RU2792648C2 - Method for desulfurization of materials and/or residues containing lead sulfate using amine compound - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used for desulfurization of materials and/or residues containing lead sulphate. The process is carried out in one or more stages. In this case, only one desulfurization reagent is used, an amine compound, which is urea.

EFFECT: invention allows to use urea, which is characterized by a high level of stability, does not lead to potentially dangerous gas emissions during the critical stages of transportation and storage.

11 cl, 8 ex, 2 dwg

Description

The field of technology to which the invention belongs

The present invention describes a method for desulfurizing materials and/or residues containing lead sulfate, such as paste formed during the disposal of used lead-acid batteries, by using urea or another similar amine compound.

In industrial practice, the paste formed during the disposal of used lead-acid batteries (mainly consisting of lead sulfate and usually a small amount of lead dioxide, lead alloys and other lead compounds) is used as a secondary raw material in primary or secondary lead smelting furnaces. In some cases, after the desulfurization operation, which consists in treating an aqueous suspension of the paste with alkali carbonate, which converts lead sulfate into carbonate, this paste is used as a raw material in small reduction furnaces for the production of secondary lead.

Various patents have been published on this topic. One of them (US patent 4220628 Striffler, Kolakowski, 1978) describes desulfurization treatment by carbonization with ammonium carbonate. There are various works that describe the method of desulfurization using sodium carbonate or bicarbonate (US patent 4769116, Olper, 1986; US patent 6177056B1, Prengaman 1999).

Some patents deal with the desulfurization treatment of a paste with an alkaline hydrate, the resulting desulfurization product being used as a feedstock in electrolytic processes for the production of lead, both in aqueous solution (U.S. Pat. No. 4,769,116, Olper, 1988) and in molten salts (U.S. Pat. , 1998).

In all of the above cases, the methods involve some application problems, such as difficulties in supplying the necessary desulfurization reagents or managing reaction by-products that are difficult to purify or at least difficult to market or, in the worst case, must be disposed of in landfills. An additional limiting factor is the low desulfurization yield achievable with these reagents, unless very slow and complex processes are used, using a large number of devices and long periods of operation.

Patent application CN103523820A discusses the desulfurization treatment of a paste with conventional desulfurization reagents such as sodium carbonate, ammonium carbonate, ammonium bicarbonate, with the addition of an amine compound, preferably selected from ammonia, urea, ethylenediamine, diethylenetriamine, triethylenediamine.

Since this is not indicated anywhere in the description or example, the inventors believe that the desulfurization step can be carried out under operating ambient conditions. Under these conditions, it is obvious that urea has only minimal activity or no activity at all. Moreover, it is obvious that in general the desulfurization reaction is carried out under the action of other compounds present in the surrounding reaction medium, such as carbonates and bicarbonates. In addition, in this case, the method claimed in the Chinese patent involves some application problems such as difficulties in supplying the necessary desulfurization reagents or managing reaction by-products that are difficult to purify or at least difficult to market.

Patent application CN102689921A discusses the treatment of lead paste with complexing agents such as mixtures of various compounds also containing urea.

In addition, the only specified process condition is the temperature, in the general range of about 1000 degrees Celsius. Since it is not expressly stated anywhere in the description or example, the inventors assume that the complexation step can be carried out at ambient pressure (1 atmosphere). Under these conditions, it is obvious that urea has only minimal activity or no activity at all.

In addition, in the only example where urea is mentioned, it is used for 30 minutes in combination with seven other compounds, the reaction temperature being between 20 and 90 degrees Celsius. Under these conditions, it is obvious that urea has only minimal activity or no activity at all.

Moreover, in all other examples given, the lead paste complexing reaction is always carried out at a temperature below 95 degrees Celsius.

Surprisingly, a new, fast, and inexpensive process has been discovered that desulfurizes materials containing lead sulfate and possibly lead oxides, such as acid battery waste paste.

The process of the present invention provides for the use of a single amine compound selected from urea, guanidine, guanine, arginine, or others. The selected compound is the only desulfurization reagent added to the material to be desulfurized. This process is carried out without the use of conventional desulfurization reagents (eg sodium carbonate, ammonium carbonate and/or ammonium bicarbonate as described in the patents mentioned above).

Compared to processes using non-amine compounds, the reaction yield is significantly improved in the process of the invention.

Compared to processes using other amine compounds (e.g., ammonium carbonate, ammonium bicarbonate, and others), the method of the invention solves to a large extent the environmental, pollution, and safety problems associated with the production, transport, storage, and handling of these compounds. .

The preferred and recommended amine compound is urea.

In the case of using urea, the supply chain is also greatly simplified, since the total average amount of urea is significantly higher compared to other amino and ammonium compounds. In addition, since urea has a high level of stability (high decomposition temperature), it does not lead to potentially dangerous gas emissions during critical stages of transportation and storage.

The desulfurization process of the present invention may be carried out in one step or in multiple steps, depending on how the amine compound used reacts with the material to be desulfurized, either directly in one step or with a previous activation step of the selected amine compound.

In the one-step process, both materials containing lead sulfate and an amine compound are charged to one reactor. This chemical interaction leads to the formation of two main products: lead carbonate (insoluble) and ammonium sulfate (soluble).

The amount of amine compound must correspond to at least the stoichiometric molar ratio to the lead sulfate contained in the paste.

If necessary, a slight excess of the amine compound may be used, as has been considered in all other desulfurization processes described in the literature.

Preferably, the process is carried out in a closed reactor in which an amine compound, preferably urea, in aqueous solution (concentration between 20% and 50% w/v) is directly reacted with the material to be desulfurized under the following operating conditions:

- the preferred temperature is between 50 and 190°C, more preferably between 90° and 190°C, even more preferably between 130° and 180°C;

- the preferred pressure is between 1 and 12 atmospheres (atm), more preferably between 2 and 12 atm, even more preferably between 4 and 12 atm;

the preferred contact time is between 5 and 120 minutes (min), more preferably between 10 and 100 minutes;

- preferably the liquid/solid ratio (by weight) is between 0.5 and 4, more preferably between 1 and 4.

Under these conditions, the desulfurization yield can even exceed 99%.

The multi-step process can be carried out when the paste slurry is not in direct contact with a solution containing the selected dissolved amine compound. Instead, the solution interacts in a separate reactor with the selected amine compound, previously "activated" by distillation or flash evaporation, or in other similar processes.

Activation of the amine compound by distillation, flashing or other similar processes, and a multi-stage method in which the previously mentioned "activation" is considered, is the second subject of the present invention.

The new multi-step process is intended to use one amine compound selected from urea, guanidine, guanine, arginine or other similar compounds as the only desulfurization reagent that can be used in the desulfurization process.

In addition, this new multi-step process can be carried out by "activating" a mixture of at least two of the previously mentioned amine compounds, or, alternatively, by "activating" an amine compound or a mixture of at least two of the previously mentioned amine compounds in the presence of auxiliary substances for "activation". These excipients should be dosed in an amount of less than 20%, compared to the weight of the amine compound or compounds used.

Substances which may be used alone or in admixture may be specifically selected from ammonium carbamate, ammonia, carbon dioxide, ammonium carbonate, ammonium bicarbonate and other similar substances.

In fact, in this new multi-stage process, in addition to the amine compound, ammonia-based compounds can also be used at least in reduced amounts, less than 20%, compared to the total mass, similarly solving environmental, pollution and safety problems related to production. , transport, storage and handling of these compounds.

A multi-step process in which an amine compound, preferably urea, or the above mixture of at least two of the previously mentioned amine compounds, is "activated" by distillation, preferably comprises:

- obtaining a solution with a concentration between 40 and 60% (w/v) of the amine compound or the above mixture of at least two previously mentioned amine compounds, preferably about 50%, and feeding the solution/mixture to a distiller;

- separately obtaining a suspension of the paste in water with a liquid/solid mass ratio between 0.5 and 2, and feeding the suspension into the reactor;

- starting the distillation of a solution of the amine compound or the above mixture of at least two previously mentioned amine compounds, at a temperature between 140°C and 190°C and a pressure between 4 and 12 atm;

- transporting the actually produced or possibly condensed distillate to a reactor containing the paste slurry, where the desulfurization process proceeds under initial conditions of ambient temperature and atmospheric pressure. At the end of the distillation of the amine compound solution at a stoichiometric ratio to the amount of lead paste, the desulfurization process preferably continues for about 30 minutes.

Also under these conditions, the desulfurization yield may even exceed 99%.

A multi-step process in which an amine compound, preferably urea, or the above mixture of at least two of the previously mentioned amine compounds, is “activated” by flash evaporation, preferably comprises:

- obtaining a solution with a concentration between 40 and 60% (wt./vol.) of the amine compound or the above mixture of at least two previously mentioned amine compounds, preferably about 50%, and feeding the solution/mixture into a closed reactor without free space above product, and heating to a temperature between 170 and 190°C, preferably 180°C, and a pressure between 8 and 12 atm, preferably about 10 atm.

- separately obtaining a suspension of the paste in water with a liquid/solid mass ratio between 0.5 and 2, and feeding the suspension into the reactor;

- feeding an additional solution of “fresh” amine compound, possibly heated, with the same concentration, into a closed reactor and forced removal of a part of the heated solution from the reactor;

- transporting the solution exiting the closed reactor into a reactor containing a lead paste slurry at an uncontrolled temperature and under pressure, causing the heated solution of the amine compound or the above mixture of at least two previously mentioned amine compounds to flash flash, and a desulfurization process.

Also under these conditions, the desulfurization yield may even exceed 99%.

At the end of the treatment, carried out in one stage or multi-stage, filtering of the suspension is carried out in order to separate the solution from the solid. In the case of processing materials containing lead sulfate, the solid is actually composed of lead compounds that do not contain sulfur.

Preferably, a washing step on the solid compound is required in order to remove solutes absorbed from the solution.

The filtered solution can be used in different ways: it can be concentrated in order to successively crystallize the salts contained in the solution, mainly ammonium sulfate. Alternatively, this solution can be used, after adjusting the pH, in agriculture to fertilize irrigation. This is possible because the main solute in the solution is ammonium sulfate, which is an excellent fertilizer, and the chemical characteristics of the solution meet the highest standards of national, European and international laws for agricultural use.

The present invention is illustrated in the two diagrams shown in FIG. 1 and 2, which should not be considered as limiting the invention.

In FIG. 1 shows a one-step desulfurization process.

The desulfurization step is carried out by loading a paste containing lead sulfate (1) as well as an amine compound (2) in an aqueous solution inside the reactor (R). The slurry obtained in the desulfurization process (3) consists of a solution containing ammonium sulfate and traces of ammonium carbonate and a carbonate paste mainly composed of lead carbonate and lead oxides, which do not react with urea.

By liquid/solid filtration (S/L) two main products are separated: lead carbonate (insoluble) (4) and ammonium sulfate (soluble) in solution (5).

The ammonium sulfate solution, filtered and freed from any suspension, can be sent to a device for the concentration and crystallization of salts, mainly ammonium sulfate. Alternatively, this solution can be used, after adjusting the pH, in agriculture to fertilize irrigation.

In FIG. 2 shows a multi-stage desulfurization process with pre-activation of an amine compound.

The amine compound (2) in aqueous solution prior to being fed into the desulfurization reactor (R) is "activated" by distillation or flashing in the preceding step (M). The activated amine compound (6) enters the desulfurization reactor (R), which is also charged with an aqueous lead paste slurry (containing lead sulfate) (1).

The resulting slurry (3) consisting of a solution containing ammonium sulfate and traces of ammonium carbonate and a carbonate paste can be processed as shown in FIG. 1.

In the following, some examples will be given in order to better understand the unexpected simplicity and effectiveness of the present invention, and which should not be construed as limiting the invention itself.

Example 1

According to the diagram in FIG. 1, the process of desulfurization of lead paste extracted from spent lead-acid batteries is carried out with the amount of lead sulfate 58%. 1000 g of lead paste, 130 g of urea and 1.5 liters of water are loaded into the reactor. The reactor is sealed and heated to a temperature of approximately 150°C. At this temperature, the pressure is about 4.7 atm (absolute atmospheres). The liquid/solid ratio (by weight) is about 1.6. After these conditions are met, the process is continued for approximately 1 hour under the same conditions, and at the end of the process, the heating of the reactor is turned off.

The resulting suspension consists of a solution containing ammonium sulfate and traces of ammonium carbonate and a carbonate paste mainly containing lead carbonate and lead oxides that do not react with urea.

Only traces of the original lead sulfate remain in the products. The degree of conversion and therefore the yield of the process exceeds 95%, providing the added value of the lead paste in comparison with the original composition. This solution, filtered and free of suspension, is sent to a device for the concentration and crystallization of salts, mainly represented by ammonium sulfate, or used as such, after adjusting the pH, for fertilization in irrigation.

Example 2

According to the diagram in FIG. 1, the process of desulfurization of lead paste extracted from spent lead-acid batteries containing lead sulfate in an amount of 65% is carried out. 1000 g of lead paste, 140 g of urea and 1.5 liters of water are loaded into the reactor. The reactor was sealed and set up as described in Example 1. The reaction conditions were maintained for 4 hours, after which the suspension was subjected to extraction and filtration in order to separate the solid phase from the liquid.

Lead paste after desulfurization has a sulfate content below 1%; therefore, the desulfurization yield exceeds 99%.

After filtering and removing the slurry, the liquid phase is sent to a device for concentrating and crystallizing salts, which are mainly ammonium sulfate, or this phase is used as such, after adjusting the pH, for fertilization in irrigation.

Example 3

According to the diagram in FIG. 2, the process of desulfurization of lead paste extracted from spent lead-acid batteries containing lead sulfate in an amount of 58% is carried out.

Unlike the previous examples, the distillation of a solution of urea (50% w/v) is carried out at a temperature of 150°C and a pressure of 4.7 atm. The condensed distillate enters the second reactor containing an aqueous suspension of lead paste.

Dissolve 130 grams of urea in 130 milliliters of water and pour into a distiller. 1000 grams of lead paste containing 58% lead sulfate is suspended in approximately 850 milliliters of water.

The distillate of the urea solution is fed to the lead paste slurry. This reactor operates under mild conditions, which means ambient temperature and atmospheric pressure. The liquid/solid ratio (by weight) is about 1. The process continues until all the urea solution has been distilled. At the end of distillation, stirring of the slurry is continued for about 30 minutes, after which the slurry is filtered. The solid phase consists of desulfurized paste. The desulfurization yield is over 99%.

The slurry-free filtered solution is sent to a device for the concentration and crystallization of salts, mainly represented by ammonium sulfate, or it is used as such, after adjusting the pH, for fertilization in irrigation. With the use of this device, a continuous mode of operation of the process is ensured.

Example 4

As indicated in Example 1 above, 1000 g of lead paste (amount of lead sulfate 58%), 130 g of urea and 1.5 liters of water are charged into the reactor. The reactor is sealed and heated to a temperature of approximately 180°C. At this temperature, the pressure is about 10 atm. The liquid/solid ratio (by weight) is about 1.6. After these conditions are met, the process is continued for approximately 1 hour under the same conditions, and at the end of the process, the heating of the reactor is turned off.

After filtering the slurry and measuring the amount of sulfate residue in the lead paste, the desulfurization yield is greater than 99%.

After filtering and separating the suspension, the liquid phase is sent to a device for concentrating and crystallizing salts, which are mainly ammonium sulfate, or this phase is used as such, after adjusting the pH, for fertilizing during irrigation.

Example 5

As indicated in Example 2 above, 1000 g of lead paste (amount of lead sulfate 65%), 140 g of urea and 1.5 liters of water are charged into the reactor. The reactor is sealed and heated to a temperature of approximately 180°C. At this temperature, the pressure is about 10 atm. The liquid/solid ratio (by weight) is about 1.6. After these conditions are met, the process is continued for approximately 1 hour under the same conditions, and at the end of the process, the heating of the reactor is turned off.

After filtering the suspension and measuring the amount of sulfate residue in the paste, the desulfurization yield is greater than 99%.

After filtering and removing the slurry, the liquid phase is sent to a device for concentrating and crystallizing salts, which are mainly ammonium sulfate, or this phase is used as such, after adjusting the pH, for fertilization in irrigation.

Example 6

As indicated in Example 3 above, the lead paste slurry is not brought into direct contact with a solution containing dissolved urea, but placed in another reactor.

The urea solution (50%) contained in a closed reactor with no headspace is heated to a temperature of approximately 180° C. under a pressure of approximately 10 atm. By supplying a "fresh" solution of the amine compound, part of the heated solution is forced out of the reactor. This solution enters the reactor, which contains the lead paste slurry, at an uncontrolled temperature and under pressure.

Under these conditions, a single evaporation of the heated urea solution and the desulfurization process take place. After transferring 130 grams of urea in solution, the process can be considered complete. After filtering the slurry and measuring the amount of sulfate residue in the lead paste, the calculated desulfurization yield is greater than 99%.

After filtering and removing the slurry, the liquid phase is sent to a device for concentrating and crystallizing salts, which are mainly ammonium sulfate, or this phase is used as such, after adjusting the pH, for fertilization in irrigation.

Example 7

The desulfurization process is carried out according to the diagram in FIG. 2 with lead paste recovered from used lead-acid batteries with 58% lead sulfate.

In contrast to the previous examples, the distillation of a solution of urea (50% w/v) occurs at a temperature of 150°C and a pressure of 4.7 atm, in the presence of an auxiliary substance, ammonium bicarbonate, in an amount equal to 5% by weight of urea.

The condensed distillate enters the second reactor containing an aqueous suspension of lead paste. Dissolve 130 grams of urea in 130 milliliters of water and pour into a distiller. 1000 grams of lead paste containing 58% lead sulfate is suspended in approximately 850 milliliters of water.

The distillate of the urea solution is fed to the lead paste slurry. This reactor operates under mild conditions, which means ambient temperature and atmospheric pressure. The liquid/solid ratio (by weight) is about 1. The process continues until all the urea solution has been distilled. At the end of the distillation, stirring of the suspension is continued for about 30 minutes, and after that the suspension is filtered. The solid phase consists of desulfurized paste. The desulfurization yield is over 99%.

The slurry-free filtered solution is sent to a device for the concentration and crystallization of salts, mainly represented by ammonium sulfate, or it is used as such, after adjusting the pH, for fertilization in irrigation. With the use of this device, a continuous mode of operation of the process is ensured.

Example 8

As indicated in Example 3 above, the lead paste slurry is not brought into direct contact with a solution containing dissolved urea, but placed in another reactor.

Urea solution (50% w/v) in the presence of the excipient, ammonium carbonate, in quantity. equal to 5% by weight of urea contained in a closed reactor without free space above the product, heated to a temperature of approximately 180°C under a pressure of about 10 atm. By supplying a “fresh” solution, part of the heated solution is forced out of the reactor. This solution enters the reactor, which contains the lead paste slurry, at an uncontrolled temperature and under pressure.

Under these conditions, a single evaporation of the heated urea solution occurs and the desulfurization process proceeds. After transferring 130 grams of urea in solution, the process can be considered complete. After filtering the slurry and measuring the amount of sulfate residue in the lead paste, the calculated desulfurization yield is greater than 99%.

After filtering and separating the suspension, the liquid phase is sent to a device for concentrating and crystallizing salts, which are mainly ammonium sulfate, or this phase is used as such, after adjusting the pH, for fertilizing during irrigation.

Claims (27)

1. Method for desulfurization of materials and/or residues containing lead sulfate, carried out in one or more stages, characterized in that it is carried out with a desulfurization reagent, which is urea. 2. The method according to p. 1, which is carried out in one stage in a closed reactor, and urea in aqueous solution in an amount between 20% and 50% wt./about. interacts directly with the material to be desulfurized under the following operating conditions: - temperature between 50 and 190°C; - pressure between 1 and 12 atmospheres (atm); - interaction time between 5 and 120 minutes (min); - liquid/solid ratio (by mass) between 0.5 and 4. 3. The method according to claim 2, in which the operating conditions are: - temperature between 90 and 190°C, preferably between 130 and 180°C; - pressure between 2 and 12 atm, preferably between 4 and 12 atm; - interaction time between 10 and 100 min; is a liquid/solid ratio (by mass) between 1 and 4. 4. The method according to claim 1, which is carried out in several stages, and the urea is activated by distillation or flash evaporation before contact with the material to be desulfurized. 5. The method of claim 4, wherein urea is mixed with one or more other amine compounds selected from guanidine, guanine, or arginine, and then the resulting mixture of amine compounds is activated by distillation or flash evaporation to react with the material to be desulfurized. 6. The method according to claim 4 or 5, wherein the urea or mixture of amine compounds is activated by distillation or flashing in the presence of an auxiliary substance, such as an ammonia-based compound, in an amount of less than 20% by weight of the amine compound. 7. The method according to any one of paragraphs. 4-6, in which urea or a mixture of amine compounds is activated by distillation, including: - obtaining a solution of urea or a mixture of amine compounds with a concentration of urea between 40 and 60% (wt./vol.) and feeding the solution into a distiller; - separately obtaining a suspension of the paste in water with a liquid/solid mass ratio between 0.5 and 2, and feeding the suspension into the reactor; - starting the distillation of a solution of urea or a mixture of amine compounds at a temperature between 140°C and 190°C and a pressure between 4 and 10 atm; - transporting the resulting and possibly condensed distillate to a reactor containing a lead paste slurry in order to complete the desulfurization process under initial conditions of ambient temperature and atmospheric pressure. 8. Process according to claim 7, wherein the desulfurization process is carried out up to 30 minutes after the end of distillation of the urea or mixture of amine compounds in a stoichiometric ratio to the amount of lead sulfate. 9. The method according to any one of paragraphs. 4-6, in which urea or a mixture of amine compounds is activated by a single evaporation, including: - obtaining a solution of urea or a mixture of amine compounds with a concentration of urea between 40 and 60% (w/v), preferably about 50%, and feeding into a closed reactor without headspace, and heating to a temperature between 170 and 190°C , preferably 180°C, and a pressure between 8 and 12 atm, preferably about 10 atm, - separately obtaining a suspension of lead paste in water with a liquid/solid mass ratio between 0.5 and 2 and feeding the suspension into the reactor; - feeding an additional fresh urea solution, possibly heated, with the same concentration into a closed reactor and forced removal of part of the heated solution from the reactor; - transporting the solution leaving the closed reactor to a reactor containing a lead paste slurry at an uncontrolled temperature and under pressure, causing a flash evaporation of the heated urea solution or a mixture of amine compounds, and a desulfurization process. 10. The method according to any one of paragraphs. 1-9, wherein the lead sulfate residue is derived from a portion of the lead paste recovered from spent lead acid batteries, or at least lead scrap, the paste having a preferred lead sulfate content of between 10 and 80% by weight. 11. The method according to any one of paragraphs. 1-10, in which the suspension obtained at the end of the desulfurization process is filtered to separate the solid and liquid phases; moreover, after filtering and removing the suspension, the liquid phase is sent to a device for concentrating and crystallizing salts, which are mainly ammonium sulfate, or this phase is used as such, after adjusting the pH, for fertilizing during irrigation.

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