Effectiveness and mechanism of cyanide remediation from contaminated soils using thermally activated persulfate

Persulfate (PS)-based advanced oxidation processes have been frequently employed for contaminant remediation, but the effectiveness of PS oxidation for the elimination of cyanide-bearing contaminants from soil, and the underlying mechanisms, have rarely been explored. This study investigated the degradation of two iron-cyanide (Fe-CN) complexes (ferricyanide and ferrocyanide) with thermally activated PS via two remediation strategies, namely one-step oxidation (direct PS oxidation) and two-step oxidation (alkaline extraction followed by PS oxidation). The two-step oxidation process was more effective for the elimination of cyanide pollutants from soil, reaching >94% remediation efficiency for both Fe-CN complexes studied. The presence of dissolved soil components, especially soil organic matter, increased consumption of PS during the remediation process. A combined analysis based on electron paramagnetic resonance (EPR), free radical scavenging, and degradation product identification revealed that SO₄^- and HO were the principal reactive radicals responsible for Fe-CN degradation. Based on the determination of radical species and identification of decomposition products, a transformation pathway for Fe-CN complexes during thermally activated PS oxidation is proposed. Overall, this study demonstrates the effectiveness of the thermally activated PS oxidation technique for cyanide elimination from polluted soil. Further study is required to verify the feasibility of this method for field applications.