Abandoned copper mine tailings deposits.Problems and possible solutions

Henrik K. Hansen

Universidad Técnica Federico Santa Maria, Chile

Copper production in Chile

6 Mton/year > 40 % of GNP is due to copper

production 35 % of world copper Several important mines and smelters

El Teniente Chuquicamata Escondida Collahuasi

Copper mine tailings Main residue from copper mining (separated

during concentration of copper minerals) Daily production: > 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

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.

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)

Chilean legislation for new mining projects

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 2007Fiscalization unit: Servicio Nacional de Geología y Minería, SERNAGEOMIN

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

Mechanical stability Tranque Ovejería, CODELCO

Small scale tailings deposit

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

8 km

Caren tailing pondWall

CuSO4 accumulation

Tailing inlet

Cu infiltration

Tailing pond monitoring by SERNAGEOMIN Studies done 1992 and 2004 Quantify tailing ponds Analyse risks

Abandoned and paralysed mining sites (FMA/P) with tailing ponds representing environmental risk : 20 %

Abandoned and paralysed mining sites (FMA/P) with tailing ponds representing mechanical risk : 33 %

Possible solutions (in Chile)

Stabilization Control of wind borne materialProtection from rainwater

ReforestationEsthetical and natural solution

Mine tailings only inorganic materialNo “natural eco-system” exisitngPyrite oxidation --> pH ?

Tailing pond: Planta M. A. Matta, III Región: Application of Bischoffite (MgCl2 6H2O), to avoid wind erosion

Tailing pond: San José de Pucobre

Tailing pond: Ojancos, III Región : Reforestation

Tailing Pond: Las Cenizas V Región: Reforestation

Tailing pondLas cenizas:

Before (1995)

After (2007)

Tailing pond Planta M. A. Matta, III Región: Reforestation

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

Conclusions

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

generally solved

Abandoned copper mine tailings deposits.Problems and possible solutions

Henrik K. Hansen and Alejandra Muñoz

Universidad Técnica Federico Santa Maria, Chile