II. R&D NEEDS AND POTENTIAL PROJECTS

D. Cyanide

1. Background

Free cyanide is a highly toxic chemical that is found in the environment at low concentrations coming from natural sources. It reaches toxic levels mostly through industrial processes such as mineral processing, electroplating, and paper-making. The Resource Conservation and Recovery Act ban on land disposal of solid waste containing cyanides poses a major waste management problem for industries using cyanide in their processes.

Cyanide is also a regulatory target because of its toxicity, incompatibility with most publicly-owned treatment plants, and danger to sewer workers and marine life. EPA has imposed limits on the quantity of cyanide in both the treated wastewater that is discharged to sewers and rivers and on any residuals from metal finishing operations (sludges, filters, filter cakes, spent solutions, etc.). A variety of electroplating and metal finishing waste streams contain metal-cyanide complexes. Metal-cyanide complexes formed in these industries include metals such as iron, nickel, zinc, cobalt, cadmium, copper, mercury, and precious metals (silver, gold, platinum).

There is some free cyanide found in electroplating wastewater from cyanide-based plating chemistries; it is one of the most toxic contaminants in the wastewater. Evaporation, while effective, has high energy costs. The commonly used cyanide destruction techniques, such as treatment with oxidizers, do not easily destroy all the cyanide. For example, iron, cobalt, and nickel cyanides are not affected by basic hypochlorite treatment and are often precipitated out into the sludge that is formed under the process. Thus, elevated levels (up to 5,000 ppm, or 0.5%) of complexed cyanide typically appear in hydroxide-precipitated, heavy-metal sludges produced during the treatment of many electroplating wastewater solutions

From an environmental perspective, cyanide-bearing processing solutions should be operated in a completely closed loop, if possible. When not possible, wastes and wastewater bearing highly toxic forms of cyanide should be detoxified to a level acceptable to the environment in which those cyanides are released.

While great strides are being made to create plating processes that do not require cyanides, there are some notable plating solutions available now without such substitutes. Examples include silver, brass, bronze, and Alballoy (an alloy of copper, zinc, and tin). Furthermore, some non-cyanide replacements for conventional plating processes have proven to be limited in application--e.g., non-cyanide cadmium, non-cyanide silver/brass, non-cyanide (sulfate) gold, and non-cyanide copper. One example of a successful non-cyanide bath is non-cyanide zinc; over the last thirty years it has replaced about 70 percent of cyanide zinc and this percentage could easily go higher.

2. Federal Survey

A surprising result of reviewing the sources for recent and ongoing R&D was the paucity of governmental funding for development and demonstration of alternatives to or recovery of cyanide. Only three studies were found, totaling $207K. EPA has supported two demonstration projects showing ZnCl as a substitute for ZnCN and CdCN baths; DOD is supporting work to develop a noncyanide-based stripping solution. The AESF Research Board is currently supporting a project investigating non-cyanide copper plating alternatives at North Carolina State University.

3. Projects

Various projects warrant investigation.

a. Study the optimization of existing baths for recovery and recycle of cyanide-containing solutions and chemicals. Drag-out tanks are often the simplest and least expensive method of recovery.


b. Evaluate polymer filtration for recovery and recycle.


c. Evaluate substitute baths as they enter the market--e.g., as used on zinc-based die castings.


d. Contributors to this Plan often voiced concern that there is not enough data or risk characterization to support regulations. More research is needed to help establish risk levels; better understanding of risks imposed by emissions would help prioritize future R&D projects.


e. Develop improved analytical procedures for total and especially amenable cyanide in water and solid wastes.


f. Determine whether complexed cyanide in F-006 wastes meet Hazardous Waste Identification Rule (HWIR) II delisting requirements.


g. Investigate the environmental impact of complexed cyanide in F-006 waste under present stabilization/disposal practices.


i. Develop low-cyanide process solutions.