Table Of ContentAL-FARABI KAZAKH NATIONAL UNIVERSITY
R. K. Nadirov
RECENT ADVANCES IN LEACHING
COPPER SMELTING SLAG
Monograph
Almaty
«Kazakh university»
2018
UDC 669.0 (075.8)
LBC 34.2 я 73
N 13
Recommended for publication by the Academic Council
(Protocol No.5, 29.12.2017) and the Editorial Committee of al-Farabi KazNU
(Protocol No.4, 29.12.2017)
Reviewers:
Doctor of Technical Sciences, professor M. S. Satayev
Doctor of Chemical Sciences V. N. Statsyuk
Doctor of Chemical Sciences G. A. Seilkhanova
Nadirov R.K.
N 13 Recent advances in leaching copper smelting slag:
monograph / R. K. Nadirov. – Almaty: Kazakh university, 2018.
‒ 118 p.
ISBN 978-601-04-3280-2
Copper smelting slag is recognized as an important raw material for
valuable metals production. A contribution to documenting current and future
best practice in copper smelting slag processing by leaching seems timely. The
focus of the monograph is on advances in the current situation in the mentioned
field. Sufficient coverage is given to the chemistry and engineering aspects of
copper smelting slag leaching.
The book may be of interest to specialists working in hydrometallurgy,
teachers and students of chemical and metallurgical faculties.
UDC 669.0 (075.8)
LBC 34.2 я 73
© Nadirov R.K., 2018
ISBN 978-601-04-3280-2 © Al-Farabi KazNU, 2018
2
CONTENT
INTRODUCTION .............................................................................. 5
1. GENERAL INFORMATION ABOUT COPPER
SMELTER SLAG ............................................................................... 8
1.1. Smelting of copper concentrate. Copper smelter slag formation ... 8
1.2. Composition of copper smelter slag .............................................. 9
1.3. Physical and mechanical properties ............................................... 13
1.4. Ways of copper smelter slag processing ........................................ 14
1.4.1. Pyrometallurgical copper smelter slag processing .............. 14
1.4.2. Flotation enrichment of copper slags .................................. 15
1.4.3. Use of slag for the production of building materials ........... 17
2. GENERAL PRINCIPLES OF LEACHING
COPPER SMELTER SLAG. MODELS AND
MECHANISM OF LEACHING PROCESSES ............................... 19
2.1. Methods of leaching smelter slag .................................................. 19
2.2. Leaching models ............................................................................ 20
2.2.1. Shrinking core model (SCM) .............................................. 20
2.2.2. Variable activation energy model. ...................................... 21
2.2.3.Thermodynamic approach ................................................... 22
2.2.4. Empirical models. ............................................................... 24
2.3. Mechanism of leaching reactions .................................................. 24
2.3.1. General issues ..................................................................... 24
2.3.2. Electrochemical mechanism of dissolution ........................ 25
2.3.3. Mechanism of silicates dissolution ..................................... 26
3. AGITATIONAL LEACHING OF SLAGS WITHOUT
PRELIMINARY THERMAL PROCESSING ................................. 28
3.1. Leaching with sulfuric acid ........................................................... 28
3.1.1. Use of sulfuric acid without additives. ................................ 28
3.1.2. Use of sulfuric acid together with hydrogen peroxide ........ 36
3.1.3. Use of sulfuric acid in conjunction with sodium chlorate ... 41
3.1.4. Use of sulfuric acid in conjunction with
potassium dichromate ................................................................... 44
3.1.5. Use of sulfuric acid together with iron (III) sulfate ............. 46
3.2. Ammonia-ammonium leaching ..................................................... 48
3.3. Leaching by using organic acids .................................................... 56
3.3.1. Use of organic acids for leaching of slags of
non-ferrous metallurgy ................................................................. 56
3
3.3.2. Use of organic acids for leaching copper
slag of Balkhash copper plant ....................................................... 57
4. ELECTROCHEMICAL LEACHING OF THE SLAG .............. 60
4.1. General issues ................................................................................ 60
4.2. Slag leaching by electrochemical activation
of sulfuric acid solution ........................................................................ 61
4.2.1. Electrochemical activation of sulfuric acid solution ........... 61
4.2.2. Electrochemical leaching of slag in
sulfuric acid solution ..................................................................... 63
4.3. Electrochemical chlorination of slag ............................................. 64
4.4. Application of the internal electrolysis for slag leaching ............... 69
5. LEACHING WITH PRELIMINARY ROASTING .................... 72
5.1. Roasting with ammonium chloride ................................................ 72
5.2. Roasting with sulfuric acid ............................................................ 81
6. BACTERIAL LEACHING ............................................................ 87
6.1. Use of microorganisms for leaching copper slag ........................... 88
6.2. Application of bioleaching for processing copper
smelter slag of Balkhash copper plant .................................................. 89
7. PRESSURE OXIDATIVE LEACHING ...................................... 96
7.1. General information on the pressure oxidative leaching ................ 96
7.2. Pressure oxidative leaching of the slag .......................................... 96
7.3. Pressure oxidative leaching of the slag
from Balkhash copper plant ................................................................. 98
CONCLUSIONS ................................................................................. 102
REFERENCES ................................................................................... 106
4
INTRODUCTION
About three-quarters of copper are produced by pyrometallurgical
methods. Application of these methods leads to the generation of so-
called copper smelter slag as a byproduct of pyrometallurgical copper
production. The production of each ton of copper is accompanied by
the formation of about 2.2 -3.0 tons of slag [1-3]. Annually about 50
million tons of copper are produced by pyrometallurgical methods in
the world; thus, the annual increase in the amount of accumulated
copper smelter slag is more than 120 million tons or more than 40
million cubic meters. This amount of slag contains millions of tons of
toxic or potentially toxic elements, such as arsenic, lead, copper, zinc.
Copper smelter slag can be considered in two aspects. First, it is a
potential source of environmental pollution, due to the inevitable
dissolution of toxic components of slag, primarily arsenic and lead.
Slag, being in open space, is exposed to various bio-hydro-climatic
conditions and over time undergo weathering processes leading to
release metallic elements. Also, the formation of fine particles of slag
takes place. This circumstance leads to pollution of ecosystems, such
as soil, as well as surface and groundwater [4-6]. Unfortunately, this
aspect is not given due attention, and the slag mountains near the non-
ferrous metallurgy enterprises represent a serious problem at present
[7-10]. In this connection, the requirements for the disposal of
metallurgical wastes are tightened all over the world.
On the other hand, copper smelter slag can be considered as a
valuable raw material resource for the production of non-ferrous
metals. Depending on the melting conditions of copper concentrates,
the following content of valuable metals in the copper smelter slag is
observed, wt. %: Cu ~ 0.5-2, Zn ~ 2-5, Pb 0.2 ~ 1. It can be noted that
the content of these metals in slags is comparable to their content in
ores, and often exceeds this content. Gold and silver are also present
in the copper slag. Also, about 40% of the total mass of the slag is iron.
Finally, silicon dioxide, which is about one-fifth of the slag, is an
important mineral raw material. Thus, the processing of copper slag
can solve two important problems. First, the negative impact of slag
on the environment will decrease, and the land previously used for slag
5
disposal will be freed. And secondly, the raw material base of the
number of non-ferrous and precious metals, as well as iron and silicon
dioxide (to a lesser extent) will expand.
However, there is a big problem that greatly hinders the extraction
of these metals from the copper slag. This problem is related to the
mineralogical composition of the slag. The slag matrix consists of
fayalite and silicon dioxide, into which the compounds (mainly
sulphide) of valuable metals are embedded. Until now, there are no
cost-effective technologies for the extraction of non-ferrous and
precious metals from copper slag.
There are three approaches to processing slags with the extraction
of valuable components: (i) flotation enrichment, (ii)
pyrometallurgical processing, and (iii) hydrometallurgical processing.
Pyrometallurgical slag processing is mainly carried out in electric
furnaces at temperatures of 1350 ‒ 1450 °С. At the same time, an
acceptable separation of copper and zinc from the slag is achieved.
However, such shortcomings as high power consumption, high capital
costs, and low environmental friendliness, do not allow
pyrometallurgical methods to be used for the processing of poor
copper slags on an industrial scale.
The most common method of slag processing is flotation
enrichment. The method consists in grinding the slag to the required
size, with further flotation in several stages. Flotation enrichment of
copper smelter slag is a well-studied process and is described in some
scientific papers. This method is implemented on an industrial scale in
some countries around the world, including China, Russia,
Kazakhstan, and others. In particular, flotation enrichment of copper
smelter slag is used at the Balkhash concentrator (Central
Kazakhstan). Over more than 70 years of operation of the Balkhash
copper smelter, more than 31 million tons of copper slag have been
accumulated. In recent years, more than 500 thousand tons of slag are
produced annually. This slag is subjected to grinding and flotation
enrichment to produce a copper concentrate with a copper content of
about 12-15 %, copper recovery to the concentrate is about 50 – 60 %.
Zinc from slag is practically not extracted. Tailings of flotation
enrichment are not used. Meanwhile, shredded enrichment tails
represent a much greater danger to the environment than the original
slag, due to the reduction in particle size.
6
The use of tailings in the construction and road industries is
difficult due to the presence of toxic components, primarily lead and
arsenic.
Hydrometallurgical methods are the most promising for
processing copper smelter slags. There is a significant number of
scientific papers on the hydrometallurgical processing of copper slag
in well-known peer-reviewed journals. Leading groups now include
scholars from China, the United States, Australia, and some other
countries. As a leaching agent, aqueous solutions of acids (sulfuric,
hydrochloric, nitric, acetic, etc.) and ammonium salts are used. To
intensify the leaching process, oxidants (ferric sulfate, sodium
chlorate, hydrogen peroxide, oxygen, iron (III) chloride, potassium
dichromate, etc.) are exploited.
In this monograph, the author summarized the latest achievements
in the leaching copper slag, including the results of his research on the
leaching of the slag of the Balkhash copper smelter.
For the convenience of perception, the book is divided into seven
chapters. The first chapter provides general information on the copper
smelter slag, the ways of its formation, properties, as well as the
methods of slag processing. The second chapter is devoted to the
principles underlying the leaching of slag. Chapters 3-7 are directly
devoted to the leaching of copper slag. Chapter 3 deals with slag leach
processes without preliminary roasting of the starting material.
Chapter 4 is devoted to the application of electrochemical methods for
leaching slag. The fifth chapter deals with the leaching of copper slag,
previously subjected to roasting with chemical agents. Biological
leaching, as well as pressure oxidative leaching of copper smelter slag,
are discussed in Chapters 6 and 7, respectively.
It is assumed that this monograph will help accelerate the
development of new efficient technologies for hydrometallurgical
processing of copper slag.
The book may be of interest to specialists working in
hydrometallurgy, teachers and students of chemical and metallurgical
faculties.
7
1. GENERAL INFORMATION ABOUT
COPPER SMELTER SLAG
1.1. Smelting of copper concentrate.
Copper smelter slag formation
The pyrometallurgical process for copper production includes
several processing steps: (i) obtaining copper concentrate (copper ore
enrichment), (ii) melting the concentrate to produce copper matte, (iii)
converting copper matte to blister copper, and (iv) blasting refining of
blister copper with obtaining anodic copper, (v) electrolytic refining
of blister copper to produce cathode copper (99.5-99.9% Cu).
Target components of commercial copper concentrate include, in
the majority, sulphide copper minerals such as chalcopyrite (CuFeS ),
2
bornite (Cu FeS ), and chalcocite (Cu S). In addition, concentrates
5 4 2
contain components such as iron sulphides (FeS, FeS , etc.), silicon
2
dioxide (SiO ), zinc sulphide (ZnS), calcium and magnesium
2
carbonates (CaCO , MgCO ), aluminium oxide (Al O ), and some
3 3 2 3
other components.
Smelting of copper concentrates carried out in special
metallurgical units (furnaces), in the presence of oxygen (air). Under
these conditions, the oxidation of sulphur and iron present in the
concentrate takes place with the formation of Cu-rich molten matte:
2CuFeS + 3.25O Cu S×0.5FeS +1.5FeO + 2.5SO (1.1)
2 2 2 2
The addition of siliceous flux (SiO ) to the charge allows to bind
2
a part of iron in the form of fayalite (2FeO×SiO , or Fe SiO ):
2 2 4
2FeO + SiO 2FeO×SiO (1.2)
2 2
To reduce the viscosity of the melt, the oxide fluxes (e.g. CaO,
CaCO ) are added to the charge. As a result of melting, two liquid
3
products are formed in a furnace: Cu-rich molten matte and copper
smelter slag. The matte is a melt of copper and iron sulphides. Slags
8
of copper smelting are rich in both iron and silicon and are a melt of
ferrosilicates with a small admixture of other oxides. The basis of
these slags is the FeO-SiO binary system.
2
Due to the segregation process (difference in densities), these
products are divided: matte as heavier, is located from below, and slag,
as more light, is located, respectively, from above. The process of
melting copper concentrate to produce copper matte, copper slag, as
well as sulphur dioxide, is presented in Fig. 1.1.
Fig. 1.1 ‒ Flowsheet of smelting copper concentrate
The following furnaces are used as metallurgical units for melting
copper concentrates: (i) reflecting furnace, (ii) autogenous melting
furnace (Vanyukov furnace), (iii) electric furnace, etc. The choice of
the furnace is determined by the characteristics of the particular
concentrate being processed.
1.2. Composition of copper smelter slag
Copper slags are characterised by a complex chemical and
mineralogical composition, depending on the composition of
concentrates, fluxes, and also the technological cycle of their
producing [11-18].
The paper [19] contains information on the chemical composition
of the copper slag obtained from the slag of some plants in Russia
(RUS), Kazakhstan (KZ) and Uzbekistan (UZ) (Table 1.1).
9
Table 1.1
Chemical composition of copper smelter slag of
some copper smelting plants [19]
Name of copper CaO+
plant Cu Zn Pb Fe S SiO2 Al2O3 MgO
Sredneuralsk
0.64 4.63 - 32.5 1.57 33.9 6.6 5.0
(RUS)
Krasnouralsk
0.43 3.0 - 34.0 - 34.0 10.0 7.0
(RUS)
Dzhezgazgan
0.55 - 0.3 18.8 - 53.2 8.5 19.6
(KZ)
Karabash
0.3 2.5 - 34.0 1.5 33.0 8.0 7.1
(RUS)
Almalyk (UZ) 0.6 0.46 0.2 33.0 1.3 34.0 7.4 5.0
Karsakpai (KZ) 0.47 1.2 0.59 20.0 - 48.1 14.5 13.0
Kirovograd
0.33 3.1 - 30.0 1.0 - - -
(RUS)
Balkhash (KZ) 0.4 0.53 0.06 22.0 0.28 40.0 10.0 -
Mednogorsk
0.25 0.35 0.04 32.0 1.0 37.0 - 7.0
(RUS)
Irtysh (KZ) 0.5 6.6 0.8 32.0 - 31.5 4.5 4.5
Differences in the chemical composition of the copper smelter slag
are due to the following factors: (i) the composition of copper
concentrates, (ii) the composition of the charge, (iii) the characteristics
of the melting unit (furnace), and (iv) the technological mode of the
smelting process [20-27]. The content of alkali metals (not listed in
Table 1.1) may also differ in the slag, depending on their content in
the starting material [28]. At a low efficiency of the firing step
preceding the melting of the material, the slag contains a relatively
high amount of sulphur [29]. In addition, the long-term presence of
slag in contact with the environment also affects the composition of
copper slags, due to chemical and physical processes involving slag
components [30].
There are two types of phases in slag: the primary phase formed
as a result of the melting of copper concentrate in the furnace; and a
secondary phase formed as a result of the environment impact
(weathering).
Fayalite and silicate glass are the main primary phases of slag. Pure
crystals of fayalite (Fe SiO ) correspond to the content of iron (II) oxide
2 4
10
