IMPROVEMENTS IN THE MANUFacture of PRECIPITATED PHOSPHATE OF LIME, AND IN THE RECOVERY OF SULPHUR FROM ALKALI WASTE
Year: 1883

page_text: LETTERS PATENT to Walter Weldon, of Rede Hall, Burstow, in the County
of Surrey, for an Invention of IMPROVEMENTS IN THE MANUFacture of
PRECIPITATED PHOSPHATE OF LIME, AND IN THE RECOVERY OF SULPHUR
FROM ALKALI WASTE, communicated to him from abroad by Emile Lombard,
of Marseilles, in the Republic of France
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the
Office of the Commissioners of Patents on the 10th August 1883.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey, -
"IMPROVEMENTS IN THE MANUFACTURE OP PRECIPITATED PHOSPHATE Of Lime,
AND IN THE RECOVERY OF SULPHUR FROM ALKALI WASTE a Communication
from abroad from Emile Lombard, of Marseilles, in the Republic of France,
"
Precipitated phosphates of lime have hitherto been manufactured by saturating
with a solid precipitant, namely calcium carbonate, solution of phosphate of lime
in hydrochloric acid.
The present invention consists in substituting for the solid precipitant thus at
present and hitherto employed in the manufacture of precipitated phosphate of
lime a solution of calcium sulphydrate, and in combining the manufacture of
precipitated phosphate of lime with the recovery of sulphur from alkali waste, by
obtaining from alkali waste the solution of calcium sulphydrate to be employed as
aforesaid, either by digesting the said alkali-waste with water under pressure, or
by any other of the various known ways of obtaining solution of calcium sulphy-
drate from the material in question, and especially the method which will be
described below.
The solution of phosphate of lime in hydrochloric acid should be placed in a
closed vessel, and the solution of calcium sulphydrate added to it gradually; or
the solution of calcium sulphydrate may be placed in a closed vessel, and the acid
solution of phosphate added to it gradually. A regular stream of sulphuretted

page_text: bydrogen, which can be utilized in well known ways, will be thus disengaged, and
there will at the same time be formed a precipitate of dicalcic phosphate; very
much purer than can be obtained by means of the precipitant hitherto and at
present used. The vessel in which this operation is performed should be provided
with a mechanical agitator.
What will probably be the most convenient way of obtaining the solution of
calcium sulphydrate required for the method of working described above will be
to treat a mixture of alkali-waste and water by a portion of the sulphuretted
hydrogen which is evolved by the reaction of solution of calcium phosphate upon
a previous quantity of solution of calcium sulphydrato.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Walter Weldon in the Patent Office on the 4th February 1884.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey,
"IMPROVEMENTS IN THE MANUFACTURE OF PRECIPITATED PHOSPHATE OF LIME,
AND IN THE RECOVERY OF SULPHUR FROM ALKALI WASTE," a Communication
from abroad from Emile Lombard, of Marseilles, in the Republic of France,
Precipitated Phosphates of lime have hitherto been manufactured by saturating
with a solid precipitant, namely, calcium carbonato, solution of phosphate of lime
in hydrochloric acid.
The present invention consists in substituting for the solid precipitant thus at
present and hitherto employed in the manufacture of precipitated phosphate of
lime a solution of calcium sulphydrate, and in combining the manufacture of
precipitated phosphate of lime with tho recovery of sulphur from alkali-waste.
The solution of phosphate of lime in hydrochloric acid which is to be used
under the present invention may be prepared in any convenient way. The modes
of preparing it will be well understood, and do not constitute any part of the
present invention.
The treatment by solution of calcium sulphydrate of the said solution of
phosphate of lime in hydrochloric acid must be performed in a vessel which
should preferably be furnished with a mechanical agitator, and which may
conveniently be either an iron vessel, or a stone vessel with indiarubber joints,
constructed similarly to chlorine stills. The said vessel should be closed, except
that its upper part should communicate with a pipe or conduit for conveying away
sulphuretted hydrogen, and should morcover be furnished with an orifice, capable
of being opened or closed at will, by which to introduce into it the solution of
phosphate of lime and the solution of calcium sulphydrate, and that its lower part
should be provided with a cock or other equivalent appliance by which the contents
of the vessel may be discharged at will. The solution of phosphate of lime in
hydrochloric acid may be placed in this vessel first, and solution of calcium sulphy-
drate be then gradually run in upon it; or the solution of calcium sulphydrate
may be placed in the said vessel first, and the solution of phosphate of lime in
hydrochloric acid be then run into it gradually. In either case, sulphuretted
hydrogen will be disengaged in a regular stream, and there will at the same time
be formed a precipitate of dicalcic phosphate, very much purer than can be obtained
by means of the solid precipitant hitherto and at present employed. At the end
of the operation, the contents of the vessel will be a solution of calcium chlorido
holding in suspension solid precipitated dicalcic phosphate. The said mixture
must then be discharged from the vessel in which the operation has been performed,
and its two constituents separated by any convenient means, as will be well
understood.
The solution of calcium sulphydrate to be used under the present invention may
be obtained in any convenient way, from calcium sulphide obtained from any
source, either by digesting such calcium sulphide with water under pressure, or
by treating by sulphuretted hydrogen a mixture of such calcium sulphide with
water, or by treating such calcium sulphide in any one of various other known
ways; but it will usually be most advantageous to combine the above described
method of obtaining dicalcic phosphate, by treating together solution of phosphate
of lime in hydrochloric acid and solution of calcium sulphydrate, with the recovery
of sulphur from alkali-waste. To this end the alkali-waste may either be digested
with water under pressure, whereby its calcium sulphide is caused to react on

page_text: water, with formation of calcium hydrate and calcium sulphydrate, according to
the equation:
2 Ca S2 H, O = Ca H, O, + Ca H₂ S₂;
or a mixture of it with water may be subjected to the action of carbonic acid gas
in such wise as to convert one-half of its calcium sulphide into calcium carbonate
and the other half thereof into calcium sulphydrate, or a mixture of the waste
with water may be treated by sulphuretted hydrogen. It is believed that the
latter method has advantages over the others. When this method is followed,
the march of the combined operation will be as follows. A solution of calcium
.sulphydrate to commence with having been obtained in any convenient way, this
will be treated by a suitable quantity of solution of phosphate of lime in hydro-
chloric acid, and all its sulphur will be so driven off as sulphuretted hydrogen.
Half the sulphuretted hydrogen so obtained will then be treated in any convenient
way, either for conversion into sulphuric acid or for the obtainment of free sulphur
from it, the processes to which ends are no part of the present invention and are
well understood, and the other half of the said sulphuretted hydrogen will be
-passed into a vessel or vessels containing a mixture of alkali-waste and water,
which mixture, especially if agitated, will readily absorb the said sulphuretted
hydrogen, with formation of the solution of calcium sulphydrate required for the
.next operation.
--
What my correspondent claims as being the novel and essential features of the
invention above set forth consists:
--
Firstly, in employing solution of calcium sulphydrate, however obtained, as the
-reagent, by which to precipitate dicalcic phosphate-from solution.of..phosphate_of
Jime in hydrochloric acid; and,
Secondly, in combining the said method of obtaining dicalcic phosphate with
the recovery of sulphur from alkali-waste, by using that body. as the raw material
from which the solution of calcium sulphydrate used to precipitate dicalcic.
phosphate from a solution of phosphate of lime in hydrochloric acid is prepared.
In witness whereof I, the said Walter Weldon, have hereto set my hand and
seal this twenty eighth day of January, in the year of our Lord One thousand
eight hundred and eighty-four.
WALTER WELDON. (L.S.)