HAUREX process
Halwachs AURum EXtraction
gold refining by batch or semicontinuous solvent extraction

blue arrows or lines identify liquids, brown solids; the weight of lines and arrows is an indication for relative solid or liquid mass flow rate in question on a logarithmic scale.
 
The process was designed to run on high-tech low emission sites. For companies which are allowed to run old polluting aqua regia processes it might be reasonable to upgrade their standards of sustainable development on the long run.
The process can run from lab scale to production capacity; it can be upscaled easily. Because of its simplicity no further process data are supplied here for reasons of confidentiality in order to prevent unauthorized copies. Any plant will be tailor made for individual customer needs and capabilities and will take into account the skills of the operators.

We are often asked about the difference between the Haurex and the aqua regia process; here it is:

1) dissolution of gold scrap

Aqua regia releases much more pollutive offgas then the Haurex process which does not use nitric acid. Therefore less expensive offgas scrubber installations are necessary, no NOx problem.

Aqua regia and the Haurex process may use the same equipment for dissolution, there is no difference; just different less pollutive chemicals used in Haurex process.

2) Cleaning of the pregnant liquor

There is no cleaning with the aqua regia process !
Gold is directly precipitated from the dissolution filtrate. That is why gold purity is >99.99% Au in very limited cases of highly pure feed materials only, normally just >99.95%; statements of aqua regia refiners claiming 99.99% Au should be treated as marketing issues. Please note that 99.99% Au cannot be determined by fire assay - but numerous refiners worldwide do.
But for jewellery alloys it is unimportant if you use >99.95% or >99.99% Au. It is a matter of company policy.

In contrast to aqua regia process the Haurex process purifies the gold bearing liquor by solvent extraction ! The gold is precipitated afterwards from the liquid pure extract.

Aqua regia and the Haurex process may use similar equipment for gold precipitation and filtration.

3) offgas cleaning

Aqua regia regia needs large NOx and HCl offgas scubbers because absorbtion of NOx is very slow.

Haurex process needs small offgas scubbers for HCl only.

4) spent liquid waste, effluents 

Liquid waste is consisting of the filtrate of gold precipitation and the spent waste gas scrubber solutions.

Haurex process produces less amount of concentrated spent liquids; only based on chlorides, no nitrates.

5) gold scrap with platinum and palladium

If you use aqua regia for platinum and palladium containing scraps (white gold, dental scrap) you will loose a considerable amount of platinum and palladium because precipitation from gold-free filtrate is incomplete (you or your customers will loose money, depending on your metal quotation)

If you use Haurex process, the precipitation of platinum and palladium from the gold-free raffinate of the solvent extraction is easy and straight forward.

HEV · D-63571 Gelnhausen · Rhönstraße 106 · phone 0049-6051-968928 · fax -968929
email :  HEV@halwachs.de   ·   internet :  www.halwachs.de