Mineralogy and environmental geochemistry of copper slag from Butte, Montana

IF 3.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Journal of Geochemical Exploration Pub Date : 2024-10-05 DOI:10.1016/j.gexplo.2024.107599
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Abstract

Herein we characterize the mineralogy, chemical composition, and environmental geochemistry of slag formed by historic (1880s to circa 1910) smelting of the copper-rich lodes of Butte, Montana. The air-cooled slag exists as monolithic “walls” that border Silver Bow Creek, the headwaters of the upper Clark Fork River Superfund site. The slag is mainly comprised of fayalite, hedenbergite, wollastonite, magnetite, and glass. Zinc is present at per cent levels in all of these phases. The overall high zinc content of the slag is partly due to the polymetallic character of the Butte ore bodies. Copper occurs mainly as tiny spheres, or “prills”, which are remnants of the molten Cu-sulfide matte that failed to separate from the slag during smelting. Minerals in the prills include bornite, chalcopyrite, chalcocite, pyrrhotite, pyrite, sphalerite, galena, elemental copper, and elemental silver. The prills are variably oxidized along shrinkage cracks that penetrate into the enclosing slag matrix. Secondary minerals, including hydrous ferric oxide and ferric clay, coat the cracks. Where the cracks meet the surface of the slag, secondary encrustations of calcite, Fe-Mn oxyhydroxides, and mixed Ca-Cu-Zn-Mn-Al-Fe sulfates have locally accumulated. Acid-base accounting tests show that the unweathered slag is non-acid-generating, with the acid potential from Fe-Cu sulfides offset by the neutralization potential of the Ca-Fe silicates (olivine, pyroxene). Interaction of the slag with synthetic precipitation (SPLP tests) confirms the slag's ability to buffer pH to values >8. Nonetheless, the SPLP leachate solutions contain ppb levels of copper, arsenic, zinc, and lead that approach or exceed current regulatory standards for protection of aquatic life (Cu, Pb, Zn) and human health (As). Leaching experiments using Silver Bow Creek water show an increase in dissolved As and W, but variable results for Cu, Pb, and Zn. Leaching of the secondary sulfate-salt deposits produced much higher concentrations of dissolved metals and metalloids which could be a source of contamination to Silver Bow Creek during heavy rain events. Based on bulk analyses, some metals in the slag, including Fe, As, Co, Mn, Pb, Zn, and W, exceed USEPA screening levels for residential and/or urban soils. Leachates containing organic acids (TCLP tests) show Pb concentrations that approach levels for the slag to be classified as hazardous waste. Rather than removing the slag walls, which have value as a form of industrial architecture, an alternate remedy currently under evaluation is to divert Silver Bow Creek around the smelter site and preserve the slag as part of a non-motorized recreational trail system in the reclaimed Butte-Anaconda mine-scape.
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蒙大拿州布特铜渣的矿物学和环境地球化学
在本文中,我们描述了蒙大拿州布特市富含铜矿的矿床在历史上(1880 年代至约 1910 年)冶炼形成的矿渣的矿物学、化学成分和环境地球化学特征。风冷炉渣以整体 "墙壁 "的形式存在于克拉克福克河上游超级基金遗址的源头银弓溪附近。矿渣主要由辉绿岩、黑云母、硅灰石、磁铁矿和玻璃组成。锌在所有这些相中的含量都达到了百分之百。矿渣中锌的总体含量较高,部分原因是布特矿体具有多金属特性。铜主要以微小球体或 "颗粒 "的形式存在,它们是熔融硫化铜锍的残余物,在冶炼过程中未能从矿渣中分离出来。颗粒中的矿物包括辉铜矿、黄铜矿、菱镁矿、黄铁矿、黄铁矿、闪锌矿、方铅矿、元素铜和元素银。棱柱沿收缩裂缝被不同程度地氧化,这些裂缝渗透到包裹矿渣的基质中。包括水合氧化铁和铁粘土在内的次生矿物覆盖在裂缝上。在裂缝与矿渣表面的交接处,局部堆积了方解石、铁锰氧氢氧化物和钙-铜-锌-锰-铝-铁混合硫酸盐等次生包裹体。酸碱核算测试表明,未风化矿渣不产生酸,Fe-Cu硫化物的酸势被Ca-Fe硅酸盐(橄榄石、辉石)的中和势所抵消。矿渣与合成沉淀的相互作用(SPLP 试验)证实,矿渣有能力将 pH 值缓冲到 8。尽管如此,SPLP 沥滤溶液中的铜、砷、锌和铅的ppb含量接近或超过了保护水生生物(铜、铅、锌)和人类健康(砷)的现行法规标准。使用银弓溪水进行的沥滤实验表明,溶解的砷和钨有所增加,但铜、铅和锌的结果却不尽相同。次生硫酸盐-盐沉积物的浸出产生了更高浓度的溶解金属和类金属,这可能是银弓溪在暴雨期间的污染源。根据批量分析,矿渣中的一些金属,包括铁、砷、钴、锰、铅、锌和钨,超过了美国环保局对住宅和/或城市土壤的筛选水平。含有有机酸的沥滤液(TCLP 测试)显示,铅浓度接近矿渣被归类为危险废物的水平。炉渣墙作为一种工业建筑形式具有重要价值,与其将其拆除,目前正在评估的另一种补救措施是将银弓溪改道至冶炼厂周围,并将炉渣作为布特-安纳孔达矿区复垦后的非机动休闲步道系统的一部分加以保护。
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来源期刊
Journal of Geochemical Exploration
Journal of Geochemical Exploration 地学-地球化学与地球物理
CiteScore
7.40
自引率
7.70%
发文量
148
审稿时长
8.1 months
期刊介绍: Journal of Geochemical Exploration is mostly dedicated to publication of original studies in exploration and environmental geochemistry and related topics. Contributions considered of prevalent interest for the journal include researches based on the application of innovative methods to: define the genesis and the evolution of mineral deposits including transfer of elements in large-scale mineralized areas. analyze complex systems at the boundaries between bio-geochemistry, metal transport and mineral accumulation. evaluate effects of historical mining activities on the surface environment. trace pollutant sources and define their fate and transport models in the near-surface and surface environments involving solid, fluid and aerial matrices. assess and quantify natural and technogenic radioactivity in the environment. determine geochemical anomalies and set baseline reference values using compositional data analysis, multivariate statistics and geo-spatial analysis. assess the impacts of anthropogenic contamination on ecosystems and human health at local and regional scale to prioritize and classify risks through deterministic and stochastic approaches. Papers dedicated to the presentation of newly developed methods in analytical geochemistry to be applied in the field or in laboratory are also within the topics of interest for the journal.
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