Due to the natural conditions, the Smolník deposit (Slovakia) was one of the few where mine waters were intensively used for the extraction of copper from the Middle Ages. In favourable periods, it was possible to obtain more metal from mine the water than from the ore (Jaško 1998). Cementation technology was unique in the world at that time. According to historical records, China (1086 A.D.) was the first in the world to use this technology (Lung 1986), but it is the Smolník location that holds this primacy within the Europe. The oldest written mention of copper production by cementation in Smolník is from 1346 (Juck 1984). The record itself was therefore the second in the world that mentions the practice of copper cementation.

The mining activities on the site ceased in 1994, and the area was subsequently flooded. The mining complex itself began to behave like a bioreactor, producing large amounts of acid mine drainage where the predominant microorganism of the given waters is the genus Gallionella (Bártová, 2020). The primary pollutants within AMD in Smolník are iron, sulfates, manganese, aluminum, copper, zinc and arsenic. Under normal conditions, the flow of mine water reaches 10 L/s^-1 with an average temperature of 14 °C. Sulfates and ferrous iron, which are products of pyrite leaching, are the dominant ions in this water (Kupka et al. 2012).

The precipitates themselves, iron ochre, are mainly formed on surfaces that are in contact with mine water. Larger pieces can be observed in places where the flow slows down and the mineral (ochre) has room to form. The main mineral in the outflow is Schwertmannite (Fe₈O₈ (OH) ₈–2x(SO₄)x • nH₂O. Along with elements such as iron and sulfur, also metalloids such as arsenic or antimony coprecipitate here. Schwertmannite has an interesting reddish color and there is a possibility of its use as a natural pigment. After drying, it is brittle and easily crushed into a fine powder. It can be easily mixed with a base medium, such as oil, and the resulting colour is intense and well usable. Smolník mine waters are currently a rare raw material, which has the potential to be used for obtaining natural pigments and metals, with the help of biohydrometallurgical approaches.

Intensive research is currently underway. Preliminary results show a great potential in a novel use of this old mining site.

Wetlands altered by mining activities are often critical ecosystems that provide essential services such as water purification, biodiversity support, and flood regulation. However, traditional monitoring tools used to assess ecosystem health are often inadequate in capturing the complex interactions between natural and ecologically engineered systems within these altered environments. This study presents an innovative framework, combining the Ecological Integrity Index (EII) and the Ecological Engineering Index (EEI), which allows for more accurate assessments of ecological health and prioritization of interventions in mine-altered wetlands. This approach addresses an existing gap in current ecosystem monitoring practices, particularly in the mining sector, where environmental degradation have long-term consequences for both ecosystems and mining operations.

The novelty of this approach lies in the integration of the EII and EEI, which offer a comprehensive, scientifically robust method for evaluating ecosystem health. The EII assesses baseline ecological conditions, focusing on biological and physical integrity of natural systems, while the EEI provides a tailored approach for evaluating and guiding interventions in ecologically engineered systems, such as constructed wetlands. For the first time, these indices are applied together to both natural and engineered environments, offering a holistic view of wetland functionality and resilience. The assessment was conducted at the Leeuspruit wetland near South Deep Gold Mine, where baseline conditions were evaluated, and targeted ecological engineering interventions were proposed based on indices’ findings.

The main findings of the study revealed that the Leeuspruit wetland, categorized as critically modified (Ecological Category E), exhibited impaired water quality, with uranium concentrations and total dissolved solids (TDS) well above acceptable levels. Biodiversity had declined, with invasive species dominating large areas. The application of the EEI identified key areas for ecological regeneration and restoration, including implementation of constructed wetlands, bioremediation systems, and buffer zones. These interventions are projected to reduce uranium levels by 50% and improve water quality within five years, while also promoting biodiversity recovery.

The implications of this work are far-reaching for the mining industry. By integrating the EII and EEI, mining operations can more effectively prioritize regeneration and restoration efforts, meet regulatory compliance, and contribute to long-term sustainability. This approach not only enhances ecological resilience but also positions mining companies as stewards of biodiversity conservation. The combined application of these indices offers a replicable model for sustainable mine water management, which can be adapted across different mining landscapes worldwide, aligning with global biodiversity and environmental sustainability goals.

In Chile, coal was extracted from underground mines beneath the Pacific Ocean, in the Arauco Basin in the Southern Biobío Region, with the operation ceasing in 1997. The mine “Chiflón del Diablo” is an abandoned coal mine and part of the Lota mining complex, registered on the tentative list to be awarded UNESCO World Heritage status. The mine has been a tourist attraction due to the exploitation beneath the coastal area. Unfortunately, since the last massive earthquake that hit the Biobio Region (February 2010), flooding of the mine was observed, requiring saline groundwater to be dewatered directly into the nearshore zone to maintain tourist activities. This water pumped from the mine out onto the beach, possessed a high concentration of chloride (~600 mM) as a consequence of the seawater intrusion process into the shafts, a phenomenon reported at many mines near the coast. The mine water discharged to the sea from the Chilean mine additionally contained elevated ferrous iron (between 2-5 mM) and sulfate (~33 mM) due to the oxidation of pyrite, the main sulfide mineral associated with the Arauco Basin. This study describes the removal of iron and sulfate in mine water with high chloride concentration by using a continuous sulfidogenic biofilm reactor inoculated with sediment samples from the “Salar of Huasco”, Chile. In the samples analyzed in the biofilm, Desulfomicrobium, a genus belonging to the order Desulfovibrionales, was the most abundant SRB, with a relative abundance of about ~30%. Feeding the mine water, with a hydraulic retention time of 25 h, it was possible to remove more than 95% of sulfate and iron by using lactate as electron and carbon source. This study highlights the use of a halophilic sulfate-reducing consortium to promote sulfidogenesis in mine water with a high chloride concentration.