Improvments in Obtaining Alumina or Ferric Oxide, or Mixtures thereof.
Year: 1898

page_text: Date of Application, 7th July, 1898
Complete Specification Left, 7th Apr., 1899-Accepted, 13th May, 1899
Improvments in Obtaining Alumina or Ferric Oxide, or
Mixtures thereof.
JOHN THEODORE HEWITT, Professor of Chemistry in the East London Technical
College, People's Palace, London, E., and of 65, Silverdale, Sydenham, London,
S.E., and FRANCIS GEORGE POPE, Assistant Lecturer and Senior Demonstrator
in Chemistry, East London Technical College, and of 92, Reighton Road, Upper
Clapton, London, N.E., do hereby declare the nature of this invention to be as
follows:-
The method of obtaining alumina from aluminium sulphate by ignition is
incapable of technical application, on account of the high price of the sulphate,
and that owing to the temperature required to expel the whole of the sulphur
trioxide from combination with the aluminium oxide, most of the sulphur trioxide
is itself resolved into sulphur dioxide and oxygen, and is thus not easily recovered
as sulphuric acid. The wear and tear of apparatus in which such a reaction is
carried out is necessarily great.
Our improvement consists in supplying superheated steam during the process
of roasting, whereby the acid may be expelled from combination at a lower
temperature, and by suitable condensing apparatus to recover the sulphuric acid
which may be used again for the extraction of alumina from aluminous materials.
To carry out such heating we introduce the aluminium sulphate into tubes or
pipes of acid- and fire-proof earthenware or of iron, and heat to redness in a
current of superheated steam until the acid is expelled as far as is desired.
The tubes may be inclined and given a slow rotatory movement, the sulphate
being introduced at the upper end and gradually passing to the lower end, steam
being passed in a contrary direction. Or the tubes may be fixed and horizontal,
or slightly inclined, the motion of the aluminium sulphate through them being
effected by conveyors of screw pattern, steam as before being blown through the
tube in a contrary direction. By either of these methods a continuous working
of the plant is effected, and moreover the purest alumina is brought into contact
with the freshest steam.
The strength of the acid condensed can be regulated by the temperature of the
condensing plant and if it be desired to deprive the escaping fumes from any acid
remaining, the steam may then be passed over layers of a suitable absorbent.
The process is further applicable to the production of ferric oxide from ferric
sulphate or to a mixture of aluminium and ferric oxides from a mixture of the
sulphates of the two metals.
Dated this Sixth day of July 1898.
JOHN THEODORE HEWITT.
FRANCIS GEORGE POPE.

page_text: Improvements in Obtaining Alumina or Ferric Oxide, or
Mixtures thereof.
JOHN THEODORE HEWITT, Professor of Chemistry in the East London Technical
College, Mile End, London, E., and of 65, Silverdale, Sydenham, in the County
of Kent, and FRANCIS GEORGE POPE, Lecturer and Demonstrator in the East
London Technical College, Mile End, London, E., and of 92, Reighton Road,
Upper Clapton, N.E., in the County of Middlesex, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particu-
larly described and ascertained in and by the following statement: -
In the decomposition of aluminium sulphate into aluminium oxide (alumina)
and sulphur trioxide by means of heat, a very high temperature must be employed.
The decomposition is moreover troublesome to complete, we are however, by the
following improvement, able to obviate these difficulties and to deprive aluminium
sulphate or aluminium sulphate mixed with ferric sulphate to any required extent
of the combined sulphur trioxide.
The aluminium or ferric sulphate or mixture of sulphates to be roasted is intro-
duced into tubes or pipes of acid- and fire-proof earthenware, or of iron, and heated
to redness in a current of superheated steam until the acid is expelled as far as is
desired.
The tubes may be inclined and given a rotatory movement, the sulphate being
introduced at the upper end and gradually passing to the lower end, steam being
passed in a contrary direction. Or, the tubes may be fixed and horizontal, or
slightly inclined, the motion of the aluminium sulphate or mixture of aluminium
and ferric sulphates through them being effected by conveyers of screw pattern,
steam being, as before, blown through the tube or tubes in a contrary direction.
By either of these methods the working of the plant is rendered continuous and the
purest alumina is always brought in contact with the freshest steam.
The escaping steam carries with it the vapour of sulphuric acid, the latter may
be condensed, its strength being determined within certain limits by the tempera-
ture of the condenser. We prefer however to condense an acid having a specific
gravity of 15 to 16 as such an acid is of a convenient strength for the further
extraction of alumina from aluminous minerals.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is:-
1
1. The heating to redness of aluminium sulphate or ferric sulphate or a mixture
of these sulphates in a current of superheated steam thereby removing the sulphur
trioxide at a lower temperature and more completely than by heating alone or
in air.
2. The rendering of the working of such a process continuous by passing the
sulphate or mixture of sulphates through a tube or tubes heated to redness in a
direction contrary to the direction of the superheated steam.
3. The recovery by condensation of the sulphuric acid evolved, in order to
utilize it again for the extraction of alumina from aluminous minerals.
Dated this fith day of Anril 1800