Keliang in the "seawater room"

Hi! This is me in the wet lab called the ‘seawater room’. This is where we pre-treat nearly all of our water samples before analysis. On this picture you can really see one of my main activities in the wet-lab. In the big can (250 Litres!) to the right of me I started yesterday to pour in about 200 l water from our neighbour fjord, the Roskilde fjord. I use this water as test water to fine tune my analysis. Since concentrations of Tc-99 in the world oceans are very low we often need to use very large water samples. 200 litres is a common volume. I ‘pick’ out the Tc-99 by adding reduced iron (Fe²⁺) to the water. This gives away some electrons to the Tc-99 which is normally present as Tc⁷⁺ (TcO₄^-) in water. It then forms Tc⁴⁺ which is very reactive contrary to TcO₄^-. When I now add NaOH to increase the pH of the water the reduced iron, calcium and magnesium in the water forms hydroxides and form large flocks that slowly falls to the bottom. It is called a precipitate. This precipitate carries all the reactive elements in the water, including my Tc-99. It takes some time for the precipitate to sink to the bottom so I usually let this go on overnight. Today the green-white precipitate (green is the colour of the Fe²⁺ and white is the colour of Ca and Mg hydroxides) has reached the bottom of the big 250 L tank. So I pumped away the water and transferred the precipitate to the white 50 L flask and then again when it settles to the bottom of the flask I pump away the water and transfer the precipitate to a glass beaker. See the picture! This is what you see in the picture! So why do I do this testing? Well, for the Antarctic cruise there are some space problems when storing the water that is collected on the ship so I need to concentrate it this way and be sure I get all Tc-99 with me using the simplest and quickest method. These days I try using as little Fe²⁺ as possible in order to minimize the precipitate without losing Tc-99.