IMPROVEMENTS IN THE MANUFACTURE OF BICHROMATE OF POTASSA AND OTHER CHROMATES
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
"
I SYDNEY PITT of Sutton in the County of Surrey, Gentleman do hereby
declare the nature of my invention for "IMPROVEMENTS IN THE MANUFACTURE
OF BICHROMATE OF POTASSA AND OTHER CHROMATES A communication to me
from abroad by Henry Bower of the City and County of Philadelphia in the
State of Pennsylvania United States of America to be as follows :-
This Invention consists of an improved method of converting the insoluble
compounds of chromic acid formed during the treatment of mixtures of chrome
ore, and earthy and alkaline bases and salts into the soluble chromates of the said
bases.
The ordinary method of making bichromate of potassa and other chromates
consists in calcining chrome ore in an oxidizing atmosphere with hydrate or
carbonate of lime and the hydrates or salts of potassa or soda and then digesting
the calcined mass in water, with such additional amounts of the said salts of the
alkalies as may be necessary to decompose any chromate of lime or magnesia that
may be present into chromates of the alkaline bases. In the manufacture of
bichromate of potassa sufficient sulphuric or other acid is then added to the clear
solution of the neutral chromate of potassa resulting from the above digesting
process to withdraw one half of the potassa from combination with the chromic
acid, forming bichromate of potassa and an equivalent amount of a potassio salt
of the acid used. This process being well known and fully described in many
technical works, need not be herein further described in detail.
In the above process after digesting the calcined mass, as above described with
water, the greater portion of the chromates present dissolves, as alkaline chromates,
and is separated by lixiviating the mass; but a considerable quantity thereof
varying from ten to twenty per cent of the total amount of chromic acid formed,
obstinately resists solution being in the state of a complex combination of chromic
acid, oxide of iron alumina and lime.
I have discovered that the decomposition of the above described insoluble
combination of chromates may be most completely and satisfactorily effected
by carbonic acid and alkaline carbonates acting simultaneously and the total
amount of chromic acid obtained in solution as alkaline chromates.

page_text: To enable others skilled in the art or science to make use of my improved
process I will proceed to describe it more fully.
The mixture of finely powdered chrome ore, lime and alkalies or alkaline salts
having been calcined as usual in an oxidizing furnace, is mixed with the additional
salts of the alkalies required and with water in sufficient quantity to form a thin
cream and to hold in solution the theoretical amount of alkaline chromate. A little
over a gallon of water to each pound of chrome ore used is generally sufficient.
For this purpose I prefer to use a high cylindrical vessel of boiler iron with
a conical bottom into which the mixture is charged. This vessel is such as is
generally used in the purification of petroleum with sulphuric acid. I add
carbonate of potash; the proportion of alkaline carbonates used should be a
quantity containing an excess of alkali equal to about five per cent over the
amount necessary to combine with the released chromic acid, the quantity of the
latter existing in the insoluble compound being determined from time to time
before treatment.
I then force into the mixture through pipes provided at their lower ends, with
numerous small holes, a current of gases containing carbonic acid purified as
herein after described, and obtained from the waste gases from furnaces coke or
charcoal, or from the gases from lime-kilns, or from any other convenient source.
The mixture of calcined matters and water is kept violently agitated either by
the permeating and escaping gases or by mechanical means if the action of the
guses is insufficient so as to hold the insoluble matter in a state of suspension
in the fluid. This treatment is continued until the chromic acid present is all or
nearly all in solution which can be readily determined by the usual chemical tests,
or approximately by the color of the insoluble portion of the mixture which being
at first a dark olive green, becomes by the action of the carbonic acid a light
yellowish brown or like the hydrated oxide of iron. The length of time required
is of course dependent upon the rapidity of the passage of the gas and the amount
thereof. In a proper apparatus it can easily be completed in twenty four (24)
hours.
The gas containing carbonic acid must of course, be washed and freed from all
traces of sulphurous acid before using, which is readily done by passing it through
washing or scrubbing towers or over or through wet carbonate of lime in mass or
powder, or by other well known means.
Any form of apparatus that will bring carbonic acid into contact with the
mixture may be used, or the mass from the calcining furnace may be exposed in its
dry state, or after being wetted, to the action of carbonic acid; or the chromate
formed and already soluble, may be first leached out, and the residue alone, or with
the additional salts of the alkalies, be mixed with water and subjected to the
action of carbonated alkali and carbonic acid; but I prefer the method as first
described.
The decomposition of the insoluble chromates being completed, the solution is
separated from the insoluble residuum, concentrated and converted into bichromate
of potassa or other chromates in the usual manner.
The residuum usually contains several per cent of undecomposed chrome ora.
The chromic acid equivalent thereto can be obtained as soluble chromate by leaving
in or supplying to the residuum a little of the salts of the alkalies and drying and
recalcining the mass which being then treated with water carbonated alkali and
carbonic acid, as before the theoretical amount of chromate corresponding to the
oxide of chrome in the ore may be obtained.
Dated thin 09th dox of Tobrnery 1881

page_text: "
I SYDNEY PITT of Sutton in the County of Surrey Gentleman do hereby
declare the nature of my invention for "IMPROVEMENTS IN THE MANUFACTURE
OF BICHROMATE OF POTASSA AND OTHER CHROMATES A communication to me
from abroad by Henry Bower of the City and County of Philadelphia in the State
of Pennsylvania United States of America and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
This invention consists of an improved method of converting the insoluble
compounds of chromic acid formed during the treatment of mixtures of chrome
ore and earthy and alkaline bases and salts into the soluble chromates of the said
bases.
The ordinary method of making bichromate of potassa and other chromates
consists in calcining chrome ore in an oxidizing atmosphere with hydrate or
carbonate of lime and the hydrates or salts of potassa or soda and then digesting
the calcined mass in water with such additional amounts of the said salts of the
alkalies as may be necessary to decompose any chromate of lime or magnesia that
may be present into chromates of the alkaline bases. In the manufacture of
bichromate of potassa sufficient sulphuric or other acid is then added to the clear
solution of the neutral chromate of potassa resulting from the above digesting
process to withdraw one half of the potassa from combination with the chromic
acid forming bichromate of potassa and an equivalent amount of a potassic salt
of the acid used. This process being well known and fully described in many
technical works need not be herein further described in detail.
In the above process after digesting the calcined mass as above described with
water the greater portion of the chromates present dissolves as alkaline chromates
and is separated by lixiviating the mass but a considerable quantity thereof varying
from ten to twenty per cent of the total amount of chromic acid formed obstinately
resists solution being in the state of a complex combination of chromic acid, oxide
of iron alumina and lime.
I have discovered that the decomposition of the above described insoluble
combination of chromates may be most completely and satisfactorily effected
by carbonic acid and alkaline carbonates acting simultaneously and the total
amount of chromic acid obtained in solution as alkaline chromates.
To enable others skilled in the art or science to make use of my improved
process I will proceed to describe it more fully.
The mixture of finely powdered chrome ore lime and alkalies or alkaline salts
having been calcined as usual in an oxidizing furnace is mixed with the additional
salts of the alkalies required and with water in sufficient quantity to form a thin
cream and to hold in solution the theoretical amount of alkaline chromate. A
little over a gallon of water to each pound of chrome ore used is generally
sufficient. For this purpose I prefer to use a high cylindrical vessel of boiler
iron with a conical bottom into which the mixture is charged. This vessel is such
as is generally used in the purification of petroleum with sulphuric acid. I add
carbonate of potash; the proportion of alkaline carbonates used should be a
quantity containing an excess of alkali equal to about five per cent over the
amount necessary to combine with the released chromic acid, the quantity of the
latter existing in the insoluble compound being determined from time to time
before treatment.

page_text: I then force into the mixture through pipes provided at their lower ends with
numerous small holes a current of gases containing carbonic acid purified as
hereinafter described and obtained from the waste gases from furnaces coke or
charcoal or from the gases from lime kilns or from any other convenient source.
The mixture of calcined matters and water is kept violently agitated either by
the permeating and escaping gases or by mechanical means if the action of the
gases is insufficient so as to hold the insoluble matter in a state of suspension in
the fluid. This treatment is continued until the chromic acid present is all or
nearly all in solution which can be readily determined by the usual chemical tests,
or approximately by the color of the insoluble portion of the mixture which being
at first a dark olive green becomes by the action of the carbonic acid a light
yellowish brown or like the hydrated oxide of iron. The length of time required
is of course dependent upon the rapidity of the passage of the gas and the amount
thereof. In a proper apparatus it can easily be completed in twenty four (24)
hours.
The gas containing the carbonic acid must of course be washed and freed from
all traces of sulphurous acid before using which is readily done by passing it
through washing or scrubbing towers or over or through wet carbonate of lime in
mass or powder or by other well known means.
Any form of apparatus that will bring carbonic acid into contact with the
mixture may be used or the mass from the calcining furnace may be exposed in its
dry state or after being wetted to the action of carbonic acid or the chromate
formed and already soluble may be first leached out and the residue alone or with
the additional salts of the alkalies be mixed with water and subjected to the
action of carbonated alkali and carbonic acid but I prefer the method as first
described.
The decomposition of the insoluble chromates being completed the solution is
separated from the insoluble residium concentrated and converted into bichromate
of potassa or other chromates in the usual manner.
The residium usually contains several per cent of undecomposed chrome ore.
The chromic acid equivalent thereto can be obtained as soluble chromate by leaving
in or supplying to the residium a little of the salts of the alkalies and drying and
recalcining the mass which being then treated with water carbonated alkali and
carbonic acid as before the theoretical amount of chromate corresponding to the
oxide of chrome in the ore may be obtained.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:-
=-
As an improvement in the process of manufacturing bichromate of potassa and
other chromates, the herein before described method of treating the calcined mixture
of chrome ore, bases and salts simultaneously with carbonated alkali and carbonic
acid gas for the purposes described.