Improving the recovery of gold and copper in a CIP operation: flotation of a sulphide copper-bearing ore

Abstract

The paper presented outlines the scientific approach taken to improve the metallurgical efficiency of a modern plant at Athens Mine. The plant is based on the CIP method of gold recovery with copper concentrate as a major by-product.

In the early stages of the operation the overall gold recovery achieved averaged 61% and copper recovery was 74%. The plant was experiencing problems in the leach, adsorption, elution and electrowinning sections mainly as a result of the presence of copper in the ore. The changes made to the operating standards, the response of the circuit to these changes and the final Circuit layout and operating conditioning resulting in a 90% gold recovery are discussed.

It was concluded that the distribution of oxygen and cyanide along the leach stream determined the extent of gold dissolution. A substantial amount of cyanide (200 – 250 mg/1 NaCN equivalent) was necessary to avoid preferential adsorption of dissolved copper onto carbon in the CIP section. Rinsing carbon in a cold caustic cyanide solution resulted in good elution of copper prior to the gold elution stage. The copper-free loaded carbon was easily treated for gold with very high elution and electrowinning efficiencies of 96 and 98% respectively. A bullion of high fineness (in the region of 98% gold and silver) was obtained and the activity of carbon after elution was reasonably high at 8 0% of virgin carbon.

One detrimental effect of the changes made to improve the gold recovery was a high residual cyanide content in the CIP tails. This was overcome by the use of the Inco process at a cost of 20 cents per tonne ore treated (current cost is 35 cents/tonne) (Zimbabwe currency).