Experimental Study on Removal of Acid from Leaching Solution of Vanadium Extracted from Stone Coal

This experiment is based on the stone coal roasting-water immersion-resin exchange-desorption-ammonium salt vanadium -calcination vanadium pentoxide process [1] proposed by the predecessors. In the original process, water leaching can leaching 70% of the vanadium in the calcined sample. Through further research, the authors found that the leaching of the slag after water leaching with dilute acid can increase the total leaching rate of vanadium by more than 10 percentage points. However, while diluting the vanadium in the water leaching residue with dilute acid, the impurities such as silicon, aluminum , iron , phosphorus, etc. also enter the acid immersion liquid. Some data indicate that the presence of impurities affects the subsequent vanadium precipitation, so the acid leaching solution must be decontaminated before being vanadium. The present experiment Acid Leaching low vanadium concentration, impurity content and high, masking vanadium with hydrogen peroxide solution, and then copper reagent complex iron impurity ions, complexes and impurities precipitated by adjusting the pH of the solution is removed , to achieve effective separation of vanadium and impurities, so that subsequent operations can smoothly recover vanadium.

First, the acid immersion liquid

Stone Coal Mine of Jiangxi sample (V ₂ O ₅ 0.87% grade) roasting the sodium, after firing twice like flooding, water and then dilute acid residue to give an acid immersion test. The vanadium concentration of the acid immersion liquid is 0.1-0.3 g/L, and the pH value is between 1.5 and 2. The main ion component analysis results are shown in Table 1.

Table 1 Analysis results of main ionic components of acid leaching solution mg/L

Second, the main reagents and instruments

Main reagents: hydrogen peroxide, sodium hydroxide, copper iron reagent. The copper-iron reagent was separately prepared into a solution having a concentration of 1 g/L, and a solution of sodium hydroxide having a mass fraction of 33% was used.

The main test equipment: 79-1 magnetic heating stirrer, SHB-III circulating water vacuum pump, Model pHs-3C pH meter, full spectrum direct reading plasma emission spectrometer.

Third, the test method

It can be seen from Table 1 that in addition to the low concentration of vanadium (281.33 mg/L), the acid leaching solution also contains a large amount of impurities such as Zn ^{2 +} , Al ^{3 +} , Fe ^{3 +} , Cu ^{2 +} . Due to the presence of a large amount of impurities, the acid immersion liquid cannot directly enter the subsequent processing operation, otherwise the subsequent vanadium vaccination efficiency is greatly reduced, and even the vanadium-bearing operation cannot be performed. Although the pH value of the acid immersion liquid can be directly adjusted to precipitate and remove the impurity ions at different pH values, the precipitates of colloids such as Al(OH) ₃ , Fe(OH) ₃ and Zn(OH) ₂ are adsorbed. The vanadate ion in the solution causes a large loss of vanadium, sometimes with a loss rate of more than 50%. According to the information, pickle liquor mainly vanadium VO ₄ ^{3 -} occurring form, VO ₄ ^{3 -} in the O ^{2 -} ions can be hydrogen peroxide (H ₂ O ₂₎ peroxy ions O _{² 2} ^- substituted, a yellow diperoxy vanadate anion complex _{[VO 2 (O 2) 2} ] 3 -, thereby masking vanadate ions in the solution, prevents vanadate ions in the solution of hydrated metal ions by hydrogen bonds "Bridge" acts to complex; and the special structure of oxygen and nitroso on the hydroxylamine molecule of the copper-iron reagent enables it to adsorb the impurity metal ions in the acid leaching solution and inhibit the colloidal particles generated by the impurity ions during the pH adjustment process. The movement in the solution causes them to precipitate and be removed, thereby achieving the purpose of purifying the acid leaching solution and reducing the vanadium loss rate.

During the test, take 400ml of acid leaching solution each time, add appropriate amount of hydrogen peroxide while stirring, react for 10min, then add a certain volume of copper-iron reagent solution, continue the reaction for 10min, and then use the pH value of the acid solution of sodium hydroxide solution to generate The impurities are precipitated, and the solid is separated after the precipitation is sufficient, and the filtrate is the purification liquid of the acid immersion liquid. The test procedure is shown in Figure 1.

Figure 1 Acid leaching solution purification and impurity removal test process

Fourth, test results and discussion

(1) Effect of pH on vanadium loss rate

In order to determine the appropriate pH precipitation point of Zn ^{2 +} , Al ^{3 +} , Fe ^{3 +} , Cu ^{2 +} plasma, the pH adjustment test was directly carried out on the acid immersion liquid. The pH values ​​of the acid immersion liquid were adjusted to 4, 5, 6, 7, and 9 with sodium hydroxide, respectively. The change of vanadium loss rate in the acid leaching solution is shown in Fig. 2.

Figure 2 Effect of pH on vanadium loss rate

It can be seen from Fig. 2 that the vanadium loss rate as a function of pH shows a peak at pH 5, and a trough occurs between pH 6 and 7. When the pH value is less than 5, mainly the Fe ^{3 +} in the acid leaching solution forms iron hydroxide precipitate. Due to the adsorption of the ferrous hydroxide colloid, the vanadium has a certain loss; as the pH increases, the acid leaching solution Al ^{3 +} begins to form a precipitate. When the pH value is 5, Al ^{3 +} completely forms Al(OH) ₃ precipitate. Due to the strong adsorption of Al(OH) ₃ colloid, the vanadium loss rate in the acid leaching solution reaches 57.90. %, the aforementioned peaks are formed; the pH value continues to rise to between 6 and 7, and the loss rate of vanadium in the solution decreases, and troughs may occur, which may result in re-dissolution of the formed Al(OH) ₃ colloid, which reduces colloid adsorption. When the pH value exceeds 7, the vanadium loss rate in the acid leaching solution increases sharply again, possibly due to the precipitation of zinc ions and copper ions, which causes the vanadium loss, and as the pH continues to rise, the calcium ions also begin to precipitate, and the solution The higher the concentration of calcium ions in the medium, the rate of vanadium loss in the acid leaching solution also increases. Since the pH value of the purification liquid is required to be 6 to 8 in the subsequent operation, the pH value at the time of selecting the precipitated impurities is 6.5.

(II) Effect of the amount of hydrogen peroxide on the loss rate of vanadium

Hydrogen peroxide is a commonly used strong oxidant. Adding it to the vanadium-containing acid immersion solution can oxidize V(IV) in the acid leaching solution to V(V), which is beneficial to the subsequent vanadium precipitation operation. At the same time, the O ₂ ^{2 -} ion of hydrogen peroxide ₃ may also be an acid infusions VO ^- ion complexation, preventing VO ₃ ^- ions to form a precipitate at a pH value change.

Under the condition that the volume ratio of the acid immersion liquid to the copper-iron reagent is 8:1 and the final pH value of the acid immersion liquid is adjusted to 6.5, the amount of the hydrogen peroxide in the hydrogen peroxide and the acid immersion liquid is measured according to the flow of FIG. The ratios are 5, 10, 15 and 20, respectively, and the change in vanadium loss rate in the acid immersion liquid is shown in Fig. 3.

Figure 3 Effect of the amount of hydrogen peroxide on the loss rate of vanadium

It can be seen from Fig. 3 that the amount of hydrogen peroxide has a significant effect on the loss rate of vanadium in the acid immersion liquid. With the increase of the amount of hydrogen peroxide, the vanadium loss rate of the acid leaching solution decreased. When the ratio of the amount of vanadium in the hydrogen peroxide solution to the acid leaching solution was 15, the vanadium loss rate decreased to the minimum value of 15.42%; The amount of hydrogen peroxide, the vanadium loss rate does not change much, almost a straight line parallel to the horizontal axis. When the ratio of the amount of vanadium in the hydrogen peroxide solution to the acid immersion liquid is less than 15, the loss rate of vanadium is large, and there may be insufficient oxygen ions to complex with the VO ₃ ^- ions, which cannot function as a complex masking. According to the test results, the ratio of the amount of vanadium in the hydrogen peroxide solution to the acid immersion liquid is preferably 15 .

(III) Effect of the dosage of copper-iron reagent on the loss rate of vanadium

Copper-iron reagents can form complexes and precipitates with various metal ions at different pH values, and are widely used in hydrometallurgy of precious metals. It has been found that the addition of copper-iron reagent can change the form of precipitation produced in the acid leaching solution, and change from colloidal precipitation to granular precipitate with larger particle size, which not only makes the solid-liquid separation process easier, but also greatly reduces Loss of vanadium during the purification of acid leaching solution caused by colloidal adsorption.

In the Case where the ratio of the amount of vanadium in the hydrogen peroxide solution to the acid immersion liquid is 15, and the final pH value of the acid immersion liquid is adjusted to 6.5, the amount of the copper iron reagent is tested according to the procedure of Fig. 1, and the copper iron reagent solution (1 g/L) When the dosages are 20mL, 30mL, 40mL, 50mL, 60mL and 80mL, the change rate of vanadium in the acid leaching solution is shown in Fig. 4.

Fig. 4 Effect of copper-iron reagent on vanadium loss rate in acid leaching solution

It can be seen from Fig. 4 that the vanadium loss rate of the acid leaching solution decreases significantly with the increase of the amount of copper-iron reagent. When the amount of copper-iron reagent is 50mL, the loss rate of vanadium reaches the minimum value of 15.42%; The amount of addition, the loss rate of vanadium does not change much. Therefore, it is determined that the amount of the copper-iron reagent is 50 mL, and the volume ratio of the acid immersion liquid to the copper-iron reagent is 8.

The copper-iron reagent can effectively reduce the loss of vanadium while promoting the sedimentation of impurity ions. It may be because the copper-iron reagent destroys the colloidal particles formed by the Zn ^{2 +} , Al ^{3 +} , Fe ^{3 +} , Cu ^{2 +} plasma. Chargeability, which weakens their adsorption of VO4 ^{3 +} .

(4) Comprehensive test

According to the above test results, the ratio of the amount of vanadium in the hydrogen peroxide and the acid immersion liquid is 15, the volume ratio of the acid immersion liquid to the copper iron reagent is 8, and the impurity sedimentation pH value is 6.5, according to the flow of Fig. 1 400mL acid leaching solution was used for purification treatment, and the main ion concentration in the acid immersion liquid was corrected by the full spectrum direct reading plasma emission spectrometer. The results are shown in Table 2.

Table 2 Concentration of main ions in acid leaching solution before and after purification treatment mg/L

It can be seen from Table 2 that after purification treatment, the Zn ^{2 +} , Al ^{3 +} , Fe ^{3 +} , and Cu ^{2 +} ions in the acid leaching solution are largely removed, while the P, Si, and Ca ^{2 +} remain in the acid leaching solution. Etc. will not adversely affect the subsequent vanadium extraction. At this time, vanadium in the acid leaching solution is mostly retained, and the vanadium loss rate is only 15.52%.

V. Conclusion

Using the masking and impurity removal effects of hydrogen peroxide and copper-iron reagents, the vanadium-containing water-leaching leaching acid leaching solution with high impurity content and low vanadium concentration is subjected to impurity removal treatment, and the amount of vanadium in the hydrogen peroxide and acid leaching solution is used. The ratio is 15. The volume ratio of acid immersion liquid to copper iron reagent (1g/L) is 8. The impurity sedimentation pH value is 6.5. The harmful impurities are removed thoroughly, and the vanadium loss rate is only 15.52%. Vanadium has created good conditions.