentrated form; in the hydrochloric solution it will be
mixed with calcic chloride, or the solution may be dried up with the ordinary driers
of the manure maker. The hydrochloric solution may also after evaporation be
treated with strong sulphuric acid, if the ordinary form of superphosphate is
preferred. Precipitation with lime may in all cases be used, though it is not
generally desirable. By these means almost the whole of the phosphoric acid in the
šlag is recovered in a marketable form. Some thirty thousand tons of phosphorus
is contained in the pig iron annually produced in the Cleveland district alone.

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 3rd
May 1879.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea,
in the County of Surrey. "IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHATES
AND MANURES."
By my Invention I effect the utilisation of the phosphoric acid contained in the
calcareous highly phosphoretic basic cinder or slag produced in treating phosphoretic
pig iron in converters or furnaces lined with lime or magnesian lime compounds.
In the Bessemer and open-hearth cinder produced in carrying out my patent
process for the removal of phosphorus in the Bessemer converter and open-hearth
processes when operating on phosphoretic pig, I find from seven to fifteen per cent.
(and sometimes more) of phosphoric acid is generally present in the calcareous slag
produced, the greater part being in combination with lime.
In order to separate the phosphates from the oxide of iron, silica, &ct., with which
they are mixed, I proceed as follows:-
The slag is first roasted with free access of air, so as to peroxidise and render
insoluble the protoxide of iron and manganese. The ground calcined slag is then
treated and agitated with cold acid so as to dissolve out the phosphates, leaving the
bulk of the iron, manganese, silica, &ct., undissolved.
The roasting may be conducted without preliminary grinding in clamps or in
kilns similar to brick kilns, but the action here is imperfect, and I much prefer that
the slag should be first ground to powder (the grinding being facilitated by the hot
slag being thrown into water), and then calcined on the bed of a reverberatory
furnace with frequent stirrings, as by an air rabble, or preferably in a revolving
calciner, as is practised in roasting ores.
A free access of air is indispensable.
A red heat (not sufficient to melt the slag) should be used for calcining.
After calcination the slag may be ground fine, and is treated with cold sulphuric
acid or a cold solution of sulphurous acid, or preferably with cold hydrochloric acid.
I prefer to agitate the slag and acid thoroughly together in any known way.
In case of sulphuric or hydrochloric acid being used the slag may be first
moistened with acid, water being gradually added, or a dilute acid of from twenty
(20) to thirty (30) per cent. strength may be used at once, which I prefer.
The solution, after settling, is drawn off from the residue, which will contain
nearly all the iron (for the purpose a vacuum or pressure filtration is useful), and
evaporated.
If the solution be in sulphurous acid the phosphate will on heating be almost at
once precipitated as a phosphate mixed with sulphate of lime, while the sulphurous
acid given off may be recovered in condensing towers in the ordinary way.
The mode of treating phosphates with sulphurous acid is well-known.
The solution in hydrochloric or sulphuric acid may be completely evaporated,
and the phosphate sold in the concentrated form; in the hydrochloric acid solution
it will be mixed with chloride of calcium, or the solution may, after partial evapo-
ration, be dried up with the ordinary driers of the mauure maker.
The hydrochloric solution may also after evaporation be treated with strong
sulphuric acid, if the ordinary form of superphosphate is preferred.
Precipitation with lime, or preferably with chalk, may in all cases be used; the
precipitated phosphate may be sold, or treated with sulphuric acid, as is now
practised.
By these means almost the whole of the phosphoric acid in the slag is recovered
in a marketable form.
Some thirty thousand tons of phosphorus is contained in the pig-iron annually
produced in the Cleveland district alone.

page_text: I claim the method herein described of separating the phosphates contained in
calcareous phosphatic slags by roasting the slags so as to render the iron, &ct.,
insoluble, and then treating them with acid, substantially in the manner described.
In witness whereof, I, the said Sidney Gilchrist Thomas, have hereunto set-
my hand and seal, this First-day of May, in the year of our Lord One
thousand eight hundred and seventy nine.
SIDNEY GILCHRIST THOMAS. (L.S.)