PROCESS AND APPARATUS FOR REDUCING STANNIC OXIDE INTO METALLIC TIN

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of PCT application No. PCT/CN2024/085812 filed on Apr. 3, 2024, which claims the benefit of Chinese Patent Application No. 202310366897.9 filed on Apr. 7, 2023. The contents of all of the aforementioned applications are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure belongs to the technical field of reduction of metal oxides, and specifically relates to a process and apparatus for reducing stannic oxide into metallic tin.

BACKGROUND

Stannic oxide is an inorganic substance existing as a tetragonal, hexagonal, or orthorhombic crystalline powder. Stannic oxide is insoluble in water, and can also hardly be dissolved in an acidic or alkaline solution. Stannic oxide occurs naturally in the form of reddish-brown cassiterite. Further, a large amount of tin-containing sludge is produced from the modern industrial production processes such as tin-plating and tin-stripping processes, and needs to be collected and treated for environmental protection. The main component of hazardous tin-containing sludge is stannic oxide. The current technologies for reducing stannic oxide into metallic tin include sodium hydroxide fusion and high-temperature reduction. The high-temperature reduction involves a chemical reaction of stannic oxide with a reducing agent such as carbon, carbon monoxide, or hydrogen at a high temperature to produce metallic tin and carbon dioxide or metallic tin and water. The sodium hydroxide fusion is as follows: sodium hydroxide is melted at a high temperature and then allowed to react with stannic oxide to produce sodium stannate and water, and then sodium stannate is converted into metallic tin through an additional reaction.

Both of the two technologies require a high-temperature operation, and thus can hardly be popularized for small-scale production enterprises to treat tin-containing sludge. Moreover, these high-temperature processes cannot meet the requirement of tin-containing sludge-producing enterprises to convert hazardous tin-containing sludge into a stannous salt or metallic tin for recycling in production, thereby reducing the environmental pollution and production cost. Therefore, there is an urgent need to develop a novel process for reducing stannic oxide into metallic tin.

SUMMARY

Stannic oxide is an inorganic powder with unique electric conductivity. In the present disclosure, a stannic oxide solid is converted into metallic tin through an electrochemical reduction reaction based on the electrical conductivity of the stannic oxide solid, and/or the metallic tin is further converted into a solid product and/or a solution product of a tin compound using an electrolyte.

A first objective of the present disclosure is to provide a process for reducing stannic oxide into metallic tin. A second objective of the present disclosure is to provide an apparatus for reducing stannic oxide into metallic tin to achieve the first objective.

A process for reducing stannic oxide into metallic tin is provided, including the following steps:

• • step 1, establishing at least one electrolytic cell provided with an anode and a cathode; connecting the anode to a positive terminal of an electrolytic power supply, and connecting the cathode to a negative terminal of the electrolytic power supply; and feeding the stannic oxide and an electrolyte solution into the at least one electrolytic cell, such that the stannic oxide directly contacts the cathode or the metallic tin on the cathode during electrolysis;
  • step 2, turning on the electrolytic power supply to initiate the electrolysis, where at the anode, an electrochemical oxidation reaction occurs to dissolve a soluble anode metal or allow evolution of chlorine and/or oxygen at an insoluble anode, and at the cathode, the stannic oxide in direct contact with the cathode and/or the stannic oxide in direct contact with the metallic tin on the cathode undergoes an electrochemical reduction reaction to produce the metallic tin; and
  • step 3, collecting the metallic tin produced from the electrolysis and/or a solid product and/or a solution product of a tin compound produced from a reaction of the metallic tin with the electrolyte solution.

In the step 1, the electrolyte solution is an aqueous solution including an organic and/or inorganic soluble electrolyte, and the organic and/or inorganic soluble electrolyte is at least one selected from the group consisting of an organic and/or inorganic soluble salt, an organic and/or inorganic soluble acid, and an organic and/or inorganic soluble alkali. Preferably, the salt is one or a combination of two or more selected from the group consisting of a sodium salt, a potassium salt, and an ammonium salt; the acid is one or a combination of two or more selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid; and the alkali is one or a combination of two or more selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, ammonium hydroxide, ammonium carbonate, and ammonium bicarbonate. When the electrolyte solution includes more than one soluble electrolyte, a concentration and proportion of each soluble electrolyte are not limited.

Since the metallic tin produced is an amphoteric metal, the metallic tin can not only react with an alkaline solution, but also react with an acid to produce a salt. For example,

• • a reaction equation of tin with sodium hydroxide is as follows: Sn+2NaOH+2H₂O→Na₂[Sn(OH)+]+H₂↑;
  • an accompanied chemical reaction is as follows: Na₂[Sn(OH)+]→SnO+H₂O+2NaOH; and
  • a reaction equation of tin with hydrochloric acid is as follows: Sn+2HCl→SnCl₂+H₂↑.

To achieve a high yield of metallic tin, a salt solution is preferably adopted as the electrolyte solution. More preferably, a soluble sulfate solution is adopted as the electrolyte solution.

In the step 1 of the process of the present disclosure, the at least one electrolytic cell may refer to an electrolytic cell without a separator, or an electrolytic cell provided with a separator to divide the electrolytic cell into an anode compartment and a cathode compartment, or both the electrolytic cell without the separator and the electrolytic cell with the separator. The separator for the electrolytic cell is a material capable of effectively blocking electrolytically generated bubbles and the stannic oxide. The separator is configured to prevent an oxidative gas from the anode compartment from entering the cathode compartment to corrode the metallic tin produced, thereby improving the yield of the metallic tin. The separator is preferably one or a laminated combination of two or more selected from the group consisting of a cation-exchange membrane, an anion-exchange membrane, a bipolar membrane, a reverse osmosis membrane, a non-ion-selective filter membrane, a proton-exchange membrane, and a filter cloth. The reverse osmosis membrane is a reverse osmosis diaphragm. When the electrolytic cell with the separator is adopted, the stannic oxide is fed into the cathode compartment and allowed to directly contact the cathode or the metallic tin on the cathode for electrification to achieve the objective of the process of the present disclosure.

The use of the electrolytic cell with the separator has the following advantages: An oxidative gas generated in the anode compartment and hydrogen generated in the cathode compartment can be separately collected and utilized, which reduces the explosion risk caused by the mixing of the oxidative gas and hydrogen. Additionally, the migration of an oxidative substance in the anode compartment to a cathode electrolyte can be minimized, thereby mitigating the corrosion to the metallic tin formed on the cathode. However, the electrolytic cell with the separator has a complex structure, high energy consumption, and a high cost.

In the step 2, under various reaction conditions when different anode materials and different electrolyte compositions are selected, different electrochemical reactions occur at the anode, leading to a variety of distinct reaction outcomes.

When a soluble metal anode is adopted as the anode, an electrochemical reaction of converting a metal into a metal ion primarily occurs at the anode. For example,

• • (1) when a metallic zinc anode is adopted, Zn-2e⁻→Zn²⁻; and
  • (2) when an iron metal anode is adopted, Fe-2e⁻→Fe²⁺.

When an insoluble anode is adopted as the anode and a chloride ion-free solution is adopted as an anode electrolyte, at least one of the following electrochemical reactions occurs at the anode to generate oxygen:

When an insoluble anode is adopted as the anode and the anode electrolyte includes a chloride ion, the following electrochemical reaction occurs at the anode to generate chlorine:

The stannic oxide in direct contact with the cathode and/or the stannic oxide in direct contact with the metallic tin on the cathode is reduced into metallic tin, which is typically accompanied by the evolution of hydrogen. During the electrolysis, stannic oxide that is first in direct contact with the cathode is reduced into metallic tin. Since metallic tin is electrically conductive, metallic tin formed on a surface of the cathode can be considered as a part of the cathode, and can reduce stannic oxide in contact with the metallic tin on the surface of the cathode to produce metallic tin. At least one of the following electrochemical reactions occurs at the cathode:

Preferably, the anode is an insoluble anode.

The inventors have discovered that increasing an opportunity for the stannic oxide to contact the surface of the cathode can effectively enhance an electrochemical reduction reaction for the stannic oxide. Therefore, any one or more of the following preferred solutions can be employed to achieve the full contact of the stannic oxide with the cathode.

Preferred solution 1: An inclined electrolytic cell is adopted, and the cathode is arranged at a low position in the inclined electrolytic cell. As a result, under a gravity action, a stannic oxide powder can accumulate around the cathode.

Preferred solution 2: The cathode is structurally improved to produce a cathode conductive carrier, which is a planar, spoon-shaped, or grooved cathode structure capable of loading a stannic oxide powder. A part or all of a contact surface of the cathode conductive carrier with the loaded stannic oxide is an electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply. When the cathode conductive carrier is provided with a groove, the higher the groove wall of the groove, the more effectively the stannic oxide can be prevented from leaving the cathode conductive carrier.

Preferred solution 3: The cathode is enclosed by a filter cloth bag and/or a filter plate to confine at least a majority of the stannic oxide within a vicinity of the cathode to increase a contact rate of the stannic oxide with the cathode. Preferably, a filter cloth bag made of a filter cloth is adopted to facilitate the cleaning and recycling, thereby reducing the operating cost.

The present disclosure can be improved as follows: A vertical electrolytic cell is adopted, that is, the cathode is arranged below at least one anode. The vertical electrolytic cell may be either an electrolytic cell without a separator or an electrolytic cell with a separator. The combination of the vertical electrolytic cell and the cathode conductive carrier in the preferred solution 2 can achieve a prominent power-saving effect. When the cathode conductive carrier is used to load the stannic oxide, electric field lines between reaction surfaces of the anode and the cathode conductive carrier are long, resulting in low current efficiency. However, the use of the vertical electrolytic cell can shorten the electric field lines between the reaction surfaces of the anode and the cathode conductive carrier, thereby solving the above problem.

Preferably, when a vertical electrolytic cell with the separator is adopted, the separator at a side of the cathode compartment that faces the anode and an inclined cover plate separator-fixing frame constitute a movable inclined cover plate separator; holes in the inclined cover plate separator-fixing frame are blocked with the separator; and an upper part in the cathode compartment is further provided with an outlet configured to discharge a gas or a gas and a liquid. This design can avoid the mixing of rising hydrogen generated with an oxidative gas generated at the anode, and enables the easy collection of hydrogen. In addition, this design can prevent the conductive stannic oxide particles from adhering to the separator to become a secondary electrode and cause damage, thereby reducing the maintenance cost of the production device. The cathode compartment provided with the inclined cover plate separator can also be regarded as a cathode conductive carrier. A movable structure design of the inclined cover plate separator facilitates the addition of stannic oxide to the cathode compartment.

Preferably, when both a separator-free vertical electrolytic cell and a cathode conductive carrier are adopted, the cathode conductive carrier is provided with a groove, a bottom of the groove is designed as a funnel-shaped structure provided with a liquid outlet pipe, and a filter medium is filled in the liquid outlet pipe. With the funnel-shaped structure characteristic of the bottom, during the electrolysis, a hydrogen-containing electrolyte can be sucked by an external force to carry away the evolved hydrogen, and the evolved hydrogen is then discharged externally, thereby preventing the hydrogen from being mixed with an oxidative gas generated at the upper anode in the electrolytic cell. The filter medium in the liquid outlet pipe at the bottom is provided to prevent stannic oxide particles from being taken away. An inner wall of the funnel-shaped structure of the bottom of the groove is preferably provided with pits configured to guide a sucked hydrogen-containing electrolyte.

The present disclosure can also be improved as follows: The stannic oxide and the electrolyte solution are mixed to produce a slurry and then the slurry is fed into the at least one electrolytic cell, such that the stannic oxide is uniformly dispersed in the electrolyte solution. The slurry serves as an ion exchange channel, and facilitates an increased amount of a stannic oxide powder to directly contact the cathode for energization.

The present disclosure can also be improved as follows: A soluble stannic salt and/or a stannous compound is produced through a reaction with the electrolyte solution during the electrolysis or at least one selected from the group consisting of a stannous salt, stannous hydroxide, and metallic tin is produced through a conventional chemical reaction to obtain a raw material recycled for production. The stannic salt can be further reduced to produce a raw material meeting production process requirements.

The present disclosure can also be improved as follows: The collected contaminating tin-containing sludge is first heated at a high temperature for a pre-treatment, such that organic matters in the tin-containing sludge are decomposed at the high temperature to produce a relatively-pure stannic oxide powder.

The second objective of the present disclosure is to achieve the first objective of the present disclosure with an apparatus for reducing stannic oxide into metallic tin in accordance with the operations described above.

An apparatus for reducing stannic oxide into metallic tin is provided, including at least one electrolytic cell provided with an anode and a cathode, where the anode is connected to a positive terminal of an electrolytic power supply, and the cathode is connected to a negative terminal of the electrolytic power supply; and during electrolysis, the cathode or the metallic tin on the cathode is in direct contact with the stannic oxide.

As a preferred solution, an inclined electrolytic cell is adopted to allow an electrochemical reduction treatment for stannic oxide, and the cathode is arranged at a low position in the inclined electrolytic cell. Thus, under a gravity action, a stannic oxide powder accumulates around the cathode, and is in direct contact with the cathode or the metallic tin on the cathode for energization to allow an electrochemical reaction.

As a more preferred solution, the cathode of the present disclosure is structurally improved to produce a cathode conductive carrier for loading stannic oxide, such that the stannic oxide is in large-area direct contact with the cathode conductive carrier to enhance a reaction rate. The cathode conductive carrier is an electrically-conductive material or a combination of an electrically-conductive material and an electrically-insulating material, and has a spoon-shaped or grooved cathode structure capable of loading a stannic oxide powder. There is one or more connection points on the negative terminal of the electrolytic power supply for an electrical connection of the cathode conductive carrier to the negative terminal of the electrolytic power supply. The more the connection points on the negative terminal of the electrolytic power supply, the more beneficial it is for achieving a uniform current distribution across a region in contact with the loaded stannic oxide.

When the cathode conductive carrier is the combination of the electrically-conductive material and the electrically-insulating material, an inner bottom and/or an inner side of the cathode conductive carrier is the electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply, and/or the electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply is provided in a groove of the cathode conductive carrier, and a remaining part is the electrically-insulating material and/or the electrically-conductive material coated with the electrically-insulating material, such that the loaded stannic oxide powder is in direct contact with the inner bottom and/or the inner side of the cathode conductive carrier and/or the electrically-conductive material in the groove of the cathode conductive carrier to allow an electrochemical reduction reaction. A part of the cathode conductive carrier that is not in contact with the loaded stannic oxide is the electrically-insulating material or is coated with the electrically-insulating material, which can effectively improve the electrical efficiency of a reaction, reduce the generation of hydrogen, and save the electrical energy.

As a preferred solution, in the present disclosure, a vertical electrolytic cell is adopted, that is, the cathode is arranged below at least one anode. The vertical electrolytic cell may be either an electrolytic cell without a separator or an electrolytic cell with a separator. When the vertical electrolytic cell is an electrolytic cell with a separator, the separator is preferably a filter cloth, which is more cost-effective than an ion-exchange membrane. In the vertical electrolytic cell with the separator, a side of the cathode compartment that faces the anode is provided with the separator, and other sides of the cathode compartment are each the separator and/or a plate.

More preferably, when the vertical electrolytic cell with the separator is adopted, the separator at the side of the cathode compartment that faces the anode and an inclined cover plate separator-fixing frame constitute a movable inclined cover plate separator arranged at a top of the cathode compartment; holes in the inclined cover plate separator-fixing frame are blocked with the separator; and an upper part in the cathode compartment is further provided with an outlet configured to discharge a gas or a gas and a liquid. The inclined cover plate separator-fixing frame is preferably a polymer resin. The inclined cover plate separator is temporarily fixed to the top of the cathode compartment by a fixing device, or is connected to the groove by a movable component. The movable component is preferably a hinge.

More preferably, when both a separator-free vertical electrolytic cell and a cathode conductive carrier are adopted, the cathode conductive carrier is provided with a groove, a bottom of the groove is designed as a funnel-shaped structure provided with a liquid outlet pipe, and a filter medium is filled in the liquid outlet pipe. The filter medium is a filter screen and/or a filter cloth, and is preferably a filter screen. An inner wall of the funnel-shaped structure of the bottom of the groove is preferably provided with pits.

The insoluble anode in the electrolytic cell is gold, platinum, an alloy thereof, a titanium-based coated insoluble anode, or conductive graphite. Preferably, a titanium-based coated insoluble electrode or a platinum metal electrode is adopted.

An electrically-conductive material for the cathode or the cathode conductive carrier in the electrolytic cell can be selected from the group consisting of gold, platinum, tin, titanium, an alloy including at least one of the aforementioned metals, stainless steel, and conductive graphite. When an electrolyte includes a chloride ion, titanium is preferably adopted as the cathode. When the electrolyte includes a sulfate ion, stainless steel is preferably adopted as the cathode. More preferably, tin is adopted as the cathode.

The present disclosure can be improved as follows: A filter cloth bag is additionally provided. The filter cloth bag is provided to wrap the stannic oxide and the cathode together, such that the stannic oxide can be in close contact with the cathode, and a tendency of a stannic oxide powder to detach from the cathode due to a flow of an electrolyte or a buoyancy of hydrogen bubbles during electrolysis can be reduced.

The present disclosure can also be improved as follows: A sensor and an automatic program controller are additionally provided. The sensor includes an acidity meter, a pH meter, a gravimeter, an oxidation-reduction potential (ORP) meter, a photoelectric colorimeter, a liquid level meter, a thermometer, a weightometer, a chlorine detector, and a hydrogen detector. As a result, the apparatus can operate automatically according to a designed program.

The present disclosure can also be improved as follows: A temporary storage tank is additionally provided. The temporary storage tank is connected to the electrolytic cell through a pipeline, and is configured to store a chemical and/or serve as a chemical reaction tank.

The present disclosure can also be improved as follows: An overflow buffer tank is additionally provided. The overflow buffer tank is connected to at least one electrolytic cell and/or cell body in the apparatus through a pipeline, and is configured to enable a smooth flow of a solution among cells/tanks.

The present disclosure can also be improved as follows: A gas-liquid separation tank is additionally provided. The gas-liquid separation tank is connected to at least one electrolytic cell and/or cell body in the apparatus through a pipeline, and is configured to enable bubbles to escape from a bubble-containing solution during a mild flow.

The present disclosure can also be improved as follows: A tail gas treatment unit is additionally provided. The tail gas treatment unit is connected to at least one electrolytic cell and/or cell body in the apparatus through a gas pipeline, and is configured to collect and treat or recycle an escaped gas. A gas guide device is a spray tower or a vacuum ejector.

The present disclosure can also be improved as follows: A solid-liquid separator is additionally provided. The solid-liquid separator is connected to at least one electrolytic cell and/or cell body in the apparatus through a pipeline, and is configured to allow solid-liquid separation for a solid-liquid mixture. The solid-liquid separator can be structurally categorized into a filter press, a centrifuge, and a filter.

The present disclosure can also be improved as follows: A stirrer is additionally provided in at least one electrolytic cell and/or cell body of the apparatus. The stirrer is configured to enable a uniform concentration and temperature of a solution. The stirrer includes an impeller stirrer and a liquid flow pump pipe stirrer.

Compared with the prior art, the present disclosure has the following beneficial effects:

1. The process of the present disclosure solves the technical problem of relying solely on a high-temperature operation to reduce tin in the prior art, and can reduce a tin oxide into metallic tin at room temperature. The process requires simple conditions and has a vast application market. Metallic tin produced by the process of the present disclosure can be directly utilized as needed or can be further converted into a tin salt for reusing through a chemical reaction.

2. The process of the present disclosure is safe and easy to implement, and involves a small equipment footprint and a low project investment cost.

3. The reduction treatment of the present disclosure can lead to metallic tin, stannous hydroxide, and a stannous salt product without introducing an additional pollution source.

4. The present disclosure can assist contaminating tin-containing sludge-producing enterprises to turn waste into treasure for environmental protection, thereby enhancing the economic benefits of these enterprises.

5. Compared with the existing technologies, the present disclosure is energy-saving and pollution-free, and meets the novel process requirement of energy conservation and emission reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an inclined electrolytic cell in the present disclosure;

FIG. 2 is a top view of a cathode conductive carrier with a structure A in the present disclosure;

FIG. 3 is a cross-sectional view along M-M of the cathode conductive carrier with the structure A in FIG. 2;

FIG. 4 is a top view of a cathode conductive carrier with a structure B in the present disclosure;

FIG. 5 is a cross-sectional view of the cathode conductive carrier with the structure B in FIG. 4;

FIG. 6 is a cross-sectional view of a cathode conductive carrier with a structure C in the present disclosure;

FIG. 7 is a cross-sectional view of a cathode conductive carrier with a structure D in the present disclosure;

FIG. 8 shows a vertical electrolytic cell adopting the cathode conductive carrier with the structure C in FIG. 6;

FIG. 9 shows a vertical electrolytic cell adopting the cathode conductive carrier with the structure D in FIG. 7;

FIG. 10 shows an apparatus for reducing stannic oxide into metallic tin in Example 1 of the present disclosure;

FIG. 11 shows an apparatus for reducing stannic oxide into metallic tin in Example 2 of the present disclosure;

FIG. 12 shows an apparatus for reducing stannic oxide into metallic tin in Example 3 of the present disclosure;

FIG. 13 shows an apparatus for reducing stannic oxide into metallic tin in Example 4 of the present disclosure;

FIG. 14 shows an apparatus for reducing stannic oxide into metallic tin in Example 5 of the present disclosure;

FIG. 15 shows an apparatus for reducing stannic oxide into metallic tin in Example 6 of the present disclosure;

FIG. 16 shows an apparatus for reducing stannic oxide into metallic tin in Example 7 of the present disclosure; and

FIG. 17 shows an apparatus for reducing stannic oxide into metallic tin in Example 8 of the present disclosure.

REFERENCE NUMERALS

1—electrolytic cell, 2—separator, 3—anode, 4—cathode, 5—cathode conductive carrier, 6—cathode insulating layer, 7—inclined cover plate separator, 8—electrolytic power supply, 9—temporary storage tank, 10—sensor, 11—automatic program controller, 12—overflow buffer tank, 13—impeller stirrer, 14—liquid flow pump pipe stirrer, 15—spray tower, 16—vacuum ejector, 17—acidic solution, 18—acidic salt-containing solution, 20—alkaline salt-containing solution, 21—neutral salt-containing solution, 22—metallic zinc, 24—metallic tin, 25—stannous hydroxide, 26—stannic salt solution, 27—stannous salt solution, 29—stannic oxide, 30—contaminating tin-containing sludge, 32—hydrochloric acid, 34—sodium hydroxide, 39—hydrogen high-altitude discharge pipe, 40—tail gas treatment unit, 41—solid-liquid separator, 42—salt-containing waste liquid, 43—stannous oxide, 44—valve, 45—pump, 47—high-temperature heating furnace, 49—filter cloth bag, 50—filter screen, 51—hinge, 52—inclined cover plate separator-fixing frame, 53—pitted funnel, 54—bubble barrier plate, 55—electrolytic-power-supply negative-terminal connection line, 56—water inlet pipe, 57—liquid outlet pipe, and 58—gas-liquid separation tank.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to make the objectives, technical solutions, and advantages of the present disclosure clear, the exemplary embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Apparently, the embodiments described are merely some rather than all of the embodiments of the present disclosure. It should be understood that the present disclosure is not limited by the exemplary embodiments described herein. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

In the description below, a large number of specific details are provided to facilitate the comprehensive understanding of the present disclosure. However, it is apparent to those skilled in the art that the present disclosure can be implemented without one or more of these details. In other examples, some technical features well known in the art are not described to avoid confusion with the present disclosure.

It should be understood that the present disclosure can be implemented in different forms and should not be construed as limited to the embodiments proposed here. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present disclosure to those skilled in the art.

In order to enable the thorough comprehension of the present disclosure, detailed structures will be set forth in the following description, so as to elucidate the technical solutions proposed in the present disclosure. The optional embodiments of the present disclosure are described in detail below. However, the present disclosure may be implemented in other ways in addition to these details.

In the embodiments of the present disclosure, an electrolytic cell, an anode, a cathode, a cathode conductive carrier, a temporary storage tank, an overflow buffer tank, a stirrer, a spray tower, a vacuum ejector, and a tail gas treatment unit are all products manufactured by Yegao Environmental Protection Equipment Manufacturing Co., Ltd. in Foshan City, Guangdong Province, China. An electrolytic power supply, a sensor, an automatic program controller, a solid-liquid separator, a separator, a valve, a pump, and a chemical raw material are all commercially-available products. Other products with similar properties to the products listed in the present disclosure may also be adopted by those skilled in the art according to conventional selection, which all can achieve the objectives of the present disclosure.

Example 1

As shown in FIG. 10, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes an electrolytic cell 1.

The electrolytic cell 1 is an inclined electrolytic cell without a separator, as shown in FIG. 1. Both an anode 3 and a cathode 4 are provided in the electrolytic cell. The anode 3 is connected to a positive terminal of an electrolytic power supply 8, and the cathode 4 is connected to a negative terminal of the electrolytic power supply 8. The anode is a gold-coated insoluble anode. The cathode is conductive graphite. The cathode 4 is arranged at a low position in the inclined electrolytic cell.

An electrolyte solution 21 in the electrolytic cell 1 is a slurry produced by mixing a sodium sulfate solution with a stannic oxide powder.

In this example, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. An electrolyte slurry was fed into the inclined electrolytic cell, and both the anode 3 and the cathode 4 were immersed in the electrolyte slurry. The cathode 4 was arranged at a lowest position in the inclined electrolytic cell and allowed to be in close contact with stannic oxide 29 in the electrolyte slurry.

2. The electrolytic power supply 8 was turned on to initiate electrolysis. At the anode 3, an electrochemical reaction of generating oxygen occurred. At the cathode 4, an electrochemical reaction of reducing the stannic oxide 29 into metallic tin mainly occurred, which was accompanied by the evolution of hydrogen.

3. The metallic tin formed on the cathode 4 was collected.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure.

Example 2

As shown in FIG. 11, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes an electrolytic cell 1 and a filter cloth bag 49.

The electrolytic cell 1 is an electrolytic cell without a separator. Both an anode 3 and a cathode 4 are provided in the electrolytic cell 1. The anode 3 is connected to a positive terminal of an electrolytic power supply 8, and the cathode 4 is connected to a negative terminal of the electrolytic power supply 8. The anode is a soluble anode made of metallic zinc 22. The cathode is conductive graphite. The cathode and stannic oxide 29 are wrapped together by the filter cloth bag 49. The filter cloth bag 49 may be replaced by a filter plate with an equivalent function to enclose the cathode. This design can confine at least a majority of the stannic oxide within a vicinity of the cathode to enhance a contact rate between the SnO₂ and the cathode.

An electrolyte in the electrolytic cell 1 is an acidic salt-containing solution 18 including sulfuric acid, hydrochloric acid, nitric acid, formic acid, citric acid, ammonium chloride, sodium sulfate, potassium chloride, and sodium citrate.

In this example, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. An acidic salt-containing electrolyte was fed into the electrolytic cell 1, and the anode 3 and the filter cloth bag 49 in which the cathode 4 and the stannic oxide 29 were enclosed were immersed in the electrolyte.

2. The electrolytic power supply 8 was turned on to initiate electrolysis. At the anode 3, an electrochemical reaction occurred, such that the metallic zinc 22 was dissolved and reacted in the electrolyte to produce a zinc salt. At the cathode 4, an electrochemical reduction reaction of reducing stannic oxide into metallic tin 24 primarily occurred, which was accompanied by the evolution of hydrogen. Additionally, a chemical reaction of an acid with the metallic tin occurred during the process.

3. The metallic tin 24 formed on the cathode 4 was collected.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure.

Example 3

As shown in FIG. 12, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes an electrolytic cell 1 and a cathode conductive carrier 5. A cathode conductive carrier 5 is adopted as a cathode 4 for the electrolytic cell 1. The cathode conductive carrier is an improved spoon-shaped cathode structure capable of loading a SnO₂ powder.

The electrolytic cell 1 is an electrolytic cell without a separator. Both an anode 3 and the cathode conductive carrier 5 are arranged in the electrolytic cell 1. The anode 3 is connected to a positive terminal of an electrolytic power supply 8, and the cathode conductive carrier 5 is connected to a negative terminal of the electrolytic power supply 8. There is a single connection point on the negative terminal of the electrolytic power supply for an electrical connection of the cathode conductive carrier 5 to the negative terminal of the electrolytic power supply 8. The anode 3 is a platinum insoluble anode. The cathode is platinum, and is the cathode with the structure A shown in FIG. 2 and FIG. 3. The cathode conductive carrier 5 is an electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply.

An electrolyte in the electrolytic cell 1 is a neutral salt-containing solution 21 of sodium sulfate. The stannic oxide 29 is loaded in a groove of the cathode conductive carrier 5 and immersed in the electrolyte.

In this example, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. The neutral salt-containing electrolyte was fed into the electrolytic cell 1, and both the anode 3 and the cathode conductive carrier 5 were immersed in the electrolyte.

2. The electrolytic power supply 8 was turned on to initiate electrolysis. At the anode 3, an electrochemical reaction occurred to allow the evolution of oxygen. At the cathode 4, namely, the cathode conductive carrier 5, an electrochemical reaction primarily occurred to achieve the reduction of stannic oxide into metallic tin 24 and the evolution of hydrogen.

3. The metallic tin 24 formed on the cathode 4 was collected.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure.

Example 4

As shown in FIG. 13, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes an electrolytic cell 1. A cathode conductive carrier 5 is adopted as a cathode 4 for the electrolytic cell 1. The cathode conductive carrier 5 is a cathode structure capable of loading a SnO₂ powder.

The electrolytic cell 1 is an electrolytic cell without a separator. Both an anode 3 and the cathode 4 are arranged in the electrolytic cell 1. The anode 3 is connected to a positive terminal of an electrolytic power supply 8, and the cathode 4 is connected to a negative terminal of the electrolytic power supply 8. The anode is a gold-coated insoluble anode, and the cathode is stainless steel. The cathode with the structure B shown in FIG. 4 and FIG. 5 is adopted. An inner bottom and/or an inner side of the cathode conductive carrier 5 is an electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply. There are two or more connection points on the negative terminal of the electrolytic power supply for an electrical connection of the cathode conductive carrier 5 to the negative terminal of the electrolytic power supply 8. The more the connection points on the negative terminal of the electrolytic power supply, the more beneficial it is for achieving a uniform current distribution across a region in contact with the loaded stannic oxide. The higher the groove wall of a groove of the cathode conductive carrier 5, the more effectively the stannic oxide can be prevented from leaving the cathode conductive carrier.

An electrolyte in the electrolytic cell 1 is an alkaline salt-containing solution 20 including sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, ammonium hydroxide, ammonium bicarbonate, and sodium sulfate. The stannic oxide 29 is loaded in a groove of the cathode conductive carrier 5 with the structure B, and the cathode conductive carrier 5 is immersed in the alkaline electrolyte.

In this example, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. The alkaline salt-containing electrolyte 20 was fed into the electrolytic cell 1, and both the anode 3 and the cathode conductive carrier 5 were immersed in the electrolyte.

2. The electrolytic power supply 8 was turned on to initiate electrolysis. At the anode 3, an electrochemical reaction occurred to allow the evolution of oxygen. At the cathode 4, namely, the cathode conductive carrier 5, an electrochemical reaction primarily occurred to achieve the reduction of stannic oxide 29 into metallic tin 24 and the evolution of hydrogen.

3. The metallic tin 24 formed on the cathode conductive carrier 5 and stannous oxide 43 generated accordingly were collected.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure. Additionally, during the process, the metallic tin 24 reacts with an alkaline substance such as sodium hydroxide to produce the stannous oxide 43. The use of the strongly-alkaline electrolyte reduces the yield of metallic tin.

Example 5

As shown in FIG. 14, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes an electrolytic cell 1, a cathode conductive carrier 5, a tail gas treatment unit 40, and a gas-liquid separation tank 58.

The electrolytic cell 1 is a vertical electrolytic cell with a separator shown in FIG. 8. The cathode conductive carrier 5 is the improved cathode with the structure C shown in FIG. 6. The cathode conductive carrier 5 is a cathode structure capable of loading a SnO₂ powder. The cathode conductive carrier 5 constitutes a cathode compartment. The cathode conductive carrier 5 is an electrically-conductive material, and an electrically-conductive material electrically connected to a negative terminal of an electrolytic power supply is arranged in a groove of the cathode conductive carrier 5. That is, an additional conductive cathode 4 is provided to increase a contact area between the SnO₂ powder and the cathode. In addition, a movable inclined cover plate separator 7 is provided at a top of the groove. The separator at a side of the cathode compartment that faces an anode and an inclined cover plate separator-fixing frame constitutes the inclined cover plate separator 7. The inclined cover plate separator-fixing frame 52 of the inclined cover plate separator 7 is rotatably arranged on the cathode compartment through a hinge 51. The separator is a filter cloth to avoid the mixing of chlorine and hydrogen generated respectively. As shown in FIG. 8, an electrolyte could be fed into the cathode compartment through a pump 45 and a water inlet pipe 56. The electrolyte in the cathode compartment then flows into a separation zone formed between a bubble barrier plate 54 and the electrolytic cell 1 through a liquid outlet pipe 57. Hydrogen is evolved within this separation zone, which can prevent the hydrogen from being mixed with chlorine and/or oxygen. The anode 3 is arranged in the vertical anode compartment. The anode 3 is connected to a positive terminal of an electrolytic power supply 8. Both the cathode conductive carrier 5 and the cathode 4 are connected to a negative terminal of the electrolytic power supply 8 through an electrolytic-power-supply negative-terminal connection line 55. The cathode 4 is arranged below the anode 3. The anode is a titanium-based coated insoluble anode and the cathode is titanium.

As a replaceable improved cathode structure in this example, a grooved cathode structure capable of loading a SnO₂ powder that is produced from the combination of an electrically-conductive material and an electrically-insulating material can be adopted. As shown in FIG. 8, the cathode conductive carrier 5 is also a grooved structure C, but the cathode conductive carrier is partially or completely coated with a cathode insulating layer 6 and an electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply is arranged at a bottom of a groove of the cathode conductive carrier 5. The electrically-conductive material serves as the cathode 4 in direct contact with the SnO₂ powder.

An electrolyte in the electrolytic cell 1 is an acidic solution 17, and hydrochloric acid is adopted in this example.

In the tail gas treatment unit 40 provided with a spray tower 15 at a top of the electrolytic cell 1, a solution of sodium hydroxide 34 is specifically used to absorb chlorine to produce a sodium hypochlorite solution.

The stannic oxide 29 is loaded in the groove of the cathode conductive carrier 5.

The gas-liquid separation tank 58 communicates with the cathode compartment. Hydrogen bubbles are separated from a cathode electrolyte through pump circulation to escape during a gentle flow.

In Example 5, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. The electrolyte was fed into the vertical electrolytic cell 1 and the gas-liquid separation tank 58. The stannic oxide 29 was loaded in the groove of the cathode with the structure C. Both the anode 3 and the cathode conductive carrier 5 were immersed in the hydrochloric acid electrolyte.

2. A pump 45-1 and a pump 45-2 were started, and the electrolytic power supply 8 was turned on to initiate electrolysis. At the anode 3, an electrochemical reaction occurred to allow the evolution of chlorine. At the cathode conductive carrier 5, an electrochemical reaction primarily occurred to achieve the reduction of the stannic oxide 29 into metallic tin and the evolution of hydrogen.

3. The metallic tin produced was allowed to react with hydrochloric acid to produce stannous chloride, such that a stannous salt solution 27 was produced and collected as a product.

4. During the process, the sodium hypochlorite solution in the tail gas treatment unit was collected for other use.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure. During the process, tin reacts with hydrochloric acid to produce a stannous chloride solution as a product. Additionally, chlorine evolved is treated for environmental protection to produce a sodium hypochlorite solution for other use.

Example 6

As shown in FIG. 15, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes an electrolytic cell 1, a high-temperature heating furnace 47, the cathode conductive carrier 5 with the structure D shown in FIG. 7, a gas-liquid separation tank 58, and a hydrogen high-altitude discharge pipe 39.

The electrolytic cell 1 is the vertical electrolytic cell without a separator shown in FIG. 9. An anode 3 is arranged at an upper part of the electrolytic cell 1. A cathode 4 is arranged in the cathode conductive carrier 5 with the structure D. The anode 3 is connected to a positive terminal of an electrolytic power supply 8, and the cathode conductive carrier 5 is connected to a negative terminal of the electrolytic power supply 8. The anode is conductive graphite, and a cathode material in the cathode conductive carrier 5 with the structure D is titanium. In this example, the cathode conductive carrier 5 with the structure D is provided with a groove, and a bottom of the groove is designed as a funnel-shaped structure provided with a liquid outlet pipe 57. A filter medium is filled in the liquid outlet pipe. A hydrogen-containing electrolyte can be sucked by an external force of a component such as a pump to carry away the evolved hydrogen, and the evolved hydrogen is then discharged externally, thereby preventing the hydrogen from being mixed with an oxidative gas generated at the upper anode in the electrolytic cell. An inner wall of the funnel-shaped structure of the bottom of the groove of the cathode conductive carrier 5 with the structure D is provided with pits configured to guide a sucked hydrogen-containing electrolyte. A filter screen 50 is provided as the filter medium in the liquid outlet pipe 57 at the bottom of the funnel-shaped structure to prevent stannic oxide particles from being taken away. The filter screen 50 can be replaced with another filtering structure such as a filter cloth.

An electrolyte in the electrolytic cell 1 is a sodium sulfate solution.

The high-temperature heating furnace 47 is configured to treat recovered contaminating tin-containing sludge 30 at a high temperature such that organic impurities are decomposed to produce a purified stannic oxide material.

The purified stannic oxide 29 was fed into the cathode conductive carrier 5 with the structure D.

In this example, an inner bottom and/or an inner side of the cathode conductive carrier 5 is an electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply. The cathode conductive carrier 5 can also be a structure combining an electrically-conductive material an with electrically-insulating material. An electrically-conductive material electrically connected to the negative terminal of the electrolytic power supply is provided in the groove, and a remaining part is an electrically-insulating material and/or the electrically-conductive material coated with the electrically-insulating material, such that the loaded SnO₂ powder is in direct contact with the inner bottom and/or the inner side and/or the electrically-conductive material in the groove to allow an electrochemical reduction reaction.

In Example 6, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. The electrolyte was fed into the vertical electrolytic cell without the separator, and both the anode 3 and the cathode conductive carrier 5 were immersed in the electrolyte.

2. Pumps 45-1 and 45-2 were started to circulate the electrolyte, and the electrolytic power supply 8 was turned on to initiate electrolysis. At the anode 3, an electrochemical reaction occurred to allow the evolution of oxygen, and the oxygen was released from the electrolytic cell 1. At the cathode 4, an electrochemical reduction reaction primarily occurred to achieve the reduction of the stannic oxide 29 into metallic tin and the evolution of hydrogen.

3. Most of the hydrogen evolved during the process was carried by the flowing electrolyte from a bottom of the electrolytic cell 1 to the gas-liquid separation tank 58, separated, and discharged through the hydrogen high-altitude discharge pipe 39.

4. The metallic tin formed in the groove of the cathode conductive carrier 5 was collected.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure.

Example 7

As shown in FIG. 16, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes an electrolytic cell 1, a solid-liquid separator 41, four temporary storage tanks 9, and three sensors 10. A cathode conductive carrier 5 in the electrolytic cell 1 is the structure B shown in FIG. 3 and FIG. 4.

The electrolytic cell 1 is an electrolytic cell with a separator, and the separator is a bipolar membrane. An anode 3 is arranged in an anode compartment. The stannic oxide 29 is fed into the cathode conductive carrier 5 with the structure B. The cathode conductive carrier 5 is arranged in a cathode compartment as the cathode 4. The anode 3 is connected to a positive terminal of an electrolytic power supply 8, and the cathode conductive carrier 5 is connected to a negative terminal of the electrolytic power supply 8. The anode is a titanium-based coated insoluble anode, and the cathode is stainless steel.

An electrolyte in the anode compartment is an alkaline salt-containing solution 20 including a mixture of ammonium carbonate and sodium hydroxide. An initial electrolyte in the cathode compartment is hydrochloric acid 32. The hydrochloric acid 32 is fed from a temporary storage tank 9-4 into the cathode compartment through a pump 45-3. A sensor 10-1 in the cathode compartment is an acidity meter configured to control the addition of the hydrochloric acid 32 by the pump 45-3. A sensor 10-2 is a gravimeter configured to detect a concentration of stannous chloride in the cathode electrolyte to control the open and close of a pump 45-1. The pump 45-1 is configured to pump the cathode electrolyte into a temporary storage tank 9-1. A sensor 10-3 in the temporary storage tank 9-1 is a pH meter configured to control the addition of sodium hydroxide 34 such that the stannous chloride reacts with the sodium hydroxide to produce stannous hydroxide. An impeller stirrer 13 is provided in the temporary storage tank 9-1.

A solid-liquid mixture including stannous hydroxide in the temporary storage tank 9-1 can be pumped by a pump 45-2 to the solid-liquid separator 41. The solid-liquid separator 41 is a filter press specifically configured to enable solid-liquid separation for the solid-liquid mixture including stannous hydroxide to produce stannous hydroxide 25 and a salt-containing waste liquid 42. The stannous hydroxide is placed in a temporary storage tank 9-2, and the salt-containing waste liquid is discharged into a temporary storage tank 9-3.

In Example 7, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. The two electrolytes were fed into the anode compartment and the cathode compartment, respectively. The stannic oxide was fed into the cathode conductive carrier 5 with the structure B. Both the anode 3 and the cathode conductive carrier 5 were immersed in the respective electrolytes.

2. The electrolytic power supply 8 was turned on to initiate electrolysis. At the anode 3, an electrochemical reaction occurred to allow the evolution of oxygen and the production of carbon dioxide. At the cathode 4, an electrochemical reaction primarily occurred to achieve the reduction of stannic oxide 29 into metallic tin 24 and the evolution of hydrogen.

3. The addition of hydrochloric acid by the pump 45-3 was controlled through the sensor 10-1, namely, an acidity meter. Hydrochloric acid reacted with the metallic tin 24 generated to produce a stannous chloride solution with a concentration continuously increasing. When the sensor 10-2, namely, a gravimeter, reached a set value, the electrolytic power supply 8 was turned off, and the pump 45-1 was started to pump the cathode electrolyte into the temporary storage tank 9-1.

4. The addition of sodium hydroxide 34 to the temporary storage tank 9-1 was controlled through the sensor 10-3, namely, a pH meter, to allow a neutralization reaction, such that a stannous hydroxide precipitate was produced in a resulting reaction solution.

5. A solid-liquid mixture in the temporary storage tank 9-1 was subjected to solid-liquid separation to produce stannous hydroxide 25.

6. The stannous hydroxide 25 produced in the temporary storage tank 9-2 was collected.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure. Stannous hydroxide was produced through a chemical reaction and recycled.

Example 8

As shown in FIG. 17, an apparatus for reducing stannic oxide into metallic tin is provided in this example. The apparatus mainly includes: two electrolytic cells 1, including an electrolytic cell 1-1 and an electrolytic cell 1-2; a tail gas treatment unit 40; two overflow buffer tanks 12, including an overflow buffer tank 12-1 and an overflow buffer tank 12-2; three temporary storage tanks 9, including a temporary storage tank 9-1, a temporary storage tank 9-2, and a temporary storage tank 9-3; two hydrogen high-altitude discharge pipes 39, including a hydrogen high-altitude discharge pipe 39-1 and a hydrogen high-altitude discharge pipe 39-2; two liquid flow pump pipe stirrers 14, including a liquid flow pump pipe stirrer 14-1 and a liquid flow pump pipe stirrer 14-2; four sensors 10, including a sensor 10-1, a sensor 10-2, a sensor 10-3, and a sensor 10-4; an automatic program controller 11; and pumps 45 and valves 44 that are configured to control the flow and transfer of a liquid and a gas.

The electrolytic cell 1-1 and the electrolytic cell 1-2 are both an electrolytic cell with a separator. A separator 2-1 for the electrolytic cell 1-1 is an anion-exchange membrane, and a separator 2-2 for the electrolytic cell 1-2 is a cation-exchange membrane. Two anodes 3 are arranged in respective anode compartments. A cathode conductive carrier 5-1 in the electrolytic cell 1-1 is the structure A, and a cathode conductive carrier 5-2 in the electrolytic cell 1-2 is the structure B. The structure A and the structure B are arranged in respective cathode compartments. Stannic oxide 29 is fed into grooves of the cathode conductive carrier 5-1 and the cathode conductive carrier 5-2. A cathode compartment of the electrolytic cell 1-1 is connected to the hydrogen high-altitude discharge pipe 39-1, and a cathode compartment of the electrolytic cell 1-2 is connected to the hydrogen high-altitude discharge pipe 39-2. An anode 3-1 of the electrolytic cell 1-1 and an anode 3-2 of the electrolytic cell 1-2 are connected to positive terminals of an electrolytic power supply 8-1 and an electrolytic power supply 8-2, respectively. The cathode conductive carrier 5-1 is connected to a negative terminal of the electrolytic power supply 8-1 and serves as a cathode 4-1, and the cathode conductive carrier 5-2 is connected to a negative terminal of the electrolytic power supply 8-2 and serves as a cathode 4-2. The anode 3-1 is conductive graphite, and the anode 3-2 is a titanium-based coated insoluble anode. Electrically-conductive materials for the cathode conductive carrier 5-1 and the cathode conductive carrier 5-2 are both titanium.

Electrolytes in the electrolytic cells are both hydrochloric acid 32. The electrolytic cell 1-1 is provided with the liquid flow pump pipe stirrer 14-1, and the electrolytic cell 1-2 is provided with the liquid flow pump pipe stirrer 14-2.

The tail gas treatment unit 40 is connected to a pump 45-1 and a vacuum ejector 16, and is specifically configured to absorb chlorine overflowing from an electrolytic cell and make the chlorine react with hydrochloric acid and ferrous chloride in an acidic salt-containing solution 18 to produce a ferric chloride solution.

The sensor 10-1 is a gravimeter, the sensor 10-2 is an acidity meter, and the sensor 10-3 is a gravimeter, which are configured to control the addition of hydrochloric acid 32 in the temporary storage tank 9-1 by a pump 45-6, a pump 45-5, and a pump 45-4, respectively. The sensor 10-4 is a chlorine concentration detector configured to prevent chlorine leakage and ensure safe production.

In Example 8, a process for reducing stannic oxide into metallic tin is provided, including the following steps:

1. The electrolytes were fed into the respective compartments of the two electrolytic cells. Stannic oxide 29 was fed into the grooves of the cathode conductive carrier 5-1 and the cathode conductive carrier 5-2. The two anodes and the two cathode conductive carriers were immersed in the respective electrolytes.

2. The two electrolytic power supplies were turned on to initiate electrolysis. At both anodes, an electrochemical reaction occurred to allow the evolution of chlorine. At both cathodes, an electrochemical reaction primarily occurred to achieve the reduction of stannic oxide into metallic tin and the evolution of hydrogen.

3. Data detected by the sensor 10-1 as a gravimeter, the sensor 10-2 as an acidity meter, the sensor 10-3 as a gravimeter, and the sensor 10-4 as a chlorine concentration detector was transmitted to the automatic program controller 11 for processing to control the addition of hydrochloric acid by the pump 45-4, the pump 45-5, and the pump 45-6, respectively, such that electrolysis in each electrolytic cell proceeded normally.

4. During the electrolysis, cathode electrolytes in the electrolytic cell 1-1 and the electrolytic cell 1-2 also reacted with the metallic tin to produce stannous chloride solutions 27. The stannous chloride solutions were allowed to flow through the overflow buffer tank 12-1 and the overflow buffer tank 12-2, respectively, and finally collected in the temporary storage tank 9-2.

5. In an anode electrolyte of the electrolytic cell 1-2, a part of Sn²⁺ ions migrated from a cathode compartment to an anode compartment and were oxidized into Sn⁴⁺ to produce SnCl₄. A resulting stannic salt solution 26 was pumped to the temporary storage tank 9-3 for temporary storage.

6. After a reaction was completed, metallic tin formed at both cathode conductive carriers was collected.

7. A ferric chloride solution in the tail gas treatment unit was collected for other use.

The above describes the reduction of stannic oxide into metallic tin by the process of the present disclosure at room temperature and ambient pressure. During the process, stannous chloride and stannic chloride solutions are produced as raw materials for other production. Chlorine evolved is treated for environmental protection to produce a ferric chloride solution for reusing.

As another feasible embodiment of the present disclosure, to increase an opportunity for stannic oxide to contact a surface of a cathode, the cathode is structurally improved to produce a cathode conductive carrier, which is a planar, spoon-shaped, or grooved cathode structure capable of loading a stannic oxide powder and can also achieve the objective of the present disclosure.

The above are merely specific implementations of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any person skilled in the art can easily conceive various equivalent modifications or replacements within the technical scope of the present disclosure, and these modifications or replacements shall fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.