Abstract
This manuscript focuses on the leaching of geogenic arsenic (As) from shale rock at different temperatures. In Japan, the utilisation of geogenic contaminated soils and rocks for construction such as in embankment is much encouraged. Therefore, when applying thermally active geo-systems such as thermal energy storage and ground-source heat pump, which are associated with ground temperature changes, we need to know its impact on the leaching behaviour of such contaminated geomaterials. In this study, the leaching of chemicals from an excavated shale rock containing geogenic As was assessed using a shaking and non-shaking batch test. In those experiments, different temperatures up to 40 ºC and contact times ranging from 6–360 h were employed. Overall, it was found out that more As was leached with elevated temperatures and its concentration was notably higher under the non-shaking condition. Further, under the non-shaking condition, its concentration was highest at 40 ºC with contact time of 360 h, whereby ca. 0.06 mg/L As was leached, which is 6 times the permissible limit of 0.01 mg/L in Japan.
Highlights
In Japan, soils and rocks excavated at construction sites are frequently reported to be contaminated with geogenic heavy metals and metalloids such as arsenic (As), fluorine (F), lead (Pb), etc.; in relatively low concentrations, due to their geologic histories [1]
The applicability of the findings in the field remains to be a challenge, because they do not fully simulate the field conditions of soil and groundwater [3], nor account for the ground temperature changes caused by the fluctuations in the daily and seasonal temperature, which are observed in shallow ground [4, 5] or in an embankment [6], as shown in Fig. 1, where the soils and rocks contaminated with geogenic heavy metals are utilised [7]
Shale rock, which was excavated in a shield-tunneling project in Japan, was used after crushing it with a jaw crusher to pass through a 2 mm-opening screen
Summary
In Japan, soils and rocks excavated at construction sites are frequently reported to be contaminated with geogenic heavy metals and metalloids (hereon heavy metals) such as arsenic (As), fluorine (F), lead (Pb), etc.; in relatively low concentrations, due to their geologic histories [1]. Leaching of these constituents in concentrations higher than the permissible limits regulated under the Japanese Soil Contamination Countermeasures Law (SCCL) often occurs due to contact with water and/or air [2].
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