Acid Rock Drainage - Mining and the Environment: From Ore to Metal - page 699

TABLE 17.1
Simple Classifi cation of Acid-generating Potential (after EGi)

Category Rationale Criteria

Barren Material is inert with respect to acid generation; includes most

highly weathered materials

0.1%S, ANC 5 kg H 2 SO 4 /t

NAF Availability of ANC is more than suffi cient to neutralize all acid that

could possibly be produced

NAPP is negative, NAG pH 4.5

PAF Acid-producing potential exceeds neutralizing potential

NAPP is positive, NAGpH 4.5

UC Cases where there is apparent contradiction between NAPP and

NAG results

NAPP is positive & NAGpH 4.5 OR NAPP is
negative & NAGpH 4.5

FIGURE 17.6
Geochemical Classifi cation Plot

12

11

10

Source:
Miller & Jeffery 1995

9

NAF UC

8

7

6

5

4

NAF - Non-acid Forming
NAG - Net Acid Generation
NAPP - Net Acid Producing Potential
PAF - Potentially Acid Forming
UC - Uncertain

3

PA F

UC

2

1
200 150 100 50

0 50 100 150 200

NAPP kgH 2 SO 4 /t

TABLE 17.2
Waste Rock Classifi cation Combining Acid-producing Potential and Salinity

Material Type Geochemical Characteristics Management Prescriptions

IA Non-acid forming

Nil/low/moderate salinity
NAG pH 4 & EC 1:5 0.8 dS/m
NAG pH 4 & EC1:2 1.5 dS/m

Suitable for general construction use and general fi ll. No specifi c geochemical
constraints. Suitable for rehabilitation works.

IB Non-acid forming

High salinity
NAG pH 4 & EC1:5 0.8-1.3 dS/m
NAG pH 4 & EC1:2 1.5-2.5 dS/m

Suitable for general fi ll.
Undesirable for rehabilitation use due to salinity. Avoid placing within 300 mm
of fi nal surfaces.

IC Non-acid forming

Extreme salinity
NAG pH 4 & EC1:5 1.3 dS/m
NAG pH 4 & EC1:2 2.5 dS/m

Can be used for general fi ll provided it is isolated within the core of any
embankment (for example water storage). Do not place within 500 mm of
rehabilitation surface.

(Continued)