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Ammonia and ammonium salts have been recognized as effective leaching agents in hydrometallurgical processes due to low toxicity and cost, easy recovery and high selective recovery of metals. New research findings on considerable advantages of leaching by these agents and elimination of problems associated with acid leaching have resulted in a new approach in the world to this method. The investigations in this field indicate more frequent use of this method for extracting copper from ore and concentrate relative to other basic metals. In this paper, an attempt was made to describe the basis and different ammonia leaching methods and present the major research activities in this field for copper. Also latest findings and related novel processes have been presented. Comparisons including assessment of advantages and disadvantages of this method relative to acid leaching method, kinetic study of copper ammonia leaching and evaluation of Eh–pH diagrams in a system containing water and ammonia are other parts of this study. Finally, by describing the studies on copper extraction from the resulting pregnant solutions, the applicable extraction agents have been reviewed.
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Ammonia Leaching: A New Approach of Copper Industry
in Hydrometallurgical Processes
Vahid Radmehr Seyed Mohammad Javad Koleini
Mohammad Reza Khalesi Mohammad Reza Tavakoli Mohammadi
Received: 26 November 2012 / Accepted: 30 October 2013 / Published online: 10 December 2013
ÓThe Institution of Engineers (India) 2013
Abstract Ammonia and ammonium salts have been
recognized as effective leaching agents in hydrometallur-
gical processes due to low toxicity and cost, easy recovery
and high selective recovery of metals. New research find-
ings on considerable advantages of leaching by these
agents and elimination of problems associated with acid
leaching have resulted in a new approach in the world to
this method. The investigations in this field indicate more
frequent use of this method for extracting copper from ore
and concentrate relative to other basic metals. In this paper,
an attempt was made to describe the basis and different
ammonia leaching methods and present the major research
activities in this field for copper. Also latest findings and
related novel processes have been presented. Comparisons
including assessment of advantages and disadvantages of
this method relative to acid leaching method, kinetic study
of copper ammonia leaching and evaluation of Eh–pH
diagrams in a system containing water and ammonia are
other parts of this study. Finally, by describing the studies
on copper extraction from the resulting pregnant solutions,
the applicable extraction agents have been reviewed.
Keywords Leaching Extraction Ammonia
The use of sulfuric acid in an acid leaching process is a
conventional method for recovery of copper, but in some
cases it is necessary to use other reactants such as ammo-
nia. Ammonia has been known as an effective leaching
agent in hydrometallurgical procedures, although it has
been less studied than the chemical agents used in leaching.
Ammonia leaching was first used for recovery of non-
ferrous metals such as copper from oxide ores or ores
containing pure copper, but gradually the use of this
technology was developed from more traditional elements
of copper, nickel and cobalt to the extractive metallurgy of
zinc, cadmium, silver and gold [1].
The aim of this paper was to review studies in various
fields of ammonia leaching of copper and extraction of
copper from the resulting pregnant solution by solvent
extraction process.
The first industrial application of this process related to
hydrometallurgical recovery of copper was put into oper-
ation in 1916, and the two factories of Kennecott in Alaska
(Fig. 1) and Calumet in northern Michigan were separately
established for copper recovery.
Although copper oxide and pure copper were first used
to recover copper due to high solubility in ammonia, later
on ammonia leaching of sulfide ores was also considered.
The common method was the use of oxide roasting at high
V. Radmehr (&)S. M. J. Koleini M. R. Khalesi
M. R. Tavakoli Mohammadi
Department of Mining Engineering, Faculty of Engineering,
Tabiat Modares University, Jalal Ale Ahmad Highway,
P.O. Box 14115-111, Tehran, Islamic Republic of Iran
S. M. J. Koleini
M. R. Khalesi
M. R. Tavakoli Mohammadi
J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104
DOI 10.1007/s40033-013-0029-x
temperatures to convert sulfides to oxides in order to
facilitate dissolution in ammonia solutions [1].
In 1947, a process (Fig. 2) in this regard was invented
by Sherritt Gordon. In this process, ammonia leaching of
sulfide minerals of copper, nickel, cobalt and iron was
conducted at a temperature of about 105 °C and air pres-
sure of 0.8 MPa. Under these conditions, copper, nickel
and cobalt were dissolved but iron was precipitated in
hydroxide form. By separating the unsolved solids, the
pregnant solution was heated to evaporate excess ammonia.
After that, first the solution was allowed to react with air to
oxidize all its thiosulfates, and was then reduced using
hydrogen. Thus, metal nickel was obtained through
reduction of amine nickel ion. It was necessary to add some
metallic nickel powder to the solution as budder to start the
reaction, or add an appropriate catalyzer to the solution to
accelerate the reaction. Reduction operations continued up
to precipitation of nickel without affecting the cobalt ions
in the solution [3]. The good results of this innovative
process led to the construction of a factory in Canada in
1954 [4].
Another innovative process in this field is the Arbiter
process. This process was introduced in 1970 in a pilot
plant in Arizona under the supervision of Arbiter Com-
pany. A few months later, a plant with 91 t of daily
copper production capacity was commercially set up in
Anaconda. In this leaching factory, ten reservoirs were
used equipped with powerful mixers connected to five
thickeners as opposite flow, each with a volume of 14 m
of which the first overflow was filtered for the pregnant
solution. The basis of this process was ammonia leaching
of chalcopyrite concentrates in presence of oxygen at
70–80 °C temperature to form amine copper sulfate and
iron hydroxide.
Fig. 1 Flow sheet of Kennecott plant
Fig. 2 Flow sheet of Gordon
process [2]
96 J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104
The charged output solution from the filter was extracted
using LIX65N, and stripped by sulfuric acid. The resulting
concentrated solution was subject to the electrolysis to
produce metal copper. Finally, lime was added to the
output raffinate and the pulp was distilled to recover
ammonia and precipitate gypsum for use.
Flow sheet of Arbiter process is shown in Fig. 3.This
process was not welcomed by the industry due to technical
and economic problems in the final stage, the recovery of
ammonia and due to weak elimination of sulfate ions from
the solution at the investigated temperature [4].
Another process to extract nickel, cobalt and copper
from pyrite flotation concentrate was developed by INCO
of Copper Cliff, Ontario, Canada with satisfactory results.
This process involves oxide roasting of sulfide concentrate
followed by rapid quenching of the calcine under reducing
conditions and eventual leaching in an ammonia–ammo-
nium carbonate solution [5].
Although most studies in the past, focused on the disso-
lution of sulfide concentrates in reactors and many of them
led to low process kinetics and high temperatures and pres-
sures being needed, most recent studies have been directed
towards the dissolution of oxide ores including malachite.
Table 1lists the titles of studies conducted in recent
decades, along with chemical agents, parameters under
study and the resulting recoveries.
In new research work [12], suitable parameters of
ammoniacal column leaching for Meskani Mine copper ore
in Iran were determined. Taguchi method was used to
design experiments and evaluate the behavior of the
parameters like ammonia concentration, acid flow rate, size
of ore and leaching time. By investigating the effect of
above parameters on copper oxide recovery rate, the opti-
mum condition for concentration, acid flow rate, size of ore
and leaching time were found to be 40 g/l, 60 cm
1–4.75 mm and 10 days, respectively. Studies showed that
the ammonia concentration and size of ore were more
important parameters. The final experiment was conducted
to confirm the optimal conditions obtained from the
Taguchi method in which the copper recovery was 80.6.
In general, ammonia leaching methods include:
Neutral method: In this method, the metals are dissolved
without any oxidizing or reducing agents. Leaching of
copper, zinc or molybdenum oxides are of this type.
Oxide method: In this method, leaching requires the use
of an oxidizer to oxidize solids such as metals or sulfide
Reduction method: In contrast to the oxide leaching
method, a reducing agent is used in this method. It is
mainly used for dissolving metals from highly oxidized
ores such as ocean floor manganese nodules and lateritic
ores [1].
Fig. 3 Arbiter process in
Anaconda mine [4]
J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104 97
Ammonia leaching has many advantages over acidic
leaching. The main advantages are as follows:
a. Marked difference of the two methods. Operations in
the alkaline solution enable the use of ores with high
carbonation, which cannot be used in acidic leaching
due to high consumption of acid.
b. The problems associated with equipment corrosion are
eliminated due to acid replacement.
c. This type of process is more appropriate for mass
leaching of low-grade ores and reservoir leaching of
high grade ores, although this choice also depends on
the grade and the amount deposited.
d. Since metals such as iron and manganese are not
soluble in ammonia or their complexion capacity with
ammonia is low, ammonia leaching has a suitable
selective capacity for the desired metal relative to the
mentioned metals, while the high solubility of these
elements in acidic factors leads to high consumption of
these agents and a non-economic leaching process.
e. In the leaching solution, ammonia prevents calcium
solubility in the presence of carbonate and small
amounts of sulfate. This results in reduced permeabil-
ity in heap due to jarosite or gypsum precipitation, and
high acid consumption in acid leaching is also avoided.
f. Another element causing problem in permeability and
drainage of the heap is silica. Unlike acid types,
ammonia does not react with different compounds of
this element such as alumina silicates and
g. Elimination of the problems associated with formation
of non-filterable precipitates during pH adjustment at
acid leaching factory and non-requirement of viscosity
solutions are other advantages of ammonia leaching.
h. After completion of ammonia leaching, problems
associated with heap washing, neutralization and
long-term monitoring to prevent acid runoff are
minimized. Moreover, the residual ammonia in the
soil can act as fertilizer for growing plants.
In addition to the above advantages, characteristics such
as low toxicity, low cost, easy recyclability and economic
gain are the main factor for increased use of ammonia in
hydrometallurgical processes particularly leaching [1,13].
a. Lower capacity of leaching of acidic compounds,
although not significantly.
b. The use of ammonia due to its high evaporation
capacity is more difficult than acidic compounds,
Table 1 Activities performed in the past decade
Topic Lixivent Parameters Recovery in
Dissolution kinetics of an oxidized copper
ore in Ammonium chloride solution
Ammonium chloride concentration, particle size, solid/
liquid ratio, stirring speed and reaction temperature
Leaching of malachite ore in NH3-
saturated water
Ammonia Ammonia concentration, particle size, temperature,
stirring speed, and solid-to-liquid ratio
Dissolution kinetics of malachite in
ammonia–ammonium carbonate
Leaching time, ammonium hydroxide, and ammonium
carbonate concentration, pH, stirring speed, solid/
liquid ratio, particle size and temperature
98 [8]
A study on the oxidative ammonia–
ammonium sulphate leaching of a
complex (Cu–Ni–Co–Fe) matte
93.8 [9]
Ammonia pressure leaching for LUBIN
Ammonia and
Temperature, oxygen partial pressure, ammonia and
ammonium sulfate concentration and stirring rate
95 [10]
Leaching of copper from tailings using
ammonia–ammonium chloride solution
and its dynamics
Leaching time, the concentration of ammonia, solid/
liquid ratio and temperature
75 [11]
Dissolution kinetics of low grade complex
copper ore in ammonia–ammonium
chloride solution
Concentration of ammonia and ammonium chloride,
ore particle size, solid-to-liquid ratio and temperature
98 J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104
although through hydrolysis of urea, the risk of its
transport can be minimized [13].
c. Extractors so far used for copper recovery from
ammonia medium do not have high efficiency.
The kinetics of copper dissolution in ammoniacal solution
has been comprehensively studied. Lu and Graydon [14]
showed that the total concentration of ammonia and oxy-
gen play an important role in determining the overall rate.
They defined the overall expression of rate as follows:
Rate ¼2ADO2 O2
8DO2 O2½þdKNHþ
In this regard, KNH3and KNHþ
4are the rate constants and
dis the diffusion layer thickness that can be determined
based on the continuity equation. According to their
studies, whenever the overall reaction was of the limited
diffusion type, penetration layer thickness was found to be
0.6 910
cm. They also showed that the dissolution
mechanism is such that due to the formation of a kind of
copper oxide during leaching process, the dissolution of
copper is inhibited. However, the cupric ion had a catalytic
effect on the dissolution of metal copper known as the self-
catalytic phenomenon.
Meng et al. [15] evaluated the effect of oxygen on
copper dissolution kinetics in ammoniacal solution. Fig-
ures 4and 5show the results of their studies. It can be
clearly seen that under low oxygen pressure, the dissolution
of copper is a linear function of leaching time. In fact, the
dissolution process is electrochemical in nature. When air
or oxygen was used as an oxidizer, in low pressure, the
reaction was controlled with diffusion phenomenon, and in
high pressure, it was controlled by surface reaction.
Similar results were obtained in studies by other
researchers such as Habashi [17] and Luo et al. [18]. Some
researchers also studied the dissolution of copper minerals
in different ammonia solutions. In a study on malachite
leaching in ammonium chloride solution [6], it was deter-
mined that the dissolution rate is controlled by a compound
kinetics. Their mathematical model for the reaction kinet-
ics is as follows:
According to their calculations, the activation energy for
malachite dissolution reaction was found to be 71 kJ/mol.
In another study [8] on malachite leaching in ammonium
carbonate solution, it was established that there are two
steps for the dissolution reaction. Firstly, the malachite was
rapidly dissolved, but after completion of 10 % of reaction,
leaching rate was reduced with the formation of needle-
structured middle phase causing surface blockage. This
phase was mainly Cu(OH)
. This stage continue to exist
with the concurrent dissolution of malachite and the middle
phase. In the second stage of the reaction and after reaching
Fig. 4 The dissolution of copper in ammonia solution as a function
of time at various concentrations of ammonia (Stirring speed of
600 rpm and oxygen pressure of 304 kPa) [16]
Fig. 5 Effect of oxygen pressure on the dissolution rate of copper in
ammonia solution (Various concentrations of NH
and 26 °C
temperature) [16]
J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104 99
90 % of the reaction, essentially all of malachite was dis-
solved and only the remaining middle phase was subject to
dissolution. Equations 3and 4show the reaction kinetics
for the first and second stages:
where X represents the solid reactant part, K
and K
constants at the leaching time. According to their calcula-
tions, the activation energy for the first and second stages
were 64 and 75 kJ/mole, respectively.
Eh–pH Diagram for the Copper–Ammonia–Water
In Cu–NH
O system, several soluble species are pres-
ent such as NH
, Cu (NH
Cu (NH
, Cu (NH
and Cu (NH
. There are
therefore many equilibrium equations in the solution
relating these components in the solution to each other. To
use these equations to understand the different reaction
mechanisms in ammonia solutions, the Eh–pH diagram is
used. Eh–pH diagram shown in Fig. 6has been determined
for 25 °C temperature, Cu activity of 0.5 and total
ammonia (NH
and NH
) concentration of 7 kmol/m
The broken lines indicate the following reactions:
According to this diagram, Cu (I) and Cu (II) complexes
with NH
are stable ionic species in neutral and alkaline
solutions. In the presence of excess ammonia, Cu(I) and
Cu(II) are also stable as Cu(NH
and Cu(NH3)
. The
following equations show oxidation–reduction reactions of
Cu (II)/Cu (I) and Cu (I)/Cu:
Cu NH3
4þe¼Cu NH3
Cu NH3
2þþe¼Cu þe¼Cu þ2NH3ð8Þ
The oxidation–reduction potential of Cu (NH3)
is more positive than that of Cu (NH
/Cu. This
indicates that Cu (NH
can oxidize metallic copper in an
ammoniacal alkaline solution. Moreover, the oxidation–
reduction potential of Cu (I)/Cu is more positive than that
of hydrogen evolution (Eq. 5), indicating that Cu(I) can be
preferentially reduced to metallic copper [17]. Figure 7
shows the schematic presentation of the process of
electrochemical dissolution of copper in ammonia solution.
There are limited electrochemical studies about ammo-
nia leaching of copper. Arzutug et al. [7] were among the
few people who used the chemical equilibrium in solution
to evaluate the general reactions in this process. Based on
their studies, during the process of ammonia leaching of
copper ore (malachite) to Cu(OH)
, first CuCO
was dissolved and was then converted to Cu(OH)
based on
the following reactions:
NH3gðÞþH2O$NH3aqðÞ ð9Þ
3aqðÞ ð10Þ
4aqðÞþOHaqðÞ ð11Þ
Cu2þaqðÞþ2OHaqðÞ$Cu OHðÞ
2sðÞ ð12Þ
The formation of Cu(OH)
is succeeded by the
following reactions:
Fig. 6 Eh–PH diagram for Cu–NH
O system (25 °C tempera-
ture, Cu activity of 0.5 and total ammonia concentration of 7 kmol/m
Fig. 7 Schematic presentation of the process of electrochemical
dissolution of copper in ammonia solution [17]
100 J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104
2sðÞ$Cu2þaqðÞþ2OHaqðÞ ð13Þ
Cu2þaqðÞþ2NH3aqðÞ$Cu NH3
2aqðÞ ð14Þ
Cu NH3ðÞ
2aqðÞþ2NH3aqðÞ$Cu NH3
Firstly, the intermediate compound Cu(NH
finally the Cu(NH
complex was formed. These
researchers [7] proposed the following general reaction
for ammonia leaching of copper:
$2Cu NH
Copper Extraction from Ammoniacal Solutions
Case Studies
Copper leaching from ore using ammonia should be fol-
lowed by selective extraction of copper using the extraction
agent in the solvent extraction process. LIX63 was the first
extraction agent used in this field. The low extraction
capacity of this extractor for copper transfer from the acidic
solution led to studying its extraction capability from the
ammonia solution. Although this extractor had a high
efficiency in the extraction of copper from ammoniacal
solutions, due to difficult stripping process, it was not
considered by the industry. Other extractor under study was
LIX64N. This extractor which is cheaper and more prac-
tical than LIX63, was commercially only used for the
recovery of copper from an ammoniacal solution in Arbiter
Process and in melting process. However, the low extrac-
tion ability of copper (12 g/l) and high ammonia loading of
it led to further studies of new extraction agents from the
ammoniacal solutions [20].
These efforts led to synthesis of P204 (D-2-ethyl hexyl
phosphate), which is an organophosphorous acid extractor.
It is reported that under 25 °C temperature, the two phase
contact time of 10 min and phase ratio of 1:1, an ammonia
solution with pH 10 and 20 % P204 concentration (volume
fraction), the copper extraction rate was found to be 93.9 %
[21]. However, P204 is highly soluble in alkaline solution,
and its commercial use in ammoniacal solution (9 \pH) is
Subsequently, a beta-D-ketone extractor called LIX54
was used. This extractor had a high extraction potential for
copper and a low loading capacity for ammonia, and
copper strip from it needed low concentrations of the acid
[22]. In 1995, ESCONDIDA in Chile used this extractor for
extracting copper from an ammoniacal solution on a pilot
scale. However, due to a reaction between a keto group of
LIX54 and ammonia and production of ketamine, the
extraction agent disappeared. Therefore, copper strip from
the charged organic phase was difficult, and finally the
pilot plant was closed [23]. So, the choice of LIX54 was
considered inappropriate for copper extraction in ammo-
niacal solution.
In addition to beta-D ketones, ketoxymes and hy-
droxymes were also used for the extraction of copper from
ammoniacal solution. The results of studying some of these
compounds such as LIX84 indicate a very high extraction
capacity of copper (more than 50 g/l) from ammoniacal
solutions [2428]. However, a hydroxeme like LIX84 had
serious problems of ammonia extraction in the ammoniacal
solution [29,30]. The ammonia present in the charged
organic phase must be eliminated by the electrolyte used
before attempting to strip copper. Otherwise, ammonia in
the charged organic phase is transferred to the pregnant
electrolyte after the stripping process, resulting in the
accumulation and precipitation of (NH
in the
charged electrolyte [29]. Recently, in another research, to
decrease ammonia extraction in the charged organic phase,
stearically hindered beta-D ketone was used. In this study,
under the temperature 25 °C, 30 min contact time of two
phases, phase ratio of 1:1, Cu concentration of 3 g/l,
3 mmol/l total ammonia concentration, water pH of 8.43
and beta-D ketone concentration in organic phase of 20 %
(volume fraction), ammonia in the water phase was far less
extracted by the organic phase (only 14.5 mg/l), while the
copper extraction rate was 95.09 %. Table 2show the
general characteristics of the chelate type extractors used in
the extraction of copper from an ammoniacal solution [20].
Extraction Mechanism
In general, extraction equilibrium between Cu
and a
chelation extractor is as follows:
Cu2þaqðÞþ2HR orgðÞ$CuR2orgðÞþ2HþaqðÞð17Þ
Table 2 Characteristics of copper extractors from ammoniacal
solutions [20]
Beta-D-ketone Hydroxeme Property
Moderate Strong Extractive strength
Excellent Good Ease of stripping
Low Moderate Viscosity
Very low Low Ammonia loading
Very good Very good Selectivity of copper
Fast Fast Kinetics
Good Good Stability
Very good Good Phase separation
Very high Very high Copper complex solubility
J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104 101
If the aqueous solution contains copper and aluminum
ions, in sufficiently high pH levels where free ammonia is
released, amine complexes will be formed in aqueous
phase as follows:
Cu2þaqðÞþmNH3aqðÞ$Cu NH3
2þaqðÞ ð18Þ
When the phases contact, ammonia in aqueous phase
may be extracted in the form of [Cu(NH
expressed as follows:
Cu NH3
aqðÞþ2HR orgðÞ
$Cu NH3
R2orgðÞþ2HþaqðÞ ð19Þ
in which HR(org) represents extractor in the organic phase,
(org) extractor-copper complex in organic phase,
](aq) amine-copper ion complex in aqueous
phase and [Cu(NH
(org) extraction compound of
and extractor in the organic phase [31].
Ammoniacal Leaching of Other Elements
In addition to studies on copper, ammonia leaching has
been used to recover some other basic elements.
Manganese nodules are in fact Ferromanganese oxide
ores containing copper, nickel and cobalt. These metal
oxides have been reported mainly in lateritic iron and
manganese minerals. Crushing these laterites using pyro-
metallurgy reduction or hydrometallurgical reductive dis-
solution is an important step for proper recovery of
precious metal. Therefore, the recovery process of man-
ganese nodules has been studied in two ways:
a. Initial pyrometallurgical preparation and then perform-
ing the metallurgical process.
b. Performing the hydrometallurgical process alone.
Initial pyrometallurgical preparation operations often
involve melting, reduction-roasting, sulfidation and chlo-
rination. Reductive dissolution takes place by Hydrochloric
acid, sulfuric acid, ammonia, etc. in the presence or
absence of reducing reactants such as sulfur dioxide, pyrite,
sodium sulfide, charcoal, alcohol, etc. [3234].
In research conducted for processing of manganese
nodules by ammonia leaching [3537], after reductive
roasting of the sample for releasing precious metal oxides
from manganese and iron oxide phase, reduction operations
were done to form copper, nickel and cobalt metals and
facilitate their ammonia leaching. During the ammonia
leaching process, in addition to dissolution of precious
metals such as copper, nickel and cobalt as stable amine
complexes, the dissolution of unwanted metals such as iron
and manganese was also prevented. Overall flowsheet of
this process is shown in Fig. 8.
Ammonia leaching has also been used for recovery of
nickel and cobalt from oxide, sulfide and complex ores. For
example, the so-called Caron process was developed to
recover nickel and cobalt from low-grade ores such as
lateritic ores with an ammonia–ammonium carbonate
solution. This process involves reductive roasting of nickel
ore followed by leaching using ammonia–ammonium
Fig. 8 Flowsheet of precious
metals’ recovery from
manganese nodules of the ocean
floor [35]
102 J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104
carbonate compound, commercially adopted in Nicaro in
Cuba, Marinduque in the Philippines and Queensland in
Australia [38].
Cadmium, gold and silver are other precious metals of
which ammonia leaching has been studied, although none
of the innovative processes used for their recovery has
found industrial application [3943].
In this review, various topics related to ammonia leaching
of copper have been studied. The history of this process,
different methods involved in it, the advantages and dis-
advantages, kinetics, Purbeh diagram, the way to extract
copper from the pregnant solution obtained and extraction
agents used are different issues described in this paper.
Evaluation of the studies shows that, despite a long history
of using this process, easy use of acidic leaching agents and
their higher leaching capacity have prevented ammonia
leaching from being accepted as an acid leaching process.
In recent years, however, due to decrease in proper reserves
for acid leaching and considerable advantages of this
method such as lower toxicity, easier recovery and eco-
nomic gain, ammonia leaching has again been looked upon
as a possible option by researchers and industrialists.
1. X. Meng, K.N. Han, The principles and applications of ammonia
leaching of metals-a review. Miner. Process. Extr. Metall. Rev.
16(1), 23–61 (1996)
2. F.A. Forward, V.N. Mackiw, Chemistry of the ammonia pressure
process for leaching Ni, Cu and Co from shrritt gordon sulphide
concentrates. J. Met. 7, 457–463 (1955)
3. E.R.W. Rousseau, Handbook of separation process technology
(Wiley, New York, 2009)
4. M.C. Kuhn, N. Arbiter, H. Kling, Anaconda’s arbiter process for
copper. CIM Bull. 67(752), 62–73 (1974)
5. C.K. Chase, The ammonia leach for copper recovery, leaching
and recovery copper from As-mined materias. W. J. Schlitt (ed).
SME/AIME. 95–103 (1980)
6. A. Ekmekyapar, R. Oya, A. Kunkul, Dissolution kinetics of an
oxidized copper ore in ammonium chloride solution. Chem.
Biochem. Eng. Q. 17(4), 261–266 (2003)
7. M.E. Arzutug, M.M. Kocakerim, M. Copur, Leaching of mala-
chite ore in NH
-saturated water. Ind. Eng. Chem. Res. 43(15),
4118–4123 (2004)
8. D. Bingol, M. Canbazoglu, S. Aydogan, Dissolution kinetics of
malachite in ammonia–ammonium carbonates leaching. Hydro-
metallurgy 76(1–2), 55–62 (2005)
9. K.H. Park, D. Mohapatra, B.R. Reddy, C.W. Nam, A study on the
oxidative ammonia–ammonium sulphate leaching of a complex
(Cu–Ni–Co–Fe) matte. Hydrometallurgy 86(3–4), 164–171
10. F.P. Mineralurgii, Ammonia pressure leaching for lubin shale
middlings. Physicochemical Problems of Mineral Processing. 43,
5–20 (2009)
11. Z. Guo-dong, L. Qing, Leaching of copper from tailings using
ammonia–ammonium chloride solution and its dynamics. Inter-
national conference on chemistry and chemical engineering
(ICCCE) (2010)
12. V. Radmehr, Determination of suitable parameters of ammonia-
cal column leaching for meskani mine copper ore. M.Sc Thesis.
University of Tarbiat Modares, Tehran, Iran (2012)
14. B. Lu, W. Graydon, Rates of solution of copper in aqueous
ammonia hydroxide solutions. J. Am. Chem. Soc. 77, 6132–6136
15. X. Meng, X. Sun, K.N. Han, A dissolution kinetics model for
metals in solutions. AIME/SME Annual Meeting in Albuquerque,
Feb. 14–17 (1994)
16. M.J. Nicol, Electrochemical investigation of the dissolution of
copper, nickel and copper nickel alloys in ammonium carbonate
solutions. JS Africa Inst. Min. Metall. 75(11), 291–302 (1975)
17. F. Habashi, Kinetics and mechanism of copper dissolution in
aqueous ammonia. Ber. Bunsenges. Phys. Chem. 67(4), 402–406
18. Q. Luo, R.A. Mackay, S.V. Babu, Copper dissolution in aqueous
ammonia-containing media during chemical mechanical polish-
ing. Chem. Mater. 9(10), 2101–2106 (1977)
19. H. Konishi, Selective separation and recovery of copper from iron
and copper mixed waste by ammonia solution. ISIJ Int. 36, 520
20. G.V. Jergensen, Copper leaching, solvent extraction, and elec-
trowinning technology (Society for Mining, Metallurgy and
Exploration (SME), Littleton, 1999)
21. Q. Dong, W. Kai-yi, C. Chun-lin, P. Chun-yue, T. You-gen, J.
Jin-zhi, Separation of nickel, cobalt and copper by solvent
extraction with P204. Trans. Nonferrous Met. Soc. China 11(5),
803–805 (2001)
22. F.J. Alguacil, M. Alonso, The effect of ammonium sulphate and
ammonia on the liquid–liquid extraction of zinc using LIX 54.
Hydrometallurgy 53, 203–209 (1999)
23. H. Hui-ping, L. Chun-xuan, H. Xue-tao, L. Qi-wen, C. Qi-yuan,
Solvent extraction of copper and ammonia from ammoniacal
solutions using sterically hindered [beta]-diketone. Trans Non-
ferrous Met. Soc. China 20(10), 2026–2031 (2010)
24. M. Mackenzie, M. Virnig, A. Feather, The recovery of nickel
from high-pressure acid leach solutions using mixed hydroxide
product-LIX84-INS technology. Miner. Eng. 19(12), 1220–1233
25. P.K. Parhia, K. Sarangi, Separation of copper, zinc, cobalt and
nickel ions by supported liquid membrane technique using LIX
84I, TOPS-99 and Cyanex 272. Sep. Purif. Technol. 59(2),
169–174 (2008)
26. R.B. Reddy, N.D. Priya, Process development for the separation
of copper(II), nickel(II) and zinc(II) from sulphate solutions by
solvent extraction using LIX 84 I. Sep. Purif. Technol. 45(2),
163–167 (2005)
27. K. Sarangi, K. Parhi, E. Padhan, A.K. Palai, K.C. Nathsarma,
K.H. Park, Separation of iron(III), copper(II) and zinc(II) from a
mixed sulphate/chloride solution using TBP, LIX84I and Cyanex
923. Sep. Purif. Technol. 55(1), 44–49 (2007)
28. B. Sengupta, M.S. Bhakhar, R. Sengupta, Extraction of copper
from ammoniacal solutions into emulsion liquid membranes
using LIX 84 I. Hydrometallurgy 89, 311–318 (2007)
29. C. Parija, P.V.R. Bhaskara Sarma, Separation of nickel and
copper from ammoniacal solutions through Co-extraction and
selective stripping using LIX84 as the extractant. Hydrometal-
lurgy 54, 195–204 (2000)
30. C. Parija, B.R. Reddy, P.V.R. Bhaskara Sarma, Recovery of
nickel from solutions containing ammonium sulphate using LIX
84 I. Hydrometallurgy 49(3), 255–261 (1998)
J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104 103
31. F.J. Alguacil, M. Alonso, Recovery of copper from ammoniacal
ammonium sulfate medium by LIX 54. J. Chem. Technol. Bio-
technol. 74(12), 1171–1175 (1999)
32. R.K. Jana, Leaching of sea nodules in acidic chloride–sulphide
media. Trans. Inst. Min. Metall. 102, C191–C194 (1993)
33. R.K. Jana, D.D.N. Singh, S.K. Roy, Alcohol modified hydro-
chloric acid leaching of sea nodules. Hydrometallurgy 38,
289–298 (1995)
34. S.B. Kanungo, P.K. Jena, Reductions leaching of manganese
nodules of Indian ocean origin in dilute hydrochloric acid.
Hydrometallurgy 21, 41–58 (1988)
35. G.P. Glasby, Marine Manganese Deposits (Elsevier Science &
Technology, Amsterdam, 1977)
36. K.N. Han, M. Hoover, D.W. Fuerstenau, Ammonia–ammonium
leaching of deep sea manganese nodules. Int. J. Miner. Process 1,
215–230 (1974)
37. R. Jana, B. Pandey, Ammoniacal leaching of roast reduced deep-
sea manganese nodules. Hydrometallurgy 53(1), 45–56 (1999)
38. F. Habashi, Nickel in Cuba. The Paul E Queneau international
symposium, extractive metallurgy of copper, nickel and cobalt.
The Minerals, Metals and Materials Society 1, 1165–1178 (1993)
39. K.N. Han, X. Meng, Ammonia extraction of gold and silver from
ores and other materials. U.S. Patent 5114687 (1994)
40. K.N. Han, X. Meng, Extraction of gold/silver from refractory ores
using ammoliacal solutions. In proceedings of Randol gold
forum. 213–218 (1992)
41. X. Meng, K.N. Han. The dissolution behavior of gold in
ammoniacal solutions, in Hydrometallurgy—fundamentals, tech-
nology and innovation, ed. by J.B. Hiskey, G.W. Warren (SME,
Littleton, CO, Printed by Cushing-Malloy, Inc. ANN Arbor,
Michigan, 1993), p. 205–221
42. X. Meng, The Leaching behavior of gold in ammonical solutions
and its practical applications. Ph.D Dissertation, SDSM&T,
Rapid City, SD. 228 (1991)
43. G. Pfrepper, Leaching of nickel and cadmium from scrap and
especially spent batteries with ammonical solution. German
(East) Patent DD 286, 190 (1991)
104 J. Inst. Eng. India Ser. D (October 2013–March 2014) 94(2):95–104
... Potassium permanganate, as a common strong oxidant, was selected as the oxidant for the leaching system. Ammonia, known for its high efficiency in leaching copper [15], was introduced into the system for the first time to promote the extractions and also act as a pH modifier. Various parameters influencing the dissolution of gold and copper were studied. ...
... However, as indicated in Figure 5a,b, the increase in glycine and ammonia concentration did not lead to a significant increase in gold extraction (copper extraction was still affected). It has been intensively reported that both ammonia and glycine can leach copper efficiently by complexation as copper-ammines (Cu(NH 3 ) 2+ or Cu(NH 3 ) 4 2+ ) and copper glycinate (Cu(Gly) 2 ), respectively [10,[15][16][17][18]. For example, Khezri et al. [18] investigated the leaching of chalcopyrite in glycine solutions, whereby 95.1% of copper was extracted using a mechanically activated sample at 0.4 M glycine, 1 L/min oxygenation and with pH level of 10.5. ...
... As shown, Cu(NH 3 ) 4 2+ and Cu(Gly) 2 may have played the roles of catalytic oxidants for gold leaching, which would lead to producing Cu(NH 3 ) 2+ to be further oxidized back by the strong oxidant permanganate. sively reported that both ammonia and glycine can leach copper efficiently by complexation as copper-ammines (Cu(NH3) 2+ or Cu(NH3)4 2+ ) and copper glycinate (Cu(Gly)2), respectively [10,[15][16][17][18]. For example, Khezri et al. [18] investigated the leaching of chalcopyrite in glycine solutions, whereby 95.1% of copper was extracted using a mechanically activated sample at 0.4 M glycine, 1 L/min oxygenation and with pH level of 10.5. ...
Full-text available
This study presents the novel idea of a cyanide-free leaching method, i.e., glycine–ammonia leaching in the presence of permanganate, to treat a low-grade and copper-bearing gold tailing. Ammonia played a key role as a pH modifier, lixiviant and potential catalyst (as cupric ammine) in this study. Replacing ammonia with other pH modifiers (i.e., sodium hydroxide or lime) made the extractions infeasibly low (<30%). The increased additions of glycine (23–93 kg/t), ammonia (30–157 kg/t) and permanganate (5–20 kg/t) enhanced gold and copper extractions considerably. Increasing the solids content from 20 to 40% did not make any obvious changes to copper extraction. However, gold leaching kinetics was slightly better at lower solids content. It was indicated that the staged addition of permanganate was unnecessary under the leaching conditions. Recovery of gold by CIL was shown to be feasible, and it improved gold extraction by 15%, but no effect was observed for copper extraction. Percentages of 76.5% gold and 64.5% copper were extracted in 48 h at 20 g/L glycine, 10 kg/t permanganate, 20 g/L carbon, pH 10.5 and 30% solids. Higher extractions could be potentially achieved by further optimization, such as by increasing permanganate addition, extending leaching time and ultra-fine grinding.
... Additionally, recovery of cobalt and nickel from both lateritic ores (Caron, 1950) and pyrrhotite flotation concentrates (Schlitt, 1980) using ammonia-ammonium carbonate solutions have been employed. Further, recent pilot-scale applications of commercial ammoniacal leaching is highlighted in Radmehr et al. (2013). Significant commercial developments include Anderson (2003) focusing on nitrogen species catalyzation in oxidizing pressure-leach system for Cu recovery, Hedjazi & Monhemius (2018) focusing on ammonia in copper-gold cyanide leach systems, and Ochromowicz et al. (2014) who focused on subsequent SX-EW recovery of Cu from ammoniacal systems. ...
The dissolution of copper during the leaching of chalcopyrite in ammonia solutions is an attractive alternative to acid sulfate leaching in the treatment of ores with high consumption of acid. Despite considerable research into this complex leaching system, a lack of understanding of the fundamental chemical drivers has delayed the implementation of the ammonia process. In the present study, various ammonium salts solutions (chloride, sulfate, carbonate) have been used to study the effect of ion association on the dissociation constant of the ammonium ion at temperatures of 25 and 35 °C. Experimental and calculated solubilities of Cu²⁺ have been obtained under different conditions and plotted in speciation distribution diagrams, in other to assess the accuracy of predictions using available thermodynamic properties. Ion association was found to significantly affect the dissociation constant of the ammonium ion in solutions containing sulfate, chloride and carbonate anions; thus, influencing the free ammonia concentration in solution. Increasing temperature from 25 to 35 °C was found to decrease the dissociation constant of the ammonium ion. These findings highlight the importance of using the correct anionic ligands for the ammonium ions and temperature in order to obtain high dissolution of copper. It has been established that solubility of copper in ammonia solution is affected by the anionic ligands, temperature and addition of chloride ions. The NH3 ligand forms strong coordination compounds with cupric or cuprous ions depending on the anionic ligand, generating an increase in solubility between pH 8.5 and 10.0. The present study, therefore, identifies important constraints on the role of varying anion associated with ammonia, temperature, pH, and addition of chloride ions and the inter-dependence of these factors in controlling Cu²⁺ solubility in ammoniacal systems. The results from the present study provides experimental pKa values and solubility constants of the various ammoniacal systems to provide commercial processing via ammoniacal routes the optimal conditions in which to maximise Cu recovery and maintain free ammonia at levels to minimise volatility and loss. The findings are directly beneficial to future commercial application employing effective ammonium-anion lixiviant strategies in the sustainable recovery of Cu.
... Применение растворов карбоната аммония в процессах электрохимического извлечения вольфрама из отходов тяжелых вольфрамовых сплавов (далее -ТВС) представляет значительный интерес ввиду существенного упрощения процесса производства паравольфрамата аммония [1]. Кроме того, реагент характеризуется низкой токсичностью и стоимостью, а также легкой регенерацией [2]. Основным компонентом ТВС типа ВНЖ и ВНЖК является вольфрам, представляющий собой «каркас» сплава, в качестве «связки» же выступают металлы подгруппы железа (Fe, Ni, Co) [3]. ...
Full-text available
Annotation. The anodic behavior of the components of the binding phases of heavy tungsten alloys of the type of W-Ni-Fe and W-Ni-Fe-Co (Fe, Ni and Co) in solutions of ammonium carbonate (0.5-1.5 M) was studied by linear voltammetry. It is shown that for all the metals under study, the areas of their oxidation are observed on the polarization curves. It was found that for iron, the passivating effect of ammonium carbonate is most pronounced at its concentration in the electrolyte of 1 M or more. The prospects of using solutions of (NH4)2CO3 for electrochemical processing of waste alloys of W-Ni-Fe and W-Ni-Fe-Co residence permit and residence permit have been revealed. Text in Russian.
... It has been previously reported that ammonia prevents calcium solubility in the presence of carbonate or small amounts of sulfate. 33 The leachability of other heavy metals such as lead, zinc, or arsenic was very low, although it was higher in water than in ammoniacal solutions. ...
In electronic and electrical industries, a huge amount of acidic cupric etching wastewater was produced during the manufacture of printed circuit board (PCB). Reclamation of copper is necessary for resource recovery and environmental protection. Herein, ammonia (NH3·H2O) and sodium hydroxide (NaOH) were investigated and compared as neutralizers to regulate the sequential crystallization of basic copper chloride (Cu2(OH)3Cl), copper hydroxide (Cu(OH)2), and copper sulfate (CuSO4·5H2O). Crystal phase and micro-morphology were analyzed by X-ray diffraction and scanning electron microscope; product quality was evaluated by laser particle size analyzer, thermogravimetry, and inductively coupled plasma. The results showed that ammonia as the neutralizer can regulate the formation of spherical Cu2Cl(OH)3 particles with compact surface, good fluidity, and low moisture-absorption-ability, which can be used as a precursor to producing Cu(OH)2 and CuSO4·5H2O with higher purity. Mechanism analysis revealed that ammonia acts as “a storage of OH⁻ and Cu²⁺” in the aqueous phase due to its weak alkalinity and the ability to complex with Cu²⁺ to form stable Cu(NH3)n²⁺. As a result, OH⁻ and Cu²⁺ were slowly released to the solution and slowed down the crystallization kinetics of copper-containing precipitates. This work proposed a promising and harmless resource recycling method, and also inspired the understanding and utilization of metal crystallization law in the ammonia buffer system.
In this study, an optimal sampling schedule was developed for leaching experiments with the objective of improving the confidence of the kinetic parameters. This study shows that there is an improvement in the confidence interval from uniform sampling and the method presented here. The optimal sampling times were determined by reducing the determinant of the covariance matrix associated with the kinetic constant, which can be expressed through the covariance matrix of the extracted fraction, X, used to generate a function to distribute the sampling times in the experiment. The method presented here requires minimal knowledge a priori of the system to be characterized. Only the kinetic expression for the system is required. The methodology was applied to a simulated case and experimental case study of ammoniacal leaching of copper slags. The simulations conducted indicated a lower value of the standard deviation of 1.40·10−4 min−1 for optimized sampling times and a value of 1.78·10−4 min−1 for uniform distribution. The experimental validation results indicated a reduction of the coefficient of variation for optimized experiments of 9.3 pct (less uncertainty) from 29.7 pct (uniform sampling) to 14.6 pct (optimized sampling). Thus, the methodology proposed here is successful in decreasing the uncertainty in laboratory leaching experiments.
The cyanide process, as the most common approach in the recovery of gold by hydrometallurgical, suffers from its high toxicity to the environment. The effect of practical parameters, viz., temperature, time, concentration, mechanical activation, and the stirring rate, was investigated using a combination of H2O2, BmimHSO4, and thiourea as green solvent to recover the gold from anode copper slime in an electrorefining plant. The leaching kinetics of Au in the selected slime was also investigated. The results showed that leaching reaches 93.48% after 20 h in the activated sample for 10 h at the temperature of 313.15 K and solvent including 60% (v/v) BmimHSO4, 50 g/L thiourea, 1/15 g/ml pulp density, 25 g/L H2O2, and an agitation speed of 400 rpm. Moreover, the leaching of Au follows the shrinkage particle model, and the diffusion of a solvent through the leaching product was the administrated mechanism. The proposed green solvent can also dissolve gold effectively and is an excellent candidate to replace harmful cyanide‐based solvents.
The ammonia leaching method for treating low-grade rhodochrosite has the advantages of a good impurity removal effect and low environmental pollution. In this paper, aiming at the low leaching efficiency of low-grade rhodochrosite treated by the ammonia leaching method, studies on enhancing the leaching efficiency of manganese by using ammonium hydrogen fluoride as an additive are carried out. The effects of different ammonia concentrations, leaching temperatures, leaching times, liquid-solid ratios, stirring rates, and the addition of ammonium hydrogen fluoride on the leaching efficiency of manganese with and without ammonium hydrogen fluoride as an additive were comparatively studied, and the parameters of ammonia concentration, ammonia leaching temperature, and ammonium hydrogen fluoride dosage were optimized in the experimental study. The results indicated that ammonium hydrogen fluoride as an additive in the treatment of low-grade rhodochrosite by the ammonia leaching method could effectively increase the leaching efficiency of manganese, and the optimal process parameters were obtained. Meanwhile, the addition of ammonium hydrogen fluoride didn’t affect the quality of the steamed ammonia product.
Roasting is an essential process before ammonia leaching of low-grade rhodochrosite ore. Thermal decomposition characteristics and phase transformation rules of low-grade rhodochrosite ore with a particle size of less than 74 µm in N2, CO2 and air were studied. MnCO3, MgCO3 and CaCO3 in rhodochrosite are decomposed into MnO, MgO and CaO at 339 ℃, 306 ℃ and 842 ℃, respectively. MnO is oxidized to MnO2, Mn2O3 and Mn3O4 at 339 ℃, 533 ℃ and 1005 ℃, respectively. The TG/DTA and phase transformation results indicated that by thermal decomposition of rhodochrosite ore in air, N2 and CO2, MnCO3 is converted into Mn2O3, MnO and MnO, respectively. MnCO3 is converted to MnO at a higher temperature in a carbon dioxide atmosphere (512 ℃) than in a nitrogen atmosphere (400 ℃).
The large generation of electronic waste (e-waste) is posing a serious threat to society. It is important to develop sustainable technology for the effective management of e-waste and the recovery of valuable metals from it. The present study employed hydrometallurgical approach for Cu and Ni extraction from waste printed circuit boards (WPCB) of mobile phones. This study demonstrates the application of ammonia-ammonium sulfate leaching for the maximum recovery of Cu and Ni. Investigations revealed that the most favourable reaction parameters for efficient metal extraction are - ammonia concentration - 90 g/L, ammonium sulfate concentration - 180 g/L, H2O2 concentration - 0.4 M, time - 4 h, liquid to solid ratio - 20 mL/g, temperature - 80 °C and agitation speed - 700 rpm. Under these conditions, 100% Cu and 90% Ni were extracted. Furthermore, the kinetic study was performed using the shrinking core model which revealed that the internal diffusion is the rate-controlling step for Cu and Ni extraction. The activation energies for Cu and Ni extraction were found out to be 4.5 and 5.7 kJ/mol, respectively. Finally, Cu was recovered with 98.38% purity using electrowinning at a constant DC voltage of 2.0 V at Al cathode. The present study provides a solution for concurrent extraction of Cu and Ni from the raw WPCB of mobile phones and selective recovery of Cu from metal leached solution. The process has the potential to recover the resources from WPCB while minimising the pollution caused by mismanagement of WPCB.
The adsorption behavior of gold in ammoniacal solutions on activated carbon was studied. The gold adsorption capacity of the activated carbon and the recovery efficiency were examined. The parameters affecting the adsorption of gold on the activated carbon included temperature, agitation speed, the concentration of cation and anion and the concentration of ammonia. It was found that the maximum gold adsorption was about 10 kg/t of carbon. The recovery of gold by the adsorption from ammoniacal solutions was found to be dependent upon the initial gold concentration. Under experimental conditions, a gold recovery of 98% was obtained after 120 hrs of adsorption. It was also found that the initial adsorption rate was relatively fast, when compared to the entire adsorption period. The apparent activation energy for the adsorption was determined to be 15.8 kJ/mol. It was believed that the kinetics of gold adsorption on the activated carbon was controlled by pore diffusion.
The paper relates to the laboratory and pilot plant studies that have been carried out by Sherritt Gordon Mines Ltd., Metallurgical Research Div., in developing the ammonia pressure leach process for extracting copper, nickel, cobalt, and sulphur from high grade nickel concentrate produced from Lynn Lake ores, and describes in some detail the chemistry of the process.
The dissolution of copper and nickel in ammonium carbonate solution was studied by techniques involving electrochemical anodic dissolution and ring-disc electrodes. The rate of oxidation of both copper and nickel by copper was shown to be controlled mainly by diffusion to the surface. Variations in rate with changes in two copper concentrations, agitation, pH, ammonia concentration, and temperature were investigated and rationalized in terms of their effects on the electrochemical half-reactions involved. Evidence was found for the passivation of nickel and nickel-copper alloys of more than 50 per cent nickel.
The adsorption behavior of silver in ammoniacal solutions on activated carbon was studied. In addition to the concentration of ammonia, the parameters that affect adsorption include temperature, degree of agitation and anion and cation concentrations. In the study, it was found that the adsorption of silver from ammoniacal solutions is dependent on the initial silver concentration in the solution. It was also found that the recovery of silver from ammoniacal solutions is not as effective as gold. The adsorption rate was relatively slow overall, despite a rapid initial adsorption. The apparent activation energy for the adsorption was measured at 30.2 kJ/mol. It was believed that the kinetics of the silver adsorption on activated carbon was limited by a mixed control mechanism.
The dissolution kinetics of malachite ore in ammonium chloride solutions has been investigated with respect to the effects of ammonium chloride concentration, particle size, solid/liquid ratio, stirring speed, and reaction temperature. It was determined that the dissolution rate increased with increasing ammonium chloride concentration, stirring speed, and reaction temperature. However, increasing particle diameter and solid to liquid ratio decreased the dissolution rate. Examination of data by heterogeneous model suggested that the dissolution rate is controlled by mixture kinetics. The following mathematical model was proposed to represent the reaction kinetics. 1 - 2(1 - x) 1/3 + (1 - x) 2/3 = 1 · 10 -5 (c) 2.10 · (d p) -1.96 · (ρ S/L) -0.64 · (n) 1.78 · e (-8500/T) · t The activation energy for the dissolution reaction was calculated as 71 kJ mol -1. Where x is the reacted fraction of the solid, c is the ammonium chloride concentration, d p is the particle diameter, ρ S/L is the solid to liquid ratio, n is the stirring speed, E is the activation energy, T is the reaction temperature and t is the reaction time.
The paper concerns itself with the low-pressure ammonia-ammonium sulphate leaching of copper concentrates. The mixing system, leach results and residue flotation are introduced and discussed. It is claimed that an excellent copper dissolution is achieved, iron is easily and cheaply discarded as Fe//2O//3 or FeS//2, sulphur is rejected as either gypsum or ammonium sulphate and FeS//2, materials of construction are well known, equipment design and development are minimal, and capital and unit costs are very much competitive with those of conventional concentrate treatment plants. Flowsheet of the process is included.
A method for the direct leaching of manganese nodules in hydrochloric acid has been patented. The leaching of oxide and sulphide minerals in dilute hydrochloric acid solutions and the effect of various chloride additions on the leaching systems have been investigated. The effect of Na2S additions on the leachability of metals from sea nodules in dilute hydrochloric acid solution was investigated.
The rates of dissolution of polycrystalline metallic copper in aqueous ammonium hydroxide solutions have been determined under various experimental conditions. Over a considerable range of conditions the dissolution has been found to be autocatalytic. The autocatalytic dissolution is well represented by a half-order rate equation. An empirical equation is presented which represents the autocatalytic rate data with an average deviation of ±4%. The rate equation is discussed in terms of a mechanism which assumes that the rate controlling process is the removal of cuprous ion species from the copper solution interface by diffusion. Data are also given for an essentially zero-order rate of dissolution observed when the dissolving medium was concentrated with respect to oxygen or very dilute with respect to cupric ion species.
The paper describes the reduction-roast ammonia leach process developed at NML for recovery of copper, nickel and cobalt from polymetallic sea nodules. A brief account of the development of a two stage ammoniacal leaching scheme with a prior pre-conditioning step is given. The necessity of monitoring redox potential in the first stage leaching to control cobalt recovery has been emphasized. Based on the two stage leaching scheme, recycle leaching has been carried out to generate leach liquor having suitable composition for the subsequent solvent extraction–electrowinning operation. The average recovery of metals in 16 cycles of leaching has been found to be 92% Cu, 90% Ni and 56% Co.
Ammonia-ammonium leaching of samples of nodules from several different locations was carried out after reduction of the nodules under gas mixtures at 400, 600, and 800°C. In accordance with thermodynamic analysis, nickel, copper and cobalt oxides in the nodules are preferentially reduced with a gas mixture of . After an initial reduction step with at 600°C, leaching at room temperature and atmospheric pressure with aqueous ammonia-ammonium carbonate and ammonia-ammonium sulfate solutions yielded high extractions of copper and nickel (> 80%), and close to 50% for cobalt. The nature of the pores in nodules from different locations appears to affect the extraction process. A lower reduction temperature is required to obtain the same extraction of nickel, copper and cobalt in a sulfate system than is necessary in a carbonate system. However, a higher manganese content results in the sulfate leaching solutions as compared to the carbonate system, where essentially none of the manganese and iron are extracted.