A Na 2 W0 4 solution purification of phosphorus, arsenic, silicon, fluorine, Na 2 W0 4 solution, silicon, phosphorus , molybdenum , fluorine, tin and other impurities must be removed in advance. According to the current production process, the impurity content of the purified Na 2 W0 4 solution (including W0 3 150g/L) is generally as follows: Mo<0.05g/L; As<0.Olg/L; P<0.Olg/ L; Si <0.05 g/L. At present, the impurity removal rate of the chemical purification process varies with the solution quality. For the solution of the standard concentrate, the Sn, S can be as high as 99.9%, except Si can be as high as 98% to 99%, and P is 95% to 99%. , As is 85% to 90%.
a Basic principle In addition to silicon in Na 2 W0 4 alkaline solution (pH = 14 or so), silicon is generally present as SiO 3 2- , and the solution is neutralized with acid or chlorine to pH = 8 to 9, 50% or more. The silicon is removed by precipitation with H 2 SiO 3 and the remainder is removed during precipitation of the magnesium salt . The neutralization and removal of silicon is:
Na 2 Si0 3 +2HC1 (or H 2 SO 4 )==== H 2 Si0 3 ↓+2NaC1 (or Na 2 S0 4 )
At this point, Na 2 SnO 3 in the solution is also hydrolyzed to a Sn(OH) 4 precipitate to remove:
Na 2 Sn0 3 +3H 2 0 ==== Sn(OH) 4 ↓+2Na0H
In order to prevent the formation of colloidal H 2 SiO 3 , the silicon removal operation should be carried out under boiling conditions, and sometimes a small amount of polyacrylamide is added as a flocculant.
Phosphorus, arsenic , fluorine, phosphorus, arsenic, and fluorine are removed by precipitation of Mg 3 ( P0 4 ) 2 , Mg 3 ( As0 4 ) 2 , and MgF 2 which are insoluble with Mg 2+ , or can be mixed with Mg 2 . + , NH 4 + forms MgNH 4 P0 4 with a smaller solubility product, and MgNH 4 As0 4 is precipitated and removed. Its main reaction is:
2Na 2 HP0 4 +3MgC1 2 ==== Mg 3 (P0 4 ) 2 +4NaCl+2HC1
2Na 2 HAs0 4 +3MgCl 2 ==== Mg 3 (As0 4 ) 2 +4NaC1+2HC1
Na 2 Si0 3 + MgC1 2 ==== MgSi0 3 + 2NaC1
2NaF+MgC1 2 ==== MgF 2 +2NaCl
Na 2 HP0 4 +MgC1 2 +NH 4 0H ==== MgNH 4 P0 4 +2NaCl+H 2 0
Na 2 HAs0 4 +MgC1 2 +NH 4 OH ==== MgNH 4 As0 4 +2NaCl+H 2 0
The solubility products of the above poorly soluble compounds are shown in Table 1 below.
Compound | Mg 3 (PO 4 ) 2 , 25 ° C | Mg 3 (PO 4 ) 2 , 100 ° C | Mg 3 (AsO 4 ) 2 , 25 ° C | MgF 2 , 27 ° C |
Solubility product | 1.62×10 -25 | 4.47×10 -32 | 2.04×10 -20 | 6.4×10 -9 |
Compound | MgNH 4 PO 4 , 25 ° C | MgNH 4 AsO 4 , 25°C | MgSiO 3 , 25 ° C | |
Solubility product | 2.5×10 -13 | ~1.8×10 -12 | 1.29×10 -12 |
b Industrial practice The operation of the magnesium salt method and ammonium magnesium salt method in the industry, process conditions, equipment, and main control factors are summarized in Table 2. [next]
method | Operation process and conditions, equipment | Main controlling factor | Advantages and disadvantages |
Magnesium salt method | Under stirring and boiling conditions, neutralize with free NaOH1±0.2g/L with 3-4mol/L HCl or Cl 2 , boil for 20~30min, add MgCl 2 solution with density 1.16~1.18g/m 3 to free NaOH0.2 ~0.4g/L, boil for 30min, clarify and filter. The main equipment is steel steam heating agitation tank and filter press | Temperature: boil The final pH=9 is appropriate | Advantages: one-time precipitation filtration to remove phosphorus, arsenic, silicon, simple operation; disadvantages: large amount of slag and loss of WO 3 |
Ammonium magnesium salt method | Under stirring and boiling conditions, use 3~4g/L, boil for 30min, add NH 4 Cl solution to pH=8~9, and precipitate the silica residue. Add NH 4 OH to the filtrate pH = 10~11, add the calculated amount of MgCl 2 solution, stir at 50 °C for 30~60min, clarify and filter | In the silicon removal stage, the temperature and pH are controlled as above. In the phosphorus removal and arsenic stages, when the pH value is too low, the ammonium and magnesium salts of phosphorus and arsenic will be hydrolyzed to form phosphorus with high solubility, magnesium arsenate (pH=7), and even ammonium ammonium double salt precipitation of tungsten (pH= 6 or so) | Advantages: small amount of slag and WO 3 loss, better impurity removal effect than magnesium method; disadvantages: need secondary precipitation filtration, more complicated operation |
After the phosphorus and arsenate slag produced by the magnesium salt method is boiled by NaOH, the slag composition (dry amount) is: 2%~9% WO 3 , 0.4%~1.4% As, 0.3%~0.5%P, 3.8%~16.7 % SiO 2 , 30.3%~44.4% MgO.
B was prepared from pure transition pure Na 2 WO 4 (NH 4) 2 W0 4 solution
a Organic solvent extraction method transformation Basic principles (1) Extractant In the tungsten extraction process, the commonly used extractants are mainly organic amines and quaternary ammonium salts, and organic amines are divided into primary, secondary and tertiary amine extractants.
In an amine extraction system, the organic phase typically consists of an amine, a phase modifier, and a diluent. As the phase modulator are tributyl alcohols, ketones and vinegar phosphate (TBP), but most of the alcohol used, as a multi-use coal oil diluent. The ratio of the above three solvents depends on the extraction conditions. The performance of some extraction systems for tungsten extraction is shown in Table 3.
Organic phase composition /%(v) | Distribution ratio D W | Extraction conditions |
10% N235+90% kerosene | 2.18 | Na 2 WO 4 stock solution: 152.7 g / L WO 3 , pH = 3.09, compared to (o / a) = 1, grade 1, room temperature |
10% TOA (n-trioctylamine) + 90% kerosene | 2.40 | |
10% TIOA (triisooctylamine) + 90% kerosene | 0.073 | |
15% N 235 +15% octanol + 70% kerosene | 18.9 | |
15% N 263 +15% octanol + 70% kerosene | 4.12 |
Note: N235 - alkylamine; N263 - quaternary ammonium salt.
When organic amines, first with an inorganic acid (common H 2 S0 4) and the organic phase separation the amine to form amine salts, for example with 2 ~ 3mol / LH 2 SO 4 action, then:
2R 3 N(org)+H 2 SO 4 (aq)====(R 3 NH) 2 S0 4 (org)
When using H 2 SO 4 ≥ 5mol/L, then: [next]
R 3 N(org)+H 2 SO 4 (aq)====(R 3 NH)HS0 4 (org)
(2) The process of extracting tungsten first acidizes the Na 2 W0 4 solution with a mineral acid (such as H 2 SO 4 ) to pH = 2.5 ~ 3.0, and tungsten (HW 6 0 21 ) 5- , (H 2 W 12 0 40 ) 6- , (W 12 0 39 ) 6-, etc. exist. When these solutions are contacted with the acidified tertiary amine, an anion exchange extraction reaction takes place.
The reaction of tertiary amines with tungsten (VI) differs in different literature reports, that is, the molar ratio of extractant to tungsten in the extract fluctuates between 1:3 and 1:2. Therefore, some authors have proposed a general formula for the extraction of tungsten from a tertiary amine, that is, in the case of Na 2 W0 4 solution pH=1~3, the volume ratio is: %Alamine336: sterol: kerosene is 7:7:86 organic The general formula of the extracted tungsten (VI) is:
n
——(R 3 NH·HS0 4 ) 2 (org)+(W x O y H z ) n- (aq)
2
=(R 3 NH)n·W x 0 y H z (org)+n(HSO 4 2- )(aq)
According to Kim et al., the anion of tungsten in the formula is (W 12 0 40 H 2 ) 6- , (W 6 0 21 H) 5- (at low tungsten concentration) and (W 12 ) in this pH range. 0 40 ) 8- .
When silicon, phosphorus, arsenic and molybdenum are present in the Na 2 W0 4 solution, they are extracted with the tungsten-forming heteropoly acid anion by the tertiary amine under the conditions of solution pH=2.5~3.0, so that not only the final tungsten product is contaminated. And it also brings difficulties to the extraction operation. For example, heteropolyacid (SiW 12 0 40 ) 4- , (PW 12 0 40 ) 3- , (AsW 12 0 40 ) 3- and the amine-derived extract are viscous materials with a density greater than 1 g/cm 3 , The overflow is blocked when it settles to the bottom of the extractor. Therefore, when these impurities are present, F - ion (added as a fluoride salt) is first added to the liquid to form H 2 SiF 6 , HPF 6 or the like which is not extracted.
(3) Stripping process In order to directly obtain the (NH 4 ) 2 W0 4 solution, industrially, ammonia (or a part of ammonium tungstate) is used for stripping tungsten. For different organic phase extract compositions, the stripping reactions are as follows:
(R 3 NH) 4 H 2 W 12 0 39 (org)+24NH 4 0H(aq)====4R 3 N(org)+12(NH 4 ) 2 WO 4 (aq)+15H 2 0
(R 3 NH) 6 (H 2 W 12 0 40 )(org)+24NH 4 0H(aq)===6R 3 N(org)+12(NH 4 ) 2 W0 4 (aq)+16H 2 0
(R 3 NH)5H(H2W 12 0 40 )(org)+24NH 4 0H(aq)====5R 3 N(org)+12(NH 4 ) 2 W0 4 (aq)+16H 2 0
It can be seen that although the composition of the extract in the organic phase is different, 1 mol of tungsten consumes 2 mol of ammonia. The concentration of ammonia used is generally 3~4mo1/L NH 4 0H, and the equilibrium water at the end of the stripping is maintained at pH=8.5.
The industrial process of using tertiary amines to extract tungsten is described in the following figure.
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The conditions and indicators of each stage of the tertiary amine tungsten extraction process are shown in Table 4.
Stage name | Technical conditions | index | Composition of each material |
extraction | Compared with (o/a)=1, mixing 2~3min, temperature 25~40°C, 3~5 level countercurrent | The tungsten extraction rate is greater than 99%, and the raffinate is less than 0.1g/L WO 3 | 1 organic phase φ /%: 10 tertiary amine + 10 octanol + 80 kerosene, acidity (H 2 SO 4 ) 0.1 ~ 0.2mol / L; 2Na 2 WO 4 liquid solution: (WO 3 ) 90~100g/L, pH=2.5~3; 3 extraction lotion and backwashing agent are pure water; 4 acidifier is (H 2 SO 4 ) 0.1~0.2mol/L; 5 stripping agent is (NH 4 OH) 3~4mol/L |
Extraction | Compared with (o/a)=4~5, mixing 2~3min, temperature 25~40°C, 3~5 level countercurrent | The WO3 content in the eluate is less than 0.5g/L | |
Back extraction | Compared with (o/a)=3 (without water phase reflux), mixing for more than 10min, temperature 25~40°C, 1st stage tank reflow | The stripping rate is greater than 99%, and the stripping solution is 250~300g/L WO 3 | |
Backwash | Compared with (o/a)=4~5, mixing 2~3min, temperature 25~40°C, 3~5 level countercurrent | Less than 0.5g/L WO 3 in the eluate | |
acidification | Compared with (o/a)=5, mixing 2~3min, temperature 25~40°C, 2~3 level countercurrent |
纳尔契斯克hydrometallurgical treatment plant conditions scheelite concentrate Su pressure cooking liquor by extraction, equipment and results are as follows.
Process conditions:
Organic phase Shanghai φ /%: 20 tertiary amine, 20 isooctanol, 60 kerosene;
Composition of feed liquid / (g·L -1 ): (W0 3 ) 45~55; (Mo) 0.03~0.05; (Si0 2 ) 0.03~0.06; (F - )0.1; (NaCl) 50~60.
Equipment extraction and washing of the organic phase are carried out in a pulse packed column with a distributor, and the back extraction is carried out in a mixing clarifier. A 1.6M titanium member column diameter pulse, high filler l0M region, with two refining zone, a pulse frequency of 50 times / min, the amplitude of 20mm, a total column volume of 30m 3, according to the production capacity of a total of two phases 50M 3 / h. The ratio in the pulse tower is about 1. Washing with water at the top of the column, compared to (o~a) (5~10):1, the tungsten-rich organic phase coming out of the column flows into the second packed column (without pulse) and is treated with a stabilizer. The diameter of the column is 1.3m. Stripping the mixer-settler with a mixing and refining chambers are 5m 3 and 16m 3. The stripped organic phase was sent to a third packed column (without pulse) for water washing and the column diameter was 1.6 m.
The distribution of tungsten and other components in the process is shown in Table 5.
Material name | WO 3 | Mo | SiO 2 | F - | NaCl | NH 3 | NH 4 Cl |
Liquid | 45~55 | 0.03~0.05 | 0.03~0.06 | 0.1 | 50~60 | ||
Raffinate (pH=2~2.5) | 0.1~0.3 | 0.01~0.03 | 0.05 | 50~60 | |||
Acidification residue (pH=1.5~2) | 0.018~0.03 | 0.01 | 0.04 | ||||
Stripping solution | 250~300 | 0.2~0.3 | 0.08~0.18 | 0.25 | 10~20 | 20~25 | |
Stripping solution | 4~8 | 3~5 | |||||
Evaporation crystallization mother liquor | 40~60 | 0.4~0.8 | 0.1~0.4 | 0.4~0.5 | (pH=7) | 40~50 |
The Na 2 W0 4 solution obtained by the American Union Carbide Corporation by pressing with soda is 55~110g/L W0 3 , 2.1~4.5g/L Mo, pH=10.5~11.0. First remove molybdenum. After removal of molybdenum, the solution contained 51.8 g/L W0 3 , 0.0012 g/L Mo, and O.75 g/L Si0 2 . The organic phase was 5 (V)% tridecylamine-10 (V)% dodecanol-kerosene. 3-stage countercurrent extraction in a mixing clarifier. The extraction was 1 compared to 0/A and the wash (0/A) was 1:0.75. Then, the tungsten was stripped with 3 mol/L NH 4 0, and the ratio (O/A) was 1: (1 to 1.1). The stripping solution was circulated to a concentration of W0 3 of (225 g/L in the (NH 4 ) 2 WO 4 solution. At this time, the stripping solution contained 0.4 g/L of Si0 2 or more. The solution was clarified at 55 ° C and 2.7 mol / L NH 4 0H for about 1.5 h to precipitate SiO 2 . Both extraction and back extraction were carried out at 50 °C.
CAS ZHAO only the like has Isolation sodium tungstate or sodium aluminate solution arsenic, phosphorus, silicon impurities as extractant with tributyl primary amine and phosphate vinegar (TBP), to obtain satisfactory results, estimates are extracted impurity heteropoly The acid form enters the organic phase and more work is needed.
b Transformation of ion exchange method A plant in Uzbekistan used a fluidized bed to convert the Na 2 W0 4 solution purified by the classical method into (NH 4 ) 2 W0 4 through AH-80II resin. The principle flow is shown in the following figure.
The Na 2 W0 4 solution contains 125 g/L W0 3 ; 0.01~0.08 g/L Mo; 0.05 g/LP, As; 115-135 g/L NaCl+Na 2 C0 3 ; pH=2.5~ 3 . The tungsten in the solution is mainly present in the form of a metatungstate ion. The solution enters from the bottom of the adsorption column 1, and the AH-80II resin (C1 - type) is suspended from the upper part into the adsorption column and suspended in the solution, and the two are relatively moved and subjected to an ion exchange process. The flow ratio of the resin to the solution is 1: (4.2~5.0), the adsorption column treatment capacity is 0.2~0.45m 3 /(m 2 ·h). When the density of the resin discharged from the bottom of the adsorption column reaches 1.36~1.40g/cm 3 , it indicates that it has been saturated and sent to the washing. When the density is less than 1.36g/cm 3 , it returns to the adsorption column to continue adsorption. The contact time of the resin with the solution in the adsorption column is 8~12h, and the exchanged liquid contains W0 3 0.02g/L, and the adsorption rate of W0 3 is 99.95%. The resin saturated with W0 3 was washed in the washing column 2 with Na 2 after washing with water of pH=2. Then enter the desorption column 3 and hydrolyze with 15%~25% ammonia. The high concentration portion of the desorption solution is sent to evaporate crystalline APT, and the low concentration portion returns to desorption. The desorbed resin is re-adsorbed after regenerating the C1 - type from 60 to 80 g/L of HC1.
When the solution according to the measurement W0 3 concentration of 15 ~ 20g / L AH-80II when the total exchange capacity of the dry resin absorbent 1g 1610mg W0 3, than the classical acid-decomposable synthetic scheelite then ammonio improved recovery process W0 3 1.3% to 1.5%, hydrochloric acid consumption by 65% ~ 70%, CaCl 2 consumption by 100%; power consumption reduced by 30% to 40%.
Under the production conditions, when the HN0 3 system is used, the resin may also be of the BII-14K ​​type.
c Precipitation of artificial white tungsten-acid decomposition method The essence is that the Na 2 W0 4 solution after purification and impurity removal is first added to CaCl 2 to convert Na 2 WO 4 into CaW0 4 precipitate, and Na + is left in the solution, thus realizing The separation of Na + from WO 4 2- , the reaction is:
Na 2 W0 4 +CaCl 2 ==== 2NaC1+CaW0 4 (s)
The resulting CaW0 4 (also known as artificial white tungsten) is then converted to H 2 W0 4 by H 2 , H 2 W0 4 and then dissolved in NH 4 OH to give a solution of (NH 4 ) 2 WO 4 .
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