cadmium (Cd)

Cadmium (Cd, atomic number 48) is a soft, bluish-white toxic heavy metal historically used in nickel-cadmium (NiCd) rechargeable batteries, cadmium plating (anti-corrosion coatings on steel hardware, electrical contacts), pigments (cadmium yellow, cadmium red in plastics and ceramics), PVC stabilisers, and the photoconductive layers of older photoconductors. The International Agency for Research on Cancer (IARC) classifies cadmium as a Group 1 human carcinogen (causally linked to lung, prostate and kidney cancers); chronic low-dose exposure also causes osteomalacia (the historic itai-itai disease in Toyama, Japan), renal tubular damage, and impaired calcium metabolism.

The regulatory restrictions are layered. The EU RoHS Directive caps cadmium at 0.01% by weight in homogeneous material of electrical and electronic equipment (10x stricter than the lead, mercury, hexavalent chromium, PBB and PBDE 0.1% limit, reflecting cadmium's higher toxicity). India's E-Waste (Management) Rules 2022 reflect the same cap. The European Battery Regulation 2023/1542 bans NiCd batteries except for industrial applications and emergency lighting. India's Battery Waste Management Rules 2022 require disclosure of cadmium content and bring NiCd batteries into the same EPR collection framework as lithium-ion and lead-acid.

The cadmium-bearing waste streams in India are: legacy NiCd batteries in cordless power tools, emergency lighting, medical equipment and older portable electronics — present in the e-waste stream until the late 2010s; cadmium-coated screws and hardware in legacy industrial equipment; cadmium-stabilised PVC in older cable insulation; cadmium-pigmented plastics in older toys, packaging and outdoor furniture. NiCd batteries dominate the cadmium hazard — a single C-cell NiCd contains 12-18 g of cadmium, against an occupational inhalation limit of 0.005 mg/m³.

Recovery from NiCd batteries uses pyrometallurgy at specialised smelters: roasting at 750-900°C drives off cadmium as vapour, which is condensed and refined to 99.9% cadmium metal by re-distillation. Nickel and iron are recovered as ferro-nickel slag. The recovered cadmium is increasingly hard to monetise — RoHS phase-out has shrunk industrial demand; most recovered cadmium reports to compound chemicals for solar (CdTe thin-film PV) or stays as a hazardous-waste-disposal residue. For Indian e-waste recyclers, cadmium is principally a hazardous handling cost rather than a revenue source: NiCd batteries must be segregated from other cells before any shredding, stored in sealed containers under cover, and sent to BWM-authorised pyrometallurgical recyclers. Mixing NiCd into a general lithium-ion shredder line is both a fire hazard (NiCd vents under crush) and contaminates the lithium-recovery hydrometallurgy with cadmium. The pragmatic operational discipline is sorting at intake, before any size reduction.