Binary Exchanges of Calcium, Magnesium, and Potassium on Thermally Desorbed Soil

Abstract

Thermal desorption (TD) remediates hydrocarbon-contaminated soil by heating the soil (200-500°C) to volatilize the hydrocarbons, effectively removing the contaminant from the soil. Knowledge of the effects of TD on remediated soil for agricultural crop production are limited, but cation exchange capacity (CEC) and selectivity for cations can be good indicators of plant productivity potential. In this study, the CEC and selectivity of cations of TD-treated and untreated topsoil and subsoil were compared using binary exchange measurements of Ca-Mg, Ca-K, and Mg-K. The tested soils were illite and smectite-dominated Mollisols that were collected near an active TD-remediation site in northwest North Dakota. Vanselow selectivity coefficients and Gibb's free energies (ΔG ex ) were computed. For all three exchanges, significant differences were observed in ΔG ex between the untreated and TD-treated topsoil. In the Ca-Mg exchange, both the untreated and TD-treated topsoil preferred Ca, whereas both TD-treated and untreated subsoils preferred Mg. For the Ca-K and Mg-K exchanges, all treatments preferred K. Cation exchange capacity values were significantly greater in the untreated subsoil of the Ca-Mg exchange and the untreated topsoil and subsoil of the Ca-K exchange than in the TD-treated soils. The differences may be caused by contrasts in soil organic C and mineralogy. Although CEC and ΔG ex differed between untreated and TD-treated soils, the cation selectivities were not altered, suggesting that the magnitude of the differences may not require alternative fertility management to retain previous soil productivity. Core Ideas• Thermal desorption is used to remediate contaminated soil.• Thermal desorption can alter Gibb's free energies.• Thermal desorption at 350°C did not change cation selectivity.

Oil spill soil remediation using thermal desorption: Project synthesis and outcomes

“…TD consistently reduced TPH levels below the 500 mg kg −1 threshold (O'Brien, DeSutter, Ritter et al, 2017), and TPH values continued to reduce over time due to natural degradation (O'Brien et al, 2019) at a rate similar to Phillips et al (2009), with half-lives of about 500 days. In addition to regular testing completed by the remediation company, 24 samples were taken each year within the TD treated plots, and none of those samples exceeded 308 mg kg −1 .…”

“…Due to these limitations, we explored the possibility of blending TDtreated soil with non-contaminated topsoil excavated from nearby the spill site. The blending process was completed by combining excavator bucket loads (0.6 m 3 ) of TD-treated material with disturbed, non-contaminated topsoil and passing them through two material screeners before being staged for replacement via a material stacker (O'Brien, DeSutter, Ritter et al, 2017). Importantly, blending the soil is not a remediation method, as diluting the contaminant does not constitute blending-nor did it speed the rate of TPH reduction (O'Brien et al, 2019).…”

“…Rather, it is a reclamation strategy to reintroduce soil organic matter and encourage recovery of microbial populations. The soil blending method was very effective at creating a uniform product (O'Brien, DeSutter, Ritter et al, 2017), and the blended soil had consistent intermediate values of a suite of soil physical, chemical, and biological properties com-pared to two source materials. These improved characteristics compared to TD-treated soil accounted for the recovery of plant growth potentials and microbial reestablishment among the treatments (Bartsch et al, 2022;.…”

“…The relatively low heating temperature did not alter soil chemistry greatly, with a slight increase in pH (O'Brien, DeSutter, Ritter et al., 2017). However, the slight decreases in cation exchange capacity (Ritter et al., 2017) and phosphorus sorption (Croat, DeSutter et al., 2020) suggest that alternate fertility plans may be required.…”

Daytime Surface Energy Fluxes over Soil Material Remediated Using Thermal Desorption

“…While thermal desorption is a fast, reliable method to reduce PHC concentrations, it does affect many soil properties. Following treatment, soils of all textures may have altered biological communities (Cebron et al, 2011), increased soil pH (Sierra et al, 2016), reduced cation exchange capacity (Ritter et al, 2017), decreased soil organic matter (SOM), and increased saturated hydraulic conductivity (O’Brien et al, 2016); all of these consequences may affect the viability of thermal desorption–treated soils for use in agronomic systems. Notably, the magnitude of effects increases as heating temperature increases (O’Brien et al, 2018b), such that textural shifts can occur when heated above 500°C.…”