Structural incorporation and thermodynamic properties of Mo6+ iniron oxides and their role in Mo immobilization in soils

在这个项目中，我们建议调查的重要性，铁氧化物的流动性和生物有效性的钼在土壤中。钼代表了几种金属酶的生物合成的关键先决条件，因此对于所有已知的生命都是必需的（Mendel & Bittner，2006;麦格拉思等人，2010年，Duval等人，2015年）。它在土壤中的流动性和生物利用度很低，并且与氧化铁的存在直接相关（Lang和Kaupenjohann，1999年）。为了评估铁氧化物对于Mo固定的重要性，先前的研究主要集中在吸附机制上（例如Goldberg等人，1996; Brinza等人，2008），而通过Fe 3+被Mo 6+的异价取代的结构掺入的可能性几乎完全被忽略（里士满等人，2004年;卡罗尔和里士满，2008年; Zemberyová等人，2010).铁氧化物具有几种结构机制，其可以允许异价取代（例如，Alberto和克拉克森，2001; Khan等人，2008; Bolanz等人，2013;乔巴努等人，2013年）。对于Mo 6+，在好氧系统中最丰富的Mo种类（巴伦等人，2009），然而，几乎不存在结构并入铁氧化物的令人信服的数据。这一巨大的知识差距可以转移到含钼铁氧化物的热力学性质。在结构上包含外来离子（如Mo 6+）的矿物可以表现出根本不同的热力学性质，因此具有稳定性（Heaney，2000）。因此，该项目有四个里程碑，包括（i）含Mo 6+铁氧化物的合成和表征，（ii）确定铁氧化物结构上包含Mo 6+的机制，（iii）提供量热数据（混合的混合物，的形成过程），并评估结构上引入的Mo 6+的影响对铁氧化物的热力学稳定性，（iv）转让收购合并机制从合成Mo 6+轴承铁氧化物，在实验室条件下形成的热力学性质，天然氧化铁在各种土壤类型。为了实现这些目标，将采用体、微米和纳米分辨率技术的组合，包括粉末X射线衍射、电感质谱、质谱仪耦合气体发射系统，利用透射电子显微镜和X射线吸收光谱技术，对Mo 6+的结构掺入机理进行了研究通过异价取代反应研究了钼在铁氧化物中的迁移规律，为进一步研究钼在土壤中的移动性和生物有效性奠定了基础。

In this project we propose to investigate the importance of iron oxides on the mobility and bioavailability of Mo6+ in soils. Molybdenum represents a critical prerequisite for the biosynthesis of several metalloenzymes and is therefore essential for all known life (Mendel & Bittner, 2006; McGrath et al., 2010, Duval et al., 2015). Its mobility and bioavailability in soils is low and directly coupled with the presence of iron oxides (Lang & Kaupenjohann, 1999). In order to evaluate the importance of iron oxides for Mo immobilization, previous studies focused predominantly on adsorption mechanisms (e.g. Goldberg et al., 1996; Brinza et al., 2008), whereas the possibility of structural incorporation by a heterovalent substitution of Fe3+ by Mo6+ was almost completely ignored (Richmond et al., 2004; Carroll & Richmond, 2008; Zemberyová et al., 2010).Iron oxides possess several structural mechanisms which can permit a heterovalent substitution (e.g. Balko & Clarkson, 2001; Khan et al., 2008; Bolanz et al., 2013; Ciobanu et al., 2013). For Mo6+, the most abundant Mo specie in oxic systems (Barron et al., 2009), however, almost no convincing data for structural incorporation into iron oxides exist. This tremendous gap in the knowledge is transferable to the thermodynamic properties of Mo-bearing iron oxides. Minerals, which structurally incorporate foreign ions like Mo6+, can exhibit fundamentally different thermodynamic properties and therefore stabilities (Heaney, 2000). Molybdenum could therefore alter its own bioavailability.Therefore, this project has four milestones including (i) synthesis and characterization of Mo6+-bearing iron oxides, (ii) identification of the mechanisms which allow iron oxides to structurally incorporate Mo6+, (iii) to provide calorimetric data (enthalpies of mixing, enthalpies of formation) of Mo-substituted iron oxides and to evaluate the effects of structurally incorporated Mo6+ on the thermodynamic stabilities of iron oxides, (iv) a transfer of the acquired incorporation mechanisms from synthetic Mo6+-bearing iron oxides, formed under laboratory conditions and their thermodynamic properties, to natural iron oxide in various soil types. In order to achieve these goals, a combination of bulk, micro- and nano-resolution techniques will be employed comprising powder X-ray diffraction, inductively- mass spectrometry, mass spectrometer-coupled gas emission system, transmission electron microscope and X-ray absorption spectroscopy techniques.It is expected that this study will significantly improve our understanding about the structural incorporation mechanisms of Mo6+ in iron oxides by heterovalent substitution reactions and establish a foundation for future research on Mo mobility and bioavailability in soils.