| Cation Removal from Drag out Baths | The Netherlands | - | Full scale |
MANUFACTURE OF FABRICATED METAL PRODUCTS # 40
Background
This case study illustrates use of a cation exchanger for continuous cleaning of drag-out baths followed by evaporation in order to facilitates water reuse.
Cleaner Production Principle
Process modification; Recovery, Reuse and Recycle
Cleaner Production Application
This technique involves use of a cation exchanger for continuous cleaning of drag-out baths and evaporation followed by water reuse.
The plant operates a three-step cascade rinse behind the plating baths and the water is used to replenish the water evaporating from the process baths. This is supplemented with demineralized water. In the original process, a final rinse with tap water occurred after the cascade.
Because of a build-up of undesired cations such as iron, copper, and nickel in the process baths, drag-out baths are now treated over a cation resin. The water of the final rinse has been substituted with demineralized water and is also treated over the resin. The process liquor is difficult to be treated. By using the waste heat of the cooling system and controlling the process bath temperature, an extra amount of water is evaporated. The resulting wastewater is still treated in a DND installation. Lifetime of the untreated baths was about five years with the original process.
In the original process, the starting power was 10 V and 15,000 Amp. The voltage increased at a rate of 1 V/A. Due to limitations in the transformers, this meant that after about five years the process baths had to be thrown away. In the current situation, the voltage increased two volts in five years of operation, and then remained stable.
Environmental and Economic Benefits
The process modification resulted in decreases in
| Sludge production from 10 tons to 0.4 tons in five years. |
| Tap water consumption from 1330 to 15 m3/yr and demineralized water consumption went up 1320 m3/yr. |
| Energy consumption decreased from 99 MWH/yr to 59 MWH/yr corresponding to a saving of more than 40%. |
| The consumption of chromic acid decreased by 2,000 liters/yr. |
| Chemicals for the DND installation decreased from 2,000 to 20 liters/yr. |
| No adverse effects on product quality were reported in the source document. Instead, the quality should have improved since foreign elements have been removed. |
The following are savings were realized using the modified process:
| Savings in Dfl/yr | |
| Less chromic acid | 3000 |
| DND treatment chemicals | 8000 |
| Waste disposal | 700 |
| Power consumption | 5340 |
| Tap water | 1900 |
Operational and maintenance costs for the five year period are as follows:
| Old Process (Dfl) | New Technology (Dfl) | |
| New chromic acid | 15,000 | -- |
| Waste disposal | 3,500 | 140 |
| Chemicals for DND | 40,000 | 400 |
| Power loss | 74,250 | 44,550 |
| Tap water | 8,600 | 100 |
| Extra demineralized water | -- | 33,000 |
| Sewage costs | 9,550 | 100 |
Costs over five years have decreased by Dfl 71,710. The payback period cannot be calculated due to incompleteness of investment data. However, based on the cost information given and the cost of an ion exchanger, it can be estimated that the payback period would be less than one year.
Constraints
No information was provided.
Contacts
Review Status
This case study was originally compiled by the UNEP IE Working Group on Metal Finishing. It underwent a UNEP IE funded technical review in 1994 for quality and completeness. It was edited for the ICPIC diskette in July 1995.
Subsequently the case study has undergone another technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.