An Improved Process for rurlying Copper Precipitates.
Year: 1885

page_text: An Improved Process for rurlying Copper Precipitates.
I JAMES YATE JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of said Invention for "AN IMPROVED
PROCESS FOR PURIFYING COPPER PRECIPITATES" which Invention has been com-
muicated to me from abroad by Ernest Deligny of 18 Rue François 1st Paris in
the Republic of France Engineer to be as follows:-
The Copper obtained by the precipitation of that metal from its solutions
arising for example from the treatment of the ores or consisting of the waters
exhausted from mines is generally contaminated with Arsenic and Antimony
which lowers the quality and consequently reduces the value of the Copper so
obtained.
Experience proves that if the Arsenic and the Antimony be not eliminated and
separated in the preliminary operations the ultimate separation of the said
impurities is impossible or practically so.
When a heap of ore is exposed to the air the Sulphurets are oxidized and there
is produced a spontaneous sulphatization that gives solutions whose copper is
separated by the action of metallic iron, these solutions containing always an
excess of Acid due to the affinity of Sulphate of Protoxide of Iron for Oxygen.
For hastening the Sulphatization of Copper Pyrites they are burnt and the
Arsenic is oxidized proportionately to the Sulphur forming a volatile Acid which
is condensed in the cooler parts of the heap and combines with the Oxides and
Sulphates Here again there is a production of Sulphuric Acid in excess of
Sulphates of Peroxide-In the presence of the excess of Acid that always attends
the Sulphatization the Arsenic combined with the Copper remains in solution.
The product of the calcination of the heap contains:-
1st The non metallic gangue of the ores.
2nd The Sulphurets of Antimony Arsenic & unburnt or only modified.
3rd The metallic Oxides insoluble or soluble in Acid liquid.
4th Metallic Sulphates and particularly the Sulphates of Peroxide and of
Protoxide of iron and Sulphate of Copper.
5th Arsenious Acid and Oxides of Antimony.
When this mixture is submitted to lixiviation there are obtained solutions
containing 1. The excess of Sulphuric Acid 2. Sulphates of peroxide and of

page_text: protoxide of Iron. 3. Sulphate of Copper Sulphate of Zinc &°. 4. Arsenious
Acid and Oxide of Antimony maintained in solution by the presence of Sulphuric
Acid in excess the first notwithstanding the presence of the Salts of Iron.
When the solution comes into contact with metallic Iron the neutralization of
the Acids in excess not only causes the precipitation of Copper by the iron but
gives at the same time to the Sulphate of Protoxide of iron the property of causing
the precipitation of the Arsenious Acid-It causes also the precipitation of Oxides
and antimoneous Acids-There is produced at the same time insoluble sub-sulphates
of iron The Copper produced by this process retains always much impurities or
the impurities carry away much copper.
The processes of purification in use for eliminating the Arsenic by calciuation
at a dull red, retransformation into Sulphurets or matt being afterwards treated by
a dry process & either give incomplete results or are very costly-This Invention
has for its object to obviate the difficulties and objections applying to the hitherto
practised processes for the purification of Copper precipitates.
It is known that the metallic Arsenites and Arseniates and notably those of
Iron and of Copper are insoluble in water or in neutral solutions-It is equally
well known that the Alkaline Arsenites and Arseniates are always soluble in water
and in neutral solutions and also that precipitated Arsenites and Arseniates are
soluble in Acids.
The ordinary process of analysing and ascertaining the quantity of Arsenic is
based upon these properties-The metallic Arsenite or Arseniate alone or not is
acted upon by an Acid and is afterwards precipitated by an Alkali--The Arsenic
remains in solution in the state of Alkaline Arsenite or Arseniate-Subsequent
washing completely eliminates the arsenic.
It has been found by experiment that it is not necessary to use an acid for
transforming metallic Arsenite or Arseniate into an Alkaline salt and that the
transformation can be obtained by the direct action of an Alkali upon the metallic
Arsenical salt.
When the Arsenical salt is of recent precipitation and has not been much exposed
to the air the reaction of the Alkali is rapid and easy. When the compound
precipitate dealt with is old and has been dried with or without heat the action of
the Alkali takes a longer time and requires greater care but it is complete.
The result of the reaction is a metallic oxide and a soluble Arseniate the latter
separable by a simple washing. It will be understood that all the Alkalis giving a
soluble Arsenical salt may be employed but generally soda will be the most
convenient.
Caustic lime decomposes the Arsenical salt of soda giving free Alkali in solution
and an insoluble Arseniate of lime. By this means the soda is regained for reuse
in the process.
In certain cases the Alkaline carbonate may be used for transforming the
compounds of Arsenic and Antimony into soluble salts separable by washing.
When the proportion of Ammoniacal and Antimonial salts at minimum is
considerable the reactions are somewhat delayed. A more rapid and effective
action is obtained by the application or employment either before or simultaneously
with the Alkali of an Alkaline nitrate which converts the Arsenites and Anti-
monites into metallic Arseniates and Antimoniates which are more quickly and
readily transformed into soluble Alkaline salts.
When there is occasion to employ the Alkaline nitrate the series of operations is
performed as follows:-vizt: 1. The precipitated Copper is treated in a solution of
Alkaline nitrate in excess. After reaction the precipitate is separated. The
solution may be employed continually until the nitrate is exhausted. 2. After
treatment with nitrate the precipitate is heated in a caustic Alkaline solution and
the solution is separated. 3. The Arseniates are precipitated by caustic lime in
order to revivify the Alkali which may be used again in a subsequent operation.
I give the following as an example of the way in which the purification of
Copper precipitates may be effected according to this Invention.
"

page_text: The precipitates are placed in a series of receptacles furnished with agitators and
heated by fire or by the injection of steam.
The first operation consists in the action by an Alkaline solution (soda for
example) which passes successively through the series of receptacles reversely to
the precipitates in such a manner that as they approach the end of their course
the precipitates undergo the action of the more caustic and pure Alkali and that on
the other hand the Alkali as it approaches and reaches the end of its course is in
a great part transformed into a soluble Arsenical salt. The Arsenical solutions
obtained are then decomposed and the Alkali is recovered.
The precipitate which has been deposited is carefully drained and then is washed
with water.
By the foregoing means I ensure the purification of the Copper precipitate from
Arsenic and Antimony.

page_text: !
An Improved Process for Purifying Copper Precipitates.
I JAMES YATE JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of my said Invention for "AN IMPROVED
PROCESS FOR PURIFYING COPPER PRECIPITATES" which Invention has been com-
municated to me from abroad by Ernest Deligny of 18 Rue Francois 1st Paris in
the Republic of France Engineer and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement :-
The copper obtained by the precipitation of that metal from its solutions arising
for example from the treatment of the ores or consisting of the waters flowing
from mines is generally contaminated with arsenic and antimony which lowers the
quality and reduces the commercial value of the copper so obtained.
Experience proves that if the arsenic and antimony be not eliminated and
separated in the preliminary operations and these substances become combined or
alloyed with the metallic copper the ultimate separation of the said impurities is
impossible or practically so.
When a heap of ore is exposed to the air the sulphurets are oxidized and there
is produced a spontaneous sulphatization that gives solutions whose copper is
separated by the action of metallic iron, these solutions containing always an excess
of acid due to the affinity of sulphate of protoxide of iron for oxygen.
For hastening the sulphatization of copper pyrites they are burnt and the
arsenic is oxidized simultaneously with the sulphur forming a volatile acid that
instead of escaping into the air in the same way as the sulphurous acid is con-
densed in the cooler parts of the heap and combines with the oxides and sulphates.
Here again there is a production of sulphuric acid in excess and of sulphates of
peroxide. In the presence of the excess of acid that always attends the sulphati-
zation the arsenic combined with the copper remains in solution.
The product of the calcination of the heap contains.
1st The non-metallic gangue of the ores.
2nd The sulphurets of antimony, arsenic etcetera unburnt or only modified.
3rd The metallic oxides insoluble or soluble in acid liquids.-4th Metallic sul-
phates and particularly the sulphates of peroxide and of protoxide of iron and
sulphate of copper.
5. Arsenious acid and oxides of antimony.
When this mixture is submitted to lixiviation there are obtained solutions
containing. 1. The excess of sulphuric acid. 2. Sulphates of peroxide and of
protoxide of iron. 3. Sulphate of copper sulphate of zinc etcetera. 4. Arsenious
acid and oxide of antimony maintained in solution by the presence of sulphuric
acid in excess, the first notwithstanding the presence of the salts of iron.
When the solution comes into contact with metallic iron the neutralization of
the acids in excess not only causes the precipitation of the copper by the iron but
gives at the same time to the sulphate of protoxide of iron the well known property
of causing the precipitation of the arsenious acid. It causes also the precipitation
of antimonious acids or oxides. There are produced at the same time insoluble
sub-sulphates of iron.

page_text: *These reactions which in theory occur in succession have never been separated
in practice.
1
The copper produced by this process always retains much impurities or the
impurities when separated carry away much copper.
"
"
The precipitates thus obtained are divided into cascara and "papucha'
according to their degree of purity.
The process of purification in use for eliminating the arsenic by calcination at a
dull red, retransformation into sulphurets or matt being afterwards treated by a
dry process etcetera either give incomplete results or are very costly.
This Invention has for its object to obviate the difficulties and objections
applying to the hitherto practised processes for the purification of copper precipi-
tates in the manner hereinafter explained.
It is known that the metallic arsenites and arseniates and notably those of iron
and of copper are insoluble in water or in neutral solutions. It is equally well
known that the alkaline arsenites and arseniates are always soluble in water and
in neutral solutions and also that precipitated arsenites and arseniates are soluble
in acids.
•
The ordinary process of quantative analysis of arsenic is based upon these
properties. The metallic arsenite or arsenicate, alone or not is acted upon by an
acid and is afterwards precipitated by an alkali. The arsenic remains in solution
in the state of alkaline arsenite or arseniate. Subsequent washing completely
eleminates the arsenic.
When the arsenical salt is of recent precipitation and has not been much exposed
to the air the reaction of the alkali is rapid and easy. When the precipitate is old
and has been dried with or without heat the action of the alkali takes a longer
time and requires greater care but it is complete if the precipitate is at a maximum
of oxidation.
The result of the reaction of an Alkali upon an Arseniate is a metallic oxide
which remains with the precipitate.
It has been found that precipitated copper saturated with the quantity of
alkaline nitrate in solution corresponding with the quantity of arsenical salts to be
converted is purified after calcination and washing.
According to this Invention the arsenites and antimonites are first converted
into insoluble arseniates and antimoniates by the action of an alkaline nitrate these
arseniates being subsequently treated with a caustic Alkaline Solution in order to
render them soluble. When the materials are exposed to the action of the Alkaline
Nitrate by a dry process as hereinafter described the subsequent treatment with the
Caustic Alkaline solution is dispensed with as in this case the Alkaline Nitrite
is decomposed in the first stages of the process and the desired combination is
afterwards effected with the Alkali resulting from this decomposition as hereinafter
explained.
In applying this Invention in practice to the elimination by means of a wet
process of the Arsenic and Antimony contaminating a Copper precipitate the
precipitate is first heated in a concentrated solution of an Alkaline nitrate and the
arsenites and antimonites in the materials under treatment are thereby converted
into arseniates and antimoniates. Other agents such as Alkalies or Alkaline Salts
may be employed in conjunction with the Alkaline nitrate, but the presence of the
latter is essential to the success of the operation.
The materials under treatment are then removed from the solution and caused
to pass through a series of vessels or receptacles furnished with agitators and
heated by the direct action of fire or by injecting steam or by other suitable
means. In these vessels the insoluble arseniates and antimoniates resulting from
the treatment with the alkaline nitrate as herein before described are acted upon
by a solution of a caustic alkali which passes successively through the series of
receptacles moving in the opposite direction to the precipitates in such a manner
that the precipitates approaching the end of their course undergo the action of the
pure solution entering the vessels and that on the other hand the alkali as it

page_text: approaches and reaches the end of its course is caused to act upon the precipitates
entering the apparatus. This process renders the arsenical and antimonial salts
soluble so that they are in part carried away by the solution and it is then simply
necessary to drain and wash the precipitate in order to remove all the remaining
traces of these impurities.
The solution employed in the second stage of the process can then be purified for
use in a subsequent operation by treatment with caustic lime which precipitates
the antimoniates and arseniates.
In place of the wet process hereinbefore described the alkaline nitrate may be
caused to act upon the impurities by a dry process. In this case the precipitates
are placed with the alkaline nitrate in a suitable furnace and heated to a dull
red heat until the arsenites and antimonites are converted into arseniates and
antimoniates. The alkaline nitrate itself is at the same time decomposed and the
resulting alkali then acts upon the materials in such a manner that a subsequent
washing completely eliminates the arsenic and antimony with which they are
contaminated.
Having now described and particularly ascertained the nature of this said
Invention and in what manner the same is to be performed I declare that what
I claim is
"
.
First. The employment of an alkaline nitrate for the purpose of purifying
copper precipitates by eliminating the impurities such as antimony and arsenic
with which such precipitates are contaminated substantially as hereinbefore
described.
Second. In eliminating impurities such as antimony and arsenic from Copper
precipitates, the wet process consisting in first converting the antimonites and
arsenites or the like into insoluble compounds by the action of a concentrated
solution of an alkaline nitrate in combination or not with other alkalies and
secondly rendering these compounds soluble by the action of a caustic alkaline
solution substantially as hereinbefore described.
Third. In eliminating impurities such as antimony and arsenic from copper
precipitates the dry process consisting in exposing the precipitates to an elevated
temperature in the presence of an alkaline nitrate, the said nitrate being at the
same time decomposed whereby the alkali is afterwards enabled to act upon the
arseniates or antimoniates or the like and render them soluble so that they may
be subsequently removed by simply washing the precipitate substantially as
berein before described.
Dated the 02nd dose of Cantomban 100K