Improvements in the Preparation of Caustic Soda Solution from Soda Residues.
Year: 1896

page_text: Date of Application, 26th Nov., 1896-Accepted, 9th Jan., 1897
COMPLETE SPECIFICATION.
Improvements in the Preparation of Caustic Soda Solution from
Soda Residues.
I, FRANZ JOSEF SEYFRIED, of Kalkerstrasse, Mulheim on Rhine, in the
Empire of Germany, Chemist and Manufacturer, 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 present invention relates to the preparation of a pure transparent solution
of caustic soda from soda residues. This object is attained in practice by purifying
the dirty red solution obtained by lixiviating the soda residues by means of hydrated
oxide of lead. This is best attained by producing the hydrated oxide of lead in
the solution itself from a lead solution, preferably a solution of nitrate of lead, and
of milk of lime. The practical carrying out of the process can by way of example
be conducted as follows, reference being made to the apparatus shown in the
drawing:
The vessel a (dissolving tank) is filled half full with water and the same heated
to boiling point by passing in steam from the steam pipe b. After the steam has
been shut off two drums of caustic soda residues whose lids have been previously
removed are lowered into the tank by means of the apparatus c. The one drum is
placed upon a banging support d arranged in the tank, whilst the second drum
may remain suspended on the chain; the steam is again passed in and the whole is
boiled until the soda residues are completely dissolved. The dirty red liquor thus
obtained is now tested by means of the hydrometer and is brought to a density
corresponding to from 36% to 40% either by the addition of water or by the
dissolving of a further quantity of soda residues as may be found requisite. The
liquor is then drawn off iuto a tank e preferably placed in the ground and after it
has somewhat cooled is forced into the upper vessel g by means of the steam jet
apparatus f. The liquor is now treated by the addition of one kilo. of nitrate of
lead which has previously been dissolved in boiling water, and a bucket-full of milk
of lime, and the fluid is allowed to settle until the solution has become as clear as
water. The clear solution is finally run off into one of the lower vessels hi from
whence the finished liquor can be drawn. By means of this process about
320 to 330 kilos. of transparent caustic soda solution are obtained from 10 kilos.
caustic soda residues of 60% to 70%.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed 1 declare that what I
claim is :-
1. The process for obtaining pure transparent caustic soda solution from soda
residues characterised by the clarification of the dirty red solution obtained by the
lixiviating of the latter by means of hydrated oxide of lead.
2. The modification of the process claimed in Claim 1, consisting essentially in
treating the solution of soda residues with a lead solution (preferably a solution of
nitrate of lead) and milk of lime.
November 26th 1896
W. P. THOMPSON & Co.,
322 High Holborn, London, W.C., Patent Agents for the Applicant.