A basic principle of the principles of ion exchange purification and transformation process is that: strongly basic anion exchange resin W0 4 2-, Cl in an alkaline solution - and impurities As0 4 3-, P0 4 3-, Si0 3 2-, The affinity of SO 4 2- and the like is different. The order of affinity of the strongly basic anion exchange resin for different anions is generally: Other anions, especially Si0 3 2- , P0 4 3- ions with relatively low relative affinity will remain in the exchanged liquid and be separated from WO 4 2- , and the cation Na + will remain in the exchanged liquid and separated from W 4 4 2- . B Industrial Practices a Principle Process See the figure below, the questions that should be explained in the figure are: [next] (1) The resin before adsorption is C1 - type, and W0 4 2- and Cl - are exchanged into the resin phase during adsorption. As0 4 3- , Si0 3 2- , P0 4 3-, etc. mainly enter the exchange liquid. c Main process conditions and technical and economic indicators The main process conditions and technical and economic indicators are as follows. Mountain Bike Pedals,Clipless Bike Pedals,Mtb Mountain Bike Pedals Xingtai Yiming Bicycle Co., Ltd , https://www.ymbicycleparts.com
W0 4 2- ≈ Cl - > SO 4 2- >As0 4 3- > P0 4 3- >Si0 3 2- >CO 3 2- > OH
Table 1 lists the commonly used tungsten metallurgical properties of the anion exchange resin, its separation factor β values may also be seen that the above rule, so that when Na 2 W0 4 solution containing the anionic impurity and Cl - form resin contacts When the concentration of C1 - in the solution is small, an exchange reaction will occur, and W0 4 2- is adsorbed, and the reaction is:
——————
2RCl ​​+ W0 4 2- ==== R 2 W0 4 + 2C1 -
The resin adsorbed with W0 4 2- is desorbed with NH 4 C1, and the reaction is:
——— ——
R 2 W0 4 + 2NH4 ==== (NH 4 ) 2 W0 4 + 2RCl
Therefore, the adsorption of Si, P, As, Sn and the like are simultaneously removed by adsorption and desorption, and the Na 2 W0 4 solution is transformed into (NH 4 ) 2 WO 4 .
a Factors affecting exchange capacity The total exchange capacity of 201×7 resin is about W0 3 360 mg/g dry resin, and the data in Table 1 is the breakthrough exchange capacity when a given concentration of Na 2 W0 4 solution flows through the resin layer. The penetration exchange capacity varies with the concentration of Cl - in the solution, the concentration of W 4 4 2- (in terms of W0 3 ), the concentration of OH - and the linear velocity. The adsorption of 210 × 7 resin has been comprehensively studied, as follows:
(1) Effect of C1 - concentration Since the affinity of C1 - for resin is similar to that of WO 4 2- , the concentration of C1 - seriously affects the exchange capacity, and the initial C1 - concentration increases from 0 g / L to 4.2 g according to the test. /L, under the same conditions, the penetration exchange capacity is reduced by about 1/2. [next]
(2) Effect of W0 3 concentration According to the exchange reaction, each exchange of 1 mol of W0 4 2- will increase 2 mol of Cl - in the solution. This concentration of W 3 3 seriously affects the exchange capacity. The test shows that when the concentration of W0 3 is from 10 g / L When it is increased to 40g/L, the exchange capacity is reduced by 50% to 60% under the same conditions.
(3) NaOH concentration Although the relative affinity of OH - to-resin is much smaller than W0 4 2- , when it is concentrated, it also competes with W0 4 2- for adsorption, when the stock contains W0 3 14.85g/L, When the initial OH - concentration is increased from 10 -3 g/L to 40 g/L, the exchange capacity is reduced by about 30%.
(4) The linear speed linear velocity is too fast, that is, when the solution flows through the resin layer, the contact time with the resin is too short, and it is too late to completely exchange, and the premature penetration occurs, so that the exchange capacity is lowered, generally 5~10 cm/min is suitable. .
b Factors affecting the desorption effect The desorption process usually uses NH 4 Cl + NH 4 0H as a desorbent. The role of NH 4 OH is mainly to prevent the pH of the solution from being too low, so that APT crystals are formed.
The concentration and flow rate of NH 4 Cl significantly affect the desorption effect as shown in the two figures below. 
(2) When the Processing Standards scheelite or wolframite concentrates concentrate, before switching liquid less impurities, generally without rinsed with eluent impurity, washed with water only after the direct desorption; complex when dealing with low-grade In the case of tungsten ore, the impurities in the liquid before the exchange are higher, and the process of leaching and removing impurities is required.
(3) The desorbed resin is a Cl - type. It can be transferred to the adsorption of the next cycle without treatment.
b Equipment China adopts ion exchange column for dynamic exchange. There is sieve plate at the bottom of the column. The pre-exchange liquid and the desorbed liquid are successively flowed through the resin layer for adsorption and desorption. The characteristics are simple structure and operation, common specifications and production. The capabilities are shown in Table 2.
Composition of crude sodium tungstate solution: W0 3 15~30g/L;
Line speed when switching: 6~l0cm/min;
Leaching and desorption line speed: 2~4cm/min;
The removal rate of adsorption process: As is 85%~95%; P and Si0 2 are 90%~95%; Sn is more than 95%;
Total removal rate of adsorption and leaching: P, As, Si0 2 and Sn are both 95% to 99%;
The total recovery of the process is greater than 99%;
Production of 1t of W0 3 consumes 0.45~0.65t NH 4 Cl, 1~1.5 kg of resin.
Product quality: After the desorption liquid is crystallized by evaporation, when the crystallization rate is controlled by about 90%, the impurities in the product APT can meet the requirements of GB10116-88APT - 0, but the content of molybdenum and tin may exceed the standard due to the high content of the raw material, K And Na may also exceed the standard due to excessive K and Na in NH 4 Cl.
Preparation of pure tungsten compound - ion exchange purification and transformation process
Table 1 Properties of some resins used for tungsten ion exchange
Brand
201×17 (717)
W A
W201
Amberlite 4200C
Amberlite 400C
Penetration exchange capacity during dynamic adsorption in the exchange column (mass ratio of WO 3 to dry resin)
0.25~0.28 (pre-exchange liquid WO 3 20g/L)
0.30~0.35 (pre-exchange liquid WO 3 30g/L)
0.28~0.31
~0.32
~0.32
Separation coefficient with different anions
β WO4 2- /MoO4 2-
(1)0.85
(2) 0.69
β WO4 2 / OH -
37.6~31.7([OH])=4~10g/L
37.9~3.08([OH]=4~10g/L)
50.7~40.9([OH]=4~10g/L)
β WO4 2 / So4 2-
2.5~3.78([SO 4 2- ])=0.04~0.8g/L
β WO4 2 / AsO4 3-
(1) 9.5~11.1 ([As]=0.04~0.16)
(2) 10.6~10.8 ([WO 3 ]=16g/L
[As]0.37~0.69g/L)
10~14([As]=0.04~.16g/L)
12.8~20.5([As]=0.04g/L)
β WO4 2 / Cl -
0.65~1.09 ([WO 3 ]=25g/L
Cl - 37~0.7g/L)
β WO4 2 / CO3 2-
33
44.7
Table 2 Specifications and production capacity of common ion exchange columns
specification
Ф1.2m×6m
Ф1.4m×7m
Ф1.5m×9m
Ф1.6m×8m
Ф2m×12m
Production capacity
0.6~0.7
t(APT)16h
1.0~1.1
t(APT)16h
1.1~1.4
t(APT)18h
1.7~1.8
t(APT)24h
4
t(APT)24h