Research Center Karlsruhe

Colloids are present in all aquatic systems. They are chemically surface active and they therefore readily absorb heavy metal ions (e.g. actinide ions). The generation of colloids may increase the sum of mobile heavy metals in water over what expected by their thermodynamic solubility. The possible environmentally relevant impact of colloids in natural aquatic systems needs therefore to be investigated and new analytical methods like LIBD are developed. The LIBD bases on the plasma generation on single particles by an intense, pulsed laser beam and the detection of the produced shock waves or plasma light emission. The method detects colloids in the lower part of the nanometer size range and is there a few orders of magnitude more sensitive than light scattering methods.

The application of the LIBD for monitoring the formation of small colloids by hydrolysis of Th(IV) as an example for an application in actinide chemistry will be shown. The method is used to monitor the initial colloid generation when metal ion concentration exceeds the thermodynamic solubility. The determination of aquatic colloids present in groundwater as well as in surface water will be demonstrated. In surface water purification plants for the production of drinking water FeCl₃ is used as a precipitation agent. The LIBD is a unique method to monitor on-line the colloid content after the purification steps. It could be proved that after precipitation and filtration not only suspended matter but also colloids are effectively removed from surface water.