Basic principle of high pressure leaching method for tungsten mineral sodium carbonate

First, the main reaction and its thermodynamic conditions

(1) scheelite

The reaction of white cast iron carbonate leaching is:

(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.

Table 1 Concentration equilibrium constant and activity equilibrium constant of reaction formula (1)

(2) Black tungsten ore

The reaction of sodium tungstate sodium carbonate leaching is:

Т.Щ.Agnov measured the reaction of synthetic FeWO ₄ , MnWO ₄ and Na ₂ CO ₃ , and found that almost all of the FeCO ₃ formed by the reaction at 200-275 ° C was hydrolyzed, and the slag contained a large amount of Fe ₃ O _{4 .} And only 3% to 11% of the produced MnCO ₃ is hydrolyzed to Mn(OH) ₂ . The concentration equilibrium constant Kc of the reaction of FeWO ₄ and MnWO ₄ with Na ₂ CO _{3 was} also measured (see Table 2).

Table 2 Kc values ​​of FeWO ₄ , MnWO ₄ , (Fe, Mn) WO ₄ and Na ₂ CO ₃ (Т.Щ.Agnov)

Second, the dynamics of the process and the factors affecting the rate of leaching

The mechanism of the reaction. 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. Ivanov noted that the leaching rate Т.Щ. Agger natural wolframite ore iron ore was significantly lower than native tungsten, tungsten ore (containing 16.14%, FeO, and 6.49% MnO), its initial velocity and temperature leaching The relationship is in the range of 225-250 °C, and the apparent activation energy is 100kJ∕mol. The temperature above 250°C is in accordance with the diffusion control law, and the apparent activation energy is 25kJ/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.

(1) Factors affecting the leaching rate:

1, temperature. When П.Ðœ.Pellov is treating scheel concentrate containing 25.1% WO ₃ , when the temperature is 280 ° C, even if the amount of sodium carbonate is only 2.25 times of the theoretical amount, the slag containing WO ₃ within 15 minutes can also be lowered. 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 Na0 ₂ CO ₃ is preferably from 70 to 200 g ∕L. The residue microscopic observation and chemical analysis showed that, when Na ₂ CO ₃ concentration exceeds 230g / L, the residue was also present in the component of approximately Na ₂ CO ₃ · CaCO ₃ double salt and trace amounts of Na ₂ CO ₃ · 2CaCO _3.

(2) Strengthening of high-pressure leaching process of sodium carbonate:

1. Mechanical activation. A large number of studies have been carried out by AH Zelikman et al., indicating that the leaching rate of the tungsten ore is significantly improved after the mechanical activation. For example, a scheelite concentrate containing 47.4% WO 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 between scheelite and Na ₂ CO ₃ is reduced from 54.78kJ∕mol to 12.71kJ∕mol, and the apparent activation energy is reduced from 46kJ∕mol to 20kJ∕mol when leaching tungsten manganese ore. .

2. Thermal activation. The ore is calcined at a high temperature and quenched. In the case of rapid cooling and rapid heat, there is thermal stress in the mineral or maintains its high temperature phase, and thus is in a high energy state, and in the mineral during quenching due to thermal stress. Cracks are generated, which are all beneficial to increase the leaching speed. Т.Щ.Agnov heat-activated scheelite containing 33.32% WO ₃ , 2.3% Mo, 30.35% CaO, 3.75% SiO ₂ , 0.5% organics, 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 rate of WO ₃ can be increased by 1 to 2 percentage points.

3. Ultrasonic activation. HH Havsky (Хавский) and other tests in a 210L capacity test showed that under the action of 5-10 kHz ultrasonic wave, when the amount of sodium carbonate is 3 times the theoretical amount, the working pressure is 0.7 MPa, the solid/liquid ratio Under the condition of 1/4, the leaching rate of scheelite is 3% to 7% higher than that without ultrasonic wave. AA Bierxin has also pointed out that under the action of ultrasonic wave, even if the amount of sodium carbonate is only 1.6 of the theoretical amount. ~1.8 times, within 2.5h, the leaching rate is 86% to 88%, which is doubled compared with no ultrasonic action.

3. Behavior of impurities and suppression of impurities during high pressure leaching of sodium carbonate

The reaction can be part of a high-pressure sodium carbonate leach process apatite feedstock, arsenopyrite, scorodite, fluorite, apatite, silicate, molybdenum ore, calcium carbonate and sodium hydrogen phosphate generated , sodium arsenate, sodium fluoride, etc. into the solution, but in addition to the leaching rate of calcium molybdate ore of 80% to 90%, the leaching rate of other impurities is very low, generally phosphorus, arsenic, silicon leaching rate All of them are 5% or less, and in the absence of an oxidizing agent, sulphide ore such as molybdenum ore, stibnite or the like does not substantially undergo a leaching reaction.

The test proves that the addition of Al ₂ O ₃ or magnesium compound 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% WO ₃ , 13.7% SiO ₂ , 0.407% P, 0.019%. In the leaching process of As in the scheelite, when Al ₂ O ₃ is not added, the final leaching solution contains Si, P and As, respectively, 0.86 g/L, 0.013 g ∕L and 0.011 g ∕L, and Al _{2 is} added. At O ₃ , the final leaching solution contains Si, P and Ag reduced to 0.0092 g ∕L, 0.006 g ∕L and 0.0065 g ∕L, respectively, and high pressure leaching of the white tungsten ore containing 31.7% WO ₃ and 1.08% SiO ₂ . At the time of adding 5.2% of the magnesium salt , the SiO ₂ content in the leaching solution is reduced to (1 to 5) × 10 ^-4 g ∕ L.

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