Chronosequence of Technosols at the Peña Colorada mine in Colima, Mexico: a short-term remediation alternative

Purpose The objective of this study was to examine the pedogenetic evolution occurring in technic hard materials from an iron mine through the characterization of a chronosequence of 0-, 15-, and 40-year-old Technosols and an older natural soil. Materials and methods Samples were taken from Technosols of different ages (0, 15, 40 years) which had developed after a layer of crushed conglomerate was placed over the top of the mine tailings, as well as from a natural soil developed on conglomerate which represented the most advanced evolutionary stage in the chronosequence. Analyses of soil micromorphological, physical, chemical, and mineralogical properties included grain size distribution; pH; electric conductivity (EC); organic matter; exchangeable bases; N-NO 3 ; available P, Fe, Zn, Mn, Cu, and B micronutrients; and clay mineralogy (by X-ray diffraction). Results Results showed that 15- and 40-year-old Technosols already displayed an advanced structural development and nutrient contents comparable to those in the studied natural soil. Such a rapid pedogenesis was due to the high clay content found within the conglomerates which can be easily incorporated into the soil and reordered within the soil groundmass. The tailings were characterized by a neutral pH (6.9) and a high EC (0.188 S m −1 ), which decreased in the upper horizons of the 15-year-old Technosols, conforming thionic horizons. Generally, similar clay mineral assemblages dominated by smectite were observed in the conglomerate, the natural soil, and the 40-year-old Technosol. Conclusion This study confirms the possibility of rehabilitating iron mine tailings with a layer of conglomerate, which mitigates against the adverse effects of mining. Results showed that the conglomerate can easily evolve into a soil within a relatively short period. However, the conglomerate cover should be thick enough to avoid acidification of the topsoil.