The monument is the main impurity in the copper electrolysis production process. In order to ensure the quality of the copper, the arsenic in the electrolyte must be controlled within a certain range. Therefore, the removal of arsenic becomes the main content of electrolyte purification. Due to the high power consumption of arsenic removal, it generally reaches 3% to 5% of the electrical energy consumption of the entire copper electrolysis process; and with the removal of a large amount of copper, the direct yield of copper decreases. Therefore, the cost of the arsenic removal process becomes an important part of the production cost of electrolysis.
At present, there are two methods for arsenic removal in domestic copper electrolysis production: electrowinning arsenic removal and solvent extraction. Electrowinning is the most important method. In addition, although a large amount of research has been conducted on methods such as a precipitation method and a membrane separation method, no report on application in production has been reported. The domestic continuous electrowinning arsenic method mainly includes “induction method for arsenic removal†from a certain factory, “Controlled cathode potential electrowinning method for copper removal and arsenic removal†from Central South University, and “parallel connection†of Yunnan Copper Co., Ltd. (hereinafter referred to as “cloud copperâ€). Circulating continuous electrowinning arsenic method". This paper will introduce the research and practice of "parallel circulating continuous electrowinning arsenic" in cloud copper.
First, the process of electrolyte purification
Each copper smelting enterprise adopts different electrolyte purification processes according to its own process characteristics and financial process knowledge. Different processes will have a significant impact on the control of the purification process and economic and technical indicators. Cloud copper was selected according to the task of electrolyte purification, that is, the balance of copper ion concentration, and the removal of electrolyte arsenic and nickel .
Figure 1 Electrolyte purification flow chart
Fig.1 Flowsheet of electrolyte purification
It effectively links the process characteristics and material characteristics between processes. That is, the copper sulfate is produced by evaporation concentration and cooling crystallization of the electrolyte, thereby reducing the concentration of copper ions in the solution and increasing the concentration of arsenic, nickel and sulfuric acid in the solution. This provides a suitable copper arsenic concentration for the solution of the arsenic removal process; a high concentration solution is provided for the nickel sulphate production process. Thereby reducing the inefficient consumption of copper in the process of arsenic removal, increasing the direct yield of copper and reducing the power consumption. If necessary, the crystallization mother liquor may be recrystallized or clarified to control the copper arsenic concentration to a suitable range.
2. Analysis of influencing factors and control factors of electrowinning arsenic removal process
The traditional electrowinning process has been plagued by the two problems of precipitation of AsH3 and low efficiency of arsenic removal. It is easy to cause arsenic abnormality in the field of arsenic removal; and the ability of arsenic removal equipment is low, energy consumption is high, and copper is directly collected.
The rate is low and the loss is large. According to its own practice and understanding, Yunnan Copper researches, tests and practices the principles, influencing factors and control factors of the arsenic removal process.
(1) Analysis of influencing factors of arsenic removal process
The morphology of arsenic in the copper sulfate mother liquor, the arsenic slag produced by electrowinning and the arsenic removal, and the arsenic removal were analyzed. Chemical analysis revealed that the arsenic in the crystallization mother liquor was completely oxidized to pentavalent arsenic after evaporation and concentration of the electrolyte by copper sulfate production. By diffraction and electron microprobe analysis X- arsenic slag, the slag in the arsenic No elemental arsenic; and all arsenic are present in the form of arsenic in the copper alloy, respectively β-Cu 3 As and Cu 2 ALS. The arsenic slag composition was (%): elemental Cu8.10, β-Cu 3 As 70.30, Cu 2 As 7.20, Cu 2 O 6.50, Cu 2 S04·5H 2 0 5 .20, and other 2.70. After analyzing the arsenic removal solution, all the arsenic is trivalent arsenic.
According to the above analysis, it can be judged that in the process of removing arsenic from the electrowinning, the removal of copper ions is first performed, and as the concentration of copper ions decreases, the cathode potential decreases. When the copper ion concentration drops to a certain value, the arsenic in the solution begins to be adsorbed in the cathode electric double layer and is reduced, so that arsenic and copper are co-crystallized together at the cathode to form an arsenic copper alloy. The electrode potential of the reaction will be higher than the potential of the elemental arsenic. As the copper ions are further reduced, precipitation of H 2 and AsH 3 gases will occur, which is to be avoided as much as possible during the arsenic removal process. Therefore, the reaction of the electrowinning arsenic process can be described by the reaction formula of Table 1.
Table 1 Electrode reaction formula of electrowinning arsenic removal process and its potential (60 ° C)
Table l Equations and potentials during removal of arsenic in electrowinning
According to the above analysis, it can be judged that the copper ion concentration, the arsenic ion concentration, and the copper-arsenic concentration ratio of the solution are important factors affecting the electrowinning process. In particular, the concentration of copper ions determines the specific reaction and sequence of the electrowinning process, and also determines the product of the cathodic reaction. How to reduce the output of elemental copper during the electrowinning process, avoid the generation of H 2 and AsH 3 gases, and precipitate the formation of arsenic alloys, which is a key factor in the overall production control. Therefore, all control actions and measures in the production process will work around the above factors.
(II) Analysis of control factors for arsenic removal process
Copper and arsenic are removed during the arsenic removal process, and the copper and arsenic ion concentrations in the solution are lowered. The law of ion concentration change in this process can be expressed by the following formula
I x q x η x -Q into C into x -Q out C out x
I total = I arsenic + I copper + I hydrogen + I arsine
Q into = Q out = Q
I x q x η x -Q (C enters x -C out x )
In the above formula, I x is the current intensity for removing copper, arsenic, and hydrogen evolution and arsine during the arsenic removal process; q x is the electrochemical equivalent of each element precipitated at the cathode; ηx is the precipitation of each element Current efficiency; C into x , C out x respectively indicate the concentration of the corresponding element in the solution at the inlet and outlet end; Q represents the amount of solution circulation.
It can be seen from the above formula that the concentration of ions controlled during the process of removing arsenic from electrowinning refers to the concentration of the three parts of the solution, the liquid and the solution in the tank. What needs to be emphasized here is the concentration of the solution between the electrodes in the arsenic removal tank. The concentration of the solution in the tank can be characterized by the difference in concentration of the influent, and the smaller the difference, the more accurately the true condition of the solution in the tank can be reflected. Therefore, the influencing factors of the arsenic removal process are: the concentration of the solution at the liquid inlet end, the circulation amount of the solution, the circulation mode of the solution, and the intensity of the current.
"Induction method for arsenic removal" is due to its control mode, that is, series circulation, and the circulation amount is low. It is difficult to ensure that the above factors are controlled during the production process, and the precipitation of arsine gas is often caused at the end stage. The "parallel circulation continuous electrowinning arsenic" adopts the parallel circulation mode of the lower in and out, and effectively solves the above problems by controlling the circulation amount of the solution, the current intensity, and the concentration of the solution at the liquid inlet and outlet.
The above analysis indicates that in order to avoid the precipitation of H 2 and AsH 3 gases in the arsenic removal process, the key is to control the copper ion concentration. According to the general requirements of production practice, the copper ion concentration is controlled at 1.5-6.5g/L to reduce the precipitation of elemental copper, reduce the loss of ineffective copper and the consumption of electric energy. It is required to form a certain ratio of copper and arsenic in the solution. And arsenic form β-Cu 3 As and Cu 2 As. Therefore, the ratio of copper to arsenic concentration of the solution is generally controlled at Cu: As = (1.7 to 3.0):1. To ensure this ratio, the solution is pretreated before arsenic removal. Usually, the mother liquor of copper sulphate is recrystallized or clarified to reduce the concentration of copper ions in the solution.
In addition, in order to verify the uniformity of the solution concentration in the tank, the efficiency of arsenic removal is further improved. The air duct was placed in the arsenic removal tank for blast stirring. It is hoped that the uniformity of the copper and arsenic concentrations in the solution between the electrodes can be improved by stirring, thereby improving the arsenic removal efficiency. However, the result was found to be the opposite, and the efficiency of arsenic removal decreased. Moreover, the crystal product precipitated on the surface of the cathode changes from the original black to red and red-black; from granular to small, and the adhesion to the cathode is significantly improved; at the same time, the concentration of copper ions in the solution is significantly decreased, and The concentration of arsenic ions increased significantly. After 8 hours of blasting, the concentration of Cu in the solution decreased from 5.62 g/L before blasting to 2.38 g/L, while As increased from 3.98 g/L to 6.23 g/L.
Through this test, it was proved that under a large circulation condition (30-40 L/min), a large amount of oxygen was precipitated from the anode, so that the solution between the electrodes in the tank was sufficiently stirred to achieve uniformity. When the blast is stirred, the diffusion ability of copper and arsenic ions will be increased. However, due to the strong adsorption advantage of copper ions in the cathode electric double layer, the adsorption amount of arsenic ions in the electric double layer is decreased, thereby making the electrode The process mainly involves the removal of copper. This indicates that in the process of arsenic removal, it is necessary to ensure a proper ratio between copper and arsenic in the electric double layer of the cathode surface, so that copper and arsenic form copper arsenic alloy to reduce the precipitation of elemental copper and the inefficient consumption of copper.
In order to reduce energy consumption, it is desirable to carry out the arsenic removal process at normal temperature to avoid energy consumption of the steam heating solution. However, according to the test, it is difficult for the silicon rectifier to increase the output current or even output when the solution is at a normal temperature or a low temperature of 30 to 40 ° C, and the output voltage at this time is in a relatively high range. Only after the Joule heat generated by the electrowinning process gradually increases the temperature of the solution, the output current of the rectifier gradually increases, and the voltage gradually decreases. Therefore, in the process of electrowinning arsenic, the solution must be warmed to 60-65 °C.
In summary, the influencing factors and control factors of the arsenic removal process are: copper ion concentration in the arsenic removal tank, arsenic ion concentration, copper and arsenic ratio, solution circulation and circulation mode, and solution temperature. And the corresponding current intensity.
Third, parallel circulation continuous electrowinning practice of arsenic removal
According to the above analysis and test, Yuntong took the “parallel circulation continuous electrowinning arsenic removal method†in the electrowinning arsenic removal process in August 1997. Through more than 10 years of production practice, good results have been achieved. This method has the following characteristics:
(1) Clean and safe at the production site
Due to the large circulation amount, the solution concentration can be accurately controlled, thereby effectively suppressing the generation of arsine gas and ensuring the safety of the production site. The phenomenon of precipitation of AsH 3 at the end stage by other electrowinning methods is avoided. The arsenic removal site was tested and AsH 3 was not detected. By covering the trough surface, the produced acid mist is systematically discharged and collected by the exhaust system and the capture system, thereby ensuring the cleanliness of the production site.
(2) High arsenic removal efficiency and low energy consumption
By pre-treating the pre-arsenic removal solution, the copper and arsenic concentration ratio of the solution is controlled within the required range, and a large circulation amount is adopted for all the arsenic removal tanks, thereby ensuring the uniformity of the copper-arsenic concentration in the solution. The matching ability and the tolerance capacity between the solution concentration and the current intensity are improved. Thereby improving the process of forming arsenic copper alloy during arsenic removal process, improving the efficiency of arsenic removal; reducing the consumption of ineffective copper, improving the direct yield of copper and reducing the power consumption. Since the solution is heated to be controlled at 60 to 65 ° C, the high voltage and low current of the tank caused by the low temperature at the initial stage of power transmission are avoided, and the tank voltage is lowered, and the power consumption is reduced.
Therefore, the arsenic removal efficiency and integrated current efficiency are above 90%; the electrical energy consumption per ton of As is low, generally 15000 kW. Below h; the ratio of copper to arsenic in arsenic slag is low, generally controlled at Cu: As = (1.8 ~ 2.8): 1, close to the theoretical ratio of β-Cu 3 As and Cu 2 As 2.545:1 and 1.696:1, thereby improving The direct yield of copper during electrolysis. Cu:As = (6 ~ 11): l in the arsenic slag before the improvement.
(3) Convenient treatment of cathode products
Through the control of the process parameters, the cathode product is reddish black and air-colored granular; the adhesion between the particles and the cathode is low, and it is easy to fall off from the cathode. Generally, the arsenic removal tank is checked and treated once a day, and the arsenic slag on the surface of the cathode is brushed into the bottom of the tank with a steel brush to avoid short circuit between the anode and cathode. According to the current situation, the arsenic slag is discharged once every 4 to 7 days. The arsenic slag is removed from the bottom of the tank by a filter bucket, and the operation time per tank is generally about 15 minutes. The arsenic slag is washed by vacuum filtration and sent to the next process for comprehensive recovery. Therefore, the operation is simple, the labor is low, and the cycle of the grooving process is short.
(4) Cathode material is simple and can be reused
The cathode material is a copper residual electrode produced during copper electrolysis, which is simple in material and good in electrical conductivity. It avoids problems such as poor conductivity when using the cathode sheet and corrosion cracking of the ear. Therefore, there has been no problem that the anode ear is blown due to the breakage of the cathode ear climbing when the cathode piece is used, and the problem of fishing the cathode piece. Due to its good and stable electrical conductivity, it ensures the electrical conductivity and safety of production under high current during the arsenic removal process. Since the cathode product is granular, it is easy to fall off; therefore, the cathode can be reused after a simple brushing.
(5) Large equipment production capacity
Due to the pretreatment of the pre-arsenic removal solution, the concentration of arsenic is increased and the concentration of copper is lowered. Due to the use of a large amount of circulating parallel flow, and a good and stable copper residual cathode. All the tanks are in the same arsenic removal state, and there is no problem of segmental copper removal and arsenic removal; at the same time, high current density (up to 320 A/m 2 or more) can be used for arsenic removal. Therefore, the equipment has a large capacity for arsenic removal. Taking cloud copper as an example, the arsenic removal capacity per tank can reach above 73 Kg/d.
Fourth, the conclusion
The "parallel circulation continuous electrowinning arsenic removal method" has achieved remarkable results in the production practice of Yuntong after more than 10 years of production. It has the characteristics of accurate and simple control, safe and stable production process, simple operation process, low labor intensity, large equipment capacity, high arsenic removal efficiency, low energy consumption and high direct yield of copper. This method was awarded the National Invention Patent (ZL200410021941.X) in 2007.
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