This work developed an environmentally-friendly soil remediation method based on BC and g-C₃N₄, and demonstrated the technical feasibility of remediating petroleum-contaminated soil with biochar/graphite carbon nitride (BC/g-C₃N₄). The synthesis of BC/g-C₃N₄ composites was used for the removal of TPH in soil via adsorption and photocatalysis. BC, g-C₃N₄, and BC/g-C₃N₄ have been characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface area analyzer (BET), FT-IR, and X-ray diffraction (XRD). BC/g-C₃N₄ facilitates the degradation due to reducing recombination and better electron-hole pair separation. BC, g-C₃N₄, and BC/g-C₃N₄ were tested for their adsorption and photocatalytic degradation capacities. Excellent and promising results are brought out by an apparent synergism between adsorption and photocatalysis. The optimum doping ratio of 1:3 between BC and g-C₃N₄ was determined by single-factor experiments. The removal rate of total petroleum hydrocarbons (TPH) by BC/g-C₃N₄ reached 54.5% by adding BC/g-C₃N₄ at a dosing rate of 0.08 g/g in a neutral soil with 10% moisture content, which was 2.12 and 1.95 times of BC and g-C₃N₄, respectively. The removal process of TPH by BC/g-C₃N₄ conformed to the pseudo-second-order kinetic model. In addition, the removal rates of different petroleum components in soil were analyzed in terms of gas chromatography–mass spectrometry (GC-MS), and the removal rates of nC₁₃-nC₃₅ were above 90% with the contaminated soil treated by BC/g-C₃N₄. The radical scavenger experiments indicated that superoxide radical played the major role in the photocatalytic degradation of TPH. This work definitely demonstrates that the BC/g-C₃N₄ composites have great potential for application in the remediation of organic pollutant contaminated soil.

Oily sludge (OS) contains a large number of hazardous materials, and froth flotation can achieve oil recovery and non-hazardous disposal of OS simultaneously. The influence of flotation parameters on OS treatment and the flotation mechanism were studied. OS samples were taken from Shengli Oilfield in May 2017 (OSS) and May 2020 (OST), respectively. Results showed that Na₂SiO₃ was the suitable flotation reagent treating OSS and OST, which could reduce the viscosity between oil and solids. Increasing flotation time, impeller speed and the ratio of liquid to OS could enhance the pulp shear effect, facilitate the formation of bubble and reduce pulp viscosity, respectively. Under the optimized parameters, the oil content of OST residue could be reduced to 1.2%, and that of OSS could be reduced to 0.6% because of OSS with low heavy oil components and wide solid particle size distribution. Orthogonal experimental results showed that the impeller speed was the most significant factor of all parameters for OSS and OST, and it could produce shear force to decrease the intensity of C-H bonds and destabilize the OS. The oil content of residue could be reduced effectively in the temperature range of 24–45 °C under the action of high impeller speed.