The processes group develops and tests hydrometallurgical flow sheets for the recovery and purification of metals from solution/pulps. The principal areas of expertise include ion-exchange, solvent extraction, and electro-winning.
Mintek’s expertise in solvent extraction (SX) covers testwork requirements from initial laboratory studies through to a complete process design package and full-scale plant commissioning. This range of capabilities includes:
- development of solvent systems for individual applications
- laboratory shake-out tests and batch counter-current tests
- small- and large-scale piloting
- process flowsheet development
- process flowsheet simulation modelling
- preliminary process design for contracting engineers
- auditing of process flowsheets and plant design
Ongoing research in solvent extraction of Base and Precious metals, Uranium, Thorium, and Rare Earths is undertaken to broaden our knowledge and to develop new technologies, as well as improve existing ones. Mintek also has excellent piloting facilities for upstream and downstream unit operations, allowing the continuous testing of solvent-extraction unit operations within integrated process flowsheets.
Ion exchange is a hydrometallurgical technique that can be effective to recover metals at very low concentrations (ppm levels), and where other separation techniques fail, selective separations may be achieved by the correct choice of ion exchange resin. Ion exchange can potentially treat poorly clarified liquors or even pulps, thus eliminating costly solid/liquid separations. The best-known metallurgical application of ion exchange is in the recovery of uranium -a process developed in South Africa in which Mintek, with its patented NIMCIX contactor, played a major role. Other industrial applications include recovery of gold, purification of electrolytes for electrowinning, removal of heavy metals from waste streams, and water purification.
Mintek has devoted a major effort to the development of resin-in-pulp/leach (RIP and RIL) processes for gold. A gold-selective resin (Dowex-Minix) developed at Mintek has been commercialised, and has proved to be particularly effective for the processing of preg-robbing ores, where activated carbon yields poor recoveries. RIL is used at Penjom mine (Malaysia) and Barbrook (South Africa). Dowex-Minix has also been evaluated successfully for the recovery of gold and silver from a heap-leach liquor.
During the past 5 years, Mintek has been involved in a number of projects for the design and piloting of fixed-bed ion exchange operations for the removal of impurities such as copper, zinc and nickel from cobalt and copper and zinc from nickel electrolyte streams, as well as the recovery of metals from effluent streams such as solvent extraction raffinates.
- MetRIXTM resin-in-pulp
Recent developments in RIP technology have focused on the recovery of Uranium and Base Metals from slurries. Evaluations have been carried out on the recovery of nickel, zinc, cobalt and copper at miniplant scale, and zinc at pilot-plant scale. A final feasibility study using this technology has been completed for a South African client.
Mintek, in collaboration with Bateman , developed the MetRIXTM continuous resin-in-pulp (RIP) process for the direct recovery of uranium from dense slurries. Preliminary feasibility studies conducted by Bateman for one of the clients indicated that this route would be much more cost-effective than the more conventional treatment options. A government grant over the past three years has allowed HMD to make a number of processing improvements, which would further allow the MetRIXTM technology to become even more cost effective. A demonstration plant on the MetRIXTM technology has been commissioned successfully. The RIP technology is applicable not only to uranium but to base metals as well.
- New fibre technology
Earlier work on using ion exchange fibres for the removal of impurities from electrolytes and low grade solutions indicated that this type of material might reduce capital expenditure and operational expenditure significantly. A supplier of these materials has been identified, and a preliminary feasibility studies are underway, such as the removal of Cu from Co electrolyte. The results indicated that it definitely would be economically worthwhile to further investigate these systems. Mintek has also developed a technique for the impregnation of organic extractants that are commercially available on fibre matrices that are available in South Africa. This would allow production of the fibres to be done in South Africa.
Mintek has special expertise in the electrowinning of base metals such as cobalt, chromium, manganese, nickel, zinc and gold, and experience in the recovery of platinum-group metals (PGMs) from effluent streams, the production of electrolytic manganese dioxide (EMD), as well as the electrowinning and electrorefining of copper. Test work is done on laboratory, pilot-plant and industrial scales. Reliable product and electrolyte sample analyses are provided by the Analytical Services Division.
Mintek has a range of laboratory and pilot-plant equipment for:
- resin evaluation and comparison
- fixed—bed applications, including counter-current circuits
- NIMCIX (fluidised-bed) evaluation
- resin-in-pulp evaluation
- a skid-mounted Resin-in-Pulp plants
- Mixer-settler equipment for continuous pilot-plant evaluations
- A Bateman pulsed column (BPC) with an internal diameter of 100 mm is also available for treating solution flowrates of 1 to 2 m3/day. A 40 mm diameter column is also available. Testing and scale-up of the BPC are done in a joint venture with Bateman Projects (South Africa and Israel).
- Laboratory-scale electrowinning cells
- Electrowinning cells for the production of EMD
- Pilot-plant-scale electrowinning cells – a full depth, full width cell housing up to two cathodes, and a deep (full depth, narrow width) cell, housing a single cathode.
- Control and test cells in cell-houses