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Recovery of hydrazine from the ruthenium tetrachloride hydrolyzed mother liquor
High-purity germanium dioxide (GeO 2 ) is obtained by decomposing high-purity germanium tetrachloride (GeCl 4 ) into deionized water. The solid GeO 2 is separated from the hydrolyzate by filtration, and the hydrazine content in the hydrolyzate is generally 2 to 4 g/L. At present, ruthenium is generally recovered by directly adding a chloride salt method to a hydrolyzate or by adding a hydrochloric acid of a different mass, and the ruthenium is recovered in the form of GeCl 4 . Chihong Company uses the second method to recover hydrazine in the hydrolyzate, which consumes 30% of industrial hydrochloric acid at about 110 t/a, and produces a distillation residue with H + concentration of 6.5 mol/L of about 200 m 3 /a. bigger. This study is to find a new environmentally friendly helium recovery process with low cost and low residual liquid production.
First, the test part
(1) Raw materials
The hydrolyzate used in the experiment was a hydrolyzed supernatant obtained by hydrolysis of high-purity GeCl 4 to form GeO 2 , which was a pale yellow acidic solution suspended with a small amount of white floating matter. The chemical composition thereof is shown in Table 1. In addition, the reagents used in the experiment were MgCl 2 ·6H 2 O, MgSO 4 ·7H 2 O, and MgO were analytically pure (produced by Daban Fine Chemical Co., Ltd., Shantou City, Guangdong Province); NaOH, NH 3 ·H 2 O was analytically pure (Manufactured by Shanghai Chemical Reagent Co., Ltd.).
Table 1 Main chemical composition of hydrolyzate
Hydrolyzed mother liquor
c(H + )/(mol·L -1 )
Ï(Ge)/(g·L -1 )
1 #
4.51
3.40
2 #
4.82
2.75
3 #
5.03
2.12
(two) experimental principle
The chemical reaction formula of high purity GeCl 4 hydrolyzed to high purity GeO 2 is:
GeCl 4 +2H 2 O=GeO 2 +4HCl
Or: GeCl 4 +(x+2)H 2 O=GeO 2 ·xH 2 O+4HCl
The hydrolyzed GeO 2 has a certain solubility (0.004 mol/L) and is a soluble crystalline oxide.
Sodium hydroxide was added to the hydrolyzate and magnesium chloride is first dissolved in water to generate the sodium germanate, the generated magnesium germanate-insoluble, chemical reaction formula of this process is:
GeO 2 +2NaOH = Na 2 GeO 3 + H 2 O
Na 2 GeO 3 +MgCl 2 =MgGeO 3 ↓+2NaCl
After filtration and drying, magnesium citrate and hydrochloric acid are added to the distillation pot at a ratio of 1:6 (mass ratio) for co-distillation. With the low boiling point of GeCl 4 (83.1 ° C), the ruthenium is recovered in the form of GeCl 4 . The chemical reaction formula is:
MgGeO 3 +6HCl=MgCl 2 +GeCl 4 +3H 2 O
(3) Test methods
The experiment was carried out at room temperature (25 ° C), and the recovery of hydrazine mainly consisted of the following steps (Figure 1):
Figure 1 Process for recovering ruthenium from ruthenium tetrachloride hydrolyzed mother liquor
(If the picture is unclear, you can call it for free)
Step 1: NaOH and NH 3 ·H 2 O were used to adjust the pH of the hydrolyzate to 7.0-8.0, and MgCl 2 , MgSO 4 and MgO were added as precipitants to form hydrazine-forming magnesium citrate (MgGeO 3 ).
Step 2: The solution obtained in the step 1 was filtered to obtain a cerium-containing filter cake.
Step 3: Drying the cerium-containing filter cake can reduce the water content of the filter cake by 40% to 60% for distillation.
Step 4: The dried dewatered cake is co-distilled with hydrochloric acid, volatilized in the form of GeCl 4 at about 70-100 ° C, and the distilled GeCl 4 is absorbed by analytically pure hydrochloric acid.
Second, the results and discussion
It has been found that the use of NaOH or NH 3 ·H 2 O to adjust the pH of the hydrolyzate has little effect on the recovery of rhodium. When NH 3 ·H 2 O is used to adjust the pH of the hydrolyzate, a certain amount of NH 3 will be emitted. Therefore, from the future industrial application, NaOH is used to adjust the pH of the hydrolyzate.
(1) Effect of Mg/Ge molar ratio on recovery of hydrazine
In the experiment, MgCl 2 was used as a precipitant, and the precipitation time was 24 h. The influence of the molar ratio of Mg/Ge on the recovery of ruthenium is shown in Table 2. It can be seen from Table 2 that as the molar ratio of Mg/Ge increases, the recovery of ruthenium is also increasing. The recovery rate of hydrazine is also high in the hydrolyzate with high strontium content, but the strontium content in the supernatant after strontium precipitation is basically the same. When the molar ratio of Mg/Ge reaches 1.5, the recovery of ruthenium is ideal, and the effect of continuously increasing the molar ratio of Mg/Ge on the recovery of ruthenium is not very obvious. Therefore, the Mg/Ge molar ratio was determined to be 1.5.
Table 2 é”— recovery rate /% under different Mg / Ge molar ratio conditions
Hydrolyzed mother liquor
n(Mg)/n(Ge)
0
0.5
1
1.5
2
2.5
1 #
65.3
92.4
95.9
98.5
99.1
99.1
2 #
57.1
90.5
94.9
98.2
98.8
98.9
3 #
41.6
87.1
93.1
97.5
98.5
98.5
(II) Effect of different magnesium compounds on the recovery rate of lanthanum
In the experiment, MgCl 2 , MgSO 4 or MgO was used as a precipitant, the molar ratio of Mg/Ge was 1.5, the precipitation time was 24 h, and the recovery of rhodium was shown in Table 3. It can be seen from Table 3 that MgCl 2 and MgSO 4 are used as precipitants, and the recovery of ruthenium is ideal, and the precipitation effect of MgO is not satisfactory, which may be because MgCl 2 and MgSO 4 can ionize Mg 2 + in aqueous solution. MgO can't.
Table 3 Effect of different magnesium compounds on the recovery of hydrazine
Magnesium compound
Recovery rate/%
MgCl 2
98.3
MgSO 4
98.2
MgO
85.3
(III) Effect of ammonium chloride on the recovery of hydrazine
According to some data, if NH 4 + is present in the solution, the hydrazine in the hydrolyzate is more likely to precipitate. In the experiment, MgCl 2 was used as a precipitant, the precipitation time was 24 h, and different amounts of NH 4 Cl were added. The recovery of hydrazine is shown in Table 4. As can be seen from the results in Table 4, the amount of NH 4 Cl added had little effect on the recovery of hydrazine.
Table 4 Effect of ammonium chloride on the recovery of hydrazine
n(NH 4 Cl)/n(Ge)
Recovery rate/%
0
98.2
0.5
98.5
1
97.8
1.5
97.1
2
96.8
2.5
95.6
(4) Effect of sedimentation time on recovery rate of plutonium
In the experiment, MgCl 2 was used as a precipitant, and the molar ratio of Mg/Ge was 1.5. The influence of precipitation time on the recovery of ruthenium is shown in Table 5. It was found by experiments that after the addition of MgCl 2 , the precipitation can be substantially completed within 4 hours.
Table 5 Effect of precipitation time on recovery of hydrazine
Precipitation time / h
Recovery rate/%
2
92.5
4
98.1
12
98.0
(5) Distillation method for recovery of antimony in antimony precipitate
After the dried cerium precipitated filter cake was uniformly mixed, the grade of the mash was determined to be 31.55%. During the experiment, 1000 g of the precipitated cake was weighed and added to 6000 g of industrial hydrochloric acid for co-distillation, and the rhodium was recovered as GeCl 4 . According to the company's many years of production experience, 1kg of niobium can produce GeCl 4 of 1576mL, and the recovery rate of distillation process is shown in Table 6.
Table 6 Recovery rate of distillation process
Hydrolyzed mother liquor
GeCl 4 theoretical yield / mL
GeCl 4 actual yield / mL
Recovery rate/%
1 #
497.2
491.5
98.85
2 #
497.2
489.5
98.45
3 #
497.2
488.5
98.25
average
497.2
489.5
98.52
Third, the conclusion
In this study, a new process for recovering ruthenium from the ruthenium tetrachloride hydrolyzed mother liquor was obtained. The process mainly consisted of adjusting the pH of the hydrolyzate with NaOH or ammonia water, adding a magnesium compound to form a magnesium ruthenate precipitate, and filtering to obtain a ruthenium precipitate. Dry and then recycle the crucible using a traditional distillation process. The recovery rate of hydrazine can be more than 98% by using this process. The optimal experimental conditions are: NaOH is used to adjust the pH of the hydrolyzate to 7-8, MgCl 2 or MgSO 4 as a precipitant, Mg/Ge (molar ratio) The ratio was 1.5:1 and the precipitation time was 4 h.
The production amount of the hydrolyzed mother liquor of Chihong Company is 110m 3 /a, and the average cerium content is 3g/L. Using this process, the cerium precipitation with a grade of 31.55% is about 1046kg, and 30% of industrial hydrochloric acid is required to be about 6.5t/a. The new process can save about 100 tons of industrial hydrochloric acid per year compared with the old recycling process, and the total recovery rate of strontium is basically the same.