Historical ferrous slag induces modern environmental problems in the Moravian Karst (Czech Republic)

Ferrous slag produced by a historic smelter is washed from the heap and transported by a creek through the cave system. There is concern that the slag fills cave spaces, abrades cave walls / calcite speleothems, and contaminates the aquatic environment with heavy metals and other toxic components. The study objectives were to better characterize the slag in its deposition site, map its transport through the cave system, characterize the effect of slag transport, and to judge the risks to both cave and aqueous environments. The study was based on methods of chemical and phase analysis supported laboratory experiments and geochemical modeling. The slag in the heap was dominated by amorphous glass phase (66 to 99 wt%) with mean composition of 49.8±2.8 wt% SiO2, 29.9±1.6 wt% CaO, 13.4±1.2 wt% Al2O3., 2.7±0.3 wt% K2O and 1.2±0.1 wt% MgO. Minerals such as melilite, plagioclase, anorthite, and wollastonite / pseudowollastonite with smaller amounts of quartz, cristobalite, and calcite were detected. Slag trace elements formally enrich the cave environment with Se, As, W, Y, U, Be, Cs, Sc, Cd, Hf, Ba, Th, Cr, Zr, Zn, and V. However, only Zr, V, Co, and As exceed specified limits for soils (US EPA and EU limits). The life of a 1 mm3 volume of slag was estimated to be 27,000 years. The mean residence time of the slag in the cave defined by the flood frequency was 47 years. The main conclusion was that the extent of slag weathering is small and that the slag does not contaminate the cave aqueous environment under given conditions. However, the slag enriched in U / Th can increase radon production as a result of alpha decay. The slag has an abrasive effect on surrounding rocks and disintegrated slag can contaminate calcite speleothems.某古冶炼厂产生的含铁炉渣（ferrous slag）经堆体冲刷后，随溪流穿过洞穴系统被搬运。现有担忧认为，炉渣会填充洞穴空间、磨蚀洞壁与方解石钟乳石（calcite speleothems），并通过重金属及其他有毒组分污染水生环境。本研究旨在精准表征沉积位点处的炉渣，绘制其在洞穴系统中的迁移路径，解析炉渣迁移带来的影响，并评估其对洞穴与水生环境的风险。本研究依托化学与物相分析方法，辅以实验室实验及地球化学模拟开展。堆体中的炉渣以非晶质玻璃相为主，占比66%至99 wt%，平均组成为：SiO₂ 49.8±2.8 wt%、CaO 29.9±1.6 wt%、Al₂O₃ 13.4±1.2 wt%、K₂O 2.7±0.3 wt%及MgO 1.2±0.1 wt%。同时检测到黄长石（melilite）、斜长石（plagioclase）、钙长石（anorthite）、硅灰石/假硅灰石（wollastonite / pseudowollastonite），以及少量石英、方石英与方解石。炉渣中的痕量元素可使洞穴环境富集Se、As、W、Y、U、Be、Cs、Sc、Cd、Hf、Ba、Th、Cr、Zr、Zn及V，但仅Zr、V、Co及As超出土壤限定标准（美国环境保护署（US EPA）与欧盟（EU）限值）。据估算，1 mm³体积的炉渣寿命可达27000年；基于洪水频率定义的炉渣在洞穴中的平均停留时间为47年。本研究核心结论为：在当前条件下，炉渣的风化程度较低，且未对洞穴水生环境造成污染。不过，富集U/Th的炉渣可通过α衰变提升氡气生成量。此外，炉渣对周边围岩具有磨蚀作用，崩解的炉渣可能污染方解石钟乳石。