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<br />,, ~ AN'r_"rAl •"'==*.1'. STRY I . $~. YC. 7, APRIL '. ;.'-."~1
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<br />Tl_!_?`i ..-......-.... _r: ~.;. ..,.a: piastre uv :.._ ..-. ~.
<br />r'roce~u:- :.
<br />walaics ion '~ detection eel to total r,~nmde pear
<br />CN- 0
<br />2nlCN) r' 0
<br />Ag(CNI; 12
<br />Cr(CN)r'' 10
<br />Fa(CN)e - 100
<br />Fe(C.N)ar- B6
<br />Ca(CN)r3' 100
<br />waeelength of irradiation, duration of irradiation, power and
<br />i geometry of rho irradiation cell, and the environment in which
<br />the sample is irradiated. When these fatten are all optimized,
<br />photnconveraion can effectively replace strong acid distillation
<br />as art analytical technique Car dissociating motel cyanide
<br />I complexes.
<br />I Weak Acld sad Cyanides Not Amenable to Chlorine-
<br />; lion. The detorminetion of free and total cyanides hen been
<br />i discussed; this leaves only two categories in the total cyanide
<br />equation (eq 1) to 6e ovalttated. The detorminetion of either
<br />the weak acid disaocieble cyanides or the cyanides not
<br />I amenable ttt chlorination will provide the value of the arbor
<br />i through subtraction. Determinations of both categorim sere
<br />investigated; however, much more success was found with
<br />I CNATC deWrminations.
<br />I By utilizing p[uceduros developed in the Gore] cyanide
<br />determination, a simplo procedure for dotefmining CNATC
<br />was developed [n chlorination determinations, a strong ox-
<br />i idizing agent, such ae calcium hypochlorite, ie added w cyerride
<br />samples. The hypochlorite seleMively oxidizes cyanide t~~-
<br />pounds from the free and week acid disaociable cyanide
<br />I categories to produce cyanate ions in the process. Yet the
<br />strong metal cyanide compounds that make up the CNATC
<br />Category era unaffected by the oxidizing agent. A 1-h reaction
<br />time ie allowed fez this proceea. Tho oxidizing agent ie then
<br />neutralized with ascorbic acid. The precipitate formed In this
<br />neutralization process u Filtered out of solution; and the intact
<br />metal cyanides are determined by using the total cyanide
<br />procedure. Table IV shows the cyanide detection of various
<br />motel cyanide complexes subjected w the silver AAS CNATC
<br />procedure. As the results indicate, near complete tetrovery
<br />is achieved for high•stability compounds, and about 40%
<br />borderline CNATC compounds, such as chromium, are re•
<br />wvered. Such a division ie vary similar to that seen with the
<br />Currently accepted ASTM Cyanides Amenable to Chlorination
<br />Procedure B (3).
<br />Chemical Iatorterencea. Some of the moat severe limi•
<br />rations with the standard methods of cyanide analysis are
<br />caused by chemical interferences. By far the most troubleaoma
<br />interference for bath distillation sad many phntodecompo•
<br />striae methods (8,13! o! tyanide analysis has bean that caused
<br />by thiocyanate; it has produced large, up to 1;1, positive in•
<br />torletence effects. 'fo further Complicate this problem,
<br />thiocyanate is generally present in Concentretiom greater than
<br />the total cyanide concentrations. The silver filter is, however,
<br />highly inert in reference to thiocyanate ions; ae a result,
<br />thiocyansta produces nn detestable interference. Moreover,
<br />as a benefit of Irradiating the sample et lower energy wave-
<br />lengths, the powntielly largo positive thiocyanate interference
<br />has bean reduced to a eigttal equivalent to a factor of 0.000'l
<br />times that of the thiocyanate concantralioa attar 46 min of
<br />irradiation. Such a vast reduction ire the++bxrved interference
<br />effect allows rite thitxpanam :n be ignored in all but the most
<br />severe cases and easily corrected for iu those cases. Besides
<br />thiocyanate. the intlu-^~•e of -,:her anions was examined at
<br />the 1U0 mg;l ley+1 `.,r ~nt!t p•,aitrve and negetivP effects;
<br />rsrhnnnle, cl4er.,;r.::; .:..:.;e, ~uiGtt?. niter;e, and nitrate were
<br />Pidu ."~ _ r. r ..~.14 F.Or,
<br />.. ~~ • .. ' ^.., detectable
<br />,.c.....s.._ .._
<br />_.... _ _.., ..i ~ .: suit tram any
<br />..,
<br />.. _..._ :. ......., ,hv,v e positive
<br />-r - .., .... ....~_. -~ . ,.' ~, :un shi,wed nu positive
<br />iutetCrrence when introduced to the silver filter. However,
<br />wizen mixed with tree cyanide solutions, no free cyanide was
<br />detected. This it e result of the sulfide reacting with the
<br />cyanide tort to produce thiocyanate, which is not detected.
<br />This reaction has been shown to prngresa rapidly at elevated
<br />pH (18). Sulfide shotild, thareforo, bo rornoved as soon ae the
<br />sample is collected, before it is stabilized. Lead acetate lost
<br />paper may ba used w indicate qqhhe presence of sulfides in the
<br />sample. Lead carbonate can Mien be added in small incro•
<br />menGt w remote the sulfides, Since the reaction of the sulfide
<br />is with the cyanide, samples Prgtranwd ae above produce no
<br />sulfide interference with the st vor AAS det.ectiun method.
<br />Fatty acids, which distill over in distillation methods, un•
<br />dergo aaponiGcation reactiorta in the alkaline absorber. Tho
<br />soap produced interferes with the detection slap. Fatty acids
<br />posed nn problem with rho silver AAS method other than
<br />occasional fillet clogging. Thiq can be easily corrected by
<br />stacking menthrane prefilters atop lire silver filter. The ia•
<br />corporation of preGlten was alsq shown to extend rho useful
<br />life of the silver filter. This igdicaws that regular use of
<br />prefilters makes econom;aal aertso.
<br />It was observed that the ailt~er filter reaction afficionCy
<br />degrades with extended use. While aew, wcll•conditionetl
<br />eilvor filters provide 11X1% of the theoretical reaction effi•
<br />cioncy. After extortded use, thatfiguro can drop w ae low ea
<br />40%. 'hvn factors were identified as important in rho lose
<br />ut filter reaelion efficiency. The first ie simple physical
<br />clogging. As more pores become clogged, the contact time in
<br />the remaining pores ie reduced,iresulting in lower reaction
<br />yiolde. A second facwt is filter poisoning. This occurs only
<br />when metal cyanide complexes Are introduced w the Char.
<br />boring the redox reaction of the ¢yattide w the silver cyanide
<br />complex, sufficient potential maN be provided to deposit the
<br />original complex metal onto lire s er filter. By utilizing K-ray
<br />fluorascetlce methods, metals such as iron wed zing mtrudutxd
<br />as metal cyanides, were identified on rite filler surface. This
<br />meud deposition may be rho resul~ of direct deposition or due
<br />w the Filtration of iruoluble metal hydroxides from the highly
<br />alkaline solutions. Such clogged or poisoned filters can be
<br />regenerated by back rinsing the titters with a 0.01 M nitric
<br />acid wash solution. This can imlprove the titter reaction ef•
<br />ficiency without damaging tits filter. Through weak acid
<br />rinsing, reaction efficiencies em loo raised back [o near 90%,
<br />although complete regeneration }ray never 6eeu achieved, Due
<br />to the above two factors, as well As othere, it is important to
<br />s(wnya ntn standard cyanide wluti~»s fur calibration purpoaee.
<br />h[ethods Fnr dealing with recopies containing silver have
<br />also been e:emined. While ailveris not commonly Cound in
<br />appreciable Concentrations in eat~r~nl waters, it may occur in
<br />industrial applications. Soluble eilvet will generally exist in
<br />either Cationic or chelated forms. hen any CNATC metals,
<br />ouch as iron, are prosarrt, simplo e({ttilibria calculations show
<br />the cyanide will preferentially cu~~ntrplea the CNATC metal,
<br />leaving the silver ion in solution The addition of a base causes
<br />all but the most tightly chelated Silver to precipitate out of
<br />solution as t}te hydroxide and n~ide. C~?merselc, tl+e di-
<br />cyanosilvor complex is extremely stable and soluble in alkali;~e
<br />solutions. As a result, the silver content of .r a:m.~:- :,ia Sa;
<br />been pli adjusted to 12 or above and tittered of ,~~ ~~~ 'gym ~r
<br />below provides o measure of the silver :° _. -.
<br />']'his allows rho free cyanide determi•.
<br />sclutirns wnteining sih~et. Si:::+•'.e
<br />r: snide rnncentration pro•.~du, ,f::
<br />the actual free cyanide contem a~ -
<br />
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