Smelter (smelting furnace)

A smelter is a high-temperature furnace that extracts metal from ore concentrates, or refines and recovers metal from scrap, by melting it with heat and chemical reducing agents. Primary smelters work from mined ore; secondary smelters, the type most relevant to recycling, recover metals from scrap and waste — lead from used batteries, copper and precious metals from e-waste, aluminium from dross and scrap, zinc from galvanising residues.

Smelting is among the most pollution-intensive operations in metallurgy. Because many ores are sulphides, primary smelting releases large quantities of SO₂; both primary and secondary smelting release particulate metal fume carrying lead, cadmium, arsenic, nickel and other heavy metals, plus CO and, where organic-coated scrap is fed, dioxins and VOCs. Heavy-metal fume is the defining hazard of secondary smelting in recycling.

For recyclers, the smelter is the final metal-recovery step in several sectors. Lead-acid battery recycling ends in a lead smelter; e-waste precious-metal recovery routes through copper smelting; secondary aluminium and zinc recycling are smelting operations. India's recycling economy has many secondary smelters, and the informal ones — backyard lead and aluminium smelting — are among the worst point sources of lead and heavy-metal pollution and worker poisoning.

Control is fume capture and gas cleaning: enclosed furnaces with capture hoods, baghouses for metal-bearing particulate (which recovers valuable metal as well as cleaning the gas), scrubbers for SO₂ and acid gases, and afterburners where organics are present. Secondary smelting requires CPCB/SPCB authorisation under the Hazardous and Other Wastes Rules 2016 and, for lead, the Battery Waste Management Rules 2022; unauthorised smelting is a primary target of board closure action. The metal recovered in the baghouse is both an emission saved and revenue earned.