Mobilization of heavy metals in mining and smelting heaps, Kupferschiefer district, Mansfeld, Germany

摘要

Large-scale smelting in the Mansfeld Kupferschiefermining district began during the late 19~th century with theintroduction of shaft furnaces in the metallurgical complexes atEisleben and Helbra. Flue gas treatment from 1904 onwardprovided considerable amounts of metalliferous sludge (Theisen-sludge) which contained up to 18 precent Zn, 14 precent Pb, 1.2precent Cu and 1.2 precent Sn. After metal recovery from thissludge ceased in 1978, more than 300,000 metric tons of "waste"were deposited in open basins on extensive heaps of slag and mining debris.At the Helbra smelting complex, suspended Theisen-sludge(grain-size<1 #mu#m) has infiltrated the fractured slag heaps andcurrently contributes both heavy-metal particles and leachate toground and surface water pollution; seepage waters contain up to2.5 g/l Zn. In addition to water pollution, the extremely fine-grained Theisen-sludge is scattered by the wind from its uncoveredstorage sites and causes additional environmental hazards.Detailed studies into the potential heavy-metal leaching fromTheisen-sludge, slag, Kupferschiefer ore and carbonaceous hostrocks indicate that dissolution and wind-borne dispersion ofTheisen-sludge are the main Zn migration mechanisms into thesurrounding environment. Very high Zn contents were releasedduring Theisen-sludge leaching experiments using both the heapmaterials and adjacent soils, and testing each under laboratory aswell as natural climatic conditions. The high Zn mobilization rateis due to ionic dissolution under natural pH-Eh conditions. Incontrast, Pb and Cu form stable secondary minerals (carbonatesand sulfates) under the same test conditions, resulting in very lowdissolved abundances (ppm levels) from the same source material.Tests of low-grade Kupferschiefer ore found that Zn, Cu and Pbwere all below 5.0 ppm in solution. Soil profiles located close tothe slag heaps show metal enrichment patterns in the topsoil thatare identical to those of Theisen-sludge, which is consistent withwind dispersion of Theisen-sludge.