Related application

[0001] This application claims under 35 U.S.C. § 119(e) the benefit of the Provisional Application No. 62/114,226, whose entirety is hereby incorporated by reference.

Background

[0002] Lead acid batteries are the most used batteries. They are used in automobiles, backup power, aircrafts, submarines, fork-lifts, golf carts etc. The global lead demand is about $22 billion and is growing at more than 4%. About 54% of this demand is met by recycling of used lead acid batteries, which makes them the most recycled item globally.

[0003] While this recycling is good, the recycling method based on 'smelting' is hazardous, polluting and energy intensive. Further, with increasing regulatory norms around the world, this smelting based recycling is becoming very expensive, both in terms of capital and operational expenditures.

[0004] Various efforts have been made to develop a non-smelting based process to recycle used lead-acid batteries. Most of these approaches fall under two categories.

1. Production of lead-oxides utilizing chemical reactions: These have not been able to gain traction because of the high purity requirements of the oxides and the high process cost.

2. Production of metallic lead using acidic electrolytes (example fluoboric, fluosilicic, or methane sulfonic acids): These have not been able to gain traction because of high capital and operational costs.

Summary

[0005] Disclosed herein is a method comprising: forming lead rich basic electrolyte by dissolving a paste comprising lead or an oxide of lead in a basic electrolyte; and forming spongy lead at a cathode by applying an electric potential across the cathode and an anode, wherein both the cathode and the anode are in contact with the lead rich basic electrolyte.

[0006] According to an embodiment, the method further comprises filtering the lead rich basic electrolyte.

[0007] According to an embodiment, the method further comprises forming the paste by desulfurizing slurry comprising a sulfate of lead.

[0008] According to an embodiment, the paste comprises a lead oxide, a lead sulfate, or lead metal. [0009] According to an embodiment, the method further comprises obtaining the paste from a lead-acid battery.

[0010] According to an embodiment, the paste is obtained from an anode of the lead-acid battery.

[0011] According to an embodiment, the paste is obtained from a cathode of the lead-acid battery.

[0012] According to an embodiment, desulfurizing the slurry comprises treating the slurry with an alkali.

[0013] According to an embodiment, the basic electrolyte comprises sodium hydroxide.

[0014] According to an embodiment, the basic electrolyte comprises sodium hydroxide in a concentration of 5-40 % by weight.

[0015] According to an embodiment, the paste is dissolving in the basic electrolyte at a temperature of 40-80 °C.

[0016] According to an embodiment, the basic electrolyte comprises a solubility enhancer that increases solubility of the paste.

[0017] According to an embodiment, the solubility enhancer comprises molecules with a plurality of hydroxyl or a plurality of amino groups.

[0018] According to an embodiment, the solubility enhancer is at a concentration of 2-15% by weight.

[0019] According to an embodiment, the basic electrolyte comprises a gelling agent.

[0020] According to an embodiment, the gelling agent comprises pectin, seaweed extracts, or carrageenan.

[0021] According to an embodiment, the gelling agent is at a concentration of 0.1-5% by weight.

[0022] According to an embodiment, the electric potential is from 1.5 to 2.5 volts.

[0023] According to an embodiment, a current density between the anode and the cathode is from 2 to 10 A/DM2.

[0024] According to an embodiment, the method further comprises collecting and compacting the spongy lead in a heated environment.

Brief description of the drawings

[0025] Fig. 1 schematically shows a flow of obtaining a paste that contains lead.

[0026] Fig. 2 schematically shows a flow of obtaining lead from the paste.

Detailed description [0027] A process described herein allows production of lead (e.g., high purity lead) without utilizing smelting, for example, from used lead-acid batteries. The process uses chemical reactions to prepare an active lead material such as lead oxides (e.g., lead monoxide (PbO) or lead dioxide (Pb0 ₂ ) obtained from used batteries), lead sulfate (PbS0 ₄ ), and free Pb, and dissolves the active lead material in a basic electrolyte. The dissolved lead is then recovered in the form of metallic high purity lead in an electrolytic cell, which can be operated at low temperatures (e.g., 40-100 °C). The same basic electrolyte can be also utilized to recover the active lead material stuck on the grid lead (battery plates grid and contacts). This recovery of active lead material cleans the grid lead and prepares them to be molded into ingots (via solid pressing or melting). The basic electrolyte undergoes a minimal destruction per reduction cycle and thus can be utilized multiple times. It can also be utilized in the chemical reactions preceding the electrolysis stage.

[0028] The basic electrolyte is prepared from an aqueous solution of sodium hydroxide mixed with lead solubility enhancers (like molasses) and organic gelling or thickening agents (like pectin). The sodium hydroxide may be in a concentration of 5-40% by weight. The solubility enhancers and gelling agents may be in an amount of 2-15% and 0.1-5% by weight, respectively.

[0029] The metallic lead formation via reduction on the cathode of the electrolytic cell can be either a continuous or a batch process depending on the design of the electrolytic cell with respect to the material movement (removal of the lead formed on cathode). The metallic lead formed can be spongy and can have a density of 1-8 g/cm ³ . This spongy lead obtained after reduction at the cathode is typically a porous matrix containing hydrogen and the basic electrolyte. The organic gelling agents help in obtaining higher density of the spongy lead. Higher density facilitates melting to obtain ingots.

[0030] The process may be also able to recover non-lead metals (example tin, calcium, arsenic, silver, barium) via reduction at the cathode at different cell potentials. This is done by bleeding lead- poor electrolyte (after recovering lead through multiple recycles) in the electrolytic cell to obtain an alloy containing lead and other metals. The non-lead metals can also be recovered by passing the electrolyte through ion-selective resins.

[0031] The spongy lead obtained after electrolysis may have a high purity, e.g., of greater than 99.5%. The spongy may not deposit or plate on the cathode of the electrolytic cell and can be easily recovered without peeling. This spongy lead does not dissolve in the basic electrolyte and the weak association of spongy lead on the cathode can be utilized to design the electrolytic cell which can be operated both under continuous or batch operations. The electrolyte may flow through the electrolytic cell, which may enhance controllability of the electrolysis parameters. [0032] The process disclosed herein may not require a separator (e.g., membranes). This is because no lead dioxide is formed at the anode. Further, the basic electrolyte and low operation temperature allows non-expensive and easily available materials (like stainless steel) to be utilized to manufacture the cell electrodes.

[0033] An example of the process as applied to used lead-acid batteries may include the following procedures A-D.

[0034] A. Spent batteries are dismantled as shown in Fig. 1. The spent sulfuric acid in the batteries is recovered and neutralized at operation 101A. The dismantled batteries are further segregated into metallic (in the form of grid lead, active lead material (lead oxides, lead sulfate, free lead and non-lead metallic impurities) and non-metallic components (such as battery containers and separators) at operations 102, 103 and 104. The metallic components are segregated in the form of grid lead and the active lead material. The active lead material may be also be classified for positive and negative plates. This can be beneficial since the active lead on positive and negative plates have different compositions.

[0035] B. The active lead material (called "paste" going forward) obtained from procedure A is treated as per the following steps as shown in Fig. 2. The active lead material is desulfurized at operation 201 to form slurry by treating it with an alkali (e.g., hydroxides of sodium and potassium) per the following chemical reaction. Desulfurization can be done in a single step (to obtain up to 90- 95% desulfurization) or can be done in a multi-step manner to obtain close to 100% desulfurization. The concentrations of the alkali can be between 5-50%.

[0036] 2NaOH + PbS0 ₄ = Na ₂ S0 ₄ + PbO + H ₂ 0

[0037] 2KOH + PbS0 ₄ = K ₂ S0 ₄ + PbO + H ₂ 0

[0038] The slurry is filtered at operation 202 to obtain a desulfurized paste (such as lead monoxide (PbO), lead dioxide (Pb0 ₂ ) and free lead (Pb)) as the precipitate and sodium sulfate (Na ₂ S0 ₄ ) as the filtrate. Sodium sulfate crystals can be obtained via standard crystallization techniques. If the negative and positive plates are treated separately, PbO and free Pb is obtained as precipitate for negative plates and a mixture of PbO, free Pb and Pb0 ₂ for positive plates. The desulfurized paste is dissolved in the basic electrolyte at operation 203, in a dissolving chamber, to form a lead rich basic electrolyte. The composition of the basic electrolyte may include sodium hydroxide in a concentration of 5-40 % by weight. The desulfurized paste may be dissolved between temperatures of 40-80 °C. Higher temperatures lead to greater solubility of the desulfurized paste.

[0039] Solubility enhancers like molasses or sugar or compounds in which there are molecules with plurality of hydroxyl or amino groups such as mannitol or glycerol (preferably 5-8 hydroxyl groups) may be added in an amount of 2-15% by weight. These solubility enhancers may help to increase the solubility of the desulfurized paste in the basic electrolyte by dissolving both the lead oxides (both PbO and Pb0 ₂ ) and free Pb. With these solubility enhancers, the desulfurized paste can be dissolved directly in the basic electrolyte to undergo electrolysis. Consumption of these solubility enhancers may be very low and the solubility enhancers may not need to be replenished or topped- up after multiple cycles. These solubility enhancers may help to the solubility to a desired level (e.g., 2-7% by weight).

[0040] Gelling agents like pectin, seaweed extracts, gelatin, or carrageenan may be added in amount of 0.1-5% by weight. Gelling agents help as a counter balance to various 'expanding' agents present in the lead-acid batteries. The gelling agents may be consumed by various degrees in the basic electrolyte and may need to be replenished from time to time. Residual lead sulfate (PbS0 ₄ ) may be converted to PbO during the dissolution.

[0041] The lead rich basic electrolyte may be filtered at operation 204. The paste dissolution of the desulfurized past may be highly controllable via the concentrations of the solubility enhancers and gelling agents. The paste dissolution may be so controlled to eliminate or minimize the filtration. The precipitate obtained is recycled and sent back to the dissolving chamber at operation 206.

[0042] The lead rich basic electrolyte is transferred into an electrolytic cell at operation 205 to produce spongy lead. The following is an example of the condition under which spongy lead can be produced:

Cell voltage of 1.5 to 2.5 Volts and a current density of 2-10 A/DM ² ;

The temperature in the electrolytic cell is maintained between temperatures of 40-100

°C.

The cathode and the anode of the electrolytic cell can be manufactured with the same or different materials. For example, the cathode can be manufactured with mild steel and the anode with stainless steel. There is no requirement of a separator between the cathode and anode.

[0043] In the electrolytic cell, high purity lead (e.g., 99.5% or more) is deposited on the cathode and oxygen evolves at the anode. There is no deposition of lead oxides on the electrodes. The lead deposited on the cathode is spongy or porous with the basic electrolyte trapped in between. The spongy lead does not plate on the cathode but rather continuously falls to the bottom of the electrolysis cell. Alternatively, based on the cell design it can also be flushed continuously or at various time intervals. The evolved oxygen can be collected at the anode and stored.

[0044] The spongy lead is collected and compacted (with any compaction mechanism) under a heated environment (e.g., between 30-200 °C) to remove the electrolyte, which can be sent back to the dissolving chamber. The spongy lead after compaction may have a metallic silvery sheen and has densities between 1-8 g/cm ³ . With multiple reuses of the basic electrolyte, the density of the spongy lead may decrease. The density of the spongy lead may be an indicator to replenish the gelling agent in the electrolyte.

[0045] The compacted spongy lead is fed into a melting pot and melted at 300-500 °C. The melted lead can be drained out and converted into ingots of high purity lead. Any remaining electrolyte in the spongy lead after compaction is recovered as dross (with some PbO) and can be tapped out. The melted lead could then be further refined or alloyed. The tapped dross may be dissolved in water to obtain sodium hydroxide in solution with PbO. This composition may be sent to the dissolving chamber.

[0046] Over a few recycles of the electrolyte (e.g., between 10-30), non-lead metallic impurities (like bismuth, barium, calcium, antimony, tin etc.) may build up. These impurities can be recovered by running electrolyte with no or little dissolved paste through the electrolysis cell. The cell can be run at various voltages to bleed the electrolyte of specific impurity metal. The bled electrolyte can be reused for further electrolysis cycles. These non-lead metallic impurities can also be removed by passing the electrolyte with no or little dissolved paste through ion-exchange resins.

[0047] C. The grid obtained in step A undergoes the following treatment to remove the paste on it. The grid can directly be melted to obtain lead metal or lead alloy. To improve the recovery and decrease the amount of dross formation during the melting process, the grid can undergo the following treatment: (a) the grid lead is washed with the basic electrolyte (optionally with agitation); (b) the cleaned grid metal obtained in can be pressed into ingots or melted; (c) the basic electrolyte utilized in washing the grid lead can be recycled.

[0048] D. The non-metallic components obtained in step A can be further segregated as containers (typically plastics) and separators. They may be broken into smaller pieces and are washed with the basic electrolyte in an agitated vessel to remove the paste stuck thereon. The basic electrolyte utilized in washing the grid lead can be recycled.

[0049] The spongy lead has low bulk density and thus does not tend to plate on the cathode. This spongy lead can have a high purity (greater than 99.5%) and have a metallic silvery sheen when compacted under a heated environment (30-200 °C).

[0050] The electrolytic cell could be designed in multiple ways to operate under continuous or batch operations. Further, the operating conditions and parameters will depend on the size of the cell utilized. There is no requirement of a membrane separator in the electrolytic cell.

[0051] The electrodes in the electrolytic cell could be manufactured in multiple shapes (not restricted to the standard square, circular, rectangular, etc.) using various conductive materials, which are stable or resistant at the operating conditions described. Therefore, and among other materials, electrodes of mild steel (cathode) and stainless steel (anode) can be utilized. The electrodes need not be static and can be continuously or intermittently moved to remove the spongy lead formed. Moreover, there can be multiple ways to set up multiple electrolytic cells electrically (that is in series or parallel).

[0052] Agitation of the electrolyte in the electrolytic cell via continuous flow may improve the spongy lead production efficiency and reduce the energy cost.

[0053] There is no liquid effluent generation in the process as the aqueous solution of sodium sulfate generated during the desulfurization stage can be sent through a crystallization process for sodium sulfate to recover water which can be reused for electrolyte preparation and desulfurization.

[0054] Experimental Data

[0055] The experiments here can be performed in any suitable order as long as it follows the process disclosed herein. These data and examples are illustrative and not limiting.

[0056] Example 1: A total of 1000 kg of used lead-acid batteries were dismantled. The following breakdown of the material was obtained as shown in Table 1.

Item Weight (kg) %

Plastics 31.5 3.15%

Acid 85.1 8.51%

Separators 57.2 5.72%

Grid Metal 221.4 22.14%

Paste (dry) 511.1 51.11%

Moisture 93.7 9.37%

Total 1000 100%

Table 1: Breakdown of 1000 kg of used lead-acid batteries

[0057] Example 2: A total of 100 kg of dry paste was taken and analyzed. It was found that it contained (on a dry basis) 60 kg of lead sulfate, 25 kg of lead dioxide, 13 kg of lead monoxide and 2 kg of free lead. It was treated with 16 kg of sodium hydroxide in multiple steps to obtain 85 kg of partially desulfurized paste (on dry basis).

[0058] Example 3: 500 kg of basic electrolyte is prepared by taking 150 kg sodium hydroxide, 45 kg molasses and 5 kg pectin with 300 kg of deionized water. 25 kg of desulfurized paste obtained in Example 2 (on a dry basis) is dissolved in the electrolyte in a 200-liter horizontal vessel equipped with a ribbon blender. The electrolyte is agitated at 50 revolutions per minute (rpm) for a total of 30 minutes at 50 °C. It was observed that there was no un-dissolved material (paste) in the electrolyte.

[0059] Example 4: 500 kg of basic electrolyte is prepared by taking 150 kg sodium hydroxide, 45 kg molasses and 5 kg pectin with 300 kg of deionized water. 32 kg of desulfurized paste obtained in Example 2 (on a dry basis) is dissolved in the electrolyte in a 200-liter horizontal vessel equipped with a ribbon blender. The electrolyte is agitated at 50 revolutions per minute (rpm) for a total of 30 minutes at 70 °C. It was observed that there was no un-dissolved material (paste) in the electrolyte.

[0060] Example 5: A simple static electrolytic cell is constructed with a 100-liter volume. It is run at a current density of 4 A/dM ² for 1 hour with the electrolyte prepared in Example 3. 1.25 kg of spongy lead is obtained with density 5 g/cm ³ after compaction. This spongy lead is melted to obtain 1.18 kg of solid high purity lead (> 99.90% pure). It should be pointed out that the spongy lead obtained had a density of 1.5 g/cm ³ prior to compaction and it was not plated on the cathode. It fell down as soon as the cell was opened and contained the electrolyte, which was recovered after compaction.

[0061] Example 6: The Example 5 is rerun by continuously flowing the electrolyte at a flow-rate of 10 liter/hour. The amount of solid high purity lead (> 99.90% pure) increased to 1.43 kg.

[0062] Example 7: Table 2 shows the composition of the high purity lead obtained in Example 5 and Example 6. The purity test was conducted by an optical emission spectrometer.

Metal wt %

Lead 99.9008

Tin 0.0010

Antimony 0.0140

Copper 0.0150

Arsenic 0.0010

Iron 0.0010

Silver 0.0021

Zinc 0.0010

Cadmium 0.0350

Nickel 0.0010

Bismuth 0.0230

Selenium 0.0020

Calcium 0.0031

Table 2: Composition of high purity lead obtained after electrolysis