Going For Gold

Demonstration plant to validate new products for gold recovery

Proprietary non-toxic products developed by the team have been proven in the laboratory to recover gold.  These products have the potential to disrupt the gold industry by providing an alternative to the use of toxic cyanide (industry standard method) and for which regulations (for its use) are becoming increasingly stringent across the globe.

Within the gold industry, there are two market segments; the large miners that use cyanide and the small miners that don’t, and currently lose typically half of the gold that they mine through the use of inefficient gold recovery practices.  The initial market to be targeted is the small to mid-cap (SME), non-cyanide using gold miners in Australia.  In this segment a confluence of challenges relating to resource size, transport costs, stringent regulatory approvals processes, and environmental constraints has resulted in significant untapped resources or, as stated above, the use of inefficient gold recovery practices.  In Australia alone the non-toxic products are estimated to unlock more than 3 billion dollars per annum of additional gold production (and more than 30 billion US dollars per annum worldwide).

In order to de-risk uptake of the products and commercial investment into the technology, a demonstration in the field at an industry acceptable scale is required.  However, investment or financial support from the gold industry to conduct such a demonstration at scale in the field is difficult to obtain.  This SIEF EDP will fund the construction and operation of a mobile demonstration plant that will demonstrate recovery of gold using the non-toxic products from various gold ores in the field at scale.  This validation will significantly accelerate the path to industry uptake (by both SME and large miners) and commercialisation of the products.  CSIRO and Eco Minerals Research are collaborators of this EDP.

A demonstration plant was constructed and operated at scale in the field to recover gold using non-toxic reagents (products) developed by CSIRO for gold recovery. The demonstration was conducted at the old Menzies stamp battery site in collaboration with Eco Minerals Research. The demonstration plant utilised the current gravity plant with a new plant installed to leach gold from the gravity plant tails. The new vats and leach solution processing plant were containerised mobile modules. The key aims were to attain the required data to validate that the CSIRO products can be applied in the leach process economically and to significantly accelerate the path to commercialisation by de-risking scale up, creating awareness and gaining industry acceptance.

During this project the plant treated battery sands (tailings) that contained a lot of fines which were largely removed using a cyclone. The coarse cyclone underflow material still contained some fines that impacted percolation (treatment) rates when leached in the vats.

During the six months of commissioning and operation of the demonstration plant the project team:
1. Treated 5600 t of battery sands, with 2400 t of coarse material being leached in the vats;
2. Initially achieved >80% recovery of the leachable gold (benchmarked against laboratory evaluations). Gold recoveries however were not sustained with decreasing leach time (increasing plant throughput to design capacity). This provided an understanding of gold recovery rate versus leach residence time (being largely influenced by the percolation rate and particle size distribution of the material being leached); and
3. Optimised the CSIRO products for treating the battery sands where:
a)thiosulfate consumption was 1.6 kg/t, which is below the target of less than 2 kg/t;
b)thiosulfate degradation was less than 0.5 kg/t (consumption was largely due to physical losses of leach solution); and
c)above targets achieved whilst maintaining the process water balance.

This project proved the CSIRO products could leach gold at scale with low thiosulfate consumption. The key information and understanding will be used to determine process economics (and cut off gold grade) for commercial adoption.

The demonstration project also de-risked the uptake of this technology which has the potential to unlock wealth in stranded gold deposits in Australia and overseas. The demonstration project particularly attained key information and understanding from the design and operation of a mobile modular processing plant targeted at small professional miners with small high grade gold deposits.

The positive outcomes from this project have encouraged the further development of the vat leach process at Menzies along with a new tank leach process to broaden the products application to a larger range of ores. This will support commercial application that will hopefully lead to successful adoption and uptake by the industry.

For further information please contact:

Dr Paul Breuer, CSIRO: paul.breuer@csiro.au