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Resource eficient Zn/Ni electroplating process

The alkaline, cyanide-free membrane coating process eliminates the production of waste water and considerably reduces the amount of fresh water and energy required.

Initial situation
EJOT Holding GmbH & Co. KG implemented at the Bad Laasphe location an innovative system for the cyanide-free Zn/Ni plating of screws (sizes between Ø 1 mm and 12 mm).
 
The barrel system was introduced to meet ecological and economic goals: to improve electrochemical efficiency, to prevent waste water discharge into the sewage system, to reduce the use of chemicals, to close the plant's electrolyte and water cycle, to extend the service life of the electrolytes through continuous monitoring, and to reduce production defects.

Technical solution
The alkaline zinc/nickel barrel installation features the following aspects:
  • Membrane technology by COVENTYA GmbH for efficient and CN-free Zn/Ni plating
  • Evaporator system for the thermal treatment of rinsing water, semi-concentrates and concentrates with the option of recovering electrolytes
  • Analytical online monitoring of the ingredients and concentrations in the electrolytes using automatic analysers

Findings
The following results were achieved during the 2009/2010 project period:
  • The plating process is free of cyanide
  • The cyanide-free alkaline Zn/Ni membrane process shows a high degree of electro-chemical efficiency (> 80%). This value is about 1.5 to 1.6 times that of a conventional plating plant. The deposition rate is between 0.07 and 0.09 µm/min at 0.3 A/dm²
  • The membrane process uses 50-60% less energy than a conventional plating system
  • Consumption of organic additives was reduced by over 50% compared with conventional plating processes
  • The need for fresh water in the plant has been reduced
  • The installation produces no waste water. The rinsing water and spent electrolytes are concentrated in an open evaporator. The exhaust vapour is dissipated over the roof.
  • The goal of recycling the exhaust vapour as a distillate for use as rinsing water could not be achieved during the project period
  • The goal of re-supplying a significant proportion of the concentrate extracted in the evaporator to the electrolyte bath was not achieved for the following reason: the refilling volume exceeds both the drag-out and the evaporation values, and the concentrate extracted in the evaporator must therefore be disposed of thermally.
  • Utilization of the concentrate is uneconomic due to the low concentrations of metal
  • The Zn/Ni plating achieved by the membrane process meets the quality requirements in all respects (particularly where coating thickness and protection from corrosion are concerned)

Conclusions
The membrane process used fulfils the economic and ecological requirements and shows an improved efficiency compared to a conventional plating process.

Source: Final Report

Reference source:
Environmental library of the Federal Environment Agency (UBA)
If you would like to borrow the project report please indicate the project number.
Wörlitzer Platz 1, 06844 Dessau-Roßlau
Phone: 0049 (340) 2103 - 2305/ -2304
Fax: 0049 (340) 2104 - 2131
E-Mail: bibliothek@uba.de


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