Improvements in the Manufacture of Chromates.
Year: 1888

page_text: Date of Application, 5th Apr., 1888
Complete Specification Left, 7th Jan., 1889
Complete Specification Accepted, 30th Mar., 1889
Improvements in the Manufacture of Chromates.
I, WILLIAM JOHN ALEXANDER DONALD, of Castle Park house, in the County of
Ayr, Chemical Manufacturer, do hereby declare the nature of this invention to be as
follows:-
In manufacturing chromates chrome ore containing from 50% to 56% of chromium
sesquioxide after being finely ground is mixed with lime and potash or soda or other
salt, according to the form of chromate desired to be produced, such salt being either
in form of carbonate or hydrate or sulphate and preferably in a hydrated or diluted
condition. This mixture in charges of a convenient quantity is then subjected to an
oxidising action in a reverberatory furnace until the oxide of chromium has been
converted into a chromate of the salt with which it was mixed. In practice a con-
siderable per centage of the oxide of chromium proves unavailable, remaining partly in
its original state and partly entering into combination with lime. On lixiviating the
furnaced charge with water this unavailable chromic oxide remains in the residue
with the lime and foreign matter contained in the chrome ore and has hitherto been
passed to the waste heaps and treated as valueless at least in connection with the
manufacture of chromates. Such residue or waste when dried consists to the extent
of from about 60% to 70% of lime and may contain from 2% to 5% of chromic
oxide I have discovered that by roasting or calcining this waste residue it may be
used to a large extent, if not wholly, and may be used repeatedly, in lieu of fresh lime
in making up the charges for the "chrome furnaces" and that the oxide of chromium
and chromate of lime it contains may thus to a large extent be recovered and rendered
available for reducing the quantity of chrome ore required in making up the charges
for the furnace.

page_text: Improvements in the Manufacture of Chromates.
I, WILLIAM JOHN ALEXANDER DONALD, of Castle Park house, in the County of
Ayr, Chemical 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 :-
On
In manufacturing chromates, chrome ore, containing by preference from 50% to
56% of chromium sesquioxide after being finely ground is mixed with lime and potash
or soda or other salt, according to the form of chromate desired to be produced,
such salt being either in the form of carbonate or hydrate or sulphate and pre-
ferably in a state of aqueous solution. This mixture in charges of a convenient
quantity is then subjected to an oxidizing action in a reverberatory furnace until
the oxide of chromium has been converted into chromate of the salt with which it
was mixed. In practice a considerable per centage of the oxide of chromium proves
unavailable part of it remaining in its original state and part of it entering into
combination with lime while a portion of it after having been converted into
chromate of calcium has been reduced back again to the state of oxide.
lixiviating the furnaced charge with water this unavailable chromic oxide remains
in the residue with. the lime and foreign matter contained in the chrome ore
and has hitherto been passed to the waste heaps and treated as valueless at least
in connection with the manufacture of chromates. Such residue or waste (commonly
called "chrome waste") when dried consists to the extent of from about 60%
to 70% of lime and may contain from 2% to 3% or more of chromic oxide-
I have discovered that by roasting or calcining this waste residue it may be used
to a large extent, if not wholly, and may be used repeatedly, in lieu of fresh lime in
making up the charges for the "chrome furnaces" and that the oxide of chromium
and chromate of lime along with any potash soda or other salt it contains may thus
to a large extent be recovered and rendered available for reducing the quantity of
chrome ore and of such potash soda or other salt required in making up the charges
for the furnace.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The treatment of what is known as "chrome waste" for the purpose of rendering
it available for the manufacture of chromates to the extent of its contained chromic
oxide and lime and potash soda or other salt and the use of the same for this
purpose all substantially as above described.
Dated this 7th day of January 1880