Acid Rock Drainage - Mining and the Environment: From Ore to Metal - page 702

Prevention
The best way to prevent oxidation of sulphides is to maintain the material in a saturated
condition, usually by storing it below the water table. An operation involving multiple pits
extending below the water table provides the potential for such an approach. After the
i rst pit has been mined, PAF waste from the next pit is placed in the base of the i rst pit,
up to the level of the water table. The upper part of the pit can be left uni lled, or may
be i lled with NAF. This approach was used towards the end of the Mt Muro project in
Kalimantan, Indonesia which involved the mining of six pits, all in reasonably close proxi-
mity. A similar approach can be used in long narrow pits and in coal strip mines. Once
excavation is complete at one end, PAF from elsewhere in the Pit can be placed at the base
of the mined out area. This approach has been used in 'P' pit at the Chatree Gold Mine in
Thailand. Whether or not the PAF can be inundated and maintained in a saturated condi-
tion, storage below grade is preferred to storage in an above ground waste rock dump, as
there is much less chance of ARD reaching the surface.

The best way to prevent
oxidation of sulphides is to
maintain the material in a
saturated condition, usually by
storing it below the water table.

Minimization and Control
Prevention, while theoretically possible, proves to be economically or practically unachiev-
able in many circumstances. Many operating mines therefore adopt an approach which
combines minimization of both oxidation and leaching with some interception and treat-
ment (see Case 17.3 ).

CASE 17.3
Compacting Outslope of Tongaloka Waste Rock Dump, Batu Hijau

away from the dump outslopes. Thirdly, under-drains are
installed beneath each dump, draining to sumps from
where any ARD that occurs is pumped to a treatment
pond for neutralization.

Waste rock dumps at Batu Hijau use a range of measures
to minimize and treat ARD. Firstly, the dumps are formed
using the bottom-up approach. This enables the formation
of a low permeability skin on the surface of each layer,

inhibiting both oxygen ingress and downward percola-
tion of rainwater. The dump outslopes also incorporate
compacted clay material below the fi nal topsoil layer (see
photo below) Secondly, PAF waste is placed preferentially