Nitrogen & Flotation of bulk Copper-Lead-Zinc-Pyrite Ores
Flotation of copper-lead-zinc ores presents one of the most complicated problems in base metal metallurgy. The problem is even more difficult when the copper, lead, and zinc content can be sufficient to justify concentration into three separate products. These ores are referred to as complex sulphide ores.
Flotation problems in general are of geological origin. The characteristics of an ore deposit have a controlling influence on metallurgical practice. Any alteration on mineral surfaces is of greatest importance because flotation is a surface phenomenon.
Selective flotation of sulphide lead-zinc ores has been practiced for many years. Unfortunately, this practice is not always applicable to copper-zinc ores due to the similar floatability of copper and zinc sulphide minerals. This is especially true when oxidation has caused dissolution of some of the copper. Bulk flotation followed by separation of the copper, lead and zinc is commonly employed. Selective flotation in three steps was an early practice on copper-lead-zinc-ores [19]. This practice is seldom used now, as the preference technique is to selectively float a bulk copper-lead concentrate with depression of zinc and iron (i.e. sphalerite and pyrite) followed by reflotation of the copper–lead tailing for selective recovery of zinc from iron and other minerals. When the ore is very complicated can be possible float a bulk copper-lead-zinc-pyrite concentrate followed by flotation of copper-lead with depression of zinc sulphide.
Sodium sulphide can be used in concentration of polymetallic and copper-zinc ores as a desorbent. In addition to that, a high consumption of Na2S is undesirable not only by economic reasons. Sometimes a high consumption required for collector desorption with a view to subsequent good selection of bulk concentrate leads to increase losses of metals in the different concentrates. Then, nitrogen is an alternative very interesting.
In Reference [17] is mentioned the use of nitrogen as a flotation gas treating a polymetallic ore of the Leninogorsk deposit. The test with the Cu-Pb-Zn-Pyrite concentrate showed that during desorption in nitrogen atmosphere, Na2S consumption can be reduced by approximately two times. During the comparative test with air and nitrogen were used the following reagents: sodium sulphide from 1.5 to 4 kg/t, activated carbon from 2 to 4 kg/t, zinc sulphate 3 kg/t, sodium cyanide 0.18 kg/t, lime 0.35 kg/t. The next table shows that the total recovery of the three metals in the test with nitrogen is higher.
Table1. Copper-lead flotation of bulk Cu-Pb-Zn-Py concentrate of the Leninnogorsk deposit; experiments performed by the principle of continuous process (adapted from [17]).
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