Abstract

There are at least five standardized methods to determine cyanides in water. These procedures have certain limitations and must be applied according to the type or components in the liquid medium. What is clear is that each step of the method applied must be well understood to avoid introducing errors that could lead to the incorrect quantification of free cyanide in solution. An important application of one of the procedures is in mineral processing, specifically in the quantification of free cyanide in residual solutions, for example, during the leaching of gold ores with cyanide. In this work, unreacted cyanide was quantified with known concentrations of cyanicide elements contained in synthetic solutions (simulating a pregnant residual solution). The free cyanide was quantified by the volumetric method based on the color change of the problem solution upon adding the titration reagent AgNO3. Experimental results show that CN and the metal form the complex Me(CN)x-, and the residual CN-, determined by the colorimetric technique, is satisfactorily quantified with an error of less than 3%; however, it is established that a limitation of this technique is the correct quantification of free cyanide if the CN- is less than 0.001g/l. The correct calculation of cyanide (without reaching saturation) that must be added to ensure the dissolution of all the gold contained in a mineral, avoids cyanide passivation and excessive contamination of groundwater and soils.

Keywords:Cyanidation; Leaching; Cyanicides; Cyanide passivation; Free cyanide