Decontamination of
Cyanide Wastes by Methods of
Catalytic Oxidation and Adsorption
WILHELM BUCKSTEEG, Director
Ruhr River Association
Essen, Germany
INTRODUCTION
Wastes of galvanic industries are of particular danger for the receiving waters
due to the content of highly toxic cyanides and metal-salts. However, the recent
technical development has made it possible to eliminate the toxic substances by
chemical treatment or by other methods. The highly toxic cyanides can be oxidized by oxidizing agents, i.e. chlorine; the metal-salts can be neutralized, and
the hydroxides which form floes may be removed by sedimentation.
A good removal of the toxic substances can be obtained in plants which are
operated by skilled operators.    The plants are run more or less automatically.
Practical experience has shown that a high percentage of removal of cyanides and
toxic metal-salts (corresponding nearly to the value that is theoretically attainable) is actually possible in such treatment plants.
Hence it is not an unrealistic demand when nowadays the institutions for water
pollution control require that the wastes of galvanic industries discharged into a
public sewage treatment plant or into the receiving water directly, may not contain more than the allowable limits of contaminants as shown in Table I.
TABLE I
LIMITING VALUES FOR WASTES OF GALVANIC INDUSTRIES FOR DISCHARGE
INTO RECEIVING WATERS (ACCORDING TO GERMAN STANDARDS)
Settleable matter         0.3  ml/1
pH            6.5 - 9.0
Metals, dissolved and undissolved
Chromium    (Cr)     2 mg/l
Copper (Cu)   1 mg/l
Zinc (Zn)   3 mg/l
Cadmium     (Cd)   3 mg/l
Iron (Fe)   2 mg/l
Cyanide (oxidizable by chlorine)         0.1 mg/l
Free chlorine            0.5 mg/l
Substances which can be extracted by petroleum ether    5 mg/l
Nevertheless death of fishes occurs again and again, particularly in areas
where a high density of galvanic factories are discharging their wastes into the
natural waters.   On the other hand some losses of oxygen may take place which
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