Cyanide decomposition - Application

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	Cyanide decomposition

Industry : Electrical and Electronics
Product : pH/ORP Meter

Introduction

Oxidation Monitoring in the Cyanide Wastewater Treatment Process

Cyanide-bearing wastewater from electroplating facilities and certain types of chemical plants is toxic and must be treated by oxidation with chlorine or chloride to bring the cyanide concentration within regulatory limits. As the speed of the oxidation reaction is closely tied to the pH value, a pH meter is used together with an ORP (oxidation-reduction potential) meter to monitor the completion of the reaction. The use of these meters also ensures that excessive amounts of chemicals (e.g., chlorine) are not used to produce the reaction. Both 2-wire and 4-wire meters are suitable for this measurement system.
The 2-wire PH202G transmitter can measure both ORP and pH. (Two transmitters are required if pH and OPR must be measured simultaneously.) A gold electrode should be used for ORP measurement of cyanide-containing solutions.

Cyanide decomposition process

Expected Benefits

-	Measures pH/ORP of cyanide wastewater continuously
-	Reduces operating costs

Process Overview

Cyanide decomposition takes place in two stages. In the primary reaction, cyanide is oxidized to cyanate under high alkaline conditions. In the secondary reaction, the cyanate is further oxidized under near-neutral conditions and converted to harmless carbon dioxide and nitrogen gases.

Solution Details

Measurement system

2-wire/4-wire ORP measurement system
2-wire/4-wire pH measurement system

Sensor
	KCl refillable ORP sensor:	OR8EFG-AU-☐☐-TT1-☐*A
	KCl refillable pH sensor:	PH8EFP-☐☐-TN-TT1-N-☐*A
	Submersion type holder:	PH8HS-PP-☐☐-T-NN-NN*A

Terminal box (when needed)
	WTB10-PH1 (for 2-wire system)
	PH8TBG*A (for 4-wire pH measurement system)
	OR8TBG*A (for 4-wire ORP measurement system)

Converter/transmitter:
	2-wire transmitter (pH/ORP):	PH202G-1-E
	4-wire pH converter:	PH400G-☐-EA*B
	4-wire ORP converter:	OR400G-☐-E-A
	Distributor (for 2-wire system):	PH201G- A☐*B

Measurement of ORP

Measurement Conditions

A gold electrode should be used to ensure accurate measurement of ORP in cyanide solutions. When the potential is near or under 200 mV during the cyanide oxidation process, a platinum electrode produces a catalytic reaction that causes hydrogen to form on the electrode surface. This generates potential and affects measured values.

Utilities

PH202G
	Power supply:	17 to 40 V DC (from distributor)
PH400G, OR400G
	Power supply:	88 to 132/176 to 264 V AC, 50/60 Hz
	Power consumption:	approx. 8.5 VA
PH201G distributor
	Power supply:	100 V: 20 to130 V DC/80 to 138 V AC, 47 to 63 Hz
	Power supply:	220 V: 120 to 340 V DC/138 to 264 V AC, 47 to 63 Hz
	Power consumption	24 V DC: approx. 200 mA
		100 V AC: approx. 7 VA
		220 V AC: approx. 11 VA