ISO 6703-2:1984 水質 — シアン化物の測定 — Part 2: 容易に遊離できるシアン化物の測定 | ページ 2

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Every member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting.

International Standard ISO 6703/2 was prepared by Technical Committee ISO/TC 147, Water quality.

0 Introduction

Cyanides may be present in water as hydrocyanic acid (prussic acid), as cyanide ions and as complex cyanides. They may be determined as total cyanide or as easily liberatable cyanide. If cyanide compounds are chlorinated, cyanogen chloride (CICN) is produced, and this compound has to be determined separately.

This International Standard comprises four parts as follows:

• Part 1: Determination of total cyanide
• Part 2: Determination of easily liberatable cyanide
• Part 3: Determination of cyanogen chloride
• Part 4: Determination of cyanide by diffusion at pH 6 ¹ =

The method described in parts 1, 2 and 3 are suitable for controlling the quality of water and for the examination of municipal sewage and industrial effluents. They are appropriate to the technology available for the destruction of cyanides in treatment plants, and are based on the separation of liberated hydrogen cyanide (or in the case of ISO 6703/3, of cyanogen chloride) by stripping with a carrier gas.

The method specified in part 4 is suitable for the determination of smaller amounts of cyanide, depending on the concentrations of copper and nickel.

This part of ISO 6703 comprises four sections. Section one deals with the liberation and absorption of hydrogen cyanide. The other three sections deal with alternative methods for the quantitative determination of cyanide ions, as follows:

• photometric method with pyridine/barbituric acid (section two);
• titrimetric method using the Tyndall effect (section three) ;
• titrimetric method using an indicator (section four).

The specification of three alternative methods is necessary because each of the methods has its advantages and disadvan tages. None can be quoted as applicable in all cases.

The applicability of each method is described in clauses 8, 16 and 24.

1 Scope and field of application

This part of ISO 6703 specifies three methods for the determination of easily liberatable cyanide (see clause 2) in water.

The methods are applicable to water containing less than 50 mg of easily liberatable cyanide (as cyanide ions) per litre, and less than 100 mg of total cyanide (as cyanide ions) per litre, but higher concentrations may be determined by suitable dilution of the sample.

The methods and corresponding ranges of easily liberatable cyanide contents for which they are suitable are as follows:

• Photometric method with pyridine/barbituric acid: 0,002 to 0,025 mg of cyanide;
• Titrimetric method using the Tyndall effect: > 0,005 mg of cyanide;
• Titrimetric method using an indicator: > 0,05 mg of cyanide.

A large number of ions and compounds interfere with the determination. These are listed in table 1, together with the concentrations below which they do not interfere. If present singly or in combination, up to limiting concentrations, they do not interfere with the separation of hydrogen cyanide. The list is not exhaustive.

If any of the limiting concentrations of the influences are likely to be exceeded, dilute the sample with distilled water before stabilization (see clause 6).

Prussiates (pentacyano complexes with iron), which cannot be destroyed by chlorination under normal conditions of waste water treatment, partly decompose (up to 50 %), releasing hydrocyanic acid under the conditions specified. If it is desired to exclude prussiates, the procedure specified in clause 6 and 7.1 has to be used. This procedure is only applicable, however, if the concentration of copper ions in the sample is less than 1 mg/l. The presence of aldehydes, e.g. formaldehyde, may give lower cyanide values because of the formation of cyanohydrin.

2 Definition

For the purpose of this International Standard, the following definition applies.

easily liberatable cyanide: Cyanide from substances with cyanide groups and a measurable hydrocyanic acid vapour pressure at pH 4 and room temperature.

Such substances include all cyanides which will undergo chlorination, especially hydrocyanic acid, alkali- and alkali earth metal cyanides, and complex cyanides of zinc, cadmium, silver, copper and nickel. Complex cyanides of iron and cobalt, nitriles, cyanates, thiocyanates and cyanogen chloride are not included.

Bibliography