Tin is a soft silver-white metal, the proportion of 7.3, melting point is 231.9 ℃. Chemical properties of tin is stable, rich malleable at room temperature, especially at 100 ℃, its malleable is very good, can expand into extremely thin foil. However, tin ductility is very poor, a pull on the break, can not be drawn into filaments. Tin is non-toxic, people often plating it on the inner wall of the copper pot, to prevent copper warm water to produce toxic copper green. Tin is afraid of the cold, and can’t stand the heat, when the temperature is lower than 13.2 ℃, the white tin becomes amorphous ash tin, become a mass of powder. When the temperature higher than 161 ℃, and white tin into a orthorhombic crystal structure of oblique Fang Xi. Rhombic tin is brittle, it breaks when you hit it, it’s malleable, it’s called brittle tin. White tin, grey tin and brittle tin are three isotropic bodies of tin.
Tin is one of the ten commonly used non-ferrous metals. At present, tin is mainly used in electronic solder, tin coated steel plate, tin chemical industry, tin alloy, float glass, tin crafts and other industries. The application of tin in the electronic industry is mainly tin solder, used for electronic welding, this field currently accounts for 70% of China’s downstream application of tin, tin plated steel plate and tin chemical products account for 8% and 12% of the downstream application, respectively.
Tin is closely related to people’s lives. For example, it is used to make wood alloy, safety valve for fuse and boiler, tin bronze and tin-containing brass. Tin base bearing alloy is an excellent wear-resisting material with low friction coefficient and good toughness, thermal conductivity and corrosion resistance. Tin can also be configured into fusible alloy, solder, printing alloy, tin bronze and tin-containing brass, etc. Zirconium base alloy containing tin is used as nuclear fuel packaging material in atomic energy industry. Tin-titanium base alloys are used in aviation, shipbuilding, atomic energy, chemical, nuclear and medical equipment and other industrial sectors; Sn – nb intermetallic compound can be used as superconductor. Tin oxide, tin tetrachloride and tin organic compounds are used as raw materials for ceramic glazes, coal dyes for printing and dyeing silk fabrics, insecticides, antifouling agents, wood preservatives and flame retardants, respectively.
The world’s proven tin reserves are about 4.8 million tons, mainly distributed in China, Indonesia, Peru, Brazil, Bolivia, Malaysia and other places. China is the world’s largest tin producer and consumer, but also the world’s largest tin resources. At present, the proved tin base reserves are 1.38 million tons, accounting for 29% of the world’s total reserves, mainly distributed in yunnan, guangxi, Inner Mongolia, hunan, jiangxi, guangdong and other places, the six provinces and regions tin mineral reserves accounted for 98% of the country’s identified reserves. The recoverable reserves are less than 1.4 million tons, mainly concentrated in yunnan, guangxi, jiangxi and hunan. The tin resources in Inner Mongolia mainly exist in the form of companion. The tin resources in gejiu city of yunnan province account for about one tenth of the world’s total and about one third of China’s.
Some analysts believe that the market demand for tin is expected to grow at an average annual rate of 2% in the future, mainly due to the growth of downstream industries and the application of tin in new fields. Since the second half of 2012, there has been a significant recovery in the field of printed circuit board mounting worldwide, which has led to a mild recovery in tin prices. The recovery of demand in the tin industry is expected to be sustained, strengthened and expanded. In addition, the replacement of tin to anode carbon in the field of lithium battery, chromium nickel in the field of stainless steel and lead in the field of polyvinyl chloride are also gradually advancing, which is expected to contribute to the growth of tin demand.
In 2013, China’s tin concentrate production is expected to return to the peak level in 2004, with a large number of imported refined tin ore raw materials and domestic smelting technology greatly improved, tin concentrate products remain the world’s first position. Nevertheless, the full utilization of limited resources must arouse our great attention. There are four sources of secondary tin resources in China
Tin industry includes tin mining, smelting, processing and consumption industries. Natural and secondary tin resources are also inseparable from these industries. The comprehensive development and utilization of secondary tin resources include the utilization of tin associated ore, co-existing ore, tailings generated in the process of ore dressing, slag and soot generated in the smelting process and other wastes.
Waste tin residue, tin ash, tin silk, tin drops, tin strip, tin block, tin paste, tin thread, tin ingot, low tin, high tin, environmental protection tin, lead tin, lead-free tin, silver tin and other tin waste are the first to be brought into our vision in the comprehensive development and utilization of secondary tin resources. Tin tailings is another important component of secondary tin resources. For a long time, the exploitation and utilization of tin ore resources have greatly promoted the development of the world economy. However, hundreds of millions of tons of tin tailings have been stockpiled all over the world, which has occupied a large area of land and become an environmental hazard. These tailings were then stored as waste, in such a large amount of “waste” contains a large number of valuable components. Along with the idea change, the understanding thorough, has called it “the artificial deposit”. With the passage of time, tin ore resources become increasingly depleted and the selected grade becomes lower and lower, some of which are close to or even lower than the early tailings. Therefore, whether the early tailings as a replacement resource, tin mine tailings as a secondary resource for development, we must pay great attention to. However, it should be pointed out that the development and utilization of tin tailings, not only get tin, or even not mainly tin, may also have little tin. At the same time, the progress of modern beneficiation and metallurgy technology, especially the great progress of fine grain beneficiation and low tin material smelting technology, also accelerates the process of tin mine tailings reuse. At present, at home and abroad, there is a lot of practical experience in the reprocessing of early tin tailings, and the comprehensive recovery of valuable metals in tin tailings has become a hot topic of research. Undoubtedly, tin tailings will be the secondary tin resources that we need to attach great importance to.
At present, China’s secondary tin resources recycling and utilization has begun to take shape, under the dual incentives of the market and the government, secondary tin resources recycling has taken up a considerable share of the market supply. Although there is no complete and systematic statistics on solid waste of tin industry in China, according to the distribution and industrial characteristics of tin mines in China, currently a large number of solid waste piles of tin industry exist in gejiu, yunnan and hechi, guangxi. Gejiu and hechi are also pilot areas where the ministry of industry and information technology of China has set up large industrial solid waste bases. In addition to gejiu, tin tailings are mainly distributed in guangxi, hunan, jiangxi, sichuan, Inner Mongolia and many other mining areas, it is understood that the tailings in these areas are basically unused, is a large number of potential resources.
Recycled tin refers to the recovery and smelting of tin-containing waste into metallic tin. Tin-containing waste includes tinplate waste, tin-containing alloy waste, hot tin-plating slag and tin-foil ash, etc. Tin-coated sheet waste generally contains 0.35% ~ 2% tin, but the amount is large, the world’s annual consumption of tin-coated sheet amounts to 18 million tons. There are a wide variety of tin alloy waste, there are a variety of babbitt bearing alloy, fusible alloy, solder, these collectively referred to as lead tin alloy, tin blue brass waste, generally containing tin 2% ~ 5% or higher, while containing lead, copper, antimony, zinc and other components of recycling value. Hot tin slag has the highest tin content and less amount. In industry, tin is generally recovered from tinplate, lead-tin alloy, tin-green brass and hot tin slag. Tin foil ash ingredient is oxidation, melting point is 1630 ℃, using 1:2 hydrochloric acid and sodium chloride mixture, electrolysis after fully mixing, is a common method for industrial. A mixture of hydrochloric acid and sodium chloride is added to the foil and then electrolyzed, which can also be obtained at the cathode of the carbon rod.
From the supply and demand background of Sikkim industry, China’s total demand for tin market will continue to grow, and the supply of tin resources is unlikely to increase significantly in the short term. Due to the shortage of tin resources, the development and utilization of tin resources must be promoted.
The utilization and deep excavation of secondary resources of tin will become the norm and will be gradually improved. Although after years of large-scale mining and production in China, the scarcity of highly concentrated high-quality tin resources is increasingly prominent, but the comprehensive utilization of tin tailings is constantly strengthened. Through the recycling and utilization of tin-containing waste, tin-tailings, tin-plated sheet waste, tin-foil ash and smelting smoke and dust, it has become a necessary supplement to China’s tin mineral resources, and it is also a concrete action to implement the development of circular economy, carry out energy conservation and emission reduction. In order to ensure the healthy and rapid development of tin industry, we must in all aspects of tin industry of continuous exploration and innovation, expand the scope and depth of the secondary tin resources, improve the level of secondary tin resources recycling, tin mining and use of limited and precious resources fully, continuously develop new application areas, let the metal tin better benefit, benefit the human world.
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