Acid rock drainage (ARD) is a major problem related to the management of mining wastes, especially concerning deposits containing sulphide minerals. Commonly used tests for ARD prediction include acid–base accounting (ABA) tests and the net acid generation (NAG) test. Since drainage quality largely depends on the ratio and quality of acid-producing and neutralising minerals, mineralogical calculations could also be used for ARD prediction. In this study, several Finnish waste rock sites were investigated and the performance of different static ARD test methods was evaluated and compared. At the target mine sites, pyrrhotite was the main mineral contributing to acid production (AP). Silicate minerals were the main contributors to the neutralisation potential (NP) at 60% of the investigated mine sites. Since silicate minerals appear to have a significant role in ARD generation at Finnish mine waste sites, the behaviour of these minerals should be more thoroughly investigated, especially in relation to the acid produced by pyrrhotite oxidation. In general, the NP of silicate minerals appears to be underestimated by laboratory measurements. For example, in the NAG test, the slower-reacting NP-contributing minerals might require a longer time to react than is specified in the currently used method. The results suggest that ARD prediction based on SEM mineralogical calculations is at least as accurate as the commonly used static laboratory methods.

The mobility of contaminants from mine waste can be assessed using different extraction methods. Aqua regia (AR) extraction is the most commonly used method in Finland. Another method is the analysis of leachate from net acid generation (NAG) tests, which is primarily designed for acid production potential assessment. We investigated the performance of single-addition NAG test leachate analysis and AR extraction in drainage quality prediction, using waste rock and drainage water samples from several Finnish waste rock sites. Our objective was to improve interpretation of the AR and single-addition NAG test leachate analysis results in drainage quality prediction. The AR extraction effectively reflected elements that occurred in elevated concentrations in drainage water, though it over-predicted Al, As, Cd, Co, Cu, and Ni in some circumneutral drainages, and Cr in general. The single-addition NAG test leachate analysis also performed well in assessing the mobility of contaminants including Al and Cr at acid mine drainage sites. As the contaminants tend to precipitate in neutral NAG test solution, the usability of the method in neutral mine drainage cases should be further investigated. Furthermore, the conclusions presented in this study are limited to waste rock samples collected from the surface of piles; future work will examine waste rock history, dump cores, drainage quality changes, etc. in more detail.

矿山固体废物所含污染物的活性迁移特征可通过不同提取方法进行评估。在芬兰, 王水提取是最普遍使用方法。另一种是净产酸实验 (NAG) 浸出液分析法, 该实验主要为产酸潜力评估而设计。利用芬兰几个废石场的废矿石和排水水样, 研究了单添加NAG实验滤出液分析法和王水 (AR) 提取法用于预测排水质量的能力。研究旨在改善AR提取法和单添加NAG滤出液分析法进行排水质量预测的解释水平。王水提取 (AR) 能够有效地反映排水可能出现的高浓度元素, 但它会过高预测近中性排水中的Al、As、Cd、Co、Cu和Ni, 普遍过高预测Cr。单添加NAG滤出液分析法也可以较好地评价污染物迁移特征, 包括酸性矿山废水条件的Al和Cr。但是, 当污染物在中性NAG试验溶液中有沉淀倾向时, 应当进一步考虑方法此时的适用性。另外, 所得结论仅限于从矸石堆表面采集的废石样品, 未来工作将更详细地研究废石堆积历史、矸石堆内部情形、排水质量变化等。

Die Mobilität von Schadstoffen aus Bergbauabfällen kann mit verschiedenen Extraktionsmethoden bewertet werden. Der Königswasseraufschluss (AR) ist die in Finnland am häufigsten verwendete Methode. Eine weitere Methode ist die Analyse von Sickerwasser aus Tests zur Netto-Säureerzeugung (NAG), die in erster Linie zur Bewertung des Säurebildungspotenzials vorgesehen ist. Untersucht wurden die Leistungsfähigkeit der Sickerwasseranalyse mit Einzelzugabe von NAG-Tests und die der AR-Extraktion bei der Vorhersage der Sickerwasserqualität von taubem Gestein und Drainagewasserproben von mehreren finnischen Bergehalden. Ziel war es, die Interpretation der Ergebnisse der AR- und Single-Addition-NAG-Testsickerwasseranalyse und der Single-Addition-NAG-Testsickerwasseranalyse bei der Vorhersage der Sickerwasserqualität zu verbessern. Die AR-Extraktion spiegelte effektiv Elemente wider, die in erhöhten Konzentrationen im Sickerwasser auftraten, obwohl sie Al, As, Cd, Co, Cu und Ni in einigen pH-neutralen Sickerwässern und Cr im allgemeinen überbewertet hat. Die NAG-Testsickerwasseranalyse mit einer einzigen Zugabe zeigte ebenfalls gute Ergebnisse bei der Beurteilung der Mobilität von Schadstoffen einschließlich Al und Cr, allerdings nur, wenn das Sickerwasser sauer war. Da die Schadstoffe dazu neigen, in neutraler NAG-Testlösung auszufallen, sollte die Anwendbarkeit der Methode in neutralen Grubenwässern weiter untersucht werden. Darüber hinaus beschränken sich die in dieser Studie vorgestellten Schlussfolgerungen auf Proben von taubem Gestein, die von den Oberflächen der Halden entnommen wurden. Zukünftige Arbeiten werden das Langzeitverhalten des tauben Gesteins, Haldenbohrkerne, Änderungen der Sickerwasserqualität usw. genauer untersuchen.

A commonly-used method in ore exploration is hydrogen peroxide ammonium citrate (HA) extraction, which has not typically been used in waste rock characterization. In this study, the sulfide specificity and leaching of other minerals in HA extraction was evaluated and its performance was compared with the aqua regia (AR) extraction for preliminary assessment of harmful element mobility. Samples collected from several different mine sites in Finland were utilized. The waste rock sample S contents ranged from 0.3% to 5.3%, and sums of the AR extractable elements As, Cd, Co, Cu, Ni and Zn range from 120 to 8040 mg/kg. The drainage types ranged from acid high-metal to neutral low-metal, with pH’s of 3.3–7.7. Mineralogical changes that took place in the HA solution were investigated by the field emission scanning electron microscope (FE-SEM) equipped with an energy-dispersive X-ray spectroscopy analyzer (EDS) and X-ray diffraction (XRD) methods. Results of the study showed that the HA extraction appears to be a more specific method for sulfide decomposition compared with AR extraction. Sulfide minerals, especially base metal sulfides pentlandite, chalcopyrite and sphalerite, decomposed efficiently in HA extraction. However, the Fe-sulfides pyrrhotite and pyrite only decomposed incompletely. The study showed that the HA extraction results can be used in the preliminary prediction of element mobility. Based on the results, the elevated As, Cd, Co, Cu, Ni, S and Zn leachability in the HA extraction appears to predict elevated drainage concentrations. If the HA-extractable sum of As, Cd, Co, Cu, Ni and Zn is >750 mg/kg, there is an increased risk of high-metal (>1000 µg/L) drainage. Therefore, the HA extraction data, e.g., produced during ore exploration, can be utilized to preliminary screen the risks of sulfide related element mobilities from waste rock material.

The objective of this study was to investigate the use of the acid production potential (AP) calculation factor and seven different S analysis methods in the preliminary mine waste characterization by analyzing and comparing 48 Finnish mine waste samples. Special attention was paid on mineralogical aspects and data produced in the exploration phase of a mining project.

According to our results, the abundance of sulfide species other than pyrite in Finnish mine waste suggests that the factor to calculate the AP should be considered based on mineralogy and would often be below 31.25. Therefore, the mineralogy-based determination of S should be preferred. However, the determination of S based on scanning electron microscope (SEM) mineralogy includes some uncertainties. Underestimation of S content may appear if not all S-bearing mineral particles have been detected, or if the amount of S is low in general. This uncertainty appears to be especially related to the samples containing elevated (> 9 wt%) amounts of serpentine, diopside, augite, and/or hornblende. Risk of overestimating AP is related to samples containing high amounts (> 4.13 wt%) of S-bearing minerals. These uncertainties can be reduced by inspecting that the SEM mineralogy-based S concentrations are in line with the energy dispersive X-ray spectrometer data. The aqua regia extractable S concentrations, which are often available in the exploration phase, appeared to be usable in the preliminary waste rock AP assessment and often comparable with the analytical total S values in the Finnish waste rock samples, especially when the samples did not contain any sulfate minerals. In contrast, the analytical sulfide S and the X-ray fluorescence methods may lead to an underestimation of AP.