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Author asks about feasible medieval metal recovery process

June 1, 2017

I'm an author so chemistry is not my strongest skill set, but I need help with a chemical process and the simplest solution for the situation: alternatively if what I propose doing would work.

Firstly the idea is not reclaim a pure metal from the solution since the story I am working on was during a time when chemistry was rather limited (even considered magical) and extracting the metal components is far more important than their purity.

The time period is medieval: The initial process is refining gold.

Gold is processed by adding a salt, which contains sodium chloride and bicarbonate of soda (a natural occurring salt at the time.) The gold is placed/buried under the salt in a crucible and placed in a furnace. This then extracts the copper, silver and zinc from unrefined gold.

Again I'm working on the process here not chemical reactions or temperatures.

What is left after the sweltering is 93% pure gold and a salt with a blue glassy slag containing the silver and copper or other alloys.

So, I get to the actual question: how to extract the metals in this salt? My initial reasoning is to dissolve the salt in water and add iron to it (possibly heating the solution) -- would this extract the metals?

Again, I do not need to extract a particular metal or all of the metals in the salt only the majority since chemistry was limited during that time. I also need to know if the metals extracted in this method could then be melted and cast (again not worried about their separation.)

Odell Coetzee
I am a author - South Africa, Pretoria

June 2, 2017

A. Hi Odell

Purification of gold is a very old process mentioned in Biblical times so by medieval times it was well developed.

The process you refer to is similar to cupellation
but more complicated for no reason.

The basic requirement is to melt the gold and simply stir it until the base metals oxidise to slag which was never considered worth recovering as there are simpler methods of smelting base metals, also well known by medieval times..

Sodium bicarbonate is rather rare in nature and would have no advantage over using potassium carbonate, natron or wood ash(potash) which was well known in the medieval world.

geoff smith
Geoff Smith

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