Tellurium Copper

[haveagojoe]

I recently discovered that some gold plated pins which have been manufactured by turning (on a lathe) may use Tellurium Copper as the substrate. These include pins such as the center pins of BNC and SMD connectors, and the ones sometimes referred to as 'pogo pins'. They tend to take a lot longer to dissolve in Copper Chloride and I think the alloying with Tellurium may be part of the reason. However it is desirable to be able to process them as the gold plating is often 24kt.

Tellurium is a metalloid element which can be added to copper to improve its strength and durability without significantly impacting its electrical and thermal conductivity. It is also added to improve machinability.

Metallic Tellurium is considered mildly toxic, and compounds of Tellurium can be highly toxic. In particular Tellurium Oxide, and Hydrogen Telluride are toxic fumes which can be formed by decomposing with heat.

Tellurium is not soluble in HCl, so will remain as a white sponge or powder when copper it is alloyed with is etched away by CuCl2 in our common "AP" process. Perhaps due to its appearance it may not be discernable from CuCL crystals with which it might be mixed. CuCl is removed with HCl but Tellurium could remain among the foils.

Tellurium is dissolved by Aqua Regia, and will precipitate with SMB. This behaviour means that it is not an easy contaminant to remove from ewaste gold refining processes, since it will stay with the gold throughout.

Tellurium is also sometimes added to gold plating as a "brightener" to improve its sheen. So when a finished button looks really nice and shiny, there is a possibility that it may still in fact be contaminated with traces of Tellurium.

I have seached the forum for Tellurium; there is some information regarding its natural deposition with gold in Gold-Telluride ore known as Calavanite. However there is very little about Tellurium contamination arising in ewaste processes.

I would be interested to hear if there are any known approaches for dealing with Tellurium from Tellurium Copper pins. Foils recovered from a Copper Chloride leach are commonly roasted to reduce Tin to Tin Oxide so that it can be removed with a HCl wash prior to dissolving the foils; presumably any Tellurium which is present will decompose as Tellurium Oxide gas during this roast. It may be that this is sufficient to remove Tellurium as a contaminant, but I think at least the toxic nature of Tellurium Oxide fumes should be highlighted as it is seldom mentioned.

The only other approach I could find was the suggestion by the infamous Dr Poe of using Hydroquinone as a selective precipitant for gold which will leave Tellurium behind in solution.

Alternatively, perhaps the types of pins manufactured by turning should only be processed by electrolysis, leaving the Tellurium Copper substrate intact.

I think a discussion around this topic would be interesting and useful, and also prudent, considering the potential toxicity hazard.

 

[Yggdrasil]

I recently discovered that some gold plated pins which have been manufactured by turning (on a lathe) may use Tellurium Copper as the substrate. These include pins such as the center pins of BNC and SMD connectors, and the ones sometimes referred to as 'pogo pins'. They tend to take a lot longer to dissolve in Copper Chloride and I think the alloying with Tellurium may be part of the reason. However it is desirable to be able to process them as the gold plating is often 24kt.

Tellurium is a metalloid element which can be added to copper to improve its strength and durability without significantly impacting its electrical and thermal conductivity. It is also added to improve machinability.

Metallic Tellurium is considered mildly toxic, and compounds of Tellurium can be highly toxic. In particular Tellurium Oxide, and Hydrogen Telluride are toxic fumes which can be formed by decomposing with heat.

Tellurium is not soluble in HCl, so will remain as a white sponge or powder when copper it is alloyed with is etched away by CuCl2 in our common "AP" process. Perhaps due to its appearance it may not be discernable from CuCL crystals with which it might be mixed. CuCl is removed with HCl but Tellurium could remain among the foils.

Tellurium is dissolved by Aqua Regia, and will precipitate with SMB. This behaviour means that it is not an easy contaminant to remove from ewaste gold refining processes, since it will stay with the gold throughout.

Tellurium is also sometimes added to gold plating as a "brightener" to improve its sheen. So when a finished button looks really nice and shiny, there is a possibility that it may still in fact be contaminated with traces of Tellurium.

I have seached the forum for Tellurium; there is some information regarding its natural deposition with gold in Gold-Telluride ore known as Calavanite. However there is very little about Tellurium contamination arising in ewaste processes.

I would be interested to hear if there are any known approaches for dealing with Tellurium from Tellurium Copper pins. Foils recovered from a Copper Chloride leach are commonly roasted to reduce Tin to Tin Oxide so that it can be removed with a HCl wash prior to dissolving the foils; presumably any Tellurium which is present will decompose as Tellurium Oxide gas during this roast. It may be that this is sufficient to remove Tellurium as a contaminant, but I think at least the toxic nature of Tellurium Oxide fumes should be highlighted as it is seldom mentioned.

The only other approach I could find was the suggestion by the infamous Dr Poe of using Hydroquinone as a selective precipitant for gold which will leave Tellurium behind in solution.

Alternatively, perhaps the types of pins manufactured by turning should only be processed by electrolysis, leaving the Tellurium Copper substrate intact.

I think a discussion around this topic would be interesting and useful, and also prudent, considering the potential toxicity hazard.

Never heard about this.
Have you found actual references to this?
The producer never use any unusual substance unless they have to or it is cheaper.

 

[haveagojoe]

Never heard about this.
Have you found actual references to this?
The producer never use any unusual substance unless they have to or it is cheaper.

That's true, the substrate is most commonly machined in brass or bronze which is also slow to dissolve in Copper Chloride, but which has inferior conductivity. Tellurium is generally only used in HiFi audio or other high-end products. However in a batch of escrap it's easily concievable that Tellurium may be present as it is sometimes added to gold plating also.

Tellurium copper alloys include CW118C, C14500 and C109, sometimes known as "free machining copper".

Here is a supplier who lists "Electrical Connector Pins" as one of the main uses for Tellerium Copper: https://www.sdnonferrous.co.uk/tellurium-copper

Here is a manufacturer who lists Tellurium Copper as a material option: https://www.mill-max.com/engineering-notebooks/pcb-pins-connectors

Googling "Tellurium Copper Connector" will give numerous hits, mostly for audio conectors. The main brand using it seems to be AECO. Johoty is a manufacturer of pogo pins who uses Tellurium Copper. Although it may not be common, it's concievable that Tellurium may be present in a variety of copper-based products which we enounter in escrap.