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MEI Online: Commodities: Metallic Ores: Uranium: Latest News: Oct.2, 2009

 
 

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:: Mintek Re-establishes NIMCIX Uranium Expertise

With the revival of interest in uranium projects over the past few years, Mintek has re-established and updated its expertise in NIMCIX ion exchange technology.

The NIMCIX contactor is a continuous ion-exchange (CIX) column developed by Mintek (then the National Institute for Metallurgy - NIM) during the uranium boom of the 1970s and 1980s. A notable breakthrough, it enabled uranium to be recovered from unclarified solutions. A number of commercial plants were built and operated successfully - the Vaal River South plant, commissioned in 1978, is still in operation and was recently upgraded with glass-reinforced plastic (GRP) columns. Two new plants, Ezulweni and Trekkopje (in demonstration phase), have been commissioned in the past 18 months.

The major variables in a NIMCIX operation include the diameter of the column, the resin flowrate, and the number and height of the stages. To assist in the design and optimisation of these variables, a spreadsheet-based model has been developed that simulates the performance of a column for specific applications. Using the model, it is easy to manipulate the variables in order to arrive at the most efficient and economical design. Mintek is currently undertaking pilot plant trials to confirm the accuracy and reliability of its current model for the adsorption circuit, and also plans to validate the model against an industrial-scale operation.

NIMCIX-type designs were also used for resin elution on several past commercial plants, although the principles were somewhat different to the columns used for extraction. Mintek is evaluating a novel countercurrent elution design that would allow continuous resin transfer, and hence a more efficient elution and a higher eluate uranium concentration. This would allow direct precipitation of uranium from the eluate, thus avoiding the extra capital and operating costs associated with a downstream solvent-extraction purification stage.

A NIMCIX column consists of between 10 and 14 stages separated by perforated plates. Unclarified pregnant leach solution is passed upwards through the column, fluidising the resin in each stage. Eluted resin is transferred into the top of the column, while loaded resin is withdrawn periodically from the bottom of the column during a period of backflow. The NIMCIX column has several advantages over conventional fixed-bed ion-exchange columns.

  • It can treat solutions that contain up to about 300 milligrams per litre suspended solids;
  • Construction and operation are simple, and capital and operating costs relatively low;
  • Operation is efficient and stable over a wide range of feed rates and concentrations;
  • Efficiency of recovery is high, and resin losses are relatively low;
  • The contactor can be successfully scaled-up to large diameter units;
  • The plant is highly automated, and start-up and shut-down are effected with ease; and,
  • Plant reliability and availability are high.

 

 

   

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