Improvements in the Manufacture of Sulphate of Lead and Lead Pigments.
Year: 1895

page_text: Date of Application, 18th May, 1895
Complete Specification Left, 18th Mar., 1896-Accepted, 18th Apr., 1896
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Sulphate of Lead and Lead
Pigments.
I, HENRY RICHARD GREGORY, of No. 5, Amerland Road, Wandsworth, in the
County of Surrey, Analytical Chemist, do hereby declare the nature of this
invention to be as follows:-
This invention relates more particularly to the manufacture of lead pigments to
be employed in the manufacture of paint and for other purposes and especially as
a substitute for white lead but it also relates to the production from galena
of a form of sulphate of lead especially suitable for the manufacture of such
pigments.
In order to produce sulphate of lead according to this invention, a suitable
quantity by weight of galena in a finely divided state is intimately mixed with an
equivalent quantity by weight of carbonate of magnesium preferably in the form
of magnesite.
This mixture is introduced into a suitable furnace for example an ordinary
reverberatory furnace which should be maintained at a low red heat the mixture
being occasionally stirred and this operation should be continued for a period of
about two hours more or less, or until the whole of the sulphur associated with the
galena becomes oxydised which will be apparent to any competent person by the
fact of the mixture assuming a light brown colour.
After this roasting operation has been completed in the manner above described
the mass is removed from the furnace and allowed to cool after which it is placed
in a vat or other suitable vessel and cold water is added thereto in such quantity
as to render the mass of a thin creamy consistency.
Sulphuric acid in quantity about equal to half the weight of the roasted mass is
then added and thoroughly incorporated with the mass by stirring and the mixture
is allowed to remain with an occasional stirring for a period of about twelve hours
after which it is washed several times with clean water until the whole of the
soluble matter has been washed away or separated from the rest of the mass.
The remaining part of the mass is then placed with a quantity of water equal
to about three parts of its own weight in a closed vessel capable of being
heated to boiling point and provided with a suitable arrangement of stirrers or
agitators.
Caustic soda or caustic potash is then added to the mass in slight excess and
the entire mixture is submitted to ebullition for a period of about one hour the
mass being constantly or continuously stirred during this operation after which
the mass is allowed to settle and the clear solution is decanted into a suitable
receiver.
The insoluble or heavy portion of the mass, remaining in the boiling vessel after
treatment with caustic soda or caustic potash as above described, contains the lead
and in order to recover this it is washed with water and then treated with nitric
acid diluted with an equal part of water the nitric acid being slightly in excess of
the quantity required to dissolve the oxide of lead present which is then converted
into sulphate of lead, by the addition of sulphuric acid to the solution. The
precipitated sulphate of lead is then washed.

page_text: In lieu of employing carbonate of magnesium as hereinbefore described a
suitable quantity of oxide of magnesium, oxide of calcium or magnesium lime-
stone, which latter may be calcined, may be substituted therefor and these
materials are employed in proportions chemically equivalent to those hereinbefore
given for the carbonate of magnesium.
The treatment with nitric acid may be conducted immediately after the first
treatment by sulphuric acid and the subsequent washing process.
Sulphate of lead obtained by the process hereinbefore described is especially
suitable for conversion into a pigment useful for various purposes by the following
means but such process of conversion is also applicable to sulphate of lead obtained
by other means than those herein before described.
For the purpose of converting the sulphate of lead, a suitable quantity thereof is
placed in an open or loosely covered vessel capable of being heated by steam or
other suitable medium and provided with means for stirring or agitating and a
quantity say about five times its own weight of water is added to the sulphate
of lead.
The temperature of this mixture is then raised by the aid of the heating medium
to ebullition or thereabout and a quantity of caustic lime or caustic magnesia
suspended in water, the proportions being for example such as will produce a
mixture of a thin creamy consistency, is then added, the proportions being
dependent upon the degree of conversion desired, that is to say, the quantity of
hydrated oxide of lead that it is required to produce in the given quantity of the
sulphate under treatment.
It is found in practice that about nine parts by weight of caustic lime or about
five parts by weight of caustic magnesia to one hundred parts of sulphate of lead
will give good results, but whilst a larger proportion of caustic lime or caustic
magnesia may be employed without detriment to the process (although any
addition to that quantity increases the cost of production of the pigment) the
minimum to obtain good results should never be below seven per cent. of caustic
lime or four per cent. of caustic magnesia.
After the addition of caustic lime and water or caustic magnesia and water as
above described, the mixture must be boiled for a period of about thirty minutes
or until it ceases to produce an alkaline re-action upon test paper and during the
boiling it must be efficiently stirred.
By the means herein before described, a proportion (about thirty per cent.) of
sulphate of lead is converted into hydrated oxide of lead and such converted
portion is in intimate combination with the unconverted sulphate.
The treatment of the sulphate of lead with an alkaline earth as hereinbefore
described may be carried out in the absence of heat, that is to say, in a cold state
but such process is more tedious than that hereinbefore described as it occupies
several hours and the product is not so perfect for use as a pigment as when
operating with the aid of heat.
The resulting compound must be well washed with water in any suitable washing
apparatus and dried by suitable means by the aid of moderate heat after which it
can be used as a pigment and may be ground with oil in the usual manner.
In applying this part of the present invention to the treatment of lead obtained
by sublimation, if the sulphate of lead be of bad colour, that is to say, when it is
not of the requisite degree of whiteness, as is sometimes the case, it should be
submitted before conversion, that is to say, before the addition of the alkaline
earth to a preliminary boiling process in a volume of water equal to about five
times its own weight and containing about one per cent. of sulphuric acid and about
one per cent. of hydro-chloric acid and this boiling is continued for about one hour
the sulphate of lead being afterwards washed in water to remove the acid.
Dated this 10th dow of Ma.. 1905

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture of Sulphate of Lead and Lead
Pigments.
I, HENRY RICHARD GREGORY, of No. 5, Amerland Road, Wandsworth, in
the County of Surrey, Analytical 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 said invention relates to the manufacture of lead pigments to be employed
in the manufacture of paint and for other purposes and especially as a substitute
for white lead but it also relates to the production from galena of a form of sulphate
of lead especially suitable for the manufacture of such pigments.
In order to produce sulphate of lead according to this invention, a suitable
quantity by weight of galena in a finely divided state is intimately mixed with an
equivalent quantity by weight of a suitable alkaline earth such as carbonate of
magnesium preferably in the form of magnesite.
This mixture is introduced into a suitable furnace for example an ordinary
reverberatory furnace which should be maintained at a low red heat the mixture
being occasionally stirred and this operation should be continued for a period of
about two hours more or less, or until the whole of the sulphur associated with the
galena becomes oxydised which will be apparent to any competent person by the
fact of the mixture assuming a light brown colour.
After this roasting operation has been completed in the manner above described,
the mass is removed from the furnace and allowed to cool after which it is placed
in a vat or other suitable vessel and cold water is added thereto in such quantity as
to render the mass of a thin creamy consistency.
Sulphuric acid, in quantity about equal to half the weight of the roasted mass,
is then added and thoroughly incorporated with the mass by stirring and the
mixture is allowed to remain with an occasional stirring for a period of about
twelve hours after which it is washed several times with clean water until the
whole of the soluble matter has been washed away or separated from the rest of
the mass.
The remaining part of the mass is then placed with a quantity of water equal
to about three times its own weight in a closed vessel capable of being heated to
boiling point and provided with a suitable arrangement of stirrers or agitators.
Caustic soda or caustic potash is then added to the mass in slight excess and the
entire mixture is submitted to ebullition for a period of about one hour the mass
being constantly or continuously stirred during this operation after which the mass
is allowed to settle and the clear solution is decanted into a suitable receiver.
The insoluble or heavy portion of the mass remaining in the boiling vessel after
treatment with caustic soda or caustic potash as above described contains the lead
in the form of hydrated oxide of lead, and, in order to recover this, it is washed
with water and then treated with nitric acid diluted with an equal part of water,
the nitric acid being slightly in excess of the quantity required to dissolve the
oxide of lead present, by which nitrate of lead is formed which is then converted
into sulphate of lead by the addition of sulphuric acid to the solution. The
precipitated sulphate of lead is then washed.
In lieu of employing carbonate of magnesium as herein before described, a
suitable quantity of oxide of magnesium, oxide of calcium or magnesian lime stone,
which latter may be calcined, or carbonate of lime or other suitable alkaline earth
may be substituted therefor and these materials are employed in proportions
chemically equivalent to those herein before given for the carbonate of magnesium.
The treatment with nitric acid may be conducted immediately after the first
treatment by sulphuric acid and the subsequent washing process.

page_text: When employing carbonate of lime as the alkaline earth, the mass after roasting
is for a period of two or three days treated with water containing carbonate of
soda which converts the sulphate of lead into carbonate of lead.
The mass is then washed to remove the soluble sulphates and the residue is
treated with dilute nitric acid, converting the carbonate of lead into nitrate of lead
which is afterwards precipitated as sulphate of lead by the aid of sulphuric acid,
the first treatment with sulphuric acid hereinbefore described being omitted.
Sulphate of lead obtained by the process herein before described is especially
suitable for conversion into a pigment, useful for various purposes, by the following
means but such process of conversion is also applicable to sulphate of lead obtained
by other means than those herein before described.
For the purpose of converting the sulphate of lead, a suitable quantity thereof
is placed in an open or loosely covered vessel capable of being heated by steam or
other suitable medium and provided with means for stirring or agitating and a
quantity say about five times its own weight of water is added to the sulphate
of lead.
The temperature of this mixture is then raised by the aid of the heating medium
to ebullition or thereabout and a quantity of caustic lime or caustic magnesia
suspended in water, the proportions being for example such as will produce a
mixture of a thin creamy consistency, is then added, the proportions being dependent
upon the degree of conversion desired, that is to say, the quantity of hydrated
oxide of lead that it is required to produce in the given quantity of the sulphate
under treatment.
.
It is found in practice that about nine parts by weight of caustic lime or about
five parts by weight of caustic magnesia to one hundred parts of sulphate of lead
will give good results but whilst a larger proportion of caustic lime or caustic
magnesia may be employed without detriment to the process (although any addition
to that quantity increases the cost of production of the pigment) the minimum to
obtain good results should never be below seven per cent. of caustic lime or
four per cent. of caustic magnesia.
After the addition of caustic lime and water or caustic magnesia and water as
above described, the mixture must be boiled for a period of about thirty minutes
or until it ceases to produce an alkaline re-action upon test paper and during the
boiling it must be efficiently stirred.
By the means herein before described, a proportion (about thirty per cent.) of
sulphate of lead is converted into hydrated oxide of lead and such converted
portion is in intimate combination with the unconverted sulphate.
The treatment of the sulphate of lead with an alkaline earth as hereinbefore
described may be carried out in the absence of heat, that is to say, in a cold state
but such process is more tedious than that hereinbefore described, as it occupies
several hours and the product is not so perfect for use as a pigment as when
operating with the aid of heat.
The resulting compound must be well washed with water in any suitable washing
apparatus in order to remove the calcic or magnesic sulphate and dried by suitable
means by the aid of moderate heat after which it can be used as a pigment and
may be ground with oil in the usual manner.
In applying this part of the present invention to the treatment of lead obtained
by sublimation, if the sulphate of lead be of bad colour, that is to say, when it is
not of the requisite degree of whiteness as is sometimes the case, it should be
submitted before conversion that is to say, before the addition of the alkaline
earth, to a preliminary boiling process in a volume of water equal to about five
times its own weight and containing about one per cent. of sulphuric acid and about
one per cent. of hydro-chloric acid and this boiling is continued for about one hour,
the sulphate of lead being afterwards washed in water to remove the acid.
I would here remark that I do not claim the herein described process for the
manufacture of lead pigments from sulphate of lead broadly considered as the
same is well known but the essential feature of this part of my invention consists

page_text: in removing the calcic or magnesic sulphate by washing and thus rendering the
product of greater value.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is :-
1. A process for the production of sulphate of lead from galena, consisting
essentially in mixing the galena in a finely divided state with a suitable quantity
of alkaline earth, roasting this compound in a suitable furnace afterwards when
cool adding water thereto, then treating the mass with sulphuric acid, then washing
the same until the soluble matter has been removed, then adding to the resultant
mass water and boiling the same, then adding caustic soda or caustic potash, then
boiling the mass, then draining off the solution, then washing the mass and treating
the same with dilute nitric acid and finally adding thereto sulphuric acid, substan-
tially as herein described and for the purpose stated.
2. A process for the production of sulphate of lead, consisting in reducing galena
by roasting the same in combination with alkaline earths and subsequently treating
the same with sulphuric and nitric acid, substantially as herein described and for
the purpose stated.
3. A process for the manufacture of lead pigments from sulphate of lead,
consisting in boiling a quantity of the sulphate in combination with water, adding
thereto caustic lime or caustic magnesia suspended in water, then boiling the mixture
and finally washing the mass to remove the calcic or magnesic sulphate and drying
the same, substantially as herein described and for the purpose stated.
Dated this 18th day of March 1896.
VAUGHAN & SON,
Agents for the Applicant.