# Yeast Extract Affecting the Transformation of Biogenic Tooeleite and Its Stability
## 1 Introduction  
Highly toxic and soluble arsenite (As(III)) is a predominant arsenic species in acid mine drainage (AMD) and its appropriate immobilization is important [1, 2, 3]. Moreover, various secondary Fe(III) minerals are found extensively in AMD, such as schwertmannite, jarosite, and goethite, which may play a key role in the removal of As [4, 5]. Although schwertmannite can adsorb up to 70 mg/g As(V), higher As concentrations inhibit its crystallization [6]. [PERSON] et al. [7] formed jarosite to remove As(V) by incorporating As into the mineral structure by substitution of the S site. Nonetheless, it is not stable under any reservoir conditions and As could be released into the environment. Since many techniques used for the removal of As(III) from aqueous solutions require a pretreatment process for chemical oxidation, there is an urgent need for direct treatment of As(III) and safe stability. Tooeleite (Fe\({}_{6}\)(AsO\({}_{3}\))\({}_{4}\)SO\({}_{4}\)(OH)\({}_{4}\)-4H\({}_{2}\)O), the only ferric arsenite sulfate mineral currently known, has a high As content (20-25 wt.%) [8]. It has attracted mineral and metallurgical researchers for its potential significance in As(III) treatment [9]. In previous studies, several chemical and biological methods to form tooeleite have been reported, but most kinds of synthetic tooeleite were not involved in stability research [10, 11, 12]. However, [PERSON] et al. [8] studied the toxicity of tooeleite synthesized at 60 \({}^{\circ}\)C and pH 2.6 with or without silica coating. Although the silica-coating significantly reduced the As leaching of tooeleite, both the pure and silica-amended tooeleite still showed much higher As leachingconcentrations than 5 mg/L [13]. Furthermore, the stability of tooeleite could be enhanced through a hydrothermal method considering the influence of critical factors, such as purity and crystallinity [14; 15]. Currently, such methods for improving mineral stability are not suitable and economical. Fe(II)-oxidizing microbes play a significant role in As attenuation through biomineralization of secondary Fe(III) minerals [4]. Biogenic tooeleite is thought to be more stable than chemogenic tooeleite due to the existence of a large quantity of natural minerals related to bacteria [11]. _Acidithiobacillus ferrooxidans_ is a typical acidophilic chemolithoautotrophic bacteria [16; 17]. [PERSON] [5] found that _A. ferro oxidans_ can oxidize Fe(II) to promote As(III)-rich precipitates, composed of As(III)-Fe(III) amorphous phase, schwertmannite, jarosite and tooeleite. [PERSON] and [PERSON] [18] first reported that tooeleite occurred in oxidized mine tailings and that primary ores were rich in pyrite and arsenopyrite. It has been reported that arsenopyrite was preferentially dissolved and tooeleite precipitated during bioleaching [19]. In addition, bacteria are effectively used in metal sulfide leaching, and extracellular polymeric substances (EPS) seem to play a pivotal role in dissolution by creating a micro reaction space [20; 21]. The organic region could also be the place where the secondary mineral was formed. Indeed, organic matter (OM) has a significant impact on regulating and inducing the formation of minerals. Iron minerals show a high reactivity towards dissolved organic matter [22; 23; 24]. Moreover, the oriented attachment of organic matter may lead to the specific morphology of mineral particles [25; 26]. The stability of schwertmannite can be improved by elevated concentrations of natural organic matter [27; 28]. Interestingly, [PERSON] [29] found that organic matter (0.01-0.05% (_w/v_)) can increase biomass of thermo-acidophilic iron-oxidizing archaeon (_Ac. Brierleyi_) as energy source and provide an environment which promotes the As(III) oxidation reaction (e.g., the EPS (Extracellular Polymeric Substances) region around the cell surface. So it can improve not only scorodite crystallinity, but also As immobilization efficiency (up to 100%).