Pyrolytic Remediation of Oil-Contaminated Soils: Reaction Mechanisms, Soil Changes, and Implications for Treated Soil Fertility

Abstract

Pyrolysis of hydrocarbon-contaminated soils offers the potential for rapid remediation without destroying soil fertility. Here we elucidate the fundamental mechanisms of pyrolytic treatment and advance understanding of the surface properties of pyrolyzed soils. Using thermogravimetry and evolved gas analysis, we identified the two stages of pyrolytic remediation. Desorption of light hydrocarbons is the dominant process for temperatures between 150 and 350 °C. Pyrolysis reactions dominate in the 400−500 °C range releasing gaseous products (hydrogen, methane, higher alkanes, and olefins) and forming a solid char. XPS analysis and partial combustion revealed that the char forms a layer coating the particles of treated soils. Since pyrolysis can effectively reduce the TPH of contaminated soils at temperatures below 500 °C, it avoids carbonate decomposition reactions that may lead to large soil pH increases and severe loss of fertility. This is a significant potential advantage over competing thermal processes that expose contaminated soil to temperatures above 500 °C.

Kinetic Study of the Pyrolytic Treatment of Petroleum-Contaminated Soils

“…As shown in our earlier publication, 22 pyrolytic remediation of petroleum-contaminated soils involves two distinct processes. Thermal desorption (evaporation) of lighter hydrocarbons is the dominant process as contaminated soils A and B are heated between 150 and 350 °C.…”

“…These weight losses will be quantified first so that they can be decoupled from losses due to either hydrocarbon desorption or pyrolysis. 22 Soils A and B Exhibit Different Weight Loss Patterns During Heating. Figure 1 presents the thermogravimetry (TG) and differential thermogravimetry (DTG) curves describing the weight losses and the rate of weight losses respectively for three TGA runs with clean soil A and another three runs with clean soil B.…”

“…Hydrocarbon desorption was found to be the main process at temperatures below 350 °C, while thermal cracking and pyrolysis reactions dominate in the 350−500 °C range producing hydrogen, light hydrocarbons, and a solid char that coats the particles of treated soils. 22 Li and co-workers 23 also used batch pyrolysis reactors to show almost complete TPH removal after 30 min at 500 °C and 50% recovery of the carbon present in the contaminated soil. Partial oil recovery is an additional potential benefit of pyrolysis that can lower its energy requirements.…”

Pyrolytic Remediation and Ecotoxicity Assessment of Fuel-Oil-Contaminated Soil

“…Many studies are conducting pyrolysis studies by artificially mixing crude oil into the soil [ 17 , 18 , 19 ]. Contaminated sites have different soil properties, moisture content, and pollutant concentrations from a lab environment; however, studies applying pyrolysis to the field samples have been limited.…”

Remediation Effect of Biomass Amendment on the Physical-Chemical Performance and Sustainable Utilization of Sandy Soil

“…Focusing on farmland soil in mining areas, Soltaninejad et al [15] characterized the physical-chemical properties of the biomass amendment developed from rice straw through elemental analysis, Fourier infrared spectroscopy, and specific surface area analysis, and verified that the prepared amendment can stabilize heavy metals Cu, Cd, As, and Zn in the soil through biomass amendment-soil culture experiment in simulated natural environment. Vidonish et al [16] tackled three modified biomass amendments compounded with ZnO, MnO and chitosan, respectively, and extracted the heavy metal distribution on each amendment under physical, chemical, and other types of adsorption; on this basis, the adsorption process was described realistically by setting up a Langmuir isotherm adsorption model and a quasi-second-order kinetic model, and the different effects between the amendments were verified in terms of the complexation of oxidation functional groups, the adsorption effect of mineral precipitation, and bio-availability.…”