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<br /> Ingredients in Acid Formation
<br /> Water - Ultimately, rain and snow provide the system with a source
<br /> of water which serves as reactant, reaction medium, and transporter of
<br /> reactant - and products (Lovell, 1970). . Engineering,-"
<br /> which.is costly and
<br /> not without_-_speculation, can - limit the movement ofwater across and
<br /> through the expanse of a mine- site; however,: some precipitation will
<br /> inevitably- contact pyritic material.
<br /> (hygen _ - Much work has been devoted to the control of AMD by
<br /> restricting diffusion of atmospheric oxygen I _into' spoil. If the
<br /> concentration of oxygen contacting the ' pyrites can be sufficiently
<br /> reduced,, then -the._formation of acid will -be limited.
<br /> + O-,ygen restriction is difficult to'achieve in the-field. .-' Based on
<br /> thermodynamic ' measures, it is nece_gary to reduce oxygen concentrations
<br /> to an unattainable level of 10 _ atmospheres (Barnes and Romberger,
<br /> 1968) before pyrite oxidation reactions are stopped. Therefore, the. .
<br /> sealing _of waste dumps and mine portals with so-called,impermeable caps
<br /> may not adequately reduce oxygen availability._ --
<br /> - Sulfides _ - The physical form of the sulfide mineral contributes to
<br /> the _-dekree-,_of,'reaction. - Smaller particles,.;because. of .their-.,greater
<br /> surface- areast tend =to react more -quickly.,-Also t les-s crystalline
<br /> forms of sulfide minerals tend to be more reactive. Dixon,. et al,
<br /> 1982). _
<br /> - Bacteria -The relationship between bacteria and AMD was probably
<br /> first considered in- - 1919 - (Onysko, et al, 1984) . St wasn't until the
<br /> late , forties '"that a -specific microorganism was 'isolated (Temple and
<br /> Koehler,, 1954). - :Today, - it is commonly: accepted.: that a family of
<br /> bacteria, typically represented by' Thiobacillus - ferrooxidans is the
<br /> principle_ catalytic agent in -.the - production of. _ acid ; in- mine
<br /> environments. This .- bacterium is- responsible ,for up.to 95X_ of,;the acid
<br /> _
<br /> generated in tailings, waste rock.,dumps, and coal;refuse.
<br /> - - Chemical `oxidation-- of ferrous- iron is kinetically limited; _
<br /> however, T. ferrooxidans can increase the rate of reaction by a factor
<br /> of greater than . 1,000,000, (Singer- and Stut_rm, 1970).: Without these
<br /> „ar_. •a sa. .. ..T .. ...a .
<br /> bacterial,�.cata`lysts,+the ,oxidizing t}.•��wte J of r errous`Aron. natural
<br /> l.: J). '' ` •4+a _..F.i Jru.w♦ f..4.r. a-..
<br /> systems_ is too slaa� o be of-any.,consequence.in�acid.formation. -
<br /> T. ferrooxidans - derives.its, .energy _by -oxidizing ferrous iron and,
<br /> to a lesser extent,' elemental sulfur, thiosulfaie, tetraihionate, and
<br /> the sulfide moiety of various noniron minerals .,I Hutchins, et al,
<br /> 1986) . Indigenous to pyritic minesoils, T. ferrooxidans thrives in the
<br /> presence of oxygen, water,, and a soil with pH;values below_.5..0,_._-,
<br /> Research has, 'shown the vulnerability,r-of. T. ferrooxidans_to the
<br /> various,' chemical-compounds including food ,preservatives-.-.organip acids,
<br /> and'- anionic'- surfactants.� Originally, bacterial inhibitors could
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