Recovery of indium from crude tin

When the indium associated with the tin concentrate is reduced and smelted, approximately 65 % of the indium is volatilized into the soot and 30 % is reduced to the crude tin. The crude crystallization in addition to tin in lead, indium, a small amount of the refined tin, in the majority of the solder, the solder containing indium and sometimes up to 0.02% to 0.03%. In the case of solder electrolytic refining, indium is dissolved in the electrolyte. When the electrolyte used repeatedly, the accumulation of indium, indium containing up to 0.3 ~ 0 .5g /L or More. YTC a rule when the electrolytic solution with HCl-SnC1 ₂ electrolysis solder, tin entrained electrolyte formed on the cathode layer of yellow concentrate on the initial level of the metal melt cathode plate, commonly known as "oil head water", as Indium raw materials. The composition of the oil head water ( g / L ) is: 28 0 ~ 430Sn, 1. 5 ~ 4.0Pb , 0. 4 ~ 0. 9Zn , 9 ~ 13Fe , 2 ~ 5In , 0.1~0.3Cd . The plant uses P ₂₀₄ extraction method to extract indium from the oil head water. The flow is shown in the figure below. The operation data is as follows:

Figure Â P ₂₀₄ extraction process of indium

Â Â Â Dilution and neutralization:
( 1 ) Dilute the head water with pure water to contain indium 1g About /L , sodium is neutralized in the neutralization tank to neutralize tin, so that tin becomes a hydroxide precipitate.
( 2 ) Neutralization process control PH = 2.5~4.0 , which can reduce the tin content of the solution to 1g /L .
( 3 ) The filtered tin hydroxide residue can be used as a tin-removing raw material, and the filtrate (neutralizing liquid) is sent to extract indium.
Indium extraction:
( 1 ) Neutralization solution plus hydrochloric acid adjustment Ph = 1~1.5 , Cl ^- = 80g /L , using P ₂₀₄ as an extractant to extract indium. P ₂₀₄ was added 50% coal-oil composition of the organic phase. The ratio of the organic phase to the aqueous phase (volume ratio) was 1 : 2 for bipolar extraction. The raffinate containing indium can be reduced to 0.07~ 0.15g /L , most of the impurities (such as iron ) remain in the raffinate.
( 2 ) The ruthenium-containing organic phase is added with an oxidizing agent hydrogen peroxide (H ₂ O ₂ ), so that Sn ^{2+ is} changed to Sn ²⁺ and remains in the organic phase, and indium is stripped with 6 mol 1 /L hydrochloric acid for three-stage back extraction. Stripping solution containing indium 40g /L, where Sn : In= 1 : 50 0 ï½ž 2000 . The extraction rate of indium is over 90 %.
( 3 ) The organic phase after indium extraction is washed with 8 mol/L hydrochloric acid to remove most of the tin, and P _{204 is} changed to H ⁺ type for return extraction. A small amount of iron in the organic phase may be added to the SnCl ₂ solution to change Fe ³⁺ to Fe ²⁺ to facilitate washing; the amount of SnCl ₂ added is Sn0. 1 ï½ž 0 .3g /L . The amount of hydrochloric acid used for washing is half the volume of the organic phase.
Indium recovery:
(1) the acidity of the solution was adjusted to pH = stripping after 3 to 4, to obtain replacement with indium sponge aluminum plate.
(2) caustic soda used as a coating agent, the sponge is melted at a temperature of 38 0 ~ 40 0 â„ƒ indium indium to give a crude (containing 90% ~ 95% In).
(3) except for crude indium thallium chloride in a molten state at 260 to ~ 28 0 â„ƒ. The herbicide added is Zn : ZnCl ₂ : NH ₄ C 1=100 : 15 : 5 .
(4) for electrolytic refining, a current density of 9 0 ~ 50A / m ^2, electrolyte pH = 2 ~ 3, the liquid temperature is room temperature, 0. 2 ~ 0.5V cell voltage in addition to the crude indium thallium, with the pole pitch 45mm .
( 5 ) The cathode indium obtained by electrolysis is vacuum distilled to produce "five-nine" high-purity indium. The conditions for vacuum distillation are: vacuum degree 13.33 2 ~ 1.333Pa , temperature 86 0 ~ 900 Â°C .
Tin recycling:
( 1 ) "Tank water" and tin hydroxide filter residue produced by tin removal, melted with caustic soda and saltpeter to produce sodium stannate. Temperature 30 0 ~ 50 0 Â°C , tin to alkali ratio is 1 : 0.5 5 ~ 0.60 , tin to nitrate ratio is 1 : 0.2 1 ~ 0.25 .
( 2 ) Water-soaked crude sodium stannate solution. The liquid-solid ratio at leaching is 4 : 1 , and the density of leaching solution is 1.18 to 1 .20g /cm ³ .
( 3 ) The leachate is delead with sodium sulfide. The amount of sodium sulfide (g) and the solution volume (ml) ratio of 1: 3, the temperature 8 0 ~ 8 5 â„ƒ.
(4) sodium stannate solution was replaced deleading sheet with tin, antimony off, the temperature is 91 to 93 Â°C .
( 5 ) The solution after depurination is concentrated. The concentration of the mother liquor in one concentration is greater than 35Be ; the proportion of the mother liquor in the second concentration is greater than 40Be .
( 6 ) The concentrated liquid is cooled and crystallized, and after filtration, it is baked and ground to obtain a first-grade sodium stannate product.
( 7 ) Comprehensive recovery rate of oil head water: Sn is higher than 98 %, and In is higher than 80 %.
It is also reported that the distribution data (%) of indium in various refining scums in the refining of crude tin in a factory is as follows: iron scum 4.7 , sulfur slag 19.8 , aluminum slag 18.2 , lead scum 44.0 , Fine tin 0.7 , loss 12.6 . It is indicated that a large amount of indium is concentrated in the lead scum, and the content is 0.91 to 0.20 %. The plant after the lead and zinc dross processing, indium chloride into the slag, and then washed with water to separate leached zinc, indium residue containing up to 0.6% to 0.8%, and then make the most of the alkali leaching of lead, zinc, tin Into the solution, while indium is enriched in the leaching slag in the form of In (OH) ₃ , and the indium is increased to 2.8 %. The slag is dissolved in hydrochloric acid, and the crude indium containing 80 % or more of indium is obtained by replacing with tin or zinc , or the indium is precipitated by sodium hydroxide and then smelted into crude indium, and the crude indium is refined into pure indium.

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