Browsing by Author "Manninen, Noora"

Liming agricultural fields with byproducts from steel industry is quite widespread, even though behavior of some heavy metals in soil is not well known. Especially chemistry of vanadium in soil is poorly understood and is very complicated due to it´s several oxidation states. Particularly soil pH and oxidation-reduction conditions are effecting to the occurrence of vanadium. It can be found in the environment mostly with oxidation states of +3, +4 and +5 with increasing solubility as the oxidation state increases. This study was made as a part of the doctoral thesis research of Inka Reijonen concerning bioavailability and toxicity of chromium and vanadium. Effects of soil organic matter content and pH on reactions of vanadyl (VO2+) were studied. The study beginned with systematic experiments that included incubation of air dried and sieved soil samples with vanadium(+4) added to the soil as VOSO4. Soil pH had been adjusted to three levels (acid soil, soil natural pH and alkaline soil) and vanadium was added as increasing concentrations. The effects of soil pH and organic matter content were examined with successive extractions. By using this method shares of different fractions of vanadium as a soluble compound and adsorbed to the surface of oxides, organic matter or mineral matter, could be studied. In addition, the same method was used to study the behavior of vanadium in field conditions where steel slag had been used for liming. The methods that were used seemed to fit for moderate concentrations of vanadium since some limitations occurred with higher concentrations. Vanadium was observed to retain mainly in organic matter in low soil pH and hence the movement into deeper soil layers was minor. Increase of pH increased the solubility of vanadium in the soil, which was assumed to be a result of oxidation of a vanadyl(+4) into a vanadate(+5). Liming a field with steel slag was observed to increase soil pH and increase the share of vanadium adsorbed to oxides and organic matter. The share of soluble vanadium in field conditions was very small compared to the total amount of vanadium in the soil. On the other hand, the share of soluble fraction was observed to increase in high vanadium concentrations as results of incubation experiments.