Improvements in the Manufacture of Chromates, Bichromates, and other Chromium Compounds.
Year: 1891

page_text: Date of Application, 6th Feb., 1891-Accepted, 4th Apr., 1891
COMPLETE SPECIFICATION.
[Communicated from abroad by JULES MASSIGNON and ETIENNE WATEL, both
of 95, Boulevard Beaumareliais, Paris, in the Republic of France, Chemists.]
Improvements in the Manufacture of Chromates, Bichromates, and
other Chromium Compounds.
I, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, 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 relates to the manufacture of chromates, bichromates and other
chromium compounds.
The several processes heretofore employed for this purpose present serious
inconveniences which render them very expensive. For example, the consumption
of fuel for effecting the oxidation in the furnaces containing the mixture of ore,
lime, and potash, or potassium salt (or soda or sodium salt) is so enormous that the
expense for fuel forms from 25 to 35 per cent. of the cost of manufacturing bichro-
mate of potash. Another inconvenience consists in the great difficulty experienced
in the stirring of the material upon the sole of the furnaces during the whole time
of the oxidation. Moreover the ore is very incompletely oxidized only two-thirds
or three-fourths of the chromium sesquioxide being utilized for the transformation
into chromic acid. There is also a loss of part of the alkali, potash or soda which
is due to volatilization, the carrying away. by hot gases, the combination with the
gangue of the ore, more especially silica, and the formation of potassium or sodium
silicate.
My said invention is designed to diminish or entirely obviate the aforesaid
inconveniences. It enables the consumption of fuel to be reduced to very consider-
able extent, the oxidation instead of taking place by the use of a great excess of
air heated to a high temperature is effected slowly at the ordinary temperature the
labour of stirring the material in the furnaces is dispensed with, all the chromium
sesquioxide of the ore is oxidized, the loss of potash or soda to which I have referred
does not occur. My invention moreover enables the employment of less expensive
potassium or sodium salts such as sulphates in lieu of caustic potash or soda which
has hitherto been used in the mixtures.
For obtaining these results I proceed in the following manner.
After the ore has been very finely pulverized it is mixed with calcium chloride
and lime or calcium carbonate in such proportions that the entire base obtained
from the caustic lime or the calcium carbonate shall be somewhat greater than the
quantity necessary for forming a calcium chromate when all the chromium
sesquioxide of the ore will be transformed into chromic acid by the oxidation.
The calcium chloride is employed in the proportion of one equivalent for three
equivalents of the total lime (caustic lime or carbonate), which proportion is suitable
for composing calcium oxychloride.
This mixture is obtained by kneading together the pulverized ore and a paste
formed either by lime and calcium carbonate or by calcium carbonate alone, slaked
or diluted in a concentrated solution of calcium chloride.
If the mixture is made with calcium carbonate it does not harden at once in
the air, but if lime and calcium carbonate are added at the same time the kneaded
mixture hardens and it can be employed for making blocks or slabs which will partly
dry in the open air.
The said mixture is then conveyed to a furnace wherein it is first heated moderately
for effecting the desiccation and then raised to a temperature which is sufficient for
effecting the reduction of the calcium carbonate to form caustic lime.

page_text: In case the operation takes place in a furnace having an ordinary sole the mixture
will be oxidized by the current of hot air much more rapidly than in the processes
hitherto employed, the consumption of fuel will therefore be less.
If however the material burned at the temperature adapted for the reduction of
the calcium carbonate is removed from the furnace, it will be sufficient to allow the
pieces of material to be exposed to the air at the ordinary temperature in order
that the complete oxidation of the chromium sesquioxide shall without any manipu
lation be gradually effected by the action of the atmospheric air as the material is
porous enough for enabling the latter to pass to the interior of the pieces.
The time required for the transformation of all the chromium sesquioxide into
chromic acid united with lime, will vary with the temperature and the moisture of
the air and also the thickness of the pieces.
It is necessary that the mixture shall contain an excess of lime, and the greater
this excess the slower will be the oxidation, part of the lime in the mixture being
carbonated by the carbonic acid of the air.
Accordingly this process enables chromic acid to be obtained in the state of
calcium chromate and after the oxidation has terminated the mixture will contain
calcium chromate and calcium chloride, calcium carbonate and caustic lime; and
sesquioxide of iron and gangue of the ore, part of which is united with the lime.
After desiccation the pieces of the material can be baked very economically in
a continuously operating lime kiln heated by gas. The oxidation will commence
when the said pieces are hot under the action of the current of air which is
introduced for cooling these pieces and for effecting the combustion of the gas.
They are then removed from the kiln in order to be exposed to the air under cover
until the oxidation is complete.
This operation is similar to that of a tile or brick making kiln, the materials
being mixed or moulded, then dried under cover near the kiln, next burnt in the
kiln and on leaving the latter they are piled up under cover or in aired chambers
close by until the oxidation is complete.
This oxidized mixture can then serve for the manufacture of chromates or
bichromates and also of chromic acids or chlorochromic acids.
For manufacturing chromates and bichromates of potash and soda the above-
mentioned mixture is lixiviated in hot water by washing so as to enable a
concentrated solution to be produced which contains all the calcium chloride and
only a small quantity of calcium chromate by reason of the great difference in the
solubility of these two substances, calcium chromate being about a hundred times
less soluble than calcium chloride.
°
For the purpose of recovering or utilizing the calcium chromate entering into
this solution, the latter can be concentrated and then serve for preparing a fresh
mixture of the material the calcium chromate which it contains will thus be extracted
by the following operation.
This solution can be utilized for manufacturing lead chromate (chrome-yellow)
by precipitating the calcium chromate by a salt of lead. In this manner will
be obtained a solution of calcium chloride deprived of chromate and ready to be
used in the operation, and the chrome-yellow is produced very economically,
whilst heretofore it has been necessary to obtain the same from potassium or sodium
bichromate.
After this washing operation the mixture is treated by a solution of sulphate or
carbonate of potash or soda and yields potassium or sodium chromate, and, if
moreover sulphuric acid is employed potassium or sodium bichromate in solution.
These solutions are filtered for separating them from the insoluble deposits,
concentrated and crystallized in order to extract from them the salts formed.
When the mixture of dry oxidized material is treated by sulphuric acid, or by
dry gaseous hydrochloric acid, chlorochromic acid can be economically obtained.
By treating the mixture with sulphuric acid and after the calcium chloride has
been removed therefrom by lixiviation and after drying, chromic acid can be

page_text: economically produced without first forming potassium or sodium bichromate as.
heretofore.
By reason of the various advantages herein before stated the improved process
enables chromates and bichromates to be manufactured at a greatly reduced cost.
Having now particularly described and ascertained the nature of this inven-.
tion, and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is :-
First. The employment of a mixture of pulverized chrome-ore, lime, carbonate
of lime, and calcium chloride.
Second. The oxidation of the ore at a low temperature by means of this mixture
after a suitable burning.
Third. The use in the operation, of calcium chloride (when the oxidation is
finished) for utilizing it for fresh operations.
Fourth. The manufacture of chromate of lead in the course of the manufacture
of chromates under the conditions herein before stated.
Fifth. The employment of this mixture for manufacturing chromates bichromates
and any chromated products.
Sixth. The improvements in the manufacture of chromates, bichromates and
other chromium compounds substantially as hereinbefore described.
Dated this 6th day of February 1891.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.