Remediation of diesel contaminated soil by using activated persulfate with Fe3O4 magnetic nanoparticles: effect and mechanisms

Abstract

In this study, Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) were assessed for their ability to enhance the activity of persulfate (PS). Various controlling factors including PS dosages, initial pH, water-soil ratio, ratio of Fe²⁺, and Fe₃O₄ MNPs to PS were considered in both the Fe²⁺/PS system and the Fe₃O₄ MNPs/PS system. Results showed that the Fe₃O₄ MNP-activated PS system exhibited high processing efficiency owing to the gradual release of Fe²⁺. This process occurred in a wide pH range (5-11), attributed to the synergistic action of sulfate radicals (SO₄^-·) and hydroxyl radicals (OH·) under alkaline conditions, effectively mitigating soil acidification. The ratio of Fe₃O₄ MNPs to PS and water-soil ratio significantly influenced the degradation rate with the highest petroleum hydrocarbon degradation rate exceeding 80% (82.31%). This rate was 3.1% higher than that achieved by the Fe²⁺/PS system under specific conditions: PS dosage of 0.05 mol/L, Fe₃O₄ MNPs to PS ratio of 1:10, water-soil ratio of 2:1, and initial pH of 11. Meanwhile, oxidant consumption in the Fe₃O₄ MNPs/PS system was halved compared to the Fe²⁺/PS system due to the slow release of Fe²⁺ and less ineffective consumption of SO₄^-·. Mechanistically, the possible degradation process was divided into three parts: the initial chain reaction, the proliferating chain reaction, and the terminating chain reaction. The introduction of Fe₃O₄ MNPs accelerated the degradation rate of pentadecane, heneicosane, eicosane, tritetracontane, and 9-methylnonadecane.

Keywords: Fe3O4 MNPs; Persulfate; Petroleum hydrocarbon; Soil remediation.