Abstract
Oil sludges are multi-component technogenic formations generated during the extraction, transportation, and refining of crude oil, the accumulation of which is associated with significant environmental risks. At the same time, these wastes can be considered as a prospective secondary raw material containing a number of rare and rare-earth elements. The aim of this study is to assess oil sludges generated at oil refineries in the Republic of Kazakhstan (Shymkent, Atyrau, and Pavlodar refineries) as a potential source for the recovery of rare and rare-earth elements based on a review of the literature, as well as to summarize information on the composition and properties of oil sludges. Analysis of the literature indicates the absence of unified technologies worldwide for the extraction and concentration of rare and rare-earth elements from petroleum processing wastes, including oil sludges. Furthermore, there is a lack of systematic monitoring data on the content of these elements in crude oil and its processed products. The study considers modern instrumental methods potentially applicable for investigating the elemental composition of oil sludges, such as neutron activation analysis, inductively coupled plasma mass spectrometry (ICP-MS), and X-ray fluorescence (XRF) analysis. Oil sludges are identified as complex technogenic objects that, according to the literature, may contain molybdenum, vanadium, tungsten, zirconium, rhenium, and rare-earth elements. The rationale for developing integrated approaches for their processing using thermal, chemical, and hydrometallurgical methods, including leaching, precipitation, extraction, and ion-exchange sorption, is provided. The findings allow considering oil sludges not only as a waste disposal object but also as a potential source of valuable components in conditions of growing demand for rare and rare-earth metals.