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Geochemical processes in freshly deposited tailings from porphyry copper ore - An environmental study different climatic regions of Chile

English title Geochemical processes in freshly deposited tailings from porphyry copper ore - An environmental study different climatic regions of Chile
Applicant Pfeifer Hans-Rudolf
Number 115921
Funding scheme Project funding (Div. I-III)
Research institution Institut de Minéralogie et Géochimie Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Geochemistry
Start/End 01.04.2007 - 31.08.2008
Approved amount 83'964.00
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Keywords (14)

ACID MINE DRAINAGE; TAILINGS IMPOUNDMENTS; PORPHYRY COPPER; CHUQUICAMATA; EL TENIENTE; HEAVY METALS; sulfates; sulfide ore; mining; mineralogy; stable isotopes; bacteria; reductive dissolution;

Lay Summary (English)

Lead
Lay summary
Mine waste is the largest volume of materials handled in the world. The weathering of minerals containing heavy metals in this waste may result in the release of acid, metal-rich water to the environment, one of the major problems the mining industry is facing today. To control and reduce this environmental impact, it is crucial to identify the main geochemical processes in these materials, as well as pathways of water and dissolved contaminants. This thesis presents the results of a geochemical, mineralogical and stable isotope study on mine waste slurry in two active impoundments in mediterranean and hyper-arid climate from their deposition in an alkaline environment to their acidification after several years of exposure. The major hydrological results were the identification of vertical contaminant and water transport in the uppermost, not water-saturated zone, triggered by capillary rise due to evaporation and infiltration downwards due to new waste deposition, and of horizontal transport in the groundwater zone. Latter zone was found to be highly dynamic due to infiltration and mixing with water from different sources, like groundwater, catchment water, and infiltration from superficial waters. At the surface of the sedimented mine waste, evaporation of pore water led to the precipitation of Na-Ca-Mg sulfates, in hyper-arid climate also Na-chlorides. In the timeframe of less than 4 years, in the uppermost sediments, weathering of surface-near minerals containing heavy metals forms an acidic oxidation zone. This process enables the transport of liberated Cu, Zn, and Fe via capillary rise to the surface, where these metals precipitated as heavy-metal sulfides and chlorides. Renewed depositing may dissolve these salts and transport them towards the groundwater zone. There, Cu was found to be partially mobile due to complexation with Cl (in Cl-rich groundwater) and dissolved organic matter (in zones with infiltration of catchment water rich in dissolved organic matter). A laboratory study on the fractionation of different stable isotopes of sulfate in different minerals contributed to the use of stable isotopes as tracer of geochemical and transport processes for environmental studies. The major result highlighted is that a detailed geochemical, stable isotope and mineralogical study permits a prediction of future contamination processes and pathways, already during the deposition of mine waste. This knowledge allows the early planning of adequate actions to reduce and control the environmental impact during deposition and after the closing of the mine waste deposition site.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
103678 Environmental assessment of mining related contamination - An integrated study combining mineralogy, geochemistry and biogeochemistry 01.08.2004 Project funding (Div. I-III)

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