Study on feasibility and mechanism of the subcritical oxidation of waste drilling mud

Abstract

Waste drilling mud (WDM) is a hazardous and refractory waste generated during the exploration of oil and gas fields. WDM has high chemical oxygen demand (COD) and high salinity, making it difficult to handle WDM. In this study, WDM was treated under subcritical conditions without and with hydrogen peroxide (H2O2) or potassium persulfate (K2S2O8). The removal efficiency of CODCr (COD was measured by potassium dichromate method) reached 98.20% ~.99.6%. The contents of twelve heavy metals in liquid products were lower than the emission limit except for arsenic. But arsenic concentration decreased by 65.25%. Those detected heavy metals were almost completely removed into solid products. In addition, after introducing K2S2O8 as an oxidant, the removal efficiency of total organic carbon (TOC) in the liquid increased by 58.34% and 13.43% compared with additive-free and H2O2, respectively. The removal efficiency of total nitrogen (TN) was the same as above, also increased by 70% and 59.26%, respectively. The results showed that the introduction of K2S2O8 was more effective in treating WDM under subcritical conditions. Moreover, the introduction of K2S2O8 can generate sulfate ions. Sulfate ions can form stable metal salts with lead and barium, which was conducive to the immobilization of heavy metals. This study provides a new way for the harmless treatment of WDM, and also further expands the application scope of subcritical oxidation.