Separation of Tungsten and Tin in Alkali Leaching Solution of Tungsten Concentrate

Nie Huaping, Wang Xiuhong, Wan Linsheng

Among tungsten products, tin is one of the most harmful and difficult to remove among many impurities. Even if trace tin is present in the finished tungsten product, it will have a serious impact on its mechanical properties and physical properties. According to the requirements of GB/T 10116-1988, in the grade 0 APT (ammonium paratungstate), the tin mass fraction requirement is less than 1×10 ^-6 , and the tin mass fraction requirement in the first grade APT is less than 3×10 ^-6[1] , but with China's high-quality tungsten ore resources are increasingly scarce, and the content of impurities such as tin in the resources for mining is getting higher and higher, and the form is more and more complicated, which causes the quality of paratungstic acid products to be greatly affected. Therefore, it is urgent and necessary to study the deep removal of impurity tin in the tungsten smelting process.

1. Test materials

The tungsten concentrate is a high-tungsten tungsten concentrate in a mine in Zhangzhou. The chemical composition is shown in Table 1.

Table 1 Chemical composition% tungsten concentrates

Simulating industrial leaching conditions, leaching tungsten concentrate with alkali to obtain tungsten leaching solution: The tungsten concentrate was placed in an XMQ-cone ball mill , after grinding for 12 hours, passing through a 320 mesh sieve, and the sieved portion was taken for testing. Weigh 100g of tungsten concentrate, leaching for 3h in boiling state with a theoretical amount of 1.6 times and a mass concentration of 500g/L NaOH solution, then pumping and washing, and diluting the filtrate (sodium tungstate solution) with distilled water is the test solution. The tungsten mass concentration (as WO ₃ ) was 20 g/L, and the tin mass concentration (in terms of Sn) was 1.78 mg/L.

2, the test part

2.1 The existence form and proportion of tin in tungsten leachate

In the tungsten leaching solution, tin exists in the state of SnO ₃ ^2- and SnS ₃ ^2- 2 ^[2] . In comparison, SnS ₃ ^2- is more harmful, even if it is present in a small amount, the product APT tin exceeds the standard ^[3] . The presence of an appropriate amount of SnO ₃ ^2- does not have a significant impact on product quality. In the subsequent process of ion exchange and recovery of tungsten, since the affinity of SnO ₃ ^2- and resin is smaller than that of WO ₄ ^2- , most of it remains in the solution and is not adsorbed by the tree finger, and the removal rate of SnO ₃ ^2- can reach 99%. ^[4] . Therefore, in the tungsten-tin separation, it is necessary to study the existence ratio of SnO ₃ ^2- and SnS ₃ ^2- in the solution.

The ratio of SnS ₃ ^2- in the tungsten leachate was determined by static adsorption using an ion exchange resin. A volume of tungsten leaching solution was weighed into a beaker containing a quantity of anion exchange resin (saturated by WO ₄ ^2- ) while stirring at room temperature. The ratio of SnS ₃ ^2- in the tungsten leaching solution of different pH values ​​was determined by the exchange method, and the results are shown in Fig. 1. As seen from Fig. 1, as the pH of the solution increases, the proportion of SnS ₃ ^2- in the solution drops sharply, which is consistent with the thermodynamic analysis results described later. It is also worth noting that a solution with a pH of 13 is more common in production. When the pH is 13, the ratio of SnS ₃ ^2- is 18.1%. It is confirmed that the removal of tin from the adsorbent solution actually means the removal of SnS ₃ ^2- .

Figure 1 Proportion of thiostannate in pH tungsten leaching solution

2.2 Thermodynamic analysis

The SnO ₃ ^2- and SnS ₃ ^2- in the tungsten leachate are not isolated but can be transformed into each other:

SnO ₃ ^2- +3S ^2- +3H ₂ O= SnS ₃ ^2- +6OH ^-

When the equilibrium constant (K) of the above reaction is calculated or calculated using thermodynamic data, the concentration ratio of SnO ₃ ^2- and SnS ₃ ^2- can be determined by knowing the concentration of S2- and OH-, that is,

3. Results and discussion

The effect of the amount of reagent, reaction temperature and reaction time on the effect of tin removal was investigated by precipitation method.

A certain amount of water was placed in a DF-1 collector type thermostatic magnetic stirrer and heated to a set temperature. A 200 mL tungsten leaching solution was weighed into a conical flask, and a certain amount of precipitant M115 was added. Place the conical flask in a water bath and slowly start magnetic stirring to make the stirring speed suitable. After stirring for a period of time, the conical flask was taken out, clarified and filtered. The filtrate was the purified liquid after tin removal, and the mass concentration of tin in the filtrate was analyzed.

3.1 The effect of reagent dosage on tin removal effect

The amount of the reagent is 1 to 7 times the theoretical amount, and the mixture is stirred for 1 hour at room temperature. The test results are shown in Fig. 2.

Figure 2 Effect of reagent dosage on tin removal effect

It can be seen from Fig. 2 that as the amount of the reagent increases, the tin removal rate gradually increases. When the amount of the reagent is 5-6 times of the theoretical amount, the removal rate of the thiostannate exceeds 90%, which is sufficient for the production needs, and it is not necessary to increase the amount of the reagent.

3.2 Effect of reaction temperature on tin removal effect

The amount of reagent was 6 times of the theoretical amount, and it was stirred for 1 hour at different temperatures to investigate the effect of temperature on the effect of tin removal. The test results are shown in Figure 3.

Figure 3 Effect of reaction temperature on tin removal effect

It can be seen from Fig. 3 that as the reaction temperature increases, the removal rate of tin decreases, and at 80 ° C, the removal rate of thiostannate decreases to 87.8%. Therefore, tin removal should be carried out at relatively low temperatures, generally at room temperature. This operation at low temperatures is obviously advantageous: on the one hand, it does not consume a large amount of energy, simplifies the equipment and the operation process, and on the other hand avoids the APT crystallization which may occur at high temperatures. However, there is a problem that the precipitate particles become fine at a low temperature, filtration and washing are difficult, and precipitation of fine particles is liable to cause mechanical inclusions, resulting in an increase in tungsten loss.

The reason for the increase in temperature and the decrease in tin rate may be:

(1) The reaction between the precipitating agent M115 and the thiostannate is an exothermic reaction, and an increase in temperature is disadvantageous for the reaction.

(2) Precipitant M115 reacts with thiosulphonate to form a poorly soluble substance. It is essentially a carrier process. When the temperature rises, the generated carrier particles agglomerate and grow, reducing the specific surface area, reducing the reactivity, and finally eliminating The tin rate is reduced.

3.3 Effect of reaction time on tin removal effect

The amount of the reagent was 6 times of the theoretical amount, and the mixture was stirred at room temperature for a certain period of time to examine the effect of the reaction time on the tin removal effect. The test results are shown in Table 2. After stirring for 1 h, the tin removal rate exceeded 93%, and the extension time was not increased. Therefore, the reaction time of precipitation and tin removal is generally controlled at 1 h.

Table 2 Effect of stirring time on tin removal effect

4 Conclusion

(1) In the tungsten leaching solution, tin exists in the form of SnO ₃ ^2- and SnS ₃ ^2- , the pH of the leaching solution is different, and the ratio between SnO ₃ ^2- and SnS ₃ ^2- is also different. The higher the pH, the lower the SnS ₃ ^2- ratio; when the pH is 13, the ratio of SnS ₃ ^2- is 18.1%.

(2) The SnS ₃ ^{2- can be} selectively removed from the sodium tungstate solution efficiently by using the precipitant M115.

(3) When the precipitant M115 is used as the tin removal reagent, the tin removal rate increases with the increase of the reagent amount, increases with the reaction time, and decreases with the increase of the reaction temperature. Reasonable process conditions are: the actual amount of reagent is 6 times of the theoretical amount, stirred at room temperature for 1 h, the tin removal rate is not less than 90%.

(4) Selective precipitation method to remove SnS ₃ ^2- in tungsten leaching solution, the process is simple, and the energy consumption is low. 1t to produce ammonium paratungstate (APT) count, consumption of copper sulfate in about 8kg, ammonium sulfide 60kg, low cost, has certain economic advantages.

Removing of Stannum From Alkaline Leaching Solution of Stannum Concentrate

NIE Hua-ping, WANG Xiu-hong, WAN Lin-sheng

(School of Material and Chemical Engineering, Jiangsu xi University of Science & Technology, Ganzhou, Jiangxi 341000, China)

Abstract :Several problems such as stannum presence states and removing of stannum of stannum from alkaline leaching solution of tungsten concentrate ore are studied. The result shows that stannum presence states and their proportion are distinctly influencde by pH value of leaching solution. The higher the pH Value of leaching of leaching solution, the lower the proportion of SnS ₃ ^2- .The SnS ₃ ^2- can be removed selectively from the soltion by precipitator M115,The removing rate of stannum can be enhancde by increasing rate of stannum is over 90% When practical dosage of precipitator is 6times of theoretical dosage and stirring time is 1 at room temperature.

Key words : tungsten concentrate ore;alkaline leaching solution;stannum;separation