Patent Grant
9257731
This invention relates to a method for regenerating waste lead acid batteries. In particular, it relates to a regeneration method for waste lead acid batteries at a large industrial scale with such characteristics as low energy consumption, low cost, high-recovery rate, etc. This method implements full cycle regeneration of waste lead acid batteries and meet with the requirement of environment protection.
The lead acid battery is widely used in many fields for power storage, such as automobile, telecommunication, railroad, ships, electric vehicles, wind power, solar energy, etc. as a consumptive-material product. It includes a pole plate made up of alloy lead; diachylon consisting of lead sulfate, lead dioxide and lead monoxide; electrolyte containing mainly diluted sulfuric acid; plastic battery enclosure, upper cover and separator, etc. Its annual consumption is huge. If every element of the waste lead acid battery can be substantially recovered for reuse, especially in the production of lead acid batteries so as to implement full cycle regeneration of the waste lead acid battery, the economic benefit is very significant and there is a great social benefit from the associated energy-saving, consumption reducing and environment protection.
However, the known conventional regeneration method of waste lead acid batteries not only wastes a large amount of resource and energy, but also merely recovers parts with high commercial value, such as pole plate and diachylon as well as plastic enclosure from the waste battery. Only simple treatment or even no treatment is made for the other parts of the waste battery, such as plastic separator and electrolyte, and some other parts are simply thrown away without any treatment. Thus, such method is unable to implement full cycle regeneration of the waste lead acid battery, leading to serious problems of environment pollution: the insufficiently treated waste batteries are themselves a serious pollution source and cause the primary pollution; then, the flaws of the regeneration process can cause the secondary pollution. As a result, the waste lead acid battery has become a difficult common environment protection problem for the world.
At present, the conventional regeneration method of waste lead acid batteries includes mainly pyrometallurgical reduction method and electrolysis reduction technology (or wet-treatment method) as detailed below:
Pyrometallurgical Reduction Process
Pyrometallurgical reduction process is a regeneration process to recover diachylon. It has the following shortcomings:
(1) During the pyrometallurgical reduction process, it will cause the secondary pollution due to the reducing agent added which produces a lot of residue. The general pyrometallurgical residue rate of non-converted desulphurization of is 25%˜30%, and the residue rate of converted desulphurization is 10%˜15%. Both type residues are the waste, which cannot be recovered by the system.
(2) During the pyrometallurgical reduction process, it cannot be avoided to produce a lot of high temperature CO2, nitride gas and minim PbO, SO2, dioxin gas to pollute the environment. Although oxygen-enriching, most-environment friendly liquefied gas or natural gas are used as fuel, and the best dust collection unit is selected, it cannot be avoided to cause the problem to pollute air due to PbO and traces of PbSO4 produced during the direct high-temperature reduction process.
(3) The metal recovery rate of the pyrometallurgical reduction process is low. The lead retained in the residue is as high as 1%˜2% for pyrometallurgical process in general. It can reach 3%˜8% in worst scenarios. As the residue contains more metal, resource is wasted and the secondary pollution will be caused.
For both the pyrometallurgical reduction process and electrolytic reduction process, it is often necessary to subject the lead sulfate (PbSO4) of the diachylon in waste batteries to a desulphurization process. At present, there are two commonly-used desulphurization methods, as follows:
(I) Raw Material Mixing High-Temperature Melting Method
At present, in the domestic market, more than 90% of smelting method to recover waste battery is using a direct coal-fired reverberatory furnace. Using this method, it is not necessary to separate metal lead and diachylon from the waste battery plate, and the diachylon is mixed directly with scrap iron, sodium carbonate, reducing coal, etc. to have a substitution reaction under a high-temperature condition. As there is no smashing and separating process for the pole plate of the waster battery, it is not an ideal condition for the diachylon in the pole plate to contact with a lead sulfate state, added in with scrap iron, sodium carbonate, reducing coal, etc. Under a high-temperature condition with direct coal burning (over 1000° C.), the lead sulfate part is separated out to produce sulfur trioxide (SO3) gas. A part of PbSO4 and scrap iron is reduced into metal lead in substitution reaction and produces a lot of iron sulfide residue. As a large quantity of air enters during combustion process, SO3 gas contents are low. It is difficult to be recovered such low concentrations of SO3 to be used in manufacturing sulfuric acid and can only be discharged as a waste. In addition, as there is no special desulphurization neutralization unit, the waste SO3 gas will cause the secondary pollution. This method produces the waste residue at a rate of 25˜30% of the initial material, further causing a serious pollution of solid waste. Furthermore, the production cost is high and resource waste is serious due consumption of a large quantity of scrap iron converted into waste residue.
(II) Smashing Pre-Treatment Substitution Method of Waste Battery at a Normal Temperature
This method is to make a smashing pre-treatment to waste battery to separate metal lead and oxide diachylon. The PbSO4 in diachylon undergoes a substitution reaction at a normal temperature with Na2CO3 or NaOH added in. Its reaction is shown as follows:
PbSO4+Na2CO3═PbCO3+Na2SO4
PbSO4+NaOH═PbO+Na2SO4
The produced PbCO3 and PbO undergo a smelting reduction reaction in the converter. During the smelting process, no SO2 is produced. This method this is substantially free of SO2 pollution. But the method consumes a large quantity of expensive Na2CO3 or NaOH material to produce the low-value Na2SO4, which has little demand on the market. The cost of smelting recovery is high and obtained sodium sulfate cannot be reused in the battery manufacture.
Table 1 is an effect comparison of the above two types of desulphurization processes.
The above two desulphurization processes adopt a substitution reaction principle, to use expensive sodium hydroxide, sodium carbonate, scrap iron, etc. to substitute low-value by-product of sodium sulfate into low-value by-product, sodium sulfate, or dangerous waste, residue, which are difficult to be reused. The material cost to be used as substitution amounts to more than 50% of the manufacture cost.
The current electrolysis reduction technology can effectively solve this problem: the reducing agent is added to produce a large quantity of residue and causes the secondary pollution during the pyrometallurgical process. It can also solve the pollution problem of producing a large quantity of high-temperature CO2, nitride gas and minim PbO, SO2, dioxin gas, etc., which cannot be avoided during the pyrometallurgical process. The electrolysis reduction technology has a higher recovery rate of metal lead and less pollution compared to the pyrometallurgical reduction process method. At present, there are mainly two types of common electrolysis reduction technology. It is described as follows:
(I) Solid Phase Electrolysis Reduction Process in a Wet Way
The main process flow is as follows: smashing and separating battery—coating plate manually with the diachylon consisting of PbSO4, PbO2 and PbO—solid phase electrolysis (NaOH electrolyte)—refining (in solid phase electrolysis, Na2SO4 is obtained)
There is no desulphurization process during the above-mentioned solid phase electrolysis reduction process. The separated diachylon after directly coating plate is electrolyzed in NaOH. During the electrolysis process, a large quantity of NaOH is consumed. NaOH produces Pb and Na2SO4 with PbSO4 in diachylon. As there are many kinds of metal oxide, such as PbSO4, PbO2, PbO, etc. in diachylon, Na2SO4 obtained during the electrolysis process electrolyte has a greater effect on the electrolyte. And electrolyte cycle system is not adopted to separate the electrolyte, causing unstable factors and higher power consumption.
(II) Electrolytic Deposition Process
The difference point to the above-mentioned solid phase electrolysis reduction process is that electrolysis deposition includes a desulphurization process. Its main flow is: smashing and separating battery—the diachylon consisting of PbSO4, PbO2 and PbO is desulphurized and converted with Na2CO3 or NaOH—thermal decomposition is used to disassociate PbO2 into PbO—silicofluoric acid is used to leach-out PbO as lead ion—deposition electrolysis reduction.
The desulphurization process in the electrolysis deposition process adopts the above-mentioned smashing pre-treatment substitution method of waste battery at a normal temperature.
Table 2 is a comparison table for the above two electrolysis processes
The electrolysis deposition process has been listed in Demonstration Catalogue for National Advanced Pollution Treatment Technology. Comparing with the current solid phase electrolysis reduction process, both processes have no waste to discharge out. They are favorable for environment protection, but there are still following shortcomings for the electrolysis deposition process in a wet way:
The purpose of this invention is to provide a process of low power consumption, low cost, high recovery rate and environment protection and able to implement full cycle regeneration process method of waste lead acid battery.
The above-mentioned purpose of the invention is implemented with the following technical scheme, which is able to implement a full cycle regeneration process method of waste lead acid batteries and includes the following steps:
The diachylon of the above-mentioned step in the invention is a mixture consisting of lead sulfate (PbSO4), lead dioxide (PbO2) and lead monoxide (PbO). The main element of the mentioned waste electrolyte is diluted sulfuric acid. The purification treatment of the mentioned waste electrolyte in Step (3a) may adopt purification treatment system of sulfuric acid.
The following improvement may be made to the invention: SO3 gas obtained in Step (4) is sent into the purification treatment of waste electrolyte of Step (3a). The sulfuric acid after being filtrated in the system is used to absorb SO3 gas. so as to obtain concentrated sulfuric acid. After it is electrolyzed and filtrated for purification again, it can be used as an electrolyte material to manufacture new battery, as a result to implement reuse of the regenerated material from waste lead acid battery.
Smelting, refining and casting mode of the grid lead obtained in the above-mentioned Step (1) and sponge lead obtained in Step (7) adopts a separated smelting mode, i.e. both of smelting, refining and casting are performed separately. As the obtained grid lead carries acid and metal oxide powder, and the sponge lead is alkaline after solid electrolysis process, clean water is used to wash the remaining material on the grid lead and sponge lead. And smelting, refining and casting are performed separately, so as to obtain alloy lead ingot and metal lead ingot separately. This way is favorable to improve use of the other heavy metals originally existing in the grid lead, so as to save precious metal put into production of alloy lead ingot and improve the value in use for the recovered grid lead. The alloy lead ingot obtained in Step (2a) may be used as a raw material to manufacture lead acid battery in the production of new lead acid battery. The metal lead ingot obtained in Step (10) may be used as a raw material of diachylon to manufacture lead acid battery in the production of new lead acid battery, as a result to implement regeneration and cycle use of waste lead acid battery.
The above-mentioned Step (1) of the invention is based on the difference of the fractionized density and particle size subdivided into every group of waste lead acid battery. In water medium, a physical method, like a smashing and gravity separating method, is used to separate it, so as to obtain grid lead, waste electrolyte, diachylon and plastic separately. During the whole production process, it is performed automatically in a wet and fully airtight way. There is no pollution created during the production process. All water is reused in cycle and in a airtight way.
Pumping is used to make gas in the system operate under a negative pressure. And then filtration is performed and spray gas is discharged.
The following improvement may also be made to the invention: the grid lead obtained in the above-mentioned Step (2a) after smelting, separating and casting can be used in manufacture of pole plate of lead acid battery.
The plastic obtained in Step (1) of the invention mainly includes polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC). Polypropylene can be reused in production of battery enclosure. Polyethylene and polyvinyl chloride can be reused in the plastic products, which do not need high quality.
In the invention, smelting in above-mentioned Step (1) means that the grid lead is put into a melting pod for smelting. Refining means that the molten lead is flew into a refining pod for refined to remove impurity in the molten lead. Casting means that the refined molten lead is poured into a mold to cast an alloy lead ingot. The melting, separating and casting the sponge lead performed in Step (10) is the same as smelting grid lead.
The above-mentioned Step (2a) and (2b), or Steps (3a) and (3b), or Steps (5a) and (5b) in the invention may separately express two steps, which may be performed synchronously.
In the desulphurization and deoxidation reaction performed for diachylon in the above-mentioned Step (4) of the invention, desulphurization means that the lead sulfated is disassociated for desulphurization. Deoxidization means that the lead dioxide is disassociated for deoxidization. The reduction reaction equation of thermal decomposition for the diachylon in a desulphurization reactor is shown as follows:
PbSO4→PbO+SO3 [a]
PbO2→PbO+0.5O2 [b]
The reaction temperature of the materials mentioned in [a] and [b] may be in the range of 705˜830° C. (keeping the material under a non-melted state). Better reaction temperature is in the range of 800˜820° C. The disassociation time of the diachylon in a desulphurization reactor is 1˜2 hours. It is not necessary to add in any reductive material like NaOH, Fe scrap, etc. during the whole desulphurization and deoxidization process of the diachylon. The concentration of obtained SO3 gas is high. It can form concentrated sulfuric acid in reaction with sulfuric acid. The sulfuric acid obtained in Step (3b) after being filtrated is used to absorb the mentioned SO3 gas. The concentrated sulfuric acid obtained may be reused in production of new lead acid battery and electrolyte after it is purified in an electrolysis way and filtrated, so as to implement regeneration and reuse of sulfuric acid. The desulphurization rate of the lead sulfate may be larger than 98% after disassociation desulphurization. The deoxidation rate is larger than 97% after the lead dioxide has disassociation deoxidation. The particle size of the obtained lead monoxide is in the range of 16˜50 MU after thermal decomposition and reduction reaction.
In above-mentioned Step (5) of the invention, the weight proportion of water added in and lead monoxide is in the range of 13:100˜18:100.
The invention may be improved further: the electrolysis reduction process in the above-mentioned Step (7) adopts solid phase electrolysis reduction process in a wet way. The electrolyte adopts sodium hydroxide (NaOH) solution. The anode and cathode coated with lead oxide paste are put into an electrolytic bath, i.e. with a certain space. The mentioned anode and cathode implement chemical reaction under the function of direct current and sodium hydroxide electrolyte to reduce lead oxide into sponge lead. Where the mass percentage concentration of the sodium hydroxide electrolyte is in the range of 80%-15%. The electrolysis time is 18˜22 hours. Voltage is 1.5-2.5 v, and current is 450-600 A/m2. The chemical reaction equation in the electrolytic bath is shown as follows:
Cathode PbO+H2O+2e=Pb+2OH− [c]
Anode 2OH−2e=H2O+0.5O2 [d]
In the solid phase reduction electrolysis process in a wet way, an electrolyte cycle filter system can be adopted. The electrolyte in the electrolytic bath is formed as a cycle loop. In the loop, a filter channel, and an electrolyte temperature and concentration control unit are set up to collect sponge lead in the electrolyte and keep the electrolyte temperature and concentration stable, which will be favorable for improving electrolysis efficiency. As the lead sulfate desulphurization efficiency can reach more than 98% in Step (4), the remaining lead sulfate is electrolyzed in the electrolyte of Step (7). Its reaction equation is: PbSO4+2e=Pb+SO42−, and then Na2SO4 is produced. Therefore, minim PbSO4 will neither cause any affection on electrolysis nor create the pollution problem due to SO2 gas separated out.
As grid lead and sponge lead are fine particles, it is not so easy to be melted like large massive lead ingot. In order to increase the direct recovery rate of metal lead, this invention adopts a screw pressure feeder to press grid lead or sponge lead directly into a melting pot. They are melted under an airtight condition as a separately melting mode. Melting process of the grid lead or sponge lead is a physical melting process to be heated indirectly in a melting pot. High-temperature flaming gas transfers heat to the melting pot indirectly. Flaming waste gas is waste gas as fuel itself, which can be used as used heat. Oxygen-enriched combustion is adopted to be more favorable for decreasing waste gas quantity.
Refining is to remove impurity in the molten lead. The mentioned impurity in this invention means minim non-reduction oxide, like lead oxide. And in the refining process, it is required to ad in metals, such as calcium, stibonium, according to the element of battery grid plate to remove the impurity in the molten lead. Some oxidant is used usually to oxidize un-necessary metal to form dross for removal.
After the above-mentioned refuting Step (10), the direct recovery rate of metal lead can reach more than 96%; Produced dross is 3˜4%. The main element of dross is lead oxide. It will be reused after being ground. The total lead recovery rate is more than 99%.
This invention may be improved as follows: the process includes a waste water treatment step: the waste water produced in the above-mentioned Steps (1)˜(10) is collected into a waste water treatment system. After it is purified, it can be reused in cycle to implement zero discharge of production water. It both complies with the requirement of environment protection and save water resource:
In order to be easy to compare, the invention process and solid phase electrolysis reduction process and electrolysis deposition process in a wet way are compared, shown in the following table:
The core of this invention is “raw material pre-treatment of waste lead acid battery—disassociation desulphurization and deoxidation of diachylon under an airtight condition—solid phase electrolysis reduction in a wet way—manufacture of new lead acid battery” process. Comparing with the current technology, as for the environment protection, low energy consumption and low cost to implement a large-scale industrial production of full cycle regeneration in a wet way, it has the following significant effect:
As shown in
The differences from Implementation Examples 1 are: in Step (4), in the desulphurization rector, the reaction temperature of the material is 805° C. C. The disassociation time of the diachylon in the desulphurization reactor is 1.8 hours. In Step (5b), the weight proportion of water in lead monoxide paste and lead monoxide is 15:100. In Step (7), the mass percentage concentration of sodium hydroxide electrolyte is 10%. Electrolysis time is 19 hours.
The differences from Implementation Examples 1 are: in Step (4), in the desulphurization rector, the reaction temperature of the material is 810° C. The disassociation time of the diachylon in the desulphurization reactor is 1.5 hours. In Step (5b), the weight proportion of water in lead monoxide paste and lead monoxide is 15:100. In Step (7), the mass percentage concentration of sodium hydroxide electrolyte is 10%. Electrolysis time is 20 hours.
The differences from Implementation Examples 1 are: In Step (4), in the desulphurization rector, the reaction temperature of the material is 815° C. The disassociation time of the diachylon in the desulphurization reactor is 1.2 hours. In Step (5b), the weight proportion of water in lead monoxide paste and lead monoxide is 16:100. In Step (7), the mass percentage concentration of sodium hydroxide electrolyte is 12%. Electrolysis time is 21 hours.
The differences from Implementation Examples 1 are: in Step (4), in the desulphurization rector, the reaction temperature of the material is 820° C. The disassociation time of the diachylon in the desulphurization reactor is 1 hour. In Step (5b), the weight proportion of water in lead monoxide paste and lead monoxide is 18:100. In Step (7), the mass percentage concentration of sodium hydroxide electrolyte is 15%. Electrolysis time is 22 hours.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008 1 0029416 | Jul 2008 | CN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CN2009/072714 | 7/10/2009 | WO | 00 | 3/31/2011 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2010/003382 | 1/14/2010 | WO | A |
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| 4118219 | Elmore et al. | Oct 1978 | A |
| 4571261 | Buren et al. | Feb 1986 | A |
| 20080128293 | Mohanta et al. | Jun 2008 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20110265969 A1 | Nov 2011 | US |
