RECOVERY OF METALLIC LEAD AND SALT VALUES FROM LEAD ORES OR FROM SPENT LEAD- ACID STORAGE BATTERIES WITH ACETIC ACID LIXIVIANT A new method which allows metallic lead and salts having commercial value to be obtained both from lead ores (primary lead) and exhausted lead-acid batteries (secondary lead) characterised by the roasting of galena based (PbS) lead ores with a poor oxygen gas mixture, at a temperature lower than 4500C to convert PbS to PbS04, by a series of mechanical operations in order to separate electrode paste of the above mentioned exhausted lead-acid batteries from the sulphuric acid solution and other exhausted batteries components (metallic lead, plastics and so on), by the treatment of roasted material or electrode paste with an acid aqueous solution containing ions of the metal having a reduction potential more negative than lead or ammonium acetate where lead (II) salts are soluble in the presence of a metal having a reduction potential more negative than lead, by the separation of metallic lead and by the treatment of the solution containing ions of the metal having a reduction potential more negative than lead with the aim to recover the salts having a commercial value and to restore the solution to be recycled in the process. When iron is used as a metal having a reduction potential more negative than lead metal, the ferrous salts present in the solution reduce the insoluble lead (IV) oxide in soluble lead (II) salts which react with metallic iron to give metallic lead. If other metal with a reduction potential more negative than leads are employed it is necessary to reduce the lead dioxide by thermal treatment or chemical reactions as for instance with hydrogen peroxide. The new method also does not produce toxic gaseous emissions. It allows the recovery of lead with a low energetic consumption and with a very low production of slags.

The present invention relates to lead recovery from exhausted acid-lead storage batteries and from lead ores.

With current technology, almost all the primary and secondary lead production is done by high temperature (more than 1000C) pyrometallurgic processes requiring more than 4 hours contact time. These processes allow a lead recovery of about 95% but they require a great energetic expenditure and produce gaseous effluents containing a large amount of sulfur dioxides and sulfur trioxides and dust containing a large amount of lead oxides and other compounds. Usually, these effluents are treated with expensive washings and abatement systems to avoid pollution and to recover lead oxides and lead contained therein.

Pyrometallurgic processes also include the use of fluxing substrates to get an easier separation of melted lead from gangue and produce slags that must be discharged as toxic materials.

The recovery of secondary led from electrode paste also use electrolytical processes, mainly in those countries where electric energy costs are competitive in comparison with thermic energy costs. These processes, due to the low current density (200-300 A/m2) needed for the lead deposit from electrolytical solutions, requires use of large volumes of acid solutions. Also, they produce muds with high arsenic and antimony concentrations, caused by the dissolution of grids fragments, contained in the electrode paste, composed by Pb-As-Sb alloys.

EPO 812923 A1 patent, extended in the USA (Application No.

08/874542), describes alternative hydrometallurgic method for secondary lead recovery from electrode paste, based on a series of redox reactions in acid aqueous solutions at a temperature lower than 1000C between bivalent lead compounds, kept in solution using suitable saline solutions, and metallic iron. In this patent a solution pH between 0 and 8 with an acetic acid concentration less than 10% is claimed. During the reaction ferrous ions are generated which reduce lead oxide (IV) to lead (II), which is then reduced by metallic iron.

In the same patent, several salts (ammonium and sodium acetates, ammonium or sodium tartrates and citrates and other substances) are claimed whose aqueous solutions allow to bring in solutions of lead compounds (II) which are present in the electrode paste (lead monoxide and sulfate). The same patent indicates as co-products ferric oxide or hydroxide and calcium or sodium sulfates and, in a particular variant, ferrous sulfate (II) obtained by concentration of the aqueous solution. EPO 812923 A1 patent, as described above, is characterised by the presence of many reactors, accessories and equipment, like filters and pumps. It also presents some drawbacks, especially because it uses solubilising solutions which should be recovered and recycled into the process due to their cost.

At the end of the lead recovery process, using for example a sodium acetate based solubilising solution, the following ions are present in solution. Fe2+, Na+, as cations, CH3COO-and S042-as anions. One step iron and sulfate ions quantitative elimination from this solution is only possible using a total iron coprecipitation as hydroxide and sulfate ions as calcium sulfate.

The obtained precipitate has no value and should be disposed of.

Selective separation,. described in the patent, implies a number of operations which largely complicate process management and does not give the certainty of a total separation between iron compounds and sulfates. In any case, whenever it should be possible to realise all is described in the EPO 812923 A1 patent, process co-products have no relevant commercial value, especially the calcium sulfate, not to mention the fact that every one Kg of treated electrode paste generates more co-products than lead.

EPO 812923 A1 patent, does not indicate any method for lead recovery from ores (primary lead) but one method for secondary lead recovery from exhausted batteries.

In this patent also, there is no mention of the presence in the electrode paste of a grey coloured substance with metallic appearance which has the same electrode paste centesimal composition. This substance is the 10-30% in weight of the total electrode paste weight. It has, in comparison with the electrode paste in powdery form, a very low reactivity under the conditions described in the patent, due to the particular aggregation existing between lead compounds even after a strong milling action. This substance, at the end of the lead recovery process, remains partially unreacted and mixed with metallic lead. It is well known that the presence of this substance should be avoided during the metallic lead fusion phase because it causes reaction which lead to a large reduction of lead fusion results, forming many lead oxide and lead oxi- sulfates.

In the patent US 5523066A, an oxidation method is claimed to convert elemental sulphur the sulphide ion present in lead ores (galena) carried out in acqueous solution containing oxidizing substances or gaseous oxygen in the presence of metal ions having different valencies. In the patent W087/02068, a galena solubilizing method in very strong acids in presence of air and of metal ions having different valencies is claimed.

The present invention is constituted by a process for the recovery of metallic lead from lead ores and from exhausted lead-acid storage batteries, characterised by the following operations: 1) treatment pf the above mentioned substances, with or without preliminary preparation with an acid aqueous solution whose lead (II) salts are soluble and with a metal less mobile than lead; or with a concentrated solution of acetic acid and ammonium acetate where lead (II) salts are soluble and with a metal having a reduction potential more negative than lead; the lead compounds present in the solution can be substituted by the above mentioned metal with a reduction potential more negative than lead.

When iron is used metal with a reduction potential more negative than lead, the ferrous salts present in the solution reduce the insoluble lead dioxide in soluble lead (II salts which react with metallic iron to give metallic lead. If other metal with a reduction potential more negative than lead are employed it is necessary to reduce the lead dioxide by thermal treatment or chemical reactions as for instance with hydrogen peroxide; 2) recovery of metallic lead, separated from the above mentioned compounds, produced by its above mentioned substitution caused by the above mentioned metal with a reduction potential more negative than lead; 3) treatment adding other compounds of the obtained acid aqueous solution containing ions of the above mentioned metal having a reduction potential more negative than lead to obtain the insolubilisation of the desired compounds of the above mentioned metal with a reduction potential more negative than lead or treatment of the concentrated solution of acetic acid and ammonium acetate containing ions of the above mentioned metal having a reduction potential more negative than lead by cooling in order to obtain the insolubilisation of the desired compounds of the above mentioned metal with a reduction potential more negative than lead.

The new patent, even though based on redox reactions between lead compounds (II) and (IV) with metals having a reduction potential more negative than lead already described in EPO 812923 A1 patent, greatly simplify these processes because it uses a medium, in which lead (II) salts are soluble and redox reactions take place, an acid aqueous solution (containing the salts of the metal with a reduction potential more negative than lead) in a first way or in a second way a very concentrated solution of acetic acid containing ammonium acetate. Because the same solvents are not employed in the new patent, when the lead recovery is carried out by the first way, it is possible to recover salts of the metal with a reduction potential more negative than lead by adding other compounds, to acid aqueous solution, to obtain the insolubilisation of the desired compounds of the above mentioned metal with a reduction potential more negative than lead, or by simple treatment of the concentrated solution of acetic acid and ammonium acetate containing ions of the above mentioned metal having a reduction potential more negative than lead by cooling in order to obtain the insolubilisation of the desired compounds of the above mentioned metal with a reduction potential more negative than lead, when the lead recovery is carried out by the second way.

This effect is possible because the metal with a reduction potential more negative than lead salts are soluble at reaction temperature and very less soluble at room temperature.

This leads to a relevant process simplification by reducing the number of steps required and reducing the amount of equipment used. Also it permits the total recovery both of the acid medium in which the reactions take place, and of the salts produced by the reducing metal used for the lead compounds reduction.

In this new patent an operative method is also described which allows the grey substance present in electrode paste to effectively decompose and to recover from it all the lead associated with the compounds which constitute it.

The new process also allows metallic lead to be obtained from ores, such as galena, operating at a temperature lower than 4500C and in comparison with the traditional pyrometallurgical process there is obtained great energy and pollution savings.

Other relevant lead ores like cerussite and anglesite can be treated in this process without any preliminary preparation.

The new patent reactions are as follows: Note: in the reactions, iron has been indicated as the reducing metal but the reactions are still valid with other metals having a reduction potential more negative than lead, such as aluminium, zinc etc. w 1). PbO + 2HA PbA2 + H20 2). PbA2 +Fe metallic Pb metallic + FeA2 3). Fe + 2HA--+ FeA2+ H2 4). PbS04 + FeA2oPbA2+FeS04 5). PbA2 + Fe metallic Pb metallic + FeA2 6) PbS04+4 ANH4~ [Pb (NH4) 4] A4 S04 7) [Pb (NH4) 4] A4 S04+Fe metallic ~ Pb metallic + PbS04 + 4 ANH4 8) 6). PbC03+2HAe PbA2+ C02 + H20 9) 7). PbA2+Fe metallic metallic + FeA2 (where HS is an acid whose lead salts are soluble in water in the first way and acetic acid in the second way).

In the case of recovering lead from galena based minerals, it is necessary to preliminary roast minerals at a temperature lower than 450oC. This is enough to oxidize lead sulfide to lead sulfate but without having those sulfur dioxide emissions which are typical in completely pyrometallurgic process which recover lead from galena operating at higher temperatures.

The reaction which takes place is the following: 10). PbS + 202- PbS04 From the resulting lead sulphate, lead recovery takes place according to 3,4,5 or 6,7 reactions. In order to accelerate the process it is recommended to carry out reaction 3 in a separated reactor.

In case mixtures to be treated contain not only sulfate, lead monoxide and carbonate, but also lead dioxide, Pb02, such as those typically coming from acid-lead exhausted batteries, it is possible to operate in different ways: A first method provides the heating of the mixture at a temperature higher than 4000C without adding any magnet in order to decompose the lead dioxide to lead oxide (II) and oxygen. This is a well known reaction and is also described in EPO 812923 Al patent extended in the USA (Application No.

08/874542).

11) Pb02- PbO + 1/2 02 Lead recovery from the lead (II) oxide formed by the thermic dioxide decomposition takes place according to the 1) and 2) reactions.

A second method provides the mixture treatment with hydrogen peroxide in order to obtain the following reaction: 12). Pb02 H202 ~ PbA2 +2 H20 + 02 The resulting solution is treated with the metal with a reduction potential more negative than lead according with the 2) reaction to carry out the quantitative lead.

The last methods (11,12) are only carried out when iron is not used as the reducing metal because the iron (II) salts react with lead (IV) oxide by the following reaction and reduce it to lead (II) compound so that the previous thermic or chemical treatment is useless.

13).Fe+2HA~FeA2 14). PbO2+4AH+2FeA2oPbA2 + 2Fe A3+2H201 15). 2FeA3+Fe-3FeA2 16). PbA2+Fe metallic, Pb metallic +FeA2 Examples Example 1 1000 grams of powder, commonly called electrode paste, obtained from exhausted acid-lead storage batteries dismantlement having the following centesimal composition PbS04 52,39% PbS02 17,66% PbO 15,76% inerts 8,24% Umidity 0,4% others (Fe, As, Sb, etc;) 2,09% Pb metallic* 3,46% *coming from batteries grids and poles Total recoverable lead 690 grams are placed in a suitable reactor containing 5000 ml of an acetic acid aqueous solution with a concentration of 10% in weight.

In this reactor, the solid mass is subjected to an energic agitation and milling action to disgregate all the solid grey substance particles present in the electrode paste. If all the operations described in the examples are carried out with only a mechanical agitation, at the end of the recovery treatment, there remains a percentage between 50 and 70% of the grey coloured mass, which is not reached while, using simultaneously a double action (agitation and milling), the entire grey mass is disgregated and it reacts. The suspension is heated at a temperature of 60oC and maintained at this temperature for 30 mins under agitation and milling, avoiding contact with air by keeping a slight nitrogen pressure inside the reactor. Subsequently, 500 grams of metallic iron shavings is added, an amount that exceeds what is needed, regarding the process stechiometry quantity and the mass is kept under agitation and milling for 45 mins at900C.

At the end of the process from the reaction mass, the aqueous phase is separated from the solid one by filtering and 243 grams of non reacted iron can be separated and can be recycled for the lead recovery process; this means that the iron used is 257 grams.

The remaining solid is washed with water and elemental analysis is performed on it giving a result that is composed of 99,97- 99,99% of metallic lead and the rest of extraneous metals formerly contained in the iron shavings used, such as nichel and manganese. The obtained lead is compressed in small cylinders with an apparent density of 9.900-10.000 g/dm3 with a metallic appearance. These cylinders are placed in a refractory material crucible and heated until 5500C obtaining 684 grams of melted lead with a recovery efficiency higher than 99%. The recovered solution is acidified using 1500 grams of sulphuric acid at 30% and is heated, recovering all the acetic acid formerly used in the test by distillation. From the distiller, 1290 grams of a crystalline solid constituted by crystallised iron sulfate is also recovered. This product is widely used in many activities, from waste water treatment to agriculture, so its emission in the market does not represent a problem.

Example 2 1000 grams of powder having the same composition of the powder reported in example 1 is treated in a muffle furnace at a temperature of 5500C for 30 mins to reduce quantitatively lead dioxide (IV) to lead monoxide (II). After cooling, the resulting mass is treated as described in Example 1 and, at the end of the reaction 682 grams of lead is recovered, the iron consumption is 200 grams and the ferrous sulfate recovery is 1000 grams.

Example 3 1000 grams of powder having the same composition of the powder reported in example 1 is treated in a muffle furnace at a temperature of 6500C for 15 mins. After cooling the resulting mass is treated as described in Example 1, adding, instead of metallic iron, 350 grams of metallic zinc, an amount that exceeds the theoretic amount needed for lead reduction; at the end of the reaction 685 grams of metallic lead is recovered, zinc consumption is 215 grams and the zinc sulfate recovery is 532 grams.

Example 4 1000 grams of powder, commonly called electrode paste, obtained from exhausted acid-lead storage batteries dismantlement having the same centesimal composition of example 1, is placed in a suitable reactor containing 5000 ml of an acetic acid aqueous solution with a concentration of 10% in weight. In this reactor, the solid mass is subjected to an energic agitation and milling action to disgregate all the solid grey substance particles present in the electrode paste. All this is heated, under agitation, at a temperature of 650C for 30 mins avoiding contact with air and keeping a slight nitrogen pressure in the reactor. Subsequently, during the 30 mins and always keeping agitation and milling, 80ml of hydrogen peroxide at 33% in weight is added, noting a solid mass decolorisation. Then 500 grams metallic iron shavings is added, an amount that exceeds what is needed regarding the process stechiometry and the mass is kept under agitation and milling for 45 mins at 45 mins at 950C. At the end of the process the aqueous phase is separated from the reaction mass by filtering and 280 grams of non-reacted iron is separated from the solid phase, that can be recycled for the lead recovery process; this means that iron use is 220 grams.

Then the process is the same as described in example 1 recovering all the acetic acid and the hydrate ferrous sulphate.

Example 5 1000 grams of powder, commonly called electrode paste, obtained from exhausted acid-lead storage batteries dismantlement having the same centesimal composition of example 1 is treated as described in example 4, with hydrogen peroxide and then with 220 grams of metallic zinc for 30 mins time, at a temperature of 800C, obtaining 683 grams metallic lead.

Example 6 1000 grams of powder, commonly called electrode paste, obtained from exhausted acid-lead storage batteries dismantlement having the same centesimal composition of example 1 is treated as described in example 4, with hydrogen peroxide and then with 70 grams of aluminium shavings for 30 mins, at a temperature of 800C, obtaining 683.8 grams metallic lead.

Example 7 1000 grams of a material containing 90% of galena is heated at a temperature of 4500C in a furnace under a poor oxygen air stream and agitation for 1 hour. During heating S02 content in the gasses coming out of the furnace is controlled, verifying its absence or, at least, its presence in traces. After cooling, the material is treated as described in example 1, recovering 770 grams of metallic lead.

Example 8 Tests reported in examples 1 to 6 are performed also replacing the acetic solution, with an acid solution for hydrochloric acid at 5% obtaining practically the same results.

Example 9 Tests as reported in examples 1) to 6) but operating the lead recovery reaction in the hydrometallurgic phase at 800C and for 60 minutes time. Similar results at for examples 1 to 6.

Example 10 1000 grams of powder having the same composition of the powder in example 1, is placed in a suitable reactor containing 5,000 ml of an acetic acid solution with a concentration of 60% in weight, 1,5000 g of ammonium acetate and 1,000 g of metallic iron shavings. In this reactor, the solid mass is subjected to an energic agitation and milling action to disgregate all the solid grey substance particles present in the electrode paste. The suspension is heated at 1000C for one hour. At the end of the process the liquid phase is separated from the reaction mass by filtering and non-reacted iron is separated from the solid phase and can be recycled fro the lead recovery process.

The remaining solid is washed with water and the elemental analysis is performed on it giving a result that is composed of 99,97-00,99% metallic lead and the rest is extraneous metals formerly contained in the iron shavings used, such as nichel and manganese. The obtained lead is compressed in small cylinders with an apparent density of 9.900-10.000 g/dm3 with a metallic appearance. These cylinders are placed in a refractory material crucible and heated until 5500C obtaining 681 grams of melted lead.

The recovered solution is treated with 220 g of sulphuric acid at 96 and cooled at 200C. A great amount of a white solid separates: it is iron sulphate which represents about 98% of the total iron (II) ions present in the solution. This solid is separated by filtering and the limpid solution containing an amount of lead in the quantity of p. p. m., is recycled to the process.

Example 11 1000 grams of powder having the same composition of the powder reported in example 1) is treated in a muffle furnace at a temperature of 550C for 30 minutes to quantitatively reduce lead dioxide (IV) to lead monoxide (II). After cooling, the resulting mass is treated as described in Example 10 but using metallic zinc as metal with a reduction potential more negative than lead for 30 minutes. At the end of the reaction 684 grams of lead and 532 grams of zinc sulfate is recovered.

Example 12 1000 grams of powder having the same composition of the powder reported in example 1) is placed in a suitable reactor containing 5.000 ml of an acetic acid solution with a concentration of 65% in weight, 1.500 g of ammonium acetate and treated with 80 ml of hydrogen peroxide at 33% in weight, noting a solid mass decolourisation. At the suspension 70 grams of aluminium shavings is added for 40 mins at a temperature of 900C obtaining 683.8 grams metallic lead and 376 grams of aluminium sulphate.

Example 13 1000 grams of a material containing 90% of galena is heated at a temperature of 4500C in a furnace under air stream and agitation for 1 hour. During heating the S02 content in gasses coming out of the furnace is a controlled verifying its absence or at least, its presence in traces. After cooling, the material is treated as described in example 1, recovering 770 grams of metallic lead and 570 g of iron sulphate.