Iм- PROVEMENTS IN THE MANUFACTURE OF ALKALIES, BEING IMPROVEMENTS IN DESULPHURIZING CRUDE SOLUTIONS OF SODA AND POTASH, AND IN OBTAINING AND REGENERATING AN AGENT TO BE USED FOR THAT PURPOSE
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by Walter Weldon at the Office of the
Commissioners of Patents on the 28th January 1879.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey. "Iм-
PROVEMENTS IN THE MANUFACTURE OF ALKALIES, BEING IMPROVEMENTS IN
DESULPHURIZING CRUDE SOLUTIONS OF SODA AND POTASH, AND IN OBTAINING
AND REGENERATING AN AGENT TO BE USED FOR THAT PURPOSE."
or
Soda-makers' vat-liquors being the solutions obtained by lixiviating crude soda
black-ash" always contain sulphide of sodium, and the corresponding solutions
obtained in the manufacture of potash by the Leblanc process always contain
sulphide of potassium. These sulphides have afterwards to be reconverted into
sulphates at considerable cost either for nitrate of soda or for long exposure to an
oxidizing atmosphere in a "finishing furnace," as the case may be, and they more-
over hold in solution sulphide of iron, the iron of which passes into the finished
products and renders them unsuitable for many important applications unless they
be first submitted to the costly operation of refining. The object of the present
Invention is to purify the said liquors from the said sulphides, and so to diminish
the cost of the manufacture of soda and potash, while at the same time obtaining
products of improved quality and also a larger yield of alkali per given quantity of
raw materials.
The first part of the present Invention accordingly consists in treating the said
liquors by artificial hydrated red oxide of manganese or other oxide of manganese,
having apart from its water of hydration nearly or about the composition of the
oxide known to chemists as Mn,Ŏ, such artificial hydrated oxide being produced
or obtained and regenerated as will hereinafter be set forth. I have found that
such artificial hydrated oxide either agitated mechanically or boiled with the said
liquors completely frees them from sulphides, the said sulphides being either.
completely converted into alkali in accordance with the equation―
2 NaS+MnO4 = 2 Na,O2 MnS + 2 MnO,,
or mainly into alkali and partly into hyposulphite, according to the equation—
14 Na,S4 Mn,O, = NaS,O, +13 Na₂O + 12 MnS.
These equations will sufficiently indicate to practical chemists the proportions of
MnO, to be employed per given quantity of sulphide in the liquors to be treated.
The second part of the present Invention consists in the means whereby I
produce and regenerate for use again the artificial oxide to be employed as above
set forth. I take a solution of sulphate of manganese or of chloride of manganese,
but preferably of chloride of manganese. To this solution I add either an alkali or
Din 71

page_text: an alkaline earth, but preferably either lime or magnesia, and of these two pre-
ferably lime. I prefer to heat the solution by injection of steam or otherwise
I add the alkali or alkaline
before adding thereto the alkali or alkaline earth.
earth in the proportion of not more than one chemical equivalent thereof per one
chemical equivalent of the salt of manganese_employed. When employing what it
-will-usually-be-most-convenient-to employ,-chloride-of.manganese and lime, I thus
obtain hydrated protoxide of manganese suspended in a hot solution of chloride of
calcium. Into this product-I-now-inject air, at-the-same-time-either-injecting-
steam or keeping the mixture hot by any other convenient means. The air rapidly
converts the protoxide of manganese into red oxide or Mn,О, and when this con-
version has proceeded so far as to have converted the protoxide into a higher oxide
which will settle more readily and to a smaller volume than the protoxide itself
would have done, I cease the injection of air and allow the mixture to repose. I
then draw off the supernatant solution, and then either wash the precipitate
several times by subsidence and decantation, or put it into a filter-press and wash
it therein, as will be well understood. When sufficiently washed the product is
ready to be employed for the treatment of solutions of soda or potash, as above
described.
From the formulæ given above it will be seen that the above prescribed treat-
ment of solutions of soda or potash containing sulphide of sodium or sulphide of
potassium produces sulphide of manganese, or MnS. This must be separated from
the purified solutions either by subsidence and decantation or by filtration, as will
be well understood, and must then be. washed until practically free from alkali.
The wash-waters should be used to dissolve more crude soda or potash. The
sulphide of manganese will usually be accompanied by more or less oxide or oxides
of manganese, and also by sulphide of iron. From this sulphide of manganese or
mixture of sulphide of manganese and other bodies, oxide of manganese for the
treatment of the next quantity of solution of soda or potash has to be regenerated.
To this end I dissolve the sulphide of manganese or mixture of sulphide. of
manganese and other bodies either in sulphuric acid or in hydrochloric acid, but
preferably in hydrochloric acid, adding if need be enough peroxide of manganese
to peroxidize the iron present, or to complete the peroxidation thereof, as the case
may be. The resulting solution I neutralize either by lime or carbonate of lime,
and I then allow it to settle in order to the separation from it of peroxide of iron
and other impurities. I-then draw off the clear solution and treat it by adding an
alkali or alkaline earth, and then injecting air, as above described.
In factories in which the manufacture of soda or potash, and what is known as
the Weldon process for the manufacture of chlorine are both carried on, the simplest
way of dealing with the sulphide of manganese, etc., resulting from the treatment
of vat-liquors as above described will be to dissolve that residue in hydrochloric
-acid,-and-send-the-resulting-solution-into-the-wells-in-which-the-liquors-from-the
Weldon stills are at present neutralized. In such cases, for each successive pro-
duction of MnO4 or other similar oxide for the treatment of the vat-liquors,
solution of chloride of manganese must be taken from the neutralized chloride of
manganese settlers of the ordinary Weldon plant.