One of crude antimony, bismuth is more common impurities, a great impact on the performance of antimony. In the 锑 refining standard, the cerium content is required to be less than 0.005%. In the existing rough boring refining process, the predecessors have not conducted special research on rough dislocation. The molten salt electrolysis refining cathode method can remove bismuth better, but it has some insurmountable disadvantages, such as high operating temperature, few kinds of impurities removed, complicated structure of electrolytic cell, and difficulty in purification and recycling of electrolyte. Etc. Further promotion in the industry needs further improvement.
The electrolyte system used in the electrolytic refining of crude aqueous solution is divided into two major categories: alkaline system and acid system. The alkaline system is mainly a sodium carbonate-sodium hydroxide system and a ruthenium sulfide system. As more alkaline system disadvantages, such as a sponge obtained only antimony cathode, depositing thin, not for electrolysis crude antimony-containing noble metal or the like, could not be promoted. At present, hydrofluoric acid-sulfuric acid system is mainly used in industrial production. The tartaric acid system and the citric acid system are small in application due to their high price. In view of the difficulty in regenerating the electrolyte of the hydrochloric acid system and the shortcomings of the cathode, the Beijing Research Institute of Mining and Metallurgy used a hydrochloric acid-ammonium chloride system instead of the hydrochloric acid system in the complex electrolysis process of the lead-lead concentrate. Separation effectively avoids the formation of pops on the cathode. However, the anode of the system is prone to chlorine gas, which is unfavorable to the environment of the electrolysis workshop.
Since the standard electrode potentials of yttrium are similar, the conventional aqueous electrolytic refining theory suggests that yttrium is not easily separated from each other in electrolysis. Therefore, the author of this paper is based on the characteristics of lead bismuth and precious metal enrichment of metal lanthanum produced from lead anode mud, and conducts experimental research on electrolytic refining and enthalpy removal. Under the conditions of room temperature and high current density, using H 2 SO 4 -NH 4 F-SbF 3 electrolyte system, oxalic acid is added to the electrolyte system as an additive, which can effectively remove impurities and obtain fine bismuth. No. 1. Impurities such as As, Pb, Bi, Fe and Ag in the crude crucible can be effectively removed and recovered by treatment of the anode slime.
First, the test
(1) Composition analysis of rough anode
The anode is made of coarse slag produced by a smelting plant in Mengzi, Yunnan, with a mass of 300g. The main components are shown in Table 1.
Table 1 Results of chemical analysis of tantalum anode
(2) Electrolyte composition
The H 2 SO4-NH 4 F-SbF 3 electrolyte system was used, and the electrolyte was prepared from distilled water, and the composition thereof is shown in Table 2.
Table 2 Basic composition of electrolyte
(3) Instruments and reagents
The instrument is: WYJ-1550 adjustable DC stabilized current power supply, DT-1000 electronic balance, C59-A type ammeter, HH-6 digital constant temperature water bath, medical distilled water machine, EPMA-100 scanning electron microscope .
The reagents are: antimony trioxide, sulfuric acid, hydrofluoric acid, ammonium fluoride, oxalic acid, etc., all of which are of analytical grade.
(4) Test methods
The electrolysis operation is carried out in a 150 mm × 85 mm × 100 mm polyvinyl chloride electrolytic cell, and the current density is controlled by an adjustable DC stabilized current source and an ammeter, and the water bath is thermostated at 25 ° C. The anode is made of coarse slab and protected by polyester bag; the cathode is made of stainless steel, the effective size is 45mm×60mm, and it is sealed with PVC soft transparent tape. The current density is 400 A/m2, the different pole pitch is 50 mm, and the tank is discharged after 24 hours of electrolysis. The schematic diagram of the installation of electrolysis equipment is shown in Figure 1.
Figure 1 Schematic diagram of electrolysis equipment
After the cathode was electrolyzed for 24 hours, the plate was peeled, crushed, and ground to a -200 mesh metal powder. After dissolving the powder with 2:1 hydrochloric acid and nitric acid, the ruthenium was complexed with tartaric acid, and EDTA complexed to mask other metal ions with 2-(5- bromo -2-pyridylazo)-5-diethylaminophenol (5 The -Br-PADAP)-Bi-NaOH polarographic catalytic wave system directly measures the ruthenium content therein. The concentration of cerium ions in the liquid after electrolysis was determined by chemical analysis. The anode mud was rinsed and collected with distilled water. After filtration under reduced pressure, the filter cake was dried in a 60 ° C dry box, and after grinding into a powder, the components were analyzed by chemical methods.
Second, the results and discussion
By changing the temperature, current density, additive concentration and other factors of electrolysis, the influence of the electrolysis on the enthalpy distribution during electrolysis was investigated. According to the standard electrode potential of impurities in the rough and its electrochemical behavior, impurities can be classified into three categories: (1) impurities that are more positive than erbium, mainly silver and sulfur. Since the rough contains arsenic and sulfur, more than 99% of the silver is not dissolved in the electrolysis process and is transferred to the anode slime. (2) Impurities close to the electrode potential and erbium, mainly copper , arsenic, and antimony. The content of copper in the rough is very small, and NH 4 + ions are present in the electrolyte, and the formed copper ammonia complex is more difficult to precipitate in the cathode; arsenic, antimony and the corresponding additives form a complex with low solubility, large Part of it remains in the anode mud. (3) Negative electrical impurities, mainly lead and iron . Lead and SO 4 2 - lead sulfate, which falls off the anode to the anode mud, thereby reducing the resistance of the anode mud, which is beneficial to the electrolysis; when the oxalic acid in the electrolyte maintains a certain concentration, about 90% of the iron is Fe The form of 3 (SO 4 ) 4 · 14H 2 O enters the anode slime, and about 10% of the iron enters the electrolyte.
(1) Effect of temperature on electrolysis process
Under the condition of no additive, keep the basic composition, current density and pole spacing of the electrolyte unchanged, change the electrolysis temperature, the range is 25-55 °C, electrolysis for 24 h, and investigate the effect of temperature change on the electrochemical behavior of the impurity 铋. The result is shown in Figure 2.
Fig. 2 Effect of temperature on the electrochemical behavior of impurity é“‹
It can be seen from Fig. 2 that the elevated temperature promotes the chemical action of the acid on the anode mud, and the impurity in the anode is largely dissolved into the electrolyte, and the amount of enrichment in the anode mud is reduced, and the content in the electrolyte is reduced. It rises and eventually enters the cathode crucible, reducing the quality of the cathode crucible.
(2) Influence of current density on electrolysis process
Under the condition of no additive, keep the basic composition, electrolysis temperature and pole spacing of the electrolyte unchanged, change the current density, the range is 100-500A/m2, and electrolyze for 24h, and investigate the change of current density to impurity é“‹The effect of electrochemical behavior, the results are shown in Figure 3.
Figure 3 Effect of current density on the electrochemical behavior of impurity é“‹
It can be seen from Fig. 3 that as the current density increases, the content of cerium entering the anode mud increases, and the cerium ion concentration entering the electrolyte decreases, and finally the cerium content of the cathode cerium is also greatly reduced. This may be because at high current densities, arsenic and antimony in the anode are easily oxidized to pentavalent, in which case niobium will enter the anode slime in the form of poorly soluble bismuth arsenate and bismuth ruthenate.
(III) Effect of the amount of oxalic acid added on the electrolysis process
1. Effect of oxalic acid addition on electrochemical behavior of impurity é“‹
The effect of the amount of oxalic acid added on the electrochemical behavior of the impurity ruthenium was investigated under the condition of a current density of 400 A/m 2 and a heteropolar distance of 50 mm at 25 ° C. The results are shown in Fig. 4 .
Figure 4 Effect of oxalic acid addition on the electrochemical behavior of impurity é“‹
As can be seen from Fig. 4, as the concentration of oxalic acid increases, the content of cerium entering the anode mud increases, the concentration of cerium ions in the electrolyte decreases, and the cerium content of the cathode also decreases. When the concentration of oxalic acid is more than 5g ∕L, the change trend of strontium ion concentration is not obvious. If the concentration of oxalic acid in the electrolyte is too high, the oxalate ion will be discharged at the cathode, which will affect the quality of the cathode deposited layer.
2. Effect of oxalic acid on the morphology of tantalum cathode
When oxalic acid is added as a herbicide to the electrolyte, a trace amount of oxalic acid is also used as a cathodic coating electron probe. It can be seen from Fig. 5(a) and Fig. 6(a) that the crystals of the crucible have a triangular pyramid structure, the sides are high-index surfaces and include steps, and electrocrystallization proceeds according to the screw dislocation growth mechanism. Figures 5(b) and 6(b) show the shape of the side steps of the triangular pyramid, respectively. The ruthenium coating obtained by adding oxalic acid has a macroscopic step density on the side of the triangular pyramid which is significantly smaller than that of the pure electrolyte ruthenium plating layer, but a corrugated microscopic step can be observed on the step surface. This may be because after the addition of oxalic acid, the impurity metal atoms on the cathode are reduced, and the microscopic steps are difficult to gather to become a macro step. If 10g of oxalic acid is added to the electrolyte, it will cause slight changes in the morphology of the cathode ruthenium, but it will not affect the smooth progress of electrolysis. Taking into account various factors, it is considered that the suitable amount of oxalic acid added is 10 g ∕L.
Figure 5 Electron probe diagram of pure electrolyte cathode raft
Figure 6 Add 10g ∕L oxalic acid cathode 锑 plate electron probe diagram
Third, the conclusion
(1) High current density and low electrolysis temperature facilitate the removal of impurities.
(2) If 10 g of oxalic acid is added to the electrolyte, cerium will enter the anode mud in the form of a poorly soluble metal complex, and the content of cerium in the cathode cerium will be reduced to 0.005% or less.
(3) The SEM image of the cathode plating layer shows that the 锑 crystal is carried out according to the screw dislocation growth mechanism, and the crystal has a triangular pyramid structure, and the side surface is a high-index surface and includes a step. The addition of oxalic acid has a slight effect on the morphology of the cathode ruthenium, but does not affect the smooth progress of electrolysis.
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