Comparison of potentially toxic metals leaching from weathered rocks at a closed mine site between laboratory columns and field observation

Abstract

Potentially toxic metals, such as Cu, Pb and Zn, are leached from weathered rocks at many closed mine sites due to the acidic environments and mineralogical modifications. The mobilized toxic metals may cause contamination of surrounding water bodies. In this study, both laboratory column experiments and field observations at a former mine located in the north of Japan were carried out to compare the leaching behavior of Cu, Pb and Zn. The thickness of the surface weathered rock was varied (10, 20 and 30 cm) for the columns experiments while porous cups for porewater sampling were set up at different depths for the field observations. Deionized water was added once a week over 75weeks to the columns to simulate rainfall while porewater was extracted by a vacuum pump in several sampling campaigns (over 18 months). Similar low pH and leaching behavior of potentially toxic metals were observed for column experiments and field observations. A moderate increase in concentration with depth was observed for Cu and Zn. However, no increase in concentration was observed for Pb. This suggests that the leaching of Cu and Zn is enhanced by the length of the flow pathway through the weathered rock layer while Pb concentration is restricted by the precipitation of insoluble Pb sulfate. Thus, the thickness of the weathered rock layer is an important parameter that should be taken into consideration to estimate the loads of some potentially toxic metals, which is important when designing remediation schemes.

Dynamics in leachate chemistry of Cu-Au tailings in response to biochar and woodchip amendments: a column leaching study

“…The specific objective was to determine the dynamics of leachate chemistry, indicated by acidity, salinity, common toxic elements and labile C, in neutral Cu-Au tailings with and without woodchips or biochar amendment under laboratory leaching conditions over 20 weeks. Column leaching has been used as a routine approach for assessing the geochemistry and toxicity of porous materials for many years [21][22][23], and it was particularly useful for mine wastes as supposed to better simulate field conditions than the batch methods [24][25][26][27]. Despite the significant deviation in leachate chemistry among replicate columns over time [23,28], column leaching was still thought to be a valuable approach to assess the medium-to long-term dynamics of mine tailings' toxicity and hydrogeochemistry.…”

Acid Mine Drainage Sources and Impact on Groundwater at the Osarizawa Mine, Japan

“…As many mines in Japan were still in operation up to the 2000s, it was possible to undertake studies in mine tunnels, including on the permeability of rock fractures [7] and the quality and quantity of AMD seepage from tunnel walls [8][9][10]. In the period since most of the mines were closed after the 2000s, further studies have been undertaken to reduce the burden of AMD treatment, which is expected to continue semi-permanently, such as studies of the formation and reaction of AMD with minerals [11], future forecast for the quality of AMD [12][13][14][15], adsorption and sedimentation of heavy metals from wastewater [16][17][18][19], mechanisms of AMD generation [20,21], and the effects of backfilling of excavated areas on the quantity and quality of AMD [22,23]. The findings of these studies have been incorporated into mine pollution control projects undertaken by the government, mine operators, and researchers with some success.…”