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• <br />gq M[NING AND MiNERA,L <br />To account for. chase interf stances, neutrali- <br />zation potentl.als ve re determined for seven <br />Duluth Conp lea. sump lee which had been sub]ected <br />[o ox Ida rive c._enolu[Son until [hey produced <br />acidic dra Snag.e. The average NP for these <br />samples, which hied been dap le [ed of their real <br />neu [r allz ac ion poten[Sa 1, vas 10.5 [/1000 t. <br />This rteucx~al iz.a [:.on potential vas largely an <br />ar[rf ac[ of [he :inaly[ic al technique rather Chan <br />a measure of al~l].icy co neu[zallze, and vas <br />apparently due co the factors meet toned by <br />Lucvitk (1986) and Fe rgueon and Erickson (1988). <br />The 10.5 tl :OCO [ NP for the leached samples <br />represented [h,e tat kground fo[ NP analyses of <br />similar rack, and vas subtracted from the I1 <br />t/L000 t NP determined for [he rock co yield an <br />available NP value of 0.5 [/1000 t. This value <br />was In close ar;reemenc with the observed <br />neutral is scion by [his rock Ln an oxidation <br />experiment, which suggests chat the NP method of <br />S ob ek e[ al. (1978) subacan[ially overestimates <br />the actual neu: retire [foe potential of chic <br />rock. Correcting far [his batkg round inter- <br />ference yields an ad]usted NP of 8.4 tj 1000 [ <br />for [he mixture, and 640 mg or 6.4 milllmo lee ae <br />CaCOS In [he m:ix Cure. <br />The rates of Lron sulfide oxidation and <br />carbonate mine rat dissolution were determined <br />based on the drainage chemistry. As indicated <br />by reaction 1, the oxidation of iron sulfide <br />minerals releases sulfate and leads [o acid <br />production. therefore, assuming <br />i) all sulfate released [o solution Ss from <br />iron sulfide oxidation and <br />if) chat all this sulfate remains in solution, <br />[he ra [e of sulfar.e release can be used to <br />approximate the races iron sulfide diaeolutlon <br />and acid producclrin ae follows (see oleo <br />Lapakko, 1988): <br />-2dFe5/dt - 2d5042 /d[ + dH+/dt (5) <br />Similarly, the dissolution of calcium carbon- <br />ate and magnesium carbonate minerals neutralizes <br />acid and releases talc Sum and magnesium, <br />respectively, to soluclon (reactions 3, 4), <br />(The assumption that ell magnesium release Se <br />from carbonate minarala La tenuous, since the <br />magnesium content of the RK fines is low.) <br />Consequently, using these reactions to represent <br />[he carbonate mlmeral dlesolut ion and similar <br />assumptions to those crated above, the oboe rued <br />concencra[Lons of colt Sum and magnesium can be <br />used co app rox lance the rates of carbonate <br />mineral dieso tartan and acid consumption, that <br />Ss: <br />-ndCaC03/dt - ndCa2+/dt -dH+/dt (b) <br />-ndMgC03/dt + ndtig2+/dC - -dH+/dt (7) <br />the value of n will be between L ant 2, Inclu- <br />sive, depending on whether reaction 3 or <br />reaction 4 la dominant. None chaises, the rat to <br />between cat ton release and carbonate mineral <br />.I <br />WFI:STES <br />d ie solution Se l:l. (Additional analysis of <br />these assumptio na and analyses will be presented <br />in a future paper.) The drainage pH will remain <br />ne u[r al as lon3 as [he rate of a~:Ld consumption <br />equals or rxce ads the rate of acid production. <br />Data from [ne inlci al 20 veeko of [he uxperl- <br />ment were used [o determine race:;. This pet lod <br />vas orb it tar lly chosen as a time frame vh Sch <br />might be used Ln a predictive tau[. During [he <br />Sn1[ial four ue~rks the concenirac ions of sulfate <br />and talc lam ve re relatively high, suggesting They <br />ve re products o.E oxidation during storage prior <br />[o the experim'n[. Conuequently, the period li tom <br />5 [0 20 veeka •+,rs used co determine release <br />races, which va~:e calc~~lated as cha product m1: <br />toncentrat ion rind [he ~:olume of rinse va ter <br />recovered dlvi~i~ed by t.~e tSme of ox ida[Son. <br />Over this p~a:: Sod the average rates of sulf:r[e, <br />calcium, and m.ii;neeLum were 0.047, 0.074, and <br />0.019 millimol~e~e/week. Th1e Sndicatee that the <br />terse of Lron calf ids oxidation and carbonate <br />mineral dlseo lincion verb 0.047 and 0.093 <br />millimoles/veelt, re ap ecC lusty. This indlcacen <br />chat the drain,t~;e shou Ld be neutral even if <br />reaction 4 ve ne the dominant buf taring reaction, <br />since the catYnn to su.Lfa[e rat iu Se 2. Tha <br />drainage vas indeed alkaline (f igura 1), and :lf <br />this mixture v~tce evaluated based solely on the <br />reaulta of chin 20 week kinetic teat, it you lrl <br />not ba claeaif:Led as an acid producer. <br />To further evaluate Chie soot lua ion, it 1^ <br />necessary co enrimate the times required co <br />deplete the ac:.cl producing irom sulfides and [:he <br />acid neutraliz7.t;g minerals. 'Thin ten ba done <br />using cha init7.e1 vaetc charact aritatlon in <br />con]unctlon vil:li the appzo:lmated ratan of Stun <br />sulfide oxideci.on and carbonate mineral dfesol.u- <br />t1on. Using ttra <br />1) average r~l~eerved sulfate re.leeea rate ar~d <br />ii) the initi.e~l sulfl.de coneens.ration in the: <br />solid to e.a timato the iron gulf ids content, <br />the time required eo deplete eh• icon sulfide can <br />be estimated e;i: <br />to + (So - `-.v)/(dSO42 /d t) (e) <br />vhcre to time co deplete the Sron sulfide in <br />the solid (weeks), <br />80 initial solid pheaa sulfur content <br />(mg). <br />Sv + sulfur va shed from the col id (aa <br />sulfate) Ln cha Initial <br />content ra Ced rineea (mg), and <br />the rate of sulfate appearance in soluclon is <br />expressed in mg/week. This yields a value of 950 <br />weeks of diaeolutlon fcr the deplec ion of the <br />iron sulfide content. <br />The time required to deplete the calcium and <br />magnet Sum carbonate coo be eatlma [ed similarly: <br />eb (Coo + Ngo - Cav - Hgv)J[d (Ce + tog)/dt) (9) <br />