Contamination of groundwater by organic pollutants leached from in-situ spent shale
- Univ. of California, Berkeley, CA (United States)
The potential for contamination of groundwater by organic pollutants leached from in-situ spent shale was studied in a series of laboratory leaching experiments. Both batch-mode and continuous-flow column experiments were conducted to study the leaching phenomenon. Experimental variables included retorting characteristics of spent shale, leaching time, initial quality of leach water, temperature of leach water, and particle size of spent shale. Several unique samples of spent shale were examined during the eaching experiments, including spent shale samples produced during combustion retorting, inert gas retorting, and combustion retorting employing recycle gas. The solid-phase organic carbon content of spent shale samples ranged from 0.2 to 3.9 percent by weight. Leachate derived from the batch-mode experiments was analyzed for organic carbon, organic nitrogen, phenols, and acid/base/netral fractions. The highest levels of organic carbon were detected in leachate derived from spent shale produced during either inert gas retorting or combstion retorting using recycle gas. The highest levels of phenols were observed in leachate obtained from spent shale produced during inert gas retorting; significant levels of organic nitrogen were also detected in various leachate samples. The most predominant organic fraction measured in leachate samples was the neutral fraction associated with spent shale produced during inert gas retorting. Batch-mode experimental results describing equilibrium conditions were analyzed according to the Freundlich and langmuir isotherm models. Those models were found to be appropriate for describing equilibrium relationships between leachate and spent shale produced during inert gas retorting. To a somewhat lesser extent, these same models were found to be appropriate for modeling equilibrium relationships involving combustion-retorted spent shale. A kinetic analysis of results derived from the continuous-flow column experiments was conducted in an attempt to identify a rate-controlling mass transfer mechanism. Internal diffusion appeared to be the most likely rate-limiting mechanism for leaching from combustion-retorted spent shale. In contrast, no single mass transfer mechanism appeared to control the leaching phenomenon for inert gas-retorted spent shale over the entire range of leaching times examined. The results presented here suggest that groundwater resources in regions of potential in-situ development may be significantly degraded in quality as a consequence of leached organic contaminants. Overall, the leaching phenomenon represents a potentially chronic problem which may preclude beneficial uses of groundwater for decades.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-05CH11231; W-7405-ENG-48
- OSTI ID:
- 1064003
- Report Number(s):
- LBL--10526
- Country of Publication:
- United States
- Language:
- English
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