JPH02182842A - Separation and recovery method of tin from iron scrap - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention removes tin from tin-plated iron scrap such as empty cans and tinplate, melts and reuses it as steel scrap, and also removes tin. It concerns the method of collection.

(Conventional technology) Since tin has a detrimental effect on the quality of steel products, empty cans,
When iron scrap made from tin-plated steel products such as tinplate is used as a raw material for steelmaking, only low-quality steel can be produced unless the tin is removed. Various methods have been proposed for separating and removing tin from tin plated steel products such as tinplate.

For example, 1) a method in which a tin-plated steel product is melted in an arc furnace or the like, and then the molten steel is exposed to a vacuum; 2) a method in which the tin-plated steel product is heated to a temperature that melts the plating layer and then rotated in a container. 3) There is a method in which the tin-plated steel product is cooled to several tens of degrees below zero with liquid nitrogen, etc., and the brittle and exfoliated tin is separated using a sieve or the like.

(Problems to be Solved by the Invention) However, the separation efficiency of these methods is actually as low as about one-third or less, and the productivity is also low, making them difficult to put to practical use.

That is, method 1) requires a high vacuum, has a slow removal rate of tin, and also evaporates a large amount of iron at the same time, resulting in a low iron yield. It is also difficult to recover evaporated tin, and even if the dust is recovered, the tin concentration is only a few percent or less, making it difficult to reuse.

Method 2) cannot remove the iron-tin alloy layer, and since the molten tin droplets wet the iron well, separation from the iron is poor. Therefore, the separation rate becomes low.

In method 3), some types of plating materials are less likely to become brittle, and the alloy layer does not become brittle, so the separation rate between iron and tin is low. Another disadvantage is that cooling requires a large amount of energy.

The present invention solves the drawbacks of the conventional tin removal techniques mentioned above, and
The present invention provides a method for separating tin and iron from tin-plated steel products with high separation efficiency and low energy usage, and further recovering tin.

(Means for Solving the Problems) The present invention involves heating tin-plated iron scrap and sulfur to 250°C or higher and 600°C or lower in a closed container in a non-oxidizing atmosphere, and then removing tin from the iron scrap. The reaction product containing tin is separated as dust, and tin is recovered from the recovered dust.

The iron scrap may be heated in a container,
It may be heated and then charged into the closed container.

The heating means may be a combustion method such as a gas burner, or may be an electric heating method such as induction heating.

Hot exhaust gas may be introduced into the container to heat it.

The container shall have a closed structure necessary to maintain a non-oxidizing atmosphere.
It is connected to a vacuum exhaust system or non-oxidizing gas supply system via a sealable lid, valve, etc.

A gas-permeable inner container such as a mesh or cage-like container may be placed inside the closed container. It is also effective to rotate and shake the inner container to better mix the iron scrap inside.

(Function) The sulfur used in the first step of the present invention acts as a detining agent, and when heated from 250°C to 600°C in a closed container, it reacts with the tin in the plating, forming a volatile compound. generate. The insect has a weight ratio of 50 to the amount of tin to be removed.
% to 250% is required. This type of iron scrap usually contains about 0.21% tin, so the amount of sulfur required for iron scrap is 0, J-2,5 by weight.
%become. The required amount of sulfur varies depending on the target removal rate, plating condition, reaction temperature, processing time, deposition in the container, mixing condition, etc. The sulfur source may be any sulfur-containing substance that volatilizes at 600° C. or lower. Elemental sulfur is preferred in terms of reaction efficiency.

The temperature during heating and reaction when the container is sealed needs to be 250° C. or higher in order for the charged sulfur and the scrap to quickly form a sulfur-tin compound, and higher temperatures are preferred. However, if the temperature exceeds 600°C, the vaporization of unreacted sulfur becomes difficult and the reaction efficiency also decreases, so it is necessary to lower the temperature to 600°C or less during the heating reaction. From the viewpoint of reaction efficiency and damage to the container, a temperature of 500°C or less is practical.

During the reaction, a non-oxidizing atmosphere is used to suppress the generation of sulfur oxides and to prevent excessive oxidation of scrap. When sulfur oxides are produced in large amounts, detinning is inhibited. Moreover, the burden of exhaust gas treatment increases.

The oxygen content in the atmosphere needs to be 3% or less, and the lower the oxygen content, the better. Moisture and water vapor also react with sulfur to produce hydrogen sulfide. This reduces tin removal efficiency and complicates exhaust gas treatment, so it is necessary to limit it. The upper limit of moisture and water vapor pressure in the atmosphere is l 00 mmHg,
Practically speaking, the lower the better, 30 mml! g or less is good. In order to reduce the moisture content, it is preferable to thoroughly dry the iron scrap before charging with sulfur, and also to remove in advance any organic matter that can generate water vapor.

A non-oxidizing atmosphere is created by introducing an inert gas.

The inert gas may be a rare gas such as argon or helium, or nitrogen or carbon monoxide. Carbon dioxide is also 50%
The following is fine. Mixtures of these gases, such as combustion exhaust gas, may also be used. However, the combustion exhaust gas preferably has a low moisture content, for example, the combustion exhaust gas from converter recovery gas. Alternatively, fuel gas such as incomplete combustion exhaust gas or blast furnace gas may be used. It is also possible to perform reduced pressure or vacuum treatment in a non-oxidizing atmosphere.

The heating time is 5 minutes or more for the reaction, and 3 hours is sufficient. Appropriate heating time depends on the temperature and the condition of the scrap, but at 400° C. or higher, it may be within 1 hour. If the heating time is too long, iron will react, which will increase the sulfur consumption rate and reduce the tin concentration in the recovered product, which is not preferable.

The second stage operation of the present invention is a step of separating the tin-containing reaction product produced in the first stage operation from the iron scrap. Since the reaction product adheres to the surface of the tin plate in the form of a film, it is easy to separate it by physical means. That is, the processed iron scrap is vibrated or dropped to peel off the product, and the product is separated into powder using known means such as wind power or a sieve. The separated dust containing tin compounds is collected using existing techniques such as sieves, cyclones, and bag filters.

A known process for producing metallic tin from sulfide-containing tin ore can be applied to the process of recovering tin from the recovered dust. That is, after oxidizing the recovered dust in a rotary kiln or the like,
The poiyaki dust is charged into an electric furnace together with a reducing agent such as coke and smelted. The recovered dust may be roasted or smelted alone, or may be used together with a tin smelting furnace raw material such as tin ore. The exhaust gas from the oxidation process is collected and desulfurized.

(Example) (1) Mix and charge elemental sulfur at a weight ratio of 0.5% with tin cuttings into a cylindrical container made of heat-resistant steel, seal the container, and use nitrogen gas to increase the oxygen concentration in the container. The atmosphere was replaced until the amount became 1.5% or less.

Thereafter, the container was placed in a gas heating furnace and heated at 450° C. for 30 minutes, and then the tin plate taken out from the container was sieved with a vibrating sieve for 10 minutes. The components of the scrap before treatment are Sn0.
85%, 80.02%, after treatment Sn0.10%, So
, 04%. The tin removal rate is 88%. The tin concentration in the dust collected as the bottom of the sieve was 18%.

(Effect of the invention) According to the present invention, tin can be easily removed and recovered from tin-plated steel products such as empty can press scraps, so tin-plated steel products such as empty can press scraps can be remelted without contaminating the steel material with tin. High purity steel can be obtained. In addition, the recovered tin compound can be effectively used as a highly concentrated tin resource.

The present invention can also be applied to separating and recovering tin from tin-containing alloys such as solder and gunmetal.

Applicant: Nippon Steel Corporation

Claims (1)

[Claims] Tin-plated iron scrap and sulfur are charged into a closed container, and the inside of the closed container is made into a non-oxidizing atmosphere.
A method for separating and recovering tin from iron scrap, which comprises heating the iron scrap to a temperature of 0° C. or more and 600° C. or less, and then separating a reaction product from the iron scrap.