Dual-listed uranium developer Bannerman Resources has achieved positive results from a membrane study, aimed at testing the potential use of nano-filtration, at its Etango uranium project in Namibia.

In 2017 Bannerman commenced the membrane study, a process to test the potential application of nanofiltration in combination with an ion-exchange (IX) recovery circuit, as part of its value improvement work at Etango.

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The preliminary results of this testwork were positive, as announced in April 2018. In late 2019 Bannerman recommissioned the Etango heap leach demonstration plant to prepare pregnant liquor solution to use in follow up testwork to advance the membrane study testwork to a definitive level, in conjunction with the company’s specialist technical advisers.

Two aspects of the membrane study testwork required further analysis to advance the findings to a definitive level:

  • The preferred process for removing iron from the finished uranium product (converter specifications for U3O8 have very low tolerances for iron); and
  • Selection of the preferred type of membrane units and definitive-level design work to incorporate nano-filtration into the process circuit.

Iron removal testwork

Confirmatory testwork regarding the iron removal process has been completed. Two alternative processes for iron removal were considered and tested:

  1. Precipitation after the nano-filtration process. Following the IX process the concentrated eluate (CE) solution passes through the nano-filtration plant upgrading the uranium and recovering the acid. Iron is then preferentially precipitated prior to the precipitation of uranium.
  2. Prior to elution in the IX process. Prior to the elution during the IX process, the resin is rinsed with a weak acid solution to remove any excess iron.

The confirmatory testwork has successfully demonstrated and confirmed that the second iron removal process is the most favourable of the two methods being considered and the preferred process route. Rinsing the loaded IX column prior to elution demonstrated that over 99% of the iron can be removed using a weak acid solution. The iron removed can also be re-used in the leaching circuit, reducing reagent costs.

The elution process can then present the CE solution with minimal iron content to the nano-filtration plant, where the uranium solution upgrades by almost ten-fold while 80% of the sulphuric acid is recovered for the processing circuit. It is considered that the IX/NF process route is likely to provide both economic and operational advantages, the final quantum of which are to be confirmed in the Etango definitive feasibility study (DFS) update.

Membrane selection and definitive-level design

Bannerman has completed a review of the most suitable membrane for the Etango project. It is considered that acid resistant membranes are generally cheaper and available in a wider variation of rejection and operating pressure ranges. The alternative, acid proof membranes, are generally more expensive, have lower uranium rejections and require higher operating pressures.

Each membrane type has different key advantages and requires different plant designs to produce the desired output stream requirements. These different plant designs can result in significantly different CAPEX and OPEX outcomes. Only once all membrane parameters for a particular feed stream are known can an economic assessment be undertaken to identify the recommended membrane. Based on the estimated CAPEX and OPEX for the different membrane types, Bannerman has now determined the most suitable membrane.

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Following completion of the membrane selection process and utilising trial performance data obtained from the Etango heap leach demonstration plant, Bannerman has completed a preliminary design to a definitive level for the nano-filtration plant for the Etango project.

Further optimisation work

The Bannerman team will continue to work through prioritised enhancement studies that have the potential to be NPV accretive through reducing anticipated capital expenditure and operating costs.

Once the optimisation phase is completed, and Bannerman observes the market signals suggesting clear opportunity to develop the Etango project, the ompany plans to conclude the DFS Update by undertaking definitive level engineering to incorporate identified project enhancements – including the membrane study – and update the procurement process.

In addition, Bannerman has continued to undertake an evaluation of project scaling and scope opportunities that might exist under various development parameters and market conditions. The DFS undertaken on the Etango project in 2012 identified a plant throughput of 20 Mtpa to generate an average production of 7.2 million pounds of U3O8 over a mine life of 16 years.

A viable throughput alternative, with a corresponding reduction in CAPEX, would provide Bannerman with enhanced flexibility to respond to uranium market conditions or changes in the availability of finance without compromising the ability to construct the world-class scale Etango mine studied in the DFS.