Zinc recovery from Dross

A. Sir:
True dross is an alloy of iron 6% and zinc 94%. Hot dip galvanizer's dross is usually between 2% to 4% iron. Thus a simple heat sweat-out procedure can theoretically recover perhaps as much as 50% zinc. If memory serves me, another possible method is the use of a third metal (I think aluminum) whereby this metal (aluminum) is added and the mix strongly heated whereby aluminum forms a stronger binary alloy with the iron (than does zinc) thus releasing the free zinc. If the dross is 3% iron each 100 pounds of dross contains 3 pounds of iron and the appropriate amount of aluminum is added to combine with the iron. A recovery approaching 97 pounds of zinc is expected and perhaps 5 pounds of iron-aluminum alloy would also be produced. Likely the people who do this as a business have worked out the details. A small batch trial would be appropriate and a book on binary metal alloys would show the best theory.
Regards,

A. Sir:
I spoke with Barry Dugan of Horsehead Zinc (formerly Zinc Corporation of America) about zinc recovery from galvanizers dross. He said that adding aluminum to dross is the process used by a few recovery companies. Both floating dross (sheet galvanizing) and some normal galvanizers dross is used. I expect using exactly the right amount of aluminum and the correct methods of mixing and heating are extremely important. Perhaps Barry could name the companies and then contact could be made and perhaps correct methods used. The book on binary alloys would also be useful for predictions and investigation of tertiary alloys. I do not have intimate knowledge of the process. I only know it exists.
Regards, Tom Cook

A. We are specialist in the field and so far the pure zinc can is coming from the fact that the way to remove it from the bath will take with it a lot of pure zinc.
Dross itself is an alloy and can only be recovered by distillation at high temperature.

A way to recover pure zinc from the dross is to remelt it in a second special shaped bath where the dross settles and the pure zinc is on the top. Us a H/D kettle which is big in order to create settling

Wilfred Sprang
WTN Air & Water Treatment BV - The Netherlands

A. There is no simple way to recover pure Zinc from dross, Prime Western grade zinc could be made by Aluminium process for SHG Zinc distillation is the only way.

As the LME price has gone up to about USD 4000.00 I hope many people will try to develop distillation process and might be some commercial company will sell there technology in near future.

Qaiser Majid     factory Lahore, Pakistan

A. Recovery of secondary and usable zinc from top dross can be possible by practising in simple furnace by heating the dross ingots, fluxing and casting process. We have carried out lot of trials and have come up with more than 85% recovery with 99% zinc purity.