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<br /> <br />ANALYTICAL -GENERAL <br />Weak acid dissociable cyanide (CNW„p) refers to all forms of cyanide except the strongly <br />complexed forms such as iron, cobalt and precious metal cyanides. The SO,/Air process (as well <br />as other commercial processes} destroy only the CNW,,o cyanide. The picric acid procedure for <br />cyanide determination is one method for determining such CNW,~ levels and is sometimes <br />referred to as cyanide-picric (CNP) to distinguish the two methods. A method provided to <br />esrimate the CNr given the CNP and iron concentration (see picric acid laboratory procedure}. <br />Free cyanide (CNF) is a measure of the unreacted cyanide in a solution and is determined <br />by the silver nitrate titration procedure. When wri[ten as CNF the chemical formula is assumed <br />to be "CN" but usually flee cyanide titradons are calibrated to give the assay in terms of <br />"NaCN". The HCN portion generally is undetected in a silver nitrate titration and significant <br />errors can result if the pH is under 10.5. This method is useless for determining cyanide in <br />SO~/Air treated effluent. A method is provided to esrimate the CNW„D based on NaCN titra.rions <br />and base metal concentrations which is useful for feed-forward control. <br />Simply cyanides are solid forms of cyanide such as Zn(CN)2 and CuCN. These can form <br />when there is no free cyanide left in solution. <br />Introduction To Picric Acid Method <br />The picric acid method is used by the operators to monitor the cyanide conceniration <br />leaving the SOa/Air reactor. By having theoperators perform their own routine cyanide analysis, <br />they will quickly learn how to obtain the best possible process performance. Conversely, it is <br />very difficult to obtain smooth trouble-free operation without this feed-back mechanism. Cyanide <br />determinations are necessary in both feed and effluent of the CND circuit Cyanide determination <br />in the feed are needed to determine the "CN load" and to calculate the SO2 requirement for <br />effective cyanide destruction. Cyanide analysis for the CND effluent indicate whether the CND <br />is operating efficiently and the target for discharge is met. <br />„~,.„w.,,,:,~ 2 <br />