 Commonwealth of Australia 2010

90.4Current risk management

Seepage of water containing cyanide products to groundwater may potentially occur, particularly below TSFs, heap leach pads and associated facilities that are unlined, have poorly designed and constructed liners or where liner integrity is violated. In general, the presence of engineering controls (e.g. liner, under-drainage, groundwater recovery system) will reduce the risk of migration of contaminants in seepage. The National Water Quality Management Strategy (NWQMS) indicates that site-specific factors, local groundwater conditions and factors other than environmental considerations determine the level of protection and consequently the level of risk management (e.g. engineering controls) required to protect these beneficial uses and ecological values. Available data show that actively managed monitoring and recovery programs are crucial to effective risk management, enabling on-going evaluation of the effectiveness of existing risk management strategies or the potential requirement to establish additional risk management measures.

Groundwater monitoring of selected analytes is a requirement of most state and territory agencies, with cyanide and related substances only a part of these requirements. In addition to free CN and WAD CN, monitoring of total CN may be appropriate to detect movement of iron cyanides. Breakdown or reaction products such as thiocyanate should also be monitored where conditions may lead to significant concentrations developing. The location of monitoring should be selected carefully to ensure that movement in various directions (not necessarily only down gradients) is detected promptly.

Limited information available on use for ore flotation suggests that in Australia the quantities used at individual sites are low, and that in contrast to gold beneficiation, the cyanide used is consumed in the process, without the large excess of free cyanide required for gold ore beneficiation. Information suggests that the forms of cyanide present in tailings are likely to be low in solubility and bioavailability, and significant release of HCN to the atmosphere may occur where process streams become acidic after the point sodium cyanide is used. However, similar standards should apply to base metal mine TSFs if cyanide is present.

A literature source (Korte et al., 2000) has proposed that the formation of open ponds should be avoided with the gold cyanidation process because of the large amount of HCN evaporating yearly from their surfaces, which they considered could accumulate in the atmosphere and may add to the contribution of greenhouse gases, such as CO₂ and methane. However, HCN is not currently listed among other gases in the atmosphere which are considered to have significant Global Warming Potential, and is not a significant source of other gases which are considered to be greenhouse gases. HCN is also not considered likely to act significantly either directly or indirectly as an ozone depletor. Modelling of the behaviour of HCN in the atmosphere based on measured concentrations and other information also indicates that the contribution of gold mine sources to global release is minor compared to the major source, biomass burning. In addition, modelling indicates that longterm accumulation is limited by its atmospheric lifetime of ~5 months. For these reasons, measures to reduce HCN release are not warranted.

Due to the hazard of cyanide to human health and the environment, relatively stringent regulations and management strategies for sodium cyanide are established in Australia. The manufacturing, procurement, industrial use, storage, handling, transportation and discharge of sodium cyanide or its residues to the environment are controlled by state and territory regulations pertaining to major hazard facilities, dangerous goods, safety and emergency procedures, emissions, waste management and protection of the environment that are enforced by means of a system of conditional permits, licenses and warrants. In addition, the major industry groups, such as sodium cyanide chemical manufacturers and mining companies, have established self-regulating programs for safety and environmental protection. These include environmental management systems (EMS), quality assurance/quality control (QA/QC) systems, safety and environmental management (SEM) systems, and Standards and Codes of Practice (e.g. Responsible Care® Program, International Cyanide Management Code). There is a general philosophy of continuous improvement within these industries. Furthermore, Australia has water quality guidelines for the protection of aquatic ecosystems for use in evaluating risks to aquatic ecosystems from aquatic releases. Thus there are various strategies and programs in existence to manage the risks to the environment from sodium cyanide.

Despite current strategies and programs for sodium cyanide, risks to wildlife are still unacceptable in some circumstances. Additional risk mitigation measures to minimise these risks are proposed (see Recommendations).