Galvanotechnics

A new preparation process for the extension of the holding time of acidic zinc electrolyte and hydrochloric acid cleaning as well as process water circulation management in electroplating

An electroplating company built a mobile treatment unit in which any impurities are eliminated from the solutions at an early stage in the process using special ion exchangers. This saves large quantities of hydrochloric acid and sodium hydroxide solution. All of the rinse water is treated in a reverse osmosis filter system and then reintroduced into the water cycle. 

 

Summary 

Initial situation 

OFTECH Oberflächentechnik GmbH is an electroplating company which electroplates iron or steel workpieces after pretreating them and then passivates them according to customer specifications. The company’s clients come from the electrical, automotive and mechanical engineering industries, and the building sector.

Before the project was implemented, only chrome VI was used for passivation.

Fresh water was used in all production stages. The waste rinse water was cleaned in the wastewater treatment system, returning values below the discharge limit. The treated wastewater was then discharged into the public sewers and was no longer available for use in the unit.

The aim of the project was to use fewer resources in the electroplating process for the acidic zinc-plating of rack-mounted parts.

In the course of the conversion an additional chrome III passivation layer was introduced as a means of effecting the step-by-step reduction of chrome VI passivation.

 

Process solution 

At the heart of the new recycling plant is a mobile retardation unit used to regenerate the zinc electrolyte and to extend the life of the hydrochloric acid bath. A highly alkaline anion exchanger is used as ion-exchange resin. Demineralised water is used to regenerate the ion exchanger.

Using a membrane-based nanofiltration unit facilitates a recovery system in which all rinse water is treated in a reverse osmosis filter system and the permeate is then reintroduced as rinse water into the water cycle. 

 

Findings 

The holding time of the acidic zinc electrolyte and hydrochloric cleaning baths has been extended due to the earlier removal of impurities in particular process solutions. This has resulted in a reduction of the number of electrolyte or baths required and, consequently, less waste. 

The optimisation of the rinsing process and the waste water flows has been enabled through the additional application of a recirculation system (membrane technology). As a result, improved cleaning efficiency and, thus, multiple usage of the rinsing water has been achieved.

This results in savings of around 28%.

With the help of the new procedure in the system applied, considerable amounts of the usually required chemicals (hydrochloric acid 10 t/a minimum) and fresh water have been saved. The specific water consumption has been reduced from 5.4 to 3.6 m3 per day.  

 

Conclusions 

The approach developed under the project is ideal for reproduction in the electroplating and other industries. 

Project Participants 

Implementing Institutions

OFTECH Oberflächentechnik GmbH

Cooperation Partner

Efficiency Agency for North Rhine-Westphalia (EFA NRW)

Technology Providers

Fischer Verutec GmbH

Further Project Information 

Project title: Neuartige Aufbereitungsverfahren zur Standzeitverlängerung von sauren Zink-Bädern und Salzsäurebeizen sowie zur Prozesswasserkreislaufführung in der Galvanik

Project number: 20110

Project period: 2007 - 2009

Project region: Germany (North Rhine-Westphalia)

Project contact:

Frau Puder

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+49 (340) 2103 3067

+49 (340) 2104 3067

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Source: Environmental library of the Federal Environment Agency (UBA)