Comparison of zero-valent iron and iron oxide nanoparticle stabilized alkyl polyglucoside phosphate foams for remediation of diesel-contaminated soils.

Stable surfactant foam might play a vital role in the effective remediation of diesel oil contaminated soil-a major environmental hazard. This paper, first of its kind, is reporting the remediation of diesel-contaminated desert soil, coastal soil and clay soil by aqueous alkylpolyglucoside phosphate (APG-Ph) surfactant foams stabilized by Fe0 and Fe3O4 nanoparticles. Zero-valent iron (Fe0, ∼28 nm) and iron oxide (Fe3O4, ∼20 nm) nanoparticles are synthesized by liquid-phase reduction and precipitation methods, respectively. The effect of these nanoparticles on foamability, foam stability, surface tension and remediation of diesel-contaminated soils are examined at various concentrations (volume %) of alkylpolyglucoside phosphate (APG-Ph) surfactant and nanoparticles (mg/l). The maximum values of foamability and foam stability recorded for 0.1 vol % APG-Ph foam stabilized by 3.5 mg/l Fe0 are 108.3 and 110.4 mL, respectively. At the same conditions, the Fe3O4 results in 99.4 and 87.5 mL, respectively, depicting the better performance of Fe0. Reduction in surface tension of 0.1 vol % APG-Ph solution (50.75 mN/m) with the addition of 3.5 mg/l Fe0 (9.51 mN/m) and Fe3O4 (19.45 mN/m) nanoparticle is observed. Both the nanoparticles enhance remediation. The foam formed with 0.1 vol % APG-Ph and stabilized by 3.5 mg/l Fe0 shows the maximum diesel removal efficiency of 95.3, 94.6, and 57.5% for coastal soil, desert soil and clay soil, respectively. On the other hand, Fe3O4 (3.5 mg/l) stabilized APG-Ph foam of the same concentration shows merely 76.0, 79.6 and 51.6% diesel removal efficiency for coastal soil, desert soil, and clay soil, respectively. The rate of diesel removal by zero-valent iron and iron oxide nanoparticle stabilized foams are found to be well described by the first order kinetic model. Higher foamability, foam stability, and reducing capacity accompanying lower surface tension, compared to those of the Fe3O4 nanoparticle stabilized foam, could explain higher diesel removal efficiency of the Fe0 nanoparticle stabilized foam.