IMPROVEMENTS IN OBTAINING USEFUL PRODUCTS FROM THE RESIDUE OF THE MANUFACTURE OF SULPHURIC ACID BY MEANS OF CUPREOUS PYRITES
Year: 1880

page_text: LETTERS PATENT to Walter Weldon, of Rede Hall, Burstow, in the County
of Surrey, for an Invention of IMPROVEMENTS IN OBTAINING USEFUL
PRODUCTS FROM THE RESIDUE OF THE MANUFACTURE OF SULPHURIC ACID
BY MEANS OF CUPREOUS PYRITES."
"
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the Office
of the Commissioners of Patents on the 9th December 1880.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey.
'IMPROVEMENTS IN OBTAINING USEFUL PRODUCTS FROM THE RESIDUE OF THE
MANUFACTURE OF SULPHURIC ACID BY MEANS OF CUPREOUS PYRITES."
The sulphur used in the manufacture of sulphuric acid is now usually that of
cupreous pyrites. The sulphuric acid manufacturer burns off the greater portion of
the sulphur of the pyrites, and the residue, known as "pyrite cinders," is then
treated for the extraction of the copper it contains. To this end it is usually
mixed with common salt, and the mixture is then calcined with access of air. The
result is to oxidize the sulphide of copper contained in the cinders with formation
of sulphate of copper, which reacts on the chloride of sodium present to form
sulphate of soda and chloride of copper. These salts, together with any other
soluble salts present are dissolved out, and from the resulting solution the copper it
contains is precipitated by metallic iron. The residual liquor from which the
copper has thus been precipitated, and which contains all the sulphate of soda
which has been formed, is thrown away. There are lost in this manner some
The main object
seventy or eighty thousand tons of sulphate of soda per annum.
of the present Invention is to utilize more or less completely the sulphate of soda
thus lost.
I accomplish this object by submitting the solution containing the sulphate of
soda to artificial refrigeration. The solubility of sulphate of soda diminishing
rapidly with diminution of temperature, a very large part of it is thus caused
to crystallize out. I separate the portion which has thus crystallized out from the
nother-liquor by any convenient method of filtration, and it then remains to
deprive it of its water of crystallization, and also of the chloride of iron and

page_text: chloride of sodium which are apt to separate out with it, as well as of any
adherent mother-liquor. I effect this object by mixing the crystals of bydrated
sulphate of soda with enough solid chloride of sodium to form a saturated solution
with the water of crystallization of the hydrated sulphate, allowance being made
for the chloride of sodium already present with the hydrated sulphate and for any
solid chloride of iron which may be present with it also. I then heat the mixture
to a suitable temperature, whereby what was a mixture of solid salts becomes
converted into a mixture of anhydrous sulphate of soda with a saturated or nearly
saturated solution of chloride of sodium, or of chloride of sodium and chloride of
iron, as the case may be. This mixture I pass into a centrifugal hydro-extractor,
or other suitable apparatus, which I keep at the temperature to which I have
heated the mixture, as nearly as may be, and by which I separate as rapidly as
possible the solid part of the mixture from the liquid part. If required to be very
pure the anhydrous sulphate of soda so obtained may then be washed, as will be
well understood.
The mother-liquor from which hydrated sulphate of soda has been separated, as
aforesaid, will still contain some sulphate of soda, though only a small proportion
of the quantity which it originally contained. This remnant of the sulphate
of soda may be utilized by adding to the mother-liquor chloride of calcium,
whereby there is formed a precipitate of sulphate of calcium, which after separation
and washing can be sold for use by paper-makers or otherwise. Or, instead of
being thus treated by chloride of calcium, the said mother-liquor may be simply
boiled to dryness and the residue calcined with access of air. There will thus be
obtained an oxide of iron useful as a pigment and for other purposes. Instead of
being treated by chloride of calcium the mother-liquor may be treated by chloride
of barium, in which case the precipitate will be an artificial sulphate of barium,
available as what is known commercially as "permanent white." Or the mother-
liquor, preferably first concentrated by evaporation, may be mixed with magnesia,
alumina, clay, oxide of iron, oxide of manganese, or other suitable substance, or
with a mixture of such substances, and the mixture be formed into bricks or cakes,
and then heated either in a current of air, which will drive off in the free state the
chlorine of its chloride of iron, or in a current of steam, which will drive off the
chlorine of the chloride of iron as hydrochloric acid.
The saturated solution of chloride of sodium obtained from the dehydration of
the hydrated sulphate of soda by means of solid chloride of sodium may be
evaporated by the waste heat of the calcining furnaces, or otherwise, and the salt
be used for mixing with more pyrites cinders. Or this evaporation may be
performed in the calcining furnaces themselves, the pyrites cinders being mixed,
instead of with solid salt, as always at present, with the said saturated solution of
salt.
Instead of the solution from which sulphate of soda is separated by refrigeration
being the solution from which copper has been precipitated, as aforesaid, it may be
the solution containing the copper, the copper being afterwards precipitated from
the mother-liquor.
It may sometimes be possible to dispense with artificial refrigeration, and to
separate hydrated sulphate of soda from the liquors in question by natural
refrigeration. In such case my Invention will be confined to the combination with
the separation of hydrated sulphate of soda from the said liquids by natural
refrigeration of the other parts of the Invention, the nature of which is above
set forth.
In order to the application of the present Invention with most advantage, it will
be desirable to wash the product of the calcination of the mixture of pyrites and
salt in such wise as to obtain liquors as strong as possible in sulphate of soda.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, and of
an Order of the Lord Chancellor, filed by the said Walter Weldon in the
Great Seal Patent Office on the 7th July 1881.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey.
"IMPROVEMENTS IN OBTAINING USEFUL PRODUCTS FROM THE RESIDUE OF THE
MANUFACTURE OF SULPHURIC ACID BY MEANS OF CUPREOUS PYRITES."
The sulphur used by manufacturers of sulphuric acid is now usually that of
cupreous pyrites. When the sulphuric acid manufacturer has burnt off the greater
portion of the sulphur of such pyrites, the residue known as "pyrites cinders." or
as "burnt ore is mixed with common salt, and the mixture is then calcined with
access of air. By lixiviating the calcined product there is obtained a solution
which contains among other salts chloride of copper and sulphate of soda. This
solution is treated by metallic iron, whereby the copper of the chloride of copper is
precipitated in the metallic state. The residual solution containing chloride of iron
aud sulphate of soda is thrown away. The principal object of the present
Invention is to utilize more or less completely the sulphate of soda thus at
present lost.
The said Invention consists, firstly, in subjecting the solution containing the said
sulphate of soda to artificial refrigeration. The solution thus subjected to artificial
refrigeration may be either what will hereinafter be called "copper liquor," being
the solution resulting from the lixiviation of the calcined product above mentioned
before that solution has been treated for the precipitation of copper from it, or it
may be what will hereinafter be called "residual liquor," being the solution
remaining after the said copper liquor has been treated by metallic iron. As the
solubility of sulphate of soda diminishes rapidly with diminution of temperature,
a considerable part of the sulphate of soda contained in the solution subjected to
artificial refrigeration is thereby caused to crystallize out.
It will sometimes be possible, especially in cold climates, and at the colder
seasons of the year, to dispense with artificial refrigeration, and to separate sulphate
of soda from the liquors in question by merely natural refrigeration. In such case,
the said first part of my present Invention need not necessarily be applied.
The sulphate of soda separated as above said, either from copper liquor or from
residual liquor, by either artificial or natural refrigeration will be in the hydrated
state. The crystals will contain over fifty-five per centum of their weight of
water. They will usually also contain or have associated with them more or less
chloride of sodium, and either chloride of copper or chloride of iron, accordingly as
they have been separated from copper liquor or from residual liquor. The second
part of the present Invention consists in combining with the obtainment of crystals
of hydrated sulphate of soda from either copper liquor or residual liquor, by either
artificial refrigeration or natural refrigeration, of a certain method of de-hydrating
the said crystals, by which method of dehydration the sulphate of soda is at the
same time purified from other salts. Having separated the crystals of hydrated
sulphate of soda from their mother-liquor by a hydro-extractor, or any other
suitable means of either filtration or drainage, I add to them enough solid chloride
of sodium to form a saturated solution thereof with the water of crystallization of
the hydrated sulphate, allowance being made for such proportion of that water of
hydration as may be required to dissolve any chloride of sodium, together with any
chloride of iron or chloride of copper or other salts, which may be already present
with the crystals of hydrated sulphate, and I then heat the resulting mixture until
it has become a mixture of anhydrous sulphate of soda, with a saturated or nearly
saturated solution of chloride of sodium, or of chloride of sodium and chloride of
iron, or chloride of copper together with perhaps a little sulphate of soda and other
salts, as the case may be. This mixture I then pass into a centrifugal hydro-
extractor or other suitable filtering apparatus, by which I separate as rapidly as
possible the solid part of the mixture from the liquid part. The former is now

page_text: nearly pure anhydrous sulphate of soda, and can easily be rendered quite pure by
a slight washing as will be well understood.
The mother-liquor, from which crystals of hydrated sulphate of soda have been
separated by either artificial or natural refrigeration, will still contain some sulphate
of soda, and the present Invention consists, thirdly, in certain methods for the
utilization of this sulphate of soda. These methods are equally applicable, whether
the mother-liquor is the solution left after first precipitating the copper of the
copper liquor, and then separating sulphate of soda from the residual liquor, or after
first separating sulphate of soda from the copper liquor and then precipitating its
copper. By one of these methods I add to the copper liquor chloride of calcium,
preferably in solution, whereby there is formed a precipitate of sulphate of calcium,
which after filtration and washing is available for use by paper-makers or
otherwise. By another method, instead of adding to the mother-liquor chloride of
calcium I add to it chloride of barium, and so obtain a precipitate of sulphate of
barium available after suitable filtration and washing as what is known as
permanent white. Or finally, I evaporate the mother-liquor to dryness, and then
calcine the residue with access of air, whereby there is obtained an oxide of iron
useful as a pigment and for other purposes.
The present Invention relates, fourthly, to the utilization of the solution of
chloride of sodium or of chloride of sodium and other salts, which results from the
dehydration, as above described, of crystals of hydrated sulphate of soda obtained
from copper liquor or from residual liquor, by means either of artificial refrigeration
or of natural refrigeration, as above set forth. This solution may be either simply
evaporated by the waste-beat of the calcining furnace or otherwise, and the
resulting solid chloride of sodium or mixture of chloride of sodium and other salts
be used for mixing with more pyrites cinders; or the evaporation of the said
solution may be performed in the calcining furnace itself, the pyrites cinders being
mixed with this solution instead of with solid chloride of sodium as always at
present.
For carrying into effect that operation of artificial refrigeration which constitutes
the first part of the present Invention I do not confine myself to any particular
method, but I would indicate that such artificial refrigeration may be performed
by placing the solution in suitable vessels or channels surrounded partially or
completely by any artificially cooled medium for abstracting heat. Mechanical
means of producing artificial cold are now well known, and various means of
artificially cooling liquids, applicable to the liquids now in question, are also well
known and will be well understood. The operation may be either intermittent or
continuous; machines in which a liquid to be cooled is passed continuously through
channels, on each side of which are other channels, through which an artificially
cooled gas, or vapour, or liquid circulates in the opposite direction, being already
in industrial use. The temperature to which the solution should preferably be
cooled will depend on the strength of the solutions, their richness in sulphate of
soda, and the proportion of their sulphate of soda which it is desired to crystallize
out. In operating upon solutions containing per thousand grain measures about
seventy-seven grains of chloride of copper, about seventeen grains of chloride of
sodium, and about two hundred and twenty grains of sulphate of soda, I have
crystallized out about half the sulphate of soda originally contained therein by
cooling the solution to between fifty and sixty degrees Fahrenheit, and have
crystallized out as much as eighty per centum of its total sulphate of soda by
cooling the solution to twenty degrees Fahrenheit. To obtain this proportion of
sulphate of soda from what is above called residual liquor the copper liquor must
be very strong in the first instance, and must not be appreciably diluted during any
of the operations which it undergoes before being treated for the crystallization of
sulphate of soda from it. In all cases in which the treatment to which the copper
liquor is subjected in intermediate operations involves the addition of more than
very small quantities of water, it will be the copper liquor which should be treated
for the crystallization of sulphate of soda from it rather than the residual liquor.

page_text: As regards carrying into effect the method of dehydrating and purifying from
other salts crystals of hydrated sulphate of soda, the combination of which with the
obtainment of such crystals from either copper liquor or residual liquor by either
artificial or natural refrigeration constitutes the second part of the present
Invention, the temperature to which the mixture of crystals of hydrated sulphate
of soda and solid chloride of sodium is heated must not be lower than that at which
crystals of hydrated sulphate of soda fuse in their water of crystallization. It is
better however to heat the mixture to a higher temperature than that. I now
prefer to heat it to nearly or quite two hundred degrees Fahrenheit, or even to a
higher temperature still. When the mixture is thus highly heated the temperature
of the contents of the filtering apparatus, if the filtration be performed quickly,
does not fall to the point at which hydrated sulphate of soda might re-form, and it
is thus not necessary to furnish the filtering apparatus with any special means of
heating its contents. The quantity of chloride of sodium which must be added to
the crystals of hydrated sulphate will depend on the quantity of adherent moisture,
and the proportion of foreign salts, if any, which may be associated with those
crystals. For pure dry crystals of hydrated sulphate of soda about fifteen to
sixteen per centum of their weight of chloride of sodium would be a suitable
proportion. But there may be already with the crystals both chloride of sodium
and other chlorides, which will proportionately diminish the proportion of chloride
of sodium to be added to them; or there may be adherent water with them, which
will increase the proportion of chloride of sodium to be added to them. If too
much chloride of sodium be added the anhydrous sulphate of soda obtained will be
contaminated by the excess thereof; if too little chloride of sodium be added the
yield of anhydrous sulphate of soda will be below the maximum possible yield.
The mixture of crystals of hydrated sulphate of soda and solid chloride of sodium
may be heated in any convenient way; perhaps the most convenient method
being to place it in a cylindrical iron vessel, which can be heated by means of a
steam-coil.
Having now described the nature of the said Invention, and in what manner the
same may be performed, I claim as the Invention to be secured to me by the
herein before in part recited Letters Patent,-
Firstly. Separating sulphate of soda from what are above respectively called
copper liquor and residual liquor by subjecting those liquors to artificial
refrigeration.
Secondly. Combining with the separation of sulphate of soda as hydrated
crystals from the above mentioned copper liquor and residual liquor, whether by
artificial refrigeration or by natural refrigeration, the method of dehydrating and
purifying such crystals, which consists in mixing them with solid chloride of
sodium, heating the mixture, and then subjecting to filtration the resulting mixture
of anhydrous sulphate of soda with solution of chloride of sodium, or of chloride of
sodium and other salts, substantially as is above described.
Thirdly. Utilizing the solution of chloride of sodium, or of chloride of sodium
and other salts, from which anhydrous sulphate of soda has been separated by
filtration, as above described, substantially as is above set forth, and
Lastly. Treating the mother-liquor left after copper and sulphate of soda have
both been separated, the former completely or nearly so by means of metallic iron,
and the latter partially by means of either artificial or natural refrigeration, from
what is above called copper liquor, substantially as is described above.
In witness whereof, I, the said Walter Weldon, have hereunto set my hand
and seal, this Sixth day of July, in the year of our Lord One thousand
eight hundred and eighty one.
WALTER WELDON. (L.S.)