Mine Rehabilitation Handbook - Mining and Blasting

6.6 Toxic Chemicals
• A wide range of chemicals may have been used for mineral
processing or ancillary activities on-site. An inventory of all the
chemical substances used on-site and their relevant Material Safety
Data Sheets should be kept on-site. A method for safe disposal of
residue materials and their containers should be determined.
• Acid and caustic solutions are commonly used for mineral
processing, other potentially hazardous materials include resins,
paints, flocculants, reagents etc.
• If any doubt exists on how to dispose of materials safely, contact
relevant authorities (refer appendix 1).
• Cyanide is used in large quantities at most gold mines. It is very
reactive and highly toxic.
• Cyanide is essentially unstable and oxidizes rapidly to more stable
products, which are generally non-toxic; however, some cyanide
complexes may be toxic to aquatic life. Both “free” and “total”
cyanide levels should be considered prior to discharge.
• Residual cyanide and other hazardous materials should be returned
to suppliers or disposed of at an approved site.
• Never bury cyanide tablets or powder - they may remain a potential
hazard for many years if soil conditions remain dry and alkaline.
• Ensure containers used to hold hazardous materials are detoxified
prior to disposal.
• Check discarded equipment especially electrical transformers for
PCB contaminated oil. Refer to the ANZECC PCB Management Plan
and the appropriate state government department for details of PCB
regulations.
6.7 Noxious Weeds
• Controlling the introduction and spread of weeds is an important
consideration in rehabilitation. Weed infestations on rehabilitated
areas can be very difficult to control and the emphasis should be on
prevention rather than cure.
• Weeds are often vigorous, persistent and good colonisers.
Consequently, they may rapidly invade sites being rehabilitated.
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• Each State and Territory has legislation relating to weed control and
lists of declared weeds – a list of declared weeds should be obtained
from the relevant State/Territory department (An indicative list of
species declared in some, not all, States is at Appendix 8). The
legislation enables governments to compel landholders and occupiers
to control certain weeds and to prevent their movement and spread.
Failure to control or eliminate these weeds is an offence under the
relevant State/Territory act. Most of the declared weeds are
agricultural weeds. Many other species, including grasses and
legumes used in agriculture, can be considered environmental weeds.
• Weeds in areas adjacent to those disturbed by mining should be
controlled to reduce the potential seed load. Be sure the mine site
does not become a source of weeds for possible infestation of
adjacent properties.
• Care must be taken to ensure that weeds are not introduced to the
area in topsoil, hay, mulch or manure or as contaminants in seed of
the desirable species. There are many examples of plant species that
have become weeds after being knowingly or unwittingly introduced
into Australia and this possibility should always be considered when
introducing exotic species in a rehabilitation program.
• Clean equipment coming on to site from other areas to remove seed
or plant pathogens.
• Fertilisers and manures should always be used carefully as they can
stimulate weed growth, seed set and spread. A vigorous cover of the
desirable plant species is often an effective impediment to invasion
by weed species.
• Early detection of weeds before they are well established can
simplify their control.
• Cultivation, hand weeding, burning and herbicides can all be used in
attempts to control weed infestations. However, control can be
difficult where desirable plants are growing amongst the weeds.
Hand weeding is expensive, but can be effective for smaller areas.
• Selective grass herbicides can be used for grass weeds in areas
revegetated with non-grass species. Herbicides can be applied
selectively using wick applicators in some cases, for example, when
the weeds are much taller than the desirable species.
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