The traditional stone coal extracting vanadium adopts the sodium roasting process. The “three wastes†generated during the vanadium extraction process are seriously polluted by the environment. The “three wastes†are expensive to treat, and most small and medium-sized vanadium plants are closed due to environmental problems. Therefore, researching a new clean-type vanadium extraction process and solving the environmental pollution caused by “three wastes†from the source has become a major issue to be solved in the stone- steam extraction industry.
In recent years, research institutes at home and abroad have carried out a lot of research on new technologies. This research proposes a clean vanadium extraction process to solve the “three wastes†pollution problem in production. The technical route is to solve the pollution problem from the source and waste recycling. Calcination roasting is adopted to avoid the generation of harmful exhaust gas during roasting, and to solve the problem of exhaust gas pollution; the advanced leaching process is selected to change the traditional leaching-vanadium open circuit (discharge after wastewater treatment) into closed loop (direct reuse of wastewater) to solve Wastewater pollution problem; waste residue recycling to solve the waste slag outlet.
First, the experimental process and method
(1) Experimental materials
The vanadium-bearing coal is an oxidized ore in a certain area of ​​Guangxi. The main chemical composition of the ore (%): V 2 O 5 1.38, C 0.52, SiO 2 54.38, Al 2 O 3 26.26, Fe 2 O 3 6.38, S0.22, CaO 6.52 , P 2 O 5 0.19, and other 4.15.
(2) Experimental reagents, equipment and analytical methods
Reagents: ammonium bicarbonate, SM-1, sodium chloride, ammonium chloride, calcium oxide; main equipment: SMCQ180mm × 200mm porcelain lined ball mill , pelletizer (homemade), muffle furnace, constant temperature water bath mixer, SHB-B88 circulating water pumps, φ3cm plexiglass exchange column (homemade), THZ-62 constant pump, HL-2 constant flow pump; analysis: ammonium ferrous sulfate volumetric method.
(3) Experimental methods
Calcination and leaching: The materials are mixed according to different proportions, mixed and watered, and placed in a porcelain boat and placed in a muffle furnace for 2.5 h. A certain amount of crushed calcined sand was weighed into a beaker, a certain amount of leaching agent was added, and the leaching material was stirred by a magnetic stirrer, and the solid-liquid separation was finally leached, and the amount of V 2 O 5 contained in the leachate and the slag was respectively measured.
Ion exchange: using a self-made exchange column, the resin filling amount is 100g, the filling height is 1/3 of the exchange column, and the two ends of the resin are compacted with a perforated ceramic piece wrapped with gauze, and the vanadium solution passes through the exchange column at a certain speed for a certain time. (The time interval is long and short) The concentration of vanadium after adsorption is analyzed. When the adsorption rate is less than 98%, the adsorption is stopped, and the adsorption capacity is calculated.
Adsorption capacity (mg/g) = Q(Co-C)/100
Q is the volume (mL) of the vanadium solution, Co and C are the concentrations of vanadium before and after adsorption, and 100 is the mass (g) of the resin.
Precipitating vanadium: Pour the enriched vanadium solution into a beaker. Add ammonium chloride under rapid stirring. When the ammonium metavanadate precipitation begins, the stirring speed is slowed down and stirring is continued for 1-2 h. The aged ammonium metavanadate crystals were coarsened, then allowed to stand for 12 h, filtered, and the filter cake was washed with a small amount of 2% ammonium chloride solution to obtain crystals of ammonium metavanadate.
Second, test results and analysis
The calcium polyvanadate formed during the calcification roasting process is less soluble in water, so it cannot be directly leached with water. In the ammonium salt leaching process, the calcium polyvanadate formed by calcination is mainly used, and reacted with ammonium hydrogencarbonate to transfer calcium ions into calcium carbonate, and a trace amount of NaHCO 3 is added to control the solution to be weakly alkaline, which is more favorable for the following reaction. get on.
During the leaching process, as long as the temperature is not too high, the NH 4 + concentration is not very high and ammonium metavanadate is not formed. Leaching under weak alkaline conditions, the leaching rate of impurities such as phosphorus , silicon, and aluminum is extremely low. After the leachate is adsorbed and desorbed by the ion exchange column, it can be used for direct vanadium precipitation, and the qualified vanadium pentoxide can be prepared by burning.
(1) Leaching condition test
1. Effect of ammonium bicarbonate concentration on leaching rate
Test conditions: leaching temperature 65-75 ° C, time 2 h, stirring speed 100 r / min, liquid-solid ratio L / S = 2: 1, change the concentration of ammonium bicarbonate solution, the test results are shown in Figure 1.
Figure 1 Relationship between NH 4 HCO 3 concentration and leaching rate
The test results show that at low concentration, the leaching rate of vanadium increases with the increase of the concentration of ammonium bicarbonate, but when the concentration of hydrogen carbonate exceeds 6%, the vanadium leaching rate is almost no longer increased. Therefore, ammonium bicarbonate The leaching concentration is preferably 6%.
2. Effect of leaching time on leaching rate
Test conditions: leaching temperature 65-75 ° C, stirring speed 100 r / min, leaching liquid solid ratio L / S = 2: 1, NH 4 HCO 3 concentration 6%, change leaching time, the test results are shown in Figure 2.
Figure 2 Relationship between leaching time and leaching rate
The results show that with the leaching time prolonged, the leaching rate of vanadium increases, but the leaching time exceeds 2h, and the leaching rate increases. Therefore, the leaching time is preferably 2~2.5h.
3. Effect of leaching temperature on leaching rate
Test conditions: NH 4 HCO 3 concentration 6%, stirring speed 100 r / min, liquid-solid ratio L / S = 2: 1, leaching time 2.5 h, change the leaching temperature, the test results are shown in Figure 3.
Figure 3 Relationship between temperature and leaching rate
It can be seen from the test results that the leaching rate of vanadium is the highest when the leaching temperature is 68 to 73 °C. The calcified roasting calcine is leached with ammonium bicarbonate solution, and the leaching temperature has the greatest influence on the leaching effect.
(2) Dynamic adsorption test of alkaline solution
Calcined calcined with stone coal calcification, leached with NH 4 HCO 3 solution, V 2 O 5 concentration 4.18 g / L, and the leaching solution was tested with 717, 714 resin respectively.
1. Effect of flow rate on adsorption rate
Under dynamic conditions, the temperature of the adsorption solution was 35 ° C, the adsorption pH was 8.0, and the flow rate of the vanadium solution was changed. The flow rate and adsorption effect are shown in Table 1.
Table 1 Effect of flow rate on adsorption effect
Adsorption flow rate /(mL·min -1 ·g -1 ) | Resin model | Penetration volume / mL | Penetration average concentration / (mg·L -1 ) | V 2 O 5 average adsorption rate /% | Penetration capacity / (mg·g -1 ) | Working adsorption capacity / (mg·g -1 ) |
0.07 | 717 | 225 | 20.81 | 99.10 | 94.0 | 155.4 |
714 | 198 | 19.82 | 99.23 | 82.8 | 120.3 | |
0.09 | 717 | 212 | 22.51 | 98.97 | 88.6 | 135.2 |
714 | 160 | 21.98 | 98.01 | 66.9 | 108.3 | |
0.16 | 717 | 121 | 25.10 | 98.12 | 50.6 | 89.3 |
714 | 105 | 25.02 | 98.30 | 43.9 | 88.2 |
It is shown in Table 1 that the penetration adsorption capacity and the working adsorption capacity decrease with the increase of the flow rate. When the flow rate exceeds 0.09 mL/(min·g), the adsorption performance is significant, so the adsorption flow rate is 0.09 mL/(min. · g) is appropriate. The adsorption effect of 717 resin on ammonium salt leaching solution is better than 714 resin.
2. Effect of pH on adsorption performance
The adsorption liquid temperature was 35 ° C, the adsorption speed was maintained at 0.09 mL / (min · g), the pH of the adsorption solution was changed, and when the adsorption rate was greater than 99%, the influence of pH on the adsorption capacity was measured. The test results are shown in Fig. 4.
Figure 4 Effect of pH on vanadium adsorption capacity
The test results show that the ammonium salt leaching solution of vanadium, 717, 714 resin in the pH range of 7.2 ~ 8.2, the adsorption capacity is higher, can reach 125mg / g and 92mg / g.
3. Effect of temperature on adsorption effect
The adsorption rate was maintained at 0.09 mL/(min·g), and the solution pH was 7.8. The temperature of the adsorption solution was changed. The results are shown in Fig. 5.
Figure 5 Effect of adsorption temperature on vanadium adsorption capacity
It can be seen from Fig. 5 that the adsorption effect of the resin is best at 40 to 50 ° C, and when the exchange temperature is higher than 60 ° C or lower than 20 ° C, the adsorption effect of the resin is poor.
(3) Wastewater recycling and reuse test after exchange
The exchanged wastewater was subjected to a continuous cycle recycling test, and a total of 5 cycle tests were conducted. The test mainly investigated the amount of NH 4 HCO 3 , the leaching rate and the product quality. The test results are shown in Table 2.
Table 2 Effect of recycled water on product quality
project | NH 4 HCO 3 | Leach rate /% | Product V 2 O 5 /% |
fresh water | 6.0 | 71.6 | 98.89 |
The first reuse | 2.5 | 72.1 | 99.10 |
The second reuse | 2.0 | 72.3 | 99.02 |
The third reuse | 2.0 | 71.8 | 98.97 |
4th reuse | 2.0 | 72.3 | 99.32 |
The fifth reuse | 2.0 | 72.0 | 99.16 |
It can be seen from Table 2 that after the exchange, the wastewater is supplemented with a small amount of NH 4 HCO 3 to be recycled for leaching. The leaching rate does not change significantly, and the product grade does not decrease. It is more leached than fresh water and reduces the amount of NH 4 HCO 3 by more than 60%. The experimental research shows that it is feasible to recycle the waste water. The reuse of the wastewater can reduce the amount of NH 4 HCO 3 and save water, and reduce the pressure on the environment caused by vanadium extraction.
The vanadium-vanadium wastewater mainly contains a relatively high concentration of ammonium chloride, metavanadate, etc., which can be used as a rinse liquid for saturated resins. The vanadium-bearing wastewater is diluted with fresh water to dilute the concentration of NH 4 Cl, and a certain amount of NaCl is added. It can be used as a de-washing liquid. After continuous re-use test, it is found that the saturated resin is eluted with (120g/LnaCI+60g/L NH 4 C1). Washing, rinsing temperature is 40-~50 °C, the concentration of V 2 O 5 in the de-washing liquid is up to 120g/L or more, the average qualified concentration is above 60g/L, the crystallization of the de-washing liquid is crystallization, and the rinsing rate is 99.2%. the above. Since the eluent is added with NH 4 Cl, it is only necessary to add about 10g/L of NH 4 Cl when the vanadium is added. The ammonium metavanadate starts to precipitate, which saves the amount of NH 4 C1 and saves water resources. Reduce the loss of V 2 O 5 .
Third, the conclusion
Calcination of stone coal calcification, using NH 4 HCO 3 and NaHCO 3 as leaching agent, the leaching solution is purified by 717 resin exchange, and the NH 4 C1 is vanadium precipitated. The purity of the product V 2 O 5 can reach the national standard above 99, the total recovery rate Up to 65%.
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