Minerals Engineering: Daniel J. Lane, Nigel J. Cook, Stephen R. Grano, Kathy Ehrig
Minerals Engineering: Daniel J. Lane, Nigel J. Cook, Stephen R. Grano, Kathy Ehrig
Minerals Engineering: Daniel J. Lane, Nigel J. Cook, Stephen R. Grano, Kathy Ehrig
Minerals Engineering
journal homepage: www.elsevier.com/locate/mineng
a r t i c l e i n f o a b s t r a c t
Article history: Custom copper smelters impose substantial financial penalties for the presence of deleterious impurity
Received 4 May 2016 elements in copper concentrates and can outright reject concentrates which contain impurity elements
Revised 30 July 2016 in concentrations that exceed specified values. Hence, there is strong motivation to remove penalised
Accepted 3 August 2016
impurity elements from copper concentrates at the mine site before shipping to custom smelters. A num-
ber of leach systems have been developed for the selective extraction of penalty elements from copper
concentrates, including: alkaline sulphide leaching (ASL); hypochlorite leaching; dilute sulphuric acid
Keywords:
leaching with aluminium sulphate; and combined pressure oxidation (POX) leaching with copper precip-
Copper concentrate
Penalty elements
itation leaching. This paper reviews these four systems with emphasis on the leaching behaviour of pen-
Selective leaching alty elements. ASL has previously been employed in industry for the selective extraction of As and Sb
Alkaline sulphide from tetrahedrite-rich copper concentrates. Sodium sulphide solution leaches As, Sb, and Hg from a large
Hypochlorite range of minerals, however, does not leach arsenopyrite, a mineral which often contains a significant por-
Radionuclides tion of the total As in copper concentrates. Hypochlorite leaching extracts As associated with enargite
minerals. This leach system benefits from superior rates of As extraction when compared with ASL,
and for this reason, has gained recent interest within the research community. Two major issues have
been identified with hypochlorite leaching of copper concentrates. These are poor reagent selectivity
towards As-bearing minerals and high levels of hypochlorite consumption. Unless these two issues are
resolved it is unlikely that hypochlorite leaching will be employed in commercial processes. Dilute sul-
phuric acid leaching with aluminium sulphate is used to extract F associated with fluorite. This leach sys-
tem also extracts F associated with apatite and chlorite. Laboratory-scale experiments and extensive
operating experience have indicated that fluorite can be substantially leached from copper concentrates
without addition of aluminium sulphate provided that the concentration of sulphuric acid in the leach
solution is sufficiently high (at least 40 g L1). POX/copper precipitation leach systems have potential
to extract a large number of penalty elements from copper sulphide concentrates while simultaneously
upgrading the concentration of copper in the concentrate. Two patented POX/copper precipitation leach
processes have been specifically developed for the deportment of penalty elements. These two processes
are reviewed in detail.
Ó 2016 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
2. Alkaline sulphide leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
2.1. The Sunshine process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
2.2. The Equity process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
2.3. The Melt process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
3. Hypochlorite leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4. Dilute sulphuric acid leaching with aluminium sulphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
⇑ Corresponding author at: Institute for Minerals and Energy Resources, The University of Adelaide, Adelaide, South Australia 5005, Australia.
E-mail address: daniel.lane@adelaide.edu.au (D.J. Lane).
http://dx.doi.org/10.1016/j.mineng.2016.08.006
0892-6875/Ó 2016 Elsevier Ltd. All rights reserved.
D.J. Lane et al. / Minerals Engineering 98 (2016) 110–121 111
Table 3 Table 4
Impurity element limits for LME Grade A copper cathode (London Metal Exchange, Leach systems for the selective extraction of penalty elements from copper
https://www.lme.com//media/Files/Branding/Chemicalcomposition/Nonferrous/ concentrates.
Chemicalcomposition).
Leach system Penalty elements leached
Element Composition, % maximum
Alkaline sulphide leach As, Sb, Hg, Bib, Teb
Ag 0.0025 Hypochlorite leach As, Teb
As 0.0005a Dilute sulphuric acid leach with F
Bi 0.00020b aluminium sulphate
Cd –a POXa leach/copper precipitation Bi, Cd, Co, Ni, Pb, Te, Tl, Zn, 238
U, 230
Th,
Co –c leach 226
Ra, 210Pb, 210Po
Cr –a a
Fe 0.0010c POX = pressure oxidative.
b
Mn –a No leaching data was found for these elements.
Ni –c
P –a
Pb 0.0005 recovery of copper (Fountain, 2013). Safe disposal of the radioac-
S 0.0015d tivity enriched flue dusts can be both complex and expensive.
Sb 0.0004a
It is clear that there is strong motivation to remove penalty ele-
Se 0.00020b
Si –c ments from copper concentrates at the mine site before shipping to
Sn –c custom smelters. One way to achieve this is to selectively leach
Te 0.00020b penalty elements from the copper concentrate. A number of leach
Zn –c
systems have been developed for the selective leaching of penalty
Sum of elements listed 0.0065
elements (see Table 4), however, published literature on these sys-
a
(As + Cd + Cr + Mn + P + Sb) maximum 0.0015%. tems tends to focus on the leaching behaviour of just one penalty
b
(Bi + Se + Te) maximum 0.0003%, of which (Se + Te) maximum 0.00030%. element from one type of mineral (e.g., the leaching of Sb from
c
(Co + Fe + Ni + Si + Sn + Zn) maximum 0.0020%.
d
The sulphur content shall be determined on a cast table.
tetrahedrite), without considering the behaviour of other penalty
elements which may be simultaneously leached from the concen-
trate. This paper reviews the four leach systems listed in Table 4. It
Te. These elements are highly insoluble in copper and conse- was an aim of the paper to encompass the leaching behaviour of as
quently even small amounts of these elements make copper cath- many penalty elements for which literature is available.
ode brittle (Fountain, 2013). Bismuth can be particularly
problematic during electrorefining since it largely dissolves in
the electrolyte (Schlesinger et al., 2011). Dissolved Bi can co- 2. Alkaline sulphide leaching
deposit with Cu onto the cathode if present in the electrolyte in
high enough concentrations (Wang, 2004). Expensive control mea- Alkaline sulphide leaching (ASL) is highly selective and for this
sures (e.g., bleeding of electrolyte followed by electrowinning) are reason has been the main leach system employed for the extrac-
often required to prevent accumulation of Bi in the electrolyte tion of As and Sb from copper concentrates. The behaviour of As
(Wang, 2004; Wang et al., 2011). Se and Te are generally of lesser and Sb in ASL depends on the mineral speciation of these elements
concern during electrorefining since typically only a small fraction in the concentrate. Sodium sulphide (Na2S) is known to dissolve As
(2%) of these elements report to the electrolyte (the majority when As occurs in the following mineral forms: enargite (Cu3AsS4),
reports to the anode slimes) (Schlesinger et al., 2011). The low tol- tennantite [Cu10(Fe,Zn)2As4S13], realgar (a-As2S2), orpiment
erance for Bi in copper cathode and the need to prevent its accu- (As2S3), and arsenic trioxide (As2O3) (Anderson et al., 2014; Baláž
mulation in the electrolyte during electrorefining is reflected by and Achimovičová, 2006; Delfini et al., 2003). Similarly, sodium
the heavy penalty imposed for this element (Fountain, 2013; sulphide is known to dissolve Sb when Sb occurs in the following
Larouche, 2001; Zanetell, 2007). Larouche (2001) points out that mineral forms: tetrahedrite [Cu10(Fe,Zn)2Sb4S13], stibnite (Sb2S3),
the NCM for Bi is typically an order of magnitude lower than the and jamesonite (Pb4FeSb6S14) (Baláž, 2000b; Baláž and
NCMs for As and Sb, and two orders of magnitude lower than the Achimovičová, 2006; Baláž et al., 1998). The chemical reactions
NCM for Pb. which take place between sodium sulphide and these As- and
An important class of penalty elements which is not shown in Sb-bearing minerals are presented in Table 5. It can be seen that
Table 1 is the naturally occurring radionuclides. Copper ore depos- As and Sb are both converted to sodium thio-anions. A number
its with associated uranium, such as the Olympic Dam Cu-U-Au-Ag of studies (Baláž, 2000b; Dayton, 1982; Edwards, 1985; Filippou
deposit, South Australia (Ehrig et al., 2012), contain 238U decay ser- et al., 2007) have reported that sodium sulphide does not leach
ies radionuclides. The International Atomic Energy Agency (IAEA) As when As occurs in the form of arsenopyrite (FeAsS). The distri-
publishes internationally recognised safety protocols for the han- bution of arsenic between arsenopyrite and soluble forms is
dling of radioactive materials (IAEA, 2012). Copper concentrates thought to place an upper limit on the extraction of As in practical
containing 238U decay series radionuclides in secular equilibrium ASL systems (Edwards, 1985). More problematic are cases where
are exempt from regulation if the activity concentrations of 238U the penalty elements do not occur as discrete minerals, but rather
and each of its 13 radioactive daughters are less than 1 Bq g1. If incorporated, at concentrations of hundreds or thousands of parts
on the other hand, the activity concentrations of the individual per million into the lattice of common sulphides (e.g., Bi within
radionuclides exceed this threshold value then costly control mea- bornite or chalcocite group phases; Cook et al., 2011).
sures may be needed during shipping for radiation protection. The Many investigators have highlighted that sodium sulphide is
radionuclides can cause additional handling issues at the site of the also an effective lixivant for the extraction of Hg, however only a
smelter. During smelting the radionuclides partition themselves few studies (Anderson, 2003; Baláž et al., 1998; Baláž and
between the various product streams (i.e. matte, slag, flue dust, Dutková, 2009) present data. Baláž and Dutková (2009) reported
and off-gas) and can become enriched within a particular stream. only minor extraction (<10%) of Hg from a tetrahedrite-rich copper
210
Pb and 210Po for instance, are known to substantially concen- concentrate from Rožňava, Slovakia, in their mechano-chemical
trate in flue dusts (BHP Billiton, 2009; Schreck, 1999; Weiss leaching process, which involves integrated milling and ASL of
et al., 1997), particularly when the flue dusts are recycled for the concentrate within the same step (Baláž, 2000b). They attribu-
D.J. Lane et al. / Minerals Engineering 98 (2016) 110–121 113
Table 5
Simplified chemical reactions which take place during ASL of copper concentrates.
ted the low extraction of Hg to electrochemical effects caused by new species of copper sulphide such as Cu1.5S (Awe and
interactions between the iron balls used for milling and the process Sandström, 2010; Curreli et al., 2009).
feed (Baláž and Dutková, 2009). Mercury was substantially A number of ASL technologies have been developed for the
extracted (>90%) from the concentrate when the same leaching treatment of industrial copper concentrates. Three of the most
process was applied to the concentrate but without milling established technologies are: the Sunshine process, the Equity pro-
(Baláž and Dutková, 2009). This result is consistent with a separate cess, and the Melt process. These technologies are reviewed below.
study by Anderson (2003), who reported 95% extraction of Hg after
12 h of ASL. According to Anderson (2003) the Hg in the copper ore 2.1. The Sunshine process
deposit at Rožňava, Slovakia is associated with the copper sulphide
mineral, tetrahedrite. A number of elements, including Hg, are The longest standing industrial application of ASL was at the
stable in the crystal structure of tetrahedrite (King, 2001). The gen- Sunshine Mine in Idaho, USA. The Sunshine process is based on
eral chemical formula for tetrahedrite-tennantite type minerals is patented technology by Holmes (1943). It was designed to leach
A10B2C4, where A = Cu or Ag, B = Fe, Zn, Mn, Cd, Cu, or Hg, and Sb from a tetrahedrite-rich copper concentrate containing approx-
C = As, Sb, Bi, or Te (Awe, 2010; Hobson et al., 2006). Mercury imately 19 wt% Sb so that the Sb content was reduced to below
can also occur separately to Cu in copper concentrates such as in 1 wt%. The leach solution consisted of: elemental sulphur; sodium
the minerals cinnabar and metacinnabar (HgS) (Anderson, 2003). hydroxide; sodium carbonate; and an alkaline-sulphide-rich elec-
According to Baláž et al. (1998), Hg is leached from cinnabar trolyte solution, which was recycled from a downstream elec-
according to Reaction 12 (see Table 5). The product of this reaction, trowinning circuit used to recover Sb from the leach solution.
Na2[HgS2], is a complex salt that requires a base such as sodium Elemental sulphur was used as a reagent since it was in ready sup-
hydroxide (NaOH) to prevent its precipitation (Baláž et al., 1998). ply from a downstream silver refinery. The sulphur reacts with
Sodium hydroxide is added to most practical ASL processes in sodium hydroxide to form sodium sulphide, sodium polysulphide
order to prevent the hydrolysis of sodium sulphide to sodium (Na2Sx, where x = 2–5), and sodium thiosulphate (Na2S2O3) accord-
hydrosulphide (NaHS), which is understood to inhibit the dissolu- ing to Reactions 13 and 14 (Anderson, 2012). Anderson and Krys
tion Sb (Anderson and Krys, 1993). (1993) reported results from an experimental investigation into
Anderson (2005) reported extractions for various metals after the influence of the initial concentrations of these species on the
leaching a range of As- and Sb-containing materials in an alkaline extraction of Sb in the Sunshine process. Increasing the concentra-
sulphide solution for 6 h at 105 °C. The leach media was prepared tion of sulphide from 75 to 150 g L1 enhanced both the rate and
by adding elemental sulphur and sodium hydroxide to water extent of leaching of Sb. Increasing the concentration of thiosul-
(100 g of S and 25 g of OH per litre). The added S reacts with phate from 0 to 100 g L1 also enhanced the rate and extent of
sodium hydroxide to form sodium sulphides (including Na2S) leaching of Sb. The rate of leaching of Sb decreased with increasing
and sodium thiosulphate (Na2S2O3) (Anderson et al., 1991). Extrac- polysulphide concentration. The total extent of leaching reached a
tions of Sb and As were >95% for all materials tested. Gold was par- maximum when polysulphide accounted for 20% of the initial sul-
tially extracted from all materials, including an enargite-rich phide content in the leach solution. Increasing the proportion of
copper concentrate (14% extraction). Anderson (2016) proposed polysulphide above this value caused substantial reductions in
that the leaching of Au is a result of polysulphide oxidation and the extent of leaching of Sb.
sulphide complexation. Extractions were negligible (<1%) for the
following metals: Ag, Co, Cu, Cd, Fe, Pb, Ni, and Zn. It has been 4S0 ðsÞ þ 6NaOHðaqÞ ! 2Na2 SðaqÞ þ Na2 S2 O3 ðaqÞ þ 3H2 OðlÞ ð13Þ
reported that ASL is effective for the extraction of Bi (Ruiz et al.,
2013) and Te (Anderson et al., 2014), however, no data has been ðx 1ÞS0 þ Na2 SðaqÞ ! Na2 Sx ðaqÞ; where x ¼ 2 5 ð14Þ
found for these two elements.
In most studies on the ASL of copper concentrates (e.g., 2.2. The Equity process
Anderson, 2003; Torres, 2011) Cu is more or less completely
retained (>99%) in the solid leach residue. Chalcopyrite (CuFeS2) Equity Silver Mines Ltd. developed their own ASL process in Bri-
has been shown to be inert in ASL systems (Awe and Sandström, tish Columbia, Canada, in order to leach Sb and As from a concen-
2010). The Cu associated with enargite, tennantite, and tetra- trate rich in Cu, Au, and Ag. The Equity process was initially
hedrite is predominately converted to covellite (CuS) and chal- operated to reduce the As and Sb contents in the concentrate from
cocite (Cu2S) (see Table 5), however, can also be transformed to around 7 wt% Sb and 4 wt% As to 0.3 wt% Sb and 1.5 wt% As
114 D.J. Lane et al. / Minerals Engineering 98 (2016) 110–121
(Dayton, 1982). In-house tests on the Equity process showed a is an order of magnitude lower than the retention times in the Sun-
non-linear correlation between the extent of leaching of Sb and shine process and Equity process. This can be attributed to superior
reagent consumption (Edwards, 1985). According to Edwards leaching kinetics in the Melt process. Reagent consumption in the
(1985), reductions in the residual content of Sb below 0.5 wt% Sunshine process is lower than that in the Melt process. The differ-
required exponentially increasing amounts of reagent. The targets ence in reagent requirements is likely due to recycle of sulphide-
for Sb and As extraction were later relaxed to 0.8 wt% Sb and 2 wt% rich electrolyte solution (produced in an electrowinning circuit
As in order to reduce reagent consumption (Edwards, 1985). The used to recover Sb) in the Sunshine process.
potential for extraction of As in the Equity process was largely lim- The Sunshine process and Equity process are no longer used in
ited by the amount of insoluble arsenopyrite in the concentrate industry. The Melt process was only ever operated at pilot scale.
feed (Edwards, 1985). Sodium hydrosulphide and sodium hydrox- Indophil Resources NL recently reported the use of an ASL process
ide were used as reagents in the Equity process. Sodium hydrosul- to selectively extract As from a copper-gold concentrate in a pre-
phide reacts with sodium hydroxide to form sodium sulphide feasibility study on the mining of copper and gold at the Tampakan
according to Reaction 15. Attempts to recycle sodium sulphide mine in the Philippines (Indophil Resources NL, http://www.
from a downstream arsenic precipitation circuit were unsuccessful indophil.com). Details of this process were not released.
(Edwards, 1985). Instead, sodium sulphide was oxidised and crys-
tallised to form high purity sodium sulphate (Na2SO4) (Edwards,
1985, 1991) which was sold to paper mills (Filippou et al., 2007).
3. Hypochlorite leaching
NaHSðaqÞ þ NaOHðaqÞ ! Na2 SðaqÞ þ H2 OðlÞ ð15Þ
Hypochlorite leaching is another leach system developed for the
selective extraction of As from copper concentrates (Curreli et al.,
2.3. The Melt process 2005; Mihajlovic et al., 2007; Viñals et al., 2003). In most studies
hypochlorite leaching is carried out at atmospheric pressure, at rel-
The Melt (mechano-chemical leaching of tetrahedrites) process atively low temperatures (20–60 °C), and at alkaline pH (pH 12–
was developed at pilot scale in Krompachy, Slovakia, in order to 12.5). Sodium hydroxide is generally added to the leach solution
leach Sb and As from a tetrahedrite-rich copper concentrate from to maintain alkaline conditions (Viñals et al., 2003).
the Maria Rožňava Mine. In the Melt process milling of concentrate The majority of research on hypochlorite leaching of copper
particles and ASL are integrated into one step (Baláž, 2000b). Dur- concentrates has focused on the extraction of As from enargite-
ing milling crystal structures become temporarily disordered and group minerals (Mihajlovic et al., 2007; Musu et al., 2009; Viñals
are theoretically more susceptible to leaching (Baláž and et al., 2003), or from enargite-rich copper concentrates (Curreli
Achimovičová, 2006). These effects are not always stable and can et al., 2005; Mitovski et al., 2015). There is general consensus in
have short relaxation times (<10 s) (Baláž and Achimovičová, the literature that sodium hypochlorite (NaClO) reacts with enar-
2006). The concept behind mechano-chemical leaching is that gite according to Reaction 16. X-ray diffraction (XRD) and scanning
leaching occurs immediately after milling, before the crystals have electron microscopy/energy dispersive spectrometry (SEM/EDS)
time to relax from their disordered state (Baláž and Achimovičová, analyses of enargite leach residues have confirmed the formation
2006). Experiments have shown mechano-chemical leaching to of insoluble tenorite (CuO) (Curreli et al., 2005; Mihajlovic et al.,
substantially improve the kinetics of Sb and As leaching from 2007; Musu et al., 2009). Laboratory-scale experiments (Viñals
tetrahedrite-tennantite group minerals (Baláž, 2000a). Maximum et al., 2003) have shown high conversions of enargite (>95%)
extraction of Sb and As is achieved within 30–40 min in the Melt within less than 1 h of leaching at reaction temperatures in the
process (Baláž, 2000a). range 40–60 °C. In these experiments the concentrations of
The operating parameters used in the Sunshine process, Equity hypochlorite and hydroxide were maintained at 0.13 M and
process, and Melt process are compared in Table 6. All three pro- 0.03 M, respectively (Viñals et al., 2003). According to Curreli
cesses operate at atmospheric pressure and close to the boiling et al. (2005) the optimum pH for the extraction of As from enargite
temperature of the slurry. The residence time in the Melt process is 12.5. The rate of extraction of As is reduced at lower values of pH
Table 6
Summary of operating parameters used in ASL technologies.
(Curreli et al., 2005). At higher values of pH, sodium hypochlorite (1) Sodium hypochlorite has relatively poor selectivity for As.
rapidly decomposes (Curreli et al., 2005). Copper sulphide minerals which do not contain As, particu-
larly covellite, react to a significant extent during hypochlo-
rite leaching (Filippou et al., 2007; Mihajlovic et al., 2007).
2Cu3 AsS4 ðsÞ þ 35NaClOðaqÞ þ 22NaOHðaqÞ (2) High additions of hypochlorite (typically 250–740 g ClO per
! 6CuOðsÞ þ 2Na3 AsO4 ðaqÞ þ 8Na2 SO4 ðaqÞ þ 35NaClðaqÞ kg of concentrate (Filippou et al., 2007)) are needed for effec-
tive extraction of As. This may partially be attributed to the
þ 11H2 OðlÞ ð16Þ poor selectivity of hypochlorite for As but also to reaction
Studies which address hypochlorite leaching of penalty ele- stoichiometry. Complete conversion of one mole of enargite
ments from minerals other than enargite are scarce. According to requires 17.5 mol of sodium hypochlorite (see Reaction 16).
Filippou et al. (2007), As associated with realgar, orpiment, tennan-
tite, and luzonite (Cu3AsS4) are readily dissolved during hypochlo- 4. Dilute sulphuric acid leaching with aluminium sulphate
rite leaching. It has also been reported that Te associated with gold
tellurides is extracted (Filippou et al., 2007) and that Sb is not Fluorine is selectively extracted from metal ore concentrates by
extracted to any appreciable extent during hypochlorite leaching leaching with sulphuric acid (H2SO4) in the presence of aluminium
of copper concentrates (Ruiz et al., 2013), however no published sulphate (Al2(SO4)3). Jomoto and Hughes (1995) present a general
data has been found to support these claims. Mihajlovic et al. equation for this leach system (Reaction 17). According to these
(2007) studied the selectivity of hypochlorite leaching by individ- two authors and to Torrisi (2001), two soluble species of alu-
ually leaching the following copper sulphide minerals in a solution minium fluoride are formed, AlF2+ and AlF+2, as well as several spe-
containing 0.3 M of NaClO and 5 g L1 of NaOH: enargite, realgar, cies of aluminium fluoride which are either insoluble or are only
covellite, chalcocite, and chalcopyrite. Analysis of the leach resi- sparingly soluble, including AlF3, AlF 2 3
4 , AlF5, and AlF6. Leaching is
dues indicated that 99% of the enargite, 97% of the realgar, 32% typically carried out at atmospheric pressure and at ambient to
of the covellite, 5% of the chalcocite, and 16% of the chalcopyrite slightly elevated temperatures (60 °C).
had reacted. This result implies poor selectivity of hypochlorite
3þ
for As-bearing minerals. mineral F þ Al $ mineral
When compared with ASL, hypochlorite leaching is typically n
þ ðAlFÞ ; where n is an integer ð17Þ
much faster. Rates of extraction of As in hypochlorite leaching pro-
cesses are generally an order of magnitude higher than rates of The role of sulphuric acid is to control the pH of the leach solu-
extraction of As in ASL processes. Nevertheless, hypochlorite leach- tion. The optimum pH for the extraction of F is thought to be some-
ing has been largely limited to laboratory-scale studies and unlike where between pH 3.0 and 4.3 (Jomoto and Hughes, 1995; Torrisi,
ASL, has not been employed on an industrial scale. Two key issues 2001). Below this range, fluoride ions react with hydrogen ions to
have been identified with the use of hypochlorite leaching for the form undissociated hydrogen fluoride, which reduces the availabil-
treatment of industrial copper concentrates: ity of fluoride ions for reaction with Al3+ and may slow the rate of
Fig. 1. Distribution of F between different mineral forms before and after leaching a zinc concentrate with dilute sulphuric acid and aluminium sulphate. All data from Torrisi
(2001).
116 D.J. Lane et al. / Minerals Engineering 98 (2016) 110–121
Copper precipitation leaching of Cu-Fe-sulphides involves the the reaction temperature and oxygen partial pressure significantly
exchange of Fe and S in the Cu-Fe-sulphide minerals for copper reduced the extraction of Zn. The influence of mineralogical com-
ions dissolved in the leach solution. During this exchange dissolved position on the extraction of Zn was studied by leaching concen-
copper ions are precipitated and Fe and some S are dissolved. The trate mixtures with varying proportions of sphalerite (0–100%),
exchange reactions are referred to as ‘‘metathesis reactions” and chalcopyrite (0–75%), pyrite (0–75%), and galena (0–75%). Pyrite
occur in both non-oxidising and reducing environments. Under additions up to 10% improved selectivity by increasing the extrac-
non-oxidising conditions bornite is converted to covellite and to tion of zinc and reducing the extraction of copper. The reduced
chalcocite according to Reaction 19 (Abed, 1999). Chalcopyrite is extraction of copper was attributed to the formation of ferrous sul-
converted to covellite according to Reaction 20 (Abed, 1999). The phate, which retards the dissolution of chalcopyrite. Pyrite addi-
formed covellite may further react to form digenite (Cu1.8S) accord- tions above 10% had the opposite effect on selectivity. The
ing to Reaction 21 (Abed, 1999). Similar reactions describe the con- increased dissolution of copper at pyrite additions above 10%
version of chalcopyrite to Fe- and S-depleted copper sulphides was attributed to the formation of high levels of free acid. The
under reducing conditions (Dreisinger and Abed, 2002; Hiskey addition of galena inhibited the extraction of Zn. According to
and Wadsworth, 1975). Chemical metathesis results in enrichment Harvey and Yen (1998), galena competes with sphalerite for oxy-
of copper in the concentrate by rejection of Fe and S from copper gen, and can therefore reduce the extent of oxidation of sphalerite
sulphide minerals as well as recovery of dissolved Cu (generated to soluble zinc sulphate. The formation of insoluble, zinc-bearing
during POX leaching) from the leach solution. plumbojarosites is also thought to account for the reduced extrac-
tion of zinc (Harvey and Yen, 1998).
Cu5 FeS4 ðsÞ þ CuSO4 ðaqÞ ! 2Cu2 SðsÞ þ 2CuSðsÞ þ FeSO4 ðaqÞ ð19Þ Anode slimes produced during the electrorefining of copper
often contain commercial quantities of Cu, Au, Ag, Se, and Te
(Cooper, 1990), and are sometimes subject to POX leaching in sul-
CuFeS2 ðsÞ þ CuSO4 ðaqÞ ! 2CuSðsÞ þ FeSO4 ðaqÞ ð20Þ phuric acid media in order to recover the Cu and Te. Former mining
company, Noranda Mines Ltd., claimed virtually complete extrac-
6CuSðsÞ þ 3CuSO4 ðaqÞ þ 4H2 OðlÞ tion of copper and at least 75% extraction of Te from anode slimes
in their POX process (Morrison, 1977). Newmont Mining also
! 5Cu1:8 SðsÞ þ 4H2 SO4 ðaqÞ ð21Þ
claimed substantial extraction of Cu, however, claimed a lower
POX/copper precipitation leaching processes tend to be opti- extraction for Te (30%) in their POX process (Yannopoulos and
mised for the enrichment of copper rather than for the deportment Borham, 1978).
of penalty elements. Many studies have focused on the behaviour There are two patented processes which deal specifically with
of Cu in both POX leaching (Dreisinger, 2006; Hackl et al., 1995; the deportment of penalty elements in combined POX/copper pre-
McDonald and Muir, 2007a, 2007b) and in copper precipitation cipitation leaching processes. One of these processes (McKay and
leaching (Bartlett, 1992; Dreisinger and Abed, 2002; Fuentes Parker, 1977) was patented by former mining company Cominco
et al., 2009a; Sequeira et al., 2008). Much less research has been Ltd. and the other (Dunn et al., 2014) by metallurgy consulting
done to understand the leaching behaviour of penalty elements company Orway Minerals Consultants (OMC). These two processes
in these processes. (hereafter referred to as the ‘‘Cominco process” and the ‘‘OMC pro-
Fuentes et al. (2009b) studied the influence of leaching temper- cess”) are reviewed below.
ature and concentration of Cu2+ ions on the extraction of ten pen-
alty elements (As, Bi, Cd, Hg, Mo, Pb, Sb, Te, Tl, Zn) during copper 5.1. The Cominco process
precipitation leaching of copper concentrates produced at the
Chuquicamata mine in Chile. Possible host sites for the penalty ele- The Cominco process was developed to separate Co, Ni, Zn, and
ments were enargite, sphalerite (ZnS), galena (PbS), and molybden- Pb from chalcopyrite-rich copper concentrates (McKay and Parker,
ite (MoS2). These minerals were identified in XRD, reflected-light 1977). Cobalt, Ni, and Zn are all dissolved in the Cominco process.
microscopy, and SEM/EDS analyses of the concentrate samples. Lead is not dissolved but is converted to a form (lead sulphate)
The following elements were substantially extracted (80%) at a which facilitates its separation from Cu by flotation. Leaching is
reaction temperature of 225 °C: Bi, Cd, Tl, and Zn. Extractions were carried out in two consecutive stages: POX leaching and then cop-
moderate (40–70%) for Pb and Te and were the lowest (20–40%) for per precipitation leaching. The products (both solid and liquid)
As, Hg, Mo, and Sb. Decreasing the reaction temperature signifi- from the copper precipitation leach are subject to differential flota-
cantly reduced extractions for all penalty elements over the range tion in order to separate the formed lead sulphate from copper
150–225 °C. The concentration of Cu2+ ions had negligible effect on sulphides.
the extraction of penalty elements over the range 1–85 g L1. A schematic of the Cominco process is shown in Fig. 2. Impure
Viñals et al. (2004) studied the dissolution of pure sphalerite in copper concentrate is fed to the POX reactor with sulphuric acid,
acidic solutions containing different concentrations of copper sul- copper sulphate (CuSO4), and an oxygen-bearing gas. Lead con-
phate. The concentration of soluble Cu2+ ions had minimal impact tained in galena reacts to form insoluble lead sulphate, presumably
on the rate of dissolution of Zn over the range 1–10 g L1. This find- according to Reaction 22 (Harvey and Yen, 1998). Cobalt, Ni, and Zn
ing is consistent with results reported by Fuentes et al. (2009b). which are present as sulphides are primarily converted to soluble
SEM/EDS analyses of partially reacted sphalerite particles revealed sulphates. Covellite, chalcocite, and bornite dissolve, forming sol-
the formation of an outer layer of copper-sulphide around a shrink- uble copper sulphate. Chalcopyrite dissolves only to a minor
ing core of sphalerite. Based on these results Viñals et al. (2004) extent. The concentration of free sulphuric acid is carefully con-
proposed that the rate of sphalerite dissolution during copper pre- trolled (10–70 g L1) in order to minimise the dissolution of chal-
cipitation leaching is controlled by diffusion of Cu2+ and Zn2+ ions copyrite. It is claimed that no more than 20% of the total Cu
through the layer of solid copper sulphide. reacts during POX leaching (McKay and Parker, 1977). A small por-
Harvey and Yen (1998) studied the extraction of zinc from arti- tion of the Cu, Zn, Fe, and Pb in the concentrate react to form insol-
ficial concentrate samples during POX leaching in sulphuric acid uble jarosites.
media. A high extraction (>90%) of Zn was reported from pure
1
sphalerite after 240 min of leaching at a reaction temperature of PbSðsÞ þ H2 SO4 ðaqÞ þ O2 ! PbSO4 ðsÞ þ S0 ðsÞ þ H2 OðlÞ ð22Þ
2
210 °C and at an oxygen partial pressure of 689 kPa. Lowering
118 D.J. Lane et al. / Minerals Engineering 98 (2016) 110–121
The products from the POX leach are fed directly to the copper 5.2. The OMC process
precipitation leach. Copper precipitation leaching is carried out at
a higher temperature than used in the POX leach, in an oxygen- The OMC process was developed for the removal of radionu-
free gas atmosphere, and at autogenous pressure. Insoluble jarosite clides from the 238U decay series, specifically 238U, 230Th, 226Ra,
210
compounds formed in the POX leach decompose. The lead and cop- Pb, and 210Po, from copper sulphide concentrates which contain
per associated with jarosites are converted to insoluble lead sul- export limiting levels of radioactivity. According to the inventors
phate and insoluble copper sulphides. Dissolved copper sulphate (Dunn et al., 2014), Co, Ni, and Zn are also removed in the OMC
reacts with part of the residual chalcopyrite to form insoluble cop- process, however, no claims are made regarding the deportment
per sulphides and aqueous ferrous sulphate (see Reactions 20 and of these elements. A simplified schematic of the OMC process is
21). These reactions lead to rejection of Fe from chalcopyrite and shown in Fig. 3. The impure copper concentrate is first fed to the
therefore result in an upgrade in the copper content of the concen- copper precipitation leach rather than to the POX leach. The pro-
trate. Virtually all of the copper is recovered (>99%) in the leach duct from the copper sulphate leach is separated by physical pro-
residue. The Co, Ni, and Zn remain dissolved in the leach medium. cesses (including, but not limited to sedimentation and filtration)
It is claimed that 85–95% of the total Co and Ni are extracted in into a predominately liquid phase stream and a concentrated
the Cominco process. No claims are made regarding the extraction slurry which contains the upgraded copper concentrate. An
of Zn. unspecified portion of the upgraded copper concentrate is washed
D.J. Lane et al. / Minerals Engineering 98 (2016) 110–121 119
external factors, such as: charge rates and restrictions on penalty Curreli, L., Ghiani, M., Surracco, M., Orrù, G., 2005. Beneficiation of a gold bearing
enargite ore by flotation and As leaching with Na-hypochlorite. Miner. Eng. 18
elements; the availability and price of reagents; and the economic
(8), 849–854.
potential of recovering valuable elements from the leachate. Dayton, S., 1982. Equity Silver on line with leach plant. Eng. Min. J. 183 (1),
78–83.
Delfini, M., Ferrini, M., Manni, A., Massacci, P., Piga, L., 2003. Arsenic leaching by
Acknowledgements Na2S to decontaminate tailings coming from colemanite processing. Miner. Eng.
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Dreisinger, D., 2006. Copper leaching from primary sulfides: options for biological
The authors acknowledge support from the Australian Research and chemical extraction of copper. Hydrometallurgy 83 (1), 10–20.
Council Hub for Australian Copper Uranium (project number: Dreisinger, D., Abed, N., 2002. A fundamental study of the reductive leaching of
chalcopyrite using metallic iron. Part I: Kinetic analysis. Hydrometallurgy 66
IH130200033), BHP Billiton Olympic Dam, OZ Minerals, and the (1), 37–57.
South Australian Department of State Development (DSD). Dunn, G.M., Bartsch, P.J., 2008. Integrated Hydrometallurgical and
Pyrometallurgical Processing of Base-Metal Sulphides. US Patent 2008/
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