Article continued (page 4): Modern Treatment Methods of Strong Chelates in Surface Technology

This process is also effective for the elimination of other chelates; it is quick, reliable, and cost effective2,4,5, as is described in the following example for EDTA.

The total break-down of EDTA has been shown by analysis by HPLC on the RP C18 reverse-phase with DA-detector2. In this case well defined peaks were shown in the spectral analysis of the strongly diluted (1:2000) old plating bath. In the diluted (1:100) sample analysis, after 2 hours of treatment, it was clearly seen that during the breaking down process, various high-molecular products are created.

The analysis of the undiluted sample after about 4 hours treatment showed clearly that not only the EDTA but also the high molecular by-products are totally destroyed.

The treatment plant basically consists of a batch-tank, the Enviolet® – UV-reactor and a chemical dosing station complete with automatic process step control. UV-oxidation yields a treated wastewater with much lower COD values and allows simple alkaline metal precipitation and flocculation to meet low metals limits at a greatly reduced treatment cost.

UV reactors need to meet demanding operating parameters:

·          The abrasive rotational stream prevents the UV-module from getting dirty (unit has a quartz glass tube and UV-lamp).

·          The induced high turbulence gives very good material transfer required for optimal process treatment even in very dirty and turbid media.

·          Components require high corrosion resistance, for acidic and chloride solutions under higher temperatures.

The treatment from UV-oxidation is achieved by recycling the water in a batch process through the Enviolet® system. The ultraviolet light starts a number of reactions:

·          The chelates absorb the UV-light and this induces chemical reactions which lead to the degradation of the chelates (via photolysis).

·          The addition of hydrogen peroxide absorbs the ultraviolet light, with the formation of highly oxidising radicals. These radicals are so reactive that under ambient temperature other reactions (thermal processes) occur resulting in a complete breakdown of organic materials to oxidised carbon. Furthermore, these radicals react with hypophosphite as well as phosphite, to form phosphate. By adding catalysts, the UV-oxidation can be significantly accelerated.

Figure 2. The treatment plant for the detoxification of Cu EDTA .

Figure 3. Cyanomat® for the treatment of Cyanide waste concentrates. System treats 6000 l/day with a cyanide concentration 45 g/l

Conclusion

The advanced Kurion a.c.k. UV-technology has proven to be a powerful tool for the treatment of complex concentrates and wastewaters in the surface technology sector. Kurion a.c.k. UV-oxidation technology provides a simple, safe, and cost effective solution for treating chelated wastewater.

Article Published in Surface World Magazine April 2007

Author: Ian Burke, Kurion Technologies Ltd.

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