Amalgam, a dental restoration material, and non-toxic metal tin, which is used as a shape memory alloy material for orthodontic wires are used in the medical industry. Also, it is a strategic material used in the steel industry, tin plating in the food industry, high-tech industry, and soldering in the electric and electronic industry.
However, the tin is a shortage resource that depends entirely on imports and needs to be self-sufficient. For this purpose, in Korea, although research to recover from waste tin is in progress, it is difficult to commercialize it due to low efficiency and generation of environmental by-products.
Therefore, in this study, Sn and O2 are separated from waste tin oxide using natural gas (CH4). A dry reduction process in which H2 is generated as a reaction by-product was proposed and the reduction behavior was investigated. In addition, the non-toxicity of recovered tin, for high purity, refining was performed and the reaction process was established.
In order to recover tin from waste tin oxide, it was performed by HSC chemistry computational theory calculation, In order to recover 1mol of tin oxide, it was confirmed that 0.62 mol of methane was required at 1,000℃. In addition, the ratio of reaction gases H2, CO, and CO2 was stabilized from the reaction temperature above 800℃. For the natural gas dry reduction test, a 20 kg class continuous production type vertical type reduction furnace was manufactured and used. Reduction experiments were conducted under conditions of 1 to 5 mol of natural gas supply at a reduction temperature of 700 to 1,000℃.
The first recovery tin was measured by measuring the recovery rate and purity by ICP (Inductive Coupled Plasma Spectrometer) analysis. A result of recovering 97.2% of tin with a purity of 99% was obtained.
In addition, the reaction by-product gas obtained a result of 23% hydrogen gas ratio and 16.6% hydrogen conversion ratio of methane gas through GC-TCD analysis.
The first recovered tin in the dry reduction process containing 0.01 to 0.4% of Pb and Sb, which are toxic substances, was subjected to electrolytic refining to control toxic substances. In the electrolytic refining experiment, the current density is adjusted in the range of 20~60 A/d㎡, and the toxic substance Pb has a standard electrode potential value similar to tin Since reduction through voltage and current control was not easy during electrolytic refining, the experiment was performed with a sulfuric acid concentration of 0.5 to 1.0 molar ratio.
As a result, Pb and Sb were completely removed at a sulfuric acid concentration of 0.75 mol and a current density of 60 A/d㎡.
As a result of the above experiment, high-purity, non-toxic tin was recovered from waste tin oxide through a natural gas dry reduction process. The possibility of hydrogen production of the reaction product was verified.
In addition, basic data on the establishment of a new waste resource reduction/recovery technology were provided by examining the reaction behavior of recovered tin from natural gas reduction.