Improvements in the Manufacture of White Lead by the Acetate of Ammonia Process, more especially in respect of the Regenera- tion and Recovery of Acetate of Ammonia from the Weak Liquors and Washings Furnished in the Process.
Year: 1892

page_text: Date of Application, 14th Jan., 1892
Complete Specification Left, 13th Oct., 1892-Accepted, 26th Nov., 1892
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of White Lead by the Acetate
of Ammonia Process, more especially in respect of the Regenera-
tion and Recovery of Acetate of Ammonia from the Weak
Liquors and Washings Furnished in the Process.
I, WATSON SMITH, of University College, London, Lecturer in Chemical
Technology, do hereby declare the nature of this invention to be as follows :-
-
In the Specification of R. W. E. MacIvor and Watson Smith, No. 16,093 of 1890,
it is stated that the weak wash liquors ultimately obtained by washing the cakes of
white lead in the filter-presses, either with water alone or first with weak liquors,
obtained by a previous washing with water in the filter-press or other filter, of the
insoluble residues left after treatment with agitation in the digestors of litharge
with hot or heated acetate of ammonia solution, and then passing these liquids
through filter-presses whilst still hot,-are run to weak liquor tanks.
Now these weak wash liquors must accumulate, whatever economic system of
washing be adopted, and it has been proposed to concentrate them for use over
again. It may be pointed out at once, that concentration by evaporation in the
economic sense is out of the question, since in any such process however carried out,
ammonia is lost and gradually the solution is found to contain di-acetate of
ammonia.
The following process, which has been experimentally proved a success, is to
deal with the weak wash-liquors, containing even as little as 1 per cent. of ammonia
or even less, by recovering from them the ammonia and acetic acid in separate
processes, afterwards uniting these elements of the acetate of ammonia in a
suitable manner to be described, and thus regenerating and recovering this
valuable product, putting it again into circulation in the process and thus reducing
the percentage of working loss upon it in the process as a whole.
The weak liquors and washings furnished in the process referred to, containing
small quantities of acetic acid and ammonia, chiefly as acetate of ammonia, and
too weak to be economically circulated any further in the process for making
white lend described in Patent No. 16,093 of 1890, are charged into a suitable
ammonia still and distilled with a sufficient excess of quicklime or milk of lime
to liberate all the ammonia, and still not an excess beyond this quantity thus
requisite.
The ammonia expelled in the distillation is condensed in sulphuric acid and
converted into sulphate of ammonia in the usual way, which is fished out and
drained in the usual and well known manner. The liquor of the still, from which
the ammonia has been expelled contains the acetic acid as acetate of lime along with
the slight excess of lime necessarily used.
This liquor is filtered in a suitable filter, the residue washed, and the solution or
filtrate is evaporated to such a degree of concentration that it may be used successfully
in the next stage of the process, or if desired it may be evaporated to dryness and
the acetate of lime, stored for use.
If fresh lime exist in the filtered liquor before evaporation, it will be contained
in the concentrated liquid as carbonate of lime and must be removed by filtration.
The right proportions of sulphate of ammonia obtained as described and of the
acetate of lime solution, which should be clear and colourless, are now taken, and
the sulphate of ammonia is dissolved in water to form a concentrated solution.
The two concentrated and clear solutions of acetate of lime and sulphate of
ammonia respectively, are now mixed in a suitable and preferably lead lined vessel,

page_text: though even a clean wooden vessel will do, and the liquid is heated to about 25°
or 30° centigrade.
Sulphate of lime is now precipitated, and acetate of ammonia remains in solution.
On letting the warm liquid stand some 12 hours, almost complete separation of the
sulphate of lime takes place.
The cold liquid is now filtered in the filter-press, and the clear liquid of acetate
of ammonia either with or without dilution with water, is then employed in the
process for acting upon oxide of lead (litharge or massicot) as described in the
process of MacIvor and Smith in Patent No. 16093 of 1890, in the manufacture of
white lead or basic carbonate of lead.
Dated 14th Januo 1900
WATSON SMITH.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of White Lead by the Acetate
of Ammonia Process, more especially in respect of the Regenera-
tion and Recovery of Acetate of Ammonia from the Weak
Liquors and Washings Furnished in the Process.
I, WATSON SMITH of University College, London, Lecturer in Chemical
Technology 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 :-
In the Specification of R. W. E. MacIvor and Watson Smith No. 16093 of
Oct. 10th 1890, it is stated that the weak wash liquors ultimately obtained by
washing the cakes of white lead in the filter-presses, either with water alone or
first with weak liquors obtained by a previous washing with water in the filter-
press of the insoluble residues left after treatment with agitation in the digestors
of litharge with hot or heated acetate of ammonia, and then passing these liquids
through filter presses whilst still hot, are run to weak liquor tanks.
Now these weak wash liquors must accumulate, whatever economic system of
washing be adopted, and it has been proposed that they be concentrated for use
over again. It may be pointed out that the question of concentration either by
evaporation at ordinary temperatures or in vacuo at reduced temperatures is attended
with the complication and difficulty that acetate of ammonia in aqueous solution on
heating loses ammonia and gradually di-acetate of ammonia is left behind. Though
loss of ammonia might be in part prevented by certain condensing arrangements
and apparatus, yet complications are added, and since the filing of Specification
No. 18693 of 29th Oct. 1891 by Watson 'Smith, the idea has occurred and its
correctness experimentally proved, that a simpler and more adequate method of
dealing with the acetates of ammonia in these weak liquors, would now be to
dispose of and eventually to treat them in the manner here-in-after described in
outline:
The weak wash liquors, or other weak liquors containing small quantities of acetic
acid and ammonia, chiefly as acetate of ammonia, and left as a residue in the weak
liquor tanks and too weak to be satisfactorily and economically used in circulation
in the process, except to a limited extent in a preliminary washing in the filter-
presses either of the fresh residues from the digestors, or of the white lead fresh
pressed from the carbonators, are charged into a suitable still and distilled there
in the usual way with slaked lime or thick milk of lime, added so as to be but
slightly in excess of the amount actually required to form with the acetic acid
of the acetate of ammonia or other acetate in small quantity, acetate of lime.
The ammonia thus set free and expelled in the distillation, is condensed in sulphuric
acid in the manner usual in the manufacture of sulphate of ammonia from the
ammoniacal gas liquors.
The sulphate of ammonia thus obtained is then used in the process detailed in the

page_text: Specification of Watson Smith, No. 18693 of 29th Oct. 1891, for treating a solution
of acetate of lime of suitable strength for the preparation of fresh acetate of ammonia
of any strength desired.
In the still, when the expulsion of ammonia is completed, is left acetate of
lime with some excess of lime and a small quantity of other foreign and chiefly
insoluble matters. The still contents are next filter-pressed, preferably hot or
at least warm, and the residue washed in the press with a small quantity of warm
water.
The liquors obtained consist of acetate of lime in aqueous solution and may be
evaporated to any desired strength with impunity, and then used in the process
described in Specification of Watson Smith No. 18693 of 1891 for the preparation
of acetate of ammonia, this process No. 18693 of 1891, serving therefore for two
important ends viz.-(1) To prepare by a more economical and advantageous
method for the purpose in view, a solution of acetate of ammonia. (2) To prepare
the way and so anticipate the recovery of acetic acid and ammonia from the weak
residual wash liquors of the white lead process No. 16093 of 1890 with its supple-
mentary improvements No. 5501 of 1891 &c., in suitable condition and forms of
combination, for employment again, and for contributing to complete the.cycle of
operations.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what I
claim is;-
In connection with the process for manufacturing white lead or basic carbonate
of lead in which the action of acetate of ammonia upon oxide of lead (litharge or
massicot) forms the distinguishing feature, or similarly of acetate of ammonia
in contact with metallic lead in any electro-chemical process;-the process as
described for chemically regenerating from weak acetate of ammonia washings
or other liquors, the acetate of ammonia in a more concentrated form, with a
minimum of loss, and so as to avoid the process of concentration by evaporation.
Dated this 19th day of July 1892.
WATSON SMITH.