Salts of heavy metals which should be disposed often are found as an aqeous solution. If the solution is disposed without any treatment this will be quite expensive because then a lot of water has to be disposed as toxic waste. So it is a good idea to think about to separate the metal salts as a precipitation. The precipitation must be completely - with complex mixtures may be this cannot be ensured. According to local regulations (Indirekteinleiterverordnung des Landes Berlin) there are threshold values for the following metals in the waste water:
Waste heavy metal salts may be collected together in the same bottle. An exception is mercury which always has to be disposed separately.