Thursday, October 2, 2008: 11:00 a.m.
Samples of chat from two piles were analyzed before and after grinding to characterize the distribution of metals (lead, cadmium and zinc) in various particle sizes of chat. This testing confirmed that metals are not evenly distributed but concentrations are inversely related to particle size. The results showed that chat is composed of a mixture of mostly angular chert particles with minor limestone and dolomite and smaller concentrations of metals. The particles range in size from 9.51 mm to less than 0.074 mm with greater than 85% of the mass larger 0.420 mm. Grinding chat particles to less than 0.149 mm resulted in low analytical variability, slightly higher metals concentrations, and revealed that further reduction in particle size does not significantly increase metals concentrations. Also, a high metals bias was observed from incomplete sieving after grinding. Removal of larger particles with sieving prior to analyses produces a biased sample with higher metals concentrations compared to bulk chat. Metals concentrations in chat depend on sample collection, sample preparation, and analytical methodologies so the grinding and sieving process is not recommended unless the entire sample is analyzed.
Samples from the two chat piles had similar distribution of particles and contained a disproportionate metals mass in the fine sizes, concentrated during milling. Metals concentrations varied significantly between the two chat piles, as did the leaching potential (from ABP tests). The presence of carbonate produced a net alkaline ABP in one sample but did not affect the total metals analyses. Additional research and risk characterization is needed for chat to evaluate beneficial reuse options and re-mining potential through more metals analyses, leaching tests (using SPLP and water), and ABP tests.