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~ II I I Ii l 111 it 1111 lil ~ ~ ~~ ~,~ ,~ 9r`~ ~ 2f p~ °1' - BRIEF NOTES ON CYANIDE ANALYSIS ~ot ,er 9 by: Harry Posey I,,~ ` 6/22/92 '"' ~X f~ 1. Free, WAD, and Total Cyanide. a. Free Cyanide is comprised of cyanide compoun s that will readily form hydrocyanic acid (HCN) gas un~er certain atmospheric conditions. Free cyanide is fatal t about 300 ppm in air (NIOSH Criteria Document, 1976). b. Weak Acid Dissociable Cyanide (WAD) is c mprised of cyanide compounds that will break down in a weak acid. Weak acids are found in some stream waters and in st mach acids. WAD cyanide analyses include both WAD and F ee cyanide species. c. Total Cyanide or Strong Acid Dissociable Cyan~de (SAD) is comprised of cyanide compounds that will break do n in strong acids. Strong acids may occur in streams that carry acid waters such as from sulfide ore bodies. Total cyanide includes all cyanide forms. 2. Analyzing for Cyanide Species cyanide analyses, like nearly all analyses, are subje t to human errors, analytical errors, machine errors, and matrix i terference errors. Most labs are able to minimize human errors ith proper training. Labs can also account for analytical and mac ine errors with quality control, clean reagents, and proper equipment maintenance. To account for matrix interference error one must either remove the interfering material prior to a lysis, or measure the abundance of interfering material and then orrect for it. Most of the analytical reports with which we have wo~ked so far have not been corrected for matrix interferences. Th se include analyses from commercial labs and from the Colorado De artment of Health. For purposes of standardization and for purposes of regu ation, the mining industry relies on EPA or other Standard ethods of Analysis. Several standard methods exist for analyzin for Free, WAD, and Total cyanide. However, there is presen ly no EPA approved method for measuring either Free cyanide or W D cyanide. There is an EPA approved method for measuring total cy nide. Most of the analyses, to date, for Free and WAD cyanid represent maximums. Most if not all of the analyses for total c snide also represent maximum values, but they are close to the tr e values.