Purpose Currently, almost all cyanide-free gold leaching processes are still in the development stage. Proactively investigating their environmental impacts prior to commercialization is of utmost importance. In this study, a detailed refractory gold concentrate process simulation with mass and energy balance was built for state-of-the-art technology with (i) pressure oxidation followed by cyanidation and, compared to alternative cyanide-free technology, with (ii) pressure oxidation followed by halogen leaching. Subsequently, the simulated mass balance was used as life cycle inventory data in order to evaluate the environmental impacts of the predominant cyanidation process and a cyanide-free alternative. Methods The environmental indicators for each scenario are based on the mass balance produced with HSC Sim steady-state simulation. The simulated mass balances were evaluated to identify the challenges in used technologies. The HSC Sim software is compatible with the GaBi LCA software, where LCI data from HSC-Sim is directly exported to. The simulation produces a consistent life cycle inventory (LCI). In GaBi LCA software, the environmental indicators of global warming potential (GWP), acidification potential (AP), terrestrial eutrophication potential (EP), and water depletion (Water) are estimated. Results and discussion The life cycle assessment revealed that the GWP for cyanidation was 10.1 t CO 2 -e/kg Au, whereas the halogen process indicated a slightly higher GWP of 12.6 t CO 2 -e/kg Au. The difference is partially explained by the fact that the footprint is calculated against produced units of Au; total recovery by the halogen leaching route for gold was only 87.3%, whereas the cyanidation route could extract as much as 98.5% of gold. The addition of a second gold recovery unit to extract gold also from the washing water in the halogen process increased gold recovery up to 98.5%, decreasing the GWP of the halogen process to 11.5 t CO 2 -e/kg Au. However, both evaluated halogen processing scenarios indicated a slightly higher global warming potential when compared to the dominating cyanidation technology. Conclusions The estimated environmental impacts predict that the development-stage cyanide-free process still has some challenges compared to cyanidation; as in the investigated scenarios, the environmental impacts were generally higher for halogen leaching. Further process improvements, for example in the form of decreased moisture in the feed for halide leaching, and the adaptation of in situ gold recovery practices in chloride leaching may give the cyanide-free processing options a competitive edge.

中文翻译：

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湿法冶金难选金精矿加工工艺模拟及门到门生命周期评价

目的目前，几乎所有的无氰浸金工艺都还处于开发阶段。在商业化之前主动调查它们的环境影响至关重要。在这项研究中，为最先进的技术构建了具有质量和能量平衡的详细难熔金精矿工艺模拟，包括 (i) 压力氧化后氰化，与替代的无氰技术相比，(ii)加压氧化，然后卤素浸出。随后，模拟质量平衡被用作生命周期清单数据，以评估主要氰化过程和无氰化替代方法的环境影响。方法 每个场景的环境指标均基于 HSC Sim 稳态模拟产生的质量平衡。对模拟的质量平衡进行了评估，以确定所用技术中的挑战。HSC Sim 软件与 GaBi LCA 软件兼容，其中来自 HSC-Sim 的 LCI 数据直接导出到。模拟生成一致的生命周期清单 (LCI)。在GaBi LCA软件中，估算了全球变暖潜势（GWP）、酸化潜势（AP）、陆地富营养化潜势（EP）、水资源枯竭（Water）等环境指标。结果与讨论 生命周期评估显示氰化的 GWP 为 10.1 t CO 2 -e/kg Au，而卤素工艺表明 GWP 略高，为 12.6 t CO 2 -e/kg Au。差异的部分原因是足迹是根据生产的 Au 单位计算的；卤素浸出法对黄金的总回收率仅为 87.3%，而氰化路线可以提取多达 98.5% 的金。添加第二个金回收装置以从卤素工艺的洗涤水中提取金，将金回收率提高到 98.5%，将卤素工艺的 GWP 降低到 11.5 t CO 2 -e/kg Au。然而，与占主导地位的氰化技术相比，两种评估的卤素加工方案都显示出略高的全球变暖潜力。结论 估计的环境影响预测，与氰化相比，开发阶段的无氰工艺仍存在一些挑战；与所调查的情景一样，卤素浸出对环境的影响通常更高。进一步的工艺改进，例如降低卤化物浸出原料中的水分，