Mineralogical and chemical characterization of wastes from the sulfuric acid industry in Falun, Sweden

 Wastes from the sulfuric acid industry are an environmental concern, because of the emission of acids, heavy metals, and sulfate to the environment. The wastes in Falun consist of 70–80% iron oxides, 10–20% silicates, less than 10% residual sulfides, and small amounts of secondary precipitates (iron hydroxides and Fe-, Zn- and Cu-sulfates). Due to the different behavior of sulfides during the roasting process, pyrrhotite and sphalerite are the major sulfide residues associated with lesser amounts of pyrite, chalcopyrite, and galena. The leachates are low-pH and enriched in Zn, Fe, and SO₄. The acid ferric Fe-rich solution promotes the dissolution of sphalerite and favors the formation of Pb-sulfate coatings on galena, providing an armoring effect which slows down the further oxidation of the galena. The residual sulfides are the potential source for acid generation and metal release. During the roasting process, iron oxides retain small amounts of sulfur and sphalerite forms alteration rims containing Zn-oxides. The iron oxides and Zn-oxides are important contributors to SO₄ and Zn in the leachates. The conditions in the waste deposit are favorable for the precipitation of Zn-, Cu-Fe-sulfates (e.g. gunningite, chalcanthite, Zn-copiapite). The highly soluble sulfates play important roles in controlling the concentrations of Cd, Cu, Fe, Zn, and SO₄ in the leachates. The mineralogical and geochemical data help to develop the reclamation strategies of this type of industrial wastes. Received: 26 April 1996 · Accepted: 27 July 1996     

The impact of the nitrogen carryover effect on economic activity and the environment

 The economic and environmental consequences of soil nitrogen tests can have significant impacts on agricultural production. Some of these are explored here. The pre-side-dress soil N-test is evaluated for a hypothetical farmer growing corn at the ARS Sustainable Agriculture Demonstration Farm site in southern Maryland. For a farmer not currently using a soil N-test, adoption of this technology can lead to the enhancement of net farm income and the reduction in nitrogen loss to the environment. This will transpire only if the farmer is currently underestimating nitrogen carryover by more than 25% or applying nitrogen fertilizer based solely on an expected plateau-yield goal. Received: 13 February 1997 · Accepted: 13 May 1997