El medio ambiente en la minería

93 ANGELSELKE The lead oxide sIag generated in the oxidation zone of the reactor runs continuously through the reduction zone where reduction and partial fuming ol zinc is accomplished by submerged injeetion of pulverized coalwith oxygen. . Fuming of zinc is a variant of the QSL-Process in order to recover 50-70% of the zinc input. The lead/zinc bearing fume can be processed in a conventional eleetrolytic zinc planto The reaction zone is equipped at its bottom part with tuyeres for injeetion powdered coal together with a controlled volume of oxygen. The reduction slag, which will be tapped continuously into slag ladles, has an average Pb-content of approx. 2% and a Zn-content of 10-15% depending on the feed materials. The primary S02-containing off-gas is taken off in the oxidation zone. The temperature of the fume carryingoff-gaswill be slightly higher than that of the liquid bath in the oxidation zone. It will be cooled in a water cooled vertical channel and further cooled down to approx. 400 oc in a waste heat boiler, cleaned in a hot gas preeipitator and then further processed in a sulphuric acid plant. Figure 5 shows a comparison between the conventional route and the QSL route for primary smelting of Iead bearing raw materiaIs. As it can be seen from figure 5 with the QSL-Teehnology the emissions are reduced by 80%, the energy consumption by 50% and the operating cost by 25% respectively. Up to now, four primary lead smelters based on the QSL– Teehnologyhave been built. The new lead smelters are located in Canada, PR China, Germany and South Korea. Latter will be commissioned during May 1992. Improved Converter Off-Gas Systems aad Controls The conventional Pierce Smith converter is due to the nature of its operation environmentalIy one of the most critical units in copper smelters. This refers to SÜ2-emissions as well as emÍSsions of critical volatilized compounds, e.g. lead and arsenic. Even when the converter-off gas is processed in a sulphuric acid plant to recover SÜ2, which is todays standard concept, it is difficult to colleet aU converter off-gas during normal blowing operation and to avoid substantial emissions of process gas when tuming the converter into and out ofstack. Big efforts have been made to improve the environmental situation and thus aIso the reliability of operation. A modem PS converter plant may be charac– terized by following features: