Molybdenum (Mo) and tungsten (W) are two elements in the same column of the periodic table. They also behave similarly in nature. The average concentration in the Earth's crust is 1.5 ppm for both elements. Molybdenum is an essential nutrient for plants and animals. At large concentrations, Mo may be toxic. This is sometimes the case for leachates from alkaline ashes. Tungsten is an important strategic metal that is used in a variety of industrial applications. It is usually mined from scheelite, CaWO4, och wolframite, (Fe,Mn)WO4. Tungsten is released to the environment, e.g. through its use in winter tires and ammunition. On the whole, the environmental behaviour of tungsten is not well known.
In the environment, Mo and W are mainly present in their anionic forms, molybdate (MoO42-) and tungstate (WO42-), and their protonated and polymerised species. Under reducing conditions (for example in the bottom sediments of lakes), other species may form because of the redu tion of Mo and W to lower valence states. It has been known for a long time that molybdate and tungstate may be bound to Fe and Al oxides in soils and sediments, and that this process may determine the dissolution of Mo and W. However, very few studies have been made to quantify this process. There are also indications that Mo and W may be bound to organic matter. The aim of this project is to quantify the binding of Mo and W to ferrihydrite (a Fe oxide) and to organic matter. This will enable better assessments of Mo and W mobility in the environment.