News

Modern wastewater technology - the DUALmEX® process by Färber & Schmid

29.11.2016

Two-step treatment process for the preparation of acidic and alkaline zinc nickel rinse- and waste water without the use of vaporiser technology

Since the widely use of zinc-nickel coating processes the greater difficultly of wastewater treatment compared to previous processes is well-known. Due to the high level of complexity of the metals it seems both technically and economically impossible to treat this wastewater in regular treatment plants. Vaporiser technology questionable in terms of energy usage and economic viability has since been introduced to electroplating industry.

With the development of the new DUALmEX^® process by Färber & Schmid, the required two-step treatment is given a chance in the electroplating industry. In the two-step treatment, a part of the metals is separated with the sludge at first batch-tank by an easily implemented hydroxidic precipitation with lime and/or caustic soda. Only metals, still dissolved by the complexing agent, in the clear water get to the second step (next batch reactor), followed by a special sulphidic precipitation. This process way drastically reduces the consumption of precipitation chemicals as there is no danger of binding metals which have already hydroxicidically precipitated again. The fundamental idea is probably as old as wastewater treatment in electroplating itself!

Why has this idea not become widespread yet?
It cannot be due to the increased plant expenditure, the additional costs are amortised in no time at all. But rather, the fully sulphidic precipitation with inorganic and organic sulphides shows very quickly results in typical colloidal precipitation. In practice, this means that the metal is precipitated in the chemical sense, however, it cannot be physically separated from the clear water by sedimentation or filtration.

What is new about the DUALmEX^® process?
Over the past few years, Färber & Schmid has developed products based on a polymer structure in the HydroMet Alpha series. The polymer precipitations do not tend to cloud and do not form colloids. Therefore the sludge can be simply transformed into a nice flocculation which easily sedimentation, using the right F&S flocculant. The result is in general very clear water.

What is the advantage of DUALmEX^®?
Practical experience shows savings of 62% in terms of the treatment chemicals for wastewater from alkaline Zn/Ni plants, or even a saving of 77% in acidic Zn/Ni processes. The process treatment safety is very high, the process is easy to automate and the plant operator is quickly trained in what is ultimately an uncomplicated process.

What are the limitations?
There are no limitations with the acidic Zn/Ni process! In the alkaline processes there are differences between the bath types from individual manufacturers. The baths differ in terms of concentration and the type of complexing agent.  The higher the concentration of the complexing agent, the less metal is precipitated in step 1 and the more HydroMet Alpha is used in metal precipitation in step 2. The saving is therefore more modest. A further disruptive factor is the formation of cyanide. Alongside the difference by using membranes in the bath, here – along with other parameters – the selection of the bath types is decisive.

Can DUALmEX^® also be used for other kinds of wastewater?
For very lightly polluted wastewater, the cost saving with DUALmEX^® is reduced. The use of DUALmEX^®, however, is not limited to Zn/Ni wastewater. Mixed waste from plating on plastics (POP) or printed circuit boards (PCB) operations can also be successfully treated.