IMPROVEMENTS IN THE PRODUCTION OF MINERAL PHOSPHATES FROM THE SLAGS RESULTING FROM THOMAS'S DEPHOSPHORISING PROCESS AND FROM SLAGS OR MINERALS OF SIMILAR COMPOSITION
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Charles Denton Abel at the Office of
.
the Commissioners of Patents on the 20th October 1888. Communicated to
me from abroad by Johannes Brandt of Berlin in the German Empire, Civil
Engineer.
"
CHARLES DENTON ABEL of N° 28 Southampton Buildings, Chancery Lane in
the County of Middlesex IMPROVEMENTS IN THE PRODUCTION OF MINERAL
PHOSPHATES FROM THE SLAGS RESULTING FROM THOMAS'S DEPHOSPHORISING
PROCESS AND FROM SLAGS OR MINERALS OF SIMILAR COMPOSITION [commu-
nicated to me from abroad by Johannes Brandt of Berlin in the German Empire,
Civil Engineer]
This invention relates to a method for the production of the mineral phosphates
in a pure state from the slags obtained in the well known Thomas's process of
dephosphorisation, or from other slags or minerals of similar composition, such
method differing mainly from the complicated processes at present employed in
that the roasting of the slag under admission of air or steam is entirely avoided,
and also that the silicic acid is in the first instance entirely removed from the slag
so that such substance does not participate in the further process. The sulphur
and sulphuretted hydrogen are also entirely removed, and an almost perfectly
chemically pure product is obtained by the extraction of the phosphates by means
of dilute acids.
For these purposes the uncalcined slag, only slightly broken up, is treated with
strong aqueous or gaseous hydrochloric acid, either under heat or at ordinary
temperatures, until all iron and manganese (even the smallest traces) are
transformed into Chlorides and all phosphates have been rendered soluble and all
silicates and sulphides susceptible of decomposition have become decomposed. The
hydrogen escaping during this process is utilised either for heating or lighting, or
as a reducing agent. The extract or solution thus obtained is now evaporated to
dryness the volatile acid employed being regained in the known manner, and the
dry powder thus obtained is then heated to redness in the presence of a current of
air or preferably of steam, whereby also the last traces of the volatile acid, or the
chlorine contained therein, can be regained.
The pulverulent product thus obtained freed from all the hydrochloric acid that

page_text: was combined with the iron and manganese, contains the iron and manganese only
in the form of oxides that dissolve only with great difficulty, and it is subjected to
a preliminary purifying process of lixiviation whereby a portion of the salt, poor
in iron and manganese, is dissolved out, leaving a residue rich in those metals. The
first named portion can then be treated in several ways. Firstly,—it is treated
with dilute aqueous volatile acids, whereby, in using hydrochloric acid, the more
readily soluble peroxides of manganese are destroyed by the addition of an
accurately determined quantity of sulphurous acid, or of another suitable readily
oxidisable substance, and the solution, almost free from iron, thus obtained is then
either evaporated, whereby the phosphates in an insoluble condition are separated
as a fine powder, while the volatile acid is disengaged and caught; or the phosphates
are precipitated by the addition of lime, magnesia, or calcined dolomite or their
carbonates.
Secondly, The same result is obtained if care is taken always to have a small
excess of phosphate of lime in lixiviating. The peroxides namely are only acted
upon when all the phosphates are dissolved, and the acid phosphates only act
slightly on the former.
:
Thirdly. The said solution is treated with dilute non-volatile acids (such as
sulphuric acid) which have the advantage of not attacking peroxides so readily;
the product is then either evaporated, thereby obtaining directly superphosphates,
or it is precipitated by means of lime, magnesia, or burnt dolomite. In heating to a
red heat the first described acid extract obtained as a dry powder by evaporation in
the presence of superheated steam, or air, the following chemical change takes
place: The phosphate of iron (Fe, (P O.) 2) Calcium oxide (Ca O) Calcium
Chloride (Ca Cl) and ferric chloride (Fe, Cl) contained in the acid extract are, in
the first instance, transformed under the influence of superheated steam, into
phosphate of lime (Ca, (PO) 2) and ferric chloride (Fe, Cl₂) which latter gives
off its hydrochloric acid.
• Experiments have shown that even with the most careful roasting of the slag
according to the existing methods, a large proportion of the iron and manganese
is not transformed into oxides, which is very detrimental for the product as with
the treatment with acid the metallic iron passes into the solution. On the other
hand, with the present method of treating the slag with hydrochloric acid or a
volatile acid having analogous action, the whole of the iron and manganese is
transformed with certainty into Oxides not readily soluble, while, by the same
operation, the silicic acid is rendered insoluble.
It should be stated that the above mentioned residue rich in iron, and manganese
can be treated direct for the production of iron or manganese steel, giving a
superior product, as the oxides exist in a nearly pure state.