Converting Minerals to Metals - Mining and the Environment: From Ore to Metal - page 273

TABLE 6.4
Nomenclature, Stability and Toxicity of Some Important Cyanide Species in Gold Mining Tailings

Analytical type (a) Log equilibrium constant (b)

and solubility data

Toxicity to fish (c)
(LC 50 in mg/L)

Term Species or

compound

1. Free cyanide free cyanide CN-HCN not applicable 9.2 0.1

0.05 to 0.18

2. Simple compounds
a) readily soluble free cyanide KCN(s) * sol 71.6 g/100 g H 2 O (25 o C) 0.02 to 0.08

sol 34.2 g/100 g H 2 O (15 o C)

0.4 to 0.7

NaCN H 2 O(s)

Ca(CN) 2 (s) -

b) relatively insoluble WAD/CATC/total CuCN(s)

19.5

-

Zn(CN) 2 (s) 15.9 -

Ni(CN) 2 (s) sol 9.1 10 4 g/100 g H 2 O

(25 o C)

-

3. Weak complexes WAD/CATC/total Cd(CN) 2 17.9 -

Zn(CN) 2

19.6 0.18

Ni(CN) 2

4. Moderately strong
complexes

WAD/CATC/total 30.2 0.42

Cu(CN) 2 16.3 -

Cu(CN) 2 21.6 0.71 (24 hours)

Cu(CN) 3 23.1 -

20.5 -

Ag(CN) 2

Fe(CN) 4 5. Strong complexes total 35.4 35.0 (light); 860 to 940 (dark)

Fe(CN) 3 43.6 35.2 (light); 860 to 1210 (dark)

Au(CN) 2 38.3 -

Thiocynate SCN - not relevant 50-200

Cyanate CNO - not relevant 34-54

(a) WAD total cyanide following acid distillation.

(b) Measure of stability, given only for comparative purposes; values quoted in the literature are quite variable.
(c) Toxicity data is given only for guidance and should be used for comparative purposes only, a dash indicates 'no relevant data found'.
(Beck, 1987, Hagelstein, 1997, Minerals Council of Australia, 1996, Richardson, 1992)
* (s)

weak acid dissociable; CATC cyanide amendable to chloride; total

solid

Source:
Environment Australia 1998

TABLE 6.5
Cyanide Code Principles and Standards of Practice

Principle Standards of Practice

1. PRODUCTION. Encourage responsible cyanide manufac-
turing, by purchasing from manufacturers who operate in a
safe and environmentally protective manner.

1.1 Purchase cyanide from manufacturers employing appropriate practices and procedures
to limit exposure of their workforce to cyanide and to prevent releases of cyanide to the
environment.

2. TRANSPORTATION. Protect communities and the envi-
ronment during cyanide transport.

2.1 Establish clear lines of responsibility for safety, security, release prevention, training, and
emergency response, in written agreements with producers, distributors and transporters.
2.2 Require that transporters implement appropriate emergency response plans and capabili-
ties, and employ adequate measures for cyanide management.

3. HANDLING and STORAGE. Protect workers and the
environment during cyanide handling and storage.

3.1 Design and construct unloading, storage and mixing facilities consistent with sound
accepted engineering practices, and quality control and quality assurance procedures, spill
prevention and spill containment measures.

(Continued)