Alternatives

Updated May 2021

Cadmium: Alternatives

Due to the hazards associated with cadmium and cadmium compounds, facilities should seek out opportunities to reduce their use wherever possible. Opportunities include adopting safer alternatives for specific functions or applications and minimizing use through improved efficiencies if alternatives are not available.

With an increase in stringent global restrictions, many companies have redesigned their products and processes to use safer alternatives. The significant reduction in use of cadmium and cadmium compounds by TURA filers indicates that toxics use reduction options are available for many applications and that Massachusetts companies are taking advantage of those opportunities. Where input substitution is not yet feasible, many facilities report improved operations and maintenance and production unit redesign in order to use cadmium as efficiently as possible. Examples of this are weirs to reduce drag out from plating baths, retooling to reduce burrs on parts, and automatic feeds to reduce waste and operator exposure.

Substantial information is available on cadmium alternatives for soldering, plating, stabilizers, and pigments used in plastics. We also provide information on emerging alternatives to cadmium-bearing batteries.

Alternatives for Plastics and Pigments Sector

Pigments in Plastic Products
Cadmium is used to create a range of yellow colors in plastics formulations.²⁵ Cadmium sulfides and sulfo-selenides are used in pigments to create a family of yellow, orange and red pigments. Cadmium yellow is created using cadmium sulfide (CdS), cadmium red is cadmium selenide (CdSe) and cadmium orange is an intermediate cadmium sulfoselenide.^25,26 Cadmium yellow is sometimes mixed with a hydrated chromium oxide pigment to create a bright, pale green mixture called cadmium green.^27,28,29 Cadmium has also been used as a weathering, light and heat stabilizer in certain plastic formulations, especially in PVC.

Processes used in Massachusetts for cadmium use as pigments and stabilizer additives include:

• Polymer compounding
• Plastic extrusion on copper wire
• Plastics blending and extruding
• Flexible plastics calendaring

A variety of alternatives are available for cadmium in yellow pigments. Some alternatives pose significant health and environmental hazards, while others are superior from a health and environmental perspective. As early as the beginning of the 1990s, many firms found that they were able to replace cadmium in the majority of pigments in which it had been previously used. Alternatives include inorganic pigments based on acid solutions of synthetic oxo-nitrides, iron oxide pigments, bismuth vanadate pigments, organic and inorganic pigment blends using titanium dioxide, mixed metal oxide titanites, and/or iron oxide, rutile tin zinc compounds and others.

Stabilizers
Cadmium has been used as a weathering, light and heat stabilizer primarily in PVC plastic formulations. In the United States, use of cadmium-bearing stabilizers has decreased since 1990. Alternatives for cadmium stabilizers include barium-zinc, calcium-zinc, antimony, organotin, and organic compound stabilizers.²⁴ While these alternatives meet the necessary performance criteria for specific applications, antimony and organotin stabilizers are not considered to be safer substitutes because of their respective high toxicities.

Alternatives for Coating and Plating Uses

Cadmium coatings are applied to various base metals to impart excellent corrosion resistance, especially in marine and alkaline environments. In addition to corrosion protection, cadmium coatings provide a low coefficient of friction and therefore good lubricity, good electrical conductivity, easy solderability, and reduced risks of operating mechanisms being jammed by corrosion debris for many components in a wide range of engineering applications throughout industry.

Methods to reduce the use of cadmium in metal plating applications include:

• Product redesign to eliminate the need for the coating.
• Use a metal deposition technology that does not require a plating bath (e.g. vapor-deposited aluminum).
• If these alternatives are not viable due to required surface characteristics or cost, various organic polymers, tin alloys, zinc, and binary alloys of zinc with cobalt, iron, manganese, nickel, and silicon offer alternatives to cadmium for a variety of applications, including:
• Metallic-ceramic coatings have successfully replaced cadmium in more expensive military applications, including landing gear axles of modern aircraft, gas-turbine-engine compressor sections, and allied parts.
• An improved method for the deposition of corrosion-resistant aluminum coatings for aerospace applications was developed. This method used ion- vapor-deposited (IVD) aluminum (a series of aluminum alloys) as an alternative.^30,31
• Aluminum-molybdenum coatings have been investigated as a possible alternative to cadmium in applications with specialized requirements, such as aerospace applications.^30,31

The ability to replace a cadmium coating with a zinc-based alloy depends on the specific characteristics required. Metallic-ceramic coatings, using zinc, aluminum, or alloys of these metals, possess the corrosion resistance characteristic of cadmium without the same environmental issues, although often at a higher cost. Replacing cadmium for plating of fasteners in military and aerospace applications may pose difficulties due to the unique requirements of those applications, although the military is evaluating alternatives to cadmium.

Alternatives for Batteries

Because it represents the biggest overall use of cadmium nationwide, it is appropriate to touch upon the availability of alternatives to nickel-cadmium (NiCd) batteries.

Currently, the principal alternatives to NiCd batteries are lead-acid, nickel-metal hydride, and lithium-ion batteries as well as fuel cells.³² Ni-metal hydride batteries possess substantially greater energy-storage capacity and power per unit weight or volume than lead-acid batteries but are very expensive.^33,34 Since 1991, rechargeable Ni-metal hydride batteries, with low discharge rates and long cycling stability, have been used for consumer applications such as portable computers, cordless appliances and communication equipment.³² A power-optimized version of Ni-metal hydride batteries are now fitted to commercialized hybrid vehicles.³⁴ Lithium-ion and sodium–nickel chloride batteries have a lower environmental impact than lead–acid, nickel–cadmium and nickel-metal hydride batteries.³⁵