Improved Manufacture of Sodium and Potassium Bichromates.
Year: 1892

page_text: Date of Application, 27th Jan, 1892
Complete Specification Left, 20th Oct., 1892-Accepted, 3rd Dec., 1892
PROVISIONAL SPECIFICATION.
[Communicated from abroad by the firm of MARC MAURICE ROTTER, of
Schiffbauerdamm 294, Berlin, Germany, Engineers.]
Improved Manufacture of Sodium and Potassium Bichromates.
I, OLIVER IMRAY of No. 28 Southampton Buildings, Chancery Lane, in the
County of London, Chartered Patent Agent do hereby declare the nature of this
invention to be as follows: :-
This invention relates to an improved commercial manufacture of sodium and
potassium bichromates wherein, in place of using mineral acids, such as sulphuric
acid or hydrochloric acid, which have heretofore been used for decomposing the
neutral sodium and potassium chromates, carbonic acid is employed, which effects
the conversion of the chromates into bichromates and bicarbonates.
The practical carrying out of this new process will in the following be described
firstly with reference to sodium chromate.
Into the cold concentrated solution of sodium chromate carbonic acid is introduced
either at atmospheric or higher pressure under stirring and cooling. For this purpose
is employed either pure carbonic acid, or this can be used in the dilute state in
which it is given off from limė kilns.
The decomposition then takes place according to the following formula:
2 NaCrO, + 2 CO, + HgO = 2 NaHCO, + NaCrO
The formed sodium bicarbonate is precipitated while sodium bichromate remains
in solution. This solution is separated from the bicarbonate, concentrated by
evaporation, and again treated in the cold with carbonic acid, whereby the
conversion into bichromate is effectually completed. The aqueous solution of
bichromate resulting from the bicarbonate is then evaporated until crystallisation
sets in, or it is calcined, according as it is desired to produce the sodium
bichromate in a crystalline or a calcined condition.
The sodium bicarbonate is dried and is again employed in place of ordinary
carbonate of soda for smelting chromium ore under addition of lime for producing
sodium chromate.
When treating potassium chromate, the process is as follows:
The cold concentrated solution of the chromate is treated, under cooling, with
carbonic acid or the waste gases of a lime kiln, within vessels provided with stirring
apparatus, potassium bichromate is thus produced together with potassium bicar-
bonate, the former being precipitated while the latter remains in solution. The
decomposition takes place according to the formula:
2 K¿CrO + 2 CO₂+ H₂O=2 HKCO, + K₂Cг₂O,.
4
The precipitated potassium bichromate is separated from the liquid and is
brought into the usual commercial form by recrystallisation.
The liquid which contains, some potassium bichromate in addition to potassium
bicarbonate, is concentrated by evaporation and is used in place of potash for
smelting chromium ore with addition of lime for the production of potassium
chromate.
Dated this 971
27th day of January
1900
2 K,CrO₁ + 2 CO₂ + H₂O=2 HKCO, + K₂Cг.„.
The precipitated potassium bichromate is separated from the liquid and is
brought into the usual commercial form by recrystallisation.
The liquid which contains, some potassium bichromate in addition to potassium
bicarbonate, is concentrated by evaporation and is used in place of potash for
smelting chromium ore with addition of lime for the production of potassium
chromate.
TW T1000
ABEL & IMKAY,
Agents for the Applicant.

page_text: completely calcined, sodium bicarbonate, containing chromium, being obtained as a
bye-product, substantially as described.
2. An improved manufacture of potassium bichromate consisting in first treating
the concentrated potassium chrómate lye in the cold with carbonic acid, then
purifying the potassium bi-chromate by recrystallisation while the potassium
bicarbonate obtained, which is converted into carbonate by concentration under
evolution of carbonic acid, is finally obtained by evaporation as potassium carbonate
containing chromium substantially as described.
Dated this 20th day of October 1892.
ABEL & IMRAY,
Agents for the Applicant.