MXPA97004353A - Improved method for the recovery of pl - Google Patents

Abstract

Improved method for the recovery of lead from accumulators of extinguished lead comprising the withdrawal from the accumulator of the sulfuric acid solution of the remaining parts and the separators placed between the electrodes and the metallic part between the electrodes as well as the grinding of the remaining parts of the accumulator to obtain a very fine powder (paste), characterized by the following operations a) treatment of the resulting powder with an aqueous solution leaving at a pH between 0 and 8, able to solubilize the sulphate and Pb (II) eloxide leaving Pb (IV) epoxide unbleached, b) metal lead reduction of bivalent lead ions, present in the soluble fraction, with metallic iron, preferably in a slight excess with respect to the stoichiometric proportions, c) reduction of lead oxide tetravalent, and d) recovery of the salts used in the stage of the process a) for the elimination of iron sulphate

Description

IMPROVED METHOD FOR RECOVERY OF LEAD DESCRIPTION OF THE INVENTION The object of the present invention is an improved method for the recovery of lead, to the elementary state, that is, in the form of metal, from the lead compounds that are present in an exhausted lead-acid accumulator. The improved method of the present invention is based on a series of oxidation reactions -reduction between the oxides and the lead sulfate with metallic iron. As a result of these reactions, the compounds lead are reduced to the zero oxidation state, while the iron is oxidized to the oxidation state 3. As is known, the accumulators, or secondary cells, have the capacity to store electrical energy transforming it into chemical energy during loading and return it by reverse transformation, during discharge. The accumulator during discharge behaves like a stack in which an oxidation -reduction reaction occurs and during charging as an electrolytic cell where the opposite redox reaction takes place. The reactions that take place on the electrodes during discharge are as follows: -on the positive electrode (cathode) Pb02 + 3H30 + HS04 + 2e = PbS04 + 5H20 REF: 24927 in the negative electrode (PED) + HS04 + H20 = PbS04 + H30 + 2e -global reaction Pb02 + Pb + 2H2S04 = 2PBS04 + H20 E? = 2.2 V During the loading the reactions are reversed to give 2PbS04 + 2H20 = Pb02 + Pb + 2H2SO In a new accumulator the active components consist of approximately 50% metallic lead and 50% lead dioxide Pb02. The accumulator is not susceptible to further charges as soon as the initial contents or fractions of the two mentioned components have been largely converted to lead sulphate in an irreversibly electrochemical manner. In such conditions both oxidized classes of lead are present either in the electrodes or in the acid sludge resulting from the destructive processes of the electrode material during the operation of the accumulator. The exhausted lead acid batteries, considered until not many years ago, are currently a dangerous source of contamination due to the presence of lead and lead and sulfuric acid, constituting at the present time an important source of metallic lead, especially in consideration of the progressive extinction of Tas ore mines of loin. Increasingly restrictive legislative provisions on pollution control have forced a full recovery of lead compounds present in the accumulators, only in Italy this recovery rides to 150 thousand tons per year. This data corresponds to approximately 94% of the total exhausted accumulators. As it is known, the current state of evolution of the technology for the recovery of lead from exhausted accumulators makes register, as in Italy, the exclusive use of pyrometallurgical processes. The use of these procedures is not yet satisfactory either from the economic profile or under the ecological consideration. They actually work, at elevated temperatures, directly on the lead compounds present in the accumulators. This technological requirement to work at temperatures of the order of 1200 = 1400 ° C inevitably leads to the formation of lead vapors of difficult and expensive removal, and the formation of lead chloride by the interaction with chlorinated plastic materials present as waste from the involved materials. This brief review of the state of the art has also recorded the methods for the recovery of lead from exhausted lead-acid batteries -based on electrolytic processes, "- have been abandoned because of their excessively high cost despite presenting emissions Very low. There is thus in a specific sector the requirement to have a method to recover the lead, from exhausted lead acid batteries. Make it simple and versatile under the technological profile, low cost and non-polluting. This requirement is completely satisfied with the new method of the present invention which also has advantages that will become apparent from the following description. In general, the improved method according to the invention for recovering lead from exhausted accumulators comprises the removal of the accumulators from the sulfuric acid solution, the involved and the separators placed between the electrodes, and the metal part between the electrodes. electrodes as well as grinding the remaining parts of the accumulator to obtain a fine powder (paste) and is characterized by the combination of the following operations: a) treatment of the resulting powder with an aqueous solution leaving a pH between 0 and 8, capable to solubilize the sulphate and the Pb (II) oxide leaving Pb (IV) oxide b) unaltered lead bivalent metal ions, present env the soluble fraction, with metallic iron, preferably in an excess light with respect to stoichiometric proportions; c) reduction of tetravalent lead oxide; and d) recovery of the salts used in the stage of process a) for the elimination of the iron sulphate formed. The solubilization of the sulfate and the Pb (II) oxides in process step a) can be obtained with an aqueous solution of a salt selected from the group comprising ammonium, potassium, sodium, ammonium tartrate, potassium, sodium acetate, ammonium chloride, ammonium sulfate, ammonium nitrate, sodium chloride, monoethanolamine salified with or as is, diethanolamine salified with or as is, diethylenetriamine salified with or as is, bisodium salts of ethylenediaminetetracetic acid, ammonium glycollates, potassium or sodium too. the reduction of the bivalent lead ions, present in the soluble fractions in process step b), can preferably be carried out at a temperature between room temperature and that of boiling, preferably between room temperature and 80 ° C, optionally under agitation. In a first embodiment, the tetravalent lead oxide in step c) is reduced to bivalent lead oxide which is introduced in step b). The reduction of the tetravalent lead oxide present in the insoluble faction, in process step c), can be obtained with a heat treatment at 650-700 ° C to give bivalent lead oxide which is introduced in stage a). The temperature of this treatment is relatively low and very far from that of the decomposition of lead sulphate present as eventual residue, so that in this phase no harmful gas or vapor emissions are verified. As an alternative, the reduction of tetravalent lead oxide in the insoluble fraction in process step c) can be achieved with a solution of divalent iron salts solution to obtain a solution containing bivalent lead oxide and trivalent iron ions that it is introduced in stage b). The removal of the ferric sulfate, in step d) can be achieved by an alkalizing treatment. This alkalizing treatment can preferably be carried out by the addition of a hydroxide selected from the group comprising: sodium, calcium, ammonium, barium and combinations thereof. In this case, the separation of the ferric hydroxide from the other solids can be obtained by effect of the different specific weight.

The present invention is not limited to the improved method for the recovery of lead from exhausted acid lead accumulators, but also extends to ferric hydroxide with high purity obtained in the first embodiment of the new method described herein. The aqueous treatment solution used in step a) must have a ph value between 0 and 8 and must be brought within that range in case the ph of the treatment solution moves away from this. the already used solutions of the treatments envisaged in stages a) and b) are poor of Pb "+ ions and enriched with Fe ++ and Fe3 ions.These are present sulfate ions previously bound to lead sulfate. solutions to the stage of solubility of the paste, it is necessary to eliminate all or part of the sulphate ions to prevent their accumulation from inhibiting the solubilization process.They are also eliminated ferrous or ferric ions when they have not already been precipitated to the hydroxide state Its concentration in the solution depends on the pH with which the lead reduction has been conducted.The trivalent iron has a pH higher than 3.5-4 and is precipitated as insoluble ferric hydroxide.The iron (II) is sometimes somewhat soluble also in the form of hydroxide but its conversion into iron (III) hydroxide is easily carried out by blowing air.

The concentration of ferric ions depends on the pH of the solution. If the nascent solution of the previous treatments with metallic iron has a low pH (less than 3), it is possible to proceed to the "total" elimination of ferric ions by precipitating them in the form of ferric hydroxide bringing the ph of the solution to the value 5.5-6 by a moderate addition of the same bases that will serve successively to precipitate the sulfate ions. The precipitation of ferric hydroxide is selective because of its excellent solubility. The conditions in which the precipitation is verified are very far from those in which the salts of the sulphate ions and the salts of lead (II) are precipitated, for which the product obtained results without these ions. Simultaneously with the addition of the bases, a stream of air or oxygen can be passed through the solution to oxidize the ions from Fe + 2 to Fe + 3 and precipitate in the form of iron (III) hydroxide. The sulfate ions can be removed from the solution by treatment with compounds whose cations are linked with the sulphate ions resulting in the formation of poorly soluble sulphates. The preferred compounds for this treatment are sodium hydroxide, ammonium calcium hydroxide and barium hydroxide. The treatment with sodium hydroxide leads to a partial elimination of the & amp; sulfates in that sodium sulfate is quite soluble in water. The product that is recovered has a certain value in the market. The treatment with ammonium hydroxide leads to the formation of ammonium sulphate, a product considered as nitrogen fertilizer. The separation of these salts can be done after concentration of the solution and fractional crystallization of its components. The treatment with barium hydroxide leads to the total elimination of sulfates, as soon as or since barium sulfate is one of the salts with lower solubility. But it is necessary to take into account the cost of barium salts and the relatively low value of barium sulfate itself. The elimination treatment of the sulphates of the solutions, common problem to all the processes of recovery of the lead of exhausted accumulators, should be valued based on the market demand and the ease of placement of the obtained sulphate. The other by-product obtained from the reactions, the ferric hydroxide has a good market value. It treats of a product of high purity that finds easily placement in the field of the metallurgy of the foundry and of the iron, also in the one of the pigments, varnishes and plastic materials. The embodiment of the present invention which provides for the reduction of the tetravalent lead oxide to bivalent lead with the ferrous ions has not yet proved entirely satisfactory under the economic profile, due to the impossibility of exercising an adequate control of its development. This important limitation is basically due to the presence of process steps in which the respective reactions unfold with different kinetics and with reactants in biphasic system (solid and liquid) These stages are the stage of reduction of the bivalent lead ion with iron metallic and the reduction stage of the lead dioxide with the ferrous ions produced in the preceding stage. To overcome this drawback, the reduction of the tetravalent lead oxide can be carried out by combining the following operations: -rejoining the solids separated in steps a) and b) constituted essentially of all the lead oxide (IV), possibly in part lead oxide ( II), metallic lead in a powdery state and excess metallic iron; - mixing the solids thus reunited with solid, liquid and / or gaseous reducing agents; - Treat the mixture thus obtained, possibly under agitation, at a temperature between 400 and 1300 ° C, with the formation of molten metallic lead in the presence of a small amount of slag and without the emission of sulphurous and sulfuric gases. In this embodiment (hereinafter also referred to as hydropyro-metallurgical variant) according to the present invention, the solid, liquid and / or gaseous reducing agents can be selected from the group of carbon, coke, solid and liquid hydrocarbons, carbon oxides and hydrogen . The treatment of the mixture, for the formation of molten metallic lead in the presence of small quantities of slag and without the emission of sulfuric or sulfuric gases, can preferably be carried out at a temperature between 700 and 1100 ° C in a time between 20 minutes and 1 hour, preferably between 15 and 50 minutes. The removal of the ferrous sulfate, in order to recover the salts used in step a), can be obtained by an operation selected from the group comprising, adding alkali metal or alkaline earth metal hydroxide, carbonate or bicarbonate, or by concentration of the solution, crystallization and separation of ferrous sulfate. An important advantage of the hydropyrometallurgical variant of the present invention is that the melting of the metallic lead in the powder state is carried out simultaneously with the reduction of the lead oxides (II and IV). Thus the bivalent lead oxide formed during the treatment of that lead powder 9 which is very reactive and easily tends to oxidize to the air as ambient lead bivalent to room temperature) is reduced to metallic lead. It is necessary to consider that the lead powder produced in stage b) must in any case be molten in a cupel to undergo refining or alloying processes, so that the step in the pyrometallurgical stage presents a small expenditure of energy, compensated for the recovery of the oxidized fraction. It is preferred to carry out the pyrometallurgical treatment in the presence of a small amount of metallic iron since the pulp does not represent a mixture of pure substances but a mixture of substances in which sulfates of other metals may be present. In this case the presence of iron serves to displace the sulfate anions, releasing these metals and allowing their recovery. the hydropyro-metallurgical variant of the present invention has important advantages with respect to the traditional processes of thermal reduction of the whole pulp either from the energy or from the environmental point of view. From the energy point of view, in a typical industrial process of thermal reduction of the pulp, conducted in a discontinuous rotary kiln, the material and energy balances are, on average, the following: pulp * 1000 kg temp. 1100-1200 ° C coal 60 kg time 4-4.5 hours iron 120 kg total energy 244nm3 of CH4 Na2C03 40 kg glass 2 kg (x) average composition of the paste PbS04 52.395 Metallic Pb 3.465 Pb02 17.665 humidity 0.4% PbO 15.76% inert 8.24% others (Fe, As, Sb etc) 2.09% total recoverable lead 68. 71%. By relating the above values to a kilogram of lead theoretically recoverable from the pulp by thermal reduction, conducted under the conditions indicated above, the following values are obtained: coal 0.0873 kg / kg Pb iron 0.174 kg / kg Pb Na2C03 0. 058 kg / kg Pb glass 0. 003 kg / kg Pb energy (CH4) 0. 35 Nm3 / kg Pb The results * e < material and energy of the mixed hydro-pyrometallurgical process object of the present invention, always carried out in the same type of pulp, with the lead sulphate obtained in the hydrometallurgical section, all the oxides (II and IV) reduced in the pyrometallurgical section and all the lead produced in section b) led to fusion in the same section, are: iron 0.139 kg / kg Pb lime 0.185 kg / kg Pb carbon 0.037 kg / kg Pb energy CH4 0.10 Nm3 kg / kg Pb. . The confrontation of the two balances makes remarkable the energetic and economic saving achievable with the present invention. This saving is traceable to a whole series of positive causes that can be summarized as follows: in the hydrometallurgical stage of the method according to the present invention, the sulphate of lead is treated, an amount that reaches 505 by weight of the paste, with a minimum of expenditure energy being the reaction conducted at low temperature, for example 80 ° C; - in the thermal stage of the method, the melting of the lead produced in the hydrometallurgical section is carried out, an operation that requires a minimum of energy expenditure, this element having a low specific heat (0.038 Cal / qsc) (D and the reduction of lead oxide ( IV), which heated, without annexation dfr some reducer, at 510-640 ° C (2) spontaneously loses oxygen reducing to lead oxide (II) .This oxide is easily and quickly reducible, carbon, CO, hydrogen and of the hydrocarbons of metals at a temperature between 300 and 600 ° C depending on the type of reducer used (3-4) .This leads to further important advantages from the energy point of view either due to the low reaction temperature or Due to the low speed of the reaction itself, in the treatment of the paste, which is made up of non-pure products where many impurities are present, it is necessary to work at a higher temperature to favor the formation slag that includes these impurities. The optimum treatment temperature is between 700 and 1100 ° C, the reduction reaction affects approximately 365 of the initial mass of the paste and this leads to a further reduction of the heat necessary to bring the product to the optimum reaction temperature. - in the thermal stage, the lead sulphate is not treated, a product that, in order to convert to metallic lead, requires the presence of a high excess of iron that serves to displace the sulfate anion and longer contact times with high reaction temperatures. From the environmental point of view, the advantages of the method according to the present invention can be summarized as follows: elimination of sulfur and / or sulfuric gas emissions caused by the reaction, at high temperature of lead sulphate; -lower emissions of carbon dioxide, since the method according to the present invention requires a smaller amount of energy; - Drastic reduction of the production of slag, being the consumption of sodium carbonate or glass reduced to a tolerable quantity. The addition of the hydropyrometallurgical variant of the present invention, of the part of the action that recovers the lead from the pulp by means of pyrometallurgical processes, does not require onerous investments as regards the pyrometallurgical section existing in those installations, since it is perfectly adapted to treat the mixture of lead (II) and (IV) oxides as long as the hydrometallurgical section is made up of a dissolution vessel, a reduction reactor and a neutralization reactor, as well as three liquid-solid separation sections that they can be done by means of filters and / or centrifuges and / or gravitational settlers. Comparing the mass-energy balances of the hydrometallurgical variants according to the present invention and the embodiments of the prior art (hydro variant) always referring to the same type of paste, results; TABLE 2 var. hydro var. hydropyrometallurgical Fe 0.33 0.139 kg / kg Pb Ca (0H) 2 0.44 0.185 kg / kg Pb H2S04 10% 2.23 1 / kg Pb carbon 0.037 kg / kg Pb energy 0.06 0.10 Nm3CH4 / kg Pb From the analysis of the data it turns out that it is still convenient to work with the hydropyrometallurgical variant, since the amount of carbon reducer or other reducer is small. The higher energy consumption is largely compensated by a significant reduction in reagents, particularly iron and lime. The economic advantages obtainable with the hydropyro-metallurgical variant according to the invention are more evident by comparing the production prices of one kg of lead. These prices do not take into account the costs of labor, ortizamiento and others, but only those of raw material and energy.

"ABLA 3 Raw material Cost Piro Hidro Method of energy + Lira / kg kg / kg Pb kg / kg Pb invention Lira / m3 carbon 150 0.0 3 0.037 iron 180 0.1 0.33 0.139 Na2C03 200 0.0 Cal 100 0.44 0.185 Glass 50 CCHH44 445500 00 ..3355 0.06 0.10 Total Liras 213 130 94 The removal of the ferrous ions formed during the reduction process in stage b) can be carried out by treating the solution of solubilization with bases carbonates, bicarbonates of alkali metals and / or alkaline earth metals, preferably by the addition of sodium hydroxide, ammonium calcium, barium, and combinations thereof as well as sodium carbonate, sodium bicarbonate, thereby obtaining a precipitate of ferrous hydroxide and a sulfate precipitate of the alkali metal and / or Alternatively, the concentration of the solution and the fractional crystallization of the ferrous sulphate and the solubilizing compound of the recycle can be proceeded with in step a) of the method. In this case, a second compound, the ferrous sulphate, of high purity, can be obtained, which finds placement in the market, for example in the field of water treatment, of the additives for fertilizers. A description of the new method according to the invention of a general nature has been given up to now. With the help of the figures and the examples, a detailed description of specific embodiments of the invention will be provided, in order to better understand the scope, advantages, characteristics and operational modalities. Figure 1 represents a block diagram of a new hydrometallurgical method according to the invention; Figure 2 depicts a block diagram of a new thermal hydrometallurgical method according to the present invention; Figure 3 represents a block diagram of another embodiment of the new method according to the present invention; Figure 4 represents a block diagram of a hydropyro-metallurgical variant of the present invention, used in example 6. EXAMPLE 1 50 grams of powder * obtained by grinding the lead-based elements present in a battery, a powder commonly called a paste. put in a container and suspended in 500 ml of water. the centesimal composition of this powder is as follows: molar ponderal (1000 g) Pb sulphate 60% 1, 98 Pb oxide (II) 20% 0.896 Pb oxide (IV) 20% 0.836 100% 3.712 In a second container, 100 grams were placed of iron, in the form of plates, with a diameter of 2mm and average length of 15-20mm. In this second vessel 500 ml of water and 100 g of sodium acetate were added. The content of the two containers was brought to the temperature of 80 ° C while a two-channel peristaltic pump provided the continuous transfer of the solution from the first container to the second and vice versa. A sufficient amount of acetic acid was added to establish the pH of the solution at 5-5.5. At the entrance and exit of the container containing iron, two filters have been placed that have the function of separating at the entrance the parts of the pasta still not dissolved and at the outlet, the smallest fractions of metallic lead and the ferric hydroxide that It is formed because of the oxidation of iron. The reaction was continued by determining the progressive decomposition of the bivalent lead ions of the solution that, after 4 hours, they had been reduced sharply. Simultaneously upon contact with the metallic iron, lucid parts formed of metallic lead formed in the metallic mass and progressively regrouped and separated from the bottom of the container. At the end of the reaction, from the filters - a red precipitate consisting of ferric hydroxide was recovered, and the metallic lead was separated from the iron and both were weighed. The aqueous phase is treated with sodium hydroxide to a pH of 5.5 - 6 and simultaneously air is blown, obtaining the double effect of oxidizing the ferrous ions to ferric and of precipitating them as ferric hydroxide that was separated from the solution by filtration. Separation of the ferric hydroxide, the solution receives the addition of another sodium hydroxide and is brought to room temperature to facilitate the separation of the sodium sulphate. The liquid phase after the correction of the pH to the value of 5.4 is used for a new cycle of treatment of the pulp in the same descriptions described above, obtaining quite similar results as recovery values of the lead and consumption of metallic iron. This operation has been repeated 5 times obtaining quite similar results such as lead recovery values, iron consumption and recovery of sodium sulfate for each cycle. The mass balances of the reactions described in this and the following examples are indicated in Table 1. EXAMPLE 2 50 grams of powder with the same composition isWing for example 1, obtained by grinding the lead-based elements present in a battery, have been treated in the same installation described in example 1. The volumes of water are the same, while as a solubilizer it is They have used 100 grams of ammonium acetate. The initial pH of the solution has been lowered to 2 by the addition of acetic acid. The temperature of the test was 70 ° C and its duration was 2 hours. At the end of the reaction as a solid, only the metallic lead was recovered since the ferric ions and the ferrous ions were present in the solution. The solution, therefore, has been treated with sodium hydroxide up to Ün ph of 5.5-6 and simultaneously air has been blown, obtaining the double effect of oxidizing the ferric ions and of precipitating them as ferric hydroxide that has been separated from the solution by filtration. After the separation of the ferric hydroxide, the solution has received the addition of another sodium hydroxide and was brought to room temperature to facilitate the separation of the sodium sulfate. The liquid phase receives the addition of acetic acid to rearrange the pH value to 2 and used for the new pulp treatment cycle in the same way - already described. operations have been repeated in 5 samples of pasta. The results obtained are indicated in Table 1. EXAMPLE 3 The same operating conditions of Example 1 have been adopted. As a solubilizer, 100 g of ammonium chloride have been used with the addition of hydrochloric acid up to a pH of 0, maintained at that value by the progressive addition of acid. The reaction temperature was 80 °. Its duration 1 hour. The successive treatments were carried out similarly to those described in example 2. The results obtained are shown in Table 1.

EXAMPLE 4 50 grams of paste have been treated at 650 ° C for 15 minutes without adding any reagent obtaining the quantitative conversion of lead dioxide into lead oxide. 50 g of the dough have been removed and treated as described in example 1. The results are shown in Table 1. EXAMPLE 5 A new method identical to that of Example 4 has been adopted, with the exception that the treatment of the dough has been carried out as in example 2. The results are shown in Table 1. Table 1 also shows the results of other tests performed with substances different from those used in examples 1-5. EXAMPLES 6-11 The results of other tests, either with the substances mentioned in Examples 1-5 or with other substances according to the present invention, are indicated in Table 1. TABLE 1 RESULTS OF THE COMPOUND REDUCTION TEST LEAD OBTAINED FROM LEAD BATTERY - Exhausted Acid. All the tests carried out were made using always the same amount of paste (50 grams) with the same composition by weight: Pb sulphate 505, Pb (II) oxide 20%, Pb (IV) oxide 20%. Ex. Process type Solvent Conc. Hydro H.-piro g / i 1 Hydro Na. acetate 100 5- 2 Hydro NH4 acetate 100 5, 5 3 Hydro NH4 Cl 100 2 4 Hydro-pyro Na acetate 100 0 5 Hydro-pyro NHL acetate 100 5--5.5 6 Hydro NH4 Cl 100 2 7 Hydro NH4 N03 100 2 8 Hydro Na Glicolate 150 3 9 Hydro-pyro Na Tartrate 100 3 10 Hydro-pyro-triethanolamine 500 2 11 Hydro NH4 Sulfate 150 4 Tem. t. Pb. obt. Faith,. consumed Type of F ° CHGG 80 4 35.7 7.8 Plate 2 70 2 36.4 7.7 plate 2 80 2 35.2 9.4 Chip 80 4 36 11.2 plate 2 70 2 37.4 11.8 chip 80 4 32 10.2 chip 75 4 27 9.7 plate 2 x 70 3 36.0 8 , 1 chip 80 4 20.2 5.4 plate 2 x 80 4 27.4 6.5 chip 75 3 15.2 7.3 chip Plate 2 x = plate or iron plate 2 mm. chip = iron chip thickness 0.3 lon.5mm. EXAMPLE 12 1000 grams of a powder obtained by grinding the lead-based elements in a battery, commonly called paste, with the following centesimal composition: PbS04 52.39% Pb02 17.66% PbO 15.76% Inert 8.24% Moisture 0.4% Other (Fe.As.Sb.etc.) 2.09% Total recoverable lead 68.71% They are placed in a reactor and treated with 2000 grams of sodium acetate dissolved in 10 liters of water at the temperature of 80 °. The solution is brought to a pH of 6 by adding sulfuric acid to 105 and keeping it under stirring for 5 minutes by means of a propeller stirrer, the suspension is filtered recovering a solid 1, while the solution is transferred to a second reactor, which it has a cone-shaped bottom to facilitate the separation of the solids by the difference of the specific weight, and it is put in contact with metallic iron in the form of a lathe for a time of 30 minutes. After the reaction time, two solids are stratified in the conical bottom of the reactor; the lower one is made up of 99% lead powder and the rest of the metallic iron powder, which is solid 2, and of an upper layer consisting essentially of ferrous hydroxide. The solids 1 and 2 are joined by adding 26 grams of carbon and with a small amount of sodium carbonate, and transferred to a porcelain crucible to be treated in a muffle furnace, with heating by means of a methane burner, to the temperature of 1000 ° C for 30 minutes. At the end of the crucible, 684 grams of metallic lead were found, in addition to a small amount of slag estimated at about 0.6% of lead weight. The remaining solution in the second reactor, after separation of the solid 2, is treated with an amount of calcium hydroxide capable of completing the precipitation of iron (II) hydroxide which has been separated by filtration.

Subsequently, another calcium hydroxide is added until the sulphates are precipitated in the form of calcium sulphate which has been recovered by filtration. The filtrate that has been recovered, it is poor of sulphate and ferrous ions and has a correct pH of 6 and is recycled in the first reactor. This operation was repeated 6 times obtaining the same results as recovery of lead, recovery of ferrous hydroxide from calcium sulphate, consumption of iron and lime. The total energy consumption equivalent to a methane / kg of lead produced was 0.10 m3 EXAMPLES 13-18 These examples are illustrated in the following Table 4. All the amounts used refer to 1000 grams of pulp that has the same composition given in example l. The hydrometallurgical treatment was carried out in all the examples at a temperature of 80 ° C for a time of 30 minutes, since the only reaction of the Pb (II) ions was to proceed the system reaction. This time is enough to completely reduce the Pb (II) ions, present in iron solution in the form of a lathe, this is chip resulting from the turning. In the totally hydrometallurgical treatment, two reactions took place in the reactor, that of reduction of the Pb (II) ions by iron and the reduction of Pb (IV) by the Fe (II) ions. the completion of these two reactions will require longer times. TABLE 4 g Example Solvent solvent Temp. ° C Time min% Pb rec. 13 Acetate Na 100/1 1100 20 98.1 14 Acetate NH4 100/1 1000 40 98.9 Acetate Na 100/1 900 50 98.6 16 NH4C1 120/1 1000 30 98.8 17 Acetate Na 120/1 1100 30 99.5 18 Acetate Ba 120/1 600 50 96.0 Methane consumption m3 / kg of lead produced: Ej 13 0.12 Ej 14 0.11 Ej 15 0.11 Ej 16 0.10 Ej 17 0.11 Ej 18 0.09 It is noted that in relation to this date, the best method known by the applicant to carry out the practice said invention is that which is clear from the present description of the invention. Having described the present invention as above, the content of the following is claimed as property:

Claims (16)

1. CLAIMS 1. - Improved method to recover lead from exhausted lead-acid batteries, which includes the removal of the accumulators of the sulfuric acid solution, the involved and the separators placed between the electrodes, and the metal part between the electrodes as well as the grinding of the remaining parts of the accumulator to obtain a fine powder and is characterized by the combination of the following operations: a) treatment of the resulting powder with an aqueous saline solution; at a pH between 0 and 8, able to solubilize the sulphate and the Pb (II) oxide leaving the Pb (IV) oxide unbleached b) metallic lead reduction of the bivalent lead ions, present in the soluble fraction, with metallic iron, preferably in a slight excess with respect to the stoichiometric proportions; c) reduction of tetravalent lead oxide; and d) recovery of the salts used in the step of process a) for the elimination of the iron sulphate formed.
2. 2. - Improved method for recovery of lead lead accumulators with the acid exhausted according to claim 1, characterized in that the solubilization of the sulfate and the oxides of Pb (II) in the process step a) can be obtained with an aqueous solution of a salt selected from the group comprising acetates of ammonium, potassium, sodium, tartrates of ammonium, potassium, sodium, ammonium chloride, ammonium sulfate, nitrate .-. ammonium, sodium chloride, monoethanolamine salified with or as is, diethanolamine salified with or as is, triethanolamine salified with acids or as is, bisodium salts of ethylenediaminetetraacetic acid, ammonium glycolates, potassium or also sodium.
3. 3.-improved method for the recovery of lead lead accumulators with exhausted acid, according to claim 1 or 2, characterized in that the reduction of bivalent lead ions, present in the soluble fractions in the process step b ) can preferably be carried out at a temperature between room temperature and that of boiling, preferably between room temperature and 80 ° C, with stirring.
4. 4.- Improved method for recovering lead from lead accumulators with exhausted acid, according to any of the preceding claims, characterized in that the reduction of the bivalent lead ions present in the soluble fraction in process step b) is perform with agitation.
5. 5.- Improved method for the recovery of lead lead accumulators with exhausted acid, according to any of claims 4, characterized in that the tetravalent lead oxide in the process step c) is reduced to bivalent lead oxide that it is introduced in process step b).
6. 6.- Improved method for the recovery of lead from lead accumulators with exhausted acid, according to any of claims 1 to 4, characterized in that, the reduction of the tetravalent lead oxide present in the insoluble faction, in the process step c), can be obtained with a heat treatment at 650-700 ° C to give bivalent lead oxide which is introduced in stage a).
7. 7.- Improved method for the recovery of lead from lead accumulators with exhausted acid according to any of claims 1 to 4, characterized in that the reduction of the tetravalent oxide, present in the insoluble fraction in the stage of the process c) , is obtained with a treatment of a solution of divalent iron salts to give a solution containing bivalent lead oxide and trivalent iron ions that is introduced in process step b).
8. 8.- Improved method for recovering lead from lead accumulators with exhausted acid, according to one of the preceding claims, characterized in that the removal of the iron sulphate in process step d) is obtained with an alkalizing treatment.
9. 9.- Improved method for recovery of lead from lead accumulators with exhausted acid according to claim 8, characterized in that the alkalizing treatment is carried out by the addition of a hydroxide selected from the group comprising sodium hydroxide, calcium hydroxide, ammonium hydroxide and barium hydroxide, or combinations thereof.
10. 10. Improved method for the recovery of lead from lead accumulators with exhausted acid according to any of claims 8 or 9, characterized in that the separation of the ferric hydroxide from the other solids is obtained by effect of the different specific gravity.
11. 11.- Improved method for the recovery of lead lead accumulators with exhausted acid according to one of claims 1 to 4 characterized in that the reduction of the tretavalent lead oxide in stage c) is carried out by combining the following operations: solids separated in steps a) and b) consisting essentially of "all lead oxide (IV), possibly in part d ^? afcJLp lead (II), of metallic lead in a powdery state and of excess metallic iron; - mixing the solids thus reunited with solid, liquid and / or gaseous reducing agents; -treat the mixture thus obtained, possibly under agitation, at a temperature between 400 and 1300 ° C, and a time comprised between 20 minutes and 1 hour, with formation of molten metallic lead in the presence of a small amount of slag and without emission of sulphurous and sulfuric gases, and Recover the molten metallic lead thus obtained by recovering the salts used in stage a) obtained by elimination of ferrous sulfate.
12. 12. Improved method for recovery of lead from lead accumulators with exhausted acid, according to claim 11, characterized in that the liquid or gaseous solid reducing agents of the group comprising carbon, coke, solid and liquid hydrocarbons, carbon oxide and hydrogen.
13. 13. Improved method for the recovery of lead from lead accumulators with exhausted acid according to claim 11 or 12, characterized in that the temperature of the treatment of the mixture is between 700 and 1100 ° C.
14. 14. Improved method for the recovery of lead from lead accumulators with exhausted acid according to claim 13, characterized in that the treatment time of the mixture is 15 minutes to 50 minutes.
15. 15. Improved method for the recovery of lead from lead accumulators with exhausted acid according to claim 11 to 14, characterized in that the removal of the ferrous sulfate for the purpose of recovering the salts used in step a) is carried out by an operation selected from the group comprising the addition of alkali metal or alkaline earth metal hydroxide, carbonate or bicarbonate or concentration of the solution, crystallization and removal of the ferrous sulfate.
16. 16.- Improved method for the recovery of lead from lead accumulators with exhausted acid as described, exemplified and claimed.