Website for the AMIRA P705 "Improved Anode & Cathode Processes in the Electrowinning of Base Metals" Project (password required)

Introduction
Research within this program addresses the challenges facing the minerals industry in the key operational areas of leaching, separation and reduction.

Leaching:
The most important step of a hydrometallurgical process is generally the first, which is leaching ie the dissolution of the valuable metal in an aqueous solution. The overall recovery of the metal and the difficulty of separating it from impurity metals are generally governed by the efficiency and selectivity of the leaching process.

Sulfide minerals are a major resource for base and precious metals. The challenge is to find efficient and selective methods for leaching the increasing important proportion of multi-element low grade mineral sulfide ores and concentrates, which are also environmentally acceptable.

Separation:
Solvent extraction (SX) and ion exchange resins are modern methods for the separation, purification and recovery of metal ions from leach solutions.

SX is used in the concentration and purification of uranium and rare earths and increasingly in the recovery of copper, nickel, cobalt and zinc. Ion exchange resins are specific solid adsorbents. Although not as widespread in its commercialisation at this stage, this technique offers the potential for the direct recovery of metal ions from pulps, as practised in the carbon-in-pulp process for the recovery of gold.

The challenge is to develop lower cost options in solvent extraction and ion exchange and improve metal recovery using these methods.

Reduction:
The final step in many hydrometallurgical processes is the reduction of the desired metal ion to a high-purity metal product. The challenge is to increase the yield and quality of the pure metal end product.

One method for metal ion reduction is electrowinning. Conventional electrowinning and refining operations are capital, energy and labour intensive. A number of new nickel/cobalt projects are now operating or undergoing feasibility studies in Australasia, with many of these using electrowinning as the final recovery step for nickel and/or cobalt. In addition, an Australian company has become the largest zinc producer in the world, most of which is produced by electrowinning.

Although not immediately obvious, reduction has much in common with leaching - both are electrochemical in nature and both involve reactions at the solid-liquid interface.

Specific Areas of Research
Current research areas and projects include:

Optimisation of the Leaching of Sulfide Minerals

• Understanding the mechanisms by which selected sulfide minerals are dissolved in conventional, pressure and biological leaching processes.
• Studying the electrochemistry of mineral particles from sulfide ores and concentrates.
• Studying the chemistry of sulfur species in the leaching of sulfide minerals.
• Investigating oxygen transfer agents and redox mediators for improving the oxidation of sulfides in selected mineral leaching systems.

Improving Solvent Extraction and Ion Exchange Technology

• Developing synergistic SX systems for recovering zinc, nickel and cobalt from leach solutions. Synergistic SX uses a combination of extractant and synergist which work together to improve metal selectivity.
• Studying organic losses in SX circuits due to organic degradation and entrainment (organic droplets trapped in aqueous solution) and developing methods to reduce losses and organic/aqueous phase separation problems.
• Applying a novel solvent extraction technique (which uses electrostatic charge) to the direct separation and purification of nickel and cobalt from nickel laterite leach solutions.
• The AMIRA P706 "Improving Solvent Extraction Technology" project - which aims to improve the design and operation of SX pulsed column and mixer-settler contactors (the vessels in which the organic solvent comes into contact with the aqueous metal-containing solution).
• Investigating the application of a novel resin-in-pulp process which uses selective ion exchange resins to recover nickel and cobalt directly from laterite processing pulps.
• Developing novel applications for ion exchange in the separation and purification of metals.

Electrowinning Processes

• Investigating the relationship between the operating conditions during the electrowinning of cobalt and the quality of the cobalt metal cathodes produced - important since cobalt tends to produce deposits of high internal stress, which can cause significant problems.
• Studying the electrochemistry of the nucleation and growth of cobalt electrodeposits.
• Investigating stress in zinc electrodeposits.
• The AMIRA P705 “Improved Anode & Cathode Processes in the Electrowinning of Base Metals” project - which aims to improve the performance of anodes of both current and new compositions, and the quality of the metal cathodes (copper, nickel or zinc) produced.

Expertise/Capabilities

- Leaching, in particular the application of electrochemistry in leaching processes
- Metal ion separation using solvent extraction and ion exchange
- Electrowinning of nickel and cobalt
- Resin-in-pulp technology

Equipment

- Modern leaching and electrochemical equipment for studies of the leaching and electrochemical characteristics of a wide range of metals and minerals
- Leaching and electrochemical equipment unique to the Parker Centre:
the Rotating Electrode Quartz Crystal Microbalance and
the High Temperature Rotating Disk Electrode apparatus
- Modern equipment for both batch laboratory and small scale continuous studies of SX and ion exchange systems

Program Manager: Professor Mike Nicol