Industrial Ecology in the metallurgy industry The Harjavalta ... - Oulu

Besides the primary metals of copper and iron, the concentrate aslo includes smaller amounts of
different heavy metals (Ni, Zn, Pb, Co, As, Sb, Bi, Ag and Au). In the case of copper, the general
concept of process is: fine dry copper sulphide concentrate and quartz sand as flux are blown
into a hot hearth furnace with oxygen (industrial), oxygen-enriched air. The products are a Cu-
Fe-S matte, SO 2 enriched off-gases, and slag. The main reaction is:
2 CuFeS 2 + 4O 2 ⇔ Cu 2 S + 2FeO + 3SO 2 (1)
The matte is further processed in a Peirce-Smith converter to obtain the metallic copper. The slag
is treated to recover its 2 % copper content. The off-gas contains about 10 - 75 percent by
volume SO 2 . Heating needed for smelting is obtained from the exothermic reaction of oxidizing
the Fe and S in the feed. The reaction is (Luomala 2002);
[ FeS] + 3 O = ( FeO)
+ SO
2 2 2 (2)
The iron forms with quartz fayalite slag:
2FeO + SiO2
= 2FeO ⋅ SiO2
(3)
The SO 2 is recovered and treated to make either SO 2 or H 2 SO 4 . The recovery of by-products and
recycling of dust and wastewater have an important effect on the environment, because dusts and
wastewater contain quite a lot of heavy metals.
The Harjavalta Copper DON process eliminates the converting stage altogether and thus greatly
simplifies the nickel process. High-grade matte is produced using only the flash smelting furnace
and electric furnace – without Peirce-Smith converters. The SO 2 is recovered and treated in the
same sulphuric acid plant as is the gas from copper smelter. The elimination of converters
reduces the investment, operating and maintenance costs significantly. The nickel flash smelting
flow sheet is shown in Figure 2.
Figure 2 The nickel flash smelting flow sheet.