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gD,-•g~+ • a":)Ow,~"as~ -- so; • (1-x)Fst' • 2s13• (I) <br />. Caruraaetlm 11afn and Snlehlde O~ditio~tea <br />et: The fiat of orygeo Ihtuugh the mrface of ta+lings b equal m the aontx of oxygen txroaimed <br />ie a vertical cohmm of tatl'atgs ender mady-sate ooodidom. Oxidadan races have previattly bees <br />estimated by eviluadmg the anrygen profile oral the effective diffmion coet~dtm» with depth based oa <br />the degree of satttruica (~. An ahxrnadve method m daamics the tape of avlphide asidatioc trees the <br />K decrease m the oxyga oeaemaation veldt time in the hadspace of a cbemba ooverhg the tailmga <br />surface. <br />a <br />~, Asssmiog stxady-etaoe aonmmption ram. Elberling a al. (n shovrod that the eooon of <br />oxygen (~ in the headapace as be daaibed as a hmaion of time whh the 6oUowlog etpruioa: <br />~~ -R~~03 v t2) <br />~~~ <br />,. Y; <br />~. <br />~' Whore Ca u the origin! atmoepbetic woceatratioe at the smrfac0. t u time, t is the firstordet rate <br />constant for mlphide mieeral oxidation, D~ b the effective diffusion coeffident for oxygen ie the <br />.' nilicga, A is the ua, sod V b the volume of the gas reservoir. The slope of the plot of IiaGC~ vtxsus <br />'~' time gives the vacua of ~~~)of when AN is lmowa Ibis tam can rhea be mbsdwted mm: <br />. ~,, <br />to calculate the 9ttt of oxygen at the surface. The flux will depend on both the ldaetic rate contact and <br />the diffiuivity. The k value rttpraeaes an average oxidstioa rate cansmt in the oxidation acne and D„ <br />teprestmts a harmonic meae of the D.r >rom the surface m the depth whore oxidation rata place. Both <br />panmaas may chattgs with depth oral ace difficult m evaluate in the fidd. Ahhoegh compete molds <br />of tailings oxidation require esthtattea of both k acrd D,x with depth, the oxygen aoawmptiots method does <br />not require sa evatoatIoe of these values or of the relative importance of theca parunaea. <br />Gas reservoirs used to ttseuure oxygen ram in the fidd eowisted of thin-walled aluminum <br />cylirdets (0.18 m LD.) of vuious latgths (OS-0.7 m) which veers mamtdly driven (non ffie taIlittga <br />leaving the top 0.01 m 0.02 m of the cohtmm above the tail'mgs mrfaa. Ae oxygen sensor, poets 6or <br />otynperature sad presstue maaarnme~, and a prtasuro rdtnse port were sealed into an aluminum Gp <br />am placed oa top of the column to form a closed gat raetvoir above the tatliegs turfaee during the <br />measurement t~lgore 3). <br />The cap was ia6talled only for the short measurement periods, tnsatiag expowre m atmospheric <br />n7'gea and ambient gu di8ttsioe between measurements. The oxygen oorta~aaat. is the headapace <br />t-as monitored every 300 sec in perbds of ti000 sx whim b a short paled compared to the ambient <br />vxidatioe dandoe. Meamranrnb was made with a vohmeta which wore tatnteaed m the <br />1001 <br />