1992-05-27_REVISION - M1988112 (3)

Home Browse Search

A s C I i' .'.N.• 4.)vT.aF`~YSiYQ.S.M.~lM1t\. " the WAD cyanide analyses are less than the total cyanide values, (e.g., sample 4, TCN = 126 mg/L; WAD CN = 112 mg/L); ' ' the WAD cyanide analyses are less than the total cyanide levels by something in excess of the calculated iron and cobalt cyanide complexes equivalent ' cyanide values (e.g., sample 4, TCN = 126 mg/L, WAD CN = 112 mg/L giving a difference of 14 mg/L. Iron, as Fe(CN16 and cobalt, as Co(CN~ , ' require about 3 mg/L cyanide and 3 mg/L cyanide to account for their presence in the total cyanide analysis over and above the WAD cyanide analysis); and 1 " the WAD cyanide analyses exceed the overall cyanide rgquirement for complexing those metals which would report to analysis. This must be the ' case if there is any free cyanide in the samples at all. (e.g., Semple 4, WAD CN = 112 mg/L. Copper, as Cu(CN)2 requires 78 mg/L cyanide, and the ' remaining WAD cyanide metals (Zn, Ni and Mn) require about 2 mg/L cyanide, giving a total of 80 mg/L cyanide needed in the WAD cyanide analysis at a minimum). ' 4.4 'FREE CYANIDE' ' None of the free cyanide determinations by either laboratory are correct. (Laboratory "C" reported the data were incorrect and noted that high levels of thiocyanate, a known interferent, were present.) The following observations substantiate this ' position: ' all Laboratory "C" free cyanide values exceed the WAD cyanid6 values which is not possible, particularly considering the levels of cyanide complexable metals in these samples (e.g., sample 4: WAD CN 112 mg/L, FCN = ' 149 mg/U; if Laboratory "A" free cyanide values are substituted for Laboratory "C" WAD ' cyanide values (Laboratory "A" WAD cyanide value are incorrect and cannot be use for computation, see above), the residual cyanide "available" is insufficient to account for the metallo-cyanide complexes present in the solutions, even taking the lowest oxidation state for those complexes (e.g., sample 4: Laboratory "A" FCN = 93 mg1L, Laboratory "C" WAD CN = ' 1 12 mg/L, a difference of 21 mg/L cyanide. A minimum of 80 mg/L difference between the FCN and WAD cyanide is required to account for the presence of the WAD metallo-cyanide species); ' 6