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MEI Online: Hydrometallurgy: Latest News: October 29th 2009


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:: Mintek Commissions New Advanced Gold Leach Facility

Mintek has commissioned a new advanced gold leach facility aimed at optimising the design and operation of gold recovery circuits from both the environmental and economic standpoints.

“The advanced leach facility bridges the knowledge gap between the gold leach process and the observable environmental impacts when residues are discharged," said Peter Lotz, head of Mintek's cyanide services group. "Better operational and management strategies help to avoid regulatory fines or plant closures, and reduce remediation costs either during operation or at the decommissioning stage. Waste minimisation is also an important part of operational sustainability."

Instead of applying the conservative, reactive approach to ameliorate environmental problems once they become apparent, it is preferable to identify up-stream process modifications which avoid the problems in the first place. "Experience has shown that this sort of pro-active management is better dealt with by metallurgical staff during the design phase or at the operational level rather than by on-site environmental personnel, hence Mintek's approach to integrate it into the process metallurgy," concluded Lotz.

The fully instrumented mini-plant is designed to supplement the widely-used bottle roll technique for gold amenability testwork by allowing the leaching kinetics of the target metal and the environmental parameters to be monitored in relation to the process conditions. The environmentally harmful elements such as cyanide, arsenic, and heavy metals are tracked in “real time” as the leach progresses. "Understanding how the chemistry of the process changes in response to variations in the controllable leach parameters will enable us to improve leach plant designs to meet environmental protection standards without compromising gold recovery," explained Sonestie Janse van Rensburg, senior scientist in Mintek's Hydrometallurgy division.

The facility makes it possible to modify and evaluate the process parameters that can be realistically changed on an operating gold plant, such as pH, Eh, oxidant addition, pulp viscosity, and cyanide concentration, and to gauge the effectiveness of staged addition of cyanide, pre-oxidation (with detailed dissolved oxygen measurements), and the addition of supporting reagents such as lead nitrate. Cyanide consumption and the concentrations of free and weak-acid dissociable (WAD) cyanide are monitored using Mintek's Cynoprobe online analyser. Total cyanide and thiocyanate as well as cyanate can be quantified using standard laboratory methods such as Segmented Flow Injection analysis. The gold dissolution kinetics can also be evaluated in conjunction with other elements, for example iron, sulphur, copper, and nickel, during the leach.




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