IMPROVEMENTS IN THE MANU- FACTURE OF SULPHATE OF ALUMINA
Year: 1877

page_text: PROVISIONAL SPECIFICATION left by Edwin Powley Alexander at the Office
of the Commissioners of Patents on the 5th September 1877. A communi-
cation from abroad by Francis Laur, of Paris, in the Republic of France,
Engineer.
EDWIN POWLEY ALEXANDER, of 14, Southampton Buildings, in the County of
Middlesex, Consulting Engineer and Patent Agent. "IMPROVEMENTS IN THE MANU-
FACTURE OF SULPHATE OF ALUMINA." A communication from abroad by Francis
Laur, of Paris, in the Republic of France, Engineer.
This Invention relates to a peculiar process for the manufacture or production
from aluminous earths containing more or less iron, such, for example, as clay,
kaolin, and the like; and by preference from the hydrates of alumina, known as
bauxite, containing from 50 to 80 per cent. of alumina, of a sulphate of alumina,
completely neutral and free, or nearly so, from iron, a result which has never
hitherto been attained commercially.
In carrying out this Invention I pour, say, about 440 pounds, avoirdupois. of
sulphuric acid, of 50° Beaumé, into a leaden vat, and raise the temperature thereof
by a jet of free steam. When the acid commences to boil I add thereto from about
242 to 286 pounds, avoirdupois, of bauxite (hydrate of alumina) in the form of
powder. After a few minutes a powerful re-action commences, and the mixture
(which before the re-action should not occupy more than about 1/8th the capacity
of the vat) will overflow even unless care be taken to add thereto, at this moment,
about 13 to 14 gallons (more or less) of water. The mixture is then allowed
to remain in the vat; and should it recommence to overflow, more water is to be
added.
After the expiration of about one hour the mixture will have returned to its
original volume. Water may then be added at will, according to the degree of con-
centration required, thus obtaining a solution of sulphate of alumina, containing
about one-half per cent. of iron in combination. The silica of the bauxite, and the
bauxite not attacked, deposit slowly, and may be readily separated by decan-
tation.
In order to obtain sulphate of alumina free from iron it is simply necessary to

page_text: introduce plates of old zinc into the ferrugenous solution (say from 61%, to 11 lbs. in
the example given). The zinc is attacked, and after 4 or 5 hours (under heat) or
one or two days (under cold), the iron is precipitated in the form of a black powder,
which deposits at the same time as the silica. The deposition having been accom-
plished, the limpid solution, which is absolutely neutral, and does not turn blue in
presence of prussiate of potash, is decanted or syphoned off.
With the quantities given above about 660 pounds, avoirdupois, of sulphate of
alumina, in solution, is obtained, which is concentrated to 45° Beaumé (under heat)
and poured into cakes in the ordinary manner.
Before precipitating, it is necessary to wash it, as it still contains a certain amount
of sulphate which it is important should not be lost. It is essential to employ a
bauxite, reduced or ground to a very fine state of division, or to increase the pro-
portion in order to obtain at once a neutral or nearly neutral solution, the ellimi-
nation of the iron being based on the fact that whilst in an acid solution of
ferrugenous sulphate of alumina the metallic zinc allows only the iron (Fe2 0%) to
pass to the minimum of oxidation (Fe O); in a neutral solution it precipitates entirely
the peroxide of iron and replaces it.