Cyanide removal groundwater

The removal of cyanide from groundwater is often necessary as part of groundwater remediation, e.g. after an accident or remediation of a contaminated site, if cyanide or cyano compounds have been handled on the property in question. Cyano compounds are extremely toxic (a few mg/kg body weight as a lethal dose) and can also outgas in combination with acids, even acid rain, as toxic hydrocyanic acid or HCN.

However, the purification of cyanide-contaminated water can be ensured with an established process using ion exchangers. However, it should be noted that only cyano complexes are bound, but not any free cyanides. Nevertheless, these are often reduced in the applications. The system is monitored analytically, which is why sufficient reserve capacity must always be ensured.

Ion exchangers generally use a combination of weakly basic anion exchangers and strongly basic anion exchangers to remove cyanide. The weakly alkaline anion exchanger is designed for higher concentrations, the strongly alkaline anion exchanger as fine purification for pre-purified or only slightly contaminated groundwater. The capacities also differ: that of the weakly basic anion exchanger is about twice as large as that of the strongly basic anion exchanger. Typically, volume flows of between 3 and 25 m³/h are cleaned in an ion exchanger system.

With regard to the specific application:
The weakly basic anion exchanger requires preconditioning, so it cannot be used directly from the bag or big bag. It should be noted that during preconditioning there is a sudden expansion in the volume of the resin bed, which can even burst steel tanks. It is therefore only possible in specially designed systems and no longer in the actual ion exchanger pressure cartridge. The advantage of weakly basic anion exchangers in cyanide removal lies in the lower follow-up costs, as the weakly basic anion exchangers can be regenerated. The strongly basic anion exchangers have such a strong bond to the cyano complex that they can no longer be regenerated economically. In principle, the strongly basic anion exchangers can be used from the bag or big bag, but depending on the batch and manufacturer, they contain a strong fishy odor that is discharged into the waste stream. This is trimethylamine, a part of the functional group of the strongly basic type I anion exchanger, which is separated as a production-related impurity and whose discharge is not permitted. We therefore always recommend subjecting strongly basic type I anion exchangers to a cleaning process before use. Both processes are carried out in a central regeneration station for ion exchangers as a service, known as ion exchanger regeneration. The water to be fed in may also require further pre-treatment to remove impurities.

In principle, cyanide can also be recycled in industrial plants. However, these systems must be protected separately, as a pH reduction takes place in the process.

Do you have any further questions about cyanide removal from groundwater? Please feel free to contact us.