Remediation of tailing ponds

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Abandoned copper mine tailings deposits.Problems
and possible solutions
Henrik K. Hansen Universidad Técnica Federico
Santa Maria, Chile
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Copper production in Chile

• 6 Mton/year
• gt 40 of GNP is due to copper production
• 35 of world copper
• Several important mines and smelters
• El Teniente
• Chuquicamata
• Escondida
• Collahuasi

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Copper mine tailings

• Main residue from copper mining (separated during
  concentration of copper minerals)?
• Daily production gt 2.000.000 ton
• (Domestic waste 15.000 ton)?
• 95 of the mineral treated ends as tailings
• Cu concentration 0.1 0.3
• Other elements of concern As, Zn, Pb
• Accumulated in tailing deposits/ponds

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Problems with tailing ponds

• Mechanical Stability
• Damn failures
• Chemical Stability
• Leaching of contaminants
• Can cause severe environmental impact, collapse
  of Tailing pond El Cobre in 1965 caused the
  death of more than 200.

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Examples of pond wall collapse

• 1928 Barahona Pond (El Teniente)?
• 1965 El cobre Pond (200 deaths)?
• 1981 Minera Las Cenizas (collapse affected
  severely the nearby agricultural activity)?
• 2002 Cobrex (15.000 t tailings spilled)?
• 2003 Minera Cerro Negro (300.000 t tailings)?

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Chilean legislation for new mining projects
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Decreto Supremo Nº 248

• Reglamento para la aprobación de proyectos de
  diseño, construción, operación y cierre de los
  depósitos de relaves
• Suggested December 2006
• Published April 2007
• Fiscalization unit Servicio Nacional de Geología
  y Minería, SERNAGEOMIN

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Mechanical stability

• Damn construction inadequate
• Specially in small and medium scale tailing ponds
• Hydrodynamic effect, e.g. rainwater accumulation
• Seismic activity
• Wind erosion/escape of wind borne material

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Mechanical stability
Tranque Ovejería,
CODELCO
Small scale tailings deposit
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Chemical stability

• Chemical reactions in the tailing ponds
• Pyrite oxidation (Air humidity)?
• Chemical reactions in the tailing ponds
• 2 FeS2(s) 7 O2 2 H2O ?
• 2 Fe2 4 SO42- 4 H
• Dissolution of Cu-sulphides
• Precipitation/settling of new solids
• Leaching/filtration

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Cu infiltration
Wall
Caren tailing pond
CuSO4 accumulation
8 km
Tailing inlet
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Tailing pond monitoring by SERNAGEOMIN

• Studies done 1992 and 2004
• Quantify tailing ponds
• Analyse risks

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Abandoned and paralysed mining sites (FMA/P) with
tailing ponds representing environmental risk
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Abandoned and paralysed mining sites (FMA/P) with
tailing ponds representing mechanical risk 33
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Possible solutions (in Chile)?

• Stabilization
• Control of wind borne material
• Protection from rainwater
• Reforestation
• Esthetical and natural solution
• Mine tailings only inorganic material
• No natural eco-system exisitng
• Pyrite oxidation --gt pH ?

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Tailing pond Planta M. A. Matta, III Región
Application of Bischoffite (MgCl2 6H2O), to avoid
wind erosion
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Tailing pond San José de Pucobre
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Tailing pond Ojancos, III Región Reforestation
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Tailing Pond Las Cenizas V Región Reforestation
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Tailing pond Las cenizas Before
(1995)? After (2007)?
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Tailing pond Planta M. A. Matta, III Región
Reforestation
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Some species used for reforestation

• Espino Acacia caven
• Aromo azul Acacia saligna
• Álamo Populus alba
• Pimiento Shinus molle
• Granado de flor Punica granatus
• Albizia Albizia lophanta
• Tamarindo Tamarix sp.
• Aromo australiano Acacia melanoxylon

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Conclusions

• Awareness of problem
• Legislacion OK for new and present project
• Problems with abandoned ponds still not generally
  solved

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Abandoned copper mine tailings deposits.Problems
and possible solutions
Henrik K. Hansen and Alejandra Muñoz Universidad
Técnica Federico Santa Maria, Chile