Metal finishing Q&As since 1989

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TV production firm has questions on Miller chlorination process for gold

2003

Dear Sir or Madame,

My name is Alison Michel, and the production company where I work, Henninger Productions, is currently creating a program discussing the modern mining, refining, and subsequent use of gold around the world. As part of this, footage was shot on-site at the Rand Refinery in South Africa, including a portion gold undergoing the Miller Chlorination Process. After reviewing the tapes back in the studio, the producers realized that they sought additional information about the process, and recruited my assistance in locating answers to their questions.

Any information related to the questions below will be very much appreciated.

-- What are the internal temperatures of the induction furnaces in which the gold is melted?

-- When the bars are poured, it seems that a heater is added to the top - is this to ensure an even cooling effect, or some other purpose?

-- During the course of refining, what appears to be gold paddles are used by the workers. Do these have a specific name? What is their precise function?

My knowledge of this topic is patchy at best, supplied mostly by the internet, and I apologize for the vague nature of these questions. I do thank you for taking the time to read this, and am looking forward to any comments that may be offered on these subjects.

Take care,

Alison Michel
TV show production researcher - Arlington, Virginia

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2003

Alison,

A thorough discussion of the Miller Chlorine method is found in many old mining texts. One of the best is, "The Metallurgy of Gold", by Sir T.K.Rose. It's listed at Amazon.

Chris Owen
Consultant - Houston, Texas

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2003

The temperature of the metal in the induction furnace is generally 1150 degrees C / 2102 degrees F for the Miller Chlorination Process. The heating of the top of the gold bar with a flame as it cools keeps the surface of the gold bar smooth and bright. It also helps minimize the shrink (large dimple) on the surface of the gold bar.

The gold paddles you refer to are .995 purity gold anodes ready to be placed in the Wohlwill electrolytic cells for refining to .9995 purity.

Jim Sivertsen
Refining & Alloys - Alden, N.Y., U.S.A.

The heater to the top of the ingot ensures it cools from the bottom up. Any residual slag floats to the top.

Alastair Muir
- Calgary, Alberta, Canada
August 4, 2009