REMEDIATION OF CHLORPYRIFOS CONTAMINATED SOILS BY LABORATORY SYNTHESIZED ZERO-VALENT NANO IRON (ZVNI) PARTICLES: EFFECT OF pH AND ALUMINIUM SALTS

Abstract

Degradation of the insecticide chlorpyrifos in contaminated soils was investigated using laboratory synthesized zero-valent nano iron (ZVNI)
particles. The synthesized ZVNI particles were determined as nano scale by scanning electron microscopic (SEM) and transmission electron
microscopic (TEM) analysis. The zero valent state (Fe0) of iron was confirmed by EDAX analysis and the morphology of the ZVNI particles was
studied by XRD. Batch experiments were conducted by treating the chlorpyrifos contaminated soil with ZVNI, our results indicate that 90% of
chlorpyrifos was degraded after 10 days of incubation. Only 32% degradation was observed with micro zero valent iron(mZVI) and no considerable
degradation was attained without ZVNI. The degradation of chlorpyrifos has followed the first-order kinetics with a rate constant and a half-life of
0.245 day-1 and 2.82 days respectively. Degradation was monitored at two different pH values i.e. pH 10 and pH 4. Chlorpyrifos degradation rate
constant was increased as the pH decreases from 10 to 4. The corresponding rate constant and half-lives were 0.43day-1 and 1.57days for pH 4,
0.18day-1 and 3.65days for pH 10. In addition, an attempt was made by augmenting Al2(SO4)3 with ZVNI and it was found that the degradation rate
of chlorpyrifos was greatly enhanced and the rate constant was rapidly increased from 0.245day-1 to 0.60day-1. Hydrolysis and stepwise dechlorination pathway of chlorpyrifos with ZVNI was the dominant reaction.