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

K Miyajima,C Noubactep

doi:10.1016/j.cej.2012.06.069

Abstract

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 10mgL−1 and mass loadings within the range of 0–90gL−1 for sand and 0–45gL−1 for Fe0 were applied. The batch reaction vessel used was a graduated essay tube containing 22.0mL of the MB solution. Shaking intensities of 0 and 75.0rpm were applied for experimental durations of 7, 21 and 45days. 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 45days in experiment with 45.0gL−1 of each material. Similarly, mixing 90gL−1 sand with 45.0gL−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.

Highlights

Metallic iron (Fe0) has been demonstrated in numerous studies to represent the best available material for subsurface permeable reactive barriers [1,2,3,4,5]
Since Fe0 alone (e.g. Fe0/H2O system) is efficient in decolourising aqueous methylene blue (MB) [40,41], the effects of sand on MB discoloration in the presence of Fe0 may be summarized in two hypothesis
MB discoloration by Fe0 is not affected by the presence of sand (Assumption 1)

Summary

Introduction

Metallic iron (Fe0) has been demonstrated in numerous studies to represent the best available material for subsurface permeable reactive barriers [1,2,3,4,5]. Song et al [14] discussed the effect of mixing Fe0 and sand on the extent of CrVI removal in batch studies, using experimental results from Kim et al [12]. The efficiency of iron-coated sand filters suggests that in the experiments of Kim et al [12], in-situ generated iron oxides were adsorbed onto sand and subsequently removed CrVI or CrIII. Varlikli et al [40] tested the suitability of Sahara desert sand (SaDeS) for removing organic (cationic and anionic) dyes from aqueous solutions They observed that MB demonstrated the strongest affinity for. SaDeS with an adsorption capacity of 11.98 mg g-1 (initial MB concentration: 11.2 mg L-1)

Background of the experimental methodology

Materials and methods

Non-disturbed batch experiments

Shaken batch experiments

Results and Discussion