Dissolution of realgar by Acidithiobacillus ferrooxidans in the presence and absence of zerovalent iron: Implications for remediation of iron-deficient realgar tailings

Abstract

Realgar (AsS)-rich tailings are iron-deficient arsenical mine wastes. The mechanisms and products of the dissolution of realgar by Acidithiobacillus ferrooxidans (A. ferrooxidans) in the presence (0.2 g and 2 g) and absence of zerovalent iron (ZVI) are investigated for three stages (each of 7 d with fresh A. ferrooxidans medium addition between the stages). SEM-EDX, FTIR, XPS and selective extraction analysis are used to characterize the solid-phase during the experiments. ZVI addition causes the systems to become more acid-generating, although pH increases are observed in the first day due to ZVI dissolution. Arsenic is released to solution due to realgar oxidation (∼30 mg L in the 0 g ZVI system in Stage I), but low concentrations are observed in the ZVI-added systems (<5 mg L) and in Stages II and III of the 0 g ZVI system. As(III) dominates the released As(T) at day 1 (83-89% of As(T)), but is largely oxidized to As(V) at day 7 of each stage (53-98% of As(T)). Arsenic attenuation is attributed to the formation of mixed As-Fe oxyhydroxides and oxyhydroxy sulfates that take up released arsenic and are abundant in the 2.0 g ZVI system, and to passivation of the realgar surface. Consequently, a new strategy that combines A. ferrooxidans and exogenous ZVI addition for treating in-situ iron-deficient realgar-rich tailings is proposed, although its long-term effects need to be monitored.

In situremediation of arsenic-rich mine tailings using slag zero valence iron

“…The variations of pH and Eh can indicate the dissolution of tailings in the environment (Fan et al , 2018b). Figure 1 shows the changes in pH as a function of time for the five test groups and the two control groups.…”

“…Free AsO 4 3− has a tetrahedral structure and gives four vibration modes ν 1 , ν 2 , ν 3 and ν 4 at 837, 349, 878 and 463 cm −1 (Liu et al , 2017a). The weathering of arsenopyrite and realgar generates arsenite as the dominant species (Fan et al , 2018b), and further oxidation converts dissolved arsenite (AsO 3 3− ) to arsenate (AsO 4 3− ). For the Re-rich group, adsorbed arsenate species showed only a weak peak at 1022 cm −1 in the FTIR.…”

“…Acidithiobacillus ferrooxidans , a common Fe-oxidising bacterium in mine areas, can accelerate the oxidation of pyrite (FeS 2 )-like sulfide minerals, to produce acid mine drainage (Singer and Stumm, 1970; Fan et al , 2018b). In the present study, the authors used A. ferrooxidans to model a biological oxidation environment with rapid acceleration of weathering so that the changes in the two mine wastes with or without ZVI could be observed immediately.…”

“…The XPS spectra were obtained at the University of Science and Technology of China, Hefei, China. Deconvolution of the raw data was fitted using CasaXPS , and the Shirley-type background was subtracted before deconvolution and fitting (Fan et al , 2018b). The compound peaks of As were determined based on the summary report on arsenopyrite by Corkhill and Vaughan (2009).…”

“…As-rich tailings are common in the Hunan Province of China due to their abundance in polymetallic deposits. Arsenopyrite can generate acid within mine waste, just like pyrite (FeS 2 ), via the following reaction: In contrast, realgar commonly occurs in low-temperature hydrothermal deposits (Lengke and Tempel, 2003; Zhu et al ., 2015; Fan et al ., 2018b) often with quartz (SiO 2 ) and calcite/dolomite (CaCO 3 and MgCa(CO 3 ) 2 ) as associated minerals, while orpiment (As 2 S 3 ) can also often be found in the surrounding rocks (Gruyter, 2014). Under aerobic surface conditions, realgar is oxidised gradually to produce arsenic and sulfuric acid via the pathway: Lengke and Tempel (2003) evaluated kinetically the acid production in a natural realgar-based mixed-flow experiment, at 25°C and pH 7−9 to give: where [H + ] prod is acidity released from oxidation, and [H + ] initial is the initial acidity (Lengke and Tempel, 2003).…”