Imagine huge silos gulping dark zinc concentrate, hot ore streams tumbling and roaring in boiling roasters, the scent
of sulfur and metal in the air, and the silver-blue luster of a sophisticated array of electrolytic tanks - this is the heart
of a modern zinc smelter. As a key hub connecting zinc ore resources with downstream galvanized steel, alloys, chemicals
and other industries, zinc smelters are not only responsible for the stable supply of zinc metal, but are also experiencing
a profound green smelting revolution at a time when environmental regulations are becoming increasingly stringent.
Quenching by fire and water: the evolution of the mainstream process
The core process of zinc smelting has evolved over the past century and is now divided into two main technology camps:
Hydrometallurgy (globally dominant, about 80% or more):
Boiling Roast - Leaching - Purification - Electrolysis: This is the classic wet process. The zinc concentrate is first oxidized and
desulfurized at high temperatures in a high-efficiency boiling roaster, which produces SO₂-containing flue gas (for acid
production) and roasted sand. The roasted sand is leached at atmospheric pressure or under pressure (acid leaching),
and the zinc is dissolved into solution to form a zinc leach solution. This solution has a complex composition, containing
iron, copper, cadmium, cobalt, arsenic and other impurities, and must be purified in depth at multiple levels (such as zinc
powder replacement, organic solvent extraction, etc.) in order to obtain a pure zinc sulfate solution that meets the electrolysis
requirements. Finally, in the electrolysis workshop, the pure solution is energized between the lead-silver anode and the
aluminum cathode, and the high-purity electrolytic zinc (>99.99%) is then deposited on the cathode plate and melted and
cast into zinc ingots after stripping. Its advantages are mature technology, high degree of automation, high product
purity, thorough sulfur recovery (acid production), and relatively controllable environmental protection.
Key upgrading points: oxygen-enriched roasting to strengthen efficiency, atmospheric pressure oxygen-enriched leaching
instead of autoclave, more efficient purification agent and process (such as inverse antimony purification), the application
of large-scale energy-saving electrolytic tanks, and the promotion of automated zinc stripping technology.
Pyrometallurgy (specific applications)
Confined Blast Furnace (ISP process): Although its market share has shrunk significantly, it still has unique value in
processing complex lead-zinc mixed ores or recovering secondary resources. It puts the sintered zinc-lead mixture
into a closed blast furnace where, under a high-temperature reducing atmosphere, the zinc vapor escapes with the
flue gases at the top of the furnace and is captured by a lead rain condenser to obtain the crude zinc, while the lead
is released from the bottom of the furnace. The slag is smelted to recover the residual valuable metals. It is characterized
by the simultaneous output of zinc and lead, strong adaptability of raw materials, but high energy consumption,
environmental pressure, complex processes.
Electrothermal method (vertical/flat pot distillation): basically eliminated, only survives in very few special scenarios.
Green transformation: the road to survival and development
Environmental protection has become the “Sword of Damocles” hanging over the heads of zinc smelters. From concentrate
transportation and storage, roasting and leaching, to flue gas and wastewater discharge, and solid waste treatment, each
link is facing unprecedented regulatory pressure. Green transformation is no longer a slogan, but a line of life and death:
The “ultra-low emission” attack on flue gas treatment:
Roasting/sintering flue gas: the main source of SO₂ and particulate matter. Two-turn, two-absorption acid production
process is standard, sulfur recovery rate of 99.5% or more. At the end of the process, high-efficiency electrostatic
precipitator/bag filter, wet desulfurization (e.g. limestone-gypsum method) and even SCR/SNCR denitrification are required
to meet the increasingly stringent “ultra-low emission” standards (particulate matter <10mg/m³, SO₂ <50mg/m³, NOx <100mg/m³).
Low concentration SO₂ flue gas (e.g. leaching, electrolysis acid mist): adopt ionic liquid desulphurization, activated coke
desulphurization and other high-efficiency technologies to achieve resource recycling or meet the standard discharge.
The ultimate pursuit of “zero discharge” of wastewater:
Graduated treatment, quality reuse: heavy metal-containing wastewater (such as leaching slag washing water, workshop
rinse water) is treated in depth through a combination of lime neutralization and precipitation, iron/aluminum co-precipitation,
and membrane separation (reverse osmosis) to remove heavy metals, arsenic, fluorine, etc. The treated water is maximally
reused for recycling. The treated water is maximally reused in the production process (e.g. slag flushing, washing), reducing
new water consumption and wastewater discharge. Evaporation and crystallization of concentrated brine is the key technical
challenge to achieve true “zero discharge”.
Solid waste resource utilization: cracking the “slag mountain” dilemma:
Zinc leaching slag (wet process main solid waste): rich in iron, a small amount of zinc and lead and rare precious metals.
Mainstream treatment is supporting the construction of rotary kiln fumigation (Waelz Kiln), recovery of zinc, lead, indium,
etc., the output of the secondary zinc oxide powder back to the mainstream process or sold, the kiln slag cured and safely
landfilled or explored as raw materials for building materials (subject to strict assessment of environmental risks). Oxygen
pressure leaching slag due to high iron content and stable sulfur form, the environmental risk of direct stockpiling or landfill
is relatively low, but resource utilization (such as recovery of iron ore concentrate) is an important direction.
Iron alum slag / needle iron ore slag (iron removal process slag): complex composition, containing iron, sulfur and residual
heavy metals, high environmental risk. Need to be safe landfill (high cost) or continued research on harmless treatment and
resource technology (such as solidification and stabilization, high temperature melting vitrification, extraction of valuable
elements).
Energy saving and intelligent upgrading:
Waste heat utilization: Efficiently recover waste heat from high temperature equipment such as roasters, fuming kilns, melting
and casting furnaces, etc. for power generation, preheating materials, heating, etc.
Process optimization: optimize process parameters through advanced control system (APC) and big data analysis to reduce
energy and material consumption.
Intelligence: Promote automated equipment (e.g. unmanned vehicles, automatic zinc stripping, intelligent inspection), build
digital twin factories to improve efficiency and safety.
Future Picture: Efficiency, Green and Circulation
The future of zinc smelters will continue to evolve in a threefold dimension:
Extreme efficiency: R&D and application of larger scale, shorter process, and lower energy and material consumption processes
(e.g., breakthrough in direct leaching technology, improved electrolysis efficiency).
Deep green: zero-emission technology (wastewater, exhaust gas), complete harmless and high-value utilization of solid waste
(e.g., zinc leaching slag to extract iron and rare precious metals), and exploration of carbon capture and utilization (CCUS)
technology.
Cyclic symbiosis: build an “urban mine” system to efficiently treat secondary resources containing zinc (waste galvanized steel,
zinc slag fume); explore synergistic treatment with steel and chemical industries (e.g., treatment of zinc dust from steel mills).
Conclusion
Zinc smelter, the industrial temple where metal and flame dance together, is undergoing a transformation. From crude emissions
to ultra-low standards, from slag accumulation to resource regeneration, from high energy consumption to intelligence, each
step is cohesive with technological breakthroughs and environmental responsibility. It not only continues to provide the
indispensable “backbone” metal for modern industry, but also interprets the possibility of harmonious coexistence of industrial
civilization and ecology with its practice of green transformation. The future of zinc smelting will be a model of a more efficient,
cleaner and smarter recycling industry. The hot ore stream will eventually cast a silver future of sustainable development.