1994-02-28_REVISION - M1988112 (2)

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SOLID PHASE CHARACTERIZATION The solid phase calcium and magnesium Content used for this Calculation must ba limited to chat present as carboaat ea. For this waste the time co deplece the 6.4 milllmoles of carbonate minerals vas tar less than chat for sulfide mineral depletion. In the inlt Sal rinses, 2.7 mil limo les of calcium and magnes Sum were released, and [he average sub- sequent release rate vas calculated ae 0.093 mi111mo les/week. ih is yie lde a came of 40 veeka for carbonate mineral depletion. It it is assumed chat [he magnee ium release Ss no[ from a carbonate mineral, the time for carbonate mineral depletion becomes Sl ve eks. The calculated times of buffering dap le[ion are con- current with a decrease in drainage pH, suggesting chat the pro]ecced dap lesion [imea are fairly accurate (f Sgu re 2). T_tle pH decreased rapidly Erom 8.7 a[ vee to 6.0 at week 56. I[ remained stable near 6.0 for about 20 weeks and [hen dropped below S. Dissolution of host rock minerals may have contributed [o th Sa final phase of buffering. SULIHARY The acid producing character of some wastes can not be clearly identified by acid-base accounts or in the time frame of klne tic testa c ondut[ed on the wastes. This study ind icatea chat a more detailed evaluation can be made by decerminiag the acid producing and acid consuming mineral content of [he vast e, the rates of acid production and acid consumption, and the times required Co deplete [he acid producing iron sulf idea and [ha acid neutral- izing minerals. The carbonate buffering mineral content of the solid tested vas deeermiaad by ad]usting the analyzed neutralization potential (Sobek et al., 1978) for background inter- ference. The ad]usced value vas 0.5 ae oppo eed co 11 t/1000 C for the analyzed value, Snd Stating chat the unad]usted value subetan- [lally owe restlmated [he [rue neutralizing potential. Second, [he races of acid production and consumption were calculated based the observed chemical release to solution over a 20 week period. Finally, the [imea required for dap letlon of sulf Sda sad carbonate buffering miners le were calculated using these rates and the initial compoe it ion of the solid. These calculated deplat ion [imea were In goad agree- ment with [he observed drainage quality. Thla ind ice ces chat £mplicatlone on [he ac ld pro- ducing character of mine wastes can 6e extended beyond the experimental time frame of kinetic tests. Ihis extension is based on solid phase charac[eriz at ion and chemical analysis of ChC drainage generated in [he kinetic ces [s. These re su Ste indicate that it Ls possible to calculate the time required [o deplece acid producing and acid consuming minerals in mine wastes. However, the conclue lone reached are based on limited data. The approach used is 10 S 0 7i fi f 5 w ,yep .• { IZ ~ {~ i et 85 6 ' ~ 3 ~ i ~ i'. -' \~ Pndlellone ~ 5 1 _ for HP depletion i 1 \ i 11 Lr \; i 0 0 l0 20 JO !0 50 60 70 80 90 Time IreekN Figure 2. Predicted depletion of solid phae• neutralization pa tential and observed pH ve. time. preliminary and the experimental methods may be modified and [ha aeaumptloae ref fined. For example, more refined solid ph~w analyeea (Pignolet-Brandom and Lapakko, 1990a, 19906) before end after kinetic exper~ma¢[a may Snc tease the accuracy of mineral deplat on rata quantifi- cation, as yell ae aeeeesirtg [~e val ldlty of aeaumptione such ae constant d eaolutfon rates over time. Additional work, some of which Ss in progre se, fie required to better assess the assumptions and methods employed. ACKNO{7LEDCEnENTS David Anconeon directed the laboratory experiment for this pro]ect. Cal Jokela and Anne Jagunich assisted Sn water quality sampling and analysis of spec if lc conductance, pN, acidity, and a1ka11- ni[y. Aqueous trace metals antl sulfate were analyzed by Albert Klaysmat aatl Jean Drotts, respectively. Albert Klaysmat vee also respons- ible for solids analysis Sn a very limited time frame. Tony Deneka and Jon Yagner were respons- ible for computer data managemknt. Financial assistance vaa provided by the LTV Steel Mining Company.