Insight into Washing of Wet and Dry Crude Oil‐Contaminated Soil

Two types of artificial oil‐contaminated soils (OCS) are prepared upon mixing sandy soil with water and crude oil in different proportion. OCS‐I represents the contaminated dry soil and OCS‐II the contaminated wet soil. Soil and crude oil are characterized through infrared spectroscopy and zeta potential analysis, and the OCS microstructure model has been discussed. It is speculated that the polarity petroleum components (e.g., non‐hydrocarbons) are higher in the oil layer of the neighboring soils, forming a “polarity bottom layer.” In OCS‐I, the “polarity bottom layer” is tightly adhered to soil and exhibits poor mobility. This layer is difficult to separate from soil through washing, thereby resulting in a low oil removal rate (ORR). In OCS‐II, the petroleum and soil are separated by a water film with high liquidity. During washing, the “polarity bottom layer” is easily separable from soil, thereby resulting in a high removal rate of polarity component in crude oil and high ORR as well. Based on the results of this study, it could be concluded that OCS‐I is much more difficult to be washed than OCS‐II when these two types of soils contain relatively same amount of substance content (oil, water, and other crude oil groups). The analysis of the soil–petroleum interface is helpful to understand the mechanism of washing wet and dry crude oil‐contaminated soil. For dry soil, the non‐hydrocarbons in petroleum are tightly adhered to soil resulting in lower oil removal. However, for wet oil‐contaminated soil, there is a water film between soil and petroleum resulting in high petroleum removal.