Segregating tailings: effects on density and water retention

Mine waste geotechnics, geochemistry and biology

Keith Seddon

ATC Williams Pty Ltd

Segregation of tailings on deposition can occur as a result of a) sub-aqueous deposition, and b) sub-aerial deposition at lower solids concentrations (i.e. when the solids concentration is less than the segregation threshold). The effects are likely to be more pronounced in the case of subaqueous deposition.

This paper presents the results of investigations of several sub-aqueous tailings facilities, with some additional data from segregating sub-areal sites.

The method of deposition will be discussed, together with the mechanism of segregation.

Field and laboratory data showing extreme variations in particle size and density will be presented, and compared to test results for non-segregated ‘all-in” tailings for the same sites.

The results indicate that following segregation both the fine and coarse splits tend towards a well sorted (poorly graded) mix, and both have significantly lower consolidated density than the all in tailings. This result is reasonably well known for the case of the segregated fines (“slimes ponds”) but less appreciated for the coarse fraction. The results suggest that if the effects of segregation are not allowed for, the overall density of the deposit can be seriously over-estimate at the design stage. Also the quantity of water retained in the tailings can significantly influence water recovery and water balance results.

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