(248a) Natural and Metal-Impregnated Clays Catalyze the Pyrolytic Treatment of Crude-Oil Contaminated Soils

Environmental pollution by petroleum hydrocarbons poses serious threats to public and ecosystem health. About 98% of crude oil spills occur on land and exposure to terrestrial spills correlate to cancer, preterm births, neurocognitive deficits, and other public health concerns that can span across generations due to genetic or birth defects. Amongst the constituents of crude oil, polycyclic aromatic hydrocarbons (PAHs) are of particular concern since they are probable carcinogens and persist in the environment due to their recalcitrance to microbial degradation.

Soils impacted by relatively high concentrations of petroleum hydrocarbons are often remediated by thermal technologies that, while fast and effective, have high energy demands and destroy the fertility of treated soils [1]. Pyrolytic treatment of soils contaminated with crude oils is an alternative approach that offers significant advantages over other thermal methods. It can efficiently remove total petroleum hydrocarbons (TPH) to meet regulatory standards and detoxify the soil by removing toxic pollutants like PAHs with lower energy requirements than incineration [2,3]. Since it is carried out at lower temperatures than other methods, pyrolytic treatment can preserve soil components responsible for water and nutrient retention since restores (at least partially) the fertility of the soil, enhancing its value for ecosystem restoration and re-greening efforts [3,4].

In this study we show that clays impregnated with non-toxic transition metals (iron or copper) can be used as an amendment to decrease the required pyrolytic treatment temperature and time. Amending a weathered crude-oil contaminated soil with natural bentonite or bentonite modified with ion-exchanged Fe or Cu, achieved almost complete (95 to 99%) removal of residual total petroleum hydrocarbons (TPH) at a pyrolysis temperature of 370°C with 15-min treatment time. More importantly, pyrolytic treatment of amended soils at the unprecedentedly low pyrolysis temperature of 300°C achieved 87% TPH removal with Cu-bentonite and 93% with Fe-bentonite. Using TG-MS experimental data, we showed that the presence of transition metals significantly lowered the onset temperature of pyrolysis reactions. These results strongly support our hypothesis about the catalytic role of the transition metals and encourage further work to elucidate the reaction mechanisms and inform the design of optimized remediation processes. To determine the feasibility of this promising pyro-catalytic soil remediation approach, techno-economic analyses must be carried out to evaluate tradeoffs of increasing treated soil volume though modified clay amendments versus decreasing energy requirements and contact time.

References:

1. J. E. Vidonish, K. Zygourakis, et al, “Thermal Treatment of Hydrocarbon-Impacted Soils: A Review of Technology Innovation for Sustainable Remediation,” Engineering, 2, 426–437 (2016).

2. Y. Gao and K. Zygourakis, “Kinetic Study of the Pyrolytic Treatment of Petroleum Contaminated Soils,” Ind. Eng. Chem. Res., 58, 10829–10843 (2019)

3. Y. Gao, P. Dias Da Silva, P. J. J. Alvarez, and K. Zygourakis, “Integrating Thermal Analysis and Reaction Modeling for Rational Design of Pyrolytic Processes to Remediate Soils Contaminated with Heavy Crude Oil,” Environ. Sci. Technol., 55, 11987–11996 (2021).

4. W. Song, J. E. Vidonish, et al., “Pilot-Scale Pyrolytic Remediation of Crude-Oil-Contaminated Soil in a Continuously-Fed Reactor: Treatment Intensity Trade-Offs,” Environ. Sci. Technol., 53, 2045–2053 (2019).