Process of Making Phosphate of Lime Fertilizers.
Year: 1895

page_text: Date of Application, 2nd July, 1895-Accepted, 28th Sept., 1895
Process of Making Phosphate of Lime Fertilizers.
1, DAVID TALBOT DAY of 1425 Euclid Place in the City of Washington, and
District of Columbia, United States of America, Mineralogist, do hereby declare
the nature of this invention and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement:-—
This invention relates to the manufacture of phosphate of lime, suitable for use
as a plant food or fertilizer without the use of an acid.
The object of my invention is to economically produce. at a suitable temperature,
from phosphate rock, a maximum amount of phosphate of lime soluble in dilute
citric acid solution, for use as a fertilizer.
I have discovered that, by heating any form of phosphate rock containing
carbonate of lime, the normal phosphate of lime which is insoluble in a dilute
solution of citric acid (one part of citric acid dissolved in twenty parts by weight of
water) is converted into a form, to a large extent, soluble in such dilute citric acid,
and that a maximum percentage of such phosphate will result, provided the
temperature is not carried to a degree at which the mass undergoes partial fusion.
If the process is conducted at the proper low temperature, the largest obtainable
amounts of such citric-acid-soluble, or available phosphate of lime is formed by the
action of the oxide of lime, formed by the decomposition of such carbonate as
occurs with the phosphate in the native phosphate of lime. In carrying out the
process the temperature is preferably kept below a strong white heat, but
above 1350° F.,-the point at which carbonate of lime loses its carbon dioxide, and
as a result, the reactions take place quantitatively.
If the product of the above operation is heated for a considerable time at a
temperature of partial fusion the percentage of citric-acid-soluble phosphate falls
nuch below the maximum, with the result that the product is injured for use as a
fertilizer, the citric acid soluble phosphate being reconverted into normal phosphate
of lime.
I have also discovered that by having a suitable percentage of silica present in
the mixture or in the phosphate rock, the operation of converting the phosphate of
lime into a form soluble in dilute citric acid, is much facilitated, the time required
to produce the result is lessened and the expense reduced. Even if silica is added
to the heated mixture, or to a heated basic slag which is less than usually soluble in
citric acid, its solubility is at once increased
The phosphate should contain naturally, or by suitable admixture, a minimum
proportion of one equivalent of calcareous base, i.e. carbonate, or oxide, or hydrate,
to each equivalent of any phosphate. A smaller proportion of calcareous base may
Le used, but it will reduce the amount of available phosphoric acid.
I preferably select phosphates which contain naturally enough silicious material
to furnish a maximum of 15% of silica in the finished product: or, in case the
phosphate rock contains little or no silicious material, a sufficient amount of silica,
such as sand, ground-quartz, infusorial earth, glass, clay, &c., is added to such rock
to produce the desired result, and, preferably, to furnish no more than a maximum
of 15% of silica in the finished product, but larger or smaller quantities may be
used. Phosphate rock poor in silica, may be mixed with phosphate rock rich in
silica in such proportion as to obtain a mixture containing the preferred percentage
of silica. The mixture of phosphate of lime, carbonate of lime and silica should be
made as uniform as convenient or practicable before it is subjected to the heating
operation.

page_text: There are many conditions and circumstances in which it will be preferable not
to control the temperature, and I have ascertained that regulation of the tem-
perature is not necessary and that a much higher temperature than that above
mentioned may be used, provided a suitable percentage of oxide of iron or alumina
is present with the phosphate of lime and compound of alkaline earthy base. My
invention therefore includes the addition to this latter mixture, or such mixture
with silica, of an iron base such as carbonate, oxide, hydrated oxide, silicate of iron,
or basic slag rich in oxide of iron, in order that the mixture may be heated to any
temperature without the danger of reconversion to normal phosphate of lime from
phosphate soluble in citric acid.
In case a mixture of phosphate of lime, a compound of an alkaline earthy base
(as carbonate of lime) and silica is to be treated, it is placed in a reverberatory or
cupola furnace, or other heating device, and heated to the desired temperature
until the results as described herein are secured. The time of beating the inaterial
varies within wide limits, depending on the nature of the phosphate used and
particularly on the natural or artificial mixing of the phosphate, compound of
calcareous base and silicious material. Thus if any forms of the above substances
are mixed together and heated to a temperature above 1350° F. for a comparatively
short time, the production of soluble phosphate begins. If the materials are hard
rock-phosphate or apatite, and the mixing has not been thoroughly done, and
especially if silica is omitted, a long heating, frequently more than forty hours, is
required for obtaining a satisfactory result unless the temperature is quickly raised
to a point a little below that of fusion. With a more intimate artificial mixture,
and especially with natural mixtures of phosphates with silicions material and an
excess of carbonate of lime, the formation of soluble phosphate. goes on more
rapidly and a satisfactory result is obtained in much less time. In the presence of
silica, the regulation of the temperature is not so necessary. I always take care to
maintain the temperature as low as practicable in order to develop the production
of the largest possible amount of available phosphate of lime and, at the same time,
avoid the conversion of any such phosphate into compounds insoluble in citric acid.
Of course the low temperature is the most economical in point of fuel supply, and,
in addition gives the most satisfactory results in the production of phosphates which
are soluble in dilute citric acid solution. This temperature can also be further
reduced to between 1,000° and 1,200° F. by the addition to the mixture of a salt of
an alkali, such as kainite, or a sulphate or muriate of potassium.
In carrying out my invention with the use of an iron base or alumina, I add to a
natural or artificial mixture of phosphate of lime and a compound of calcareous
base, such as carbonate, oxide, or hydrate, a suitable percentage of ordinary
hematite or its cquivalent in other iron compound, or alumina, and then heat the
mixture in a suitable furnace, to a temperature above 1350° F., and it may
be 2500° F. or above, so as to deliver the product from the furnace in a fluid
condition. In this operation ten per cent, or more of iron compound may be used,
dependent upon the temperature to which the mass is to be heated, and my
invention is not limited to any particular proportion of iron compound to be added
to the mixture.
By this process a partial or entirely fused product or slag, soluble in dilute
citric acid, is readily obtained.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The process of manufacturing a phosphate of lime, substantially soluble in
dilute citric acid, which consists in beating a natural or artificial mixture of
phosphate and a calcareous base in a suitable furnace to the temperature at which
carbonate of lime gives up its carbonic acid, and keeping the temperature below
the temperature of partial fusion and securing a maximum of citric-acid-soluble
phosphate, as described.

page_text: 2. The process of manufacturing a phosphate of lime soluble in dilute citric acid,
which consists in heating a natural or artificial mixture of phosphate and an
alkaline earthy base and a potassium salt, such as sulphate or muriate, in a suitable
furnace, to a temperature below that at which carbonate of lime ordinarily gives
up its carbonic acid and maintaining such low temperature, much below the
temperature of partial fusion, as described.
3. The process of manufacturing phosphate of lime soluble in dilute citric acid,
which consists in heating a mixture composed of phosphate rock containing a suitable
percentage of silica, and a calcareous base in a suitable furnace to the temperature
at which carbonate of lime gives up its carbonic acid and keeping the temperature
well below partial fusion and securing a maximum of citric-acid-soluble phosphate,
as described.
4. The process of manufacturing phosphate of lime soluble in dilute citric acid,
which consists in heating a natural or artificial mixture of phosphate or basic slag,
a calcareous base, and added silica, to a temperature above that at which carbonate
of lime would give off its carbonic acid, and maintaining such temperature, as
described.
5. The process of manufacturing basic phosphate of lime which consists in
heating a mixture of phosphate of lime, an alkaline carthy base, an oxide of iron
or aluminum or any suitable compound of iron or aluminum to a temperature
above the point at which the carbonate of lime gives up its carbonic dioxide, as
described.
Dated this 2nd day of Jul 1805
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.