A Separation Method of Tungsten-Tin Ore

China is the world's largest producer of tungsten and a major producer of tin. Southern Yunnan and Western Yunnan of China are the main origin of tungsten-tin paragenic ore. Since it is difficult to apply the conventional methods (gravity concentration, froth flotation or magnetic separation) to separate the tungsten-tin ore, thousands of tons of them have been wasted. When tungsten exists as an impurity in tin concentrate, it is not only wasted, but also affects the cost of tin metallurgy and the quality of tin products; while tin exists in tungsten products as impurities, even if the amount is very small, the quality of tungsten products has been adversely affected.

In order to achieve the purpose of tungsten-tin ore separation, tungsten-tin refractory paragenic ore is used as raw material to convert tungsten and tin into soluble structure, and then control different conditions, respectively transfer them into solution to separate them, and then deeply convert them into ammonium paratungstate and tin oxide, the method is as follows:

1) When the ore size is -200 mesh ≥ 95%, in a slightly boiling state (90-95° C), a concentration of 15-18% (solid-liquid ratio 1:3) of nitric acid is used as the acid decomposition agent, a low concentration control oxidation has carried on , so that the nitrate is reduced into NH₃, which avoids excessive nitrogen oxides and the causing of  pollution hazard. Sufficient and economical reaction time is 2.5 hours, and the decomposition rate of tungsten is greater than 97%.

2) Due to the heating for increasing the reaction rate, a small amount of nitric acid decomposes and produce nitrogen oxides. Nitric acid might react with some gangues and produce nitrogen oxides. For this purpose, nitrogen is sprayed with ammonia water and NH₄NO₃ is obtained.

3) The use of cheap carbonic acid light ammonia as a precipitation and conversion agent to recover the metal ions entering the solution during the conversion of tungsten, and the NO^-3 and excess residual HNO³ are all converted into NH₄NO₃, which eliminates waste liquid pollution.

4) The crude tungstic acid and cassiterite mixture obtained by acid hydrolysis conversion is dissolved in ammonia water to make tungsten into solution in the form of ammonium tungstate, which is separated from cassiterite and insoluble impurities.

5) Use macroporous strong alkali gel resin for separation and purification, the resin grade as product purification is 201×7, the concentration of test solution is 40-45 (WO3g/l), and the resin grade recovered of mother liquor is D296. The test solution concentration is 15-20 (WO3g/l). Ammonia water and ammonium chloride are used as desorbents in product purification, and then concentrated and crystallized to obtain high-purity ammonium paratungstate. The mother liquor is recycled to the next step.

6) Preparation of stannous solids: The tin slag after tungsten immersion is mixed with lignite and stabilizer after dry grinding according to the selected particle size, and then reduced in a special electric heating furnace with water vents and a thin crucible. stable. The process conditions were: tin slag: lignite = 1:0.2, tin slag: stabilizer = 1:0.04; reduction temperature was 800 ± 50 ° C; the reduction time is 1 hour. Under this condition, the stannous conversion stability rate is ≥97%.

7) Sulfuric acid leaching of stannous: In order to prevent residual tungsten in the tin slag from entering the solution, the acid is used to leaching tin, and for the next step of liquid phase oxidation to obtain tin dioxide, sulfuric acid is selected as the leaching agent. The concentration of sulfuric acid is 7 molar, and the amount of sulfuric acid is: solid: liquid (7 molar concentration) = 1:2, the leaching reaction temperature is constant boiling point, and the leaching time is one hour. Under this condition, the stannous leaching rate is greater than 98. %.

8) The SnSO4-H2SO4 system obtained after leaching out stannous sulfuric acid is unstable, and spontaneously precipitates hydrated tin dioxide. Therefore, by adding a liquid phase oxidant and adjusting the acidity, the precipitation of tin oxide is promoted completely. The addition of the corresponding inhibitor causes the contaminated impurities to not affect the quality of the tin dioxide product. The primary and secondary factors for the selected tin-free conditions are: sulfuric acid content of the system (A), amount of liquid phase oxidant (B), amount of impurity inhibitor (C), reaction temperature (D), and adjustment of sulfuric acid to the system. The sulfuric acid content is 0.9 mol/l, the liquid phase oxidant is used, tin: oxidant = 1:0.6, the inhibitor is used, tin: inhibitor = 1:0.01, the reaction is carried out at normal temperature, and the oxidized sinter tin ratio is greater than 96%.

9) The obtained hydrated tin dioxide is firstly dried at a low temperature to remove surface water, and then (SnO)3•2H2O and Sn(OH)2 are thoroughly oxidized in advance to adjust the acid preparation process. , all converted to tin dioxide, the dry material is pulverized to -100 mesh ≥ 95% to increase the surface area of ​​secondary oxidation, and then in the special double-layer reverse long box type resistance furnace before 600 ° C ( The first half) stays for 15 minutes, is thoroughly dehydrated by medium-temperature calcination, and the material changes from white to gray, that is, the material has been completely dehydrated, and the "stained" (SnO)3•2H2O and Sn(OH)2 are converted into taco of SnO. ,

In order to fully oxidize this part of SnO to tin dioxide, push the material to the secondary high temperature zone in the middle of the electric furnace for secondary forced oxidation (adjust a certain amount of air if necessary), determine the temperature and time of burning according to the shade of color, and the temperature 850 ° C is appropriate, the time is 10-20 minutes. The visual standard for complete oxidation is that all of the off-white is converted to white, that is, a qualified tin dioxide product is obtained.

The advantages of the method are as follows:

1) Use nitric acid conversion, ammonia leaching separation and treatment of tungsten tin refractory symbiotic ore, enabling tungsten to completely enter the solution to achieve separation from tin, ensuring the stability of the high oxidized cassiterite, It can be completely separated without entering the tungsten phase;

2) Purify and recover tungsten with macroporous strong base quaternary ammonium gel resin, which has good industrial effect;

3) Stabilization of stannous and stable with SnSO4-H2SO4 system liquid phase oxidation to obtain tin dioxide not only realizes the complete separation of residual tungsten, but also obtains high quality tin dioxide products, avoids the serious pollution of nitrogen oxides in the process of tin dioxide.

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