STUDY OF MIGRATION FORMS OF METALS IN RIVERS AFFECTED BY ACID MINE DRAINAGE OF THE KIZEL COAL BASIN

Abstract

The relevance. The surface watercourses of the basin of Chusovaya river, the largest tributary of the Kama river on the area of the Perm Krai (Russia), are exposed to impact of acid mine drainage. The study of the metal behavior in the rivers affected by acid mine drainage is necessary for understanding the features of the component migration in natural-technogenic waters; research of geochemical processes and mechanisms that contribute to removal of the toxic elements from solutions; forecast of secondary pollution due to dissolution of the formed compounds due to the change of physical-chemical conditions. The results obtained in the area under study may reflect the specifics of the geochemical behavior of metals in other polluted rivers of the Kizel coal basin affected by acid mine drainage of similar composition. The aims are to study the migration forms of metals in streams polluted by mine waters, to determine the main secondary mineral phases that contribute to the removal of toxic elements from solution, and to assess the stability of particles of formed minerals during migration in the river network. Objects: acid mine drainage from the «Taezhnaya» mine of the Gremyachinskoe deposit of the Kizel coal basin, laden with high concentrations of sulfates and heavy metals, and rivers polluted by mine waters: Bolshaya Gremyachaya, Yuzhnaya Vilva, Usva and Chusovaya. Methods. Physical-chemical modeling of the migration forms of metals in solutions and calculations of the saturation degree were performed using the PHREEQC program code with the WATEQ4f thermodynamic database. Results of the research showed that metals (Al, Fe, Mn, Zn, Ni, Pb, Cd, Li) occur in the form of free ions and sulfate complexes both in the acid mine drainage and in contaminated water with pH of 2,9–3,4. In the river Yuzhnaya Vilva, below the site of mixing with mine affected water of the Bol. Gremyachaya river and further downstream, Fe and Al form only hydroxo complexes. For Ni and Pb, the predominant forms of migration are carbonate complexes. The presence of Li, Cd, Mn and Zn, in neutral river waters, mainly in form of free ions suggests that the principal mechanism of their precipitation is sorption on Fe and Al hydroxides and oxyhydroxides, as well as on clay minerals. Negative saturation indices for sulfate minerals, common for acid mine drainage, showed the instability of these mineral phases in neutral and slightly alkaline waters.

Keywords

• acid mine drainage
• physical-chemical modeling
• phreeqc
• migration forms of metals
• complex ions
• saturation index