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Environmental fate & pathways

Adsorption / desorption

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Description of key information

FeSi in particulate form is immobile in soil and sediment.  Adsorption/desorption behaviour of dissolved FeSi constituents is governed mainly by inorganic soil and sediment materials. Each constituent behaves in a characteristic way, depending highly on local environmental conditions. Generally, the adsorption of these constituents in organic materials is weak and therefore less important.

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Additional information

The adsorption/desorption behaviour of FeSi constituents are governed mainly by inorganic soil and sediment materials. Adsorption to organic materials is less important. Sorption of dissolved silica in soil/sediments is known to be controlled remarkably by solid-phase constituents like clay minerals and oxides and to a lesser extent by solid organic matter (McKeague 1963) . Therefore, existing silica studies have focused on adsorption studies on mineral constituents. Adsorption/desorption characteristics and information on speciation properties of FeSi alloy constituents can be found in the literature. Silica in dissolved form is always in electro-neutral form (Si(OH)4) in water at the most prevalent environmental pH conditions (pH <9). The speciation of ferro and ferri iron may instead vary a lot, and transformations are likely and follow prevailing environmental conditions. Factors such as redox potential, pH, ionic strength and ionic composition, temperature, and DOM/POM dominate the environmental fate of iron (“iron cycle”). The adsorption/desorption properties of iron are therefore highly dependent on prevailing conditions, and therefore highly variable quantitative figures and Kd values for iron can be given. Specific FeSi grades (composition modifications) of ferrosilicon include Periodic Table IIA group alkaline earth metals. These grades include barium containing inoculant FeSiBa and strontium containing FeSiSr. These IIA constituents are predominantly in the II+ valency state cations in the environment. As with all IIA group elements, highly insoluble precipitates may be formed with some anions (e.g., sulphates), effectively limiting soluble background concentrations. The predominant forms of dissolved zirconium in soil and surface waters are the Zr(OH)4 molecule and the Zr(OH)5- anion in the most alkaline waters.