Research on the treatment technology of oil-containing sludge and elution waste liquid from hot washing in a heterogeneous mixed system

The oil-containing sludge produced in the process of oil and gas field extraction is high in yield, difficult to degrade, and harmful to the environment, and in actual practice, it is often treated by the thermal washing method. However, there are problems such as low efficiency of chemical cleaning agents, high price, and secondary pollution. Based on the conventional thermal cleaning technology, we designed a new method to remove oil from oil-containing sludge and elution waste liquid by using inorganic solid particles as heterogeneous cleaning agents and adsorbents, respectively, and investigated the adsorption mechanism of elution waste liquid. The results showed that under the conditions of hot washing temperature of 40 ℃, stirring intensity of 200 r/min, stirring time of 30 min, liquid-solid ratio of 10∶1, and NaCl addition of 0.02 g, the oil content in the sludge could be reduced from 25.9% to 3.0%. This was achieved under the optimal detergent ratio of petroleum ether∶rhamnolipids∶g-C₃N₄ =2 mL∶1.25 g/L∶0.02 g. Meanwhile, the TiO₂ dosage was 400 mg/L, and the oil removal rate in the elution waste liquid reached 96.42%. The results of adsorption kinetics and adsorption isotherms showed that the liquid film diffusion rate in the elution waste liquid was greater than the intra-particle diffusion rate, and the adsorption was physical adsorption and multilayer adsorption. The study provides theoretical guidance for the separation of oil from oil-containing sludge and elution waste liquid.