『Abstract
Mine tailings discharged to river systems have the potential
to release significant quantities of major and trace metals to
waters and soils when weathered. To provide data on the mechanisms
and magnitudes of short- and long-term tailings weathering and
its influence on floodplain environments, three calendar year-long
column leaching experiments that incorporated tailings from Potosi（iの頭は´）, Bolivia, and soil from unaffected downstream
floodplains, were carried out. These experiments were designed
to model 20 cycles of wet and dry season conditions. Two duplicate
columns modeled sub-aerial tailings weathering alone, a third
modeled the effects of long-term floodplain tailings contamination
and a fourth modeled that of a tailings dam spill on a previously
contaminated floodplain. As far as was practical local climatic
conditions were modeled. Chemical analysis of the leachate and
column solids, optical mineralogy, XRD, SEM, EPMA, BCR and water-soluble
chemical extractions and speciation modeling were carried out
to determine the processes responsible for the leaching of Al,
Ca, Cu, K, Na, Mg, Mn, Sn, Sr and Ti. Over the 20 cycles, the
pH declined to a floor of ca. 2 in all columns. Calcium, Cu, Mg,
Mn and Na showed significant cumulative losses of up to 100%,
60%, 30%, 95% and 40%, respectively, compared to those of Al,
K, Sr, Sn and Ti, which were up to 3%, 1.5%, 5%, 1% and 0.05%,
respectively. The high losses are attributed to the dissolution
of relatively soluble minerals such as biotite, and oxidation
of chalcopyrite and Cu-sulfosalts, while low losses are attributed
to the presence of sparingly soluble minerals such as svanbergite,
cassiterite and rutile. These results strongly suggest that the
release of tailings to floodplains should be limited or prohibited,
and that all tailings should be removed from floodplains following
dam spills.』
1. Introduction
2. Methods and materials
3. Results and discussion
3.1. Net neutralisation potential
3.2. Controls on pH evolution
3.3. Mineralogical controls on metal mobility
3.3.1. Al, Sn and Ti
3.3.2. Ca, Mg and Sr
3.3.3. Na and K
3.3.4. Cu
3.3.5.Mn
3.4. Constraints on leachate volume
3.5. The significance of oxidation as an agent of sub-aerial
tailings weathering on floodplains
4. Conclusions
Acknowledgements
References