It has been many years since my bromine experience, and my memory has grown dim. However, everything I learned came from researching old mining journals in the public library. Many of them address ores and ore processing. I keyed in on what they liked to call mispickel gold ore.
Bromine is an element, as we all know. It is a (heavy) brown fluid, which is how it was administered to the agitation tank, although dissolved in a solution of cyanide and water. That it works is beyond question-----prior to the introduction of bromine I was removing only a trace of gold from ore that assayed in excess of 300 oz/ton. The final assay of the processed ore indicated I had removed greater than 99% of the gold, although only about half the silver that was contained within was recovered.
My agitation tank held only 20 gallons. To it I would add a fluid ounce of bromine, then refresh when the free cyanide level dropped, a sure sign that it was being consumed in the digestion of the gold.
It is important that one maintain a proper pH when using bromine (and cyanide)---which I recall to be no greater than 10. On more than one occasion I had to add traces of sulfuric acid to the agitation tank because the pH had risen beyond an acceptable level. Again, my memory has grown dim, so that value may not be correct. It was also important that I not allow the level of free cyanide to exceed .02%.
Bromine was killer expensive when I inquired. They wanted something like $50 for what I recall to be 500 ml, so I did some research and managed to find a case of four five pint bottles for just over $120. It was ordered from the company that recovers bromine from the ocean, with their location at that time somewhere in the south-east of the US. I used about a third of one bottle, so buying the case was clearly a winning deal. I expect that, today, you won't be able to duplicate that experience, however. Government agencies have made it virtually impossible for the average guy to procure chemicals.
Harold
