More efficient water management

In CSIRO’s Process Magazine ( February 2006) Whitney Macdonald writes about the ability to predict the environmental and economic effects of making multiple changes in a water circuit, without actually changing anything. This is a powerful tool for many sectors of the mining industry. Its a tool to predict what effects making a change to its plant will have on total output and processing economics. Among other benefits, it will help management of problems like cyanide and acid rock drainage (ARD), the latter being subject of one of the features in IM’s forthcoming March issue. That issue will also look closely at process engineering.

Macdonald explains that researchers within the Parker Centre’s Technology Transfer and Gold Programs in Perth, Western Australia, have developed a modelling platform that merges the flowsheet package SysCAD with the thermodynamic chemistry package HSC. The outcome is a powerful prediction tool that better enables industry to focus its efforts on implementing processing strategies with greater economic and environmental benefits.

The interfaced modules were put to a rigorous test that started in April 2005. The gold team, led by CSIRO Minerals’ Dr John Rumball and research engineer Scott Munro, used almost ten years’ worth of data to model the effects of a dozen different gold processing scenarios – predicting both favourable and unfavourable outcomes for variables such as lime consumption and cyanide levels in tailings. Munro says the modelling system predicted a 30% reduction in cyanide going to the tailings dam, both in net concentration and the total mass of cyanide discharged, while at the same time, generating up to a 20% decrease in reagent costs. Furthermore, less cyanide consumption means less cyanide to be destroyed. This of course is significant, both environmentally and economically.

Subsequent models have also included the effects of gold and copper leaching and adsorption onto activated carbon. The ability to have a detailed understanding of the water chemistry provides an ideal stepping stone to understanding the adsorption of copper onto activated carbon. When activated carbon is used to separate gold from cyanide solutions and is contaminated by the presence of copper, this seriously affects recovery and economy.

Combining water chemistry modelling with adsorption and leaching processes has provided a comprehensive tool to monitor a number of interdependent factors and find the best operating conditions.

Macdonald concludes that while the cost savings for reagents such as lime and cyanide may not immediately balance out against the cost of implementing modelled strategies, such as installing a new thickener, the long-term benefits may justify any initial costs. Individual companies can assess the associated costs on multiple levels after having the solutions offered by the newly integrated modelling platform. "By optimising a plant according to the predicted processing strategies, companies will be able to achieve better economic, social, and environmental outcomes," Munro says.