Aluminum magnesium vanadium oxide

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Description of key information

No adsorption/desorption studies are available for Aluminium Magnesium Vanadium oxide. However, the adsorption/desorption behaviour of the different metals in the environment is well known. The undissolved fraction of the substance will deposit in soil or sediment, and the dissolved metals will undergo speciation in function of the environmental conditions.

Additional information

Due to its low solubility, Aluminium Magnesium Vanadium oxide will mainly remain undissolved under environmental conditions and will deposit in soil or sediment. A minor fraction may dissolve into the aqueous phase. In this case each metal will undergo speciation in function of the environmental conditions. The speciation of metals in the environment depends on several parameters, such as pH, redox potential and the presence of anions.

Experimental data on the adsorption/desorption behaviour of Aluminium magnesium vanadium oxide are not available, but the fate of the individual metals in the environment has been thoroughly investigated.

 

Aluminium

A number of chemical factors can alter the speciation of aluminium, thereby affecting the extent of adsorption and desorption of aluminium on suspended particles, as a result aluminium speciation is complex and changes significantly with changes in pH.  In the absence of organic matter, Al3+ is the predominant aluminium species at low pH (less than 5.5). As pH increases above 5.5, aluminium-hydroxide complexes formed by hydrolysis become increasingly important and dominate aqueous aluminium speciation (see Figure 4.2.1-1 attached; provided by the Aluminium REACH Consortium). The presence of a moderate amount of organic matter in soft water (2 mg/L as dissolved organic carbon or DOC is used here) results in organically complexed aluminium being the dominant aluminium form when the pH is between 4 and 7. Above pH 7, anionic aluminium hydroxide predominates, although organically complexed aluminium remains the second most important form of dissolved aluminium.

Aluminium speciation can also include the formation of insoluble polymeric aluminium-hydroxide species. Polymeric aluminium hydroxides tend to exist as amorphous colloids and solid phases. The kinetics of this transformation to polymeric species, including aqueous colloids and amorphous precipitates, depends on many factors but typically occurs over a time scale of minutes to hours. Subsequent formation of more crystalline solid phases may take additional time, as much as a few days. As a result of these relatively slow transformations from dissolved to crystalline forms of aluminium, there is a considerable range of solubilities that have been reported for aluminium hydroxide solid phases (Lindsay and Walthall, 1996). As a result of this dynamic chemistry, the amount of aluminium associated with suspended particles is dependent on the chemical conditions. Factors that are known to affect aluminium speciation, such as pH and DOC, are also known to affect adsorption and desorption from particle surfaces. To illustrate this further, the amount of aluminium associated with suspended particles was estimated by chemical simulation that included aqueous aluminium speciation (inorganic and organic), aluminium solubility, and complexation by NOM. For these simulations a NOM concentration of 4 mg/L (2 mg/L as DOC) and a total suspended solids (TSS) concentration of 1 mg/L were chosen to represent a reasonable lower bound for the range of values of these substances that would be expected in the environment. Suspended particles were assumed to be composed primarily of silica (80%) with a small amount of clay (10%) and particulate organic matter (10%). Aluminium concentrations were set to the maximum allowable by solubility with amorphous gibbsite at a temperature of 20⁰C. Under these conditions, the amount of aluminium bound to particles as a result of surface complexation (i.e. adsorption) was pH dependent, but was typically less than 8% of the total aluminium at pH 6, and was further reduced to below 1% at pH values above 7 (see Figure 4.2.1.-2A attached). This distribution was similar in both soft and hard waters. The corresponding Log Kd values for this distribution are shown in Figure 4.2.1.-2B attached, with values between 3 and 5. Very similar results were obtained with higher DOC concentrations of 4 mg/L.

 

Magnesium

Magnesium is ubiquitously present in soil and sediment systems either as free dissolved ion or in bound form, e.g. as hydroxid, sulphate, carbonate or phosphate, depending on pH, redox conditions and available anions.

 

Vanadium

Vanadium occurs mostly as vanadium(IV) and vanadium(V) in natural waters. In diluted oxic solutions, it exists as H2VO4- or HVO42-. Under anoxic conditions, cationic vanadyl VO2+ exists and forms very stable complexes with oxygen donor ligands. Also the sorptive behaviour of vanadium varies significantly depending on environmental conditions and type of soil. Both vanadium(IV) and vanadium(V) have been shown to specifically adsorb to Al2O3 and TiO2 surfaces. Gäbler et al. (2009) investigated the adsorption of vanadium in in laboratory experiments with 30 different german soils, selected to cover a representative pH range and a large variability of sorption relevant soil properties (organic carbon, clay content and oxalate soluble Mn). The study revealed pronounced differences in vanadium adsorption of different soils. Sandy soils show the lowest vanadium sorption strength. For these soils a vanadium solution concentration of 10 µg/L corresponds to adsorbed vanadium amounts between 0.7 and 4.7 mg/kg while for top soils and subsoils it corresponds to adsorbed vanadium amounts of 1.7 12 mg/kg, 40 - 100 mg/kg and 4.5 - 19 mg/K, respectively (Gäbler et al., 2009; and references therein). Experimental Kd values ranging from 1.70 to 360.91 L/kg have been determined for different soils have been reported by Magdi Selim (2013).

 

In conclusion, the adsorption/desorption behavior of the metal constituents of Aluminium Magnesium Vanadium oxide strongly depend on the environmental conditions and the type of soil. Based on the available literature, the behaviour of these metals in soil systems has been intensely investigated and is well understood. The testing of Aluminium Magnesium Vanadium oxide for adsorption is therefore not considered necessary.

 

Reference

Gäbler, H.-E., K. Glüh, A. Bahr, J. Utermann (2009) Quantification of vanadium adsorption by German soils, Journal of Geochemical Exploration, 103, 37-44

Lindsay W. L. and Walthall P. M. (1996). The solubility of aluminium in soils. In The environmental chemistry of aluminium. (G. Sposito, ed.), pp. 333–361. USA: Lewis Publishers, Boca Raton

Magdi Selim, H. (2012) Competitive Sorption and Transport of Heavy Metals in Soils and Geological Media, CRC Press, Taylor & Francis Group