Combined neutralization–adsorption system for the disposal of hydrothermally altered excavated rock producing acidic leachate with hazardous elements
Highlights
► Mechanisms of hazardous element release include dissolution and pyrite oxidation. ► Volcanic ash sampled near the site was capable of adsorbing As(V), Pb, Cu and Zn. ► The combined system effectively minimized the release of As, Pb, Cu and Zn. ► Immobilization of the toxic elements occurred via co-precipitation and adsorption.
Introduction
Hydrothermally altered rocks, which are widely distributed in geologically active volcanic regions like Japan, are formed due to the migration of superheated fluid/water called hydrothermal solutions through fractures and fissures in rocks. Enrichment of these rocks with toxic elements like Pb and As preferentially occurs in and around precipitated pyrite grains, which are oxidized upon exposure to the atmosphere producing acidic leachate containing these toxic elements (Igarashi et al., 2008, Tabelin and Igarashi, 2009). Tunnels for roads, railways and other projects in the island of Hokkaido have excavated these kinds of rocks, which are potential sources of soil and groundwater contamination. At the moment, excavated altered rocks are being disposed of by applying landfill liners to prevent the interaction of the rock and rainwater similar to those utilized in the disposal of municipal and industrial wastes (Lundgren and Soderblom, 1985, Katsumi et al., 2001, Wijeyesekera et al., 2001, Malusis et al., 2003, Rapti-Caputo et al., 2006), but this method is very expensive and impractical so that alternative methods are being explored.
Leaching of As and Pb from altered rocks and their mechanisms of release are both strongly pH dependent (Tabelin and Igarashi, 2009, Tabelin et al., 2012a). In addition, minor and trace minerals that have strong effects on the pH of the rock when in contact with water (e.g., calcite and pyrite) are important in the mobilization of these hazardous elements (Tabelin et al., 2010, Tabelin et al., 2012a, Tabelin et al., 2012b). The best way to immobilize As and Pb from altered rocks is through adsorption and precipitation, respectively, and these processes are most effective in the circumneutral pH range (Tabelin and Igarashi, 2009, Tabelin et al., 2010, Tabelin et al., 2012a). Based on these previous studies, we have developed a disposal method called the neutralization–adsorption system as a simple and low cost alternative to special landfilling. The principles behind this system are simple: identify the mechanisms of As and heavy metal release from the altered rock, minimize the extent of these mechanisms, and provide additional countermeasures to immobilize any hazardous element released from the rock. In contrast to traditional landfills that prevent the interaction of wastes with water through the use of special barriers, the concept of this system more closely resembles a permeable reactive barrier (PRB). In this proposed system, water is allowed to percolate into the waste, albeit at a lower infiltration rate, and the “loaded” leachate would then pass through the adsorption layer where immobilization of the hazardous elements would take place. A conceptual model of this new neutralization–adsorption system is presented in Fig. 1.
The Teine mine area, which is located northwest of Sapporo, Hokkaido, Japan, consists of Late Miocene andesite tuff breccia and mudstone, extruded by altered andesite (propylite). The veins occur mainly in altered andesite, which are grouped into Mitsuyama, Koganezawa and Bannozawa (Imai, 1999). The mine produced gold (Au), silver (Ag) and copper (Cu) from 1893 until 1971 (Watanabe, 1936, Watanabe, 1943, Watanabe, 1944, Sugimoto, 1952, Imai, 1978). A new tunnel was constructed near the Mitsuyama deposit in 2006 to collect acid mine drainage for the new water treatment system installed in this mine. The construction of this new tunnel excavated hydrothermally altered rock rich in hazardous elements like As, Pb, Cu and Zn.
The main goal of this study is to evaluate the effectiveness of the neutralization–adsorption system in the immobilization of toxic elements like As and heavy metals such as Pb, Cu and Zn. The neutralizer and adsorbent selected for our experiments are calcium carbonate (CaCO3) and partly-weathered volcanic ash, respectively. To achieve our goal, we first evaluated the effects of CaCO3 on the leachate chemistry through batch neutralization experiments. Second, batch adsorption experiments using the ash sample with high amorphous aluminum (Al) and iron (Fe) mineral contents were carried out to characterize its adsorption capacity and affinity for As, Pb, Cu and Zn. Finally, column experiments were conducted using different neutralization and adsorption configurations to compare the effects of using neutralization only and a combined neutralization–adsorption system. If this alternative disposal system is effective, it could provide a more economical, practical and safe way of disposing these hazardous excavated rocks.
Section snippets
Hydrothermally altered rock, volcanic ash and calcium carbonate
The hydrothermally altered rock sample used in this study was collected from the bulk excavated rock stored in an interim disposal site that had already been exposed to the atmosphere for ca. 6 months. This interim disposal site is used until the final disposal of the rock and/or while waiting for the thawing of snow in winter. The test material (i.e., partly-oxidized altered rock) was selected because it would most likely represent the actual waste rock for disposal. The rock sample was air
Properties of the altered rock and volcanic ash
The chemical and mineralogical compositions of the altered rock and partly-weathered volcanic ash used in this study are listed in Table 2, Table 3, respectively. The altered rock sample contains significant amounts of S at 10.6 wt.%, which could be attributed to the presence of pyrite. It also has significant As, Pb, Cu and Zn contents at 150, 375, 68 and 62 mg/kg, respectively. Results of the leaching experiment of the altered rock sample using deionized water illustrated that its pH was acidic
Dissolution of soluble phases and pyrite oxidation
Exposure of pyrite to the atmosphere results in its rapid oxidation commencing with the oxidation of S2− species (Schaufuss et al., 1998). This process is further enhanced in the presence of water or moisture that could strip reaction products exposing new sites on the pyrite surface. Reaction products from the atmospheric oxidation of pyrite include Fe-sulfates, Fe oxyhydroxides and oxides, which are more soluble than pyrite especially under acidic conditions (De Donato et al., 1993, Schaufuss
Conclusions
This paper describes the mitigation potential of a combined neutralization–adsorption system for excavated altered rocks producing acidic leachate. The findings of this paper are summarized as follows:
- (1)
Addition of at least 2% CaCO3 in the batch experiments effectively neutralized the leachate of the altered rock and immobilized most of the As and heavy metals dissolved in it.
- (2)
The partly-weathered volcanic ash used in this study adsorbed both As and the heavy metals, and the corresponding KF
Acknowledgments
The authors wish to acknowledge Eco Management Co., Ltd. for the preparation of samples and Horonobe Research Institute for the Subsurface Environment for the mineralogical and chemical analyses of the samples. Part of this research was supported by the Japan Society for the Promotion of Science (JSPS) grants-in-aid for scientific research. Finally, the authors wish to thank the anonymous reviewers for their valuable inputs to this paper.
References (33)
- et al.
Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: a review
Applied Geochemistry
(2008) - et al.
Spatial distribution of iron and sulphur species on the surface of pyrite
Applied Surface Science
(1993) - et al.
The kinetics of the oxidation of pyrite by ferric ions and dissolved oxygen: an electrochemical study
Geochimica et Cosmochimica Acta
(2000) - et al.
Leaching behavior of arsenic from various rocks by controlling geochemical conditions
Minerals Engineering
(2008) - et al.
Performance-based design of landfill liners
Engineering Geology
(2001) - et al.
Clay barriers — a not fully examined possibility
Engineering Geology
(1985) - et al.
Flow and transport through clay membrane barriers
Engineering Geology
(2003) - et al.
Oxidation of pyrite in low temperature acidic solutions: rate laws and surface textures
Geochimica et Cosmochimica Acta
(1986) - et al.
Pyrite oxidation at circumneutral pH
Geochimica et Cosmochimica Acta
(1991) - et al.
Pyrite oxidation in carbonate-buffered solution: 1. Experimental kinetics
Geochimica et Cosmochimica Acta
(1988)
Pollution risk assessment based on hydrogeological data and management of solid waste landfills
Engineering Geology
Mechanisms of arsenic and lead release from hydrothermally altered rock
Journal of Hazardous Materials
Factors affecting arsenic mobility from hydrothermally altered rock in impoundment-type in situ experiments
Minerals Engineering
Mobilization and speciation of arsenic from hydrothermally altered rock in laboratory column experiments under ambient conditions
Applied Geochemistry
Surface oxidation of pyrite under ambient atmospheric and aqueous (pH = 2 to 10) conditions: electronic structure and mineralogy from X-ray absorption spectroscopy
Geochimica et Cosmochimica Acta
Sorption of heavy metal from aqueous solution by volcanic ash
Comptes Rendus Chimie
Cited by (72)
A review of passive acid mine drainage treatment by PRB and LPB: From design, testing, to construction
2024, Environmental ResearchSustainable recovery and resynthesis of electroactive materials from spent Li-ion batteries to ensure material sustainability
2024, Resources, Conservation and RecyclingPotentially toxic elements (As, Cd, Cr, Hg, and Pb), their provenance and removal from potable and wastewaters
2023, Current Trends and Future Developments on (Bio-) Membranes: Membrane Technologies in Environmental Protection and Public Health: Challenges and OpportunitiesAttenuation performance of geosynthetic sorption sheets against arsenic subjected to compressive stresses
2023, Geotextiles and GeomembranesBioremediation of acid mine drainage – Review
2023, Alexandria Engineering Journal