Introduction: Industrial value and challenges of silver slag treatment
Globally, more than 500,000 tons of silver slag is produced every year, and the silver content is usually between
0.5% and 8%, of which lead and zinc smelting slag and electronic waste slag account for more than 70%.
Traditional landfill disposal not only wastes resources, but also leads to the risk of contamination by heavy
metals such as silver and antimony. With the silver price exceeding $800/oz, the efficient recovery technology
of silver slag has become a key track of resource recycling. In this paper, we deeply dismantle the six core
processes such as fire enrichment and wet extraction, and discuss the cutting-edge direction of environmental
protection governance and high-value utilization.
Silver slag classification and composition characteristics
1. Typical silver slag type and characteristics
Slag type Silver content (g/t) Main associated elements Generation scene
Lead smelting slag 200-800 Pb 20%-35%, Zn 5%-10% lead electrolysis anode sludge treatment
Copper anode sludge 3000-8000 Cu 15%-25%, Se 2%-5% Copper electrolysis refining
Electronic waste slag 500-1500 Au 50-200g/t, Pd 100-300g/t PCB crushing and sorting
Zinc leaching slag 50-200 Zn 8%-15%, Fe 20%-30% Wet zinc refining process
Thermal enrichment: the core process for large-scale recovery
1. Melting pool melting technology upgrade
Oxygen-rich side-blowing melting:
Oxygen concentration> 85%, melting temperature 1250-1300 ℃, silver recovery rate increased to 92%
The silver content of slag is reduced from 0.08% to 0.03%, and the energy consumption per ton of slag
is reduced by 40% compared with that of traditional reflector furnace.
Noble lead furnace refining:
Staged temperature control (800 ℃ → 600 ℃), silver, antimony, bismuth gradient precipitation
Output of crude silver alloy purity of 95%, lead content <3%
2. Vacuum distillation purification breakthrough
Process parameters:
Distillation temperature 950 ℃, vacuum degree 10-²Pa, silver evaporation rate of 0.8kg / (m ² - h)
Silver purity jumped from 90% to 99.95%, gold, palladium enrichment in the residual phase
Economic benefits: treatment of lead slag containing 5% silver, single-ton profit increase of 1200 U.S. dollars
Hydrometallurgy: technological innovation for precise extraction
1. Thiourea leaching system optimization
Leaching conditions:
Fe³+ concentration 5g/L, thiourea dosage 25g/L, liquid-solid ratio 5:1
Silver leaching rate of 98.5%, leaching time shortened from 24h to 8h
Selective replacement:
Zinc powder replacement preferentially reduces silver (Eh value -200mV), copper, iron inhibition rate>90
Purity of silver powder 99.2%, zinc consumption reduced to 1.2 times the theoretical value.
2. Innovative silver chloride extraction process
Reaction control:
NaCl concentration 200g/L, chlorine rate 0.5L/min, pH 1.5-2.0
Silver chlorination rate of 99%, lead, antimony dissolution rate of <5
Electrolytic refining:
Titanium-based coating anode + stainless steel cathode, current density 300A/m²
Cathode silver purity 99.99%, DC power consumption 850kWh/t
Environmental protection treatment: heavy metal
risk control program
1. Arsenic-antimony synergistic curing technology
Pharmaceutical formula:
Iron salt + phosphate compound stabilizer, molar ratio As:Sb:Fe:P=1:1:3:2
Toxicity leaching concentration (TCLP) arsenic <0.5mg/L, antimony <0.3mg/L
Engineering application: compressive strength of curing body＞15MPa, meet the
standard of building material filler.
2. High-efficiency purification system for exhaust gas
Three-stage treatment process:
Cyclone dust removal: removal of > 10μm particles, efficiency 95
Wet electric dust removal: PM2.5 capture rate of 99%, synchronous desulfurization of 30%
Activated carbon adsorption: dioxin emission concentration <0.1ng-TEQ/m³
Operation and maintenance costs: tons of slag treatment costs reduced by 25%
compared with the traditional program
High-value utilization: from crude silver to functional materials
1. Nanosilver preparation technology
Liquid phase reduction method:
Ascorbic acid reduction of AgNO₃, particle size control 20-50nm, specific surface area>50m²/g
Antimicrobial rate >99.9%, suitable for medical dressing coating
Green synthesis: plant extracts instead of chemical reductants, 80% reduction of wastewater toxicity
2. Development of silver-based composite materials
Silver tin oxide electrical contacts:
Ag 88%-SnO₂ 12%, hardness HV 85, conductivity 90% IACS
Electrical life upgraded to 150,000 times, compared with traditional silver cadmium materials to
improve environmental protection
Photovoltaic silver paste recycling:
Acid washing - calcination method to extract silver powder, purity 99.95%, fineness D50 = 1.2μm
Recycled silver paste photoelectric conversion efficiency equal to the original material
Future Trends: Integration of Intelligence and Low Carbonization
1. Digital twin system application
Real-time collection of 200+ parameters such as melting temperature, leaching solution potential, etc.
AI dynamic optimization of the silver recovery path, the comprehensive recovery rate increased to 96%.
2. Hydrogen reduction green silver refining
Hydrogen reduction of silver oxide, the reaction temperature is reduced from 1000℃ to 400℃.
CO₂ emissions per ton of silver reduced from 12 tons to 0.5 tons, with a purity of 99.9%.
3. Biological leaching technology breakthrough
Acid-resistant bacterial species (Acidithiobacillus ferrooxidans) leaching silver slag
Silver leaching rate of 85%, acid consumption reduced by 60%, leaching cycle shortened to 5 days
Conclusion: Technology-driven value reconstruction of silver slag
Silver dross treatment is shifting from “pollution control” to “resources + technology” double-wheel drive.
With the maturity of vacuum distillation, chlorination and other technologies, silver recovery cost is
expected to drop to less than 12 U.S. dollars / ounce. In the new energy, electronics industry demand
driven by the next five years, silver slag resource market size will exceed 8 billion U.S. dollars. Enterprises
need to focus on the layout of low-carbon processes and high-value product development, build
“recovery - purification - application” of the whole chain of competitiveness.