Environmental Engineering Reference
In-Depth Information
metal production in general is a complex process comprised of a series of sequential
operations aimed at the separation of the metal fraction from the mined ore. The
first step is the separation of the desired principal mineral from the native one- in
the case of copper, this is chalcopyrite. Here, at this first stage some 99.5 % of the
material processed becomes waste mineral almost immediately. Second, the sepa-
rated concentrate then is subjected to selective refining. For copper, iron sulfide is
partially oxidized to produce a slag phase and a waste gas stream bearing sulfur di-
oxide. The melt (referred to as a matte), is then sulfur-oxidized to copper metal. The
waste gas from further oxidation contains additional sulfur dioxide together with
oxides from less noble metals known as fume. Finally, the impure copper is purified
in an electro-winning process and separated from more noble metals contained in
the mineral including precious metals such as silver and gold.
The local environmental damage of smelting has affected many parts of the
world (Chapter 2 mentioned some of the earliest cases in Japan of such gross pol-
lution from sulfur dioxide at the Ashio mine) and emissions include the minor toxic
elements arsenic, mercury, selenium and tellurium. The overall resource balance
from a single copper smelter in a year producing 20 million t can be summarized
as follows:
• discarded minerals: 40 billion t;
• sulfur, 20 million t;
• iron oxide, 20 million t;
• smaller amounts of other metals;
• electricity and fuel.
Considering such figures shows that recycling of metals should be seriously consid-
ered both to preserve limited resources, and to minimize emissions of the hazardous
elements which accompany the refining process. In contrast to the large impact of
mining and refining, recycling these metals has the advantage of avoiding mining
operations and also avoiding the concentration of potentially undesirable elements
left on the surface of the earth. Recycling does, however have the challenge of how
to obtain the raw materials for recycling and the potentially high costs associated
with collection of the materials to be recycled and separation from other waste ma-
terials. We will now consider some current issues related to recycling of non-ferrous
metals.
13.2
Recycling Non-ferrous Metals- the Current Position
As mentioned above, the use of virgin ore has a strong negative impact on the
environment from both a geographical point of view (destruction of landscape and
production of large amounts of tailings, etc.) and in terms of global emissions of
carbon dioxide (from energy use) and toxic gases. Also the potential economic dif-
ficulties of recycling materials have also been mentioned; in particular relatively
high labor costs may make recycling economically unfavorable. It is thus important
