A lab-scale experimental system accommodating soil and plants was designed to evaluate the applicability of constructed wetlands (CWs) to mine drainage treatment. Synthetic wastewater containing Cd (0.11 mg/L) and other minerals (pH 6.8) was prepared based on the chemical composition of an actual neutral mine drainage (NMD). In lab-scale CWs consisted of a column (ID 12.5 cm, H 50 cm) filled with pumice stones and loamy soil were planted reed (Reed-CW) or cattail (Cattail-CW) plants. Some were left unplanted (Unplanted CW). The synthetic NMD (2.0 L) was treated in a 1-week cycle sequencing batch mode in the CWs in a greenhouse. The unplanted CW removed cadmium sufficiently to satisfy the effluent standard (0.03 mg/L) from the NMD, mainly by soil adsorption. Presence of the emergent plants, especially cattail, enhanced metal removal possibly by filtration with their elongated roots and metal sulfide precipitation by sulfate-reducing bacteria in the rhizosphere of the Cattail-CW.

Acid mine drainage (AMD) releasing from abandoned mines in Japan sometimes contains a high level of manganese (Mn) over the effluent standard (10 mg dm^–3) with cadmium (Cd) and zinc. Cadmium is normally precipitate as hydroxides at pH 9–10, while it can be removed at a lower pH range of approximately 8–9 by surface complexation with metal hydroxides such as ferrihydrite and gibbsite. In this study, we examined the removal performance of Cd by manganite (γ-MnOOH) which is trivalent Mn oxide by an adsorption experiment, and found the Cd concentration decreased over pH 9.0 below the effluent standard (0.03 mg dm^–3), which the surface complex equilibrium constant was Log K = –4.0. A neutralizing experiment of the AMD containing Mn (39 mg dm^–3) and Cd (0.077 mg dm^–3) from the X mine showed the Cd was removed at pH 8–10, and a chemical equilibrium calculation revealed the surface complexation on γ-MnOOH was the main removal mechanism. Our results therefore suggest the Mn oxidation and surface complexation with the product is the controlling factor Cd removability during the neutralization of AMD containing Mn.

For revegetation of mine dumping sites, introduction of tolerant plant species to tailings is needed. We compared initial shoot growth of the plants grown in tailings with that of control plants grown in Kanuma pumice to evaluate the tolerance to tailings among various species; one crop species, ine (Oryza sativa L. cv. Nipponbare); three revegetation species, yomogi (Artemisia princeps), medohagi (Lespedeza cuneate G. Don), and creeping red fescue (Festuca rubra L.); and two native species, mizudokusa (Equisetum fluviatile L.) and susuki (Miscanthus sinensis). The growth of the plants grown in tailings was significantly lower than that of control plants for ine, yomogi, and medohagi, but not for mizudokusa and susuki. We evaluated whole-plant respiration of ine, yomogi, and mizudokusa, and did not observed significant difference between the plants grown in tailings and control plants; however, Fe concentration in roots was significantly higher in the plants grown in tailings in all of the evaluated species. It is probable that the high Fe accumulation caused by tailings induces reduction of growth for crop and revegetation species, while does not affects native species because of their tolerance to high Fe concentration. Effective use of native plants may help revegetation of the dumping site.

This paper describes the geochemistry of acid mine drainage (AMD) and river water around the Date Mine in southwest Hokkaido, Japan. The mine is located in a sulfide deposit that contains pyrite and generates AMD, which is currently being neutralized; however, the introduction of a passive treatment system (PTS) is being considered. In preparation for the introduction of the PTS, this study aims to evaluate the environmental impact of untreated AMD flowing into rivers. The flow rate of the river depends on precipitation, and the ratio of AMD to that of the river was in the range 0.0014–0.018. In mixing experiments of AMD and river water based on measured results, the formation of iron and copper precipitates with increasing pH was observed, which suggests the possibility of self-purification phenomena of heavy metals in the river. The calculated oxidation rate of Fe(II) increased with pH. The surface complexation model in PHREEQC reproduced Cu concentration decrease due to coprecipitation with iron hydroxide. Assuming that untreated AMD is mixed with the river water, the Fe²⁺ concentration decreased from 0.19 mg L^–1 to 0.003 mg L^–1 in the river.

To understand water mass balance and behavior of major elements in river basin is an important issue in advancing the management of abandoned and closed mines. This paper describes the response of river runoff due to rainfall, and the relationship between water mass balance and river water quality. In the river basin around the Ningyo-toge Mine, the runoff increased when it rained more than 50 mm d^–1 and continued for several days after the rain, while in case of heavy rain over 500 mm, the effect of intermediate runoff extended to the next month. The river water quality was Na–Cl type in the upstream, while it was Na–HCO₃ type or Ca–HCO₃ type in the middle to downstream, and contained dissolved Si in the entire river basin. Based on the measured anions and cations, it is inferred HCO₃^– and Ca²⁺ results from the dissolution of carbonate minerals, and that Na⁺ and Cl^– are derived from sea salt. Since a correlation between the concentration of Si and runoff was observed, the Si concentration may be regulated by both groundwater flow to the river and the dissolution rate of feldspar.