New or Improved Means for Facilitating Extraction of Alumina from Aluminous Ores.
Year: 1898

page_text: COMPLETE SPECIFICATION.
New or Improved Means for Facilitating Extraction of Alumina
from Aluminous Ores.
I, EMILE RAYNAUD, of Tessenderloo, in the Kingdom of Belgium, Chemist, 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:-
My invention consists in new or improved means, permitting of extraction with
the aid of sulphurous acid of the alumina contained in bauxite, kaolin, argillaceous
earths, silicates, and other aluminous ores which are either non-attackable or attack-
able with difficulty by acids even after having been calcined.
According to my invention, the ore is crushed, and afterwards heated after having
been mixed with any sulphuretted body, such as residues resulting from the manu-
facture of soda, pyrites and the like an alkaline sulphuret or a mixture capable of
producing alkaline sulphuret while being heated being preferably used. As the
essential object of the operation is, to produce disaggregation of the aluminous matter
and not transformation of its alumina into an aluminate, only a slight proportion of
sulphuretted matter is added and the calcining temperature is kept below that which
would be required for the formation of an aluminate.
For example if bauxite be operated on, it will suffice to add thereto about 10 per
cent. of its weight of a mixture of sulphate of soda with the carbon necessary for
the reduction. To facilitate the reactions, a small quantity of solvents such for
example as alkaline chlorides may be added. This operation can be effected in a
furnace of any kind such as a reverberatory furnace, a muffle furnace, a retort furnace,
a rotary furnace &c.
After having been subjected to this treatment the aluminous matters are obtained
in such a state, that acids will act thereon with the greatest facility.
The said matters may then be charged into a suitable receptacle containing water
into which sulphurous gas is passed, the solution is then clarified and afterwards
heated in order to set free the sulphurous acid and obtain a precipitate which can be
easily transformed into pure alumina by slightly calcining it. Or if it be desired to
obtain sulphite of alumina free from alkaline salts.it suffices to wash or lixiviate the
matters when they leave the furnaces and then to subject them to the action of

page_text: sulphurous gas as above. The washing waters contain all the alkaline salts and can
be utilized.
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
For extracting alumina from aluminous ores which are either non-attackable or
attackable with difficulty by acids, the treatment hereinbefore described consisting in
heating the ore with a sulphuretted body, or a mixture capable of its generation,
without transforming the alumina into an aluminate, in order to obtain a product,
from which the alumina can afterwards be easily extracted by subjecting it to the
action of sulphurous gas in presence of water, clarifying the solution, heating it and
calcining the precipitate obtained.
Dated this Twenty-second day of October 1898.