Rust in Ice: The Geochemistry of Iron in Freezing Water
Iron trapped in ice plays an important role in many frozen environments. Freezing produces small and highly reactive iron oxide (rust) nanoparticles. The particles are produced in ice particles in atmosphere, iceberg or frozen soils. Once released to the environment by melting, the particles react with organic matter and contaminants. This project explains how these particles form and react, and eventually water chemistry on the Moon and Mars, or how we can make new materials by deep freezing.
The project is financed by the Swedish Research Council.
Icebergs, atmospheric ice and frozen soils all have a point in common: they trap iron minerals that are crucially important to environmental processes on Earth. When liquid water freezes, these minerals become trapped between micrometer-sized ice crystals where surprising transformations occur. These minerals often transform to a mineral called ferrihydrite. Ferrihydrite particles are very reactive because they expose a very large surface area, as they are often only 1 to 10 nm wide, and are unstable. They always convert to more stable iron oxide minerals (such as the pigment in Falu rödfärg) but in their days to years of existence, they play important roles on how elements, nutrients and contaminants are distributed in water, land and air.
That ice hosts important reactions may at first be surprising, as we have long regarded frozen environments to be inert, but the time has not come that we explore this rich chemistry. The liquid water trapped in ice often becomes highly concentrated in salts and minerals because they cannot be incorporated in ice. These high concentrations trigger many chemical reactions and, in particular, those leading to the formation of ferrihydrite are very important to understand processes in frozen environments. Some include changing compositions of iron and organic matter in soils, ponds and mires in boreal and arctic settings of northern Sweden. Others are the production of ferrihydrite in atmospheric ice and even icebergs that feed marine phytoplanktons driving the biological productivity of oceans. Research groups are even contemplating the idea of fertilizing oceans with these forms of iron nanominerals as a means to pump CO2 out of the atmosphere.
Although transformation of iron minerals in ice are clearly important, very little is known on how these transformation occurs. This project was therefore developed to show how iron is transformed and how it catalyzes reactions in ice. Our research group at Umeå University has a long history of using advanced methods in chemistry to study the environment, and in this project we will use our skills to understand the geochemistry of ferrihydrite locked in ice. We have identified important areas that need to be developed to help the research community better consider the roles that ice plays on reactions involving ferrihydrite. In particular, this work will focus on the interactions of ferrihydrite with organic matter because of its widespread occurrence in nature.