Silver electrolytic refining is a core technology for the recycling of
precious metal resources, which can extract silver metal with a purity
of up to 99.99% from Dore metal in copper/lead anode sludge, waste
electronic products, cyanide gold sludge smelting by-products, and
silver-containing wastes through the electrochemical purification
process. This technology has the advantages of high recovery rate,
low pollution emission and large-scale production, and has become
an important support for global circular economy and green metallurgy
transformation. In this paper, we will systematically analyze the process
flow, technological innovation and industrial value of silver electrolytic
refining, and reveal its key role in the efficient utilization of resources.
I. Raw material sources and process framework
of silver electrolytic refining
Raw material diversity: from industrial by-products to urban mines
The main raw materials for silver electrolytic refining include:
Metallurgical by-products: anode sludge from copper/lead electrolytic
refining (containing 10%-25% silver), silver alloy in cyanide gold sludge
from gold smelting (Ag-Au-Cu);
Electronic wastes: waste circuit boards, contact materials, silver-plated
devices (containing 0.5%-5% silver); Electronic waste: waste circuit boards,
contact materials, silver-plated devices (containing 0.5%-5% silver),
silver-plated devices (containing 0.5%-5% silver). 0.5%-5%);
Jewelry waste: silver jewelry processing debris, silver-containing solder
and failed catalysts;
Other resources: medical film, photovoltaic backplane silver paste, waste
silver-zinc batteries and so on.
The silver content of these raw materials varies significantly (0.1%-90%),
and they need to be converted into anode plates suitable for electrolysis
through pre-processing (crushing, sorting, and fusion casting).
Core process: three-step purification method
Typical silver electrolytic refining process consists of three major stages:
Pre-treatment and alloy preparation: raw materials are melted by fire melting
(1200-1300°C) to remove impurities, and cast into crude silver anode plates
with 80%-95% silver content;
Electrolytic refining: in silver nitrate electrolyte (Ag⁺concentration 80-150g/L, pH
1.5-2.5), the Crude silver anode is dissolved under direct current (current
density 250-400 A/m²) and pure silver is deposited on titanium or
stainless steel cathode;
Anode reaction: Ag → Ag⁺ + e-
Anode reaction: Ag → Ag⁺ + e-
Cathode reaction: Ag ⁺ + e- → Ag
cathodic reaction: Ag⁺ + e- → Ag
Tail liquid treatment: electrolytic waste liquid recovers residual silver through
copper replacement or chemical precipitation, and the nitric acid is recycled,
realizing the closed-circuit environmental protection production.
Technical Advantages and Process Innovation
Purity and Economy Double Enhancement
Electrolytic refining can directly produce national standard 1# silver ingots with
purity of 99.95%-99.99%, which is a significant enhancement compared with the
traditional gray blowing method (purity of 99.9%). Taking the anode sludge
containing 30% silver as an example, the silver direct recovery rate is over 98%,
and the energy consumption per ton of electrolytic silver is about 1,500kWh,
which reduces the processing cost by 40% compared with the chemical method.
Breakthrough in Adaptability to Complex Raw Materials
For raw materials containing impurities such as platinum, palladium, bismuth, etc.,
the industry innovatively adopts:
Multi-stage Electrolysis System: the first electrolysis removes copper and lead, and
the second electrolysis purifies silver;
Pulse Current Technology: improves the cathode crystallization density and reduces
the short circuit of dendrites through the intermittent power supply;
Optimization of Additives: the synergistic use of sodium lignosulphonate and gelatin
inhibits the co-deposition of impurity ions, and improves the whiteness of the cathode silver.
Green process upgrading
Traditional nitric acid system has the problem of NOx emission, the new generation
of technology through:
Closed electrolyzer design: equipped with gas absorption tower, NOx will be
converted into nitric acid for reuse;
Thiosulfate electrolyte: replacing the nitric acid system to realize no acid mist emission;
Waste residue resourcing: anode sludge is processed by the silver-splitting furnace
to recycle gold, platinum group metals and selenium-tellurium rare elements.
Application Scenarios and Industrial Value
The Key Link in the Closed Loop of Nonferrous Metals Smelting
In copper/lead smelters, silver electrolytic refining raises the silver recovery rate of
anode sludge from 85% to 99% of the traditional process, and the annual processing
capacity of a single production line can reach 200 tons of silver metal. With an annual
output of 500,000 tons of copper smelter, for example, supporting silver electrolysis
workshop annual output value of more than 600 million yuan.
The “precious metal bank” developed by the city mine
The annual production of global electronic waste exceeds 50 million tons, containing
about 15,000 tons of silver (accounting for 15% of the supply of mineral silver).
Through the silver electrolysis refining, used cell phone circuit boards can be
extracted 2-3g silver / kg, industrial-grade recycling costs compared to primary
mining 60% lower. Japan's “urban mine” strategy, silver electrolysis capacity has
supported 30% of its silver demand self-sufficiency.
The core hub of the precious metal refining industry chain
The high purity silver ingots produced by electrolysis can be directly used in
high-end fields such as photovoltaic silver paste, electronic contacts, antibacterial
materials, etc., and the added value of its processing can be increased by 3-5
times compared with that of crude silver. In China's silver deep processing
industry, electrolytic silver raw materials account for more than 80%.
Fourth, technical challenges and future trends
Micro-trace impurity control
5G electronic devices on silver purity requirements rise to 99.999%, the need
to develop ultra-clean electrolyte dynamic filtration system (≤ 0.1 μm) and
on-line mass spectrometry monitoring technology, bismuth, antimony and
other impurities will be controlled at ppm level.
Low-carbon process innovation
The industry is exploring:
Green power coupling: using photovoltaic/wind power to drive electrolysis,
cutting the carbon footprint of a single ton of silver by 70%;
Bio-leaching pretreatment: using acidophilic bacteria to decompose sulfides
in anode sludge, reducing energy consumption for smelting;
AI model for regeneration of electrolyte: real-time optimization of the balance
between nitric acid replenishment and metal ions, reducing chemical
consumption by 30%.
Miniaturized Distributed Refining
Aiming at the dispersed characteristics of electronic waste, the company has developed
a containerized mobile electrolysis device, which realizes the local treatment of
materials containing more than 0.5% silver and reduces the cost of transportation
and centralized smelting.
Conclusion
Silver electrolytic refining technology has constructed a closed-loop system of
“resource-product-renewable resource” by efficiently recovering precious metals
from industrial by-products and municipal wastes. With the advancement of global
carbon neutrality and the expansion of the electronic information industry, this
technology will continue to promote the upgrading of precious metal smelting in
the direction of low-consumption, high-value, and zero-waste, and provide core
support for green manufacturing and circular economy. It is expected that by 2030,
electrolytic refined silver production will account for 40% of the global silver supply,
becoming a strategic technology pillar for sustainable resource utilization.