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~~ <br />values dwing the test. The latter objective may be attainable by adding hydrogen peroxide in <br />smaller doses, although the overall extent of iron sulphide oxidation rr~siy be aFfected by such an <br />approach. In addition, potential Net NP elevation due to ferrous :.ron in solution ~::ould be <br />examined. If such interference were verified it could be addressed by titrating to .a higher <br />endpoint pH er increasing the time required to determine endpoint stabilization. <br />SUMMERY <br />A modificztion of the Net Acid Productio..a Test compared favourabl}~ with the Net NP <br />values determined by the standard ABA, Modified ABA, and B. C'. Research Initial Test <br />predictions for ten samples containing an excess of iron sulphide minerals relative to calcium and <br />magnesium carbonate minerals. The NAP prediction of whether or not acid would be produced <br />was generally in good agreement with the aforementioned static tests. Disagreement was <br />observed for two samples which the standard ABA classified as acid producing based on Net NP <br />values of -29 and -26 kg CaCO,/t. The remaining tests classified ac:.d production potential as <br />inconclusive based on values in the range of -20 to +20 kg CaC:Oa/[. Thus, the NAP <br />predictions were not noticeably different from those by the other static: tests. <br />Solids analyses indicated 95 to 99 percent of the sulphur initially present was oxidized <br />during the test. Nonetheless, the Net NP values determined by the i1AP Tests were typically <br />higher than those determined by the other static tarts and by solid phsa:se analyses. Apparently <br />the elevated Net NP values were the result of exa;ssive attack of host rock minerals during the <br />hydrogen peroxide digestion. Samples with high inineralogic Net NP were more prone to such <br />dissolution since more acidic conditions would be produced Burin€; the hydrogen peroxide <br />digestion of these solids. Feldspars, particularly calcic feldspars, and pyroxenes were apparently <br />susceptible to such dissolution. Incomplete oxidation of ferrous iron released from iron <br />carbonate minerals may have further contributed to elevated Net NP values. <br />The study described herein reports results from a small set of samples and examination <br />of a wider set of samples is required to establish greater confidence in the NAP Test . <br />However, suitability of the test for laboratory and field use is indicatex and has the significant <br />advantage over other static tests in not requiring analysis of total su]I~hur or sulphur species. <br />The test does not apparently allow identification of samples with an excess of NP relative to <br />APP. This, however does not preclude using the test qualitatively in tlae field for decisions on <br />waste placement. Caution should be exercised in using the results of the: NAP test quantitatively' <br />as results tend to indicate higher Net NP values than values based on mineralogy. The <br />discrepancy of equivalent Net NP values from those of standard A.BA or other static tests <br />increases with increasing sulphur content. Again, However, as a qualitative field test, the margin <br />of error is likely Yo be acceptable. <br />Further work is in progress on a larger simple group to define further the NAP Test <br />conditions and limitations to allow greater confidence, accuracy and reproducibility in its use. <br />l57 <br />