Significance and Use

Cyanide and hydrogen cyanide are highly toxic. Regulations have been established to require the monitoring of cyanide in industrial and domestic wastes and surface waters.

It is useful to determine the aquatic free cyanide to establish an index of toxicity when a wastewater is introduced into the natural environment at a given pH and temperature.

This test method is applicable for natural water, saline waters, and wastewater effluent.

1. Scope

1.1 This test method is used to establish the concentration of free cyanide in an aqueous wastewater or effluent. The test conditions of this method are used to measure free cyanide (HCN and CN ^- ) and cyanide bound in the metal-cyanide complexes that are easily dissociated into free cyanide ions at the pH of 6. Free cyanide is determined at pH 6 at room temperature. The aquatic free cyanide can be determined by matching the pH to the water in the receiving environment in the range of pH 6 to 8. The extent of HCN formation is less dependent on temperature than the pH; however, the temperature can be regulated if deemed necessary for aquatic free cyanide to further simulate the actual aquatic environment.

1.2 The free cyanide method is based on the same instrumentation and technology that is described in standard test method D6888 , but employs milder conditions (pH 6-8 buffer versus HCl or H ₂ SO ₄ in the reagent stream), and does not utilize ligand displacement reagents.

1.3 The aquatic free cyanide measured by this procedure should be similar to actual levels of HCN in the original aquatic environment. This in turn may give a reliable index of toxicity to aquatic organisms.

1.4 This procedure is applicable over a range of approximately 2 to 500 ? g/L (parts per billion) free cyanide. Sample dilution may increase cyanide recoveries depending on the cyanide speciation; therefore, it is not recommended to dilute samples. Higher concentrations can be analyzed by increasing the range of calibration standards or with a lower injection volume. In accordance with Guide E1763 and Practice D6512 the lower scope limit was determined to be 9 ? g/L for chlorinated gold leaching barren effluent water.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in 8.6 and Section 9 .

2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

ASTM Standards

D1129 Terminology Relating to Water

D1193 Specification for Reagent Water

D1293 Test Methods for pH of Water

D2036 Test Methods for Cyanides in Water

D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water

D3856 Guide for Management Systems in Laboratories Engaged in Analysis of Water

D4841 Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents

D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis

D6512 Practice for Interlaboratory Quantitation Estimate

D6696 Guide for Understanding Cyanide Species

D6888 Test Method for Available Cyanide with Ligand Displacement and Flow Injection Analysis (FIA) Utilizing Gas Diffusion Separation and Amperometric Detection

D7365 Practice for Sampling, Preservation and Mitigating Interferences in Water Samples for Analysis of Cyanide

E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

E1763 Guide for Interpretation and Use of Results from Interlaboratory Testing of Chemical Analysis Methods

Keywords

amperometry; aquatic free cyanide; diffusible cyanide, flow injection analysis; free cyanide; gas diffusion separation; Amperometric detection; Cyanides; Flow injection analysis (FIA); Gas diffusion ;

ICS Code

ICS Number Code 13.060.50 (Examination of water for chemical substances)

DOI: 10.1520/D7237-10

ASTM International is a member of CrossRef.

ASTM D7237