The Appropriate Management of Tailings Dams (Slag Accumulation Sites)

Sustainable mine development and operation require efforts to minimize impacts on the environment.
At closed mines, we treat wastewater containing heavy metals discharged from drifts and manage tailing dams that collect slag discharged by mineral ore processing facilities. We have enacted safety measures at 42 tailing dam locations we manage in Japan. In regard to stabilization work, we responded to revisions to management standards for accumulation sites made in light of the Great East Japan Earthquake in 2011, and in the period up to 2020, we invested a total of approximately ¥4.5 billion.
Furthermore, as treating wastewater requires removing heavy metals until water quality meets wastewater quality standards, it is a key part of the management of closed mines, so a portion of treatment costs are subsidized by the Japanese government. In recent years, there has been increasing attention on passive treatment technologies that use microbes to remove heavy metals.
As passive treatment is a natural method of purifying wastewater that does not require the use of force or chemicals, it is expected to be introduced as a process that is lower cost and more environmentally friendly than wastewater treatment using chemicals. Since 2016, we have been working with JOGMEC to check the effectiveness of the technology through verification testing at our Yaso Mine (Fukushima Prefecture), which closed in 1970.

Domestic Mines That Are Now Closed/Suspended

Management Framework for Mines That Are Now Closed/Suspended

SMM’s management of mines that are now closed or suspended includes daily, 24-hour treatment of wastewater emerging from mines and accumulation sites, and maintenance of old mines and slag and spoil accumulation sites, in order to prevent mine pollution.

Konomai Mine (closed: October 1973), Kitami Mine (closed: October 1963), Yoichi Mine (closed: October 1963), Kunitomi Mine (closed: March 1945), Yaso Mine (closed: October 1970), Omiya Mine (closed: June 1950), Sazare Mine (closed: July 1979), Besshi Mine (closed: March 1973), Okuchi Mine (closed: September 1977)

as of July 1, 2021, dates in parentheses are closure/suspension dates

Stabilization work at the Okuchi slag sccumulation site no.1

greened state following the work