1994-02-28_REVISION - M1988112 (2)

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It is important to note that the NAP Net NP of samples RK-~ and TL-4 was lower than the mineralogic Net NP and for sample RK-3 the '• •~:,P Net NP was •:.dy sli,~lrt;y higher than the mineralogic Net NP. The mineralogic Net NP values for these three samples ranged from -48 to -67 kg CaCO3/t, suggesting that conditions during the hydrogen peroxide oxidation should have been fairly acidic. Nonetheless, the NAP Net NP values indicated little, if any, excessive acid neutralization by minerals other than those containing calcium carbonate or magnesium carbonate. The wmbined quartz, mica, and clay (chlorite, kaolinite, montmorillonite) content of these samples ranged from roughly 60 to 80 percent (Table 2). The NAP Net NP values indicate that these minerals did not dissolve extensively, with attendant acid geutralization, despite the aggressive nature of the solution generated during the hydrogen peroxilde oxidation. The extremely low Net NP value determined for sample RK4 is most unusu&1. The NAP Test determined a Net NP of -103 kg CaCO~/t of this sample. However, the maximum acid production based on the sulphur wntent of this sample (2.9 percent) is 91 kg C~CO,/t. This discrepancy is difficult to explain other than by error introduced in sample splittihg. APPLICATION OF THE NAP TEST The NAP Test has been proposed as a static test which could be applied in tote field. The results for these ten samples suggest that although predictions by the NAP Test a#e reasonably consistent with those of other static tests, application of the NAP Test in the >field requires several precautions. First, the NAP Test is subject to the same limitations as other static tests. That is, it does not determine the availability of acid-producing and acid-consuming minertals nor their relative rates of reaction. These limitations are of particular concern in predicting if waste rock will produce acidic drainage. These concerns can be addressed qualitatively by determining the mode of occurrence ofrron sulphide, calcium carbonate, and magnesium carbonate mineral in individual rock units contributing to mine waste. Kinetic tests will provide a mor@ quantitative determination of availability and relative reaction rates, and must be conducted on particle sizes which reflect the sulphide and carbonate mineral occurrence in the mine waste. Second, the NAP Test often overestimates the Net NP by amounts dependent upon the sample composition. The potential for overestimation increases as the mineralbgic Net NP decreases below zero. The potential overestimation also increases with the content of minerals which dissolve under conditions of the test, but will not maintain a neutral drainage in the field. This potential error can be reduced by subjecting a series of well-characterized stimples from rock units of concern to the NAP Test. The results from this testing will quantif}}(( the error in Net NP and provide a means of calibrating subsequent measurements on samples from the rock unit. Furthermore, sources of error in the NAP Test may be reduced by additional procedural modifications. Results from the present test indicated close to 100 percent oxidation of the iron sulphides present in the samples examined. The excess acid neutralized by silicate mineral dissolution may be reduced by maintaining lower reaction temperatures or higher solution pH 156