Among many metals, tin, with its unique properties - low melting point, excellent corrosion resistance,
non-toxic and easy to alloy - has become an indispensable basic material for modern industry. From
the tin-plated sheets (tinplate) that protect steel, to the solder that connects electronic components,
to the backbone of bronze alloys, tin is everywhere. The core element that brings tin materials to life
is tin smelting - a sophisticated industrial art that combines ancient wisdom with modern technology.
Traceability: the initial form of tin ore
Tin's journey begins deep in the earth's crust. The predominant primary tin ore is cassiterite, which is chemically
composed of tin dioxide. These ores are usually found deep within granite deposits or alluvial mines of varying
grades (tin content). The mined raw ore undergoes a series of rigorous pre-treatment:
Crushing and milling: Crushing the bulk of the ore to a suitable size to create the conditions for subsequent separation.
Beneficiation (core): Enrichment of cassiterite by taking advantage of the differences in the physical and chemical properties
of cassiterite and vein minerals (e.g. quartz, feldspar):
Gravity Separation: The most commonly used method, such as jig, shaking table, spiral chute, utilizing the density
difference sorting, especially for sand tin ore.
Flotation: For fine-grained embedded or complex primary ores, the addition of specific agents causes cassiterite
to selectively attach to air bubbles and float.
Roasting (if necessary): Processing of ores containing impurities such as sulphur, arsenic, etc., which are volatilized
and removed by heating to improve the quality of the concentrate.
After these steps, a tin concentrate (Sn content usually >40%) is obtained, which is the starting point for the tin smelting charge.
Smelting: Metamorphosis at high temperatures
When the tin concentrate enters the smelting process, the core objective is reduction - the reduction of tin dioxide from
cassiterite to tin metal using carbonaceous reducing agents (coke, coal) at high temperatures. The mainstream processes are:
Reflection furnace melting:
Principle: In a long hearth, fuel combustion produces high-temperature flames and furnace gases that directly heat
and melt the charge (tin concentrate + reductant + flux).
Process: The charge undergoes drying, preheating and reduction reactions in the hearth. The reduced liquid tin settles
to the bottom of the furnace due to its high density, forming a coarse tin layer; veinstones and impurities float up to
form a slag layer.
Characteristics: Long history, intuitive operation, strong adaptability, especially suitable for handling raw materials
with large fluctuations in impurity content.
Electric furnace melting:
Principle: the use of electric arc heat or resistance heat to provide the high temperature required for melting.
Process: similar to the reflecting furnace, but more concentrated heat source, higher temperature, more precise control.
Characteristics: Relatively high energy consumption, but the furnace atmosphere can be controlled, especially suitable f
or processing concentrates containing iron, tungsten and other refractory impurities high or complex tin materials.
Melting core reaction:
SnO₂ + 2C → Sn + 2CO (high temperature)
Melting products are mainly:
Crude tin: about 80-95% tin, containing iron, arsenic, antimony, lead, bismuth and other impurities.
Slag: Mainly composed of iron silicate and other veinstone oxides, containing about 5-20% tin, need to
be further processed and recycled.
Soot: Containing volatile metal oxides (such as arsenic, lead, zinc) and some fine-grained tin, which must be
efficiently collected and treated.
Refining: The pursuit of ultimate purity
Impurities in crude tin seriously affect its performance and use, and refining is a key step in obtaining high-purity
refined tin (Sn >99.85%). Depending on the type and content of impurities, multi-stage combined operations
are often used:
Melting and condensation method:
Principle: the use of tin and impurities (mainly iron, arsenic) melting point differences and solubility in the tin solution
with the temperature change.
Melting: slow cooling of the crude tin melt, the high melting point of FeSn₂ (hard head) crystals precipitated floating or sinking.
Condensation: Stirring the melt at a slightly higher temperature and adding sawdust, etc., to oxidize impurities such as
arsenic and adsorb them in the slag (charcoal slag).
Characteristics: simple operation, low cost, is an effective means of preliminary removal of iron, arsenic.
Fire refining:
Add sulfur in addition to copper: add elemental sulfur, and copper to generate high melting point Cu₂S slag skimming.
Add aluminum in addition to arsenic, antimony: add metal aluminum, and arsenic, antimony generation of high melting
point compounds (AlAs, AlSb) slag skimming.
Crystallization separation method (continuous crystallizer):
Principle: the use of tin and lead in the solidification process of the solubility difference.
Process: The controlled liquid alloy is slowly cooled and crystallized in special equipment, where lead is enriched in
the unsolidified liquid phase and tin in the crystals. By repeating the process several times, it realizes the efficient
separation of tin and lead.
Characteristics: It is the mainstream and efficient method to deal with high lead and crude tin.
Electrolytic refining:
Principle: Crude tin is cast into anode, pure tin sheet as cathode, in a specific electrolyte (such as silicofluoride, sulfuric
acid) through direct current. Under the action of electric current, the anode tin is dissolved, and the cathode deposits
refined tin of very high purity.
Characteristics: The product has the highest purity (>99.99%), and can effectively remove a variety of impurities
(such as lead, bismuth, antimony). However, the investment and operating costs are high.
After these refining steps, we finally get the refined tin ingot that meets the national or international standards.
Recycling and environmental protection: the wisdom of the closed loop
Modern tin smelting is not only production, but also a key node of resource recycling and environmental protection:
Slag treatment: Adopting technologies such as smelting furnace or electric furnace depletion, blowing pulverized coal
and air into the molten slag, so that the residual tin, lead, zinc, etc. in the slag volatilize into the soot recycling, and the
tin content of the final slag can be reduced to <1%, which meets the standard of waste or building materials utilization.
Fume treatment: High-efficiency dust collection system (bag, electric dust collection) captures the fume. These soot is
rich in tin, lead, zinc, indium and other valuable metals, is an important secondary resources, usually returned to the
smelting system or specialized treatment recovery.
Exhaust gas treatment: Smelting flue gas contains SO₂, particulate matter and so on. Heat recovery through waste
heat boilers, electric dust collection/bag filtering, and desulfurization processes such as limestone-gypsum or
bi-alkaline methods are used to ensure compliance with emission standards.
Wastewater treatment: Wastewater generated from the smelting process is neutralized, precipitated, filtered, etc.
to achieve recycling or standard discharge.
Waste Tin Recovery: Recovery of tin from tin-containing wastes (such as tinplate trimmings, waste solder, electronic
wastes) is becoming increasingly important, with technologies such as pyrolysis, electrolysis, vacuum distillation,
etc., which constitutes an important part of the sustainable development of the tin industry.
Light of the future: innovation-driven development
In the face of resource, energy and environmental constraints, tin smelting technology continues to innovate:
Reinforcement smelting: such as top-blowing submerged bath smelting and other high-efficiency reinforcement
technologies to improve reaction strength and reduce energy consumption.
Green and low-carbon: Explore carbon reduction paths such as oxygen-rich combustion, renewable energy
application and carbon capture.
Intelligent: Apply big data and AI to optimize production process control and improve efficiency and stability.
Complex material processing: Research and develop new processes for efficient and economical processing of
low-grade ores, complex polymetallic ores and electronic wastes.
High-purity and special tin materials: Meet the demand for ultra-high-purity tin (6N, 7N) and special forms
(spherical solder powder, solder paste) in high-end fields such as semiconductors and new energy.
Conclusion
Tin smelting, the transformation from dark ore to silver metal, has condensed the wisdom of countless
engineering techniques. It is not only about the birth of a metal, but also the solid backing of the modern
industrial system in the fields of precision manufacturing, electronic communications, green packaging and
so on. In the pursuit of an efficient, clean and recycling future, tin smelting technology will continue to evolve,
contributing its irreplaceable “tin” power to the progress of human society. Whether you are looking for
high-quality tin raw materials or exploring cutting-edge tin application technologies, a deeper understanding
of the mysteries of tin smelting is the first step to a successful cooperation.