CASE STUDY 3

Simultaneous metal recovery and wastewater treatment in plastic electroplating production

The third case study is a typical example of processes with moderate wastewater flow rates but heavy load of heavy metals that may causes serious environmental problems. Wastewater effluents of this type can be found in electroplating, mineral processing, electric, electronic and chemical industries.In this project, the case study 3 will focus on a plastic electroplating and the main objective is to simultaneously recover resources and purify water in order to reduce fresh water consumption and global environmental impact. This case study will be hosted by the company BIA GmbH in Solingen (Germany).Since BIA acts as a global player in plastic electroplating and produces at different places in the World (Germany, Mexico, China and Slovakia) generating more than 30.000 m³ wastewater per year, the developed approach will address a global problem. It is important to note that all these countries currently strictly regulate the release of nickel (0.5 to 2.5 ppm, except China) and chromium (0.5 to 1.2 ppm). The proposed approach developed in Solingen is intended to be replicated and taken into operation in the other production sites.

Case-study-3

Electroplating facilities usually operate different plating lanes. A typical plating lane mainly consists of a series of treatment and rinsing baths (up to 30 in total). Plastic parts to be electroplated hang on flight bars which move and transport a certain amount of liquid containing electrolytes from bath to bath (approx. 0.3 L/Flight Bar). In this case study, every 4 min a new flight bar is plated. The contamination of further treatment baths with different metals or additives may have a considerable negative impact on the final product quality and must be avoided. Therefore, the rinsing process (Fig 1.7) plays a key role in this process and has to be carefully operated. Rinsing water is highly polluted and has a content of 10-20% electrolyte concentration (mostly metal sulfates, MeSO4) when discharged.

Currently, these electrolytes cannot be reused and this loss additionally drives up the process costs. In the process to be studied, approx. 126 m³ rinsing water are produced per week corresponding to 6.048 m³/year. Plastic electroplating is a very sensitive process and product quality requirements are high. Rinsing is a critical step in this process. The chemical composition of the treatment baths is complex and subject to particular attention during production operations. Beside metal sulfate, they usually contain numerous additives such as organic compounds (TOC) and boric acid. During electroplating, organic compounds are usually electrochemically broke down and only reusable.