技术报告-尾矿库设计及评估 (英文)(13)

技术报告-尾矿库设计及评估 (英文)

Design and Evaluation of Tailings Dams

copper tailings. In active pits, embankments may be necessary to keep the tailings from the active area.

However, since seepage from the tailings can adversely affect the stability of the pit walls or embankments, it

is unusual to see disposal in active pits. Williams (1979), for example, discusses a failure due to pore water

pressure in the floor of a pit in Australia. Ritcey (1989) notes that the hydrogeological parameters affecting

the migration of seepage and contaminants are poorly understood, so tailings with toxic contaminants or

reactive tailings may be poor candidates for this type of impoundment. The U.S. Bureau of Mines points out

that other limitations for using active open pits for tailings disposal are loss of the pit areas for future

resources, and subsequent mine operating and design restrictions to which mine operators would be

subjected.

Subaqueous disposal in a deep lake or ocean is also a possible disposal method. Underwater disposal may

prevent the oxidation of sulfide minerals in tailings, thus inhibiting acid generation. Subaqueous disposal has

recently been practiced by eight mines in Canada, with three still active as of 1990 (Environment Canada

1992). Subaqueous disposal is used in areas with high precipitation, steep terrain, or high seismicity or, in

Canada, where its use predated current regulations. This method is also limited to coarse tailings that can

settle quickly. CANMET (Canadian Centre for Mineral and Energy Technology) completed a bench-scale

16-year simulation of deep-lake disposal using Ottawa River water (Ritcey and Silver 1987). They found

that the tailings had little effect on pH when using ores with a low sulfide content. Ripley, et al. (1978),

found that the tailings can cover large areas on the ocean or lake floor and cause turbidity problems if the

disposal practice is not designed correctly. There is little data on the long-term effect of subaqueous disposal

(Environment Canada 1987), although it is being studied in Canada and peer reviewed by CANMET

(CANMET 1993).

A variation on subaqueous disposal in the ocean or lakes would be permanent immersion of tailings in a pit or

impoundment. This could present many of the same advantages of underwater disposal (i.e., reduced

oxidation of sulfide minerals) but also would require long-term attention to ensure constant water levels and

possibly monitoring for potential ground water impacts.

2.2Types of Impoundments

There are two basic types of structures used to retain tailings in impoundments, the raised embankment and

the retention dam. Because raised embankments are much more common than retention dams, they are

emphasized in this report. Either type of structure, raised embankments or retention dams, can be used to

form different types or configurations of tailings impoundments. The four main types of impoundments

include the Ring-Dike, In-Pit, Specially Dug Pit, and variations of the Valley design. The design choice is

primarily dependent upon natural topography, site conditions, and economic factors. Most tailings dams in

operation today are a form of the Valley design. Because costs are often directly related to the amount of fill

material used in the dam or embankment (i.e., its size), major savings can be realized by minimizing the size

of the dam and by maximizing the use of local materials, particularly the tailings themselves.

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