Effects of mixing granular iron with sand on the efficiency of methylene blue discoloration

Abstract

The influence of granular sand on the efficiency of metallic iron (Fe-0) for the discoloration of a methylene blue (MB) solution was investigated in the current work. The initial MB concentration was 10 mg L-1 and mass loadings within the range of 0-90 g L-1 for sand and 0-45 g L-1 for Fe-0 were applied. The batch reaction vessel used was a graduated essay tube containing 22.0 mL of the MB solution. Shaking intensities of 0 and 75.0 rpm were applied for experimental durations of 7,21 and 45 days. Results provide clear evidence that both Fe-0 and sand were independently effective for the discoloration of MB. However, the latter material was significantly less effective, recording 54.0% compared to 82.0% recorded for the Fe-0 after 45 days in experiment with 45.0 g L-1 of each material. Similarly, mixing 90 g L-1 sand with 45.0 g L-1 of Fe-0 depicted a MB discoloration efficacy of 72.0% demonstrating that the discoloration capability of the Fe-0 was significantly 'masked' by the presence of sand. This observation provides clear evidence to question the common approach of using adsorbents for contaminant accumulation in the vicinity of Fe-0 materials in order to facilitate chemical reduction by Fe-0. Further research is required to determine the relative affinity of different materials that can be used in Fe-0 mixtures for maximum contaminant removal efficacies. (C) 2012 Elsevier B.V. All rights reserved.