Honeywell UDA2182 manual Appendix C Cyanide Waste Treatment, Uses of cyanide solutions

Appendices

15.4 Appendix C - Cyanide Waste Treatment

Introduction

Uses of cyanide solutions

Cyanide solutions are used in plating baths for zinc, cadmium, copper, brass, silver and gold. The toxic rinse waters and dumps from these operations require destruction of the cyanide (typically to a level below 0.1 ppm) before its discharge.

Technique for cyanide destruction

The technique most often used for cyanide destruction is a one or two-stage chemical treatment process. The first stage raises the pH and oxidizes the cyanide to less toxic cyanate. When required, the second stage neutralizes and further oxidizes the cyanide to harmless carbonate and nitrogen. The neutralization also allows the metals to be precipitated and separated from the effluent.

Consistent treatment and stable control in this type of process requires well-mixed reaction tanks with enough volume for adequate retention time. See Figure 15-3. Retention time is calculated by dividing the filled or usable tank volume by the waste flowrate. Typically it is 10 minutes or more.

CAUSTIC

HYPOCHLORITE ON/OFF

ORP

CYANIDE

WASTE

ON/OFF

pH

PROPORTIONAL RECORDER

ACID

ON/OFF

pH ANALYZER

HYPOCHLORITE CONTROLLER

ORP

NOTE: The separate pH and ORP measurements and control shown in the first stage may be handled with a single UDA2182 Analyzer with combined input.

CYANIDE TO CYANATE	CYANATE TO CARBONATE	SETTLING	SLUDGE
	AND NEUTRALIZATION

Figure 15-3 Cyanide Treatment System

204 UDA2182 Universal Dual Analyzer Product Manual January 2009