With the rapid development of modern industry, the use of molybdenum continues to increase, and its price continues to rise, but high-quality molybdenum resources are becoming less and less. A certain amount of vanadate is contained in various types of molybdenum minerals and molybdenum-based spent catalysts, which are harmful impurities of molybdenum products. Therefore, it is necessary to prepare a pure molybdenum compound by removing vanadate.

The properties of molybdate and vanadate in aqueous solution are very similar and separation is difficult. Some existing methods for separating molybdate and vanadate include ammonium salt precipitation method, solvent extraction method, electrochemical ion exchange method, electrochemical reduction back extraction method, and chelate resin adsorption method. Ammonium salt precipitation method and solvent extraction method are not complete for the separation of molybdate and vanadate. The latter three methods can make the vanadium carbonate mass fraction of ammonium molybdate product less than 0.0015%, but electrochemical ion exchange method and electrochemical reduction The extraction process is complicated, and the chelating resin has a low adsorption capacity and is not ideal for industrial use. The experiment investigated the removal of vanadate from a solution of ammonium molybdate using a strong basic anion exchange resin.

First, the test part

(1) Test instruments, reagents and analytical methods

Strong alkaline anion exchange resin D231-II, Zhejiang Shengguang Industrial Co., Ltd. products.

The test liquid is prepared from ammonium molybdate, ammonium metavanadate and deionized water. The mass concentration of molybdenum is 62.36 gL, the mass concentration of vanadium is 0.52 gL, and the pH is 6.5-7.5.

Hydrochloric acid, sodium hydroxide, ammonium molybdate and ammonium metavanadate were all analytically pure.

Solution concentration of molybdenum in the 722S spectrophotometer measured with copper thiocyanate ion catalyzed process, with vanadate concentration of ferrous ammonium sulfate titration, chloride ion concentration was determined by silver nitrate titration, the pH value pHS -25 digital pH meter determination.

Ion exchange column: Ф 2.5 cm × 200 cm.

(2) Test methods

The resin was first soaked in deionized water for 24 h, fully swollen and then washed with deionized water until no impurities; alternately treated with 40 g of hydrochloric acid solution and 40 g of sodium hydroxide solution twice, each time soaked for 8 h with 2 times the volume of resin and used Deionized water was washed until neutral; finally, it was converted to chlorine type with 4 times resin volume of 40 gL hydrochloric acid solution, and then washed with deionized water until neutral.

200 mL of the treated D231-II resin was charged in the exchange column. At room temperature, the prepared solution was passed from top to bottom through the resin layer, the flow rate was controlled to 200 mL/h, and the exchange column effluent was taken once every 2 hours. The mass concentration of molybdenum and vanadium is measured.

The adsorption was stopped when the mass concentration of vanadate in the effluent of the exchange column reached 0.02 g/L. After the resin is saturated with adsorption, desorb with 4 times the volume of the resin in 50 g / L aqueous ammonia solution (or 50 g of sodium hydroxide solution), wash with deionized water to pH = 8, and then transfer with 4 times the resin volume of 50 g / L hydrochloric acid solution. It is a chlorine type, and after washing with deionized water until the pH is neutral, adsorption is carried out for the next cycle.

Second, the test results and discussion

(1) Adsorption

The adsorption test curves for the three cycles are shown in Figures 1-3.

Figure 1 Adsorption curve of vanadate on resin in the first cycle

Figure 2 Adsorption curve of vanadate on resin in the second cycle

Figure 3 Adsorption curve of vanadium for resin in the third cycle

It can be seen from Figures 1-3 that D231-II resin has adsorption effect on molybdate and vanadate in the liquid. When the volume of the effluent is 1 times the volume of the resin, the molybdate starts to penetrate, and then the molybdate in the effluent The mass concentration increases rapidly; when the volume of the effluent is 8 times the volume of the resin, the mass concentration of molybdate in the effluent is substantially the same as that in the feed solution, while the vanadate is not detected; when the volume of the effluent is 20 times the volume of the resin At the time, a trace amount of vanadate was detected in the effluent. If the vanadate mass concentration 0.02 g/L is used as the failure end point, the adsorption capacity of the resin to vanadate is about 16.0 g/L, and the amount of the treatment liquid is 26 times the resin volume.

(two) desorption

The removal of vanadate in the ammonium molybdate solution by the strong basic anion exchange resin D231-II is very effective. The mass concentration of vanadate in the effluent reached 0.02 g/L as the adsorption end point, and the resin was desorbed at this time. The resin was first rinsed with water to remove residual adsorbent solution, then desorbed with 4 times resin volume of 50 g/L aqueous ammonia solution, and then washed with deionized water to pH=8. The analytical test curve of 3 cycles is shown in Fig. 4. ~6 is shown. The resin adsorption capacity, elution amount and elution rate are shown in Table 1.

Figure 4 Analytical curve of molybdate and vanadate in the first cycle of resin

Figure 5 Analytical curve of molybdate and vanadate in the second cycle of resin

Figure 6 Analytical curve of molybdate and vanadate in the third cycle of resin

Table 1 Adsorption parameters of D231-II resin for 3 cycles

It can be seen from Table 1 that the analytical results of the three cycles are basically the same, and the vanadate elution rate is above 99%, indicating that the D231-II resin has good repeatability of vanadate adsorption and high elution rate. As a macroporous strong basic anion exchange resin, D231-II resin has a special pore structure and specific surface area. The adsorption selectivity to vanadate is higher than that of molybdate in the range of pH 6.5-7.5. At the same time, the resin has strong anti-pollution ability, high adsorption capacity, temperature resistance, stability and mechanical strength, and is very suitable for adsorption and separation of vanadate from the actual solution.

Third, the conclusion

The test results show that: D231-II resin can be used to separate vanadate from ammonium molybdate solution; when the solution pH is 6.5-7.5, D231-II resin has high adsorption selectivity to vanadate, and the adsorption rate is more than 99%; Desorbed with dilute ammonia (diluted lye), the vanadate elution rate is above 99%. D231-II resin has high resistance to oxidation, acid and alkali, and organic solvent resistance, and has high mechanical strength. Under normal conditions, the annual loss rate is less than 5%. The use of D231-II resin to adsorb vanadate from ammonium molybdate solution has a simple process, good separation effect, no special equipment, easy to master technology, and automation.

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