Recycling of lead waste

Abstract

A method for recovering lead-containing waste, comprising: (a) dissolving the lead-containing waste in an aqueous solution of a first acid to form a solution of a first lead salt; (b) adding a second acid to the solution of the first lead salt to form a lead-poor solution and a precipitate of a second lead salt; and (c) converting the precipitate of the second lead salt into lead-containing oxide, wherein the solubility of the first lead salt in water is higher than that of the second lead salt. The method can be used to recover waste slurry of lead-acid batteries.

Description

Technical Field

[0001] The present invention relates to the recycling of lead-containing waste. In particular, the present invention relates to a method for recycling lead-containing waste into lead oxides. The method is particularly suitable for recycling lead-acid battery slurry. Background of the Invention

[0003] Lead-acid batteries are widely used in industries such as automobiles due to their rechargeable nature and relatively low cost.

[0004] During discharge, the lead and lead dioxide on the battery plates are converted to lead sulfate. Charging the battery converts the lead sulfate back to lead and lead dioxide. Although lead-acid batteries are rechargeable, over time the lead sulfate crystallizes into large, passive crystals in the battery plates, which reduce the tendency of the lead sulfate to convert back to lead and lead dioxide. This results in a deterioration in battery performance. Eventually the battery will have to be replaced.

[0005] In Europe and the United States, a high percentage of scrap lead-acid batteries are recycled. In a typical process, scrap batteries are shredded and lead-containing solids are separated from other battery waste components, such as plastic materials and electrolytes. Lead-containing solids originate from battery plates, which consist of battery grids and battery slurry. The battery waste slurry is sent to a smelter for pyrometallurgical processing into lead ingots. The lead ingots can then be used to make new lead-acid batteries. For example, the lead ingots can be used to make new battery grids, or they can be oxidized using a Barton jar or ball milling process to produce lead oxides, typically a mixture of lead oxide and free metallic lead. This lead oxide can then be reused as an active redox material in lead-acid battery plates.

[0006] These conventional recycling processes are highly energy intensive, with temperatures of around 1100°C required for the decomposition of lead sulphate. Conventional recycling processes can also be highly polluting. In particular, sulphur dioxide, nitrogen dioxide and often lead particles are produced in high temperature smelters. Specialised equipment and time are required to prevent pollutants from being released into the atmosphere. These can represent significant expenses in the recycling process.

[0007] Recently, methods have been developed that enable more efficient treatment of lead-acid battery waste. WO 2008 / 056125 discloses a method of mixing battery waste slurry with aqueous citric acid to produce lead citrate. The lead citrate can then be converted to lead oxide by calcination. This allows the direct production of lead oxide from battery waste slurry without the need to process intermediate lead ingots.

[0008] The process disclosed in WO 2008 / 056125 has many advantages. In particular, the lead oxide is produced directly from battery waste slurry, thereby avoiding the costs and logistics associated with downstream processing of lead ingots into lead oxide. In addition, the citrate acts as a fuel during the combustion process, thereby reducing the energy that needs to be supplied to the calciner. The temperature at which lead citrate is converted to lead oxide is also lower than the temperature required for lead sulfate to decompose, further reducing the energy burden of the recovery process. In fact, the process disclosed in WO 2008 / 056125 releases approximately 400mWh of energy per 1000 tons of batteries.

[0009] In order to reuse the lead oxide as a slurry for making battery plates, it must be of very high purity. Lead ingots produced by conventional smelting techniques typically exhibit impurity levels of less than 0.1 wt%, and typically less than 0.01 wt%. Therefore, a commercial process for recycling lead-acid batteries by alternative routes would also ideally provide a lead product with these purity levels. Unfortunately, the lead oxide produced by the process disclosed in WO 2008 / 056125 is not of sufficient purity to be used directly in batteries, but requires further processing before use.

[0010] Another disadvantage of the process disclosed in WO 2008 / 056125 is that it requires a large excess of citric acid to convert a sufficient proportion of the lead present in the battery waste slurry into lead citrate. This means that the cost of implementing the process is highly dependent on the cost of citric acid, making the economic feasibility of the process susceptible to fluctuations in the price of citric acid.

[0011] In summary, while the process disclosed in WO 2008 / 056125 represents an important step forward in the recycling of spent lead acid batteries, the process relies on the use of large excess amounts of citric acid and the quality of the slurry produced by the process is generally not high enough for direct use in battery plates.

[0012] He et al., Minerals, 2017, 7(6), 93, disclose another method using citric acid. This method addresses some of the disadvantages of the method disclosed in WO 2008 / 056125. However, this method requires the use of high temperatures, relatively long dissolution times, and high reagent concentrations. Therefore, it does not represent an attractive, commercially viable method for recycling lead-acid battery slurry.

[0013] Zhu et al. proposed another method for recycling lead-acid battery slurry in J. Hazard Mater., 2013, 250-251, 387-396, in which citrate is formed. The paper discloses reacting each of PbO, PbO2 and PbSO4 with a mixture of sodium citrate and acetic acid, respectively, and then applying the mixture of sodium citrate and acetic acid to the lead-acid battery waste slurry. However, the purity of the lead citrate obtained by this method is not significantly different from the purity of the lead citrate obtained according to the method disclosed in WO 2008 / 056125.

[0014] Sun et al. disclosed another method for recovering battery slurry in Journal of Power Sources, 2014, 269, 565-576. According to this method, the lead-acid battery waste slurry is converted into lead acetate, the lead acetate is crystallized and purified using glacial acetic acid, and the purified lead acetate is calcined to obtain lead oxide. However, the solubility of lead acetate in aqueous systems is very high. This means that considerable effort will be required to crystallize lead acetate salts from the aqueous phase. This will inevitably result in a large loss of lead load in the aqueous phase. Therefore, the method disclosed by Sun et al. cannot be expanded on an industrial scale.

[0015] There is a need for a method of recycling lead-containing waste, particularly waste from lead-acid batteries, that addresses one or more of the above problems. In particular, there is a need for a method that provides lead oxides of sufficient purity for direct use in battery plates, that can achieve a high percentage of lead recovery from the lead-containing waste (e.g., essentially zero losses), and / or that does not require the use of large amounts of excess reagents. Summary of the invention

[0016] The present invention utilizes the water solubility of different lead salts to provide a method for producing high-quality lead oxide from lead waste in the absence of excess citric acid. Specifically, the method uses an acid, such as acetic acid, which forms a lead salt with high water solubility to dissolve the lead waste. Subsequently, a second acid, such as citric acid, is added to the solution to precipitate a second lead salt with low solubility but high purity. The precipitate of the second lead salt can then be converted into lead oxide.

[0017] The use of an acid that forms a first lead salt with relatively high water solubility means that a higher proportion of lead-containing waste can be dissolved compared to when using an equivalent amount of citric acid. Unlike prior art methods, a high level of conversion can be achieved by adding a stoichiometric amount of citric acid (or other second acids that form relatively low-solubility salts) to the dissolved lead. In addition, when the second acid is added, the acid originally used to dissolve the lead-containing waste is regenerated and can be reused. Therefore, the invention provides a method for recovering lead-containing waste that minimizes the burden of reagents.

[0018] In a first aspect, the present invention provides a method for recycling lead-containing waste, the method comprising:

[0019] (a) dissolving the lead-containing waste in an aqueous solution of a first acid to form a solution of a first lead salt;

[0020] (b) adding a second acid to a solution of the first lead salt to form a lead-depleted solution and a precipitate of the second lead salt; and

[0021] (c) converting the precipitate of the second lead salt into lead-containing oxides,

[0022] The solubility of the first lead salt in water is higher than that of the second lead salt.

[0023] The present invention also provides a lead oxide material obtainable by the method of the present invention, as well as a battery plate comprising the lead oxide material and a lead-acid battery comprising the battery plate. DETAILED DESCRIPTION

[0024] Lead waste

[0025] The invention provides a method for recycling lead-containing waste.

[0026] The lead present in the lead-containing waste used in step (a) may be in various forms. For example, the lead-containing waste may contain metallic lead (referred to herein as Pb) or lead in the form of a compound, such as lead oxide (lead (II) oxide is referred to herein as PbO, lead (IV) oxide is referred to herein as PbO2), lead carbonate (referred to herein as PbCO3) or lead sulfate (referred to herein as PbSO4). It should be understood that these materials may be present in the form of a compound of materials, such as PbO.PbSO4, 3PbO.PbSO4 or 4PbO.PbSO4.

[0027] Preferably, the lead-containing waste used in step (a) includes at least one of Pb, PbO and PbCO3. More preferably, the lead-containing waste used in step (a) may include at least one of PbO and PbCO3, preferably also including Pb. The lead-containing waste used in step (a) may also include PbO2.

[0028] The lead-containing waste used in step (a) may also include lead in the form of PbSO4. However, the lead-containing waste may also be substantially free of PbSO4, either because there is no PbSO4 in the source of the lead-containing waste or because the lead-containing waste has been desulfurized. The lead-containing waste used in step (a) preferably contains less than 10 wt% PbSO4, preferably less than 1 wt%, more preferably less than 0.1 wt%. Lead can be desulfurized using a variety of methods, which will be discussed in more detail below. In a preferred desulfurization method, PbSO4 is converted into PbO or PbCO3.

[0029] The content of different lead-containing substances in the lead-containing waste may vary depending on the source of the lead-containing waste. The lead-containing waste used in step (a) preferably contains at least 5 wt% of lead (II) compounds, such as PbO or PbCO3, preferably at least 10 wt%, more preferably at least 20 wt%.

[0030] Non-lead components may also be present in the lead-containing waste, for example in an amount of at least 0.1 wt%, although they are typically present in an amount of less than 10 wt%, preferably less than 5 wt%, such as less than 3 wt% or less than 1 wt%. Non-lead components may include metal compounds, carbon and fibers. Metal compounds include barium sulfate, which is an additive that is typically included in lead-acid battery plates to minimize or control the crystallization of lead sulfate. Insoluble carbon materials include carbon black (which is typically added as an expander for lead-acid battery plates), graphene and carbon nanotubes. Fibers typically included in lead-acid battery plates include lignin sulfonates. Non-lead components may also include polymers or glass, such as from separators that can be used in lead-acid batteries.

[0031] The method of the present invention is particularly suitable for recycling lead-acid battery slurry. Therefore, in some embodiments, the lead-containing waste used in step (a) is derived from lead-acid battery slurry. Lead-acid battery slurry typically contains PbSO4, PbO, PbO2 and Pb. The proportions of these components in the lead-acid battery slurry of a single cell may vary greatly, depending on the degree of "consumption" of the battery, that is, the degree of use. For example, the lead-acid battery slurry of a battery that is rarely used may itself be "waste", but will typically contain relatively large amounts of Pb (e.g., greater than 30wt%) and PbO, and relatively small amounts of PbSO4. In addition, if the lead-acid battery slurry is taken only from the negative plate, it may not contain any PbO2.

[0032] However, lead-acid battery waste is usually composed of slurries from a large number of batteries, so its content of different lead-containing materials is standardized to some extent. Lead-acid battery waste slurry may contain at least 40wt% PbSO4. Lead-acid battery waste slurry may contain at least 5wt% PbO. Lead-acid battery waste slurry may contain at least 10wt% PbO2. Lead-acid battery waste slurry may contain at least 1wt% Pb.

[0033] In the case of desulfurization of lead-acid battery waste slurry, PbSO4 is usually converted to PbO, but may also be converted to PbCO3 or other lead compounds. Therefore, the lead-containing waste used in step (a) preferably contains at least 40 wt% of at least one of PbO and PbCO3. During the desulfurization process, the amount of PbO2 and Pb in the lead-containing waste generally remains unchanged.

[0034] Lead-acid battery slurry can be obtained from lead-acid batteries by known methods. For example, lead-acid battery slurry can be obtained by a method of crushing one or more lead-acid batteries and separating the lead-containing waste from other components of the battery (such as plastic material and electrolyte).

[0035] Leaded waste can also be obtained from many other sources, including cable sheathing, lead sheeting from the construction industry, paints, nuclear storage items, and PbO based electrical ceramics. Leaded waste may come from mining, metallurgy or chemical plants. Leaded waste may be the product of PbS ore mining, which has been oxidized by roasting to contain PbO and / or PbSO4 and impurities such as silica.

[0036] In some cases, the method of the present invention is used to recycle electric arc furnace dust. Electric arc furnace dust is a residue from the steel production process. The presence of zinc in the dust and the increasing cost of disposal have led to schemes to recycle the dust. This is usually done using the Waelz process, in which zinc-containing materials are processed in a rotary kiln furnace. The process is usually carried out in the presence of carbon (e.g. in the form of coke), and preferably also in the presence of calcium oxide (CaO) or silicon dioxide (SiO2). The kiln is usually operated at a temperature of 1000 to 1500°C.

[0037] However, electric arc furnace dust contains many impurities, including lead-containing compounds. Therefore, in some embodiments, the lead-containing waste used in step (a) is derived from electric arc furnace dust.

[0038] The lead-containing waste used in step (a) may be electric arc furnace dust obtained directly from steel production, preferably in desulphurized form. In other words, the electric arc furnace dust has not been subjected to further treatment steps, such as a zinc recovery process, other than desulphurization. After step (a), the lead load has been dissolved and the remaining solid waste may then be sent to a zinc recovery process, such as the Waelz process.

[0039] However, in a preferred embodiment, the lead-containing waste used in step (a) is the material remaining after zinc has been removed from electric arc furnace dust (e.g. in the Waelz process). This material is known as slag (or Waelz clinker) and typically contains at least 40 wt% PbSO4. Thus, the lead-containing waste used in step (a) may be slag from the Waelz process. The slag has preferably been desulphurised prior to use in step (a), e.g. using the process described below, and will therefore contain at least 40 wt% of at least one of PbO and PbCO3, preferably PbO.

[0040] In the case where the lead-containing material used in step (a) is a slag from a Waelz process, the slag has preferably been pre-treated with heat. It is believed that this can remove carbonaceous materials used in the Waelz process and that may be present in the Waelz slag, for example at least 10 wt%. In some embodiments, the method of the present invention includes a step of pre-treating the Waelz slag with heat, but in other embodiments the slag has been pre-treated. In the case where desulfurization is also carried out, this is preferably carried out after the pre-treatment heating step.

[0041] The pretreatment of the slag may be carried out at a temperature of at least 500° C., preferably at least 550° C., more preferably at least 600° C. The pretreatment of the slag may be carried out at a temperature of up to 800° C., preferably up to 750° C., more preferably up to 700° C. The pretreatment of the slag may be carried out at a temperature of 500 to 800° C., preferably 550 to 750° C., more preferably 600 to 700° C.

[0042] The pretreatment of slag can be carried out for at least 15 minutes, preferably at least 30 minutes, more preferably at least 45 minutes. The pretreatment of slag can be carried out for up to 4 hours, preferably up to 2 hours, more preferably up to 90 minutes. Therefore, the pretreatment of slag can be carried out for 15 minutes to 4 hours, preferably 30 minutes to 2 hours, more preferably 45 to 90 minutes.

[0043] Lead-containing waste may exist in various forms, such as in the form of dust, slag or sludge, or even in the form of minerals. However, the lead-containing waste used in step (a) is usually in a pulverized form, such as granules or powder, in the recovery method of the present invention. For example, the lead-containing waste used in step (a) can be in the form of granules, wherein the granules pass through a screen having openings with a diameter of 1000 μm, preferably 500 μm, more preferably 250 μm.

[0044] Step (a) - Dissolving in a First Acid

[0045] In step (a) of the process according to the invention, the lead-containing waste is dissolved in an aqueous solution of a first acid. This results in the formation of a solution of a first lead salt.

[0046] It should be understood that the first lead salt has a lead cation and an anion from the first acid. In a preferred embodiment, the first lead salt is a lead (II) salt. The solubility of the first lead salt in water is preferably at least 100 g / L, preferably at least 200 g / L, more preferably at least 300 g / L. The solubility mentioned herein refers to the equilibrium solubility in water at 25°C.

[0047] The first acid is preferably a Bronsted-Lowry acid, i.e. a proton donor. The first acid may be an organic acid or an inorganic acid, however the preferred first acid is an organic acid. A particularly suitable organic acid is acetic acid, which forms a solution of lead acetate Pb(CH3COO)2. Other organic acids that may be used include carboxylic acids, such as maleic acid, lactic acid and acrylic acid. Suitable inorganic acids include nitric acid.

[0048] The aqueous solution of the first acid preferably has a molar concentration of at least 0.1 mol / L, preferably at least 0.25 mol / L, more preferably at least 0.5 mol / L. The aqueous solution of the first acid preferably has a molar concentration of at most 7 mol / L, preferably at most 3 mol / L, more preferably at most 1.5 mol / L. Therefore, the molar concentration of the acidic aqueous solution of the first acid may be 0.1 to 7 mol / L, preferably 0.25 to 3 mol / L, more preferably 0.5 to 1.5 mol / L.

[0049] The leaded waste is preferably added to the first acid aqueous solution in an amount of at least 10 g of leaded waste per liter of acid aqueous solution, preferably at least 50 g, more preferably at least 80 g. The leaded waste can be added to the first acid aqueous solution in an amount of up to 650 g of leaded waste per liter of acid aqueous solution, preferably up to 300 g, more preferably up to 150 g. Therefore, the leaded waste can be added to the first acid aqueous solution in an amount of 10 to 650 g of leaded waste per liter of acid aqueous solution, preferably 50 to 300 g, more preferably 80 to 150 g.

[0050] An acidic environment (i.e., a pH of less than 7, preferably at most 6.5, more preferably at most 6) is typically present throughout the dissolving step (a). Thus, both the aqueous solution of the first acid and the solution of the first lead salt may exhibit a pH value of less than 7, preferably less than 6.5, more preferably less than 6. Throughout step (a), the pH typically does not drop below 2. All pH values ​​mentioned herein may be measured using conventional methods, such as using a pH probe.

[0051] The lead-containing waste can be dissolved in the aqueous solution of the first acid at a temperature of at least 0° C., preferably at least 10° C., more preferably at least 15° C. The lead-containing waste can be dissolved in the aqueous solution of the first acid at a temperature of up to 90° C., preferably up to 50° C., more preferably up to 30° C. Therefore, the lead-containing waste can be dissolved in the aqueous solution of the first acid at a temperature of 0 to 90° C., preferably 10 to 50° C., more preferably 15 to 30° C.

[0052] It will be appreciated that higher temperatures and higher concentrations of first acid are typically used in the dissolution step (a) where larger amounts of lead-containing waste are used.

[0053] The lead-containing waste is typically dissolved in an aqueous solution of the first acid at ambient pressure, ie without applying or removing pressure.

[0054] Dissolution of the lead-containing waste in the aqueous solution of the first acid may be accelerated by agitating the mixture, for example by stirring or ultrasound.

[0055] The lead-containing waste can be dissolved in the aqueous solution of the first acid for at least 1 minute, preferably at least 5 minutes, and more preferably at least 15 minutes. The lead-containing waste can be dissolved in the aqueous solution of the first acid for up to 120 minutes, preferably up to 60 minutes, and more preferably up to 45 minutes. Therefore, the lead-containing waste can be dissolved in the aqueous solution of the first acid for 1 to 120 minutes, preferably 5 to 60 minutes, and more preferably 15 to 45 minutes.

[0056] In some embodiments, it may be desirable to contact the lead-containing waste with a redox agent. Dissolution of the lead-containing material is aided by converting a material that is not in the +2 oxidation state to the +2 oxidation state. For example, a redox agent can convert a lead-containing material such as PbO2 in the +4 oxidation state to PbO, which then readily reacts with an aqueous solution of a first acid to form a soluble salt. Without the use of a redox agent, the conversion of PbO2 to a salt is typically quite slow. A redox agent can also assist in the conversion of metallic lead to PbO, although Pb can also form a salt with the first acid without contact with a redox agent.

[0057] Preferably, the redox reagent is a reducing agent, for example for lead compounds in the +4 oxidation state. Preferably, the redox reagent is also an oxidizing agent, for example for metallic lead. Particularly preferred redox reagents include hydrogen peroxide, which acts as both an oxidizing agent and a reducing agent. However, other redox reagents may also be used. For example, metal hydrides, hydrogen or inorganic salts may be used as reducing agents. Organic redox reagents may also be used.

[0058] The redox reagent may be brought into contact with the lead-containing waste before or during step (a) of the recovery method. When the redox reagent is brought into contact with the lead-containing waste in step (a), the redox reagent may be introduced into the aqueous solution of the first acid before the lead-containing waste dissolves, or the redox reagent may be introduced immediately when the lead-containing waste has partially dissolved.

[0059] The redox reagent can be used in the form of a solution having a molar concentration of at least 1 mol / L, preferably at least 3 mol / L, more preferably at least 5 mol / L. The redox reagent can be used in the form of a solution having a molar concentration of up to 25 mol / L, preferably up to 20 mol / L, more preferably up to 15 mol / L. Therefore, the redox reagent can be used in the form of a solution having a molar concentration of 1 to 25 mol / L, preferably 3 to 20 mol / L, more preferably 5 to 15 mol / L.

[0060] The redox reagent solution may be added to the aqueous solution of the first acid in an amount of at least 1 ml of the redox reagent solution per liter of the aqueous solution of the acid, preferably at least 5 ml, more preferably at least 10 ml. The redox reagent solution may be added to the aqueous solution of the first acid in an amount of up to 100 ml of the redox reagent solution per liter of the aqueous solution of the acid, preferably up to 50 ml, more preferably up to 30 ml. Thus, the redox reagent solution may be added to the aqueous solution of the first acid in an amount of 1 to 100 ml of the redox reagent solution per liter of the aqueous solution of the acid, preferably 5 to 50 ml, more preferably 10 to 30 ml.

[0061] In some embodiments, it may be desirable to add an alkali metal acetate, such as sodium acetate (CH3COONa), in step (a) of the method. The alkali metal acetate desulfurizes by converting PbSO4 into PbO. However, it is generally preferred to carry out step (a) in the substantial absence of alkali metal ions. Therefore, desulfurization is preferably carried out as a pretreatment step, which will be described in detail below.

[0062] In some embodiments, the lead-containing waste used in step (a) may include materials that are insoluble in the aqueous solution of the first acid and thus the material is retained as an insoluble material in the solution of the first lead salt. Insoluble materials may be present in the lead-containing waste in an amount of at least 0.01wt%, more typically at least 0.1wt%, and more typically at least wt1%. For example, lead-acid battery slurry typically contains 2-5% insoluble materials, more typically 3-3.5wt%. However, other lead-containing wastes (e.g., waste recovered from landfills) may contain higher levels of insoluble materials, e.g., up to about 60wt%.

[0063] Insoluble materials can include one or more metal compounds such as barium sulfate, carbon such as carbon black, graphene and / or carbon nanotubes, and fibers such as lignin sulfonates. In some embodiments, the insoluble material includes metal compounds, carbon and fibers. The insoluble material may also include polymers or glass. The insoluble material may also contain some lead, although this is generally less preferred. For example, the insoluble material may include Pb, for example if it is present in a relatively large particle size or has a short dissolution time, or PbSO4.

[0064] When the lead-containing waste contains insoluble materials, these materials are preferably recovered from the solution formed in step (a). This is a major advantage of the present invention. By dissolving the lead-containing waste in the aqueous solution of the first acid, an opportunity is provided to remove insoluble components that represent impurities in the lead-containing oxide but are valuable and present in their separated form. This is different from the prior art methods, in which the lead citrate suspension is directly prepared from the lead-containing waste. In some embodiments, the recovered insoluble materials are reused.

[0065] Suitable methods for recovering insoluble material from the solution of the first lead salt formed in step (a) include filtration, but a variety of other methods may be used, such as settling tanks or centrifugation.

[0066] Step (b) - Precipitation using a second acid

[0067] In step (b) of the present invention, the second lead salt is precipitated by adding the second acid to the solution of the first lead salt. This results in the formation of a lead-poor solution and precipitation of the second lead salt.

[0068] It should be understood that the second lead salt has a lead cation, while the anion comes from the second acid. In a preferred embodiment, the second lead salt is a lead (II) salt. The solubility of the second lead salt in water is lower than that of the first lead salt, for example, at least 100 g / L lower, preferably at least 200 g / L lower, more preferably at least 400 g / L lower. The solubility of the second lead salt in water is preferably at most 10 g / L, preferably at most 1 g / L, more preferably at most 0.1 g / L.

[0069] As with the first acid, the second acid is preferably a Bronsted-Lowry acid, i.e., the second acid is a proton donor. The second acid may be an organic acid or an inorganic acid, however, the preferred second acid is an organic acid. Particularly preferred is citric acid, which forms a lead citrate precipitate. Since the solubility of lead citrate in aqueous conditions is very low, the "loss" of citrate remaining in the solution is minimal.

[0070] The lead citrate precipitate is typically present as a compound having the formula Pb3(C6H5O7)2. Some lead citrate may also be present in its unstable Pb(C6H8O7) form, for example if an excess of citric acid is present, although the lead citrate precipitate typically consists of Pb3(C6H5O7)2. Advantageously, trilead citrate requires lower amounts of citric acid to form than monolead citrate. The lead citrate precipitate may be in a hydrated form, typically Pb3(C6H5O7)2xH2O, where x may be from 1 to 3.

[0071] The second acid is preferably added to the solution of the first lead salt in up to a stoichiometric amount to form the second lead salt from the lead ions in the solution of the first lead salt. By using a stoichiometric amount or slightly less than the stoichiometric amount of the second acid, it is ensured that the second acid is fully converted into the second lead salt. This is different from the prior art methods, in which a large amount of excess citric acid, extended reaction time and heating are usually required to achieve high conversion rates. In fact, by adding citric acid or another second acid for the first time in step (b), the method of the present invention ensures that the reaction between the second acid and the lead-acid battery waste slurry can be effectively quantitative.

[0072] The second acid may be added to the solution of the first lead salt in an amount of up to 100% of the stoichiometric amount required to form the second lead salt, preferably up to 98%, preferably up to 95%. The second acid may be added to the solution of the first lead salt in an amount of at least 60% of the stoichiometric amount required to form the second lead salt, preferably at least 75%, more preferably at least 80%. Thus, the second acid may be added to the solution of the first lead salt in an amount of 60 to 100% of the stoichiometric amount required to form the second lead salt, preferably 75 to 98%, more preferably 80 to 95%.

[0073] The amount of lead ions present in the solution of the first lead salt can be measured using known techniques. The amount of lead ions can be measured directly (e.g., using a lead ion sensor) or indirectly. The amount of the second acid required can then be calculated based on the measured amount of lead ions.

[0074] It should be understood that the stoichiometric amount of citric acid used to convert the lead ions in the solution of the first lead salt into Pb3(C6H5O7)2 is 0.67 moles of citric acid per mole of lead ions. This is demonstrated by the following equation, where lead acetate is converted into lead citrate:

[0075] 3Pb(CH3COO)2+2C6H8O7→Pb3(C6H5O7)2+6CH3COOH

[0076] Therefore, citric acid can be added to the solution of the first lead salt in an amount of at most 0.67 moles of citric acid per mole of lead ions in the solution, preferably at most 0.65 moles, more preferably at most 0.63 moles. Citric acid can be added to the solution of the first lead salt in an amount of at least 0.40 moles of citric acid per mole of lead ions in the solution, preferably at least 0.50 moles, more preferably at least 0.55 moles. Therefore, the amount of citric acid added can be 0.40 to 0.67 moles of citric acid per mole of lead ions in the solution of the first lead salt, preferably 0.50 to 0.65 moles, more preferably 0.55 to 0.63 moles.

[0077] The second acid may be added to the solution of the first lead salt in powder form or as an aqueous solution.

[0078] An acidic environment (i.e., pH below 7) is generally present throughout the precipitation step (b). Due to the release of the first acid, the pH will generally decrease during the precipitation step (b), for example, by at least 0.1, preferably by at least 0.2, more preferably by at least 0.3. The pH value will generally not drop below 2 throughout the step (b).

[0079] The precipitation of the second lead salt may occur at a temperature of at least -10°C, preferably at least 0°C, more preferably at least 5°C. The precipitation of the second lead salt may occur at a temperature of up to 80°C, preferably up to 40°C, more preferably up to 30°C. Thus, the precipitation of the second lead salt may occur at a temperature of -10 to 80°C, preferably 0 to 40°C, more preferably 5 to 30°C.

[0080] The second lead salt is typically precipitated from a solution of the first lead salt at ambient pressure (ie, without applied or removed pressure).

[0081] Precipitation of the second lead salt from the solution of the first lead salt may be accelerated by agitating the solution, for example by stirring or ultrasound.

[0082] The precipitation of the second lead salt can occur for at least 2 minutes, preferably at least 5 minutes, more preferably at least 10 minutes. The precipitation of the second lead salt can occur for at most 120 minutes, preferably at most 60 minutes, more preferably at most 45 minutes. Therefore, the precipitation of the second lead salt can occur for 2 to 120 minutes, preferably 5 to 60 minutes, more preferably 10 to 45 minutes.

[0083] The precipitate of the second lead salt is preferably separated from the lean lead solution before conversion to lead-containing oxide. This enables water-soluble impurities present in the lead-containing waste to be removed as part of the lean lead solution. Suitable methods for separating the second lead salt precipitate from the lean lead solution include filtration, but a variety of other methods, such as settling tanks or centrifugation, may also be used. Smaller mesh sizes are generally preferred to ensure that all of the second lead salt precipitate is captured. However, in some embodiments, the size of the second lead salt precipitate means that a larger mesh size may be appropriate.

[0084] The separated second lead salt can be washed, for example, with water to remove any water-soluble impurities from the precipitate.

[0085] The second lead salt can also be purified. Suitable purification methods include recrystallization. However, the method of the present invention does not usually require purification and can also provide a highly purified second lead salt. Therefore, no matter whether the second lead salt has been purified, the second lead salt preferably contains up to 5wt% impurities (i.e., non-second lead salt materials), preferably up to 1wt%, more preferably up to 0.1wt%. Purity can be measured using known methods, such as spectroscopy, such as ICP-AES (inductively coupled plasma atomic emission spectroscopy). ICP-AES can be carried out as described in detail in the embodiments.

[0086] The poor lead solution is included in the first acid for dissolving the lead-containing waste in step (a). Although the acid forms a relatively soluble first lead salt in step (a), the first lead salt can be converted into a second lead salt in step (b). In a preferred embodiment, the poor lead solution is recovered and used as an aqueous solution of the first acid for dissolving the lead-containing waste in step (a). By reclaiming the poor lead solution, the first acid is not consumed but can be reused. Therefore, in the recovery process, the first acid can be regarded as a catalyst rather than a reagent.

[0087] The lean lead solution may also contain residual lead, preferably in the form of a dissolved first lead salt. This is particularly true when the second acid is used in less than a stoichiometric amount in step (b) (compared to the lead ions in the solution of the first lead salt). Recovering the residual lead as part of the lean lead solution ensures that no lead is lost in the process of the invention.

[0088] Step (c) - Conversion to lead oxide

[0089] In step (c) of the method of the present invention, the precipitate of the second lead salt is converted into a lead-containing oxide. The lead-containing oxide includes PbO and usually also includes some metallic lead. For example, the lead-containing oxide may include metallic lead in an amount of at least 1 wt %. Typically, the metallic lead content in the lead-containing oxide does not exceed 40 wt %.

[0090] Preferably, the precipitate of the second lead salt is converted to the lead-containing oxide by calcination. This comprises introducing the second lead salt precipitate into a calciner and heating it to a temperature at which the salt decomposes and / or burns to produce the lead-containing oxide. Advantageously, where the second lead salt is lead citrate, the citrate acts as a fuel and burns during calcination, thereby reducing the energy required.

[0091] Calcination can be carried out at a temperature of at least 250°C, preferably at least 300°C, more preferably at least 325°C. Calcination can be carried out at a temperature of up to 1000°C, preferably up to 600°C, more preferably up to 450°C. Thus, calcination can be carried out at a temperature of 250 to 1000°C, preferably 300 to 600°C, more preferably 325 to 450°C. These temperatures are particularly suitable for the calcination of lead citrate precipitates. These temperatures generally provide lead-containing oxides comprising a mixture of PbO and Pb, with lower temperatures generally used to prepare lead-containing oxides that do not contain Pb.

[0092] Calcination can be carried out in an atmosphere comprising oxygen. It is understood that higher amounts of oxygen generally favor the formation of PbO, while low oxygen environments generally favor the formation of metallic lead.

[0093] Calcination can be carried out at an oxygen partial pressure of at least 0.01 atm, preferably at least 0.05 atm, more preferably at least 0.1 atm. Calcination can be carried out at an oxygen partial pressure of up to 5 atm, preferably up to 1 atm, more preferably up to 0.5 atm. Thus, calcination can be carried out at an oxygen partial pressure of 0.01 to 5 atm, preferably 0.05 to 1 atm, more preferably 0.1 to 0.5 atm. For example, calcination can be carried out in air at atmospheric pressure, i.e. without applying or removing pressure.

[0094] Calcination can be carried out for at least 10 minutes, preferably at least 20 minutes, more preferably at least 30 minutes. Calcination can be carried out for up to 6 hours, preferably up to 2 hours, more preferably up to 1 hour. Therefore, calcination can be carried out for 10 minutes to 6 hours, preferably 20 minutes to 2 hours, more preferably 30 minutes to 1 hour.

[0095] An advantage of the process of the present invention is that the process is suitable for preparing very high purity leaded oxides. Therefore, the leaded oxide preferably contains a total amount of at least 99 wt% PbO and Pb, preferably at least 99.5 wt%, more preferably at least 99.9 wt%. Leaded oxides with these purities are comparable to those obtained using the Barton jar process or ball milling process (in which the lead ingots are oxidized). Purity can be measured using known methods, such as spectroscopic techniques, such as ICP-AES (inductively coupled plasma atomic emission spectroscopy). ICP-AES can be performed as described in detail in the examples.

[0096] In some cases, metallic lead Pb rather than lead oxides may be the desired product, in which case temperatures in excess of 1000° C. are preferably used in step (c) of the invention. Reducing agents such as carbon monoxide or coke may also be used, in which case temperatures below 1000° C. (e.g., 400 to 600° C.) may also be used. Preferably, the partial pressure of oxygen in the system will be limited, for example, to at most 0.000167 atm. Inert gases such as nitrogen or vacuum may be used to displace oxygen from the reaction environment.

[0097] In other cases, lead citrate may be the desired product, in which case the process of the invention will not include step (c).

[0098] Further processing of lead oxides

[0099] In some embodiments, the method of the present invention produces a lead-containing oxide as the final product of the method. Thus, the present invention provides a lead-containing oxide material obtainable by the method of the present invention. However, in other embodiments, further processing of the lead-containing oxide is required.

[0100] For example, lead-containing oxides can be processed into battery plates. Lead-containing oxides can be processed into battery plates by known methods. For example, lead-containing oxides can be combined with one or more battery plate additives and an acid to form a slurry. If necessary, the lead-containing oxide can be crushed before mixing with the battery plate additive and the acid. Sulfuric acid is typically used as the acid, which converts the PbO in the lead-containing oxide into PbSO4. Suitable battery plate additives include those listed above and include metal compounds, insoluble carbon, and fibers. In some embodiments, one or more insoluble components that can be recovered at the end of step (a) of the present invention can be used as a battery plate additive. The slurry can then be applied to a grid (typically a lead alloy grid) and allowed to cure.

[0101] The battery plates can in turn be incorporated into lead-acid batteries. The battery plates can be incorporated into lead-acid batteries using known methods. For example, the battery plates can be placed into a plastic battery housing and the battery can then be charged with sulfuric acid. After the battery is assembled, the lead acid in the battery plates, such as PbSO4, is converted to PbO2 on the positive plate and to metallic lead on the negative plate by applying an electric current.

[0102] Therefore, the present invention provides a method for preparing a battery plate from lead-containing waste. The present invention also provides a method for preparing a lead-acid battery from lead-containing waste. The present invention also provides a battery plate obtainable by the method of the present invention, and a lead-acid battery comprising the battery plate.

[0103] Pretreatment of lead waste

[0104] As mentioned above, lead-containing waste generally contains PbSO4. For example, lead-acid battery waste slurry and arc furnace dust both contain PbSO4. In these embodiments, the method of the present invention preferably includes a pretreatment step of desulfurizing the lead-containing waste. This is because PbSO4 will not react with the aqueous acid in step (a) of the present invention in most cases. It should be understood that the pretreatment step occurs before step (a).

[0105] The pretreatment step preferably comprises desulfurizing the lead-containing waste by converting PbSO4 into another lead-containing compound, typically a lead (II) compound. In a preferred desulfurization method, PbSO4 is converted into PbO or PbCO3, more preferably into PbO. PbO or PbCO3 is then reacted with the aqueous solution of the first acid in step (a) of the present invention to form a first lead salt.

[0106] The conversion of PbSO4 to PbO can be achieved by contacting the lead-containing waste with an alkali. A variety of alkalis can be used in the pretreatment step. Suitable alkalis include alkali metal hydroxides such as NaOH, KOH or LiOH. The stoichiometric amount of the reaction with NaOH is shown below:

[0107] PbSO4+2NaOH→Na2SO4+PbO+H2O

[0108] The alkali may be added in an amount of at least 1.5 moles of alkali per mole of lead sulfate in the lead-containing waste, preferably at least 1.75 moles, more preferably at least 2 moles. The alkali may be added in an amount of up to 3 moles of alkali per mole of lead sulfate in the lead-containing waste, preferably up to 2.5 moles, more preferably up to 2.25 moles. Thus, the amount of alkali added may be 1.5 to 3 moles of alkali per mole of lead sulfate in the lead-containing waste, preferably 1.75 to 2.5 moles, more preferably 2 to 2.25 moles.

[0109] Adding too much or too little alkali may result in the formation of lead hydroxide instead of PbO. However, a large amount of lead hydroxide in the mixture may result in agglomeration. To ensure that the appropriate amount of alkali is added, it is generally preferred to monitor the PbSO4 content in the lead-containing waste during the pretreatment step and add alkali until the PbSO4 content is reduced to a target level. The target level may be at most 500 ppm, preferably at most 300 ppm, and more preferably at most 100 ppm, based on the weight of the lead-containing waste.

[0110] Monitoring can be by measuring the content of PbSO4 in the lead-containing waste directly, for example using a spectroscopic technique such as ICP-AES. ICP-AES can be performed as described in detail in the examples. Alternatively, it can be performed indirectly by monitoring parameters related to the amount of PbSO4 in the lead-containing waste.

[0111] The conversion of PbSO4 to PbCO3 can be achieved by contacting the lead-containing waste with a carbonate. Suitable carbonates include alkali metal carbonates, such as Na2CO3, K2CO3 or Li2CO3.

[0112] The amount of carbonate added may be at least 0.75 mole of carbonate per mole of lead sulfate in the lead-containing waste, preferably at least 0.85 mole, more preferably at least 1 mole. The amount of carbonate added may be at most 1.5 moles of carbonate per mole of lead sulfate in the lead-containing waste, preferably at most 1.25 moles, more preferably at most 1.1 moles. Therefore, the amount of carbonate added may be 0.75 to 1.5 moles of carbonate per mole of lead sulfate in the lead-containing waste, preferably 0.85 to 1.25 moles, more preferably 1 to 1.1 moles.

[0113] As previously mentioned, it is generally preferred to monitor the PbSO4 content in the lead-containing waste during the pretreatment step and add carbonate until the PbSO4 content is reduced to a target level, for example a target level of at most 500 ppm, preferably at most 300 ppm, more preferably at most 100 ppm, based on the weight of the lead-containing waste.

[0114] The desulfurization pretreatment step may be carried out at a temperature of at least 0°C, preferably at least 10°C, more preferably at least 15°C. The desulfurization step may be carried out at a temperature of up to 90°C, preferably up to 50°C, more preferably up to 30°C. Thus, the desulfurization step may be carried out at a temperature of 0 to 90°C, preferably 10 to 50°C, more preferably 15 to 30°C. It should be understood that while heat will not be applied to cause the reaction to exceed these ranges, the heat generated in the reaction itself may increase the reaction temperature to exceed these values.

[0115] The pretreatment step is typically performed at ambient pressure, ie, without application or removal of pressure.

[0116] The pretreatment step can be accelerated by agitating the mixture, for example by stirring or ultrasound.

[0117] The pretreatment step may preferably be carried out for a period of time until the target level of PbSO4 is reached. Typically, the desulfurization step may be carried out for 30 minutes to 24 hours, preferably 1 to 12 hours, more preferably 1.5 hours to 10 hours.

[0118] Filtration may be used to separate the desulfurized lead waste from the aqueous phase, but a variety of other methods may also be used, such as settling tanks or centrifugation. The desulfurized lead waste may optionally be washed (eg with water) and dried before use in step (a).

[0119] Once the pretreatment step is complete, sulfate ions (e.g., in the form of dissolved Na2SO4 if NaOH or Na2CO3 is used in the pretreatment step) can be removed from the desulfurized leaded waste along with the aqueous phase. The sulfate ions can be separated, for example, by crystallization due to evaporation of water, and optionally used in other applications. For example, the recovered sulfate can be used to produce glass. At least some of the energy required for the evaporation of water can be recovered from the calcination process that can be used to form the leaded oxide in step (c).

[0120] Lead-containing waste that has been desulfurized (e.g., by converting PbSO4 to PbCO3), such as lead-acid battery slurry, can also be obtained commercially or using a suitable commercial system. For example, desulfurized lead-containing waste can be obtained using a commercial system, wherein the target level of PbSO4 is at most 30% by weight of the lead-containing waste, or at most 10%. If desired, the commercially available desulfurized waste can be further desulfurized, for example, using the method disclosed herein, to obtain a target level of PbSO4 of at most 500 ppm, preferably at most 300 ppm, and more preferably at most 100 ppm, based on the weight of the lead-containing waste. However, in step (a) of the present invention, excess PbSO4 can also be simply separated together with other insoluble materials (e.g., barium sulfate, carbon and organic fibers).

[0121] Example

[0122] The invention will now be illustrated by the following non-limiting examples.

[0123] In the examples, X-ray diffraction was performed on a D8 Advance Bruker diffractometer and analyzed using Highscore software. The following settings were used: Cu Kα radiation, Ni-0.012 filter; run at 40 kV and 40 mA; range: 5 to 90° 2θ; step size: 0.03°; scan rate: 3.5° min -1 .

[0124] Thermogravimetric analysis and differential scanning calorimetry experiments were performed using a STA 409 EP Netzsch apparatus. The following settings were used: in static air (chamber approximately 0.15 L); sample size: 20 to 30 mg; temperature range: 0 to 600°C; heating rate: 5°C / min.

[0125] Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was performed using a Perkin Elmer Optima 8000 ICP-OES. The following settings were used: gas: argon; plasma gas flow: 8 L / min; auxiliary gas flow: 0.2 L / min; nebulizer gas flow: 0.7 L / min; RF power: 1500 Watts.

[0126] Solid samples (usually 0.10 g to 0.50 g of powder) analyzed using ICP-AES are treated differently to suit the specific composition of each sample so that it is completely dissolved in an aqueous medium. Each treatment involves combining 1, 2 or 3 different solutions in a specific order. The solutions used are 70 wt% nitric acid, 30 wt% hydrogen peroxide and 1 M potassium hydroxide (all 99.9% pure). The preparation is then completed by mixing 100 ml of nitric acid of the selected concentration so that the concentration in the final solution nitric acid reaches 2 wt%.

[0127] The standard solutions were originally purchased from Sigma, but considering the matrix effects, standard solutions were subsequently prepared using ultrapure elements from Sigma, deionized water, and pure nitric acid.

[0128] Example 1: Recycling of battery waste slurry mixture

[0129] Desulfurization

[0130] A representative mixture of battery waste slurry was dried, ground and sieved to a size of less than 250 μm. The resulting dry powder contained mainly PbSO4 (70 wt%).

[0131] To the dried powder (30.00 g) was added a solution of NaOH (7.96 g) in water (60 ml). The resulting suspension was stirred at 400 rpm for 2 hours at room temperature. The powder was then separated from the suspension by filtration, washed with deionized water and air-dried under suction.

[0132] The final mass of the powder obtained was 24.41 g, close to the calculated amount of 24.46 g.

[0133] X-ray diffraction analysis could not detect any residual lead sulfate (PbSO4, PbO.PbSO4, 3PbO.PbSO4 or 4PbO.PbSO4) in the product. As expected, the main phases detected were PbO, PbO.H2O and PbO2. ICP-AES measurement of this powder sample showed a sulfate ion content of 0.1 wt% (compared to 18.22 wt% for the untreated slurry), which can be attributed to the BaSO4 additive.

[0134] ICP-AES analysis of the filtrate showed that it did retain the SO4 extracted from the slurry 2- ions and most of the Na extracted from NaOH + ion.

[0135] Dissolve

[0136] The desulfurized lead-acid battery slurry (10.00 g) was dissolved in a solution of glacial acetic acid (5.2 ml) in water (100 ml), and then H2O2 (2.0 ml, 30 wt%) was added. The dissolution of most of the solids could be directly observed within a few tens of seconds, producing a clear colorless solution with a small amount of insoluble material suspended in the liquid phase. The mixture was stirred at 500 rpm for 5 minutes at room temperature.

[0137] The clear, colorless solution was then filtered. The filtrate (3.4 wt% of the slurry) was analyzed and showed mainly BaSO4, carbon and fibers.

[0138] Lead citrate precipitation

[0139] Solid crystals of citric acid (5.17 g) were added to the filtrate from the dissolution step. Precipitation of white lead citrate started immediately, but the solution was allowed to react for 1 hour at 80°C with stirring at 400 rpm. The solution was then filtered, the filtrate (lead citrate) recovered, dried and weighed. The mass obtained was 13.12 g, very close to the expected 13.32 g. X-ray diffraction was used to confirm that the powder obtained was entirely Pb3(C6H5O7)2; thermogravimetric analysis of pure Pb3(C6H5O7)2 and the synthesized powder showed a perfect match. ICP-AES analysis of the powder showed a complete absence of S, Ba, Sn, Al, Fe, Zn and Sb (0%); the Cu content was of the order of 10 ppm; and the Na content was of the order of 500 ppm.

[0140] Using a more severe washing regimen, the Na content was reduced to below 100 ppm, demonstrating that the Na content in the above examples is related to water quality and washing efficiency.

[0141] Calcination of lead citrate

[0142] Lead citrate (10.00 g) was heated in a muffle furnace at 350°C in air for 1 hour and then cooled to room temperature. The resulting orange / yellow / green powder (lead monoxide) was then recovered and analyzed. The expected mass of Pb3(C6H5O7)2 burned to PbO was 6.70 g. The actual mass of the material obtained by this process was 6.18 g; this is because some of the PbO was reduced to lead metal (Pb) during the calcination combustion process. Differential scanning calorimetry confirmed the presence of Pb.

[0143] The powder was analyzed by XRD to confirm that the phase obtained was PbO. ICP-AES was used to confirm the high purity of the material, comparable to the purity levels of lead citrate described above.

[0144] Example 2: Recycling of used battery negative electrode grids

[0145] Desulfurization

[0146] The spent negative electrode grid (100 g) was immersed in a solution of KOH (37 g) in water (250 ml) and reacted for 8 hours under low-speed stirring (50 rpm). The grid, which was light gray / white before the reaction, gradually turned green as PbSO4 (white) was converted to βPbO (green). After the reaction, the grid was removed from the clear solution and the slurry was easily separated from the metal current collector, which was then rinsed, dried and analyzed.

[0147] XRD could not detect the residual PbSO4 after the reaction, and the detected components were mainly PbO, PbO hydrate, lead hydroxide and metallic Pb. The sulfate content in the slurry was confirmed by titration analysis, which showed that the sulfate content of the slurry after the reaction was less than 0.1wt%.

[0148] Dissolve

[0149] The desulfurized slurry (50.00 g) was then dissolved in aqueous acetic acid (400 ml, 8 wt%) and stirred at 400 rpm for 10 minutes. Since the grid was a negative plate and did not contain any PbO2, no H2O2 was added. The solid volume in the suspension was significantly reduced due to dissolution.

[0150] The solution was then filtered and the filtrate was analyzed to be mainly BaSO4, carbon, fibers and metallic Pb fragments from the mesh, accounting for 7 wt% of the total mass of the slurry.

[0151] A portion of the solution was evaporated to crystallize the material expected to be lead acetate. The XRD pattern of the crystals showed a perfect match with pure lead acetate trihydrate, and thermogravimetric analysis of the crystals showed a similar decomposition pattern, confirming that the resulting solution was indeed a lead acetate solution.

[0152] Lead citrate precipitation

[0153] A citric acid solution (10 ml, 50 wt%) was added to the filtrate (200 ml) and stirred at room temperature for 10 minutes. A white solid precipitate was immediately observed. The precipitate was then filtered off, dried and weighed. The mass obtained was 12.76 g, close to the expected 12.88 g, corresponding to the maximum amount of lead citrate that can be formed with the amount of citric acid used.

[0154] XRD and thermogravimetric analysis showed a perfect match with Pb3(C6H5O7)2.

[0155] Combustion of lead citrate

[0156] The precipitate was burned in a muffle furnace at 400 °C in air for 1 h and analyzed under XRD. The color change from pure white to bright orange indicated the formation of PbO, which was confirmed by XRD analysis. The only other phase that could be detected was metallic Pb.

[0157] Example 3: Production of lead citrate using sulfate-rich lead slurry

[0158] Experiments were conducted on lead-acid battery waste slurry with a PbSO4 content of about 75wt%.

[0159] Desulfurization

[0160] In the first experiment, the lead paste was desulfurized using a stoichiometric amount of NaOH. In the second experiment, the lead paste was desulfurized using a stoichiometric amount of Na2CO3. In both experiments, the measured weight loss was close to the theoretical weight loss expected for desulfurization.

[0161] Dissolve

[0162] 5.00 g of desulfurized slurry sample was taken from each desulfurization experiment. The sample was mixed with acetic acid (2.15 ml), H2O2 (1.00 ml, ~35%) and deionized water (50 ml) respectively. The resulting mixture was stirred at 400 rpm for about 30 minutes at room temperature. The mixture was filtered and the insoluble components were recovered.

[0163] Lead citrate precipitation

[0164] A stoichiometric amount of citric acid was added to both filtrates. Lead citrate was immediately observed to form as a fine white precipitate in both experiments. The mixture was stirred at 400 rpm for 1 hour at room temperature using a magnetic stirrer. The mixture was filtered and the white precipitate was dried at 80°C overnight. XRD analysis showed characteristic peaks of Pb3(C6H5O7)2 in both experiments.

[0165] Example 4: Recovery of desulfurized slurry

[0166] A commercially available desulfurized lead slurry was obtained. The as-received desulfurized slurry had been partially desulfurized to a level of about 28 wt% PbSO4 (using carbonate). The slurry used in Example 3 is theoretically a representative feed slurry for a commercial desulfurization process, which was used to provide the as-received desulfurized slurry in Example 4.

[0167] Dissolve

[0168] The desulfurized slurry (10.00 g) was mixed with acetic acid (4.3 ml), H2O2 (3.00 ml, 35%) and deionized water (100 ml). The resulting mixture was stirred at 400 rpm for less than 5 minutes at room temperature. The mixture was filtered and the insoluble components were recovered.

[0169] Lead citrate precipitation

[0170] A stoichiometric amount of citric acid was added to the filtrate. Lead citrate was immediately observed to form as a fine white precipitate. The mixture was stirred at 400 rpm for 1 hour at room temperature using a magnetic stirrer. The mixture was filtered and the white precipitate was dried at 80°C overnight. XRD analysis showed characteristic peaks of Pb3(C6H5O7)2.

[0171] Combustion of lead citrate

[0172] The dried precipitate was heated to 350°C in a muffle furnace at a rate of 5°C / min and maintained for 1 hour. The sample was allowed to cool to room temperature before analysis using XRD. Impure lead oxides were obtained.

[0173] For comparison, lead citrate produced by the carbonate desulfurization route in Example 3 was heat treated in the same manner. XRD analysis showed that pure lead-containing oxide was generated, and the lead-containing oxide contained both PbO and metallic Pb.

[0174] Example 5: Recycling Electric Arc Furnace Dust

[0175] A sample of steel industry dust was obtained. The sample had previously been subjected to conventional zinc recovery processing and contained approximately 60 to 70 wt% PbSO4. The sample was desulfurized using NaOH and then converted to lead citrate and calcined.

[0176] Preliminary recovery experiments on the sample indicated that the process of desulfurization and conversion to lead citrate was slow. Further analysis of the sample indicated that C and SiO2 were present in an amount of about 20 to 30 wt%, which is believed to be coated on the sample particles.

[0177] Samples of the as-received material were preheated to 500 and 600°C to determine the optimal pretreatment temperature required to eliminate carbon. The samples were heated at a rate of 5°C per minute and the temperature was maintained at 500 or 600°C for 1 hour. Although the amount of carbon was reduced in both samples, the sample treated at 600°C showed a more significant reduction in carbon than the sample treated at 500°C.

[0178] The pretreated samples were desulfurized with NaOH, converted to lead citrate, and then calcined in air at 450°C to obtain lead oxides. The lead oxide products contained PbO and metallic Pb, with the highest purity coming from the samples pretreated at 600°C.

Claims

1. A method for recovering lead-containing waste, the method comprising: (a) dissolving the lead-containing waste in an aqueous solution of a first acid to form a solution of a first lead salt; (b) adding a second acid to the solution of the first lead salt to form a lead-depleted solution and a precipitate of the second lead salt, wherein the second acid is citric acid and is added to the solution of the first lead salt in an amount of up to 0.67 moles of citric acid per mole of lead ions; and (c) converting the precipitate of the second lead salt into lead-containing oxides, wherein the first lead salt has a higher solubility in water than the second lead salt, and the lead-containing waste is derived from lead-acid battery slurry, and The lead-depleted solution containing residual lead is recycled and used as the aqueous solution of the first acid in step (a).

2. The method according to claim 1, wherein the lead-containing waste comprises at least one of Pb, PbO and PbCO3.

3. The method according to claim 1 or claim 2, wherein: The solubility of the first lead salt in water is at least 100 g / L; The solubility of the second lead salt in water is at least 100 g / L lower than that of the first lead salt; and / or The solubility of the second lead salt in water is at most 10 g / L. The method of claim 1 , wherein the first acid is an organic acid.

5. The method according to claim 1, wherein the lead-containing waste is dissolved in the aqueous solution of the first acid: The molar concentration of the aqueous solution of the first acid is 0.1 to 7 mol / L; in an amount of 10 to 650 g of waste material per liter of aqueous solution of the first acid; Performed at a temperature between 0 and 90°C; Performed under ambient pressure; Duration is between 1 and 120 minutes; and / or Carry out under agitation.

6. The method of claim 1, wherein the lead-containing waste is contacted with a redox agent.

7. The method of claim 1, wherein the lead-containing waste comprises material that is insoluble in the aqueous solution of the first acid, and the method further comprises recovering the insoluble material from the solution of the first lead salt.

8. The method of claim 7, wherein the insoluble material comprises one or more of metal compounds, carbon and fibers.

9. The method of claim 1, wherein the second acid is added to a solution of the first lead salt: Adding 0.4 to 0.67 moles of citric acid per mole of lead ion; At temperatures between -10 and 80°C; Performed under ambient pressure; Duration is between 2 and 120 minutes; and / or Carry out under agitation.

10. The method of claim 1, wherein the precipitate of the second lead salt is separated from the lead-depleted solution.

11. The method of claim 1 , wherein the lead-depleted solution comprises residual lead in the form of a dissolved first lead salt.

12. The method of claim 1, wherein the precipitate of the second lead salt is converted to a lead-containing oxide by calcination.

13. The method of claim 12, wherein the calcining: At a temperature of 250 to 1000°C; is carried out at an oxygen partial pressure of 0.01 to 5 atm; and / or The time ranges from 10 minutes to 6 hours.

14. The method of claim 1, wherein the lead-containing oxide comprises at least 99 wt% of PbO and Pb in total.

15. The method of claim 1, further comprising processing the lead-containing oxide into a battery plate, and optionally incorporating the battery plate into a lead-acid battery.

16. The method according to claim 1, wherein the lead-containing waste used in step (a) is substantially free of PbSO4.

17. The method according to claim 1, wherein the lead-containing waste contains PbSO4, and the method further comprises a pretreatment step in which the lead-containing waste is desulfurized and reused in step (a).

18. The method of claim 17, wherein the pre-treatment step comprises contacting the lead-containing waste with: an alkali or a carbonate.

19. A method according to claim 17 or claim 18, wherein the method comprises monitoring the pre-treatment step until the PbSO4 content in the lead-containing waste is reduced to a target level.

20. The method of claim 19, wherein the monitoring of the pre-treatment step is performed indirectly by monitoring a parameter related to the amount of PbSO4 in the lead-containing waste.

21. The process of claim 18, wherein the base is an alkali metal hydroxide and is used in an amount of 1.5 to 3 moles of base per mole of lead sulfate in the lead-containing waste.

22. The method of claim 18, wherein the carbonate is an alkali metal carbonate and is used in an amount of 0.75 to 1.5 moles of carbonate per mole of lead sulfate in the lead-containing waste.