CN102367578B - Combined method for electrolyzing and recovering lead - Google Patents

Abstract

The invention provides a method for electrolytic recovery of lead from lead plaster, comprising: (1) washing the lead plaster with deionized water and carrying out solid-liquid separation to obtain a mixture containing lead sulfate, lead and lead dioxide and dilute sulfuric acid solution; (2) reacting the solution with excess NaOH solution and performing solid-liquid separation for the second time to obtain a mixed solution containing Na ₂ [Pb(OH) ₄ ] and sodium hydroxide, and containing Pb and A solid mixture of PbO ₂ ; (3) the mixed solution containing Na ₂ [Pb(OH) ₄ ] and sodium hydroxide is carried out in an ion-exchange membrane electrolyzer comprising a staged electrolysis of a constant current electrolysis stage and a constant voltage electrolysis stage to recover pure lead; and (4) adopting two-stage voltage-controlled constant-current electrolysis of the mixture of lead and lead dioxide in combination with electrodeposition to recover pure lead. The method of the invention can significantly reduce the lead recovery of reducing agent, alkaline substance and electric energy consumption, and improve the purity of the recovered lead.

Description

Combined method of electrolytic recovery of lead

technical field

The invention belongs to the technical field of lead recovery by electrolysis. The invention relates to a method for recovering lead from waste battery lead paste by electrolysis. The method pretreats and separates the lead substance in the waste battery lead paste and the compounds containing lead in different valence states, and then according to the lead Different valence states adopt different electrolysis methods for joint electrolysis to realize the recovery of high-purity metallic lead.

Background technique

The regeneration and recycling of resources is the key to the sustainable development of human society and an important way to reduce environmental pollution. Lead-acid battery, as a battery with cheap price, mature technology and stable performance, has been widely used in electric vehicles, automobiles and energy storage power sources since it was invented by Plante in France in 1859. Although lead-acid batteries are facing competition from lithium-ion batteries and nickel-metal hydride batteries in recent years, lead-acid batteries with a history of 160 years still occupy more than 55% of the global market, and their output value is increasing with the strong demand for automobiles and lead-acid batteries. Its own improvement has steadily increased. According to statistics, 86% (8.1 million tons) of the world's annual refined lead production is used in the manufacturing process of lead-acid batteries. The steady development of lead-acid batteries has caused a shortage of lead resources in the world. How to realize the efficient recovery of waste lead-acid batteries is the basic way to realize the recycling of lead resources and reduce the environmental pollution of lead-acid batteries.

A lead-acid battery is composed of a lead negative electrode and a lead dioxide positive electrode. During the discharge process, the lead at the negative electrode and the lead dioxide at the positive electrode undergo a redox reaction in the presence of sulfuric acid and transform into lead sulfate. At the same time, unreacted lead and lead dioxide remain in the positive and negative electrodes. In discarded lead-acid batteries, due to the long-term charged and oxidized state of the positive electrode grid, the lead on the electrode plate is oxidized into lead dioxide and lead sulfate, and at the same time loses its support for the lead paste, resulting in softening of the positive electrode and causing the battery to fail. Therefore, in the scrapped lead-acid battery, there are not only Pb, PbSO ₄ , PbO and PbO ₂ from the lead paste, but also lead compounds from the metal lead corrosion on the grid and tabs. These complex compositions exacerbate the difficulty of the lead recovery process.

For nearly half a century, people have mainly used pyrometallurgy to recover lead in lead-acid batteries. Because lead is easy to volatilize or oxidize at high temperature, a large amount of lead-containing dust, sulfur dioxide and lead-containing waste residues are likely to be produced during the pyrometallurgy process, which not only reduces the recovery efficiency of lead, but also causes serious secondary lead pollution to the environment. . After continuous improvement, the most successful pyrometallurgy technology can achieve a lead recovery rate of 90%. Nevertheless, hydrometallurgy can largely avoid the disadvantages of pyrometallurgy, which has aroused the interest of many researchers.

How to use an effective, clean and efficient recycled lead method to effectively reduce the compounds in the lead paste to obtain pure metallic lead has become a difficult point in the recycled lead process. The composition of lead compounds in waste lead-acid batteries is complex, and the composition and ratio of each battery are not the same. In order to simplify the lead regeneration process, currently reported patents on wet lead regeneration usually pre-oxidize the lead paste to convert various lead-containing compounds in waste lead-acid batteries into PbSO ₄ ; followed by desulfurization Reaction to obtain PbCO ₃ or PbO; then use fluoboric (silicic) acid or tartaric acid solution to dissolve to obtain soluble lead salt; and finally electrolyze the soluble lead salt to reduce to obtain lead.

In terms of soluble lead salts, the representative regenerated lead process is the electrolysis process of acidic fluoroborate (silicon) acid solution. Due to the excessive lead dioxide often appearing in discarded lead-acid batteries, the researchers invented the method of adding lead powder, sulfur dioxide, iron powder, ferrous ions, and even hydrogen peroxide to reduce the excess lead dioxide in the sulfuric acid medium. The method of obtaining lead sulfate from lead. The purpose of this pre-redox conversion process is to fully convert lead and lead dioxide in the material into PbSO ₄ . Subsequently, the researchers used sodium hydroxide, sodium carbonate, ammonium carbonate or ammonia water as the alkaline desulfurization agent and desulfurization reaction between lead sulfate to obtain Pb(OH) ₂ , PbO or PbCO ₃ . These compounds can be dissolved in HBF ₄ or H ₂ SiF ₆ to obtain a lead fluoborosilicate-fluoborosilicate mixed solution. The mixed solution can be electrolyzed to obtain electrodeposited lead at the cathode, oxygen at the anode, and a small amount of lead dioxide by-product at the same time. For details, refer to the USBM process reported in 1985 (Journal of Metals, 1985, 37 (2): 79-83), The US patent US.Patent 4769116 [P] of Italian Engitec company and the Italian Ginatta company patent US. Patent 4451340 [P].

Although the advantage of this type of process is that it can directly obtain electrolytic lead, the serious shortcomings of this type of process itself have seriously restricted the industrial application of these processes, and the described shortcomings generally include the following points:

1. The pre-redox reaction process takes a long time, and consumes a large amount of reducing agents such as Pb, Fe and SO ₂ and sulfuric acid at the same time, which not only increases the cost of this step, but also increases the processing cost of the subsequent alkaline desulfurization;

2. The power consumption is relatively high. The voltage of the electrolyzer in the electrolysis process is 2.7-3.2V, and the energy consumption per ton of lead is generally about 700-950KWh;

3. There is a relatively high concentration of lead ions remaining in the pre-oxidation reduction process and electrolytic waste liquid, which is not only highly corrosive to equipment, but also highly toxic to the environment;

4. A large amount of lead dioxide by-products are precipitated during the electrolysis process of the anode, which reduces the recovery efficiency of lead and leads to a large load of secondary reduction treatment.

In response to the above shortcomings, some studies have used potassium sodium tartrate or citric acid to complex the electrolytic process of the compound that dissolves lead to overcome the shortcomings of fluoboric acid. For example, "Chen Weiping, a new technology for wet recovery of waste lead battery filler [J]. Journal of Hunan University, 1996, 23(6): 111-116". However, this process also has problems such as high energy consumption in the electrolysis process and a large amount of lead dioxide by-product in the anode.

In order to reduce the necessary pre-redox conversion process in the soluble lead salt electrolysis process, and at the same time overcome the problems of anode lead dioxide by-products produced by the discharge of soluble lead ions at the anode, the researchers invented the direct A wet process in which the paste is coated on the plate for cathodic electrolytic reduction. For example, German Patent (DE3402338A) and British Patent (GB 1368423 and GB1428957) in 1985 have successively reported that lead paste is fixed on a metal cathode, and then electrolytic reduction is carried out in dilute sulfuric acid solution to obtain the method for lead powder and sulfuric acid. Subsequent Chinese patent ZL200710157084.X (a method for electrolytically reducing and regenerating lead resources in lead-containing plaster of waste lead-acid batteries) and Chinese patent ZL2008101114308.3 (method for recycling waste lead-acid battery battery lead by acid wet electrolysis) passed Semi-continuous electrolysis or the combination of dual power sources and activators further improves the reduction speed and efficiency of lead sulfate, realizes the direct reduction of lead paste in lead-acid batteries and recovers up to 30% of the by-product sulfuric acid in the electrolysis process.

The advantage of this acidic solid-phase electrolysis method is that lead powder and sulfuric acid can be directly electrolyzed, but its electrolysis process in an acidic solution requires a single-cell electrolysis voltage as high as 2.9-3.1V, which makes the electrolysis process lead to 100 per ton of lead. The energy consumption of electrolysis is as high as 920KWh/t(Pb). In addition, the oxidation loss of metal lead powder with high specific surface area in the smelting process is another reason that affects its application.

In order to reduce the high power consumption of acidic solid-phase electrolysis due to the high theoretical electrolysis voltage, some researchers have invented the wet-process regenerated lead technology of direct solid-phase reduction of lead paste in alkaline medium to obtain lead powder. Representative processes such as Chinese patent CN88103531 and related literature "solid-phase electrolysis - a new technology for regenerating lead [J]. Regeneration and Utilization of Nonferrous Metals, 2005, (12): 16-17" report the regenerated lead craft. Further improved patents by later researchers include: Chinese patent CN02132647.9 reported in 2002 and Chinese invention patent (ZL200910024467.9) by Lei Lixu's research group at Southeast University. The above-mentioned invention is characterized in that the positive and negative electrode paste obtained by crushing the battery is directly ground with water to make it into a viscous paste, and then coated on a metal mesh or metal frame electrode to make a cathode, and then use The stainless steel electrode is used as the anode, and the sodium hydroxide solution is used as the electrolyte for constant current electrolysis. Some patents report the use of constant-voltage electrolysis current changes to assist in judging the end point of electrolysis. Alkaline solid-phase electrolysis reduces the voltage of the electrolysis process to a great extent, thus saving the energy consumption of electrolysis to a certain extent.

Some patents in recent years have improved some shortcomings of the early alkaline paste on this basis. For example, it is proposed to use a rectangular frame with a grid structure as the cathode to increase the amount of paste, and to control the end point of electrolysis by means of constant voltage electrolysis and the change of current during constant voltage electrolysis. The advantage of this method is that it greatly increases the amount of lead loaded in a single operation, thereby reducing manual labor to a certain extent. The disadvantage is that the composition of the lead paste in each batch is complex, so the impedance of each batch of cathodes is different. It is very large, which leads to significant changes in the current during the actual electrolysis process. It is difficult to judge the end point of electrolysis based on the drop of the electrolysis current of a specific batch to 15-35% of the peak current. Therefore, there are often a large number of incompletely reduced in the actual product. lead compounds. In addition, because constant voltage electrolysis has the characteristics that the electrolysis current fluctuates according to the content of active substances and the impedance of the plate, the actual current in the mid-term of electrolysis is very large, so that a large part of the voltage is lost on the polarization of the electrode and the internal resistance of the solution, which makes The actual power consumption of this method is very uneconomical, usually as high as 547-880 kWh.

The recent characteristic work also includes the method of separating the positive and negative plates by mechanical means, and then electrolyzing in the electrolyte to obtain lead and lead dioxide powder. Since the positive electrode of the lead-acid battery is easy to swell and soften, it is particularly difficult to sort the swollen and softened positive plate by this method. Since the process produces equal amounts of lead and lead dioxide powder, the recovery efficiency of actual lead metal is only 50%.

The inventor found in the analysis of the lead paste components that the lead sulfate in the lead paste obtained from waste lead-acid batteries usually only accounts for 35-45% of the total weight of the lead paste, while the lead powder and lead dioxide are respectively 15-25% and 30-40%. The content of lead oxide is less. In the existing electrolysis process, for the convenience of electrolysis, researchers pre-oxidize and reduce lead and lead dioxide in sulfuric acid, so that Pb reacts with PbO ₂ and H ₂ SO ₄ to form PbSO ₄ . Often because the content of PbO ₂ is higher than that of Pb, people often add a certain amount of reducing agent (such as Fe, SO ₂ and Pb) to reduce the PbO ₂ to PbSO ₄ . This process not only consumes a large amount of reducing agent And sulfuric acid, as well as corresponding equipment resources, but also add a lot of extra NaOH to the subsequent desulfurization process to consume this part of the newly increased PbSO ₄ . In addition, the power consumption in the process of preparing regenerated lead by electrolysis of soluble lead salts is as high as 600-1000 degrees per ton, which is much higher than the level of 550 degrees per ton of lead in the existing fire method, resulting in dim prospects for industrialization.

In the alkaline solid-phase electrolysis process, although the alkaline electrolyte can reduce the energy consumption of the electrolysis process to a certain extent, in fact, due to the limitations of the existing process conditions, it is impossible to selectively select the different compounds in the lead paste. Instead of permanent electrolysis, a single high cathodic polarization electrolysis method is used, so that the actual cell pressure during the electrolysis process is also as high as 1.9-2.6V, and the energy consumption per ton of recycled lead is as high as 550-880 kWh, plus alkali The non-continuous mechanized operation of the permanent solid phase paste method has caused difficulties in actual industrial production.

In summary, the existing lead recovery technology still has the following disadvantages:

1. In the pretreatment step of lead recovery, it is often necessary to consume a large amount of reducing agent and a large amount of alkaline substances to desulfurize the sulfur-containing compounds in lead, which greatly increases the process cost; and

2. The lead recovery process still needs to consume a lot of electric energy.

Contents of the invention

An object of the present invention is to provide a method for reclaiming lead that can significantly reduce the consumption of reducing agents, alkaline substances and electric energy. The method selectively pre-separates lead elemental substances and compounds containing lead in different valence states in lead waste, And then according to the different valence states of lead, different electrolysis methods are used for combined electrolysis to realize the recovery of high-purity metallic lead.

According to one aspect of the present invention, the present invention provides a method for electrolytic recovery of lead from lead plaster, comprising: (1) washing the lead plaster with deionized water and performing solid-liquid separation to obtain lead sulfate, lead and a mixture of lead dioxide and dilute sulfuric acid solution; (2) reacting the solution with excess NaOH solution and performing solid-liquid separation for the second time to obtain Na ₂ [Pb(OH) ₄ ] and sodium hydroxide A mixed solution, and a solid mixture containing Pb and PbO ₂ ; the mixed solution containing Na ₂ [Pb(OH) ₄ ] and sodium hydroxide is carried out in an ionic membrane electrolyzer including a constant current electrolysis stage and a constant voltage electrolysis stage and (4) using a two-stage voltage-controlled constant-current electrolysis of the mixture of lead and lead dioxide in combination with an electroplating type electrodeposition refining process to reclaim pure lead.

Since the molar relationship between Na ₂ [Pb(OH) ₄ ] and PbO is 1:1, for the convenience of description, the following part of this patent directly adopts the concentration of PbO to equivalently represent the concentration of dissolved PbO in the solution.

In one embodiment, the concentration of the excess sodium hydroxide solution is 2 to 15 mol/L, preferably 3-9 mol/L, and the reaction is carried out at a temperature of 20 to 120°C, preferably 45 to 105°C.

In one embodiment, the conditions of constant current electrolysis are: electrolyte temperature 60 to 120°C; cathode current density 50 to 3500A/m ² ; anode current density 400 to 5000A/m ² ; ion membrane apparent current density 100 to 4500A/m ² ; and

The conditions of the constant voltage electrolysis are: the temperature of the electrolyte is 40 to 115°C, the concentration of lead oxide in the electrolyte is greater than 5g/L; when the concentration of lead oxide in the electrolyte in the electrolytic cell is reduced to below 5g/L, use Continue electrolysis at constant voltage, control the cell pressure of constant voltage electrolysis to 1.0 to 2.0V, and constant voltage electrolysis time to 100 to 1200min. When the concentration of lead oxide in the solution is 0.2g/L or below, stop electrolysis.

In one embodiment, the conditions of constant current electrolysis are: electrolyte temperature 65 to 105°C; cathode current density 300 to 1000A/m ² ; anode current density 500 to 4000A/m ² ; ion membrane apparent current density 300 to 4500A/m ² ; and

The conditions of the constant voltage electrolysis are: the temperature of the electrolyte is 65 to 105°C, and the voltage of the constant voltage electrolysis is between 1.35 and 1.95V.

In one embodiment, the staged electrolysis is performed sequentially in a constant-flow cationic membrane electrolyzer and a constant-pressure cationic membrane electrolyzer, or sequentially in the same cationic membrane electrolyzer.

In one embodiment, the two-stage voltage-controlled constant-current electrolysis combined with electrodeposition refining process includes: (1) adopting constant-current electrolysis mode, at a voltage of 0.3 to 1.2V, in 0.5 to 8.5M hydrogen oxidation In the sodium solution, the lead dioxide in the mixture is reduced to lead oxide; (2) the voltage is adjusted to 1.2 to 1.9V, and electrolysis is continued so that the lead oxide is reduced to lead; and (3) the lead obtained by reduction is Conduct an electroplating-type electrodeposition refining process together with the lead in the mixture, control the current density of the electrodeposition refining process to be 50 to 3500A/ ^m2 , preferably the current density is 100 to 1200A/ ^m2 , and the corresponding electrolytic voltage is 0.02 to 3500A/m2. Between 0.09V, pure lead is obtained at the cathode.

The lead recovery method of the invention can significantly reduce the consumption of reducing agents, alkaline substances and electric energy, and the recovered lead has a purity of more than 98%. In addition, the process of the lead recovery method of the present invention is carried out continuously and cyclically, which can meet the requirements of industrialization.

Description of drawings

Figure 1 is a flow chart of one embodiment of the method of the present invention; and

Fig. 2 is the schematic diagram of ion-exchange membrane electrolyzer used in the method of the present invention.

Detailed ways

Exemplary embodiments will be described in more detail hereinafter with reference to the accompanying drawings. The drawings described are intended to illustrate the invention, not to limit it.

The inventors found that the lead paste contains PbSO ₄ , PbO ₂ and PbO as well as elemental lead. Since the elemental lead does not need to participate in the electrochemical reaction, only the reduction of the other three different valence states of lead is considered in the actual process. Each substance has its own specific reduction potential, for example, the reduction potentials of the three compounds PbSO ₄ , PbO ₂ and PbO are:

PbSO ₄ +2e＝Pb+SO ₄ ^2- E ⁰ ＝-0.355V

PbO+2e+H ₂ O=Pb+2OH ^- E ⁰ ＝-0.578V

PbO ₂ +2e+H ₂ O=PbO+2OH ^- E ⁰ =0.248V

According to the electrode potential data, it can be seen that among the above three compounds in the same electrolyte environment, PbO ₂ is the easiest to reduce, and PbO is the most difficult to reduce. That is to say, for the PbO ₂ in the composition, a lower electrolysis voltage can be used, while for the PbO in the composition, a higher electrolysis voltage should be used to ensure the smooth progress of the electrolysis. However, the existing electrolytic lead recovery process does not consider the potential difference between different valence states of lead, but uses high cathodic polarization reduction for electrolysis, resulting in high actual electrolysis energy consumption.

The present inventors further found that, for example, under the same condition that oxygen is used as the oxygen evolution reaction, the equilibrium potential of oxygen under alkaline conditions is E ⁰ =0.401V, so 1 mol of PbO and PbO ₂ are gradually divided into stages using the present invention The potential and electric energy of reduction to lead are as follows (wherein the electric quantity of 1 mol electron is calculated as 26.8Ah):

(1) PbO:

Theoretical electrolysis voltage: 0.401-(-0.578)＝0.898V

Theoretical electrolysis electric energy: 2*26.8Ah*0.898V＝48.13Wh

(2) PbO ₂ (PbO ₂ -PbO-Pb):

Part I: Reduction of _PbO2 to PbO

Theoretical electrolysis voltage: 0.401-0.248＝0.133V

Theoretical electrolysis electric energy: 2*26.8Ah*0.133V＝7.13Wh

The second part: the PbO produced by reduction is further reduced to Pb

Theoretical electrolysis voltage: 0.401-(-0.578)＝0.898V

Theoretical electrolysis electric energy: 2*26.8Ah*0.898V＝48.13Wh

The total energy consumption is: 7.13+48.13＝55.26Wh

According to the electrolysis mode of soluble lead salt, 1 mol of Pb and ₁ mol of PbO2 are actually converted into 2 mol of +2-valent lead compound. The electrolysis conditions of acidic conditions and alkaline conditions are as follows:

(1) Acidic conditions (2mol Pb ²⁺ )

At this time, the acidic precipitation potential of oxygen is E ⁰ =1.229V, and the reduction of Pb ²⁺ to Pb is E ⁰ =-0.126V.

Theoretical electrolysis voltage: 1.229-(-0.126)=1.355V

Theoretical electrolysis electric energy: 4*26.8Ah*1.355V＝145.26Wh

(2) Alkaline conditions (2mol PbO)

Theoretical electrolysis voltage: 0.401-(-0.578)＝0.898V

Theoretical electrolysis electric energy: 4*26.8Ah*0.898V＝96.27Wh

Solid-phase electrolysis is also equivalent to treating 1 mol of Pb and 1 mol of PbO ₂ as 2 mol of PbO with the same electrolysis voltage for electrolysis.

Through the above detailed calculations, the inventors found that the present invention obtains a single electrolysis object through a simple and effective solid-liquid separation mode and adopts a selective electrolysis mode, which can theoretically obtain the lowest electrolysis energy consumption of 55.26Wh, which is far less than the current There are levels of 145.26Wh in acidic mode and 96.27Wh in alkaline mode.

That is, for Pb and PbO ₂ in a solid mixture, only the +4-valent lead in PbO ₂ needs electrons to be reduced to Pb. Considering the high oxidizing property of _PbO2 , the power consumption of the electrolysis process was saved by performing two continuous staged reduction processes on _PbO2 . Subsequently, the electroplating redeposition process is adopted to dissolve the powdered lead powder at the anode, and then electrodeposit again at the cathode to obtain dense electrodeposited lead.

It should be noted that the lead oxide content in waste lead plaster is very low, it can be considered that it reacts with waste sulfuric acid to generate lead sulfate during the washing stage, or is separated into a solid mixture containing Pb and _PbO2 as a solid during solid-liquid separation . Since the lead oxide content is very low, it can usually be ignored unless otherwise specified.

Thus, the present invention is a method of lead recovery that significantly reduces the consumption of reducing agents, alkaline substances and electrical energy. Figure 1 is a flow chart of one embodiment of the method of the present invention. Referring to Figure 1, waste lead-acid batteries are crushed and screened to obtain waste plastics, grids and lead paste. Routine recycling of waste plastics and grids. The components of lead paste mainly include lead, lead sulfate, lead dioxide, lead oxide and waste sulfuric acid. The lead paste obtained from the waste lead-acid battery is washed with deionized water and separated from solid and liquid to obtain a mixture containing lead sulfate, lead and lead dioxide and a dilute sulfuric acid solution. React the above-mentioned washed mixture with excess NaOH solution and separate solid-liquid for the second time, so that PbSO ₄ and NaOH in it are reacted to form a mixture containing Na ₂ [Pb(OH) ₄ ], Na ₂ SO ₄ and NaOH solutions and solid mixtures containing Pb and _PbO2 . According to the oxidation-reduction potentials of lead in different valence states, the mixed solution of Na ₂ [Pb(OH) ₄ ] containing +2-valent lead and the solid mixture of lead dioxide and lead containing +4-valent lead were carried out respectively. Independent electrolysis mode to recover lead separately.

Therefore, the present invention provides a method for electrolytic recovery of lead from lead plaster, comprising: (1) washing said lead plaster with deionized water and carrying out solid-liquid separation to obtain lead sulfate, lead and lead dioxide mixture and dilute sulfuric acid solution; (2) reacting the solution with excess NaOH solution and performing solid-liquid separation for the second time to obtain a mixed solution containing Na ₂ [Pb(OH) ₄ ] and sodium hydroxide, and containing Pb and PbO ₂ solid mixture; (3) the mixed solution containing Na ₂ [Pb(OH) ₄ ] and sodium hydroxide is electrolyzed in two stages of constant current and constant voltage in an ion-exchange membrane electrolyzer to obtain pure lead; and (4) using a two-stage voltage-controlled constant-current electrolysis of the mixture of lead and lead dioxide in combination with electrodeposition to recover pure lead.

In one embodiment, the concentration of the excess sodium hydroxide solution is 2 to 15 mol/L, preferably 3 to 9 mol/L, and the reaction is carried out at a temperature of 20 to 120°C, preferably 45 to 105°C.

Specifically, the mixture of lead and lead dioxide is first used in dilute NaOH in a two-stage voltage-controlled constant-current electrolysis mode to gradually reduce the lead dioxide in the mixture to lead oxide and lead at the cathode, and then the reduction is obtained The lead powder is transferred to another electrolytic cell as a new anode, and the metal lead in the lead powder is transferred to the electrolyte in the constant current electrolytic refining mode, and is electrodeposited to the metal cathode to form dense metal lead.

In one embodiment, the electrolysis of the mixture of lead and lead dioxide includes: (1) using constant current electrolysis mode, using a voltage of 0.3 to 1.2V in a sodium hydroxide solution of 0.5 to 8.5M The lead dioxide in the mixture is reduced to lead oxide; (2) the voltage is adjusted to 1.2 to 1.9V, and the electrolysis is continued so that the lead oxide is reduced to lead; and (3) the reduced lead and the mixture are Electrodeposit together with the lead in it to get pure lead.

Compared with conventional electrolysis of a mixture of lead and lead dioxide, the two-stage voltage-controlled constant-current electrolysis mode of the present invention combined with electrodeposition can further reduce power consumption and obtain denser metals with higher industrial value lead.

A mixed solution containing Na ₂ [Pb(OH) ₄ ], NaOH and Na ₂ SO ₄ is carried out in an ion-exchange membrane electrolyzer, and sequentially includes constant current electrolysis and pulse electrolysis. The constant current electrolysis can be carried out in one ionic membrane electrolyzer first, and then transferred to another electrolyzer for pulse electrolysis. The difference between the two ionic membrane electrolyzers is that the power supply is different. Constant current electrolysis and pulse electrolysis can also be performed sequentially in the same electrolyzer by replacing the power supply. The result of electrolysis is to obtain lead at the cathode and oxygen at the anode.

In one embodiment, taking the constant flow cationic membrane electrolyzer and the pulsed cationic membrane electrolyzer as examples, the staged electrolysis process includes the following steps:

(1) Inject the electrolyte solution containing Na ₂ [Pb(OH) ₄ ], NaOH and Na ₂ SO ₄ into a constant-current cationic membrane electrolyzer for constant-current electrolysis, wherein the conditions for constant-current electrolysis are: the temperature of the electrolyte is 60 to 120°C, preferably 65 to 105°C, more preferably 75 to 100°C; cathode current density of 150 to 3500A/ ^m2 , preferably 300 to 1000A/ ^m2 , more preferably 400A/ ^m2 ; anode current density of 400 to 5000A/m ² , preferably 500 to 4000A/m ² ; the apparent current density of the ionic membrane is 300 to 4500A/m ² ;

(2) When the Pb(OH) ₄ ^2- concentration is reduced to 5g/L (calculated as lead oxide), the electrolyte containing Na ₂ [Pb(OH) ₄ ], NaOH and Na ₂ SO ₄ is injected to a constant pressure Carry out constant voltage electrolysis in a type electrolytic cell until the concentration of Pb(OH) ₄ ^2- is less than 0.2g/L (calculated as lead oxide), wherein the condition of constant voltage electrolysis is: the temperature of the electrolyte is 40 to 115°C, preferably 65 to 105°C, more preferably 85 to 100°C; the cell pressure of constant voltage electrolysis is 1.0 to 2.0V, preferably 1.35 to 1.95V, and the constant voltage electrolysis time is 100 to 1200min until the concentration of lead oxide in the solution is 0.2g/L or The electrolysis is stopped at the following time.

In one embodiment, in one embodiment, the electrolysis of the mixed solution containing Na ₂ [Pb(OH) ₄ ] and NaOH comprises constant current electrolysis followed by constant voltage electrolysis, wherein,

The conditions of the constant current electrolysis are: electrolyte temperature 60 to 120°C; cathode current density 150 to 3500A/m ² ; anode current density 400 to 5000A/m ² ; ion membrane apparent current density 300 to 4500A/m ² ; and

The conditions of the constant voltage electrolysis are: the temperature of the electrolyte is 40 to 115°C; the cathode current density is 60 to 2000A/ ^m2 ; the cell pressure of the constant voltage electrolysis is 1.0 to 2.0V, preferably 1.35 to 1.95V; The time is 100 to 1200min, and the electrolysis is stopped when the concentration of lead oxide in the solution is 0.2g/L or below.

In one embodiment, the staged electrolysis is performed sequentially in a constant-flow cationic membrane electrolyzer and a constant-pressure cationic membrane electrolyzer, or sequentially in the same cationic membrane electrolyzer.

Figure 2 is a schematic diagram of an ionic membrane electrolyzer used in one embodiment of staged electrolysis. Referring to Figure 2, the ionic membrane electrolyzer includes a DC (or constant voltage) power supply 1; an electrolyte inlet 2 containing Na ₂ [Pb(OH) ₄ ], NaOH and Na ₂ SO ₄ ; lead cathode sheet 3; electrodeposited lead 4 lead concentration sensor 5; electrolyte outlet 6 containing NaOH and Na ₂ SO ₄ ; cationic membrane 7 (such as Nafion cationic membrane); nickel-plated anode 8; NaOH storage tank 9; crystalline NaOH storage tank 10.

Under the action of an electric field, Pb(OH) ₄ ^2- is deposited on the lead cathode sheet 3 to form electrodeposited lead 4, ^OH- produces oxygen (not shown) at the nickel-plated anode 8, and Na ⁺ is released from the anode through the selective cation membrane move towards the cathode. NaOH is supplemented at the anode end during the staged electrolysis process. When the NaOH in the NaOH storage tank is consumed too much, add crystalline NaOH to the NaOH storage tank. The electrolytic solution after staged electrolysis contains NaOH and sodium sulfate.

The specific reaction is as follows:

Cathode: [Pb(OH) ₄ ] ^2- +2e=Pb+4OH ^- (III)

Ion membrane: 2Na ⁺ _(anode) → 2Na ⁺ _(cathode) (IV)

Anode: 2OH ^- -2e＝1/2O ₂ +H ₂ O (V)

Total reaction: Na ₂ [Pb(OH) ₄ ]=Pb+1/2O ₂ +2NaOH (VI)

The present invention utilizes the principle of selective permeation of the cationic membrane, that is, the cationic membrane allows Na ⁺ to migrate from the anode to the cathode, thereby increasing the NaOH concentration at the cathode, and blocking [Pb(OH) ₄ ] ^2- from the migration of the cathode to the anode, Therefore, the by-product lead dioxide is prevented from being generated at the anode during the electrolysis process, and the industrially useful by-product oxygen can be generated at the anode.

The staged electrolysis adopted in the present invention can improve electrolysis efficiency and reduce power consumption. Most of the lead is rapidly electrolytically deposited during constant current electrolysis. During the constant voltage electrolysis, the constant voltage mode is used for subsequent electrolysis to achieve energy-saving and thorough electrolysis in a low-concentration lead ion solution. Since pulse electrolysis is non-continuous high-current electrolysis, it automatically reduces its corresponding response current according to the decrease of ion concentration in the solution, which ensures the efficiency of electrolysis on the one hand and the depth of electrolysis on the other hand. If it is continuous high-current constant-current electrolysis, the water in the cathode is bound to be reduced during the electrolysis process and a large amount of hydrogen is produced as a by-product, resulting in a decrease in current efficiency.

In the present invention, adding NaOH at the anode end can maintain the Na ⁺ concentration at the anode end, thereby maintaining the continuous progress of the electrolysis reaction, and the added NaOH can be directly used as a raw material for the next cycle to complex PbO.

In the present invention, adding crystallized NaOH to the NaOH storage tank during the staged electrolysis can not only increase the concentration of NaOH in the NaOH storage tank, but also prevent exothermic and boiling phenomena caused by direct NaOH solid addition. Crystalline NaOH (NaOH·2H ₂ O) is obtained, for example, by treating NaOH solid with ice water.

The sodium sulfate in the electrolytic solution is further precipitated by adding NaOH·2H ₂ O to the electrolytic solution containing NaOH and sodium sulfate after the segmental electrolysis process is completed, and the precipitated sodium sulfate is filtered. The remaining NaOH solution is returned to the above alkali leaching purification process for recycling. The looping process includes the following steps:

(1) Add crystalline NaOH to the electrolyte solution containing NaOH and sodium sulfate after electrolysis, and gradually precipitate Na ₂ SO ₄ ·10H ₂ O crystals;

(2) After the electrolyte solution is filtered through the sodium sulfate crystals, the electrolyte solution (mainly NaOH) is returned to the above-mentioned alkali leaching purification process for recycling.

The present invention can make to adding crystallized NaOH during the circulation process: (1) under the same ion effect, impel the sodium sulfate in the electrolytic solution to separate out, reach the purpose of non-evaporation directly reclaiming sodium sulfate; (2) the added NaOH directly serves as The raw material of the next cycle is used to complex PbO; (3) Adding crystalline NaOH hardly produces exothermic and boiling phenomena, which is more conducive to the precipitation of sodium sulfate than non-crystalline NaOH. The sodium sulfate and oxygen produced are recovered as by-products.

It can be seen that the combined use of selective electrolysis and staged electrolysis in the present invention can further reduce power consumption, and the whole process can be carried out continuously and cyclically. In addition, valuable by-products such as Na ₂ SO ₄ ·10H ₂ O crystals are also produced.

In summary, the method of the present invention has the following characteristics:

(1) During the implementation of the present invention, the present invention removes sulfuric acid and other soluble impurities mixed in the original lead plaster by the first pre-washing method, thereby reducing the consumption of NaOH and improving regeneration for the subsequent desulfurization process help with the purity of the lead;

(2) In the second solid-liquid separation process, the present invention utilizes alkaline NaOH to carry out timely and effective separation of the +2-valent lead compound in the cleaned lead plaster, thereby obtaining the compound containing only +2-valent lead ion Alkaline solutions of Na ₂ [Pb(OH) ₄ ] and mixtures of isolated lead powder and lead dioxide powder; and

(3) carry out independent electrolysis to the lead compound of different valence state:

A, using the staged ion membrane electrolysis method to thoroughly electrolyze the compound of +2 valent lead in the solution;

B. Use two-step electrolysis to gradually reduce the PbO ₂ in Pb and PbO ₂ , make it gradually transform into PbO and Pb, and finally use the electroplating electrodeposition refining method to electrodeposit the lead powder obtained from the above reduction again into a dense electrolytic lead.

The method of the invention can greatly save the consumption of acid, reducing agent, alkaline substance and electric energy, so that the whole method is suitable for industrial application.

Example

Example 1

The 12V, 10AH waste lead-acid batteries sold on the market were crushed and separated to obtain 2.6kg of lead paste. Get wherein 200 grams of lead plaster and wash with 150ml deionized water and filter to obtain 2% (wt.) dilute sulfuric acid and 196 grams of lead plaster. Then the lead plaster and 1 liter of 10M NaOH were subjected to alkaline desulfurization reaction at 95° C., and after keeping the reaction time for 1.5 h, hot filtration was performed immediately to obtain 1 liter of NaOH solution containing 70 g/LPbO and 95 grams of Pb and PbO _. solid mixture.

The lead-containing mother liquor enters the electrolytic cell for ionic membrane electrolysis after conventional standing and purification. Firstly, constant current electrolysis was carried out in the electrolytic cell, the cathode and anode current densities were controlled to be 700A/m ² , the electrolysis temperature was 90°C, and the electrolysis voltage was 1.44V. When the electrolysis time reaches 100min, when the lead concentration is detected to be less than 5g/L at this time, it will enter the constant voltage electrolysis stage. At this time, the electrolysis temperature was controlled to be 80° C., and the constant electrolysis voltage was 1.60 V. When the electrolysis actually reaches 600min, the concentration of lead oxide in the electrolysis mother liquor is reduced to below 0.2g/L. After electrolysis, the actual concentration of NaOH was raised to 10M again by adding NaOH to the electrolytic mother liquor after electrolysis, and then the electrolyte was cooled to 5°C, at this time, sodium sulfate decahydrate crystals were precipitated in the solution. The mother liquor is subjected to solid-liquid separation to obtain 10M NaOH solution and sodium sulfate crystals, and the lead-containing NaOH mother liquor is returned to the desulfurization process for recycling.

Separate and obtain 95 grams of solid mixture containing Pb and PbO ₂ and prepare it with 5 grams of 2M NaOH solution to obtain a brown paste, which is then extruded on a 6*8cm ² strip-shaped metal mesh electrode to form a thickness of about 3mm layer of lead compound. It is then immersed in an electrolytic cell containing an alkaline electrolyte for a staged cathodic reduction reaction. First, a current density of 20mA/cm ² (960mA) was used for slow electrolysis until the cell pressure rose to 0.99V, so that the lead dioxide in the mixture was gradually transformed into lead oxide in the electrolytic cell. Then the electrode is transferred to the rapid electrolysis stage, using 100mA/cm ² (4800mA) for the second stage of electrolysis, so that the lead oxide in the mixture gets electrons and electrolyzes into metal lead powder. At this time, the electrolysis temperature was controlled to be 80°C, and the electrolysis voltage was 1.32V. When the electrolysis voltage rises to 1.85V, stop the electrolysis and take out the lead powder electrode, and move it into another electrolytic tank for alkaline electrolytic refining process. The lead powder is used as the anode of the electrolytic cell, and the pure lead flakes (6*8cm ² ) are used as the cathode for alkaline electrolytic refining. At this time, the lead powder on the mesh electrode gradually undergoes anodic oxidation and dissolves, and at the same time, electrolytic lead is obtained on the lead cathode plate. The electrolytic cell adopts 9M NaOH electrolyte containing 70g/L PbO, the electrolysis temperature is 75°C, the current density is 50mA/cm ² , and the cell voltage of the electroplating electrolytic refining is 0.083V.

After testing and calculation, the cathode lead has obtained 152 grams of metallic lead, its purity is 99.991%, and its current efficiency is 98.9%. The total energy consumption of the direct electrolysis process of lead paste is 332kWh/t (Pb), and the comprehensive recovery rate of lead is 98.6%.

Example 2

Take a 12V, 45Ah waste lead-acid battery for automobiles, and the total weight of the battery pack is 13.2 kg. Use conventional mechanical methods to crush and separate waste batteries to obtain lead paste, grids, separators and plastics.

Get about 5.9 kg of lead plaster and 5 liters of 2% dilute sulfuric acid after washing with 6 kg of lead plaster powder obtained in the above process and 5 liters of deionized water.

The lead plaster obtained by solid-liquid separation and 27 liters of 10.5M NaOH were subjected to alkaline desulfurization reaction at 100°C. After keeping the reaction time for 1.0h, they were immediately filtered while hot to obtain 28 liters of NaOH solution containing 75g/L PbO and 2.8 kg of a solid mixture containing Pb and _PbO2 .

The alkaline solution containing 75g/L lead oxide obtained by the above process is injected into the cathode chamber of the ion-exchange membrane (Nafion982) electrolyzer, and the anode chamber is then injected with 12M NaOH solution. The anode of the electrolytic cell is sprayed with nickel foam of 2.2mg/cm ² Pt ₄₀ Ru ₂₀ C ₄₀ catalyst as the anode, and the cathode is a sheet electrode made of pure lead. Adjust the power output and electrolyte flow rate to make the electrolytic cell perform a stable electrolysis process, control the current density of the cathode and anode to 20mA/cm ² , the electrolysis temperature to 85°C, and the electrolysis voltage to 1.35V. When the lead oxide concentration in the electrolyte drops to 5g/L, stop the constant current reaction and enter the constant voltage electrolysis mode. At this time, the electrolysis temperature was controlled to be 85° C., and the constant electrolysis voltage was 1.50 V. When the electrolysis time reaches 650min, the concentration of lead oxide in the electrolysis mother liquor drops below 0.2g/L. After electrolysis, the actual concentration of NaOH was raised to 10M again by adding NaOH to the electrolytic mother liquor after electrolysis, and then the electrolyte was cooled to 5°C, at this time, sodium sulfate decahydrate crystals were precipitated in the solution. The mother liquor is subjected to solid-liquid separation to obtain 10M NaOH solution and sodium sulfate crystals, and the lead-containing NaOH mother liquor is returned to the desulfurization process for recycling.

Separated to obtain 2.9 kg of solid mixture containing Pb and PbO ₂ , add 3% 2M NaOH solution relative to its weight for deployment, make it gradually form a viscous brown paste, and then coat it on a 20*30cm ² strip metal On the mesh electrode, a lead compound layer with a thickness of about 6mm is formed. It is then immersed in an electrolytic cell containing an alkaline electrolyte for a staged cathodic reduction reaction. Firstly, a current density of 15mA/ ^cm2 (9A) is used for slow electrolysis until the pressure of the electrolytic cell rises to 0.9V. This process makes the lead dioxide in the mixture obtain electrons in the electrolytic cell and gradually transform into lead oxide. Then the electrode is transferred to the stage of fast electrolysis, and 80mA/cm ² (48A) is used for the second stage of electrolysis, so that the lead oxide in the mixture can obtain continuous electrons and be transformed into metallic lead powder. At this time, the electrolysis temperature was controlled to be 85°C, and the electrolysis voltage was 1.35V. When the electrolysis voltage rises to 1.85V, stop the electrolysis and take out the lead powder electrode, and move it into the electrolytic cell 2-2 to carry out the alkaline electrolytic refining process. The lead powder is used as the anode of another electrolytic cell, and two pure lead flakes (20*30cm ² ) are used as the cathode for alkaline electrolytic refining. At this time, the lead powder on the mesh electrode gradually undergoes anodic oxidation and dissolves, and at the same time, electrolytic lead is obtained on the lead cathode plate. The electrolytic cell uses 9M NaOH electrolyte containing 70g/L PbO, the electrolysis temperature is 80°C, the current density is 50mA/cm ² , and the voltage of the electroplating electrolytic refining cell is 0.089V.

After testing and calculation, 4.4 kg of metallic lead was obtained from the cathode lead, the purity of which was 99.991%, and the current efficiency was 98.9%. Except for the self-discharge of the electrolytic cell 2-1, the net power consumption of the direct electrolysis process of all lead pastes is 325kWh/t(Pb), and the comprehensive recovery rate of lead is 99.0%.

Example 3

From the 12V, 14Ah lead-acid battery workshop, 13 kg of scrap negative plates mixed with waste lead-acid battery positive plates were obtained. After the waste battery plates were crushed, about 10 kg of lead powder was obtained, and the main components were Pb and PbSO in the electrodes themselves. _4. PbO and a small amount of PbO ₂ .

Get about 10 kilograms of lead plaster powder and 5 liters of 0.2% dilute sulfuric acid after washing the 10 kilograms of lead plaster powder obtained in the above process and 5 liters of deionized water.

The lead plaster obtained by solid-liquid separation and 50 liters of 11M NaOH were subjected to alkaline desulfurization reaction at 100°C. After keeping the reaction time for 1.0h, they were immediately filtered while hot to obtain about 50 liters of NaOH solution containing 89g/L PbO and 3.7 kg of a solid mixture containing Pb and _PbO2 .

The alkaline solution containing 89g/L lead oxide obtained by the above process is injected into the cathode chamber of the ion-exchange membrane (Nafion2030) electrolyzer, and the anode chamber is then injected with 12M NaOH solution. The anode of the electrolytic cell is a nickel anode sprayed with 2.5mg/cm ² Pt ₄₀ C ₆₀ catalyst, and the cathode is a sheet electrode made of pure lead. Adjust the electrolysis power supply and electrolyte flow rate to make the electrolysis cell perform a stable electrolysis process, control the current density of the cathode and anode to 50mA/cm ² , the electrolysis temperature to 95°C, and the working voltage of the electrolysis cell to 1.31V. At this time, dense electrolytic lead generation was observed at the cathode. When the lead oxide concentration in the electrolyte drops to 5g/L, stop the constant current reaction and enter the constant voltage electrolysis mode. At this time, the electrolysis temperature was controlled to be 95° C., and the constant electrolysis voltage was 1.45V. When the electrolysis time reaches 670min, the concentration of lead oxide in the electrolysis mother liquor drops below 0.2g/L. After electrolysis, the actual concentration of NaOH was increased to 10M by adding NaOH to the electrolytic mother liquor after electrolysis, and then the electrolyte was cooled to 5°C. At this time, a very small amount of sodium sulfate decahydrate crystals were precipitated in the solution. The mother liquor is subjected to solid-liquid separation to obtain 10M NaOH solution and sodium sulfate crystals, and the lead-containing NaOH mother liquor is returned to the desulfurization process for recycling.

Separated to obtain 3.7 kg of solid mixture containing Pb and PbO ₂ , add 3% 2M NaOH solution relative to its weight for preparation, make it gradually form a dark viscous paste, and then coat it on a 30*50cm ² strip On the metal mesh electrode, a lead compound layer with a thickness of about 3 mm is formed. It is then immersed in an electrolytic cell containing an alkaline electrolyte for a staged cathodic reduction reaction. First, the current density (15A) of 10mA/ ^cm2 is used for slow electrolysis until the voltage of the electrolytic cell rises to 1.15V. This process makes the lead dioxide in the mixture obtain electrons in the electrolytic cell and gradually convert it into lead oxide. Then the electrode is transferred to the fast electrolysis stage, and 100mA/cm ² (150A) is used for the second stage of electrolysis, so that the lead oxide in the mixture can obtain continuous electrons and be transformed into metal lead powder. At this time, the electrolysis temperature was controlled to be 85°C, and the electrolysis voltage was 1.31V. When the electrolysis voltage rises to 1.75V, stop the electrolysis and take out the lead powder electrode, and move it into another electrolytic tank for alkaline electrolytic refining process. The lead powder is used as the anode of the electrolytic cell, and two pure lead flakes (30*50cm ² ) are used as the cathode for alkaline electrolytic refining. At this time, the lead powder on the mesh electrode gradually undergoes anodic oxidation and dissolves, and at the same time, electrolytic lead is obtained on the lead cathode plate. The electrolytic cell 2-2 uses 9M NaOH electrolyte solution containing 75g/L PbO, the electrolysis temperature is 85°C, the current density is 50mA/cm ² , and the voltage of the electroplating electrolytic refining cell is 0.079V.

After testing and calculation, the cathode lead obtained 7.7 kg of metallic lead with a purity of 99.991% and a current efficiency of 99.2%. The power consumption is 319kWh/t(Pb), and the comprehensive recovery rate of lead is 99.1%.

Example 4

From the lead-acid battery manufacturer, the lead-acid battery for automobiles returned to the factory ahead of schedule due to the softening of the positive plate was obtained. The battery is mechanically crushed and washed to obtain the lead slime mainly containing _PbO2 positive electrode and relatively complete negative electrode grid.

Get about 10 kilograms of wet lead mud and 5 liters of dilute sulfuric acid containing 3% after getting 10 kilograms of lead mud powders obtained in the above process and washing with 5 liters of deionized water.

The lead slime obtained by solid-liquid separation and 30 liters of 12M NaOH were subjected to an alkaline desulfurization reaction at 100°C. After keeping the reaction time for 1.5h, they were immediately filtered while hot to obtain about 30 liters of NaOH solution containing 75g/L PbO and 6.8 kg of a solid mixture containing Pb and _PbO2 .

The alkaline solution containing 75g/L lead oxide obtained by the above process is injected into the cathode chamber of the self-generating ion membrane (Nafion2030) electrolyzer, and the anode chamber is injected with 12M NaOH solution. The anode of the electrolytic cell is sprayed with a porous nickel foam anode, and the cathode is a sheet electrode made of pure lead. Adjust the output power of the power supply and the flow rate of the electrolyte to make the electrolytic cell perform a stable electrolytic process, control the current density of the cathode and anode to 30mA/cm ² , the electrolysis temperature to 90°C, and the working voltage of the electrolytic cell to 1.342V. Precipitation of electrolytic lead can be observed at the cathode of the electrolytic cell. As the concentration of lead oxide decreases, the electrolysis voltage of the electrolysis process increases slowly.

When the lead oxide concentration in the electrolyte drops to 5g/L, stop the constant current reaction and enter the constant voltage electrolysis mode. At this time, the electrolysis temperature was controlled to be 99° C., and the constant electrolysis voltage was 1.43V. When the electrolysis time reaches 630min, the concentration of lead oxide in the electrolysis mother liquor drops below 0.2g/L. After electrolysis, the actual concentration of NaOH was increased to 10M by adding NaOH to the electrolytic mother liquor after electrolysis, and then the electrolyte was cooled to 5°C. Due to the low content of lead sulfate in the raw material, almost no sodium sulfate decahydrate crystals were precipitated in the solution at this time. After the mother liquor is subjected to solid-liquid separation to obtain 10M NaOH solution and impurities, the lead-containing NaOH mother liquor is returned to the desulfurization process for recycling.

Separated to obtain 6.8 kg of solid mixture containing Pb and PbO ₂ , adding 3% NaOH solution relative to its weight for deployment, making it gradually form a dark viscous paste, and then coating it on a 30*50cm ² strip On the metal mesh electrode, a lead compound layer with a thickness of about 7mm is formed. It is then immersed in an electrolytic cell containing an alkaline electrolyte for a staged cathodic reduction reaction. Firstly, the current density (15A) of 10mA/ ^cm2 is used for slow electrolysis until the pressure of the electrolytic cell rises to 0.95V. This process makes the lead dioxide in the mixture obtain electrons in the electrolytic cell and gradually convert it into lead oxide. Then the electrode is transferred to the fast electrolysis stage, and 80mA/cm ² (120A) is used for the second stage of electrolysis, so that the lead oxide in the mixture can obtain continuous electrons and be transformed into metallic lead powder. At this time, the electrolysis temperature was controlled to be 85°C, and the electrolysis voltage was 1.41V. When the electrolysis voltage rises to 1.9V, stop the electrolysis and take out the lead powder electrode, and move it into another electrolytic tank for alkaline electrolytic refining process. The lead powder is used as the anode of another electrolytic cell, and two pure lead flakes (30*50cm ² ) are used as the cathode for alkaline electrolytic refining. At this time, the lead powder on the mesh electrode gradually undergoes anodic oxidation and dissolves, and at the same time, electrolytic lead is obtained on the lead cathode plate. The electrolytic cell uses 9M NaOH electrolyte containing 75g/L PbO, the electrolysis temperature is 80°C, the current density is 50mA/cm ² , and the voltage of the electroplating electrolytic refining cell is 0.090V.

After testing and calculation, the cathode lead obtained 8.1 kilograms of metallic lead with a purity of 99.991% and a current efficiency of 98.7%. The power consumption is 317kWh/t(Pb), and the comprehensive recovery rate of lead is 99.2%.

The present invention has been described in detail above through preferred embodiments and specific examples. However, those skilled in the art should understand that the scope of the present invention is not limited thereto, and any modifications or changes that do not depart from the present invention are within the scope of the present invention.

Claims (6)

1. A method of electrolytic recovery of lead from lead plaster, characterized in that it adopts combined electrolysis, comprising: (1) Washing the lead paste with deionized water and separating the solid and liquid to obtain a mixture containing lead sulfate, lead and lead dioxide and a dilute sulfuric acid solution; (2) React the solution with excess sodium hydroxide solution and perform a second solid-liquid separation to obtain a mixed solution containing Na ₂ [Pb(OH) ₄ ] and sodium hydroxide, as well as lead and dioxide Solid mixtures of lead; (3) The mixed solution containing Na ₂ [Pb(OH) ₄ ] and sodium hydroxide is subjected to staged electrolysis in an ion-exchange membrane electrolyzer including a constant current electrolysis stage and a constant voltage electrolysis stage to recover pure lead, wherein Stop electrolysis when the concentration of lead oxide in the solution is less than 0.2g/L; and (4) The mixture of lead and lead dioxide is subjected to two-stage voltage-controlled constant-current electrolysis combined with electrodeposition to recover pure lead, In (3), the conditions of constant current electrolysis are: electrolyte temperature 60°C to 120°C; cathode current density 150A/m ² to 3500A/m ² ; anode current density 400A/m ² to 5000A/m ² ; The apparent current density of the ionic membrane is 300A/m ² to 4500A/m ² ; and The constant voltage electrolysis conditions are: electrolyte temperature 40°C to 115°C; constant voltage electrolysis tank pressure 1.0V to 2.0V; constant voltage electrolysis time is 100 minutes to 1200 minutes, The constant current electrolysis of the two-stage voltage control combined with electrodeposition comprises: (a) reducing lead dioxide in the mixture to lead oxide in a 0.5M to 8.5M sodium hydroxide solution at a voltage of 0.3V to 1.2V in a constant current electrolysis mode; (b) adjusting the voltage to 1.2V to 2.0V, continuing the electrolysis to reduce the lead oxide to lead; and (c) subjecting the reduced lead together with the lead in the mixture to an electroplating electrodeposition process to obtain pure lead. 2. The method according to claim 1, wherein the concentration of the excess sodium hydroxide solution is 2mol/L to 15mol/L, and the reaction is carried out at a temperature of 20°C to 120°C. 3. The method according to claim 2, wherein the concentration of the excess sodium hydroxide solution is 3mol/L to 9mol/L, and the reaction is carried out at a temperature of 45°C to 105°C. 4. The method of claim 1, wherein, The conditions of the constant current electrolysis are: electrolyte temperature 65°C to 105°C; cathode current density 300A/m ² to 1000A/m ² ; anode current density 500A/m ² to 4000A/m ² ; ion membrane apparent current density 300A/m ² to 4500A/m ² ; and The constant voltage electrolysis conditions are: the temperature of the electrolyte is 65° C. to 105° C.; the cell pressure of the constant voltage electrolysis is 1.35 V to 1.95 V; the constant voltage electrolysis time is 100 minutes to 1200 minutes. 5. The method according to claim 1, characterized in that, the step-by-step electrolysis is carried out sequentially in constant-flow cationic membrane electrolyzer and constant pressure cationic membrane electrolyzer, or sequentially in the same cationic membrane electrolyzer proceed. 6. The method according to claim 1, characterized in that, in the electroplating electrodeposition process mode, the current density for controlling the electrodeposition process is 50A/m ² to 3500A/m ² , and the corresponding electrolysis voltage is 0.02 V to 0.09V, pure lead is obtained at the cathode.

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