Contaminant source and mobilization in industrial wastes in Dalälven river drainage area, Sweden

Abstract

From a summary of mineralogical and geochemical studies, this paper presents patterns of contaminant source, mobilization, and retention in three types of industrial wastes deposited in the Dalälven river drainage area in central Sweden. These industrial wastes contain significant amounts of sulfides and have been subjected to atmospheric oxidation for several tens to hundreds of years. They are the major sources of metals and non-metal contaminants discharged into the Dalälven river. The collected data are of considerable value toward the remedial management of this kind of industrial wastes. The mill-tailings initially contain carbonate minerals which neutralize the acidity and maintain the leachate pH at near neutral values at the bottom of the oxidation zone (about 40 cm deep beneath the surface). The acid neutralization results in a great deal of precipitation of ferric iron hydroxides, leading to the formation of Fe-precipitated layers - a potential barrier to metal movement and O2 diffusion downward through the tailings. The mine waste dump is composed of coarse-grained rock fragments and has been covered by crushed limestone since 1985 in an attempt to neutralize the acid leachate. However, limestone cover has much less buffering effect than expected. As a result, the underlying soil and ground water contains high levels of SO4, Fe, and other metals, and have low pH values. The sulfuric acid industry wastes consist of 70-80% iron oxides which are porous in texture. The porous texture provides a large surface area for the adsorption of SO4. During roasting, sphalerite acquired alteration rim which is composed of Zn-oxides. The mineralogical properties of the SAI wastes play an important role in the formation of hydrated sulfates of Fe and Zn. Due to the occurrence of these highly soluble sulfates, in situ flushing is a practical remedial approach for the SAI wastes, and a cleansing project is carrying out in Falun.