Cyanide Cn Cas 57125 Hydrogen Cyanide Hcn Cas Background

Cyanide is a product of natural animal and vegetative decay processes and also is a component in many industrial waste streams. It is used extensively in mining to separate metals, particularly gold, from ores. In water, an equilibrium exists between the ionized (CN-) and unionized (HCN) forms, the fraction of each depending on pH (see Equation 7.1 and Figure 7.1).

Below pH = 9, the predominant form is HCN. HCN is more toxic than CN- and is the dominant form in most natural waters. HCN is volatile while CN- is nonvolatile.

The most common industrially used form, hydrogen cyanide, is used in the production of nylon and other synthetic bers and resins. Some c yanide compounds are used as herbicides. The major sources of cyanide releases to water are discharges from metal nishing industries — iron and steel mills and organic chemical industries. Disposal of cyanide wastes in land lls is a major source of releases to soil.

Cyanides are not persistent when released to water or soil and are not likely to accumulate in aquatic life. They rapidly evaporate and are broken down by microbes. They do not bind to soils and may leach to groundwater. (Cyanide-containing herbicides, such as Tabun, have moderate potential for leaching but are readily biodegraded; therefore, they are not expected to bioconcentrate.)

Soluble cyanide compounds, such as hydrogen and potassium cyanide, have low adsorption to soils with high pH, high carbonate, and low clay content. Soluble cyanide compounds are not exptected to bioconcentrate.

Insoluble cyanide compounds, such as the copper and silver salts, adsorb to soils and sediments and have the potential to bioconcentrate. Insoluble forms do not biodegrade to hydrogen cyanide.

exchange, lime softening, and alkalinity adjustment,

Background Level Cyanide

7 8 9 10 11

figure 7.1 Distribution of cyanide between the HCN and CN- forms, as a function of pH. Health Concerns

7 8 9 10 11

figure 7.1 Distribution of cyanide between the HCN and CN- forms, as a function of pH. Health Concerns

Short-term exposure to cyanide compounds above the MCL may cause rapid breathing, tremors, and other neurological effects. Long-term exposure at levels above the MCL may cause weight loss, thyroid effects, and nerve damage. There is inadequate evidence for carcinogenicity from lifetime exposures in drinking water.

Drinking Water Standards

Maximum contaminant level goal: 0.2 mg/L. Maximum contaminant level: 0.2 mg/L.

Other Comments

Treatment/best available technologies: Ion-exchange, reverse osmosis, chlorination.

Fluoride (F-), CAS # 16984-48-8 Background

Most soils and rocks contain trace amounts of uoride. Much higher concentrations are found in areas of active or dormant volcanic activity. Common uoride-containing minerals include uorite (or uorspar, CaF2), cryolite (Na3AlF6), and uorapatite (Ca 5F(PO4)3). Weathering of minerals is the main source of uoride in unpolluted w aters, where concentrations are usually less than 1 mg/L, but may sometimes exceed 50 mg/L. Where dissolved calcium is present, the formation of uorite may limit uoride concentrations. High uoride concentrations are more lik ely in water with low calcium concentrations. Groundwater usually contains higher concentrations than surface water, and groundwater concentrations as high as 10 mg/L are common.

The formation of uoride comple xes may be important in solubilizing beryllium, aluminum, tin, and iron in natural waters. Addition of uoride to drinking w ater and toothpaste for reducing dental caries, and its subsequent discharge in sewage, also contribute to aquatic uoride. Dischar ges from aluminum, steel, and phosphate production are important industrial sources of uoride in w ater.

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