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Environmental Protection and Technology

Preventing Environmental Pollution

Preventing Pollution

Preventing Air Pollution

We operate relatively large-scale plants such as cement factories and copper smelters, which emit dust, sulfur oxides (SOx) nitrogen oxides (NOx), as a result of burning coal in the manufacturing process. At each plant, we strive to minimize emissions of air pollutants by improving the stability and efficiency of operations, in addition to installing advanced exhaust gas purification systems.


Preventing Water Pollution

We treat effluent appropriately at all our facilities and manage it by imposing management targets that are even stricter than effluent standards. In addition to measures such as installing dikes to prevent chemical or oil leaks, and inspecting equipment on a daily basis, we also conduct regular training aimed at preventing the spread of substances in the event of a leak.


Chemical Management

We handle a diverse range of chemical substances in our plants. Each plant is taking steps to reduce usage and switch to less hazardous substances by developing processes and introducing new equipment in accordance with the characteristics of each chemical substance. We take these and other measures to minimize the emissions of hazardous chemical substances into the environment.


Waste Management

To contribute to building a resource-recycling society, we take comprehensive measures to reduce waste and recycle resources from waste we have produced. We also engage in recycling operations. At the Yokkaichi Plant, we work to reduce the sludge generated from the polycrystalline silicon manufacturing process. Reduction of sludge generation had been an issue at the Yokkaichi Plant because approx. 4,000 tons of sludge from the plant is sent to landfills every year and it accounts for 80% of all land-filled industrial waste from the Company. We reduced sludge generation by 20% from fiscal 2013 to fiscal 2020 by improving wastewater treatment, upgrading the equipment, and reviewing the treatment process.


Managing Abandoned Mine

Purpose of activities Activities during fiscal 2020 Self-
Targets/plans for activities from fiscal 2021 onwards
  • Managing abandoned mines
  • Ongoing training of engineers managing abandoned mines
  • Upgrading aging facilities
  • Tailings dam reinforcement work
  • Ongoing training of engineers managing abandoned mines施
  • Upgrading aging facilities (continued)
  • Tailings dam reinforcement work (continued)

Self-assessment grades A: Target achieved B: Target mostly achieved C: Target not achieved

Managing Abandoned Mines

We are a company with its origins in the mining industry. The Mitsubishi Materials Group owns a wide range of mines around Japan, including limestone, coal and nonferrous metal mines, such as copper, lead and zinc mines. Operations at all of our non-ferrous metal mines have now been suspended or discontinued. Currently, we are managing 21 abandoned mines in 14 locations. We have continued to implement the following controls and management programs for our abandoned mines on a long-term basis, pursuant to Article 5 of our Code of Conduct, which states, “[Environmental Management] We will work to manage our environmental impact and promote the effective use of natural resources and recycling.”

  • Management of tailings dam (sites used to store rubble from mining minerals, slag and sediment from mine drainage treatment).
  • Maintenance of excavated mine drift and drainage routes; implementation of safety measures at disused mine mouths and subsidence sites.
  • Treatment of acidic drainage containing heavy metals from the above sites.

We continue to preserve and maintain sections of mine drift in some abandoned mines as cultural heritage sites or tourist facilities to exhibit their former conditions and preserve historical mining technologies for future generations.

Facility Upgrading and Environmental Countermeasures for Abandoned Mines

Since 2015, our Group has been implementing responses to deteriorating natural disasters and other risks by conducting protective construction to guard against contamination and other threats, reinforcing tailing dams to prevent uncontrolled release of slag and sediment in the event of major earthquakes, reducing wastewater at the source and upgrading aging facilities and by fiscal 2019, we had completed appropriating an environmental countermeasure reserve for work expenses.
In addition to introducing these construction-based solutions, we are directing efforts toward R&D of new technologies for reducing the volume and improving the quality/treating the drainage water in mines and training human resources to handle future operations. We intend to continue our efforts to enhance efficiency and reduce the environmental burden in our management of abandoned mines.

Abandoned Mitsubishi Materials (non-ferrous) Mines

Abandoned Mitsubishi Materials (non-ferrous) Mines

Overview of Acid Mine Drainage Treatment at Abandoned Mines

Broadly speaking, acid mine drainage can be generated in two ways. There is the acidic water in the pits (mine water) containing heavy metals, generated through contact between oxidized minerals and rainwater and groundwater, which can fill the underground pits and mining cavities formed in mineralized belts due to mining operations. Then there is the permeated water (wastewater) generated when small amounts of heavy metals, which are contained in slag and other substances in the tailings dams, come into contact with rainwater and surface water. The acid mine drainage goes to processing plants, where it undergoes neutralization and the removal of heavy metals. The water is then discharged into rivers according to wastewater standards.

Overview of acid mine drainage treatment at abandoned mines

Overview of Acid Mine Drainage Treatment at Abandoned Mines

Major Management Tasks for Abandoned Mines

The Group controls acid mine drainage treatment, tailings dams, mine drifts and entrance drifts at the abandoned mines under its management. Acid mine drainage treatment involves the appropriate processing. Tailings dam control involves preventing stored slag and sediment from leaking out in case of dam body collapse. Mine drift and entrance drift control involves inspections to maintain waterways for acid mine drainage and sealing entrances to prevent injuries due to third-party trespassing and mine drift collapse. In particular, acid mine drainage control is carried out around the clock every day of the year.

Acid mine drainage treatment facilities (Yatani Mine)Acid mine drainage treatment facilities (Yatani Mine)

Tailings dam management (Ikuno Mine)Tailings dam management (Ikuno Mine)

Tailings Dam Reinforcement

Drawing on lessons learned from the leakage of slag and sediment from tailings dams during the Great East Japan Earthquake, the Ministry of Economy, Trade, and Industry revised its relevant technical policies in November 2012. Based on this, we evaluated the stability of the tailings dams at abandoned mines managed by the Group, which revealed that measures needed to be implemented at 10 locations. Thus, we started construction work to design and implement stability measures at the locations in fiscal 2016.

Reinforcement work by soil stabilization at the Ikuno Mine Tailings DamReinforcement work by soil stabilization at the Ikuno Mine Tailings Dam

Wastewater Reduction at the Source

In an effort to decrease the burden and risks of acid mine drainage due to environmental change (large-scale typhoons and guerrilla rainstorms) in recent years, we are conducting construction work to separate clear and waste waters as a way to preempt potential accidents. One way of doing this is to cover exposed surfaces of mineralized belts on a large scale, using the latest technology (chipcrete). This prevents rainwater from coming into direct contact with the mineralized belts, which is expected to reduce the amount of water to be processed as well as the burden of contamination.

Contamination containment work by slope seeding called Chip-creteat the Komagi MineContamination containment work by slope seeding called Chip-creteat the Komagi Mine

Human Resources Development

All the Group’s non-ferrous metal mines are abandoned and some time has passed since the mines were closed down. As such, we have seen a decrease in relevant human resources as engineers with skills in non-ferrous metal mining have either retired or reached advanced age. In order to continue to sustainably manage abandoned mines, we are aggressively training young workers with little mining experience, and setting up a variety of educational programs for workers (including programs for acquiring skills for the management of abandoned mines and for obtaining relevant qualifications). In this way, we strive to transfer mine management skills.

Worker training (mine drift management)Worker training (mine drift management)

Worker training (basic training)Worker training (basic training)

Joint Industry-academic Activities

In fiscal 2018, we opened an endowed laboratory in the field of environmental conservation in mining at Hokkaido University. In addition to lecturing students, this laboratory engages in a variety of research projects and activities related to the protection of the mining environment. We also receive the cooperation and instructions of experts from other universities and research institutions about our development and studies on new environmental conservation technologies, including technologies for unpowered mine drainage treatment that use natural depuration by microorganisms, etc. (passive treatment), technologies for greening former mining sites, and studies of methods to assess the impact of acid mine drainage on the surrounding environment.

Endowed laboratory opened at Hokkaido University (a class being given at the laboratory)Endowed laboratory opened at Hokkaido University (a class being given at the laboratory)

Field test of passive treatmentField test of passive treatment

Communication with Local Residents

To promote local residents’ understanding of our measures for preventing mining-induced pollution at our abandoned mines, we proactively hold sessions to explain countermeasure work and offer facility tours. We also strive to contribute to local communities through tree-planting and the release of juvenile fish as environmental activities, as well as participation in and cosponsoring of local events and festivals. In addition, we accept inspection tours of our mining facilities by students and researchers from Japan and overseas. We thus offer our facilities as locations for research and development and skills training related to the prevention of mining-induced pollution.