Improvements in Obtaining Chromates and Bichromates of Potash and Soda.
Year: 1891

page_text: Date of Application. 3rd July, 1891
Complete Specification Left, 31st Mar., 1892-Accepted, 28th May, 1892
Improvements in Obtaining Chromates and Bichromates of Potash
and Soda.
A communication from SAMUEL PEACOCK, of Bridgeton, in the State of New
Jersey, United States, and HUGH ALLEN GALT, of Philadelphia, in the
State of Pennsylvania, United States, Technical Chemists.
I, THOMAS GOODALL of 149, Onslow Drive, Glasgow, in the County of Lanark,
North Britain, Lace-curtain Manufacturer, do hereby declare the nature of this
invention to be as follows, that is to say:
The said invention comprises processes for obtaining chromates and bichromates
of potash in which the use of the valuable salts of potash is omitted until after the
calcining stage of the process, whereby the loss of any of these salts by volatiliza
tion is avoided; the process is equally applicable to the obtaining of chromates
and bichromates of soda.
The usual method of manufacturing chromates and bichromates of potash consists
in calcining chrome ore in an oxidising atmosphere with lime and salts of potash,
the latter being in sufficient quantity to attract by virtue of its superior affinity
all, or nearly all, of the chromic oxide, leaving the greater part of the lime
untouched which acts merely as a flux or vehicle and facilitates the operation.
The resultant mass is then lixiviated with hot water and the neutral chromates of
potash resulting from the process being soluble are removed, and, by the addition
of sulphuric or other acid, converted into bichromates and separated by crystalli-
zation or other well known methods.
In the above process there is necessarily a large loss of the salts of potash in the
calcining stage of the process, either by volatilization or by their being mechanically
carried up the chimney. This loss amounts at times to 25 per cent. of the salts
used, and forms commercially a very considerable element in the cost of manufacture
of the bichromate.
In carrying out the invention this loss of the valuable salts of potash is avoided
by deferring their use until after the calcining stage of the process. This is
accomplished by restricting the calcining stage to the production of chromate of
lime which has hitherto, on account of its insolubility, been looked upon as a waste
product, and afterwards converting the chromate of lime into chromate of potash
by a process hereinafter described.
There are placed in the calcining furnace along with the chrome ore, lime, either
caustic or carbonate, and a very small quantity of a soda salt. The following
are convenient proportions for use in applying the invention:
500 pounds of finely powdered chrome ore, containing say 50 per cent, chromic
oxide;
500 pounds of caustic lime, or its equivalent in carbonate of lime;
60 pounds of soda ash.
When these have been mixed intimately together, either with or without water,
and calcined in the usual manner in a reverberatory furnace, as there is an insuffi-
cient quantity of the soda salt to exhaust the chromic oxide from the ore, by far the
greater portion of it passes to the lime. The soda salt is used only to facilitate
the formation of the chromate of lime, which in practice is best accomplished when
there is present about 25 per cent. of the amount sufficient to exhaust all the
chromic oxide from the orc.
Salts of potash may of course be used in place of the soda ash, but the com-
parative cheapness of the soda salts and the fact that a given weight of soda will
utilize more chromic oxide than the same weight of potash, gives them the

page_text: preference. In determining the quantity, it must be borne in mind that the chief
aim is the formation of chromate of lime, the production of chromate of soda being
kept at a minimum, and consequently only so much soda ash being used as will
facilitate the production of the largest quantity of chromate of lime.
At the end of the calcining process the resultant mass comprises chromates of
lime and soda. The charge is withdrawn from the furnace and lixiviated with hot
water, whereby the soluble chromate of soda is washed out and may afterwards be
converted into bichromate of soda by the usual method; but the insoluble chromate
of lime remains behind in a complex combination with oxide of iron, magnesia,
and alumina.
To effect the recovery of the remaining insoluble chromates and convert them
nto chromates of potash, the residuum of calcined material, after the soluble
chromate has been washed out is treated according to either of the following two
methods, depending on the adaptability of the plant-First--treatment of the
residuum of calcined material with a hot solution of sulphate of potash. The mass
is repeatedly washed with the hot solution, which is drawn off from the bottom
and returned to the top of the lixiviating tank, where it is again heated by a steam
coil or any other suitable device until the decomposition of the insoluble chromate
is effected the soluble chromate of potash formed being readily separated and may
be converted into bichromate in the usual manner. Second treatment of the
residuum of calcined material with carbonic acid gas thereby converting the
insoluble chromates into soluble bichromates, and converting the latter into
bichromates of the alkalies by the addition of alkaline salts.
In this last operation other saltz of potash may be used in place of sulphate, as
well as sulphate or other salts of soda, when it is desired to produce chromate or
bichromate of soda, and the temperature of the solution may be varied as is found
to effect the best results. As the salts of potash are not used until the lixiviating
stage of the process they suffer no loss, and all of the potash used enters into the
final product.
The process has been described with reference to the production of bichromate
of potash but it is equally applicable to the production of bichromate of soda, or
other bichromates depending merely upon the base of the salt used in the lixiviating
process.
Dated this Second day of July 1801
EDMUND HUNT,
Per pro D. Ferguson,
Applicant's Agent.
COMPLETE SPECIFICATION.
Improvements in Obtaining Chromates and Bichromates of Potash
and Soda.
A communication from SAMUEL PEACOCK, of Bridgeton, in the State of New
Jersey, United States, and HUGH ALLEN GALT, of Philadelphia, in the
State of Pennsylvania, United States, Technical Chemists.
I, THOMAS GOOdall, of 149 Onslow Drive, Glasgow, in the County of Lanark,
North Britain, Lace-curtain 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, that is to say —
The said invention comprises processes for obtaining chromates and bichromates
of potash in which the use of the valuable salts of potash is omitted until after
the calcining stage of the process, whereby the loss of any of these salts by
volatilization is avoided; and the process is equally applicable to the obtaining of
chromates and bichromates of soda.
The usual method of manufacturing chromates and bichromates of potash
consists in calcining chrome ore in an oxidizing atmosphere with lime and salts of

page_text: potash, the latter being in sufficient quantity to attract by virtue of its superior
affinity all, or nearly all, of the chromic oxide, leaving the greater part of the
lime untouched which acts merely as a flux or vehicle and facilitates the operation.
The resultant mass is then lixiviated with hot water and the neutral chromates of
potash resulting from the process being soluble are removed, and, by the addition
of sulphuric or other acid, converted into bichromates and separated by crystalliza-
tion or other well known methods.
In the above process there is necessarily a large loss of the salts of potash in
the calcining stage of the process, either by volatilization or by their being
mechanically carried up the chimney. This loss amounts at times to 15
per cent.
of the salts used, and forms commercially a very considerable element in the cost
of manufacture of the bichromate.
In carrying out the invention this loss of the valuable salts of potash is avoided
by deferring their use until after the calcining stage of the process. This is
accomplished by restricting the calcining stage to the production of chromate of
lime, which has hitherto, on account of its insolubility. been looked upon as a waste
product, and afterwards converting the chromate of lime into chromate of potash
by a process hereinafter described.
There are placed in the calcining furnace along with the chrome ore, lime, either
caustic or carbonate, and a very small quantity of a soda salt. The following
are convenient proportions for use in applying the invention:-
500 pounds of finely powdered chrome ore, containing, say 50 per cent, chromic
oxide.
500 pounds of caustic lime, or its equivalent in carbonate of lime.
60 pounds of soda ash.
When these have been mixed intimately together, either with or without water,
and calcined in the usual manner in a reverberatory furnace, as there is an.
insufficient quantity of the soda salt to exhaust the chromic oxide from the ore,
by far the greater portion of it passes to the lime. The soda salt is used only to
facilitate the formation of the chromate of lime, which in practice is best
accomplished when there is present about 25 per cent. of the amount sufficient to
exhaust all the chromic oxide from the orc.
Salts of potash may of course be used in place of the soda ash, but the com-
parative cheapness of the soda salts and the fact that a given weight of soda will
utilize more chromic oxide than the same weight of potash, gives them the
preference. In determining the quantity, it must be borne in mind that the chief
aim is the formation of chromate of lime, the production of chromate of soda being.
kept at a minimum, and consequently only so much soda ash is used as will
facilitate the production of the largest quantity of chromate of lime.
At the end of the calcining process the resultant mass comprises chromates of
lime and soda. The charge is withdrawn from the furnace and lixiviated with hot
water, whereby the soluble chromate of soda is washed out and may afterwards be
converted into bichromate of soda by the usual method; but the insoluble chromate.
of lime remains behind in a complex combination with oxide of iron magnesia and
alumina.
To effect the recovery of the remaining insoluble chromates and convert them
into chromates of potash, the residuum of calcined material, after the soluble
chromate has been washed out is treated according to one or other of the following
methods, depending on the adaptability of the plant-First, treatment of the
residuum of calcined material with a hot solution of sulphate of potash. The
mass is repeatedly washed with the hot solution, which is drawn off from the bottom
and returned to the top of the lixiviating tank, where it is again heated by a steam
coil or any other suitable device until the decomposition of the insoluble chromate.
is effected, the soluble chromate of potash formed being readily separated and may
be converted into bichromate in the usual manner. Second, treatment of the
residuum of calcined material with carbonic acid gas thereby converting the

page_text: insoluble chromates into soluble bichromates and converting the latter into
bichromates of the alkalies by the addition of alkaline salts.
Instead of the solution used according to the first method containing only sulphate
of potash it may contain also sulphate of soda, the quantity of sulphate of potash
being not more than enough to form bichromate with the chromic acid present.
Mono-chromates are formed but on subsequently adding a suitable quantity of
sulphuric acid it combines with the soda leaving all the potash to be utilized as
bichromate.
In these operations other salts of potash may be used in place of sulphate, as
well as sulphate or other salts of soda, when it is desired to produce chromate or
bichromate of soda, and the temperature of the solution may be varied as is found
to effect the best results. As the salts of potash are not used until the lixiviating
stage of the process they suffer no loss, and all of the potash used enters into the
final product.
The process has been described with reference to the production of bichromate
of potash, but it is equally applicable to the production of bichromate of soda, or
other bichromates depending merely upon the base of the salt used in the lixiviating
process.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :
Obtaining chromates and bichromates of potash and soda by first calcining
chrome ore with lime and a small quantity of an alkaline salt, secondly, dissolving
out soluble salts from the calcined materials, and thirdly treating the insoluble
chromate of lime with a hot solution of a suitable alkaline salt substantially as
hereinbefore described.
Dated this Twenty-fourth day of March 1892.
EDMUND HUNT,
Applicant's Agent.