Best Treatment Plan for Cyanide Cadmium Plating Wastewater

A. Hi Andrew,
You may want to keep cadmium wastes separate depending on what your waste hauler / waste processor has to say about costs and recycling.

The treatment consists of conventional cyanide oxidation (probably two-step), followed by neutralization/precipitation, solids-liquid separation, and filter pressing. I wouldn't use a sludge dryer on cadmium, but some people do.

You can probably electrolytically recover the bulk of the cadmium before end-of-pipe treatment if you can arrange for a drag-out tank in your rinsing system.

The manufacturers of tank linings offer lining systems for secondary containment areas. Or you can have fiberglass or polypropylene secondary containment pans fabricated.

A. Andrew,

Actually, while the treatment is effective that Ted mentions, you're probably under intense scrutiny for cadmium discharge - (I know of no one who isn't!) There are alternatives that can get you to almost non-detect with no sludge generation, and relatively easy treatment of the waste water.

Cadmium cyanide complex is actually very weak, and the treatment responds well to certain ion exchange treatments, as it is possible to remove the cadmium from the cyanide complex by a stronger attraction to the functional ion on the specific resin. This allows the cadmium to be regenerated from the resin free of cyanide (and safely) with acid, at which point the metal can be reclaimed by one of a number of ways, such as electrowinning, etc.

The waste water that is discharged from the ion exchange system is essentially sodium cyanide free of metal, and is then easily treated by alkaline chlorination or some other oxidation technique. Depending upon your specific quantities and flows, a cost effective system to treat and minimize waste in this fashion is affordable.

A. More than a dozen years ago I worked on secondary containment projects regularly. The rule was:

1.) All fluids contained by a secondary containment structure must be compatible. E.g., no cyanides in common with acids; no flammables in common with oxidizers, etc.

2.) The containment must be capable of holding no less than 150 % of the volume of the largest tank within the containment.

A. Andrew, I won't recommend this since I don't want to be named a defendant if you have a spill, but common EPDM roofing material makes an excellent mobile secondary containment material. It costs about $.50 a square foot and is impervious to just about everything but solvents. I know of several installations that have been using it for over 5 years with little or no breakdown of the material. Best of all, when you want to rearrange you just clean it, roll it up and move it. You can use whatever material you like for the berm.