Preparation of a novel self-floating and magnetic adsorbent and its enhanced separation of stable forms of Cd from oil and gas field drilling solid waste

Abstract

Drilling solid waste (DSW) is a typical byproduct of drilling operations in oil and gas fields. The characteristics of DSW are influenced by both the background soil properties and any added additives. Heavy metal (HM) contamination, particularly cadmium (Cd^2 +), poses a significant environmental challenge due to its toxicity to nearly all living organisms, including plants. DSW samples from the Tarim Oilfield, Xinjiang, China, were analyzed for HM content and its form distribution. The total Cd content was 48 mg/kg, with 41.1 % as unstable HM and 58.9 % as stable HM, exceeding the standard (DB 65/T 3997–2017). Conventional methods for remediating HM-contaminated soil, such as chemical washing and adsorption, are commonly used. X-ray diffraction (XRD) analysis revealed that the DSW has a crystalline carbonate structure, which is disrupted when treated with strong acids. Thus, in this study, a modified self-floating magnetic hollow glass microsphere (FHGM) was employed to remediate HM-contaminated DSW without the use of acidic washing agents. FHGM has a hollow structure, floats within 30 s, and possesses a saturation magnetization near 9, allowing for effective self-flotation and magnetic response, which facilitate its separation from the DSW. The results show that when the solution pH was 8, contact time was 240 min, the dosage of Fe₃O₄ was 0.6 g and the proportion of heavy metals to FHGM= 100:1, the removal efficiency of Cd from DSW using FHGM reached 78.8 %. Notably, the removal rate of HMs from the FeMn and OM fractions was high, indicating that FHGM enhances the migration of stable HMs. Furthermore, using centrifugal force at 17,232 x g, Cd and FHGM were effectively separated, with the material being recycled up to five times, FHGM still retain approximately 73.2 % of their initial adsorption capacities. Therefore, enhanced separation of stable-state Cd from DSW using FHGM presents an effective new treatment technology. The preparation of FHGM also means that it provides a new green and economic treatment method for the remediation of heavy metal pollution in the solid phase (not limited to DSW).