Specific Gravity of Expansive Chromium Ore Processing Residue with Complex Microstructure

Abstract

Abstract Specific gravity tests were performed on chromium ore processing residue (COPR), an expansive industrial byproduct of the historical processing of chromite ore, to determine if the complexity and heterogeneity of the particle microstructure may cause erroneous specific gravity results using ASTM D854-06 Method B as the baseline procedure. In complex, reactive industrial residuals such as COPR, specific gravity is an important indicator of the extent of weathering that has occurred. Specific gravity for weathered hard-brown (HB) COPR significantly differs from that of unweathered gray-black (GB) COPR, and laboratory testing can indicate the position of COPR along the GB to HB pathway. The difference between a “true” and an “apparent” specific gravity that accounts for the inclusion of closed pores was determined. Oven-drying of COPR at the ASTM standard temperature of 110±5°C does not cause mineral dehydration to affect specific gravity results. The apparent (avg.=3.146) and true (avg.=3.355) specific gravities of GB COPR are statistically different and should be reported as such. Pre-processing of GB COPR by mechanical grinding is necessary to open intraparticle voids, determined to be 6.2 % by volume, to the atmosphere and thus approach the true specific gravity.