Patent Application
20240328022
This application claims the priority of Chinese Patent Application No. CN202211072401.9, entitled “An electrochemical metallurgical process for extracting metals and sulfur from metallic sulfides”, filed on Sep. 2, 2022, the disclosure of which is incorporated herein by reference in its entirety.
The electrochemical metallurgical method described in this invention aims to extract metals and sulfur from metal sulfides, within the technical domain of the metallurgical chemical industry.
Sulphides are the main source of extraction of most metals and have important economic value. More than 300 kinds of sulfides have been found in nature. In modern metallurgy, the treatment method of metal sulfide is mostly high-temperature chemical process. However, the method of extracting metals from metal sulfides is more complicated than that of oxidized ores, mainly because sulfides cannot directly reduce metals with carbon. There are three main ways to extract metal from metal sulfide: first, through oxidation roasting, and then through reduction or other ways to get metal or alloy; The second is through matte smelting, and then through blowing, refining and other ways to get metal; The third is through sulfation roasting, and then through leaching, electrodeposition and other ways to get metal.
Oxidation roasting of metal sulfides involves heating the sulfide below its melting point to facilitate oxidation, converting the sulfide into a metal oxide. The primary objective of this process is to eliminate some or all of the sulfur present in the metal sulfide. During roasting, sulfur escapes as sulfur dioxide flue gas. The resulting metal oxides can be further processed through various methods. They may be reduced back to metals or alloys using reducing agents, or they can be extracted through leaching, electrodeposition, or similar techniques. For instance, in lead metallurgy, lead sulfide and other sulfides present in lead sulfide concentrate are subjected to high-temperature, oxidizing conditions to produce lead-containing oxides. These oxides are then reduced using carbon to obtain crude lead, which is subsequently refined. Similarly, in zinc metallurgy, the aim is to remove sulfur from zinc sulfide concentrate through oxidation roasting, thereby converting zinc sulfide into zinc oxide. Following this, zinc is extracted through sulfuric acid leaching and subsequent electrodeposition. Oxidation roasting finds widespread application in the extraction processes of various metals, including antimony, mercury, and others.
Metal sulfides, including copper sulfide, are commonly found alongside iron sulfides and are often extracted using the matte smelting process. Matte smelting operates on the principle of utilizing the higher affinity of the main metal and sulfur compared to iron or other impurity metals. Additionally, iron exhibits a greater affinity to oxygen compared to the main metal.
During matte smelting, conducted under high temperature and controlled oxidation conditions, iron is oxidized to ferrous oxide. Subsequently, gangue and flux materials are added to facilitate slag removal, resulting in the fusion of metal and sulfur, or multiple metal sulfides, into matte. Matte smelting is conducive to retaining sulfur in the matte, as it allows only a small portion to convert to sulfur dioxide due to controlled oxidation atmosphere. For example, copper matte is a product of this process. Further extraction of metal from matte involves processes such as blowing and refining. In the blowing process, sulfur is converted to sulfur dioxide. Matte smelting is also employed in the extraction of metals such as lead, molybdenum, antimony, bismuth, and cobalt. This method is favored for its ability to efficiently extract metals while retaining sulfur within the matte, ensuring effective utilization of resources and minimizing environmental impact.
Sulfation roasting of metal sulfides exploits the variations in decomposition temperature among sulfates, as well as the boiling point of the compounds and their water solubility. By carefully controlling the temperature, metal compounds can be converted into sulfates or into the gas phase. Some sulfates may decompose into insoluble oxides, allowing for the extraction of metal through leaching or directed separation. For instance, in the pyrometallurgy of copper and cobalt concentrate, the objective is to convert copper, cobalt, and other valuable metals into water-soluble sulfate compounds under precise control of furnace atmosphere and temperature. This process results in the conversion of sulfur into sulfur dioxide and iron into iron trioxide to the greatest extent possible. Copper sulfate, cobalt sulfate, and similar compounds can then be obtained through methods such as electrodeposition to extract the metals or alloys. Sulfation roasting is also utilized in the extraction processes of metals such as zinc, nickel, vanadium, and others. This method allows for efficient extraction of metals by harnessing the chemical properties of sulfates and their derivatives.
In summary, the treatment of metal sulfides results in the oxidation of most sulfur to sulfur dioxide. Sulfur dioxide emissions can pose significant atmospheric pollution, necessitating the installation of flue gas desulfurization facilities in metallurgical enterprises. While much of the recovered sulfur dioxide is utilized in the production of sulfuric acid, transporting sulfuric acid presents logistical challenges and limitations on transportation distance, making long-term storage impractical. Furthermore, during smelting processes for metals like lead and antimony, carbon dioxide is also generated, which undermines efforts to reduce carbon emissions and achieve carbon reduction goals. These environmental concerns highlight the importance of implementing sustainable practices and developing alternative solutions to mitigate the impact of metallurgical processes on the environment.
The invention introduces an electrochemical metallurgical method tailored for treating metal sulfides, facilitating the extraction of both metal and sulfur from these compounds. The method involves immersing a metal sulfide electrode into an electrolyte for electrolysis, resulting in the production of cathodic metal and anodic sulfur. This process enables the extraction of both metal and sulfur while concurrently mitigating the emission of harmful gases like sulfur dioxide typically generated during conventional smelting processes. Consequently, it alleviates environmental pressures, reduces the necessity for importing sulfur, and exhibits traits such as a streamlined process, minimal investment requirements, and absence of sulfur dioxide pollution.
Embodiment 1: An electrochemical metallurgical method for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 2: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 3: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 4: An electrochemical metallurgical method for extracting metals and sulfur from metal sulfides, the specific steps are as follows:
Embodiment 5: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
The chemical composition of the bismuthite concentrate in the present embodiment, which is obtained from a bismuth smelter in Hunan, is shown in Table 1:
Table 1 Chemical composition mass fraction (%) of bismuth sulfide concentrate from a bismuth smelter in Hunan
Electrolyte with water as solvent, electrolyte 180 g/L bismuth chloride, 150 g/L hydrochloric acid, oxidant 25 g/L iron sulfate, no additives; Control the distance between the electrode is 120 mm, the tank voltage is 3.1V, the current density is 200 A/m2, the electrolyte temperature is 45° C., the cycle speed is 10 L/min, and the electrolysis is powered on. When the anode residue rate is about 10%, the power is stopped, the anode and cathode are removed, and the anode and cathode products are stripped by ultrasonic method. The product enters the subsequent process, and the residual electrode returns to the anode preparation process.
Embodiment 6: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 7: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 8: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 9: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 10: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 11: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 12: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
Embodiment 13: An electrochemical metallurgical process for extracting metals and sulfur from metal sulfides, the steps are as follows:
The cyclic voltammetry curve of the matte in the above electrolyte is shown in
Table 6 Chemical composition of cathode product copper (%)
Raman diagram of anode product sulfur is shown in
Table 7 Sulfur chemical composition of anode product (%)
As can be seen from the above chart, the purity of both copper and sulfur is high, which shows that the electrochemical metallurgy method of extracting metals and sulfur from metal sulfides can be applied to practical production.
Example 14: An electrochemical metallurgical method for extracting metals and sulfur from metal sulfides, the steps are as follows:
The embodiments of the invention are described in detail above, but the invention is not limited to the embodiments above, and various changes can be made within the scope of knowledge possessed by ordinary technicians in the field without deviating from the purpose of the invention.
The beneficial effects of the invention are:
(1) The metal sulfide electrode undergoes electrolysis in the electrolyte to extract cathode metal and anode sulfur, facilitating metal and sulfur extraction while reducing harmful gas emissions such as sulfur dioxide, thereby alleviating environmental pressure, decreasing sulfur import volume, and offering advantages such as a streamlined process, lower investment, and absence of sulfur dioxide pollution.
(2) Adjusting the semiconductor type of the metal sulfide electrode to P-type prevents the occurrence of the current “self-limiting effect” during anode electrolysis, ensuring smoother and more efficient electrochemical reactions.
(3) In the preparation process of the metal sulfide electrode, adding an adjusting element to enhance conductivity helps the electrode achieve higher current densities at lower tank voltages during anode electrolysis, enhancing overall electrolysis efficiency.
(4) By incorporating a reinforcing agent in the preparation process of the metal sulfide electrode, the mechanical properties of the electrode are improved. This reduces the residual electrode rate and labor intensity during production, contributing to more efficient and manageable electrode handling.
In order to more clearly illustrate technical solutions of embodiments of the invention or the prior art, drawings will be used in the description of embodiments or the prior art will be given a brief description below. Apparently, the drawings in the following description only are some of embodiments of the invention, the ordinary skill in the art can obtain other drawings according to these illustrated drawings without creative effort.
A method for improving liquid crystal rotation obstacle according to the first embodiment of the invention specifically includes steps as follows.
Step one: The metal sulfide is transformed into an electrode, referred to as a metal sulfide electrode. Throughout the preparation process, the composition of the metal sulfide can be tailored by incorporating additional elements, while the mechanical properties can be enhanced by introducing reinforcing agents. Potential elements that can be added include copper, manganese, cobalt, sulfur, molybdenum, tin, bismuth, lead, zinc, selenium, antimony, tellurium, and cadmium. The mass of the added element ranges from 0% to 50% of the mass of the metal sulfide. Additionally, reinforcing agents such as carbon fiber, stainless steel fiber, copper fiber, or lead fiber can be introduced, with the mass of the reinforcing agent ranging from 0% to 10% of the mass of the metal sulfide.
Preferably, the additive element is one or more kinds of copper, sulfur, tin, and the additive element mass is 5% to 15% of the mass of metal sulfide;
Preferably, the reinforcing agent is carbon fiber or stainless steel fiber, and the reinforcing agent quality is 0.5%˜1% of the quality of metal sulfide;
Metal sulfide primarily behaves as a semiconductor, with N-type semiconductor characteristics when used as the anode. However, its conductivity at the anode is often limited due to intrinsic properties. To facilitate smooth electrolysis at the anode, adjustments are made to its composition to transform it into a P-type semiconductor. When utilizing natural sulfide concentrates, metallurgical intermediates, or by-products as the anode, their high impurity content and poor electrical conductivity pose challenges. To ensure smooth electrolysis, the content of elements within them is adjusted to enhance their electrical conductivity. Moreover, metal sulfides tend to be brittle, leading to electrode breakage during the electrolytic process. Adjustments are made to the elemental proportions or additional materials, such as carbon fiber, are incorporated during the preparation process to augment its mechanical strength.
Step two: The metal sulfide electrode anode, along with the anode and cathode, is placed into the electrolyte to establish an electrode array. Parameters such as the distance between electrodes, tank voltage, current density, electrolyte temperature, and cycling speed are adjusted for the electrolysis process. During this process, the sulfur element within the metal sulfide is oxidized and adsorbed in elemental sulfur form at the anode, while metal ions migrate into the electrolyte. Reduction reactions occur on the surface of the cathode, resulting in the production of pure metal substances. The products from the anode and cathode are then stripped. The cathode materials may include titanium, copper, stainless steel, lead, zinc, aluminum, or graphite. The vertical section shape of the cathode corresponds to that of the anode, while the longitudinal section shape may vary, such as square, round, triangle, trapezoid, pentagon, or fan. The longitudinal section area of the cathode typically ranges from 1 cm2 to 10 m2. The thickness or radius of the cathode ranges from 0.2 mm to 3000 mm.
Parameters such as the distance between electrodes, tank voltage, current density, electrolyte temperature, and cycling speed are adjusted for the electrolysis process. During this process, the sulfur element within the metal sulfide is oxidized and adsorbed in elemental sulfur form at the anode, while metal ions migrate into the electrolyte. Reduction reactions occur on the surface of the cathode, resulting in the production of pure metal substances. The products from the anode and cathode are then stripped. The cathode materials may include titanium, copper, stainless steel, lead, zinc, aluminum, or graphite. The vertical section shape of the cathode corresponds to that of the anode, while the longitudinal section shape may vary, such as square, round, triangle, trapezoid, pentagon, or fan. The longitudinal section area of the cathode typically ranges from 1 cm2 to 10 m2. The thickness or radius of the cathode ranges from 0.2 mm to 3000 mm.
Preferably, the cathode is titanium, copper, stainless steel, lead or aluminum, the longitudinal section shape is square, the longitudinal section area is 200 cm2˜0.6 m2, the thickness of the cathode is 1.5˜6 mm;
The number n of the anode ranges from 1 to 1000, and the number of cathodes is n+1; Preferably, the number of anodes n ranges from 35 to 350;
The metal sulfide can exist in a pure form or as a mixture, encompassing various compounds such as lithium sulfide, sodium sulfide, magnesium sulfide, aluminum sulfide, potassium sulfide, calcium sulfide, manganese sulfide, iron sulfide, ferrous sulfide, cobalt sulfide, copper sulfide, cuprous sulfide, zinc sulfide, molybdenum sulfide, silver sulfide, cadmium sulfide, tin sulfide, antimony sulfide, lead sulfide, and bismuth sulfide. Mixtures of metal sulfides may include natural sulfide concentrates, metallurgical intermediate products, or by-products. Examples of natural sulfide concentrates comprise, but are not limited to, pyrite, green vanadite, chalcopyrite, bornite, chalcocite, cuprite, fahlerite, arsenophenite, cobaltite, quartzite, wolframite, sulfotin, tetrahedrite, columnite, sulfotinite, antiantimonite, disulfide tin, trapezite, manganese sulfite, and pyroxene. Additionally, metallurgical intermediate products or by-products may include copper matte, cobalt matte, lead matte, antimony matte, iron matte, copper matte, and bismuth matte.
Preferably, metal sulfides: sodium sulfide, tin sulfide, aluminum sulfide, antimony sulfide, bismuthite, manganese sulfide, sphalerite, galena, copper matte.
The preparation of the metal sulfide electrode can be accomplished through various methods, including the thermal spraying method, hot plating method, physical vapor deposition method, chemical vapor deposition method, casting method, or powder metallurgy method. Specifically, the physical vapor deposition method encompasses techniques such as vacuum evaporation method and magnetron sputtering method, while the casting method includes approaches like sand casting method and solid casting method. Additionally, the powder metallurgy method involves techniques like the press method and centrifugal forming method.
Preferably, the thermal spraying method involves melting the metal sulfide powder using a heat source and forming the metal sulfide electrode on the substrate's surface by controlling the pressure of the protective gas. The pressure typically ranges from 1 to 20 MPa. Plasma arc heating is a preferred heat source, and the pressure is preferably maintained between 5 to 15 MPa for optimal results.
In the vacuum evaporation method, the metal sulfide powder is introduced into the evaporation container, and the vacuum is adjusted. The powder is then heated to deposit metal sulfide electrodes onto the substrate. The vacuum level typically ranges from 10−6 to 102 Pa. Resistance heating is the preferred heating method for this process.
In the magnetron sputtering method, the substrate is connected to the anode, while the metal sulfide target is connected to the cathode. The vacuum is pumped below 10−3 Pa, and argon gas is introduced to maintain the vacuum within the range of 10−2 to 10 Pa. Power is then applied to obtain metal sulfide electrodes through magnetron sputtering. The material of the sulfide target may include magnesium sulfide, zinc sulfide, calcium sulfide, aluminum sulfide, or cadmium sulfide, with aluminum sulfide being preferred.
In the chemical vapor deposition method, a protective gas is filled in the chemical vapor deposition setting. Metal powder and sulfur powder are placed in the evaporator and heated to evaporate into the reaction chamber, where they react and deposit on the substrate to form the metal sulfide electrode. Argon gas is preferred as the protective gas in this method.
The hot plating method involves melting the metal sulfide in a melting furnace, and the substrate is then immersed in the liquid metal sulfide for hot plating to produce the metal sulfide electrode.
In the sand casting method, a cavity is prepared using mold sand and core sand. The molten metal sulfide is poured into the cavity from a melting furnace, followed by cooling and solidification. The metal sulfide electrode is obtained through sand cleaning.
Similarly, in the solid casting method, foam is buried in sand, and the metal sulfide is melted in a furnace. The molten metal sulfide replaces the foam, and upon cooling and solidification, the metal sulfide electrode is obtained by removing the sand.
When employing the hot plating method, sand casting method, or solid casting method, it is preferable to use a vacuum induction furnace, vacuum arc furnace, induction furnace, or reverberatory furnace.
In the press method, metal sulfide powder and forming agent are mixed evenly into a mold, pressed to form a green body, and then sintered to obtain the metal sulfide electrode. The pressing molding pressure typically ranges from 10 to 30 MPa, with a pressing speed of 1 to 15 mm/s and a pressure holding time of 0.1 to 10 hours. Preferred parameters include a pressure of 20 to 25 MPa, a pressing speed of 10 to 12 mm/s, and a holding time of 1.5 to 2 hours.
In the centrifugal forming method, the metal sulfide powder and forming agent are uniformly mixed and placed into a mold. Centrifugal force is then applied to the mold to achieve shaping, resulting in a green body. This green body is subsequently sintered to obtain the metal sulfide electrode. The centrifugal forming speed typically ranges from 500 to 4500 revolutions per minute (r/min), with preferred speeds falling between 3000 and 3500 r/min.
During sintering, the atmosphere is maintained as a protective gas environment. The sintering temperature typically ranges from 400 to 1200 degrees Celsius (° C.), with preferred temperatures falling between 750 and 1200° C. The duration of sintering ranges from 0.1 to 10 hours, with preferred sintering times being 1.5 to 2 hours.
Protective gases include but are not limited to argon, nitrogen, carbon dioxide;
The average particle size of the metal sulfide powder is 1 nm˜1 mm.
The substrate material for the metal sulfide electrode can be chosen from metals, graphite, or composite materials. For metal substrates, options include but are not limited to copper, zinc, lead, tin, aluminum, titanium, stainless steel, aluminum alloy, lead alloy, titanium alloy, manganese alloy, copper alloy, zinc alloy, tin alloy, tungsten alloy, and molybdenum alloy. Composite substrates can include conductive materials such as conductive silicone rubber, conductive plastic, and conductive fiber. Preferred substrate materials include titanium, stainless steel, titanium alloy, lead alloy, or conductive fiber due to their suitability for electrochemical processes and their ability to withstand harsh conditions during electrolysis.
The substrate can feature various longitudinal section shapes such as square, circular, triangular, palisade, or porous. Its longitudinal section area typically ranges from 1 cm2 to 10 m2. with a thickness or radius of 1 mm to 2000 mm. The adhesion thickness of the metal sulfide on the substrate usually falls between 1 mm to 30 mm.
Preferred longitudinal section shapes for the substrate include square, circular, triangular, palisade, or porous, with a longitudinal section area preferably ranging from 180 cm2 to 0.35 m2 and a thickness or radius ranging from 1 mm to 3 mm. The adhesion thickness of the metal sulfide on the substrate is preferably 3 mm to 20 mm.
For metal sulfide electrodes prepared by casting or powder metallurgy methods, they typically take the shape of a cuboid with two ears. The length can range from 100 mm to 2500 mm, the width from 100 mm to 2000 mm, and the thickness from 1 mm to 100 mm. Preferably, the length is between 800 mm to 1200 mm, the width is between 500 mm to 700 mm, and the thickness is between 45 mm to 60 mm.
Forming agents used in the process include but are not limited to starch, sulfur, molybdenum disulfide, graphite powder, paraffin wax, and rosin. Among these, sulfur or graphite powder is preferred.
The electrolyte contains a solvent, electrolyte, oxidizer, additive, the solvent is water or organic solvent, organic solvent is anhydrous acetic acid, methanol, acetonitrile, tetrahydrofuran one or more; Preferably, the organic solvent is one or more of methanol, acetonitrile, tetrahydrofuran;
The electrolytes used in the process include sulfuric acid, perchloric acid, hydrobromic acid, hydrochloric acid, silofluoric acid, carbonic acid, phosphoric acid, nitrite, hydroiodic acid, tartaric acid, oxalic acid, citric acid, hydrofluoric acid, acetic acid, hypochloric acid, boric acid, bismuth chloride, bismuth sulfate, bismuth fluorosilicate, sodium chloride, lithium perchlorate, magnesium perchlorate, molybdenum chloride, sodium sulfate, aluminum chloride, sodium nitrate, molybdenum sulfate, copper chloride, copper sulfate, lead chloride, lead fluosilicate, cadmium chloride, antimony chloride, silver nitrate, stannous sulfate, zinc chloride, sodium acetate, sodium nitrite, sodium borate, zinc sulfate, manganese chloride, cobalt chloride, ammonium sulfate, cobalt sulfate, sodium oxalate, sodium tetrafluoroborate, sodium sulfide, sodium hydroxide, calcium sulfonate, potassium methanol, aluminum stearate, ammonium chloride, tetraethyl tetrafluoroborate, and ammonium tetrafluoroborate. The concentration of the electrolyte in the solution typically ranges from 0.1 g/L to 1000 g/L.
Preferably, the electrolyte comprises one or more of sulfuric acid, hydrochloric acid, silicofluoric acid, sodium tetrafluoroborate, sodium chloride, stannous sulfate, aluminum chloride, ammonium chloride, sodium sulfide, sodium hydroxide, bismuth chloride, bismuth silicofluorate, manganese chloride, ammonium sulfate, zinc sulfate, zinc chloride, lead chloride, lead fluorosilicate, copper sulfate, and copper chloride. The concentration of the electrolyte typically ranges from 10 g/L to 240 g/L.
As for the oxidizer, it can be ferric chloride, potassium permanganate, oxygen, hydrogen peroxide, fluorine, ozone, ferric sulfate, chlorine, bromine vapor, sodium dichromate, or a combination thereof. The oxidizer can either be in gas form or non-gas form, with a flow rate of 0.01 L/min to 5 L/min for gas and a concentration of 0.1 g/L to 1000 g/L for non-gas oxidizers.
Preferably, the oxidizer includes sodium perchlorate, ferric chloride, potassium permanganate, oxygen, hydrogen peroxide, ferric sulfate, or sodium hypochlorite. When using oxygen as the oxidizer, the flow rate ranges from 0.1 L/min to 0.15 L/min, and when using a non-gas oxidizer, the concentration in the electrolyte ranges from 10 g/L to 45 g/L.
Additionally, additives such as gelatin, bone glue, leather glue, thiourea, β-phenol, powder glue, sodium lignosulfonate, carbolic acid, tannin, diphenylamine, phenol, or borax can be used. The content of additives in the electrolyte ranges from 0 g/L to 1000 g/L. If the additive content is 0, then the electrolyte does not contain any additives.
Preferably, the additive is gelatin, bone glue, thiourea, β-phenol, cresol sulfonic acid, sodium lignosulfonate, casein one or more.
When the electrolyte contains additives, the preferred content of additives is 8˜30 mg/L;
The distance between the same plate is 1˜1000 mm, the tank voltage range is 0.1˜10V, the current density control range is 1˜1000 A/m2, the electrolyte temperature range is 25˜100° C., the cycle speed range is 1˜100 L/min, the anode residue rate is 1%˜ 25%;
Preferably, the distance between the same plate is 18˜120 mm, the tank voltage range is 1.5˜3.5V, the current density control range is 150˜450 A/m2, the electrolyte temperature range is 25˜60° C., the cycle speed range is 5˜30 L/min, the anode residue rate is 5%˜20%;
The method of stripping the product is ultrasonic method, mechanical method or manual method.
The principle of extracting metals and sulfur from metal sulfides relies on semiconductor electrochemistry. From a physical perspective, semiconductor behavior determines the electrochemical reactions occurring at the electrode interfaces. In semiconductor electrochemistry, when a semiconductor is of N-type, the charge carriers are free electrons. When the cathode is polarized, the abundance of free electrons in the conduction band increases, facilitating reaction occurrence. However, when the anode is polarized in an N-type semiconductor, few subsequent holes in the valence band participate in the reaction at the semiconductor/electrolyte interface. Instead, many subsequent electrons in the conduction band are repelled and flow away from the interface. As polarization increases, the rate (ic) of electrons participating in the cathode reaction increases. However, the electron concentration at the semiconductor/electrolyte interface can become even lower than the hole concentration. This phenomenon leads to a “self-limiting effect” on the current, where the current reaches a saturated value (is). Therefore, in electrolysis involving semiconductor anodes, N-type semiconductors are not suitable due to this self-limiting effect. Conversely, when cathode polarization occurs in the valence band of P-type semiconductors, a similar self-limiting effect and saturation current can be observed. However, when a P-type semiconductor electrode is oxidized, there is no self-limiting effect, allowing smooth anodic polarization reaction in the valence band. Hence, in the electrolytic process, P-type semiconductors are more suitable for use as anodes.
The typical polarization curves of N-type and P-type semiconductors illustrate these behaviors. In
From a chemical point of view, when oxidizing agents (such as hydrogen peroxide) are higher than S2− in metal sulfide (Me2Sx), the oxidizing agent can oxidize S2− to sulfur, the relevant reaction equation is (1); At the same time, when the metal sulfide is an anode, a positive voltage is applied, and the anode oxidizes, and the relevant reaction equation is (2); The sulfur element in the metal sulfide is oxidized and adsorbed on the anode plate in the form of sulfur element. As the sulfur element is oxidized, the metal ions enter the electrolyte, and the reduction reaction occurs on the cathode surface to form the metal. The relevant reaction equation is shown in (3).
Me2Sx+xH2O2+2xH+→2Mex++xS+2xH2O (1)
Me2Sx-2xe−→2Mex++xS (2)
Mex++xe−→Me (3)
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022110724019 | Sep 2022 | CN | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2022/142708 | Dec 2022 | WO |
| Child | 18743648 | US |
