Chemical species of chromatite of an industrial landfi ll in the León valley, Guanajuato, Mexico

Abstract

Chromium is a commonly identifi ed contaminant in soils and groundwater and is widely used in industries. Disposal of industrial solid wastes can cause health and environmental risks due to the leaching and seepage of Cr(VI) from soil to groundwater. In order to improve remediation strategies and make better predictions about the mobility of contaminants, it is critical to understand the time-dependent metal sorption behavior on soil, as well as the mechanism of the sorption reactions, and the dominant chemical species. This study demonstrates that interfacial reactions (e.g., adsorption, desorption, oxidation or reduction) between chromium and minerals play an important role in the spreading of chromium, and could present preferential pathways for chromium mobility in the subsurface environment. Soil samples were collected in a landfi ll (source) of chromium wastes and their morphology and predominant chemical species were determined. Column experiments were performed on contaminated silty-clayey sand, using deionized water as eluent. It was found in this study that, after 72 h, more than 80% of sorbed chromium was eluted with deionized water, and the total chromium content in the leachate were higher than the permissible limits for human consumption established by Mexican offi cial norms (0.05 mg/L). The Cr(VI) removal effi ciency decreased signifi cantly with time and it was independent of the initial pH, indicating that Cr(VI) was poorly adsorbed. UV-Vis analysis indicated that the oxidation state of chromium was Cr(VI). DRX analysis led to the conclusion that CaCrO4 (chromatite), is the main mineral species of Cr(VI), and is predominant in the range of pH from 7 to 8.5. An important effect is that the sorption presented to the pore scale can have consequences on the regional scale because it can retard the mobility of this pollutant during the dispersion process.