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Returning Water to the Bosom of Nature Cleaning Urban Water Using Water as an Energy Source |
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The entrance to Konomai Mine as it appears today. From the initial discovery here in 1915 until the mine’s closing in 1973, it produced some 73 tonnes of gold and 1,240 tonnes of silver. |
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Returning Water to the Bosom of Nature |
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Preventing pollution Winter in Mombetsu is fierce. In the coldest period the temperature can fall below -30°c. Mombetsu is a city in northeastern Hokkaido, on the Okhotsk Sea. About 30 km south is an area called Konomai. Located between mountains, in winter the area is buried under a meter or more of snow, and in summer it is not unusual to encounter wild deer or foxes. Konomai Mine was once characterized as “the biggest goldmine in the Orient.” At its peak in the 1940s, 13,000 miners, their families, and attendant merchants lived in the area. But output started to decline in the mid 1950s, and by 1973 the mine was closed. Now, 30 years later, no-one lives in the Konomai vicinity anymore. Derelict buildings dot the landscape, and the area is choked with greenery. The verdant natural surroundings make it hard to imagine that once a bustling mining town stood here, with a population of over 10,000. Yet even today, Sumitomo Metal Mining Co., Ltd., which used to operate the “biggest goldmine in the Orient,” has an operations site at the Konomai mine, with four employees commuting daily from Mombetsu. They come to keep tabs on the water coming out of the mine: Sumitomo Metal Mining has assiduously kept up this part of its operations, even so long after the mine’s closure. According to Ichiro Abe, an executive officer and senior deputy general manager of Mineral Resources Division at Sumitomo Metal Mining, “Rock in the vicinity of gold and silver bearing quartz veins seams generally contains pyrites, which, after mining, react with water. Heavy metals contained in the surrounding soil and rocks then dissolve in the resulting acidic water, so this mine water cannot be allowed to run off freely into waterways. Also, water leaches from non–mineralized waste rock and residue after piled at dump sites, and this wastewater—or effluent—can contain trace amounts of the cyanide used in extracting the gold, so the dumps cannot be just left behind either. The company that had the mining rights is required to treat mine water, not just during mining, but for as long as it continues to effuse after the mine has closed as well.” |
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Battling with Nature |
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| Sumitomo Metal Mining manages abandoned mines at seven locations in Japan, and Konomai is the largest such operation. Seigo Akiyama, a senior mining engineer in the Mineral Resources Division’s Engineering Department, says: “At Konomai, we make and conduct supervisory control for about 10 km along the Mobetsu River. In no circumstances can untreated water be allowed to find its way into the river, and we believe we have a corporate responsibility to do everything we can to make sure that doesn’t happen. It’s not an easy job, so it’s also important to try to lighten the load for the people who have to do the work at the site. What I mean is that we have to take a long-term perspective, one looking several decades into the future, to come up with a system that provides complete security at the water-management end and burdens people as little as possible. Fortunately, so far we’ve had no major problems at the abandoned mines we manage; but when you look around the world, it seems that there are some mines that do let their mine wastewater run off uncontrolled.” At Konomai, mine water is neutralized with lime, and the substances that contain heavy metals are separated out in a settling tank. The resulting sludge is mechanically dewatered into cake, which is transported away with heavy equipment to its final disposal site. At the same time, the supernatant water from the settling tank, or thickener, is held for a further period in a settling pond where the quality of the water is tested at regular intervals before it is finally discharged into the river. On the other hand, wastewater is also treated by oxydization in multi-stage aeration tanks and settling ponds and tested for quality before release into the river. The scale of the operation at Konomai is such that simply carrying out the daily inspections requires a motor vehicle and almost two hours to get around to all the required test sites. Site Manager Hidenori Terabe, who has worked at Konomai for 18 years, says: “Things are most difficult when we get hit by heavy rains. A lot of rain swells the volume of mine water and brings the threat of overflow. And if the water in the settling ponds rises too high, it can breach the banks. Another danger is that the pipelines carrying mine water to the settling tanks and ponds could get clogged, causing an overflow incident. When the forecast is for heavy rain, we’re even more careful with inspections in anticipation of the bad weather, and after the rain stops we go back and thoroughly check all the equipment once again. Fortunately, we have settling ponds in two locations that together have a capacity of about 37,000 cubic meters, and we have sensors at key spots to check for any irregularities. They automatically forward an alert if they detect something wrong, so we haven’t had any contamination accidents.” |
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Fulfilling responsibility to society | |||
| Terabe says that five years ago a new neutralization plant was built at the Konomai site at a cost of some ¥400 million. This brought greater automation and made it possible for staff members to take two consecutive days off, whereas previously the site had to be manned 365 days a year. This is the sort of thing Akiyama was referring to when he spoke of a system that “burdens people as little as possible.” Says Terabe: “Sometimes a job will take us several hundred meters into the mining gallery. Since we’re using machinery, we have to be very careful about safety. The assumption is that the job will go well. It’s stressful because there’s absolutely no room for water pollution or accidents. And this is not a job that will be done and over with in a decade or two—it could continue almost indefinitely. We’re working with nature, and sometimes to protect nature we find ourselves in an uphill battle against it; but getting the job done is the company’s responsibility and the mission we’ve been charged with.” Since there is no longer any mining at closed mines, obviously this water-treatment work generates no economic benefits. On the contrary, Sumitomo Metal Mining lays out ¥400 to ¥500 million annually for such operations at seven locations around Japan. According to Executive Officer Abe: “Just because a water-treatment work doesn’t generate any economic benefits doesn’t mean that we in any way see it as retrograde. Our company is in business because of the benefits it derived from nature, and in this day and age, fulfilling our responsibilities to society is a lifeblood of the company. Water-treatment operations such as that at Konomai serve to support the company in a big way.” Japan is largely regarded as a world leader in both the management of abandoned mines and the technology for treating mine water. In fact, Sumitomo Metal Mining is providing assistance in the form of technical training for the treatment of mine water in Bolivia through JICA, the Japan International Cooperation Agency. If mine water were to flow untreated into water-ways, it would pollute not only nearby rivers, but also the ocean those rivers flow into. Japan’s technology is being put to work to prevent such unhappy outcomes. |
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