Silver chloride

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Silver chloride (AgCl) is an insoluble salt formed by silver ions and a chloride source. Small amounts can be dissolved as a complex ion in strong chloride solutions. When silver chloride is stored for later treatment into metallic silver it is strongly recommended that it is stored wet, dried silver chloride is much harder to deal with than wet.

Forming silver chloride is usually avoided by refineries as far as possible, but there will always be some made as byproducts in various processes, as for example when low silver gold alloys are directly digested in aqua regia.

Contents

Formation

Silver chloride is formed whenever a soluble silver salt is mixed with a chloride salt. Silver chloride is precipitated as a white, sometimes cottage cheese like sludge.

Solubility

Reduction back to silver

Karo syrup

( Please look up and enter GRF search silver+chloride+karo+syrup )

(Main article Silver chloride reduction to metal with sugar)

A classical way of recovery of silver chloride is to first turn it into silver oxide by addition of lye and then reduction back into metal with a sugar, commonly Karo's syrup (dextrose or sucrose sugars are best).

Steel and sulfuric acid

  • Mix silver chloride with 5-10% sulfuric acid and some iron nail or other iron scrap.
  • Tumble or move regularly until the silver chloride is converted into silver.
  • Take a small sample and wash thoroughly to get the iron sulfate out.
  • Add a little borax and soda ash, then melt and watch the results.
    • Slag should be creme colored if all iron sulfate was washed out.
    • Slag is black if there is some iron sulfate left.
    • Dense white smoke means there is some silver chloride left and the slag looks metallic.
  • When the test sample melts without issues the batch is ready and can be washed and melted.

Ref : GRF : Lou gives some advises on silver chloride conversion

( Please look up and enter GRF search silver+chloride+steel+sulfuric )

Reduction with formic acid

( Please look up and enter GRF search silver+chloride+formic )

Reduction in furnace

( Please look up and enter GRF search silver+chloride+furnace )

Silver chloride can be converted back into silver by smelting with sodium carbonate. Care must be taken to not heat it too fast and be aware of not inhaling any white fumes. The white fumes contains silver chloride and can be lethal in extreme cases. GSP on the hazards of furnace reduction.

GSP http://goldrefiningforum.com/phpBB3/viewtopic.php?f=50&t=20719#p212791

The Kunda method. US Patent #4388109. About 0.74g of Na2CO3 per g of AgCl, very well blended (an electric blender was used in the patent). According to a graph I have in another book, at 420C, only about 30% of the the AgCl will be converted to Ag. It needs to be heated to 550-600C for about an hour. If it exceeds 625C, it forms a solid chunk and you won't be able to leach it. It is then cooled, pulverized, and leached with water, which dissolves everything but the silver powder.

I would dry the AgCl before blending with Na2CO3. The blender will break it up, I would think, into face powder.

Reference : GRF topic on silver chloride reduction

Smelting with zinc. Silver chloride + zinc -> silver + zinc chloride. Source : IPMI pyrometallurgical video on youtube.

Solubility in chloride solutions

In strong chloride solutions, for example concentrated aqua regia, AgCl forms a complex ion that is soluble and give yellow solutions. Up to ( Please look up and enter GRF search silver+chloride+solubility ) g/liter can be dissolved in concentrated aqua regia. Other concentrated solutions with Cl- can dissolve some AgCl.

AgCl + Cl- <=> [AgCl2]-

References

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