The first question is what form of cyanide you want to measure, given that mill tailings contain free cyanide, gold cyanide, WAD cyanide and other more stable forms.
One cannot therefore plug in a "pH style" probe to measure "cyanide".

The top end system developed by CSIRO-was installed about 5 years ago at the Cowal Gold Mine. They use high performance liquid chromatography (HPLC) to provide accurate quantitative determinations of the chemical composition of "samples taken along the course of the ore treatment process".

It is NOT an online system.
A somewhat cheaper system is Gas Diffusion which takes about 2 hours to measure free cyanide.

Atmospheric cyanide gas analysis can and should be a continuous monitoring but this may not be what you are looking for, but something every cyanidation plant needs.

The process is to measure free cyanide. On the other hand you could give me information about CSIRO system?Regarding the gas diffusion system! You know if this is used to measure free cyanide leaching processes?

From your question, I assume you have an idea of what cyanide analyzer you want to install. Is this correct?

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There is a gas diffusion based system that is ideal for what you want to do. Reading is less than 3 minute cycle. It is designed for leaching circuit control.