BFI VDEh-Betriebsforschungsinstitut GmbH

Initial situation:

The process water occurring in steel production and surface treatment (galvanising) can be contaminated with elevated zinc levels. There are also discussions about significantly lowering the current discharge limits for surface treatment from 2 mg/L to 1 mg/L to 0.1 mg/L, which requires immediate action in process management and wastewater treatment. In the batch processes of steel production, the rapidly changing Zn contents within a few minutes and the large volumes of water to be treated with high solids contents present a challenge. The commercial atline-analysers for zinc do not meet the requirements of the steel industry.

Project targets:

• Development of a representative sampling method from solids-loaden process water
• Development of a fast and robust at-line measurement of the total zinc content in particle-laden process water and thin sludge,
• Prediction of the zinc content of process waters,
• Development of integration concepts for atline measurement and partial flow process water treatment for compliance with zinc discharge limits and reuse of ferrous sludge.

Innovative approaches:

• Use of ultrasound to develop representative sampling from process water contaminated with solids,
• Adaptation of the reagents for photometric zinc measurement to avoid the interfering influences of iron,
• Use of ultrasound and induction to accelerate the dissolution of zinc-containing solids with acid,
• Prediction of the zinc content in process water and sludge using simulation of production and process water treatment,
• Targeted partial flow treatment or time-limited full flow treatment based on the prediction and zinc atline measurement.

Benefits for the industry:

• Rapid analysis of the total zinc content
• The combination of process data and atline analytical data enables needs-based and therefore economical zinc removal as part of process water treatment and the utilisation of low-zinc, iron-containing sludge.
• Possibility of optimising scrap quality/purchase prices as well as partial process water treatment and sludge recycling with the aid of the simulation developed.

The BFI work includes the development of representative sampling as well as the simulation of the zinc content and partial stream treatment with precipitation and microfiltration. The TZW is working on the development of rapid acid dissolution and Fe-insensitive photometric measurement of the total zinc content.

About the project:

Project duration: 07/2022 – 12/2024

Funding provider: Federal Ministry for Economic Affairs and Climate Protection