IMPROVEMENTS IN TREATING INSOLUBLE PHOSPHATES FOR RENDERING THE PHOSPHORIC ACID IN THE SAME AVAILABLE
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Herbert John Haddan at the Office
of the Commissioners of Patents on the 24th July 1883. Communicated to
hin from abroad by Albert Henri Koefoed and Thomas Bliss Stillman, both
of New York, United States of America
HERBERT JOHN HADDAN, of Kensington, Middlesex, "IMPROVEMENTS IN
TREATING INSOLUBLE PHOSPHATES FOR RENDERING THE PHOSPHORIC ACID IN THE
SAME AVAILABLE a communication to me from abroad by Albert Henri Koefoed
and Thomas Bliss Stillman, both of New York, United States of America,
This invention relates to the method of treating the insoluble phosphates of iron
and alumina and rendering the phosphoric acid in the same soluble and available.
The rock containing the insoluble phosphate is finely powdered and mixed with
powdered dolomite (or limestone) and calcined in a furnace at a high temperature.
The result of the heating is as follows:-The phosphoric acid in the native rocks is
separated from the iron and alumina and unites with the magnesia and lime as
phosphates of magnesia and lime. The carbonic acid in the dolomite is driven out
at a heat lower than that required to separate the phosphoric acid from the iron
and alumina, so that the lime and the magnesia being in the caustic state
immediately absorb the phosphoric acid driven off from the iron and alumina
forming phosphate of magnesia and lime.
The iron and alumina remains in the condition of insoluble oxides and as such
are not affected by the later treatment of acid.
After heating which can be performed in any furnace capable of producing the
required heat, the mass is allowed to cool and then pulverized finely before it is
subjected to the action of sulphuric acid to form super phosphates or to get free the
phosphoric acid. In place of sulphuric acid, any acid that will set free the
phosphoric acid may be employed, as for example, muriatic acid.
If after the calcination of the phosphate rocks and digestion with sulphuric acid
or any acid capable of rendering the phosphoric acid soluble, water either hot or
cold is added, the soluble portions filtered off and the water in the filtrate driven
off by heat, the mass after drying will be found to be very rich in phosphoric acid
and being in the form of a dry powder it can be added directly to any fertilizer
[Price 2d1

page_text: and distributed by drills or it can be packed up for the market without further
treatment.
This process as is seen furnishes means for forming concentrated solutions or
dried salts of a mixture of phosphoric acid, soluble phosphate of lime and phosphate
of magnesia, either separately or together, which by concentration will produce a
residue containing from twenty to forty per cent and over of phosphoric acid.
The addition of the sulphuric acid above mentioned to the calcined mass of
dolomite or limestone and phosphate rock, give rise to the following reaction: The
sulphuric acid combines with the lime forming sulphate of lime which is insoluble,
at the same time separating the phosphoric acid from the lime rendering the acid
free. By the addition of water sufficient to form a liquid mass and subsequent
filtrations the separation of the soluble material from the insoluble material can be
attained, the soluble material being composed of or containing free phosphoric acid;
also traces of phosphate of magnesia and sulphate of magnesia, and more or less
soluble phosphates of lime that pass into solution as also some free sulphuric acid.
These soluble substances are separated from the oxides of iron and alumina and
sulphate of lime, and by concentration by evaporation a material can be obtained
very rich in phosphoric acid. The filtration or separation can be performed by
settling tanks or preferably by pressure filters. The proportions of materials may
vary but the following have been found to give good results. To one hundred
parts of the phosphate add seventy five parts of dolomites and if carbonaceous,
inatter is used add about thirty parts of coal, coke or any substitute to serve as a
combustible or heating agent.