Improvements in and relating to the Art or Process of Manufacturing Phosphoric Acid from Phosphatic Material.
Year: 1891

page_text: Date of Application, 15th Sept., 1891-Accepted, 17th Oct., 1891
COMPLETE SPECIFICATION.
Improvements in and relating to the Art or Process of Manufacturing
Phosphoric Acid from Phosphatic Material.
I, CHARLES GLASER, a citizen of the United States of America, residing at
227 East German Street, in the City and County of Baltimore and State of
Maryland, one of the United States of America, Manufacturer and Chemist,
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:-
+
The ordinary and known process of manufacturing phosphoric acid from phos
phatic material consists of two main steps, (1st) treating the phosphatic material
with dilute sulphuric acid, obtaining a weak solution of phosphoric acid, (2nd) con-
centrating this solution (after separation) by evaporation.
My improvement consists in the following modification of the above process.
Having obtained the weak phosphoric acid in the ordinary way, I use this instead
of water to dilute sulphuric acid, and treat a new charge of phosphatic material
with sulphuric acid so diluted. Separating the solution obtained by this treatment,
I have in it phosphoric acid of greater strength than that first obtained. Using
this stronger phosphoric acid as a diluent I repeat the process on a new charge of
phosphatic material with the result of again enriching the phosphoric acid..
Having repeated this process as often as may be found convenient and practically
advantageous, each time using the last obtained phosphoric acid as a diluent, and
having thus obtained without evaporation phosphoric acid of much greater strength
than can be so obtained in the ordinary way, I proceed to complete its concentration
by the usual process of evaporation.
The advantages gained by this improvement are as follows:-
Fuel is saved by effecting a large part of the concentration without evaporation.
There is less sulphate of lime in solution to be separated in the evaporating
process, because the diluent phosphoric acid does not dissolve it as water does.
There appears also to be an advantage in the more perfect decomposition effected
by this mixture of acids, rendering an excess of sulphuric acid less necessary.
To illustrate my process I will now give the following example (a knowledge of
the usual process being presumed).
Having sulphuric acid of say 50° Beaume, I dilute this with water to say 15° B.,
and with a sufficient amount of this weak acid I treat in usual manner a charge of
phosphorite in a vat which I will call "A." Then by filtering I obtain from this,
phosphoric acid of about 10° Beaume, and also the washings of the filtrate, which
I keep separate.
Taking the same amount of strong sulphuric acid as before, I dilute this with the
phosphoric acid just obtained, using the same volume of said acid as I used of water
before (any deficiency may be made up with the reserved washings). With this so
diluted acid I treat in like manner as before a like charge of phosphorite in another
vat, which we will call "B." Filtering the contents of this I obtain phosphoric
acid of about 20° Beaume, and also the washings of the filtrate which will be richer
than before.
Again taking strong sulphuric acid and diluting it in like manner with the
phosphoric acid last obtained, I treat with it a like charge of phosphorite in a third
vat "C." Filtering the contents of this vat I get phosphoric acid of about
30° Beaume, besides the washings.
The acid may be further enriched by repeating the process described, but beyond
the point now reached, about 30° Beaume, filtration will be difficult, and I there-
fore proceed to complete the concentration by evaporation in the usual way.

page_text: Although I have described the process of filtration in the vats, "A," "B,”
and "C" as consecutive, it is to be understood that after starting, the three
processes may be in simultaneous operation, each process being indefinitely repeated
in the vat appropriated to it. Again, the arrangement as described above is for
three vats and digesting processes; the number may be increased or diminished with
some advantages according to circumstances.
The washings of the filters will be of various degrees of richness; they should
be kept separate accordingly, that they may be used, by addition to the solvents, or
otherwise, to the greatest advantage.
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:
As a new and useful improvement in the art of manufacturing phosphoric acid,
first diluting sulphuric acid with phosphoric acid (instead of with water) and then
treating successive charges of phosphatic material with sulphuric acid diluted with
phosphoric acid of increasing degrees, by the system of applying the phosphoric
acid derived from each charge as a diluent to the sulphuric acid used in treating the
succeeding charge, substantially as hereinbefore described.
Dated this 15th day of September 1891.
JENSEN & SON,
77, Chancery Lane, London, W.C., Patent Agents.