Heavy metals are indispensable for many production processes, yet their use leaves behind wastewater that contains heavy metal. To minimize environmental pollution, national goverments and international organisations have established limits for heavy metals in waste waters and exhaust gases which may not be exceeded.
 

 
Usually, heavy metals in waste water are precipitated by adding sodium hydroxide or lime during neutralization. However, the results of this process are far from satisfying in many cases: The remaining heavy metal concentrations are too high. A complete hydroxide precipitation does not take place especially in the presence of complexing agents.