Improvements in the Manufacture or Regeneration of Chromates or Bi-chromates from Waste Battery or other Liquors or from Chrome Alum or Sesqui Salts of Chromium.
Year: 1898

page_text: Date of Application, 15th Feb., 1898-Accepted, 2nd Apr., 1898
COMPLETE SPECIFICATION.
Improvements in the Manufacture or Regeneration of Chromates or
Bi-chromates from Waste Battery or other Liquors or from
Chrome Alum or Sesqui Salts of Chromium.
I, JAMES YATE JOHNSON, of 47, Lincoln's Inn Fields, in the County of London,
Gentleman, do hereby declare the nature of this invention (which has been
communicated to me from abroad by Herman Dercum, of 1725, Master Street, in
the City and County of Philadelphia, State of Pennsylvania, one of the United
States of America, Gentleman), and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement:-
In the action of primary batteries in which a bichromate, such as bichromate of
potash, or of soda, and free sulphuric acid, are used, the chemical action which
results in the production of the electric current has the effect of reducing the
bichromate to green chromium sulphate, which frequently crystallizes out in the
battery solution in the form of chrome alum.
The object of this invention is to take the waste liquor of these batteries, or the
chrome alum, which is its main ingredient, and from it to regenerate the more
valuable bichromate for new utilization. It is to be understood, that this invention
is not limited to the regeneration of bichromate of potash, or of soda, from waste
battery liquid but may be applied to the green chromium compounds corresponding
to those produced in this battery action. This object is attained according to this
invention as follows:-
In regenerating the bichromate of potash, or of soda, from the waste liquor of a
primary battery, in which bichromate of potash, or of soda, is originally used,
and where sulphuric acid is present in excess, the proceeding is as follows:-
I first add milk of lime, because a large excess of acid in these chrome liquors,
even when neutralized with caustic soda, or potash, still remains in the solution as
sulphate of soda, or sulphate of potash, which salts interfere with the subsequent
crystallization of the bichromate." Therefore it is much more advantageous to
neutralize the free sulphuric acid with slacked lime in a condition like thin cream,
and known as "milk of lime," as then both the sulphuric acid and the lime are
removed in the form of insoluble sulphate of lime:
Slacked lime is moreover the cheapest material that can be chosen to neutralize
the free acid, so necessary for economical use of the oxidising agent.
In carrying out the process milk of lime is added as long as the white precipitate
of sulphate of lime forms, or until litmus test paper shews that the acid reaction
has disappeared and the solution has become neutral. It must not be added in
excess, or to alkaline reaction, as the chromium hydrate then begins to be thrown
out and the bleaching powder does not act readily in alkaline solution.
But with the solution just neutral, or still faintly acid, the bleaching powder,
which is used as oxidising agent, can be added. This begins its oxidising action
in the cold but is aided by heat. The separated calcium sulphate, from the
neutralization of the free sulphuric acid, need not be filtered off before beginning
the oxidation with the bleaching powder as this causes the formation of additional
quantities of calcium sulphate, being itself a calcium compound.

page_text: In carrying out the process, the solution, if strongly acid, is first prepared by
the use of milk of lime and then the reduced chromium salt is oxidised by the
action of calx chlorata, U.S. Pharmacopoeia, known commonly as bleaching powder
(chloride of lime).
Bleaching powder has long been known as an energetic oxidising agent and the
possibility of its oxidising green chromium oxide, or hydrate, has also been noticed
by writers, but the application of this oxidising agent for the purpose of generating
a valuable product such as bichromate of potash, or of soda, and the detailed
methods of its application, are, as far as I know, new, and it is I believe the most
efficient means for converting the green chromium compounds which are of small
value into the chromates from which they originally were formed, and which are
of considerable value as commercial products.
After this oxidising is completed, calcium sulphate which has formed is filtered
off and the solution is concentrated down to the point of crystallization.
Bichromate of potash, or of soda, can then be crystallized out, and, if necessary,
purified by re-crystallization, to free it from any sulphate of zinc which may have
been in the original solution. Purification is however not necessarily part of this
special process.
In case solid chrome alum, which frequently separates out in battery cells, or
either of the green salts known as sesqui salts of chromium, is available as a start-
ing point, the previous treatment with milk of lime is not necessary. Such salts
can be at once dissolved into a concentrated solution and be acted upon by the
bleaching powder.
In the waste liquor which was taken for the following quantitative tests, besides
the chrome alum, there was present sulphate of zinc, sulphate of soda, and
considerable free sulphuric acid as impurities.
As an illustration I may give two quantitative experiments which were made to
ascertain the relative amounts of bleaching powder required according to whether
milk of lime was, or was not, used previously to effect neutralization of the free
sulphuric acid.
100 grams of the chrome solution, containing the impurities mentioned above,
representing 13.42 grams of CrO, (corresponding to 19-74 grams of potassium
bichromate) after neutralization of the free acid, required, for oxidation, 38·04 grams
of a bleaching powder containing 28 per cent. of available chlorine. On the other
hand, 100 grams of the same solution, oxidised with the same bleaching powder,
without previous neutralization of the free acid, required 58-68 grams of the bleach-
ing powder. So, as slacked lime is cheaper than bleaching powder, it is obviously
more economical to follow the first method.
The above figures shew however that 38.04 parts of bleaching powder, of 28 per
cent. strength, will regenerate 19.74 parts of bichromate of potash.
The re-action obtained is as follows:-
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It will be seen that the process herein before described for the regeneration of
chromates or bichromates involves the use of only very cheap chemicals and
therefore that the said regeneration in this way is very economical and
practicable.
Bichromate may be regenerated from other waste products having the green
chromium compounds which result from the reduction of chromates, whether in
the solid form, or in solution, and a simple chromium salt, or the double salt,
known as chromium alum, or liquors containing them, may form the starting
point.
I do not claim the use of bleaching powder in a broad sense for the oxidation of
a lower oxide of chromium to a higher one, but the specific treatment of chrome
alum or sesqui-salts of chromium or liquors containing them for the production of
alkaline bichromates, such as potassium or sodium bichromate.

page_text: Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. In the manufacture, or regeneration, of chromates, or bichromates, the herein
described process consisting in subjecting chrome alum or the green salts known as
sesqui-salts of chromium, to the action of the substance known commercially as
bleaching powder, (calx chlorata).
2. In the manufacture, or regeneration, of chromates, or bicromates, the herein
described process consisting in subjecting waste liquors containing green chromium
salt to the action of the substance known commercially as bleaching powder, (calx
chlorata)..
3. The process herein described of regenerating bichromates, or chromates, from
waste liquors in which free sulphuric acid is present, the said process consisting in
first adding to the said liquor, milk of lime to neutralize the free acid, and then
oxidizing the chromium compound present to a chromate, or bichromate, by the use
of the substance known commercially as bleaching powder (calx chlorata).
4. The process herein described of regenerating bichromates, or chromates, from
waste liquors in which free sulphuric acid is present, the said process consisting in
first adding to the said liquor, milk of lime to neutralize the free acid, then
oxidising the chromium compound present to a chromate, or bichromate, by the use
of the substance known commercially as bleaching powder (calx chlorata), and
finally, in connection with the preceding steps, the obtaining of the chromate by
concentration of the solution, after filtering the sulphate of lime and crystallizing,
or re-crystallizing, to free it from impurities.
ו י
of Dahnuem 1900
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.