IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF ALUMINA
Year: 1881

page_text: LETTERS PATENT to Conrad Semper, of Philadelphia, Pennsylvania, United
States of America, Chemist, for an Invention of "IMPROVEMENTS IN THE
COMPLETE SPECIFICATION filed by the said Conrad Semper at the Office of
the Commissioners of Patents on the 7th July 1881.
CONRAD SEMPER, of Philadelphia, Pennsylvania, United States of America,
Chemist. "IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF ALUMINA."
The object of my Invention is to produce from ferruginous aluminous material,
such as bauxite, a sulphate of alumina free from iron.
I have discovered that by adding to a solution of ferruginous sulphate of
alumina a small quantity of a solution of sulphate of copper, sulphate of zinc,
sulphate of manganese, or other salt of a metal, which with prussiate of potash will
give flocculent insoluble precipitates, and further adding to the mixture a solution
of prussiate of potash or other soluble prussiate, the iron in said ferruginous
solution, together with the metal which has been added as described, is precipitated,
and the iron so precipitated as Prussian blue is enveloped by the prussiate of the
metal, of which a solution has been added, so that both precipitates are readily
separated by settling out, or by other kindred method.
I do not confine myself to the time and proportions at and in which the above
solutions of soluble metallic salts shall be added and precipitated by the prussiate
of potash, or other soluble prussiate. This can be done either in the raw liquor
containing silica and undecomposed raw material, or in the clear solution of
ferruginous sulphate of alumina after said silica has settled out or has been
removed, or in the solution of sulphate of alumina which has been previously
treated with prussiate of potash, and from which the Prussian blue which was
formed has been for the most part removed.
I prefer for economical reasons to add the solutions of soluble metallic salts after
the sulphate of alumina solution has been treated with prussiate of potash or other
soluble prussiate, and after the Prussian blue bas been removed therefrom.
The following is a convenient method of practising my Invention.
A ferruginous solution of sulphate of alumina obtained in the usual way, and
of which the percentage of peroxide of iron is known, is treated with a sufficient
quantity of a soluble prussiate, such as prussiate of potash, soda, etc., to precipitate
or change all said peroxide of iron into prussiate of iron or Prussian blue. Four
....31

page_text: parts of prussiate of potash will generally suffice for every part of per oxide of
iron.
When the precipitation of Prussian blue is effected, the solution is pumped or
conveyed by air pressure or by other suitable means into a filter press, in the
compartments of which the Prussian blue will for the most part accumulate, while a
moderately clear solution but still strongly colored by Prussian blue will pass
through the cloth and be collected in a tank. This colored solution of sulphate of
alumina is now treated with a very small proportion of a solution of a soluble
metallic salt, iron alone excepted, preferably sulphate of copper, and if an excess of
prussiate of potash or other soluble prussiate has not been previously employed a
quantity of said soluble prussiate is added and the mixture briskly stirred. At
once there will be noticed the formation of a very floculent precipitate of prussiate
of copper which will readily subside, carrying with it all traces of prussiate of iron
or Prussian blue remaining in the solution obtained from the filter press.
This solution, which has thus been treated with a soluble metallic salt and
soluble prussiate is then passed through a second filter press, and a perfectly clear,
colorless solution of sulphate of alumina entirely or almost entirely free from iron
will pass through and can be treated in the usual way by concentration or other
method to produce an article of commerce suitable for every use, to which sulphate
of alumina can be put.
The quantity of metallic salt necessary to effect a thorough separation is very
small.
I have obtained very good results with five parts of sulphate of copper for 1000
parts of iron originally precipitated, but the proportions to be employed may be
left to the judgement and experience of the operator.
The Prussian blue obtained by this process can be used after washing it, which
can be done thoroughly in the filter press in the usual way for paints.
If it is desirable it can be decomposed by alkali or milk of lime, and the prussiate
of potash or soda or lime solution obtained can be utilized as hereinbefore explained,
while the resulting hydrated per oxide of iron will form an excellent material for
metallic paints.
The prussiate of copper, of which if this metal should have been employed
there will be very little, can also be decomposed and utilized in the same
manner.
It is thus seen that an aluminous cake free from iron is produced from
ferruginous aluminous material with the least possible waste or loss of material.
Having thus described my Invention, I claim,-
1. The process of manufacturing sulphate of alumina free from iron, from
ferruginous aluminous material, which consists in the addition to a solution of
ferruginous sulphate of alumina, of prussiate of potash, or other soluble prussiate
and sulphate of copper or other soluble salt of a metal, for the purpose specified.
2. The process of manufacturing sulphate of alumina free from iron, which
consists in the addition to a solution of ferruginous sulphate of alumina of
prussiate of potash or other soluble prussiate and sulphate of copper, or other
soluble salt of a metal, and in the separation of the clear sulphate of alumina
solution from the precipitates by suitable means, and in the concentration of said
aluminous solution for the purpose specified.
In witness whereof, I, the said Conrad Semper, have hereunto set my hand
and seal, this 21st day of June A.D. One thousand eight hundred and
nights anA 1001