Carrier-microencapsulation of arsenopyrite using Al-catecholate complex: nature of oxidation products, effects on anodic and cathodic reactions, and coating stability under simulated weathering conditions

Abstract

Mining activities often generate large amounts of sulfide-rich wastes containing arsenopyrite (FeAsS), which when dissolved releases toxic arsenic (As) and generates acid mine drainage (AMD) that are both disastrous to the environment. To suppress arsenopyrite dissolution, a technique that selectively coats sulfide minerals with a protective layer of Al-oxyhydroxide called Al-based carrier-microencapsulation (CME) was developed. Although a previous study of the authors showed that Al-based CME could significantly limit arsenopyrite dissolution, nature of the coating formed on arsenopyrite, including its electrochemical properties, is still not well understood. Moreover, stability of the coating once exposed to weathering conditions remains unclear. Better understanding of these important issues would greatly improve Al-based CME especially in its application to real mine wastes. In this study, nature of the coating formed by Al-based CME was investigated using SEM-EDX, DRIFTS and XPS while the electrochemical properties of the coating were evaluated by cyclic voltammetry and chronoamperometry. Meanwhile, stability of the coating was elucidated using consecutive batch leaching experiments and weathering cell tests.SEM-EDX, DRIFTS and XPS results indicate that the protective coating formed on arsenopyrite by Al-based CME was mainly composed of bayerite (α-Al(OH) 3 ), gibbsite (γ-Al(OH) 3 ), and boehmite (γ-AlO(OH)). These Al-based coatings, which have insulating properties, made arsenopyrite less electrochemically active. The coatings also limited the extent of both the anodic and cathodic half-cell reactions of arsenopyrite oxidation that suppressed As release and acid generation. Weathering cell tests indicated that the oxidation of CME-treated arsenopyrite was effectively limited until about 15 days but after this, it started to gradually progress with time due to the increasing acidity of the system where Al-based coatings became unstable. Nonetheless, CME-treated arsenopyrite was less oxidized based on the released amounts of Fe, As and S suppressed by 80, 60 and 70%, respectively, compared with the one treated with control.

Enhanced Cementation of Co2+ and Ni2+ from Sulfate and Chloride Solutions Using Aluminum as an Electron Donor and Conductive Particles as an Electron Pathway

“…Following these equations, it is expected that the stoichiometric amount of Al dissolves when cementation occurs; however, the dissolved Al concentration after cementation was less than 3 ppm (Tables S1 and S2), which means that most of the Al 3+ was precipitated as Al-(oxy)hydroxide [7,32]. As shown in Figures 2c and 3c 6) and ( 7)).…”

Metallic Iron for Environmental Remediation: The Fallacy of the Electron Efficiency Concept

“…Fe 0 for Wastewater Treatment Fe 0 has been used for wastewater treatment for many decades (Obiri-Nyarko et al, 2014;Antia, 2020;Lanet et al, 2021). Applications encompass the recovery of important elements (Vollprecht et al, 2018;Vollprecht et al, 2020), and the treatment of wastewaters from domestic (Wakatsuki et al, 1993), industrial (Oldright et al, 1928;Gould, 1982;Vollprecht et al, 2020), and agricultural sources (Anderson, 1989;James et al, 1992;Erickson et al, 2007). In all these applications, FeCPs serve as contaminant scavengers and the systems are designed to produce enough scavengers.…”

Stabilization and encapsulation of arsenic-/antimony-bearing mine waste: Overview and outlook of existing techniques

“…The encapsulation techniques aiming to passivate arsenopyrite have been focused on the development of phosphate (Jones et al, 2003;Harris & Lottermoser, 2006) and metal (oxyhydr)oxide (Park et al, 2018a(Park et al, , 2018b(Park et al, , 2020 coatings.…”

“…These protective layers minimized the release of As from arsenopyrite by approximately 4-5 times (Park et al, 2018a(Park et al, , 2018b. It was found that, as weathering progressed, increasingly acidic conditions provoked a gradual dissolution of the Al oxyhydroxide-coating, thus reducing its protective effect (Park et al, 2020). Two strategies were proposed to increase the long-term stability of this method: increasing coating thickness or blending the Al oxyhydroxide-coated arsenopyrite with neutralizing materials to maintain pH conditions within the stability range of Al oxyhydroxides (approximately 4.5-8.5).…”