Rollog Mark, Cook Nigel J, Guagliardo Paul, Ehrig Kathy, Gilbert Sarah E, Kilburn Matt
School of Chemical Engineering, The University of Adelaide, Adelaide, SA, 5005, Australia.
Centre for Microscopy, Characterisation, and Analysis, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia.
Geochem Trans. 2019 Sep 5;20(1):4. doi: 10.1186/s12932-019-0064-0.
Production of radionuclide-free copper concentrates is dependent on understanding and controlling the deportment of daughter radionuclides (RNs) produced from U decay, specifically Ra, Pb, and Po. Sulfuric acid leaching is currently employed in the Olympic Dam processing plant (South Australia) to remove U and fluorine from copper concentrates prior to smelting but does not adequately remove the aforementioned RN. Due to chemical similarities between lead and alkaline earth metals (including Ra), two sets of experiments were designed to understand solution interactions between Sr, Ba, and Pb at various conditions. Nanoscale secondary ion mass spectrometry (NanoSIMS) isotopic spatial distribution maps and laser ablation inductively coupled-plasma mass spectrometry transects were performed on laboratory-grown crystals of baryte, celestite, and anglesite which had been exposed to different solutions under different pH and reaction time conditions. Analysis of experimental products reveals three uptake mechanisms: overgrowth of nearly pure SrSO and PbSO on baryte; incorporation of minor of Pb and Ba into celestite due to diffusion; and extensive replacement of Pb by Sr (and less extensive replacement of Pb by Ba) in anglesite via coupled dissolution-reprecipitation reactions. The presence of HSO either enhanced or inhibited these reactions. Kinetic modelling supports the experimental results, showing potential for extrapolating the (Sr, Ba, Pb)SO system to encompass RaSO. Direct observation of grain-scale element distributions by nanoSIMS aids understanding of the controlling conditions and mechanisms of replacement that may be critical steps for Pb and Ra removal from concentrates by allowing construction of a cationic replacement scenario targeting Pb or Ra, or ideally all insoluble sulfates. Experimental results provide a foundation for further investigation of RN uptake during minerals processing, especially during acid leaching. The new evidence enhances understanding of micro- to nanoscale chemical interactions and not only aids determination of where radionuclides reside during each processing stage but also guides development of flowsheets targeting their removal.
生产无放射性核素的铜精矿取决于对铀衰变产生的子放射性核素（RNs），特别是镭、铅和钋的行为的理解和控制。目前，奥林匹克坝选矿厂（南澳大利亚）采用硫酸浸出法在熔炼前从铜精矿中去除铀和氟，但不能充分去除上述放射性核素。由于铅与碱土金属（包括镭）之间存在化学相似性，因此设计了两组实验来了解锶、钡和铅在不同条件下的溶液相互作用。对在不同pH值和反应时间条件下暴露于不同溶液的重晶石、天青石和白铅矿的实验室生长晶体进行了纳米二次离子质谱（NanoSIMS）同位素空间分布图和激光烧蚀电感耦合等离子体质谱横断面分析。对实验产物的分析揭示了三种吸收机制：重晶石上几乎纯的硫酸锶和硫酸铅的过度生长；由于扩散，少量铅和钡掺入天青石；通过耦合溶解-再沉淀反应，白铅矿中的铅被锶大量取代（钡对铅的取代程度较小）。硫酸氢根的存在增强或抑制了这些反应。动力学模型支持实验结果，表明有可能将（锶、钡、铅）硫酸盐体系外推至硫酸镭体系。通过纳米二次离子质谱直接观察颗粒尺度的元素分布有助于理解置换的控制条件和机制，这可能是从精矿中去除铅和镭的关键步骤，因为可以构建针对铅或镭，或理想情况下针对所有不溶性硫酸盐的阳离子置换方案。实验结果为进一步研究矿物加工过程中，特别是酸浸过程中放射性核素的吸收提供了基础。新的证据增进了对微观到纳米尺度化学相互作用的理解，不仅有助于确定放射性核素在每个加工阶段的位置，还指导了针对其去除的工艺流程的开发。
