Drainages from two mines in the Ancash region of Peru were enriched with Al, As, Fe, and Mn, and Zn. Both pilot-scale and laboratory-scale slag reactors were employed to remove Mn and Zn. The column system effectively reduced Mn and Zn concentrations to <0.1 mg/L for both mines, with a residence time of 14.4 hrs in the slag reactor. Additionally, As was removed to <0.09 mg/L, likely due to coprecipitation and adsorption by Fe, even in the absence of a dedicated As adsorption reactor. These results suggest efficacy of the complex passive treatment system to treat Al, As, Fe, Mn, and Zn as well as possible utilization of coprecipitation-adsorption by Fe to reduce As and Zn concentrations in passive treatment system. The adsorption efficiency can be further enhanced by design improvement in the future.

Mine water treatment is carried out in about 100 abandoned mines in Japan, which costs a large amount of money each year through active treatment (AT). There are only a few domestic examples of passive treatment (PT), therefore Japan has been researching PT for implementation. This study aimed to develop PT technology for manganese (Mn) using a contact oxidation method with Mn-oxidizing bacteria (MnOB) as a sustainable alternative to AT.

The test site was in cold district in Japan, where there is heavy snowfall and temperatures drop to around -10°C in winter (from December to March). The average water chemistry of the targeted mine water was pH 7.1, 65.8 mg/L soluble Mn, and 10.2 mg/L soluble zinc (Zn). The system was divided into two sequential biological processes: a bioreactor filled with limestone (20-40 mm) for pH stabilization and a bioreactor using fiber filter materials as inorganic carriers for enhancement of microbial activity. The test was conducted from September 2023 at a mine water flow rate of 30 to 570 mL/min (hydraulic retention time (HRT) in limestone bioreactor from 1 to 7 days) with air pump aeration at the bottom of the two sequential bioreactors.

After acclimating MnOB in each reactor, soluble Mn average removal rates in the effluent of limestone bioreactor and the following bioreactor using fiber filter reached 89.0 % and 96.5 % to the original concentration in the mine water respectively during the non-winter period (from April to November), associated with remarkable removal rate of soluble Zn. In the limestone bioreactor, the maximum soluble Mn removal efficiency was 40.0 g/m³-reactor/day during the non-winter period. In the winter period, the limestone bioreactor achieved a maximum soluble Mn removal efficiency of 15.5 g/m³-reactor/day, due to low water temperatures below 5°C, possibly causing to less microbial activity.

The findings of this study suggest that a PT system using the contact oxidation method with MnOB is capable of removal of soluble Mn and Zn without chemical reagents use. This system, despite microbial process, showed applicability in various mine sites in cold district. However, the relationship between water temperature, HRT, and the soluble Mn removal rate has not been fully understood. Therefore, further tests are being on-going under different conditions to reveal the relationship above and assess the sustainability of Mn and Zn removal in the system.

This paper explores the application of mine water injection and storage technology in the Ordos Basin, focusing on its hydro-geological framework and practical implementation strategies. 15 hydro-geological framework of mine water injection and storage are systematically delineated. Based on the projects, the study also evaluates six different well construction methods and operational modes. And the case study of the MC-1 well in the Muduchaideng coal mine provides insights into the challenges and successes of long-term mine water injection. The detailed implementation plans, hydro-geological testing, operation timelines and consideration for re-operation were presented to provide the option methodology for sustainable mine water resource management in the arid and semi-arid areas.

Continuous mine water treatment is carried out in approximately 100 abandoned mines by active treatment in Japan. The research and development of passive treatment techniques have been conducted to reduce the treatment costs, especially focusing on a treatment process with short hydraulic retention time (HRT) applicable to a limited area available for the treatment in Japan.

A large-scale passive treatment test has been performed with a water flow rate of 100 L/min in a domestic abandoned mine site since 2020. The targeted acid mine drainage (AMD) has a pH of 3.6, and contains 38 mg/L Fe, 16 mg/L Zn, 4.6 mg/L Cu and 0.06 mg/L Cd. The AMD was initially pre-treated for Fe using an Fe oxidizing/removal process with Fe oxidizing bacteria in media composed of a mixture of rice husk and limestone (20-40 mm). The effluent from this process was then introduced into two vertical flow bioreactors (VFRs) of sulfate-reduction. The VFRs of sulfate-reducing process were filled with a mixture of rice husk and limestone (20-40 mm) at a 1.5 m thickness (HRT of 22.5 hours).

In this study, appropriate nutrient conditions for sulfate-reducing process with short HRT were investigated. At one of the VFRs, three different nutrient conditions with continuous ethanol feed were tested from 2020. The first test was conducted by feeding only ethanol (final concentration of 36 mg/L). The second and third conditions involved feeding ethanol (final concentration of 24 mg/L) with an initial addition of rice bran on the surface of the media as a supplemental nutrient. The weight of rice bran for second and third conditions were 300 kg (0.3wt% of media) and 1000 kg (0.8wt% of media) for approximately 26000 m³ of annual water flow, respectively.

Total Zn removal was shown to be effective in non-winter period (from April to November) under the three conditions. In winter season (from December to March), concentration of total Zn in effluents were sharply up to 7.4 mg/L under only ethanol addition condition, whereas the conditions with initial rice bran addition gradually resulted in total Zn conc. of 1.9 mg/L (300 kg) and 0.03 mg/L (1000 kg) at most in effluents. The test is continuously conducted to evaluate appropriate nutrient condition for metal removal and its sustainability.

Pilot-scale trials using Dispersed Alkaline Substrate (DAS) reactors for the treatment of AMD at a closed Sb mine in Abbaretz, France have been conducted (). The experiments demonstrated substantial iron precipitation leading to progressive head loss, which was an indicator of clogging over time. In this study, to better managed this phenomenon, we develop a method to estimate the volume occupied by iron precipitate. This information was then used for modelling the pilot-scale experiments (iron precipitation, system performance, and long-term operational viability).

To define the volume occupied by iron precipitate, a fixed-bed limestone reactor (0.25 L) was used to simulate AMD treatment over a time period. The reactor was analyzed using X-ray tomography, which allowed precise measurement of porosity variation and the in-situ volume of iron precipitate. This in-situ measurement is critical, as determining the volume of iron oxyhydroxide precipitates is typically challenging due to their low density. The ability to correlate dissolved iron concentrations directly with the volume of precipitate provides valuable insights into the operational lifespan of passive treatment systems, including both DAS reactors and other structures such as settling ponds.

To better understand the chemical interactions at play, a geochemical model was developed using PHREEQC software, paired with the Thermoddem database. The reactive transport model simulated key processes such as calcium carbonate dissolution and iron precipitation, as well as the resulting effect on porosity and metal retention under varying residence times. The model illustrated the neutralization of the AMD acidity by the DAS, through calcite dissolution. As consequences, the increasing pH of the effluent allowed Iron, Cobalt and Zinc to precipitate in the form of hydroxide. Different scenarios were modelled, including 24, 36, and 48-hour residence times in the DAS, to predict system efficiency and lifespan. The simulations reproduce correctly experimental data, showing strong agreement for parameters such as pH, iron removal rates, and the accumulation of precipitates.

These findings are crucial for improving the design and performance of full-scale DAS reactors. The insights gained from both the laboratory experiments and the reactive transport modeling will inform future applications, enabling more efficient AMD treatment and extending the operational lifespan of passive treatment systems.