Chemical and water engineering company Cwenga Technologies is currently running pilot trials to remove uranium from acid mine drainage (AMD) and groundwater using ion-exchange technology.

Cwenga Technologies director Ed Hardwick says that the process involves a pretreatment stage in which ion-exchange resins are used to remove uranium or other metals from water.

He explains the ion-exchange resin process: “Uranium in neutralised water will normally form the anionic complex UO2(CO3)34-. “When this is passed through an anion- exchange resin in the sulphate form, the uranium complex will displace sulphate.

“The uranium complex has an affinity for the resin about a hundred times greater than that of sulphate, with the result that uranium values are reduced to low parts-per-billion (ppb) levels.

“The capacity of the resin is in the order of a few grams for each litre, and this means that the cycle times are extremely long. In the case of a uranium concentration of 100 ppb, it will take six months to exhaust the resin bed. At this stage, it is regenerated with sulphuric acid, and this returns the resin to the sulphate form.

“The uranium eluate can then be recovered in a conventional uranium processing plant.”

Hardwick points out that, owing to the long cycle time, the chemical costs amount to a few cents for each kilolitre. “We run the pilot plant for three months before needing to regenerate the resin. The cost of chemicals involved in the process is minimal.”

He says that there are a number of possible uses for the by-products of the treatment of AMD.

The uranium removed by the process can also be used in uranium plants or purified and used for nuclear fuels.

Other technologies include reverse osmosis, different precipitation techniques and the barium carbonate system; and Rhodes University has developed a biological system that is able to remove sulphates.

Hardwick says that Cwenga, which is based in Johannesburg, would like its process to be applicable to any one of the competitive technologies aimed at tackling the AMD challenge.

“It is unnecessary to have a whole bunch of competing technologies fighting with each other for potential business. Different technologies can all contribute to solving the problem. There is no one-size-fits-all solution, because mine water differs from one geological area to the next.”

Meanwhile, Cwenga is also applying its technologies to other applications, such as base-metals removal. Hardwick says that copper, nickel and cobalt can be recovered economically, and actually cover the cost of the process.

The company has a number of pilot plants in Zambia, used for the removal of copper and cobalt from tailings dams. Hardwick says that some of the streams in Zambia have ten times the recommended copper levels. “The company has also put in a proposal for a mine drainage project in Botswana and is building a plant due for the Philippines in a couple of days,” he concludes.

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