Internal report 636
The increasing process water inventory at the Ranger uranium mine has become a major operational issue for Energy Resources of Australia Ltd (ERA). Following an assessment of potential technology options, ERA decided that brine concentration was the most viable option to reduce the inventory. The full-scale brine concentrator plant at Ranger was commissioned in September 2013 and the electrical conductivity of the distillate was stabilised in early October 2013. The aims of this study were to assess the toxicity of a distillate sample from the full-scale brine concentrator plant, and to identify the cause/s of any observed effects.
On 7 October 2013, following the stabilisation of distillate water quality, samples of the distillate were collected. Five tropical freshwater species (Chlorella sp. (green algae), Lemna aequinoctialis (duckweed), Hydra viridissima (green hydra), Moinodaphnia macleayi (cladoceran) and Mogurnda mogurnda (fish)) were exposed to a limited concentration range of the distillate (0, 25, 50 and 100%). Additionally, for all species except Chlorella sp., undiluted samples of distillate were amended by adding calcium (Ca), sodium (Na) and potassium (K) at 0.5, 1.0 and 0.4 mg L-1, respectively (termed “100% amended”). Amending these salts of the distillate to concentrations representative of local natural waters aimed to determine if observed effects were due to reduced essential ions.
Chemical analyses from the full-scale plant showed that the distillate sample was a highly-purified water and contained less metals and major ions compared to the sample from the pilot plant. The toxicity of the full-scale-plant distillate was higher than that of the pilot-plant product, which was consistent with the higher purity. Some degree of toxicity was observed for all five species. Addition of Ca, Na and K to the distillate sample resulted in markedly improved performance of the organisms and indicated that a major ion deficiency is the primary cause of effects observed in the distillate. The outcomes of this study have been used to inform regulatory approvals concerning discharge of the distillate to the environment.