Characterizing the impact of pyrite addition on the efficiency of Fe0/H2O systems

Rui Hu,Xuesong Cui,Minhui Xiao,Chicgoua Noubactep,Willis Gwenzi

doi:10.1038/s41598-021-81649-y

Rui Hu, Xuesong Cui + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-81649-y

Copy DOI

Abstract

The role of pyrite (FeS2) in the process of water treatment using metallic iron (Fe0) was investigated. FeS2 was used as a pH-shifting agent while methylene blue (MB) and methyl orange (MO) were used as an indicator of reactivity and model contaminant, respectively. The effect of the final pH value on the extent of MB discoloration was characterized using 5 g L−1 of a Fe0 specimen. pH variation was achieved by adding 0 to 30 g L−1 of FeS2. Quiescent batch experiments with Fe0/FeS2/sand systems (sand loading: 25 g L−1) and 20 mL of MB were performed for 41 days. Final pH values varied from 3.3 to 7.0. Results demonstrated that MB discoloration is only quantitative when the final pH value was larger than 4.5 and that adsorption and co-precipitation are the fundamental mechanisms of decontamination in Fe0/H2O systems. Such mechanisms are consistent with the effects of the pH value on the decontamination process.

Highlights

Background to the experimental methodologyAt neutral pH values, immersed reactive Fe0 corrodes and generates solid iron corrosion products (FeCPs), which progressively coat the surface of sand
Strong surface interactions with positively charged species is responsible for the observed methylene blue (MB) discoloration, but no methyl orange (MO) discoloration occurs in the single-sand s ystem[44,61]
The concept that adsorption and co-precipitation are the fundamental mechanisms of contaminant removal in Fe0/H2O systems is consistent with many experimental observations

Summary

Introduction

At neutral pH values, immersed reactive Fe0 corrodes and generates solid iron corrosion products (FeCPs), which progressively coat the surface of sand. The extent of sand coating depends among other factors on: (i) the Fe0 intrinsic reactivity, (ii) the volume of the solution, (iii) the initial pH value of the solution, (iv) the F e0/sand ratio, and (v) the duration of the experiment. The removal efficiency of the system for individual contaminants depends on the final pH value, the extent of sand coating, and the availability of “free” FeCPs. The final pH value determines the speciation of the contaminant and the surface charges of sand and FeCPs50. When a FeS2 mineral is added to a Fe0/sand system (at a given Fe0:sand ratio) a pH shift to lower values occurs. The larger the pH shift the larger the amount of FeCPs generated, which will in turn precipitate at pH > 4.5 and induce contaminant removal by adsorption and co-precipitation

Objectives

Methods

Results

Conclusion