Water Online

November 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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By Dr. Felix Zelder C yanide is an essential chemical compound for a large number of industrial processes and products that are part of our everyday lives. Unfortunately, cyanide is also one of the most lethal chemical substances known to mankind. A few hundred milligrams of this compound in solution, or ppm in air, are enough to cause severe to lethal damage in adults if ingested or inhaled. Moreover, it is particularly harmful for aquatic life and habitats. According to the International Cyanide Management Code, the mining industry consumes about 6 percent of the annual hydrogen cyanide output (>1M metric tons) to remove gold from ore, a process that is more than 100 years old. Cyanide is also used to process foods and produce pharmaceuticals, cosmetics, and plastics. Its ability to form soluble complexes with metals such as zinc, silver, copper, and gold in water, together with its ability to aid anode corrosion and conductivity, makes cyanide an essential component of many electroplating processes. Why Is The Management Of Cyanide Important? Each year, the mining and electroplating industries rely on large amounts of useful, but toxic cyanide. Unfortunately, voluntary or involuntary release of this compound into surface waters does occur, posing a severe threat to animals, humans, and aquatic life. In 2000, about 100,000 cubic meters of cyanide- containing wastewater was spilled in Baia Mare (Romania), heavily contaminating the Danube and other rivers in Eastern Europe and affecting the ecosystems, health, and economies of local communities. Tightening regulations imposed by local and regional governments to avoid similar disasters have led to increased cyanide management costs and the reevaluation of internal processes. For companies in the mining and electroplating industry, proper cyanide management plays a prominent role in decreasing costs, minimizing the chances of provoking environmental disasters, and avoiding bad publicity. In this context, the rapid, accurate, and safe detection and quantification of cyanide in water helps companies to control the quality of their internal processes, comply with regulations, and ensure the absence of toxic substances in their wastewaters. Current State Of Methods For Free Cyanide Detection Today, companies interested in the detection of free cyanide in water can choose from a wide range of techniques with variable precision, time consumption, reliability, and equipment requirements. For the exact quantification of free cyanide, techniques such as gas diffusion coupled with amperometric detection offer excellent results, but are rather time-consuming and require specialized equipment. However, colorimetric detection of free cyanide offers an attractive alternative to those interested in binary outputs: It is a semiquantitative method with great versatility in terms of speed, sample preparation, and equipment needed. Colorimetric detection methods are based on the interaction of free cyanide with an indicator that changes color upon reaction. These methods are simple, less time-consuming, and might not require specialized equipment. They are, however, not necessarily less prone to interferences arising from other chemical species, something that, in many cases, hinders their reliability. Furthermore, several of these methods use harmful compounds, thereby putting the safety of their users at risk. The current market offerings for the colorimetric detection of free cyanide can be divided into three categories based on the technology used. Chlorinating Reagents (K├Ânig Reaction) This traditional detection method is based on the reaction of free cyanide with chloramine T to form cyanogen chloride, which subsequently reacts with pyridine and barbituric acid to form a red-blue dye. Most commercially available free cyanide tests are based on this technology, broadly adopted by the electroplating industry. Users of this method must be aware of their possible exposure to organic solvents, harmful reagents, and highly toxic reaction intermediates. Silver Nitrate Titration Commonly used in both the mining and electroplating industry, this method is based on the ability of free cyanide to form complexes with silver in solution. In short, a silver nitrate solution is added to the free cyanide-containing sample, where free cyanide complexes with silver. 24 wateronline.com n Water Innovations Understanding your detection needs when it comes to free cyanide can help you choose the most suitable detection method. A Practical Framework To Improve The Management Of Cyanide In Industrial Wastewaters

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