Abstract
Roasting of sulfide ores to produce sulfuric acid began on an industrial scale in the middle 1800′s and is still used extensively worldwide. The residual, pyrite cinders, have commonly been disposed in the environment where they pose a potential and serious threat to aquatic life. In this project, two profiles in a pyrite cinder deposit in Bergvik, Sweden, have been sampled and a comprehensive mineralogical characterization have been carried out. The objectives were to investigate the composition and morphology of pyrite cinder grains and the speciation of sulfur, Pb and Zn in the solid phase. Scanning electron microscopy showed pyrite cinder grains with a core of the ore minerals pyrite and sphalerite enclosed in layers of iron oxides/hydroxides (mainly hematite). XANES analysis, supported by X-ray diffraction analysis, SEM-EDS and bulk element analysis, showed that content of the residual sulfur in the cinder is mainly sulfides, 55–80%, predominately sphalerite. The remaining mass of sulfur is assumed to be adsorbed or precipitated as secondary sulfate minerals, predominantly associated with the grain surfaces. Calculated saturation indexes indicated barite, anglesite and perhaps aluminite. EXAFS spectroscopy indicated that about half of the Zn was bound to O and half was bound to S. LCF analysis of EXAFS spectra indicated that the main Zn species were sphalerite (40–50%) and franklinite (10–20%). The remaining Zn was associated with iron oxides/hydroxides and Zn minerals like hydrozincite or possibly zinc oxides. SEM-EDS analysis showed Pb precipitate located on both the surface of the grains and in the interior as inclusions. The analytical interpretation indicated anglesite.
Highlights
Roasting of sulfide ores to produce sulfuric acid began on an indus trial scale in the middle 1800′s and is still used extensively worldwide
The disposal sites are mainly located in the surroundings of pulp mill plants, where the sulfuric acid was used in the process of producing wood pulp
The sampling was carried out November 27th, 2013 at the former pulp mill plant in Bergvik outside Soderhamn in Sweden where about 110 000 m3 pyrite cinder has been landfilled along the shore of Lake Smalsjon until the middle of the 1960′s
Summary
Roasting of sulfide ores to produce sulfuric acid began on an indus trial scale in the middle 1800′s and is still used extensively worldwide. Sulfur dioxide is released and iron oxides, mainly hematite (Fe2O3) and magnetite (Fe3O4), are formed. As pyrite is the most abundant sulfide mineral, the residual is called pyrite cinder and contains mainly iron, oxygen, sulfur and trace elements such as Cd, Cu, Pb, Zn and As. In Sweden large amounts of pyrite cinders have histori cally been disposed in the environment, commonly adjacent to surface water where they pose a potential and serious threat to aquatic life. The disposal sites are mainly located in the surroundings of pulp mill plants, where the sulfuric acid was used in the process of producing wood pulp
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