Graduation Trends in Machinist and Machine Shop Technology Programs in Two-Year Colleges in Great Lakes and Plains States: 2000 – 2006

The purpose of this study was to determine how two-year colleges have responded to the transformation towards a greater percentage of high-skilled workers in manufacturing industry. About 147 two-year colleges in Great Lakes and Plains States were investigated, and the study found that graduation trends in the programs and regions studied have declined, and in some cases, states and schools have lost their capacity to offer certain programs

Petrographic and spectroscopic characterization of phosphate-stabilized mine tailings from Leadville, Colorado

The use of soluble PO43- and lime as a heavy metal chemical stabilization agent was evaluated for mine tailings from Leadville, Colorado. The tailings are from piles associated with the Wolftone and Maid of Erin mines; ore material that was originally mined around 1900, reprocessed in the 1940s, and now requires stabilization. The dominant minerals in the tailings are galena (PbS), cerrusite (PbCO3), pyromorphite (Pb-5(PO4)(3)Cl), plumbojarosite (Pb0.5Fe3(SO4)(2)(OH)(6)), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5.2H(2)O). The tailings were treated with soluble PO43- and lime to convert soluble heavy metals (principally Pb, Zn, Cu, Cd) into insoluble metal phosphate precipitates. The treatment process caused bulk mineralogical transformations as well as the formation of a reaction rind around the particles dominated by Ca and P. Within the mineral grains, Fe-Pb phosphosulfates, Fe-Pb sulfates (plumbojarosite), and galena convert to Fe-Ca-Pb hydroxides. The Mn-Pb hydroxides and Mn-(+/-Fe)-Pb hydroxides (chalcophanites) undergo chemical alteration throughout the grains during treatment. Bulk and surface spectroscopies showed that the insoluble reaction products in the rind are tertiary metal phosphate (e.g. (Cu,Ca-2)(PO4)(2)) and apatite (e.g. Pb-5(PO4)(3)Cl) family minerals, pH-dependent leaching (pH 4,6,8) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 150 for many metals; particularly Pb2+, Zn2+, Cd2+, and Cu2+. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca2+, PO43-, Pb2+, Zn2+, Cd2+ and Cu2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids. (C) 2002 Elsevier Science Ltd. All rights reserved