By: George M. Potter1, Samuel Oti-Atakorah2, and Casper Dzomeku3
May 7th, 2004 (Archives)
The Ashanti ore deposit at Obuasi can be described as double refractory. Mineralogical analysis of the ore reveals three main characteristics namely: very fine gold locked up within the lattice structure of arsenopyrite and pyrite, which can be transitional in nature. Secondly, the presence of graphitic schist (sheared schist) with active carbon which promotes "preg robbing" (adsorption of gold in solution by naturally occurring active carbon) and finally quartz vein with finely scattered free gold with the highest concentration being at the Quartz - Graphitic schist boundaries. In addition, few very fine-grained graphite intergrowths are also present in the gangue.
The importance therefore of an aggressive and effective free gold recovery system cannot be over emphasized for the attainment of a meaningful plant recovery.
Operationally, an effective free gold recovery system is also a requirement to minimize gold lock-ups in the twenty-four (24) BIOX® reactors (895.5m3/tank), seven Edward roasters and in the mills for better gold accounting and reconciliation.
Increasing importance has therefore been given to gravity concentration systems at AGC Obuasi plants and significant developments have recently been achieved. The achievement has improved free gold recovery from 8% to 16% of the total gold recovered at the Pompora Treatment Plant (PTP) and the elimination of the nugget effect has significantly improved metallurgical accounting.
The coming online of the PTP upgrade saw dramatic changes in AGC's free gold recovery philosophy. The PTP Upgrade Gravity Design apart from its aggressive approach to the free gold recovery, focused on key issues including:
- The need to maximize free gold recovery with minimal capital expenditure.
- Ability to eliminate lock-ups in the numerous ball mills, leach tanks and BIOX® reactors.
- Achievement of representative head grade for better gold reconciliation and accounting.
- Minimize losses to "Preg Robbers"
- Maximize level of automation to avert the security risk of human involvement.
The paper discusses the various past gravity circuits operated by AGC and their shortcomings. It also discusses the basis of the PTP upgrade gravity circuit design and the proven benefits. The paper finally highlights free gold recovery circuits operated outside the milling circuits and outlines the future objective of AGC gravity circuits.
Download the full report:
Developments in Gravity Concentration Circuit in Ashanti Goldfields Company, Obuasi
38 kbs| 6 page Acrobat Info Sheet
1. General Manager - Processing, AGC Ltd., Obuasi.
2. Manager, Research and Development - Processing, AGC Ltd., Obuasi.
3. Metallurgical Superintendent, AGC Lt, Obuasi.
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