Particle size control of biogenic scorodite during the GAC-catalysed As(III) oxidation for efficient arsenic removal in acid wastewaters

Silvia Vega-Hernandez,Jan Weijma,Cees J.N Buisman

doi:10.1016/j.wri.2020.100128

Silvia Vega-Hernandez, Jan Weijma + Show 1 more

Open Access

https://doi.org/10.1016/j.wri.2020.100128

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Abstract

The synthesis of biogenic scorodite combined with the oxidation of As(III) catalysed by granular activated carbon (GAC) was previously demonstrated. However, the colloidal size of the formed scorodite particles is still a bottleneck, as it would hinder the easy separation of the precipitates in a full-scale application. Here, we studied the effect of GAC concentration on biological scorodite precipitation at thermoacidophilic conditions in batch experiments. Higher arsenic removal efficiency and precipitation of larger and more stable scorodite particles were found only in biotic tests and at low catalyst concentration of 4 g L−1. Furthermore, with 4 g L−1 GAC, the Fe and As predominantly precipitated in solution while with 20 g L−1 GAC the Fe and As predominantly precipitated on the GAC. For experiments with 4 and 20 g L−1 of GAC, the average particle size was 66 and 2.6 μm, respectively. This could be explained by the lower saturation level of the solution at the lower GAC level. This study shows for the first time that the oxidative catalytic capacity of GAC can be used to influence crystallization of scorodite.

Highlights

Arsenic (As) is a toxic metalloid which is widely dispersed throughout the earth’s crust where it is commonly associated with ores of Cu, Zn, Au and Ag [1]
Arsenite oxidation was evaluated in batch tests containing 0, 4 and 20 g LÀ 1 granular activated carbon (GAC) with initial concentrations of 510 mg LÀ 1 As(III) and 490 mg LÀ 1 Fe(II) (Fig. 1A)
The results presented here demonstrate the impact of the concentration of GAC on the precipitation of scorodite starting from As (III) and Fe(II) containing medium, inoculated with thermoacidophilic iron-oxidizing microorganisms

Summary

Introduction

Arsenic (As) is a toxic metalloid which is widely dispersed throughout the earth’s crust where it is commonly associated with ores of Cu, Zn, Au and Ag [1]. The mining and metallurgical industries exploiting these ores contribute substantially to the economic development of metal-exporting countries [2]. It results in the generation of acid effluents with high concentrations of As between 500–10,000 ppm, mainly in the trivalent form, As(III) [3]. The removal and immobilization of arsenic is commonly accomplished by co-precipitation with lime and ferric salts [4]. The precipitated arsenic-rich solids are chemically not entirely stable. The suitability of such precipitates for long-term storage has been questioned, as uncontrolled emissions of arsenic from stored arsenic-rich solid waste results in unacceptable environmental hazards [5,6]. A proper management of these residues for the disposal and storage becomes even more urgent

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