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Noble metal extraction in the refining process, the solvent extraction method has a large energy production, separation and impurity ions, high precious metal recovery, product purity and ease of operation, low cost and ease of automation and other obvious advantages, which solvent extraction method The study of separating precious metals has received great attention. Type palladium extractant range summed up in an organic compound containing sulfur, oxygen-, nitrogen- and phosphorus-containing and the like. Neutral sulfur-containing extractant thioether has a relatively high extraction selectivity for metal palladium. Some progress has been made in the extraction of palladium from various structurally different alkyl sulfides. In this paper, [PdCl 4 ] 2 - in an acidic solution was extracted with self-made mercaptoethyl sulfide and found to have good extraction properties.
First, the experiment
(1) Reagents and instruments
Reagent: thioethyl thioether homemade. The optimum process conditions for the synthesis are: n (decanethiol): n(CH 3 CH 2 Br):n(KI)=1:1.2:0.08, with water as the solvent, the reaction temperature is controlled at 75 ° C, and the reaction is carried out for 2 h. The yield was 80.1% and the product purity reached 99%.
PdCl 2 , produced by Tianjin Guangfu Fine Chemical Research Institute, is purely analytical. Furfuryl mercaptan, bromo ethane, NaOH, KI, chloroform and aqueous ammonia were of analytical grade. Cyclohexane and odorless kerosene is chemically pure.
Instrument: WFX-I10 atomic absorption spectrophotometer, electric oscillator.
(2) Preparation of test solution
0.8330 g of PdCl 2 was weighed on an electronic balance, and an appropriate amount of 2 mol/L hydrochloric acid and an appropriate amount of distilled water were added to dissolve in a 100 mL beaker, and the volume was adjusted in a 250 mL volumetric flask. In the obtained liquid to be extracted, Ï[Pd(II)]=2.000 g/L, and c(HCl)=0.5 mol/L.
Organic phase: The mercaptoethyl sulfide is dissolved in a solvent such as chloroform, cyclohexane or odorless kerosene to prepare an extractant organic phase at a desired concentration.
(3) Experimental methods
In a certain comparison, pipette the required volume of the organic phase and the Pd(II)-containing extract to 10 mL of the ground tube, and then place the tube in the electric oscillator for a period of time after shaking. Stand still. Pipette a certain amount of raffinate into a 10mL volumetric flask, dilute to the mark with 0.1mol/L hydrochloric acid, and analyze the content of Pd(II) in the raffinate with WFX-I10 atomic absorption spectrophotometer. . The content of Pd(II) in the organic phase can be determined by subtractive subtraction.
Second, the results and discussion
(1) Effect of different diluents on the extraction of Pd(II) from mercaptoethyl sulfide
At room temperature, chloroform, cyclohexane and odorless kerosene were used as diluents respectively. In the extract, Ï[Pd(II)]=1.000g/L, c(H + )=0.5mol/L, The effect of thioether on the extraction performance of Pd(II) is shown in Table 1.
Table 1 Effect of different diluents on the properties of Pd(II) extracted from mercaptoethyl sulfide
Thinner
Mercaptoethyl sulfide concentration /%
Pd (II) extraction rate /%
Chloroform
Cyclohexane
Odorless kerosene
10
10
10
87.8
91.5
96.3
Table 1 shows that the concentration of mercaptoethyl sulfide is 10%. When chloroform, cyclohexane and odorless kerosene are used as diluents, the extraction effect of decylethyl sulfide on three kinds of diluents on Pd(II) Both are better, the phase separation is rapid, and the interface is clear and clean, but the extraction rate of Pd(II) is the highest in odorless kerosene. Therefore, this experiment uses odorless kerosene as a diluent for mercaptoethyl sulfide.
(2) Effect of thiol ethyl sulfide concentration on Pd(II) extraction performance
Fix Ï[Pd(II)]=1.000g/L at room temperature, compared with O/A=1, extraction time t=30min, c(H + )=1.0mol/L in the extract to be studied The effect of the concentration of thioether on the extraction performance of Pd(II) is shown in Figure 1.
Fig.1 Effect of thiol ethyl sulfide concentration on Pd(II) extraction performance
Figure 1 shows that the extraction rate of Pd(II) increases with the increase of the concentration of mercaptoethyl sulfide. When the concentration of mercaptoethyl sulfide is 8%, the extraction rate of Pd(II) has reached 92.5%, and then the concentration of mercaptoethyl sulfide is increased, and the extraction rate of Pd(II) is relatively small. When the concentration of mercaptoethyl sulfide is 30%, the extraction ratio of Pd(II) is 99.7%. This indicates that the extraction performance of mercaptoethyl sulfide on Pd(II) is good under the experimental conditions.
(III) Effect of acidity on the properties of Pd(II) extracted from mercaptoethyl sulfide
At room temperature, Ï[Pd(II)]=1.000g/L was fixed, and the concentration of mercaptoethyl sulfide was 8%. Compared with O/A=1, extraction time t=30min, the acidity of the liquid to be extracted was investigated. The effect of Pd(II) extraction performance is shown in Figure 2.
Fig. 2 Effect of acidity on the properties of Pd(II) extracted from mercaptoethyl sulfide
Figure 2 shows that the extraction rate of Pd(II) increases with the increase of HCl concentration in the extract. Under the experimental conditions, when the concentration of HCl increases to 2.5mol/L, the extraction rate of Pd(II) is higher. 94.7%, and then increase the concentration of HCl, the extraction rate of Pd (II) almost no increase. This experiment shows that the acidity has a great influence on the extraction of Pd(II) by mercaptoethyl sulfide, which may be related to the mechanism of the extraction of Pd(II) by mercaptoethyl sulfide. When the acidity is increased, the positive charge density of the S atom in the thioether may be increased, which is favorable for extracting the [PdCl 4 ] 2 - ion by the ion association mechanism.
(IV) Effect of extraction time on the properties of Pd(II) extracted from mercaptoethyl sulfide
At room temperature, Ï[Pd(II)]=1.000g/L was fixed, and the concentration of decylethyl sulfide was 8%. Compared with O/A=1, the acidity of the solution to be extracted was 1.0mol/L. The effect of time on the extraction performance of Pd(II) is shown in Figure 3.
Fig. 3 Effect of extraction time on the properties of Pd(II) extracted from mercaptoethyl sulfide
Figure 3 shows that under the experimental conditions, the extraction rate of Pd(II) has not changed much after 9 min extraction, reaching 92.2% or more. This indicates that the extraction of Pd(II) by mercaptoethyl sulfide is a fast equilibrium reaction.
(5) Effect of extraction of Pd(II) on mercaptoethyl sulfide
At room temperature, fixed Ï[Pd(II)]=1.000g/L, decyl ethyl sulfide concentration 8%, extraction time 2min, acidity of the extract to be 1.0mol/L, compared with extraction The effect on the performance of fixed Pd(II) extraction is shown in Figure 4.
Figure 4 Effect of extraction of Pd(II) on mercaptoethyl sulfide
Figure 4 shows that as the ratio of (O/A) increases, the extraction rate of Pd(II) from decyl ethyl sulfide increases gradually. When O/A>1, the increase in extraction rate of Pd(II) is small compared to the increase. The higher the ratio, the higher the extraction rate of Pd(II), but the lower the concentration of Pd(II) in the organic phase is not conducive to the concentration of Pd(II). Therefore, in practical applications, it can be controlled to be around 1 or so.
(6) Effect of Pd(II) concentration in aqueous phase on Pd(II) performance of mercaptoethyl sulfide
At room temperature, the concentration of mercaptoethyl sulfide is 8%, the extraction time is 2 min, and the acidity of the extract is 1.0 mol/L. Compared with O/A=1, the concentration of Pd(II) in the aqueous phase is investigated. The effect of the extraction of Pd(II) by ethyl ethyl sulfide is shown in Figure 5.
Figure 5 Effect of palladium concentration in feed solution on palladium extraction rate
It can be seen from Fig. 5 that as the concentration of Pd(II) in the aqueous phase increases, the extraction rate of Pd(II) gradually decreases. This is because the concentration of Pd(II) in the feed liquid is smaller, and the same concentration of plutonium The greater the chance that the ethyl thioether will extract Pd(II) into the organic phase, the higher the extraction rate of Pd(II).
(7) Extraction of Pd(II) saturation capacity by mercaptoethyl sulfide
At room temperature, the liquid to be extracted Ï[Pd(II)]=1.000g/L, c(HCl)=1.0mol/L, and the extraction time was t=5min, compared to O/A=1. The extraction liquid containing Pd(II) was continuously extracted with 2% organic phase of 30% mercaptoethyl sulfide, and the extraction rate was analyzed. The results are shown in Table 2.
Table 2 Experiment of Pd(II) saturation capacity
Number of extractions
Ï[Pd(II)]/(g·L - 1 ) in the organic phase
Pd (II) extraction rate /%
1
2
3
4
5
6
7
8
9
10
0.996
1.991
2.984
3.974
4.961
5.945
6.922
7.893
8.861
9.823
99.6
99.5
99.3
99.0
98.7
98.4
97.7
97.1
96.8
96.2
Table 2 shows that as the number of extractions increases, the extraction rate of Pd(II) gradually decreases, but the decrease is not large. When the experiment was carried out to the 10th time, the experiment could not proceed due to the severe loss of the organic phase. Therefore, it can be considered that the saturation capacity of Pd(II) extracted by 30% mercaptoethyl sulfide in a hydrochloric acid medium will be greater than 9 g/L.
(8) Stripping performance of Pd(II)
At room temperature, Ï[Pd(II)]=0.965g/L in the Pd(II) organic phase was fixed, and the stripping time was t=30min. The ammonia water was used as the stripping agent to investigate the concentration of ammonia water and compare it to Pd(II). The effect of stripping performance is shown in Figure 6.
Figure 6 Effect of ammonia concentration on Pd(II) stripping rate
It can be seen from Fig. 6 that as the concentration of ammonia water increases, the stripping rate of Pd(II) increases first and then decreases. When the concentration of ammonia water is 10mol/L, the stripping rate of Pd(II) is the highest at different ratios. In addition, when the ratio of the volume of the stripping agent to the volume of the organic phase is increased by 1:2, 1:1, 2:1, 3:1, the stripping rate of Pd(II) in the same concentration of ammonia water is sequentially Raise. When the concentration of ammonia water was 10 mol/L, A/O = 3:1 was stripped. After the stripped organic phase is washed with water, the extract of Ï[Pd(II)]=1.000g/L is extracted, and the cycle is repeated, and the concentration of Pd(II) in each raffinate is analyzed, and each time is calculated. Extraction rate. The stripping time was 30 min each time, and the results are shown in Table 3.
Table 3 Cyclic performance of mercaptoethyl sulfide
Thioethyl thioether use times
Pd(II) extraction rate /%
1
2
3
4
5
6
7
8
99.8
99.7
99.5
99.1
98.6
98.3
97.8
97.4
It can be seen from Table 3 that after the repeated use of mercaptoethyl sulfide for 8 times, the extraction ratio of Pd(II) is 97.4%, which is still relatively high. It is indicated that mercaptoethyl sulfide has good extraction performance for Pd(II) and can be recycled repeatedly.
Third, the conclusion
The performance of self-made mercaptoethyl sulfide to extract Pd(II) from acidic medium was studied. The experimental results show that odorless kerosene can dissolve thiol ethyl sulfide well, and decyl ethyl sulphide has excellent extraction performance for Pd(II) in odorless kerosene. With the increase of the concentration of mercaptoethyl sulfide, the extraction rate of Pd(II) gradually increased. When the concentration of mercaptoethyl sulfide was 8%, the concentration of the solution to be extracted was compared with O/A=1. c(H + )=1.0mol/L, after 1 min extraction, the reaction has reached equilibrium, and the extraction rate of Pd(II) is greater than 92.2%. The extraction rate of Pd(II) with mercaptoethyl sulfide increased with the increase of acidity of the extract. The saturation capacity of Pd(II) extraction was determined experimentally, and it was higher than 9g/L under the experimental conditions. When Pd(II) was back-extracted with ammonia water, the concentration of ammonia water was 10mol/L, and the stripping performance of Pd(II) was the highest. With the increase of A/O, the stripping rate of ammonia to Pd(II) gradually increases. The RP[Pd(II)]=0.965g/L in the Pd(II)-containing organic phase and the stripping rate of the ammonia water concentration of 10mol/L reached 99.8%. It is shown that the extraction of Pd(II) by mercaptoethyl sulfide is relatively good and has certain industrial application value.