Influence of water-rock interaction on the pH and heavy metals content of groundwater during in-situ oil shale exploitation

In this paper, step-by-step groundwater-rock interaction experiments were performed to investigate the migration of heavy metals (Pb, Cr, Zn) into the water and the pH change of oil shale and oil shale ash aqueous solutions (hereinafter OS solution and OSA solution, respectively) during the in-situ production of oil shale. For geochemical calculations the PHREEQC software was used to simulate pH variation in the aqueous solutions at different temperatures and CO2 partial pressures (PCO2). The pH of most solutions was between 6.95 and 7.49 and changed significantly with increasing reaction time. The simulated data were closest to the experimental results at PCO2 = 10 –2. A clear effect of reaction temperature and pH on the Pb content in the aqueous solutions was observed. The Pb content in the OSA solution was 0.36–0.47 μg/L, being higher than that in the OS solution (0.13–0.26 μg/L). The Cr content in OS and OSA solutions was from 0.55 to 0.70 μg/L. The Zn content in the OS solution was 1.17–3.61 μg/L, being significantly influenced by reaction temperature.