In the field of lead and gold refining, thermal and electric processes
are like “twin engines”, jointly supporting the technical system of
precious metal purification and efficient resource recovery. In the
face of crude lead or lead alloy raw materials containing copper,
tin, silver and other impurities, the two processes complement
each other in terms of energy consumption, purity and
environmental protection by virtue of their differentiated
technical routes. This article will dismantle the core principle,
process flow and applicable scenarios to provide smelting
enterprises with selection reference.
I. Fire Refining: High-temperature chemical
reaction for efficient purification
Fire refining takes high-temperature smelting as the core, and realizes
impurity separation step by step through oxidation, sulfurization and
other reactions, which is especially suitable for dealing with raw
materials with complex composition and high impurity content.
1. Process flow and key technology
Melting and precipitation of copper: after the crude lead is melted
(450-500 ℃), sulfur is added to generate copper sulfide slag, and
more than 90% of copper is removed by mechanical slagging;
Oxidation of tin removal: heating to 600-650 ℃ and drum into the
air, tin preferentially oxidized to SnO₂ into the slag phase;
Silver extraction: the use of zinc metal (Parkes method) or alkaline
melt (sodium nitrate + sodium hydroxide), enrichment of silver
after distillation or electrolytic recovery;
Deep refining: vacuum degassing or melt covering to reduce lead
oxidation, spectral testing to ensure lead purity ≥ 99.9%.
2. Core advantages
Wide adaptability: it can deal with high impurity raw materials
containing Cu＞0.5% and Sn＞1%;
High resource recovery rate: the enrichment degree of copper,
tin and silver in the floating slag reaches 40%-60%, which can
be directly entered into the downstream smelting;
High capacity of single line: daily processing capacity can reach
more than 500 tons, which is suitable for large-scale
continuous production.
3. Limitations and challenges
High energy consumption: high-temperature smelting link
accounts for more than 60% of the overall energy consumption;
High pressure on environmental protection: sulfide flue gas and
lead dust need to be matched with efficient purification system;
Difficult to remove trace impurities: bismuth, antimony and other
metals need additional processing.
Electro-refining: electrochemically driven
precision purification
Electrorefining selectively separates metals through electrolytic
reaction, which is suitable for raw materials with extremely high
requirements for lead purity (>99.99%) or containing precious
metals (gold, platinum group).
1. Process flow and key technology
Anode preparation: crude lead is cast into anode plate, silver,
bismuth and other precious metals are enriched in anode mud;
Electrolysis tank configuration: lead silicofluoride solution is used
as electrolyte, and the cathode is made of pure lead or
stainless steel plate;
Electrolysis reaction:
Anodic dissolution: Pb → Pb²⁺ + 2e-
Cathodic deposition: Pb²⁺ + 2e- → Pb
Impurities toward: copper, tin and other metals with high potential
remain in the anode mud, silver and gold are recovered
through the anode mud.
2. Core advantages
Ultra-high purity: the purity of cathode lead can reach over
99.995%, which meets the demand of high-end electronics
and medical fields;
Precious metal recovery: silver and gold content in anode mud
is enhanced by 5-10 times, with remarkable economic benefits;
Environmental protection advantage: closed-circuit recycling
electrolyte, no sulfide exhaust emission.
3. Limitations and challenges
High pretreatment requirements: raw materials need to remove
most of copper and tin in advance (fire pre-treatment);
Limited production capacity: long electrolysis cycle (3-7 days),
single line daily processing capacity usually <200 tons;
High operation cost: electricity consumption accounts for
40%-50% of the production cost, and the electrolyte
needs to be purified regularly.
Fire VS Electric: Selection Logic and
Scenario Adaptation
1. Raw material characteristics determine process selection
Pyrolysis prioritizes the scenario:
Raw materials have many types and high content of impurities
(such as recycled lead, polymetallic ore);
Valuable metals such as copper and tin need to be
recovered simultaneously;
The capacity requirement is >300 tons/day.
Electromethod priority scenario:
Products are used in semiconductor, nuclear shielding and
other ultra-pure lead fields;
Raw materials contain precious metals such as gold and
platinum group;
There is already a thermal pre-treatment line, and deep
purification is required.
2. Cost and benefit comparison
Investment cost: the investment in equipment of thermal process
is 30% lower, but the investment in environmental protection
facilities is high; electrolytic process needs supporting
electrolyzer and rectifier system;
Operation cost: energy consumption of thermal method
focuses on fuel, and electric method focuses on electricity
consumption;
Comprehensive benefit: the value of precious metals in anode
mud of electric method can offset more than 50% of processing cost.
3. Trend of technology integration
The head enterprises in the industry mostly adopt the combined
process of “thermal pretreatment + electric refining”:
Pyrolysis quickly removes 80%-90% of impurities and reduces
the load of electrolysis;
Electro-refining realizes final purification and precious metal
recovery, and enhances the added value of products.
Fourth, technical innovation and
future direction
1. Green upgrading of pyro-refining
Oxygen-enriched smelting: Oxygen concentration increased
to 30%, fuel consumption reduced by 25%;
Intelligent temperature control system: AI dynamically adjusts
furnace temperature, reducing lead volatilization loss;
Resourcefulness of slag phase: floating slag directly prepares
copper-tin alloy, reducing intermediate smelting links.
2. Efficiency breakthrough in electro-refining
High current density electrolysis: adopting titanium-based coating
anode, the current density is increased to 300A/m², and the
capacity is increased by 40%;
Electrolyte regeneration technology: on-line purification of
ion-exchange resin, extending electrolyte life to more than 2 years;
Modularized electrolyzer: plug-and-play design, supporting
flexible capacity expansion.
3. Decarbonization and digitalization
The hydrogen substitution test for thermal smelting has
entered the pilot stage, and carbon emissions can be
reduced by 60%;
Digital twin system simulates the refining process in real
time, with impurity removal rate prediction accuracy of 95%.
Conclusion
Thermal and electric refining are not “either/or” competitors,
but a synergistic combination based on raw material
characteristics and product demand. Thermal refining is good
at “extracting the best from the crude”, while electric refining
is good at “striving for perfection”. With the tightening of
environmental regulations and the growth of demand for
high-end materials, the in-depth integration of the two
processes and technological innovation will continue to
promote the lead and gold refining industry to the direction
of high efficiency, green and high value.