Formation of surface protective coatings on arsenopyrite using Al-catecholate complex and its mode of inhibition of arsenopyrite oxidation

Ilhwan Park,Naoki Hiroyoshi,Mayumi Ito,Kazuki Higuchi,Kensuke Seno,Hiroyuki Inano,Carlito Tabelin,A Orbecido,V Bungay,A Beltran,K Aviso

doi:10.1051/matecconf/201926806015

Abstract

Arsenopyrite is the most common arsenic-bearing sulfide mineral in nature. It is readily oxidized and releases toxic arsenic (As) into the environment when exposed to atmospheric conditions via anthropogenic activities like mining, mineral processing, extractive metallurgy, and underground space developments. Carrier-microencapsulation (CME) is a technique that uses metal(loid)-organic complexes to selectively form protective coatings on the surfaces of sulfide minerals. In this study, CME using Al-catecholate complexes (i.e., Al-based CME) was investigated to suppress the oxidation of arsenopyrite. Aluminum(III) and catechol form three complex species depending on the pH and among them, [Al(cat)]+ was the most effective in suppressing arsenopyrite oxidation. Its suppressive effect was improved as [Al(cat)]+ concentration increased due most likely to the formation of a more extensive surface protective coating at higher concentrations. Surface characterization of leaching residues using SEM-EDX and XPS indicates that CME-treated arsenopyrite was covered with bayerite (γ-Al(OH)3). The results of electrochemical studies showed that the surface protective coatings suppressed both anodic and cathodic half-cell reactions of arsenopyrite oxidation.

Highlights

Arsenopyrite (FeAsS) is the most common arsenicbearing sulfide mineral in nature
The sample was analyzed by X-ray powder diffraction (XRD) and confirmed that it was mainly composed of arsenopyrite with pyrite and quartz as minor minerals
The three Al-catecholate complexes were prepared at pH 5, 7, and 10, and used for the leaching experiments to investigate how they affect arsenopyrite oxidation

Summary

Introduction

Arsenopyrite (FeAsS) is the most common arsenicbearing sulfide mineral in nature. This mineral is readily oxidized when exposed to atmospheric conditions, leading to the release of arsenic (As) into the environment as explained by the following reaction: Arsenic is a strictly regulated substance because of its toxicity. Prolonged exposure even to minute amounts of As increases the risks of developing several types of cancers [1] To mitigate this problem, carrier-microencapsulation (CME), a process that forms a protective coating on the surface of sulfide minerals, was developed by the authors [2–5]. In CME, a redoxsensitive organic compound (e.g., catechol, 1,2dihydroxybenzene, C6H4(OH)2) is used to transform relatively insoluble metal(loid) ions, such as Ti4+, Si4+, and Al3+, into soluble complexes. These complexes are stable in solution, they are oxidatively decomposed on the surfaces of sulfide minerals like pyrite (FeS2) and arsenopyrite that dissolve electrochemically. As a consequence of this oxidative decomposition, metal(loid) ions are released and rapidly precipitated near the mineral surface, which form protective metal(loid)-oxyhydroxide coatings

Methods

Results

Conclusion