Tobias S. Rötting

Sequential extraction and DXRD applicability to poorly crystalline Fe- and Al-phase characterization from an acid mine water passive remediation system

Abstract Iron and Al precipitates play very important hydrochemical and environmental roles in aquatic environments affected by acid mine drainage. Despite their great importance, reliable characterization of these precipitates is problematic due to the high proportion of amorphous or poorly ordered mineral phases comprising these precipitates and because of their coexistence with intermediate to highly crystalline phases. To facilitate and improve the characterization of poorly ordered Fe and Al phases, a coupled differential X-ray diffraction (DXRD) and sequential extraction (SE) study was performed on a set of samples from an acid mine water passive treatment system. The results of these techniques indicate the presence of schwertmannite and goethite in the upper 5 cm of the passive treatment reactive material. Furthermore, a progressive decrease of the SO42- adsorbed to the schwertmannite surface is suggested by one of the SE steps. The presence of hydrobasaluminite and amorphous Al(OH)3 is suggested on the basis of SE and thermodynamic modeling analysis. These techniques also allow a quantitative estimation of the proportion of each mineral present. As a result, a complete study of the distribution of each mineral throughout the reactive material profile and the role of each phase in removing metals from the mine water can be obtained. This information is useful, not only to improve the reactive material design, but also to understand the natural processes taking place in aquatic systems affected by mining.

In-situ remediation of acid mine drainage using a permeable reactive barrier in Aznalcóllar (Sw Spain)

Following on the accident occurred in Aznalcóllar in 1998, whereby a huge amount of acid mine drainage and heavy metal-bearing pyritic sludge was released to the Agrio river valley with the subsequent contamination of groundwater, a subsurface permeable reactive barrier (PRB) was installed to mitigate the long-term impacts by the spillage. The PRB material consisted of a mixture of limestone and vegetal compost. A particular characteristic of the Agrio aquifer is its high water flow velocity (0.5-1 m/d), which may pose difficulties in its remediation using PRB technology. The present study reports the 36-month performance of the PRB. Vertical differences in water velocity were observed within the PRB, with the deeper part being slower and more effective in neutralizing pH and removing heavy metals (Zn, Al, Cu). On the other hand, partial sulfate removal appeard to be restricted to the bottom of the PRB, but with no apparent influence on downgradient water quality. The results are finally compared with the other four reported existing PRBs for AMD worldwide.

A Rich Vein? Mining and the Pursuit of Sustainability†

The removal of a nonrenewable natural resource such as metals or petrochemicals hardly meets the definition of “sustainable”. However the methods used to extract the materials can be designed for overall environmental protection. Theoretically controllable variables include water use, transportation methods, and potential remediation/landscape alteration for the postclosure period. Further, in the case of metals, recycling means that the long-term sustainability of such resources can be realized. Amezaga et al. review how mining practices have evolved to consider sustainability over the last few decades and remark on what challenges still need to be overcome.

Natural pretreatment and passive remediation of highly polluted acid mine drainage

Acid mine drainage (AMD) from the Iberian Pyrite Belt has high acidity and metal concentrations. Earlier pilot experiments, based on limestone sand dispersed in wood shavings (dispersed alkaline substrate; DAS) have been shown to be an efficient treatment option. However, complete metal removal was not achieved, principally due to the high ferrous iron concentration in the inflow AMD. In order to oxidize and remove iron, a natural Fe-oxidizing lagoon (NFOL) was added prior to treatment with limestone-DAS. The NFOL comprises several pre-existing Fe-stromatolite terraces and cascades, and a lagoon with a volume of 100 m(3) built near the mine shaft. Downstream of the NFOL, the limestone-DAS treatment consists of two reactive tanks of 3 m(3) each filled with limestone-DAS reactive substrate, connected in series with two decantation ponds of 6 m(3) each and several oxidation cascades. The AMD emerging from the mine shaft displayed a pH near 3, a net acidity of 1800 mg/L as CaCO(3) equivalents, and mean concentrations of 440 mg/L Zn; 275 mg/L Fe (99% Fe(II)); 3600 mg/L SO(4); 250 mg/L Ca; 100 mg/L Al; 15 mg/L Mn; 5 mg/L Cu; and 0.1-1 mg/L As, Pb, Cr, Cd, Co, and Ni. The oxidation induced in the NFOL enhanced ferric iron concentration, showing an average of 65% oxidation and 38% retention during the monitoring period. The whole system removed a mean of 1350 mg/L net acidity as CaCO(3) equivalents (71% of inflow); corresponding to 100% of Fe, Al, Cu, Pb and As, and 6% of Zn.

Long term remediation of highly polluted acid mine drainage: a sustainable approach to restore the environmental quality of the Odiel river basin.

During 20 months of proper operation the full scale passive treatment in Mina Esperanza (SW Spain) produced around 100 mg/L of ferric iron in the aeration cascades, removing an average net acidity up to 1500 mg/L as CaCO(3) and not having any significant clogging problem. Complete Al, As, Cd, Cr, Cu, Ti and V removal from the water was accomplished through almost the entire operation time while Fe removal ranged between 170 and 620 mg/L. The system operated at a mean inflow rate of 43 m(3)/day achieving an acid load reduction of 597 g·(m(2) day)(-1), more than 10 times higher than the generally accepted 40 g·(m(2) day)(-1) value commonly used as a passive treatment system designing criteria. The high performance achieved by the passive treatment system at Mina Esperanza demonstrates that this innovative treatment design is a simple, efficient and long lasting remediation option to treat highly polluted acid mine drainage.

Passive treatment of acid mine drainage with high metal concentrations using dispersed alkaline substrate.

Passive treatment systems based on the dissolution of coarse calcite grains are widely used to remediate acid mine drainage (AMD). Unfortunately, they tolerate only low metal concentrations or acidity loads, because they are prone to passivation (loss of reactivity due to coating) and/or clogging (loss of permeability) by precipitates. To overcome these problems, a dispersed alkaline substrate (DAS) composed of a fine-grained alkaline reagent (calcite sand) mixed with a coarse inert matrix (wood chips) was developed. The small grains provide a large reactive surface and dissolve almost completely before the growing layer of precipitates passivates the substrate, whereas the dispersion of nuclei for precipitation on the inert surfaces retards clogging. Chemical and hydraulic performance of DAS was investigated in two laboratory columns fed at different flow rates with natural AMD of pH 2.3 to 3.5 and inflow net acidity 1350 to 2300 mg/L as CaCO(3). The DAS columns removed 900 to 1600 mg/L net acidity, 3 to 4.5 times more than conventional passive treatment systems. Regardless of the flow rate employed, Al, Fe(III), Cu, and Pb were virtually eliminated. Minor Zn, Ni, and Cd were removed at low flow rates. High acidity removal is possible because these metals accumulate intentionally in DAS, and their precipitation promotes further calcite dissolution. During 15 mo, DAS operated without clogging at 120 g acidity/m(2).d, four times the loading rate recommended for conventional passive systems; DAS may therefore be capable of treating AMD at sites where influent chemistry precludes the use of other passive systems.

From highly polluted Zn-rich acid mine drainage to non-metallic waters: Implementation of a multi-step alkaline passive treatment system to remediate metal pollution

Complete metal removal from highly-polluted acid mine drainage was attained by the use of a pilot multi-step passive remediation system. The remediation strategy employed can conceptually be subdivided into a first section where the complete trivalent metal removal was achieved by the employment of a previously tested limestone-based passive remediation technology followed by the use of a novel reactive substrate (caustic magnesia powder dispersed in a wood shavings matrix) obtaining a total divalent metal precipitation. This MgO-step was capable to abate high concentrations of Zn together with Mn, Cd, Co and Ni below the recommended limits for drinking waters. A reactive transport model anticipates that 1 m(3) of MgO-DAS (1 m thick × 1 m(2) section) would be able to treat a flow of 0.5 L/min of a highly acidic water (total acidity of 788 mg/L CaCO(3)) for more than 3 years.

Stakeholder participation within the public environmental system in Chile: Major gaps between theory and practice

The main objective of this paper is to present a critical analysis of the stakeholder participation process within the Environmental Impact Assessment System in Chile, after ca. 14 years of being enforced. This analysis is sustained by the description and analysis of the stakeholder participation possibilities in a representative rural area of North-Central Chile. The Environmental Basis Act 19300, enacted in 1994, considers the participation of the local community in the environmental impact assessment of new projects. However, this possibility is very limited and difficult to exert, often resulting in frustration for the participants. This is due to a number of reasons, such as the imbalance of resources and knowledge among the majority of participating communities and project proponents, the complexity and administrative and legal constraints to participation, and the dominant interest of the Central Government in approving investments, specifically in energy and natural resources related projects, which generate wealth and jobs. Also, the States rush to develop Internet-based communication and management systems has built a barrier for poor, traditional communities. This factor is clearly reflected in the case study considered. Results show that there is generally a significant lack of knowledge about institutions and participation tools. From this base, we intend to raise concern on these selected aspects that could be addressed to improve the effectiveness of the existing framework, both in Chile and in other developing countries, where immature environmental impact assessment and public management systems face similar pressures in relation to the sustainable use of their natural resources. Finally, some basic steps are proposed in order to make the community participation an effective tool for sustainable development.

Acid mine drainage in the Iberian Pyrite Belt: 2. Lessons learned from recent passive remediation experiences

The Iberian Pyrite Belt (IPB), SW Spain and Portugal, contains about 100 abandoned mine wastes and galleries that release acid mine drainages (AMD) to the Tinto and Odiel rivers. In situ passive remediation technologies are especially suitable to remediate the drainages of these orphan sites. However, traditional remediation systems, designed for coal mines, have been demonstrated inefficient to treat the IPB mine waters. Due to their high acidity and metal loads, large amount of solids precipitate and fast clogging of porosity or passivation (coating) of the reactive grains occurs. To overcome these problems, the dispersed alkaline substrate (DAS) a mixture of fine-grained limestone sand and a coarse inert matrix (e.g., wood shavings) was developed. The small grains provide a large reactive surface and dissolve almost completely before the growing layer of precipitates passivates the substrate. The high porosity retards clogging. However, calcite dissolution only raises pH to values around 6.5, at which the hydroxides of trivalent metals (Al and Fe) precipitate, but it is not high enough to remove divalent metals. Caustic magnesia (MgO) buffers the solution pH between 8.5 and 10. A DAS system replacing limestone with caustic magnesia has been tested to be very efficient to remove divalent metals (Zn, Cd, Mn, Cu, Co, Ni, and Pb) from the water previously treated with calcite.

Water Quality Assessment of the Mining-Impacted Elqui River Basin, Chile

Multivariate data analysis techniques were used to identify the interrelationships between the physical–chemical analyses of 22 parameters sampled monthly from 1991 to 2007 at 16 monitoring stations along the Elqui river and its tributaries to characterize the scale of the geogenic and anthropogenic impacts on the river’s water quality. Principal component analysis was used to identify the differences and similarities between variables in the watershed. Factorial indices, computed to highlight the sections of the river and tributaries more influenced by hydrothermal, mining or agricultural activities, made it possible to synthesize groups of parameters with similar characteristics into a single value.ZusammenfassungVon 1991 bis 2007 wurden an 16 Beobachtungstationen entlang des Elqui-Flusses und seinen Zuflüssen monatlich 22 physiko-chemische Parameter gemessen. Der Grad geogener und anthropogener Einflüsse auf die Wasserqualität wurde mit multivariaten Analysen untersucht. Hauptkomponentenanalyse wurde angewendet, um Unterschiede und Ähnlichkeiten zwischen Variablen in dem Wassereinzugsgebiet zu identifizieren. Um Abschnitte des Flusses und seiner Zuflüsse mit stärkerem Einfluß hydrothermaler, bergaulicher oder landwirtschaftlicher Aktivitäten hervorzuheben, wurden faktorielle Kennzahlen berechnet. Damit war es möglich, Gruppen von Parametern ähnlicher Besonderheiten in einen Einzelwert zusammenzuführen.ResumenSe utilizaron técnicas de análisis multivariante para identificar las relaciones entre los análisis de 22 parámetros fisicoquímicos obtenidos mensualmente desde 1991 hasta 2007 en 16 estaciones de monitorio a lo largo del Río Elqui y sus tributarios, en función de caracterizar de la escala de los impactos geogénicos y antropogénicos sobre la calidad del agua del río. El análisis de componentes principales (PCA) fue usado para identificar las diferencias y similitudes entre variables de la cuenca. Los índices factoriales, estimados para destacar las zonas del río y sus tributarios más influida por las actividades minerales, hidrotérmicas o agrícolas, permitieron reunir grupos de parámetros con similares características dentro de un solo valor.抽象化学水质监测指标之间的关系,以研究地质成因和人类活动作用对流域水质的影响程度。利用主成分分析法(PCA)识别了流域内各变量之间的差异与相似性。利用因子分析突出了埃尔基河及其支流受热液、采矿和农业活动的影响程度,使具有相似特征的多元变量转化为单一变量成为可能。