Deep dislocation of zinc electrowinning solution with copper sulfate additive

With the increasing scale and capacity of zinc smelting, the demand for zinc resources has increased, and the raw materials used in smelting and processing have become more and more complicated. A company designed annual production capacity of 100,000 t of ingot production line, production process as follows: a zinc concentrate roasting hot acid leaching a jarosite pollution iron. As the raw material is a high iron sphalerite, and high cobalt, up to 0.03% to 0.05% (cobalt content industry peers typically 0.01% to 0.015%), 2 to 3 times higher than the industry, conventional method can not meet the requirements inverse antimony Therefore, the company has adopted the new process of removing cobalt from high temperature strontium salt for the first time in China. Since strontium salt is added in both purification processes, it is inevitable that the strontium content in the new liquid will exceed or increase in the new liquid; In addition, due to the different origin of the raw materials supplied, the content of strontium in the raw materials varies greatly, which also causes the enthalpy to change in the solution. The excessively high standard of bismuth in zinc electrowinning has caused large-area burning of the cathode zinc plate, which seriously affects the quality of cathode zinc and reduces the current efficiency. Therefore, the content of zinc in the industry is generally controlled below 0.1 mg/L. The method of removing bismuth from zinc electrolysis mainly includes zinc powder replacement and precipitation, and iron hydroxide adsorption coprecipitation method. It has been reported in the literature that the effect of hail reduction can also be achieved in the presence of copper ions and zinc powder, but there is no relevant research data. And reports on practical applications. When the content of bismuth exceeds the standard in industrial production, the over-standard solution is generally returned to the neutral leaching process, or returned to the first process of purification. This treatment method reduces production efficiency and improves consumption of auxiliary materials. On the basis of the literature report, this paper systematically studied for the first time systematically the addition of the additive copper sulfate and zinc powder to replace the deep dislocation process. The process step is simple, and only the additive copper sulfate is added in the last stage of the conventional three-stage purification process, and the effect can be achieved by replacing with a small amount of zinc powder, and has a good promotion and application prospect.

First, the experiment

(1) Raw materials

The experimental solution was collected from a zinc smelting plant of a company. It is a standard for the removal of copper, cadmium , cobalt, nickel and other major impurities after two stages of purification. The impurity element content is shown in Table 1. It can be seen from the data in Table 1 that after the second purification, the content of copper, cadmium, cobalt and nickel in the solution has dropped below 1 mg/L, reaching the requirement of the electrowinning solution. Although the enthalpy changes greatly before and after purification, the concentration after purification is far from the requirement of the quality of the electrowinning zinc solution (the concentration of strontium must be less than 0.1 mg/L).

Table 1 Content of impurity elements in the solution after purification in the second stage / (mg·L ^-1 )

A part of the solution containing higher strontium was prepared by adding bismuth potassium tartrate (AR, Tianjin Kaitong); the copper sulphate solution was prepared from copper sulfate pentahydrate crystal (AR, Tianjin Kaitong).

(2) Experimental methods

The experiment simulates the third purification process of the industrial process, that is, under the condition that most of the main impurities have been removed, the residual impurity elements in the solution are replaced with a smaller amount of zinc powder, so that the quality of the electrowinning liquid is qualified. The volume of the experimental solution was 1500 mL, the reaction temperature was controlled at 65 ° C, and the zinc powder (self-produced by a smelter, the elemental zinc content was above 98%) was added in an amount of 1 g/L. Operation steps: 1500mL of zinc electrowinning solution is placed in a 4L beaker, and the beaker is placed in a digital water bath thermostat (SHA-C digital water bath thermostat, Beijing) for heating and stirring, when the temperature rises to 65 °C The zinc powder was intermittently added in batches, and after stirring uniformly, copper sulfate was added in batches to observe and control the reaction conditions. After 1 hour, the reaction was stopped, filtered, and the filtrate was tested.

The three elements of copper, cadmium and nickel were measured on a WFX-110B atomic spectrophotometer (Beijing Ruili Analytical Instrument Co., Ltd.) using a copper hollow cathode lamp, a cadmium hollow cathode lamp and a nickel hollow cathode lamp.

Cobalt element was determined by nitroso R salt spectrophotometry on a 721 spectrophotometer (Shanghai Precision Scientific Instrument Co., Ltd.). The lanthanum element was determined by the malachite green spectrophotometry on a 721 spectrophotometer.

Second, the results and discussion

(1) Effect of the amount of copper sulfate on the effect of removing radon and other ionic behaviors at low cerium concentration

From the industrial site, the bismuth solution with a high content of bismuth (the content of strontium was about 1.58mg/L) was taken. The effect of the addition amount of copper sulphate on the deep deodorization effect and other ion content in the purification liquid was investigated. The results are shown in Fig. 1. 2 is shown.

It can be seen from Fig. 1 and Fig. 2 that when copper sulfate is not added, the substitution of zinc powder for copper, cobalt, cadmium and nickel impurities at low bismuth concentration is still effective, so that their concentrations are further lowered, and the enthalpy changes even Small, indicating that the simple zinc powder replacement can not achieve the purpose of deep purification. After the addition of copper sulfate in the solution system, the effect of removing the cerium is very obvious, and the concentration of cerium is greatly reduced. The cerium content index in the solution reaches the requirement of the zinc hydride solution. In addition, under the action of the same amount of zinc powder, the concentration of copper, cadmium, cobalt and nickel decreased more than that without the addition of copper ions, indicating that the addition of copper sulfate is also better for the deep purification of impurity elements such as copper, cadmium, cobalt and nickel. Effect.

Mechanism of copper sulfate solution is explained as follows: zinc dust displaces one cell environment metal, copper zinc powder adhered to the surface, forming a group of micro cells, there is a local region surrounding the copper-zinc solution may be considered microbattery In order to meet the requirements of the electrolytic cell, it is necessary to have a cathode, an anode plate and an external power source. Then, the elemental copper particles displaced in this region (referring to the alloy particles which are present alone and not attached to the zinc powder) or the zinc powder act as a plate, and the external power source is a Zn-Cu microbattery; This virtually forms an electrolytic cell environment. The material of the anode and cathode plates may be metallic copper or metallic zinc, or it may be a pairing of two metals. When the microbattery is discharged, the material is separated from the cathode of the electrolytic cell. The reduction reaction occurs in sequence according to the order of the standard electrode potentials.

Table 2 shows the standard electrode potentials of several major element electrode pairs contained in the zinc smelting purification solution. It can be seen from Table 2 that the potential of the zinc electrode pair is the most negative and the most reductive, the copper electrode has the most positive potential, followed by the potential of cadmium, cobalt and nickel. According to the order of the electrode potentials, the order of the metal elements precipitated from the cathode is: Cu>Sb>Ni>Co>Zn, and the first precipitated metals are copper and bismuth. Therefore, after the addition of copper ions, the most obvious ion removal effect should be copper, followed by copper, but since the copper ions themselves are additives, the reduction of copper ions is also the largest according to the actual purification ratio, which is not discussed here. It can be seen from the data that cadmium, cobalt and nickel have a small decrease, but the strontium concentration decreases most obviously, which is related to the fact that the electrode potential of bismuth is larger than that of other ion potentials. From the microscopic analysis to the macroscopic actual zinc electrowinning industry, when the ion content exceeds the standard, the order of the metal precipitated from the cathode is also in the order of Cu>Sb>Ni>Co>Zn, which reflects the copper and tantalum in the production result. Various burning phenomena of cobalt, nickel and cadmium. Therefore, the mechanism of deep purification of Cu, Ni, Co and Cd ions by copper ions is well explained by the electrochemical theory system of the primary battery-electrolytic cell.

Table 2 Standard electrode potentials of several metal elements (V)

It can be seen from Fig. 1 and Fig. 2 that as the amount of copper sulfate increases, the degree of purification of each ion further increases. Although the concentration of strontium ions tends to decrease gently, the amount of copper ions increases. Conducive to the purification of various impurity ions. This can also be explained from the electrochemical theory system of the primary battery-electrolytic cell: when the amount of copper sulfate increases, the amount of elemental copper displaced in the system increases, and the number of micro-batteries that can be formed increases correspondingly. The plate is mainly composed of metal zinc. Combined with metallic copper, the absolute number of plates that can be formed is also increased, which is beneficial to the entire electrochemical reaction, thereby facilitating the purification effect of impurities.

In the actual industrial electrowinning production, when the cesium ion concentration drops to 0.1 mg/L, the quality of electrolytic zinc is little affected. In the deep purification, after a certain amount of copper ions is added, the concentration of cerium ions will drop to a certain level. When the amount is lower than 0.1 mg/L, further reduction is required, and additional measures must be taken.

It can be seen from Fig. 1 and Fig. 2 that when the initial solution contains about 1.58 mg/L of strontium, the amount of copper sulfate added is about 25 mg/L, and the hydrazine reaches deep purification and removal, less than 0.1 mg/L, which satisfies electricity. The quality of the effusion is required, and other impurity ions are further purified and removed.

(2) Effect of the amount of copper sulfate on the effect of removing radon and other separation behaviors under moderate radon concentration

Figures 3 and 4 show the effect of the amount of copper ions on the purification of impurities in the solution at a medium enthalpy concentration (锑 concentration of 3.08 mg/L). It can be clearly seen from the figure that without the addition of copper ions, the concentration of ruthenium after purification is reduced by about half, but it still cannot meet the requirements of the effusion. As the amount of copper ions increases, the degree of purine purification gradually increases. When the amount of copper sulfate added reaches 0.25g/L, the depth purification of the hydrazine reaches the standard. The results show that when the concentration of the boiling water increases, the amount of added copper ions should be increased accordingly to meet the requirements of deep purification.

(III) Effect of the amount of copper sulfate on the effect of removing strontium and other ionic behaviors under high strontium concentration

Under the condition of relatively high radon concentration (锑15.15mg/L), the effect of copper ion concentration on impurity removal rate in electrowinning liquid was investigated, as shown in Figures 5-6.

It can be seen from Fig. 5 that with the increasing amount of copper sulfate, the purification rate of strontium is obviously increased until the amount of copper sulfate is 0.66g/L, and the removal rate of strontium tends to be gentle, when the amount of copper sulphate is 0.82. When g/L, the concentration of strontium can reach the quality requirement of effusion. It can be seen from Fig. 6 that as the amount of copper sulfate added increases, the nickel content declines most obviously. From the viewpoints of the effect of removing bismuth, the amount of copper sulfate and the amount of residual copper ions, it can be seen that when the amount of copper sulfate is 0.82 g/L, the purpose of deep purification and mites can be achieved.

From the above results, it can be found that when the concentration of lanthanum changes, the amount of added copper sulfate also changes accordingly. To achieve the requirement of deep purification, the amount of copper sulphate added should be controlled within a certain range.

Third, the conclusion

(1) The direct purification of zinc powder can not achieve the requirements of deep purification. After the addition of copper sulfate, the deep purification and removal of bismuth are significant, and it is beneficial to further purify the ions of copper, cobalt, cadmium and nickel.

(2) As the concentration of strontium changes, the amount of added copper sulfate should also change accordingly. When the concentration of bismuth is 1.58mg/L, the control of copper sulphate is above 0.025g/L, and the zinc powder is 1g/L, the sputum can be removed by the standard; when the cerium concentration is 3.08mg/L, the control of copper sulphate is 0.25g. Above /L, the net removal can reach the standard; when the concentration of barium is 15.16mg/L, when the copper sulfate is controlled above 0.82g/L, the barium is removed.

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