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

The influence of granular sand on the efficiency of metallic iron (Fe0) 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 to 90 g L-1 for sand and 0 to 45 g L-1 for Fe0 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 Fe0 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 Fe0 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 Fe0 depicted a MB discoloration efficacy of 72.0 % demonstrating that the discoloration capability of the Fe0 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 Fe0 materials in order to facilitate chemical reduction by Fe0. Further research is required to determine the relative affinity of different materials that can be used in Fe0 mixtures for maximum contaminant removal efficacies