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<br />
<br />mass versus retention period) would be used in
<br />the fmal process design.
<br />The general construction of the Biopass System
<br />would involve layering the organic matter in the
<br />bottom of the lined solution pond, upon which a
<br />set of lateral, perforated plastic drain pipe
<br />would be laid to equally distribute any drainage
<br />from the pads. The individual laterals would be
<br />joined at the opposite end of the Biopass System
<br />into a single header with a riser extending
<br />above the inle[ pipe. The riser would make a 90
<br />degree bend and pass through the liner out into
<br />the ground to allow discharge of excess and
<br />treated solution, in the event sufficient drainage
<br />entered the Biopass System to flood its bottom
<br />portion and the organic matter. Flooding of the
<br />organic matter would no[ be of concern, since
<br />the bacterial processes are anaerobic. The inlet
<br />line into the Biopass System would contain a
<br />one-way device to allow solution to enter, but
<br />would then close to exclude oxygen.
<br />Above the organic matter and drain pipes would
<br />be an additional compacted layer of fill material
<br />and a fatal vegetated soil layer. The purpose of
<br />the two upper layers would be to maximize
<br />runoff, while promoting removal of excess
<br />water [ltough evapotranspiration. The volume
<br />of allowable drainage that can enter the Biopass
<br />System before an excess and accumulation of
<br />water begins, is being determined through
<br />additional hydrological modeling. A generalized
<br />schematic of the Biopass System is presented on
<br />Figure 1.
<br />In the event excessive draindown volumes and
<br />shottened retention periods are anticipated on
<br />an infrequen[ basis, a second lined barren or
<br />pregnant pond could be used to receive partially
<br />treated solution from the Biopass System
<br />through another distribution system. The second
<br />lined pond would be filled with soil and
<br />vegetated with plant species specifically chosen
<br />for the particular climate, and possessing the
<br />ability to absorb and evaporate excess solution
<br />and to selectively concen[rate residual metals.
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<br />
<br />6.0 CONCLUSIONS
<br />The Biopass System provides an effective
<br />approach to treatmen[ of long-term draindown
<br />from heap leach pads and greatly reduces the
<br />need for and expense of chemical treatment or
<br />detoxification of rinse solutions.
<br />The continuous flow laboratory studies have
<br />demonstrated that the removal efficiencies for
<br />cyanide, sulfate, ni[rate and metals were equal
<br />to or greater than anticipated form the
<br />literature.
<br />Currently, full scale Biopass Systems are being
<br />designed for installation at two mining
<br />operations in Nevada, which are undergoing
<br />closure. The Nevada Department of
<br />Environmental Protection has approved the
<br />basic design of [he Biopass System for use as a
<br />primary heap leach closure option.
<br />In addition to closure of a heap leach operation,
<br />the Biopass System also fmds utility in the long-
<br />term treatment of leachate or seepage from
<br />tailings impoundments.
<br />7.0 REFERENCES
<br />Adams, D., Altringer, P., and Gould, W.,
<br />"Bioreduction of Selenate and Seleni[e", U.S.
<br />Bureau of Mines, Salt Lake City, Utah,
<br />Proceedines from the International
<br />Biohydrometallurgy Symposium 1993, Jackson
<br />Hole, Wyoming, August, 1993.
<br />Altringer, P., Lien, R., and Gazdner, K.,
<br />"Biological and Chemical Selenium Removal
<br />from Precious Metal Solu[ions", Proceedines of
<br />Environmental Management for the 1990's,
<br />SME Annual Meeting, Denver, Colorado,
<br />February, 1991.
<br />Altringer, P., Lien, R., and Dinsdale, B.,
<br />"Advances in Biological Cyanide
<br />De[oxifica[ion", Proceedines of the Randol
<br />Conference, p. 395, Vancouver, British
<br />Columbia, Canada, 199?.
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