Pre-flux Iron Removal – Chemical Process
The effects of carry-over of ferrous iron into the kettle are well known but few galvanizers have successfully used iron reduction equipment to achieve the potential zinc savings.
Equipment alone is not sufficient to achieve zinc savings. Gongda Galvanizing has developed equipment and fee based support programmes to deliver financial and quality benefits
The process
- Oxidation of soluble ferrous iron to insoluble ferric with hydrogen peroxide.
- Use of pre-flux management software to
- maintain ferrous iron at or below 0.5 g/l in the pre-flux solution
- maintain a balanced salt in pre-flux to assist drying
- Maintain correct acidity in the pre-flux bath
The benefits
- Radical reduction in dross make
- Large zinc use reductions through excellent flow-off of high fluidity alloy.
- Control of coating weight is enhanced.
- Smoother, brighter surface appearance
- More consistent results
- No pre-flux to be disposed of
- Potential to eliminate rinse discharge
What Can be Achieved by Ferrous Iron Reduction
A CASE STUDY ON THE IMPACT OF A SERVICED PRE-FLUX FERROUS IRON REDUCTION UNIT - AUSTRALIA
An Australian general galvanizer, contracting to steel fabricators to galvanize manufactured products, has had a pre-flux iron removal unit in commercial use since April 2001.
In June 2000 the Company was processing 4000 tonnes per year with a zinc usage of 86 kg of zinc per tonne of steel.
As at October 2001 production had increased to 10,000 tonnes per year with a zinc usage of 49 kg per tonne. The increased production resulted from improved customer satisfaction – quality improvement as a result of reduced ferrous iron entering the kettle.
Well managed iron reduction in pre-flux, where ferrous iron in the pre-flux was consistently maintained at or below 0.8 g/l, brought about this saving of 37 Kgs of zinc per tonne of work.
Based on the increased tonnage of 10,000 tonnes per year and a zinc price of US$2,300 per tonne this reduction in zinc use of 37 Kgs per tonne equates to a cost reduction of US$851,000 per year.
In this plant the technology has been run both with and without our technical support. Without support the zinc consumption increased from 49 kgs per tonne of work to approximately 64 kgs per tonne or an increase of 15 kgs per tonne. Gongda Galvanizing recommends use of its support service to maximize cost savings
The amount which can be saved by correct application of iron removal is dependent on the existing efficiency of the production line. Some companies are now able to run their pre-flux at fairly low iron levels and thus smaller savings will be achieved using iron reduction equipment
Practical experience indicates that savings of 10 Kgs to 25 Kgs per tonne of work are achievable in most galvanizing plants