An Improved Process for Preparing at the Same Time Neutral Sulphate of Soda and Precipitated Phosphate of Lime.
Year: 1892

page_text: Date of Application, 8th Feb., 1892-Accepted, 12th Mar., 1892
COMPLETE SPECIFICATION.
An Improved Process for Preparing at the Same Time Neutral
Sulphate of Soda and Precipitated Phosphate of Lime.
We, LUDWIG BRUNNER of Wetzlar in the Empire of Germany and ADOLF
ZANNER of Laeken in the Kingdom of Belgium, both Doctors of Medicine, 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 refers to an improved process for preparing at the same time
neutral sulphate of soda and precipitated phosphate of lime by means of bisulphate
of soda.
Bisulphate of soda is dissolved in water and treated with sulphuric acid solution
of spent or refuse phosphates so that the carbonate of lime and phosphate of lime of
the phosphates in the acid and the acidulated phosphates of lime are made
available.
It is generally sufficient to employ the above mixture or a trifling excess of
bisulphate of soda which it is best to employ at the usual temperature of 25
to 30° Réamur.
Only when a large quantity of phosphates are to be decomposed, is it desirable
to employ a higher temperature or an important excess of bisulphate of soda.
After the decomposition is finished the phosphate sediment formed is separated
from the solution by means of the filtering press. It is then washed and the water
it is washed in may be used again in another mixture of bisulphate of soda.
This phosphate sediment which generally retains from 1 to 3 per cent. of
phosphoric acid can be dried and used for manuring purposes.
The solution thus gained which really contains neutral sulphate of soda and
acidulated calcium phosphate may be precipitated with milk of lime or calcium
carbonate or by a weak alkaline reaction until neutral, whereby the monocalcium,
dicalcium and tricalcium phosphates become separated whilst sulphate of soda in
solution remains.
This precipitated calcium phosphate is then filtered away from the neutral
sulphate of soda solution and the water with which it is washed can be employed
again for the same purpose or for restoring the milk of lime.
Na₂SO, CaH (PO)2 + СаH₂O₂ = Na₂SO4 + Ca₂H, (PO4)2 + 2 H₂O.
If one is obliged to use the phosphates with a large excess of bisulphate of soda,
the precipitated solution will contain free sulphuric acid and the precipitate
becomes as a muddy sediment.
This is then removed for the same purpose as before with the milk of lime as
precipitate.
It is then cleared or filtered again and when further additions of milk of lime
are made the phosphate of lime is precipitated.
The resulting precipitate which consists of bi- and tricalcium phosphate may be
employed after drying, as manure or for the restoration of hyperphosphates.
The remaining solution of neutral sulphate of soda may be either used as such or
evaporated to crystallisation.
Certain worthless mixtures of salts of lime which are sometimes retained by the
sodium sulphate solution after its clarification or filtration are thus separated.

page_text: are allowed to take place one after the other in flat vessels connected together, the
salts of lime are generally all left behind in the first vessel.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is:-
1. The treatment of phosphates with a solution of bisulphate of soda as herein
explained.
2. The precipitation of the remaining solution of neutral sulphate of soda by
means of milk of lime or calcium carbonate as herein explained.
3. Obtaining neutral crystallised sulphate of soda by evaporating the filtered
solution after the separation of the precipitated phosphate of lime, as herein
described.
Dated this 8th day of February 1892.
S. S. BROMHEAD,
97, Newgate Street, London, E.C., Agent for Applicants.