|
2.1
INTRODUCTION
Copper (Cu) is an essential metal that has had a relevant importance since early human
civilization going backwards as long as 6 000-7 000 years ago (Themelis, 1994; Hong et al.,
1996; Radetzki, 2009). Initially, it was used for production of primitive tools, vessels and
coins due to its easy stretching and possibility of shape formation. Subsequent discovery of
properties such as heat and electric conductivity caused that copper has gained an even more
prominent value. Nowadays, copper is considered as one of the most widely produced metals,
indispensable for humans and thus essential for the global market. It is used for a variety of
applications such as power transmission, building, electronic and related industries (Radetzki,
2009). Expansion of the copper demand has increased its mining and production. In 2012, the
world copper mine production reached 16.7 million tons. Smelter and refinery production
were maintained at approximate levels of 16.7 and 20.1 million tons, including primary and
secondary production (ICSG, 2013). Due to the fact that copper reserves are considered to be
non-renewable, undiscovered copper resources receive important attention in mineral supply
assessments (Svedberg & Tilton, 2006).
On the other hand, industrial activity related to mining and processing of copper is a reason of
growing environmental concern. Considering this industrial activity, it should be noticed that
apart from advantages arising from effective production, this industrial sector produces huge
amounts of metallurgical wastes (slags) that are classified as “potentially hazardous” (Ettler et
al., 2009; Kierczak et al., 2013). Pyrometallurgical processes extract metals from ores,
however, depending on the process efficiency some residual amounts of the metals still
remain in the waste materials.
Metallurgical wastes are mostly dumped close to the centre of industrial activity, but in case
of inappropriate isolation of the disposal site, it may entail serious environmental
consequences (Gee et al., 1997; Manz & Castro, 1997; Sobanska et al., 2000; Parsons et al.,
2001; Lottermoser, 2002; Ettler et al., 2003; Piatak et al., 2004; Reuter et al., 2004; Vdović et
al., 2006; Ettler et al., 2009; Maweja et al., 2010; Vítková et al., 2010; Piatak & Seal, 2010;
Yang et al., 2010; Kierczak et al., 2013; Ettler & Johan, 2014). Biogeochemical weathering
and physical erosion of non-protected wastes may mobilize metallic elements. Then, local
migration of pollutants and further transfer to large distances make the remediation of
polluted areas difficult or in some cases even impossible. That is why appropriate isolation of
wastes as well as frequent environmental monitoring of disposal sites are necessary to prevent
the deterioration of environmental quality.
The distribution of metallic elements in various phases occurring in metallurgical wastes
constitutes an important factor governing mobility of these elements during weathering. The
presence of some metal-bearing phases showing relatively high susceptibility to alteration
could increase the potential risk of metal mobilization from slags, therefore not only the total
CHAPTER 2: COPPER METALLURGICLA SLAGS- CURRENT KNOWLEDGE AND FATE:
A REVIEW
13
metal concentration, but also the solid speciation (phase composition) should be considered in
order to ensure safe disposal (Ettler et al., 2002; Ettler et al., 2005; Ettler et al., 2009; Piatak
& Seal, 2010; Kierczak et al., 2013). Another important factor governing stability of disposed
slag wastes is the indigenous microorganisms present at the dumping site (Willscher &
Bosecker, 2003). The activity of these microbes may contribute to the alteration of slags and
mobilization/immobilization of metallic elements. Therefore, this aspect of bioweathering is
especially interesting and important for investigations of the alteration of metallurgical slags
(Yin et al., 2014, van Hullebusch et al., 2015).
According to current guidelines of waste management, disposal of metallurgical slags is
considered as the least favourable method (Lottermoser, 2011). From environmental point of
view, pyrometallurgical slags are undesirable materials. Therefore, recent attention given to
sustainable waste management has focused on methods allowing reuse of metallurgical
wastes instead of their disposal. Reuse of slags as additives for building and construction
materials, concretes and abrasive materials has been recently applied (e.g. Shi & Qian, 2000;
Gorai et al., 2003; Al-Jabri et al., 2006; Moura et al., 2007; Shi et al., 2008; Al-Jabri et al.,
2009; Al-Jabri et al., 2011; Najimi et al., 2011). However, application of these materials for
engineering purposes can be justified only in the case if prior analysis of the materials proves
their inertness. Moreover, (bio)recovery of metals remaining in the wastes is a promising
technology for the future (e.g. Banza et al., 2002; Altundoǧan et al., 2004; Baghalha et al.,
2007; Deng & Ling, 2007; Yang et al., 2010; Vestola et al., 2010; Tshiongo et al., 2010;
Kaksonen et al., 2011; Ahmed et al., 2012; Nadirov et al., 2013; Muravyov and Fomchenko,
2013). Besides advantages derived from the recovery of valuable compounds, it is also
important that extraction of metals decreases the hazardousness of the metallurgical wastes
and consequently allows further reuse or safe disposal. Undoubtedly, (bio)recovery is
currently the most desired solution to reuse these kinds of materials. However, it requires
advanced development of the process as well as investment outlays. Therefore, metal
recovery technologies and adaptation of processing conditions ensuring high recovery
efficiencies receive considerable attention.
The main objective of this review paper is to present the current knowledge about
metallurgical slags generated during processing of copper including their chemical and phase
composition, environmental risk and fate. Special attention is given to gathering information
about environmental stability and prediction of the environmental hazard related with these
wastes. Additionally, this review paper presents achievements in the field of metal recovery
from these waste materials, including comparison of various (bio)leaching and (bio)recovery
methods and their efficiency.
CHAPTER 2: COPPER METALLURGICLA SLAGS- CURRENT KNOWLEDGE AND FATE:
A REVIEW
14
Do'stlaringiz bilan baham: |
