Proposed code of practice for management of end-of-life lamps containing mercury: chapter 9

9. Recycling of Materials

Materials recovered from the processing of end-of-life mercury-containing lamps should be recycled whenever possible. These materials include, but are not limited to, mercury and mercury compounds, phosphor powder, other metal, glass, and plastic. Mercury may be recovered by way of thermal treatment/desorption, chemical oxidation, chemical precipitation, adsorption treatment, and distillation. Mercury recovery processes are described in the Basel Convention Technical Guidelines for the Environmentally Sound Management of Wastes Consisting of Elemental Mercury and Wastes Containing or Contaminated with Mercury (PDF document, 862KB) adopted in October 2011, and include:

• Thermal treatment/desorption: Physical separation process whereby a mercury-containing material is heated to a high temperature to volatilize and separate the mercury from the other material, and then the mercury is collected. Thermal treatment system consists of two major components: the desorber that is equipped with a mercury vapour technology to recover the mercury, and an off-gas treatment system to prevent mercury emissions to the environment (UNEP 2011).

• Chemical oxidation: Chemical oxidation (using oxidizing reagents such as sodium hypochlorite, ozone, hydrogen peroxide, chlorine dioxide and free chlorine gas) is applied to elemental mercury and organomercury compounds to destroy the organics and to convert mercury to a soluble form (i.e., mercury halide, such as HgCl₂ or HgI₂), which can then be separated from the waste matrix and sent for further treatment. Chemical oxidation is effective for treating liquid waste containing or contaminated with mercury (UNEP 2011).

• Chemical precipitation: Chemicals are used to transform dissolved mercury to an insoluble solid, or to adsorb dissolved, colloidal or suspended mercury that is precipitated, and removed from a liquid matrix (UNEP 2011). 

• Adsorption treatment: Chemical separation process whereby a mercury-containing or -contaminated liquid matrix is passed through an adsorption material, and the mercury is adsorbed on the surface of the material through chemical forces such as hydrogen bonds, dipole-dipole interactions and van der Waals forces (UNEP 2011).

• Distillation: Mercury is purified through a process involving a series of selective evaporation and condensation. The liquid mercury is heated to a temperature at which the impurities evaporate, or the mercury itself evaporates, and mercury is collected. The distillation process is performed multiple times, with the purity increasing each time, to achieve high-purity elemental mercury (UNEP 2011).