A Basic principle a Main reaction and thermodynamic conditions
The leaching reaction of scheelite scheelite sodium carbonate is:
CaW0 4 (s)+Na 2 C0 3 (aq) ==== Na 2 W0 4 (aq)+CaC0 3 (s) (1)
According to the measurement, the concentration equilibrium constant Kc and the activity equilibrium constant Ka of the reaction formula (1) are shown in Table 1. From the table, it is known that the Kc value of the reaction decreases as the amount of soda increases. Wolframite wolframite carbonate leaching reaction is:
Temperature / °C | 90 | 175 | 200 | 225 | 250 | 275 | 300 | |||||||||
Sodium carbonate consumption (multiple of theoretical amount) | 1.0 | 1.0 | 1.0 | 1.5 | 2.0 | 2.5 | 0.75 | 1.0 | 1.5 | 2.0 | 1.0 | 1.5 | 2.0 | 1.0 | 1.0 | |
Kc | (п.M. Pellov) (1958) | 0.46 | 1.21 | 1.45 | 1.19 | 0.96 | 0.67 | 1.56 | 1.52 | 1.49 | 0.99 | 1.85 | 1.61 | 0.97 | ||
T.щ.Agnov (1986) | 0.97 | 1.46 | 1.52 | 1.37 | 0.99 | 1.63 | 1.57 | |||||||||
Ka (Agnov) | 1.15 | 1.34 | 1.51 | 1.66 | ||||||||||||
(Fe,Mn)W0 4 (s)+Na 2 C0 3 (aq)Na 2 W0 4 (aq)+FeC0 3 (s) (or MnC0 3 (s))
Or FeW0 4 (s) + Na 2 C0 3 (aq) Na 2 W0 4 (aq) + FeC0 3 (s)
MnW0 4 (s) + Na 2 C0 3 (aq) Na 2 W0 4 (aq) + MnC0 3 (s)
FeC0 3 (s)+2H 2 0 Fe(OH) 2 (s)+H 2 C0 3 (aq)
He(OH) 2 (s)Fe 3 0 4 (s)+2H 2 0+H 2
MnC0 3 (s)+2H 2 0 Mn(OH) 2 (s)+H 2 C0 3 (aq)
T. III. Agnov measured the reaction of synthetic FeW0 4 , MnW0 4 and Na 2 C0 3 , and found that at 200-275 ° C, almost all of the FeC0 3 produced by the reaction was hydrolyzed, and the slag contained a large amount of Fe 3 0 . 4 , and only 3% to 11% of the produced MnC0 3 is hydrolyzed to Mn(OH) 2 . The concentration equilibrium constant Kc of the reaction of FeW0 4 and MnW0 4 with Na 2 C0 3 was also measured (see Table 2).
materials | Sodium carbonate dosage: 1 times the theoretical amount | The amount of sodium carbonate is 2 times the theoretical amount. | |||
200 ° C | 225 ° C | 250 ° C | 275 ° C | 225 ° C | |
FeWO 4 | 1.10 | 1.51 | 2.25 | 3.00 | 0.80 |
MnWO 4 | 1.39 | 1.51 | 1.56 | 1.53 | 0.94 |
Synthetic (Fe, Mn) WO 4 , Fe: Mn = 1:1 (molar ratio) | About 1.3 | ||||
Natural wolframite | 1.1 | ||||
b. Kinetics of the process and the factors affecting the leaching rate. Many authors tend to think that when the temperature is above 155 ° C and the stirring speed is fast enough, the process is controlled by chemical reaction, so increasing the temperature can greatly speed up the reaction and shorten the reaction. time. T. class. Ivanov noted that the leaching rate Agger natural wolframite ore iron ore was significantly lower than native tungsten, tungsten ore (containing 16.14% FeO and 6.49% MnO), the relationship of the initial leaching rate in the temperature 225 to 250 The reaction control law is in the range of °C, the apparent activation energy is 100kJ/mol, and the temperature above 250°C is in accordance with the diffusion control law, and the apparent activation energy is 25 kJ/mol. For tungsten-manganese ore (containing 13.75% MnO, 4.89% FeO), the reaction is controlled in the range of 225-300 °C, and the apparent activation energy is 100 kJ/mol. For the above two kinds of ores, as the reaction progresses at a certain temperature, the product film gradually thickens and gradually transitions to diffusion control.
Factors affecting the rate of leaching:
(1) Temperature II. When M. Pellov treated the scheel concentrate containing 25.1% W0 3 , when the temperature was 280 ° C, even if the amount of sodium carbonate was only 2.25 times of the theoretical amount, the slag contained within 15 min W0 3 can also be reduced to 0.048%. Therefore, Pellov and others believe that increasing the temperature to reduce the amount of sodium carbonate and increase the leaching rate is one of the current efforts of high-pressure leaching of sodium carbonate. At the same time, however, the leaching rate of impurities also increases. PB Kui has also produced similar results.
(2) The amount of sodium carbonate and the initial concentration of sodium carbonate When the initial concentration is constant, the amount of sodium carbonate increases the leaching rate; when the amount of sodium carbonate is constant, the initial concentration decreases the leaching rate. Therefore, it is generally considered that the initial concentration of Na 2 C0 3 is preferably from 70 to 200 g/L. Microscopic observation and chemical analysis of the residue showed that when the concentration of Na 2 C0 3 exceeded 230 g/L, the residue also contained a double salt with a composition of approximately Na 2 C0 3 ·CaC0 3 and a trace amount of Na 2 C0 3 ·2CaCO 3 .
Strengthening of sodium carbonate high pressure leaching process:
(I) Mechanical activation AH Zelikman et al. have conducted a large number of studies, indicating that the leaching rate of the tungsten ore is significantly improved after the mechanical activation. For example, a scheelite concentrate containing 7.4% W0 3 under the same conditions, when previously activated in a centrifugal mill, has a leaching rate of 96.9%, and the leaching rate is only 84.9% without activation.
The experiment also shows that the apparent activation energy of the reaction of scheelite with Na 2 C0 3 is reduced from 54.78 kJ/mol to 12.71 kJ/mol, and the apparent activation energy of leaching tungsten-manganese ore is reduced from 46 kJ/mol to 20 kJ/mol. .
(2) Thermal activation The ore is calcined at high temperature and quenched. In the case of quenching and rapid heat, there is thermal stress in the mineral or maintains its high temperature phase, so it is in a high energy state, and at the same time due to quenching Thermal stress causes cracks in the minerals, which are beneficial to increase the leaching speed. T. ILK. Anovov thermally activated scheelite containing 33.32% W0 3 , 2.3% Mo, 30.35% Ca0, 3.75% Si0 2 , 0.5% organic matter, and then the theoretical amount of sodium carbonate at 225 ° C When the leaching is carried out under the condition of 2.5 times, the leaching rate of W0 3 can be increased by 1 to 2 percentage points.
(3) Ultrasonic activation of HH Havsky (XaBCKHri) and other equipment in a capacity of 210L test shows that under the action of 5-lOkHz ultrasonic wave, when the amount of sodium carbonate is three times the theoretical amount, the working pressure is 0.7MPa. Under the condition of 1/4 solid/liquid ratio, the leaching rate of scheelite is 3%~7% higher than that without ultrasonic wave. AA Behsinksky also pointed out that even under the action of ultrasonic wave, even sodium carbonate Only 1.6 to 1.8 times the theoretical amount, within 2.5 h, the leaching rate is 86% to 88%, which is doubled compared with no ultrasonic action.
c behavior of sodium carbonate and impurities during extraction under pressure high pressure sodium carbonate impurity suppressed during the extraction of the apatite starting material, arsenopyrite, scorodite, fluorite, apatite, silicate, aluminum portion can be calcium carbonate ore response sodium hydrogen phosphate, sodium hydrogen arsenate, sodium fluoride into solution, but addition of calcium molybdenum ore leaching takes rate of 80% to 90%, other impurities leaching The rate is very low. Generally, the leaching rates of phosphorus, arsenic and silicon are all below 5%. In the absence of oxidant, sulfide ore, such as molybdenum ore, stibnite , etc., basically do not undergo leaching reaction.
Tests have shown that the addition of A1 2 0 3 or magnesium compounds during the high-pressure leaching of sodium carbonate is beneficial to inhibit the leaching of SiO 2 and some phosphorus and arsenic, for example, containing 12.75% W0 3 , 13.7% Si0 2 , 0.407% P, O. In the leaching process of 019% As white tungsten ore, when A1 2 0 3 is not added, the final leachate contains Si, P and As are 0.86g/L, O.013g/L and 0.O11g/L, respectively. When A1 2 0 3 was added, Si, P and As in the final leachate were reduced to 0. 0092g/L, O.006g/L and 0.0065g/L, respectively, for white containing 31.7% WO 3 and 1.08% SiO 2 . When high-pressure leaching of tungsten ore is carried out, 5.2% of magnesium salt is added , and the content of SiO 2 in the leaching solution is reduced to (1~5) and 10 -4 g/L.
B Industrial Practices a The equipment autoclave is available in both vertical and horizontal versions. The vertical kettle volume is usually 3~5m 3 . Autoclave reactor body horizontal low-alloy steel welded, a diameter of about 1.5 ~ 1.8m, length 10 ~ 15m, a wall thickness of 25 ~ 30mm, the rotation speed is generally 2 ~ 3 r / min, the autoclave contents ball, during rotation It can remove the scale on the wall of the kettle, and the steam and slurry pass through the steam pipe and the slurry pipe respectively.
b Process The process is divided into continuous operation and intermittent operation. The equipment flow of the continuous high pressure leaching of the vertical kettle in the chemical treatment plant of Golden Island White Gold Company of Australia is shown in the figure below. Continuous operation facilitates mechanization and automation, while the amount of steam is uniform, energy consumption is low, and equipment production capacity is high. After a factory in the former Soviet Union changed the intermittent operation to direct steam heating for continuous operation, the production capacity was doubled. [next]
   c Technical conditions and technical and economic indicators
The technical conditions and technical and economic indicators of some factories are shown in Table 3.
raw material | Process conditions | Leaching result | Remarks | ||||
Na 2 CO 3 dosage (multiple of theoretical amount) | Liquid/solid | Temperature / °C | Time / h | Leach rate /% | Slag containing WO 3 /% | ||
Low grade scheelite ore containing 10% to 25% WO 3 | About 5 | 190~200 | 1.5~2 | 98 | 0.2~0.6 | The recovery rate from medium mine to APT is 95% | |
8%~15% WO 3 in low grade scheelite | 4~5, plus a theoretical amount of 0.5 times NaOH | Pulp density 1.7g/cm 3 | 80 | 4 | 97.5~98.7 | About 0.1 | Leaching mother liquor composition / (g · L -1 ): 45WO 3 , 2F, 1Si |
Tungsten ore contains 45%~50% WO 3 , 5%~6% Mo | 3.5~4, when using two stages of leaching time is 2.5~3 | ~3 | 99 | Leaching mother liquor composition / (g·L -1 ): 100~130WO 3 , 5~8Mo, 80~90Na 2 CO 3 , 1.5~2SiO 2 , 3~4F | |||
Tungsten fine mud contains 12.6% WO 3, of which white tungsten and black tungsten each account for about 50%: 0.019% As, 0.14% Mo, 0.49% P, 13.7% SiO 2 | 3.85, plus 3% NaOH | 1.3~1.5 | 210 | 2~3 | 98.06 | 0.3 | Two-stage cross-flow leaching |
3.85, plus 5% of Al 2 O 3 | 97.61 | 0.35 | Two-stage cross-flow leaching | ||||
Tungsten fine mud contains: 28.86% WO 3 , of which black tungsten accounts for 39.2% of total tungsten | 4.5, plus 5% NaOH | 2.8 | 210~220 | 2~3 | 96~98 | 0.6~0.8 | Leachate composition / (g · L -1 ): 86WO 3 ; 0.135 SiO 2 ; 0.1P; 0.05As |
Black and white tungsten mixed tungsten concentrate | 2.2, plus a theoretical amount of 0.2 times NaOH | 230 | 2 | 99 | |||
Tungsten fine mud contains 16.5% WO 3 , 21% SiO 2 | 3.0, plus 2% NaOH, 3% Al 2 O 3 | 185~195 | 2 | 98~99 | 0.15~0.2 | Leachate composition / (g · L -1 ): 0~80WO 3 , 0.005As, 0.01P, 0.02Si, 1~2F | |
   d sodium carbonate recovery
Since the amount of sodium carbonate in the boiling is up to 2.5 to 5 times the theoretical amount, a large amount of Na 2 CO 3 remains in the mother liquor, wherein Na 2 CO 3 /WO 3 reaches 0.8 to 1.6 (mass ratio). There are many methods for recovering sodium carbonate from the mother liquor, but no industrialization has been reported. For details, see pages 72-77 of Reference [1].
references:
1. Li Honggui, editor. Non-ferrous metal extraction metallurgy manual: rare high melting point metal coil (top). Beijing: Metallurgical Industry Press, 1999
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