To my friend, nemesis, and, a damned good refiner, Harold,
A friendly discussion.
I disagree with your idea that soda ash will reduce base metal oxides to metal. It doesn't work out chemically, as I will prove.
You are aware that we disagree on the use of soda ash for fluxing pure gold. Your contention, as I understand, is that soda ash reduces the base metal oxides to metals, thus re-contaminating the gold. A question is, Do you assume this because soda ash reduces silver chloride or, did you read it somewhere? Hoke? I sure don't remember it in Hoke. Easiest reading technical book I've ever read, BTW. I've probably read and studied Hoke from 10 - 20 times, cover to cover. If fact, the first time I ever heard it was from you. You did make me think about it. It kinda made sense, seeing that it reduces silver chloride to silver metal or, does it?
Soda ash is used widely to help clean gold. I have met about 100 pro refiners that use it. I have never seen the reduction thing in print and, I have read a lot of stuff.
I have found that the silver chloride is not reduced by the soda ash. The soda ash does not act as a reducing agent in this melt system. The soda ash (Na2CO3) converts the silver chloride to silver carbonate. The HEAT reduces the Ag2CO3 to silver metal, not the soda ash. In the 1st equation, below, the silver valence is +1 on both sides of the equation. If reduction had occurred, the valence would have gone from +1 to Zero, like in (3), below.
This is a quote from the silver chloride chapter in the yellow IPMI notebook that both of us own, page 9. Verbatim quote.
I conclude that soda ash does not act as a reducing agent in the melt
What if copper, nickel, etc., went through the same 3 equations? In the CRC Handbook, it gives the decomposition temp. of silver oxide (equation 3) as 644 deg F. There is none given for either of the val.+1 or val.+2 copper oxides. Valence +1 copper oxide has the lowest melting point of the two, 2255 deg F. Maybe, it decomposes at 3500 deg F. It doesn't say. You find very little copper metal in nature, BTW. For nickel, etc., their positions are even higher, than copper, on the electromotive series. They want to be metals even less than copper. Nickel oxide melts at 3614 deg F. And, the metal oxides must melt before they can become reduced.
The soda ash could easily create carbonates with the base metals, which decompose to oxides at low temps. However, the reduction temperatures of the base metal oxides (equation 3) are much higher than that of the gold melt. The metal oxides will stay in the slag and will not contaminate the gold. The use of soda ash will not contaminate the gold, period.
I conclude, without a doubt, that soda ash will definitely not reduce any base metal oxides in the gold melt.
Gold is more efficiently cleaned using soda ash, along with borax and niter.
A friendly discussion.
I disagree with your idea that soda ash will reduce base metal oxides to metal. It doesn't work out chemically, as I will prove.
You are aware that we disagree on the use of soda ash for fluxing pure gold. Your contention, as I understand, is that soda ash reduces the base metal oxides to metals, thus re-contaminating the gold. A question is, Do you assume this because soda ash reduces silver chloride or, did you read it somewhere? Hoke? I sure don't remember it in Hoke. Easiest reading technical book I've ever read, BTW. I've probably read and studied Hoke from 10 - 20 times, cover to cover. If fact, the first time I ever heard it was from you. You did make me think about it. It kinda made sense, seeing that it reduces silver chloride to silver metal or, does it?
Soda ash is used widely to help clean gold. I have met about 100 pro refiners that use it. I have never seen the reduction thing in print and, I have read a lot of stuff.
I have found that the silver chloride is not reduced by the soda ash. The soda ash does not act as a reducing agent in this melt system. The soda ash (Na2CO3) converts the silver chloride to silver carbonate. The HEAT reduces the Ag2CO3 to silver metal, not the soda ash. In the 1st equation, below, the silver valence is +1 on both sides of the equation. If reduction had occurred, the valence would have gone from +1 to Zero, like in (3), below.
This is a quote from the silver chloride chapter in the yellow IPMI notebook that both of us own, page 9. Verbatim quote.
This high temperature technique proceeds as follows:
(1) 2AgCl + Na2CO3 = Ag2CO3 + NaCl
(2) Ag2CO3 = Ag2O + CO2
(3) 2Ag2O = 4Ag + O2
Reaction (2) and (3) occur by thermal composition. The silver carbonate of reaction (2) completely decomposes at 225 deg C. The silver oxide of reaction (3) completely decomposes at 340 deg C.
I conclude that soda ash does not act as a reducing agent in the melt
What if copper, nickel, etc., went through the same 3 equations? In the CRC Handbook, it gives the decomposition temp. of silver oxide (equation 3) as 644 deg F. There is none given for either of the val.+1 or val.+2 copper oxides. Valence +1 copper oxide has the lowest melting point of the two, 2255 deg F. Maybe, it decomposes at 3500 deg F. It doesn't say. You find very little copper metal in nature, BTW. For nickel, etc., their positions are even higher, than copper, on the electromotive series. They want to be metals even less than copper. Nickel oxide melts at 3614 deg F. And, the metal oxides must melt before they can become reduced.
The soda ash could easily create carbonates with the base metals, which decompose to oxides at low temps. However, the reduction temperatures of the base metal oxides (equation 3) are much higher than that of the gold melt. The metal oxides will stay in the slag and will not contaminate the gold. The use of soda ash will not contaminate the gold, period.
I conclude, without a doubt, that soda ash will definitely not reduce any base metal oxides in the gold melt.
Gold is more efficiently cleaned using soda ash, along with borax and niter.