Effects of operational parameters and common ions on the reduction of 2,4-dinitrotoluene by scrap copper-modified cast iron
2015
Fan, Jin-Hong | Wang, Hong-Wu
Scrap Cu-modified cast iron (CMCI) is a potent material for the reduction of 2,4-dinitrotoluene (2,4-DNT) by a surface-mediated reaction. However, the effects of operational parameters and common ions on its reduction and final rate are unknown. Results show that the 2,4-DNT reduction was significantly affected by Cu:Fe mass ratio and the optimum m(Cu:Fe) was 0.25 %. The slight pH-dependent trend of 2,4-DNT reduction by CMCI was observed at pH 3 to 11, and the maximum end product, 2,4-diaminotoluene (2,4-DAT), was generated at pH 7. Dissolved oxygen (DO) in the water reduced the 2,4-DNT degradation and the formation of 2,4-DAT. CMCI effectively treated high concentrations of 2,4-DNT (60 to 150 mg L⁻¹). In addition, varying the concentration of (NH₄)₂SO₄ from 0.001 to 0.1 mol L⁻¹ improved the efficiency of the reduction process. The green rust-like corrosion products (GR-SO₄ ²⁻) were also effective for 2,4-DNT reduction, in which Na₂CO₃ (0.01 to 0.2 mol L⁻¹) significantly inhibited this reduction. The repeated-use efficiency of CMCI was also inhibited. Moreover, 2,4-DNT and its products, such as 4A2NT, 2A4NT, and 2,4-DAT, produced mass imbalance (<35 %). Hydrolysis of Fe³⁺ and CO₃ ²⁻ leading to the generation of Fe(OH)₃ and conversion to FeOOH that precipitated on the surface and strongly adsorbed the products of reduction caused the inhibition of CO₃ ²⁻. The 2,4-DNT reduction by CMCI could be described by pseudo-first-order kinetics. The operational conditions and common ions affected the 2,4-DNT reduction and its products by enhancing the corrosion of iron or accumulating a passive oxide film on the reactivity sites.
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