Cyanide Destruction Project Description

The Canada Department of National Defense required an electroplating wastewater disposal solution for cyanide rinse water. An ozone batch oxidation system, Model SX-1, was provided to the Defense Department in Victoria, British Columbia, Canada. A Model SX-1 is a skid-mounted recirculation batch system consisting of a vertical contact tank, magnetic drive recirculation pump, ozone venturi eductor, oxygen and ozone generators, balance barometer, ozone destruct system, and a touch screen computer control package. A rinse water sample was pilot tested to oxidize 15 - 50 PPM of cyanide, 0.5 - 4 ppm silver, 1 - 4 pmm cadmium, 1 - 28 ppm copper 0.1 - 0.3 ppm zinc at pH ranging from 7 to 10. The SX-1 has been designed to oxidize and reduce the total cyanide level from approximately 200 mg/L to less than 1 mg/L within 1 day at a pH level of 10. In actual operation, rinse waters with higher concentrations where oxidized within 6 hours.

Ozone is a reactive oxidant that will chemically oxidize cyanides, metals, and other contaminants in water. Cyanide is oxidized by ozone in an alkaline solution using a ratio of about 3.5 ppm ozone to 1 ppm of cyanide at a pH greater than 9. Since the ozone generated is small, no precautions or preventative measures are required for access to ozone production areas. However, an ambient ozone monitor is provided mounted on the oxidation skid. The set point is set at 0.1 ppm ozone and if this value is exceeded, the ozone monitor will sound an audible alarm and initiate a system shutdown.

The ozone generators generate ozone by means of a pulsed high voltage corona discharge. Dual ozone generators are placed in parallel utilizing the high-purity oxygen feed from the oxygen generator. There is a solenoid valve controlled with a time delay such that the oxygen purges the ozone generator and ozone piping of moisture.

The venturi eductor is located in the recirculation piping on the discharge side of a magnatic drive recirculation pump. Using the recirculated water flow as the motive force pulls a slight vacuum, which draws the ozone gas into the eductor, where it is dispersed into the recirculated water as tiny ozone-rich bubbles. The bubbles are piped into the ozone contactor, discharged through a spray nozzle, and allowed to rise to the water surface while contacting the waste water. The ozone that dissolves into the waste water reacts with the cyanide and metals in solution, destroying the cyanide, and precipitating the metals as oxides or hydroxides.

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