T. Beisheim, A. Charitos, J. Güntner, M. Wrobel L. Hedstrom, J. Hammerschmidt, H. Storch
Flash smelter operation is affected though the increasing arsenic content within copper concentrates,
since: (i) recirculation of smelter copper rich dust will lead to increasing arsenic loads and (ii) control
of the arsenic content within the smelter slag will become more challenging. Pre-smelter removal of
arsenic is of increasing importance, as low As level is a key issue for marketing copper concentrates.
Partial roasting can pre-treat arsenic rich concentrates to achieve marketable As levels. On the other
hand, as As control in the smelter is another major concern, the treatment of the smelter flue dust
(post-smelter) provides for an arsenic bleed since removal takes place prior to dust recirculation.
Partial roasting technology is presented through Codelco División Ministro Hales (DMH) unit data.
The unit includes roasting-, gas cleaning-, sulphuric acid- and effluent treatment plant sections. Performance
data include (i) operation at – and exceeding – the 110 % production rate of 605.000 tpy
(ii) de-arsenifying of the enargite rich feed to an arsenic content of approx. 0.25 wt.-% and (iii) removal
of antimony by 60 – 70 %. The fluidized bed roaster furnace is operated at 630 – 720°C and
oxygen deficit. The calcine has a sulphide sulphur content of 20 wt.-%. Innovations – in terms of
energy integration of the sulfuric acid plant with the roasting plant allow for an increase of the calcine
sulphur content which is beneficial for the downstream smelter. Arsenic is stabilized as calcium arsenate.
Moreover, the “the flash smelter flue dust treatment process” is discussed based on experimental data
from the Outotec R&D-centre in Frankfurt. The process achieves similar results in terms of a residual
arsenic calcine content of 0.2 – 0.3 wt.-%, prior to recycling to the smelter. In addition, arsenic can
be collected as an arsenic trioxide residue with a concentration of above 90 %. The process differs
with regard to “classical” partial roasting since (i) the arsenic is present in copper and iron arsenates
(ii) coal is needed as a heat source and reducing agent (iii) it utilizes a bed of size enlarged calcine
particles (resulting from pre-treatment of the dust and coal) to counteract the dust fine particle size
(d80 < 10 μm) and intensify reducing reactions (iv) the off gas stream is relatively small which allows
its treatment in the existing smelter sulphuric acid plant unit.