Article continued (page 3): Modern Treatment Methods of Strong Chelates in Surface Technology

Electrolysis of “Electroless Copper” bath

Electrowinning recovers the dissolved copper, but the chelates still remain or are changed electrochemically to other chelates. EDTA “disappears” to a great extent, but under detailed analysis, is found to be replaced by other homologues of EDTA, for example: EDTriA, EDDA-N,N, EDDA-N,N’, EDMA as well as IMDA that are formed through the electrolysis. In this case the separation of the stream prior to treatment is also necessary to achieve consent levels. Not all the chelates are destroyed, which leads to subsequent problems in the effluent treatment plant, for example, remobilisation of the heavy metals from the precipitate.

Table 3. Contents of the electroless CuEDTA bath and levels after treatment with the KURION ACK UV-process.

Cyanide Treatment / Cyanide Destruction in  contaminated process waters

The traditional cyanide destruction / cyanide treatment is achieved by hypochlorite treatment. This method in practice produces acceptable results as far as the metal levels are concerned. If the wastewater contains metals such as nickel or silver, these, as a rule, can cause major problems. If a total cyanide limits are imposed and Ferro cyanides are present, then traditional Hypochlorite treatment will rarely achieve the required discharge consent criteria. In addition this treatment has another disadvantage in that the transformation of cyanide with hypochlorite creates large amounts of toxic chloramines. The chloramines result from the reaction of the excess of hypochlorite with ammonia created in the process.

UV Cyanide Destruction / Cyanide Treatment Process

CN^- + H₂O₂ --> CNO^- + H₂O

CNO^- + 2 H₂O --> NH₄⁺ + CO₃^2-

^{further acidification}

+ 2H⁺   ->  NH₄⁺ + CO₂ + H₂O

and, if further oxidation occurs

à N₂ + CO₂ + H₂0

The UV light enhances the formation of OH - radicals:

H₂O₂  + UV à 2 OH^.

Figure 1. Enviolet® 36 UV-Reactor process technology, UV process is controlled to maintain optimal performance conditions through a patented process. The UV- facility includes process control and safety interlocks, also the dosing and mixing of the chemicals are fully integrated.

Waste water treatment using Enviolet® – UV-oxidation or Cyanomat®

During UV-oxidation the organic chelates and cyanides are broken down. The inorganic phosphoric substances (hypophosphite and phosphite) can be oxidized to phosphate. Properly applied, this process can be used for all strong chelates.

The electrolytes containing chelates (for example, EDTA, tartrate, citrate, etc.) or the chelates of Zn-Ni electrolytes are oxidized through UV-oxidation under standard reaction conditions to the inorganic carbon dioxide (CO2). This process can be compared with the “cold” combustion in the water phase.

The metals and solvent in the wastewater remain contained during the UV-oxidation. After the UV-oxidation the metals are precipitated with a traditional alkaline flocculent, whereas for chemical nickel, a lime flocculent is offered to eliminate the phosphates and calcium phosphate. This is now possible because the chelates have been eliminated, there are no more strongly complexed metals in the water and all phosphorus-containing substances are oxidized to phosphate.

Table 3. Contents of the electroless CuEDTA bath and levels after treatment with the Kurion ACK UV-process.
 

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This page was last reviewed 27/01/09