Major and trace metal mobility during weathering of mine tailings: Implications for floodplain soils

• Published in: Applied geochemistry Vol. 27; no. 3; pp. 562 - 576
• Main Authors: Kossoff, David, Hudson-Edwards, Karen A., Dubbin, William E., Alfredsson, Maria
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.03.2012; Elsevier
• Subjects: alluvial soils; aluminum; biotite; calcium; chemical analysis; climatic factors; copper; dry season; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; floodplains; Geochemistry; leaching; long term effects; magnesium; manganese; mine tailings; oxidation; Pollution, environment geology; rivers; scanning electron microscopy; sodium; strontium; tin; weathering; wet-dry cycles; X-ray diffraction; Bolivia; South America; experimental studies; mobility; trace metals; optical mineralogy; mica; cycles; aluminum; biotite; pH; sheet silicates; silicates; tailings dams; soils; scanning electron microscopy; rivers; models; calcium; dissolution; weathering; leaching; extraction; chemical analysis; contamination; speciation; floodplains; mines; tailings; leachate
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2011.11.012

► Magnitudes and mechanisms of metal mobility during tailings weathering were determined. ► By the end of the weathering experiments all leachates had pH of ∼2. ► Release of Ca, Cu, Mg, Mn and Na and retention of Al, K, Sr, Sn and Ti was observed. ► Dissolution of primary sulfides and silicates controls metal mobility. ► The release of tailings to floodplains should be severely limited or prohibited. 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 Potosí, 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.