2008 Issue

UTAH ENGINEERS COUNCIL JOURNAL 39 In addition to the initial bench-scale col- umn study, BDU-33 iron collected from three different military ranges was analyzed using acid digestion and the toxicity characteristic leaching procedure (TCLP) for composition of material, variability in iron, and potential leachability of hazardous byproducts such as lead or mercury. The laboratory results for the acid digestion indicated that the content of the BDU-33 practice bomb material is pri- marily iron with trace amounts of calcium, manganese, aluminum, and sodium. The TCLP tests indicated that there were not leachable quantities of heavy metals that could adversely impact groundwater. Addi- tionally, the tests were consistent between all BDU-33 iron sources tested, suggesting that BDU-33 iron from any military range could be used as a source of iron in PRBs. Given that the results from these tests and the initial bench-scale column study indicated that the practice bomb iron might be suitable for use in PRBs, Hill AFB set out to find an eco- nomic method to reduce the four-inch minus BDU-33 iron to the grain-size distribution optimal for iron/contaminant reactions. Through searches of companies related to the mining, crushing, and process equipment industry, Hill AFB identified 29 companies with technology which might reduce the four-inch minus BDU-33 iron to the required grain-size distribution. Of the 29 companies contacted, only nine requested to receive a preliminary sample of four-inch minus prac- tice bomb iron to test. Due to the density (204 pounds per cubic foot), hardness, and resistance to fracture of the BDU-33 iron, many vendors believed that attempts to crush the iron material would result in excessive equipment damage. Of the nine receiving a preliminary sample of the four-inch minus BDU-33 iron, only Schutte-Buffalo Hammer Mill of Buffalo, New York was able to success- fully and economically crush the four-inch minus practice bomb iron to the desired grain-size distribution and at a production rate necessary for a PRB field installation. The Schutte-Buffalo Hammer Mill crush- ing system that was successful in reducing the four-inch minus practice bombs consists of a hammer mill (Figure 3). In the hammer mill process, material is fed into the hammer mill’s chamber, typically by gravity, where the material is struck by a series of hammers (rectangular pieces of hardened steel) which are attached to a shaft that rotates at high speed inside the chamber. The material is crushed or shattered by the repeated ham- mer impacts, collisions with the walls of the crushing chamber, and particle-on-particle impacts. Perforated metal screens, or bar grates covering the discharge opening of the hammer mill retain coarse materials for further crushing while allowing the properly sized materials to pass as finished product. For a production scale application continued on page 40 Figure 2. Granular BDU-33 Practice Bomb Iron Bench-Scale Column Study Figure 3. Generalized Hammer Mill Representation