Vanadium-bearing coal is an important vanadium resource in China. The method of extracting vanadium from vanadium-bearing coal can be roughly divided into two categories. The first one is for the specific area of ​​stone coal mine using traditional roasting technology for sodium and calcification. Calcination without salt and composite additives, such methods are gradually eliminated due to environmental pollution caused by the large amount of toxic gases such as S0 2 , HC1 and Cl 2 in the roasting process; the other is the direct wet leaching method, such as Shaanxi Zhongcun vanadium mine adopts the “direct sulfuric acid leaching-solvent extraction-ammonia salt vanadium-drying pyrolysis†wet process to extract vanadium. However, for a long time, only the sulfuric acid is directly leached from Nakamura vanadium ore, and its leaching rate is less than 80%. In order to improve the recovery rate of vanadium, on the basis of the above process, the effect of adding fluorine-containing leaching agent on vanadium leaching of sulfuric acid leaching Zhongcun vanadium ore and subsequent processes such as extraction was studied, and good results were obtained.
First, the experimental part
(1) Raw materials and reagents
Vanadium-bearing coal (provided by the mine) main components: 0.9% V 2 O 5 , 1.2% Fe 2 0 3 . The vanadium ore is an adsorbed vanadium ore and is mainly composed of tetravalent vanadium.
The main ore type is carbon siliceous rock mudstone type vanadium ore and partially (carbonaceous) mudstone type vanadium ore.
Reagents: sulfuric acid (98%, technical grade); lime (high quality, technical grade); fluorine-containing aids (homemade).
Extractant: 10% P204 + 5% TBP + 85% sulfonated medium oil.
(2) Test process
1. Leaching test. The leaching test was carried out in a 2 m 3 enamel reactor, and 500 kg of stone coal vanadium ore (particle size of -0.018 mm particle size accounted for 95%), 500 kg of water, 100 kg of concentrated sulfuric acid were sequentially introduced into the reactor, mechanical stirring was started, and 10 kg of oxygen was introduced. The infusion was heated and heated to 90 ° C for 24 h. After the leaching is completed, the leaching system is filtered and washed with a centrifuge (500 kg of washing water), and the filtrate and the washing liquid are collectively referred to as a leaching solution, and the total volume thereof is measured, and the sample is sampled. After the sampling is completed, the pH of the leaching solution is neutralized with a base to 2 to 2.5 for 60 minutes, and the mixture is filtered by a centrifuge, and the filtrate is subjected to reduction to be the next stage extraction liquid (ie, the extract liquid), and sampled and analyzed. All samples were colored gold belongs to the Guangzhou Institute of Analytical Center by ICP analysis (the same below).
2. Extraction test. The equipment used in the extraction test was a plexiglass mixed clarification tank (the effective volume of the mixing chamber was 1 L, the volume ratio of the mixing chamber to the clarification chamber was 1..3, and the double-blade slurry was stirred at a speed of 800 r/min).
The extraction process conditions were: room temperature, compared with (O/A) 1..1, 10-stage countercurrent extraction, mixed phase time 12 min. The organic phase (0) is 10% P204 + 5% TBP + 85% sulfonated medium oil; the aqueous phase (A) is the filtrate after the leachate is neutralized by the lime milk (ie, the extract liquid, wherein A 1 is not fluorine-containing Infusion, A 2 is a fluorine-containing leaching agent).
The extraction operation is as follows: firstly add half of the organic phase (0), half of the aqueous phase (A) in the mixing tank mixing chamber and the clarification chamber, and use two 20L lower mouth glass bottles as the high level tank. One of them is equipped with organic phase (0) and the other is filled with water phase (A 1 or A 2 ). Stirring is started. The organic phase is continuously fed into the organic phase at a flow rate of 40 mL/min, and the flow rate is at the water phase feed port. 40 mL/min continuously enters the aqueous phase (A 1 or A 2 ), and after a certain time, the raffinate is taken at the discharge residue.
Second, the test results and discussion
(1) Effect of fluorine-containing leaching agent on vanadium leaching rate
The effect of the fluorine-containing leaching agent on the leaching of vanadium by sulfuric acid is shown in Table 1.
Table 1 Effect of fluorine-containing leaching agent on vanadium leaching from sulfuric acid
Test conditions | Leachate | Extract | ||||||
Volume / L | Ï(V 2 O 5 )/ (mg·L -1 ) | Ï(Fe 2 O 3 )/ (mg·L -1 ) | V 2 O 5 amount / g | V 2 O 5 leaching rate /% | Ï(V 2 O 5 )/ (mg·L -1 ) | Ï(Fe 2 O 3 )/ (mg·L -1 ) | Ï(F)/ (mg·L -1 ) | |
No fluoride aids Fluorine-containing aid | 980 980 | 3673 4270 | 5073 5102 | 3599 4185 | 80 93 | 3342 3886 | 4616 4608 | / 4450 |
As can be seen from Table 1, the vanadium leaching rate was 80% when no fluorine-containing fluxing agent was added, and vanadium leaching rate was 93% when fluorine-containing fluxing agent was added. The fluorine-containing leaching agent can effectively increase the leaching rate of vanadium. The reason is mainly that the material composition of vanadium-bearing coal is relatively complicated, and the vanadium occurrence and valence state vary. There are usually more than three kinds of vanadium ore in the same ore body, without fluoride The infusion is only leached out of the vanadium (IV)-impregnated portion, but after the addition of the fluorine-containing leaching agent, the vanadium which is more difficult to be immersed is also leached. Because the more difficult to dip part of vanadium ore structure is stable and compact, the addition of fluorine-containing leaching agent can destroy its stable structure, making the ore particles loose and porous, and the Fe(III) in the air oxygen or leachate can easily enter the pores to make it insoluble in acid. The vanadium is oxidized to a tetravalent vanadium which is soluble in acid, allowing vanadium to be released.
(2) Effect of fluorine-containing aids on extraction rate
The effect of the fluorine-containing leaching agent on the extraction rate is shown in Table 2.
Table 2 Effect of 10 stages of countercurrent extraction extract on extraction
Numbering | Raffinate / (mg·L -1 ) | Extraction rate /% | Remarks | ||||
V 2 O 5 | Fe 2 O 3 | F | V 2 O 5 | Fe 2 O 3 | F | ||
1 | 927.0 | / | / | 72.26 | / | / | A 1 , 10h |
2 | 272.3 | / | / | 91.85 | / | / | A 1 , 15h |
3 | 100.2 | / | / | 97.00 | / | / | A 1 , 20h |
4 | 33.5 | / | / | 99.0 | / | / | A 1 , 25h |
5 | 33.0 | 4099 | / | 99.1 | 11.2 | / | A 1 , 30h |
6 | 1081 | / | / | 72.18 | / | / | A 2 , 10h |
7 | 315.2 | / | / | 91.89 | / | / | A 2 , 15h |
8 | 113.6 | / | / | 97.10 | / | / | A 2 , 20h |
9 | 38.5 | / | / | 99.0 | / | / | A 2 , 25h |
10 | 37.0 | 4050 | 4290 | 99.2 | 12.1 | 3.6 | A 2 , 30h |
It can be seen from Table 2 that when the extraction tank is continuously fed for 25 hours, the extraction reaches equilibrium. At this time, the vanadium extraction rates of the fluorine-containing system and the fluorine-free system are 99.2% and 99.1%, respectively, and the extraction rates of iron are 12.1% and 11.2%, respectively. At the same time, it was found that the extraction rate of vanadium was basically the same in each period when the equilibrium was not reached, so it indicated that the fluorine-containing leaching agent had no effect on the extraction and separation of vanadium. The reason is mainly related to the characteristics of the extractant. P204 is an acidic extractant, and the acid extractant HA only extracts cations. The extraction effect is related to the valence of the cation and the ionic radius. In the sulfuric acid system (pH 2), vanadium in the extract solution is present in the form of (VO) S0 4 . VO 2+ stable in the aqueous phase, VO 2+ and F - generates only ionic compound does not form complex ions, despite the presence of the F system, but it does not change the ionic radius and the valence of vanadium, and therefore The extraction of vanadium by fluorine-containing assisted immersion is not affected. For the extraction of iron from P204, since the iron in the extract solution is Fe 2+ , Fe 2+ and F − do not form complex ions. Therefore, the effect of P204 on iron extraction is basically the same in both cases.
(III) Treatment and recycling of nitrogen-containing raffinate
The main components of the fluorine-containing raffinate are Fe 2+ , H + , SO 4 2- , F - , where Ï(Fe 2+ )=4.5g/L, Ï(SO 4 2- )=80g/L, Ï (F - ) = 4.2 g / L, and the acidity was pH = 2. The lime milk rice neutralized the residual liquid, and the main reaction occurred during the neutralization process:
Ca(OH) 2 +H 2 SO 4 =CaSO 4 +2H 2 0
Ca(OH) 2 +FeS0 4 =Fe(OH) 2 1↓+CaS0 4
Ca(OH) 2 +2HF=CaF 2 +2H 2 0
As Ca(OH) 2 is continuously added, when the pH is raised to 7-8, Fe will settle in the raffinate (the measured Fe concentration is 80 mg/L), and a large amount of CaS0 4 will precipitate. . However, k sp (CaF 2 )=1.46×10 -10 , k sp (CaS0 4 )=5.0×10 -6 , CaF 2 is more likely to precipitate, and the supernatant F concentration is 0.2 g/L, so the milk is used. The supernatant of the neutralized raffinate is returned to the leaching tank and F does not accumulate. At the same time, the experiment also showed that the supernatant returned to the leaching tank and did not affect the intrusion effect.
Third, the conclusion
(1) The fluorine-containing leaching agent can effectively increase the leaching rate of vanadium, and the leaching rate of vanadium leaching by sulfuric acid is 80%, and the leaching rate of vanadium can reach 93% after adding 2% fluorine-containing leaching agent.
(2) Using 10 stages of countercurrent extraction, with or without fluorine-containing leaching agent, the extraction rate of vanadium can reach more than 99%. The fluorine-containing leaching agent has little effect on the extraction and extraction separation of vanadium.
(3) The raffinate of the fluorine-containing leaching agent is neutralized by the lime milk until the pH is 7-8, and the supernatant liquid is returned to the leaching tank without causing the accumulation of F.
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