arsenic (arsenic)

Arsenic (As, atomic number 33) is a metalloid with grey, yellow and black allotropes, occurring in compound semiconductors of major commercial importance in electronics. The IARC classifies arsenic and its inorganic compounds as Group 1 human carcinogens (causally linked to lung, skin, bladder and kidney cancers, with substantial epidemiological evidence from West Bengal and Bangladesh groundwater contamination); the WHO drinking water guideline is 10 µg/L, India's IS 10500 standard is 50 µg/L (with maximum permissible 50 µg/L and desirable 10 µg/L).

In electronics, the principal arsenic-bearing material is gallium arsenide (GaAs) — a compound semiconductor used in high-frequency RF amplifiers (mobile phone power amplifiers, satellite communication front-ends, military radar), high-brightness red LEDs, laser diodes for optical communications and CD/DVD readers, and concentrator photovoltaic cells. A typical smartphone power amplifier die contains 50-150 mg of GaAs; a satellite radar module several grams. GaAs is also used as a substrate for indium gallium phosphide (InGaP) and aluminium gallium arsenide (AlGaAs) heterostructures in high-end optoelectronics.

Arsenic hazard during e-waste handling arises from three pathways. Mechanical breakage — shredding GaAs-bearing devices generates fine arsenic-containing dust; XRF spot-checks on e-waste workshop air in India have found arsenic dust at 5-30 µg/m³ against the occupational limit of 0.2 mg/m³ (relatively safe) but at 100-500 µg/m³ on filter samples from balers handling RF amplifier scrap (above limit). Open burning — uncontrolled combustion of GaAs ICs releases arsenic oxide (As2O3) fumes, which are inhalation-toxic and bioavailable. Acid leaching — hydrometallurgy dissolves arsenic into the leach liquor, where it must be precipitated separately (typically as ferric arsenate or calcium arsenate) and routed to dedicated hazardous-waste disposal — sometimes called the "arsenic problem" in copper smelter pyrometallurgy.

For Indian e-waste recyclers, arsenic management is primarily about source segregation and dust control. RF amplifier ICs identified by their package style (small SOP/QFN with characteristic GaAs die thickness signature on XRF) should be segregated at the dismantling stage rather than shredded with general PCBs. Granulator hoods must capture dust at 0.75-1.0 m/s face velocity to baghouse filtration, with the captured dust treated as hazardous waste (HW category 26.1 under HWM Rules 2016). Workers handling GaAs-bearing material need N95 or higher respirators, biological monitoring (urinary arsenic, hair sampling), and rotation off the workstation if exposure exceeds 50 µg/g creatinine in urine. The trade-off worth noting is that arsenic, like cadmium and beryllium, has no economic recovery pathway in current Indian e-waste infrastructure — it is exclusively a containment and disposal cost, born by the recycler with no offset revenue.