RO114351B1 - Process for recycling lead from active waste and lead batteries - Google Patents

Abstract

The invention relates to a process combined, hydropirometalurgic, of recycling of lead from the active masses sulphate and oxidized, resulting in the storage of new, unformed, and dismantling of lead-acid batteries, treatment. The process comprises a precursor, of hydrometallurgical desulphurization by treatment in a chemical reactor with aqueous solution concentrated, Na OH, in closed circuit at ambient temperature, in which, besides PbO, there is also obtained Na 2 SO 4 x 10 H 2 O or / and Ba SO 4, recoverable, a reduction step of Pb (OH) 2 resulting in PbO, by dehydration and heating final at 150 ° C, and a carbotermic reduction step of PbO in a rotary kiln at 800 ° C. The obtained lead is treated in a pot of refining at 550 ° C to remove impurities.

Description

The invention relates to a process for recycling the lead and separating the recoverable impurities from the sulphate and oxide active masses of the used lead acid battery plates, as well as from the residues from the operation of passing the plates during manufacture.

Hydrometallurgical processes for the recycling of lead from oxidized and sulphated active mass wastes are known, such as that of patent RO 97787/1989, which consists in carbonating PbS0 ₄ from these active masses with (NH ₄ ) ₂ CO ₃ dissolving PbC0 ₃ resulting with acid. fluoboric, electrolytic separation of lead, transformation of Pb0 ₂ into PbS0 ₄ with H ₂ S0 ₄ and oxygenated water, followed by processing PbCO ₃ . This hydrometallurgical process has the disadvantage of some economical costs, for a high efficiency recovery of the lead (90 ... 95%), having to be continued with a pyrometallurgical process of separating the lead by melting.

The pyrometallurgical processes for the recycling of lead from waste are more convenient for industrial application, but to be environmentally friendly, the temperature of the liquid lead in the short rotary kiln of carbotermic reduction must not exceed 800 ° C, and that of the refining pot 500 ° C, the voltages of vapors at these temperatures of the liquid lead being 5.4 x 10 ² mmHg, respectively 1.6 x 10 ' ⁵ mm Hg. (O. Kubaschewski et al., Metallurgica! Thermochemistry, Pergamon Publishing, Press, Oxford, 1967).

Thus, the pyrometallurgical recycling of lead from the sulphate and oxidized active mass wastes with the average composition in table 1, in a short rotary kiln, through the concomitant reactions:

PbS0 ₄ + Na ₂ C0 ₃ = Pb0 + Na ₂ S0 ₄ + C02 (1) PbS0 ₄ + 2Na0H = Pb0 + Na ₂ S0 ₄ + H ₂ 0 (2)

PbO + C = Pb + CO (3) has the following disadvantages:

- the need to raise the batch temperature to over 1000 ° C, in order to evacuate the slag in the liquid phase, containing Na ₂ SO ₄ , which has T _topjre = 852 ° C and PbO with T _topjre = 886 ^o C, although the carbothermal reduction does not require a temperature higher than 800 ° C;

- the relatively high amount of reactive flux of Na ₂ CO ₃ , (reaction (1)) or NaOH, (reaction (2)), favors the capacity, productivity and energy consumption of the furnace;

- at insufficient dosing of the reactive flux, according to reactions (1) and (2), there is a danger of releases of SO ₂ and SO ₃ in the atmosphere, the dissociation temperature of PbSO ₄ being about 1000 ° C;

- the product of the desulfation reaction consisting of 50 molar percent PbO and Na ₂ SO ₄ , after removal of CO _S (reaction (1)) or H ₂ 0, (reaction (2)), has a liquid temperature greater than 800 ° C;

- metallic cinnamon or coke, used as a reducing agent, according to reaction (3), impurifies sodium sulphate obtained in relations (1) and (2), with cinnamon ash, (1%) or metallurgical coke (8%), to which are added the hard-fusible metal compounds of the batch.

There are procedures, such as the ELTA industrial process, [Z. Vaysgant et al., A Low Temperature Technique for Recycling Lead / Acid Battery Scarp Without Wastes and with Improved Enviromental Control, Journ. of Power Sources; 53, (1995)], which for the elimination of these disadvantages uses the separate recycling of the anodic and cathodic plates used by a pyrometallurgical process that includes a preparatory phase of hydrometallurgical desulfation at ambient temperature, after the reaction:

PbS0 ₄ + 2Na0H = NaS0 ₄ + Pb (OH) _s , (4)

After this process, the precipitate Pb (0H) ₂ is removed from the filter and charged in metal pallets, for drying, in electric ovens with reverberation, where the reaction takes place:

Pb (OH) _a -> PbO + H ₂ 0 _vapors . (5)

For carbothermal reduction

RO 114351 Bl a PbO, ELTA utilizes a flow composed of a mixture of KCl and Na ₂ CO ₃ , 1: 1, dosed at 1 ... 2% by mass of the batch; the temperature being 7O5 ± 55 ° C. The refining process adopted is electrolysis.

The advantages of using caustic soda (reaction (2)), instead of Na ₂ CO ₃ , (reaction (1)), are its high water solubility (6 times higher than Na ₂ CO ₃ ), and in preventing the formation of by-products, (PbC0 ₃ , PbCO ₃ x, Pb (0H) ₂ ], with decomposition temperatures above 400 ° C and 315 ° C, respectively. Also, hydrometallurgical processing of lead waste, allows to perform the operations of disintegration in the wet state of the used battery plates, so, after the breakage of the tanks, in order to remove them and the separators between the plates, the separation of the active masses in mills with hammers and the seating, can be done in the wet state, a way by which the risk of air pollution with harmful aerosols of Pb is eliminated (PbS0 ₄ , Pb0 ₂ , etc.).

Prior hydrometallurgical desulfation allows the introduction into the recycling process of paste waste with high humidity (about 20 ... 25%), which can also be impurities and residual sulfuric acid.

In addition to the disadvantage of using a relatively expensive flow, the ELTA process, at a reactive flow composition close to the eutect of the KCI system - Na ₂ C0 ₃ , with 53.2% Na ₂ CO ₃ and T _tap = 587 ° C, requires a prior melting. of the components K CI ( _melting T = 775 ° C) and Na ₂ C0 _3: ( _melting T = 856 ° C).

The problem that arises in the case of the recovery of lead and other chemical substances, from the oxidized and sulphated active masses of the used lead-acid battery plates, is to find a process of ecological and economic recycling, in terms of material and energy consumption, which allows to achieve a yield of about 95%, simultaneously with an adequate purity of the recovered substances.

The invention solves this problem by a combined metallurgical hydro-pyro4 process, comprising a precursor phase of hydrometallurgical desulfation at ambient temperature with Na OH, a reduction of Pb (0H) ₂ resulting, to PbO, by dehydration of Pb (OH) ₂ at 145 ° ... 150 ° C, in the drying cabinet and the carbothermal reduction of PbO to Pb melted with a reactive flow composed of a mixture of NaOH and Na ₂ C0 ₃ salts, with an initial architectural composition with 63% Na ₂ CO ₃ and melting T = 480 ° C, which is used in several batches. As its viscosity increases, as a result of the ash dissolution resulting from the coal or metallurgical coke used, as well as other solid particles of harder fusible compounds, the NaOH content of the reactive stream gradually increases, until its composition becomes eutectic, with 25.6% Na ₂ CO ₃ and _melting T = 288 ° C. By loading in the short rotary kiln the components of the perceptual components of the Na OH - Na ₂ C0 ₃ salt mixture in a dosage of 1% of the mass of the batch, this flow requires a prior melting.

The liquid lead, reduced from PbO in the short rotary furnace, with the chromo-magnesite refractory lining, is transferred into a heated refractory cast iron pot, at 5OO ... 6OO ° C for refining, in a duplex system. The refining consists in the selective elimination, by thermal means, of the impurities that exceed the allowed limits, with the help of specific reagents.

The invention is further illustrated in connection with FIG. 1 ... 4, which represents:

FIG. 1, the hydrometallurgical recovery technological flow;

FIG. 2, vertical section through the refining pot;

FIG. 3, vertical section through a device for disassembly, disassembly and disassembly, Harris;

FIG. 4, vertical section through an immersion alloying device.

The electrode plates of modern, maintenance-free batteries consist of hard grids of Pb alloys, which support the mass deposited in the form of paste, in a mass ratio of 1: 1. The negative plate grids are made of Pb - Ca alloys with

RO 114351 Bl approx. 1% As, and the positive ones, from Pb - Sb alloys with about 1.7% Sb modified with □, □ 2% Se.

The incompatibility of melting together the grating waste of Pb-Ca and 5 Pb-Sb-Alloy grids requires the prior separation of the used plates according to polarity.

The used cathode plates are grayish-gray, with non-corroded grating; the anodic ones are dark brown (as a result of Pb0 ₂ content), with strongly corroded grating. The average mass content of Pb and compounds of these plates is presented in table 1. Table 7

Active table PbO,% Pb0 ₂ ,% PbS0 ₄ % Pb% additives Unformed plate 67.8 - 12 20 0.2 Used cathode 8.2 - 41.1 50.5 0.2 Worn anode 0.6 48.4 50.8 - 0.2

The additives, (0.2%) are mainly 20 organic substances.

The permissible limits of impurities in lead intended for the production of active masses (pastes) are 0.001% by weight for the elements Ag, As, Cu, Fe, Sb, Sn and 25 Zn and 0.01% for Bi and Ca.

According to the process, in a first precursor phase, a hydrometallurgical desulfation of PbS0 ₄ is achieved, by using caustic soda, according to reaction (4), with the use of Na ₂ SO ₄ , produced according to the technological flow of Fig. 1, after Previously, the active mass wastes were mechanically disaggregated, ground and wet, thus avoiding the risk of air pollution. According to the diagram in Fig. 1, the excess caustic soda lye from the filtered solution is removed with residual sulfuric acid (from spent batteries), at 40 pH = 6.0 ... 6.5, and by evaporation of water from the solution The resultant Na ₂ SO ₄ is obtained as a recoverable by-product, Na ₂ SO ₄ • 10 H ₂ 0; (crystallized decahydrate). Also, by treating the remaining Na ₂ 45 SO ₄ solution, with aqueous Ba (0H] ₂ solution, BaSO ₄ precipitates in NaOH solution with pHr <3. After 24 hours, the residue of BaSO ₄ e matures. separated by filtration from solution 50 diluted with Na OH and then dried at 105 ° C, after which it can be used industrially.

The diluted NaOH solution is reintroduced into the technological stream as a reagent in the pre-preliminary, hydrometallurgical desulfation phase.

The wet decanted mass of Pb (0H) ₂ is dried in the drying cabinet at 105 ° C, in hot air stream; In the final drying phase, the cabinet room temperature is raised to 150 ° C for dehydration of the mass and reduction to PbO; (reaction (5)).

In a second phase, pyrometallurgical, lead oxide (PbO) or lead dioxide (PbO ₂ ) which decomposes successively by reactions: 3 Pb0 ₂ -Pb ₃ 0 ₄ + 0 ₂ at 344 ° C and Pb ₃ 0 ₄ -3PbO + 1/2 0 ₂ at 500 ° C, at atmospheric pressure, existing in the composition of the active mass wastes to which PbO produced by the hydrometallurgical desulfation of the initial mass is added, is reduced carbotermically to the molten lead, according to the reaction (3), in the rotary kiln of carbothermal reduction, at a temperature of about 800 ° C. The rotary kiln has a diameter of the interior space approximately equal to the length, so that by rotating the furnace about a horizontal axis, the temperature is kept constant throughout the mass of the batch.

The flux flux of fusion is composed of a mixture NaOH - Na ₂ C0 ₃ with variable composition between that of peritecRO 114351 Bl eutectic with 25.6% Na ₂ CO ₃ and _melting T = 288 ° C, flux which does not require prior melting of the components.

In the carbothermal reduction furnace, the whole quantity of NaOH is first introduced at the operating temperature (8OO ° C), and then the corresponding amount of calcined soda is added to the architectural composition. Slag collected from a batch can serve as a flow for a new batch. To this end, in proportion to the dissolution of the ash resulting in the reduction of carbothermal and hard-to-fuse impurities, in the reactive flow, small amounts of NaOH - Na ₂ C0 ₃ flux are added until the percentage eutectic composition is obtained. In this way, the acceptable viscosity of the flow can be maintained in several batches. If this viscosity becomes too high, the reactive flow is regenerated by dissolving in hot water, decanting, filtering and evaporating the solution.

The insoluble, dusty waste is processed for the purpose of capitalizing on the useful elements, not resulting in unusable slags.

The use of a carbotermic reduction furnace of 10 t Pb capacity, requires a filter of dust retention from the hot gases, with a flow rate of exhaust of 10.0Q0m ³ / h.

In a third phase, the batch of crude liquid Pb is transferred from the carbothermal reduction furnace into a refining pot with the configuration according to FIG. 2, suitable for the use of Harris-type or immersion-refining devices; (Figure 3).

The pyrometallurgical refining of the batch of crude liquid Pb is done in order to reduce the concentration of impurities under the tolerance limits, by classical methods. In this phase, the reactive flux with the eutectic composition of the NaOHNa ₂ C0 _{3 system} has the role of protection and refinement and is dosed between 0.25 and 0.5% by mass of the batch.

The removal of As, Sb and Sn from the crude liquid lead bath at temperatures of 450., .420 ° C is done according to the Harris process, which is based on the oxidation of these elements, dissolved in liquid Pb, with sodium nitrate, by thermal decomposition. of it at 38D ° C, after reaction

2NaN0 ₃ -Na ₂ 0 + 2 (/ V0 ₂ ] + ^ 0 ₂ ; (6)

The process involves the use of a recirculation device, by pumping molten Pb, in the form of thin vines through a peritetic mixture of molten salts, of the NaOH-NaCl system, with 29.8% NaCl and _melting T = 385 ° C; (Figure 3).

The oxidation chemical reactions, which occur simultaneously, are:

2 [As] _Pb + 2NaN0 ₃ + 4NaOH = 2Na ₃ As0 ₄ + 2H ₂ 0 + N ₂ ; (7) 2 [Sb] _Pb + 2NaN0 ₃ + 4NaOH = 2Na ₃ SbO ₄ + 2H ₂ 0 + N ₂ ; (8) 5 [Sn] _Pb + 4NaN0 ₃ + 6NaOH = 5Na ₂ SnO ₃ + 3H ₂ 0 + 2N _a ; A)

Zinc removal from the lead bath is performed at 400., 350 ° C and is based on the reaction stoichiometry:

3 [Zn] _Pb + C2Cl ₆ = 3ZnCl ₂ + 2C; (10) wherein hexachlorethane having the sublimation temperature of 187 ° C is considered in the gaseous phase. Zinc chloride, with _melting T = 262 ° C and _boiling 732 ° C, being in the liquid phase, dissolves in the reactive stream, the carbon being accumulated in it in the form of graphite particles The introduction into the lead bath of 100 g hexachlorethane compressed pills, coated in Pb thin sheet, is made by means of the immersion stirring device (fig. 4).

In this way, the level of Zn content in the Pb bath can be lowered below the limit of 10 ' ³ %.

The removal of copper from the crude Pb bath is done at 34O ... 33O ° C, by the reaction of fine decomposition with sulfur added to the metal bath:

[2Cu] _Pb + S = Pb + Cu ₂ S; (11) depending on the degree of sulfur saturation of the Pb bath, it can be reached

RO 114351 Bl a

decrease in Cu content corresponding to several ppm.

bismuth removal from lead bath crude compound is made by precipitation of Mg ₂ ternary Bi ₂ at 340 ... 330 ° C, using a pre-alloy Mg Ca (30% Ca) having _topjre T = 620 ° C, which is dissolved in the bath of Pb by means of the immersion alloying device of fig. 4. The characteristic reaction to precipitation is:

2 [Bi] _Pb + [MgCa] _Pb + Pb = Mg ₂ CaBi ₂ + Mg ₂ Pb; (12) below, an example of the application of the process according to the invention is presented.

For the recycling of lead and the valorisation of the chemical substances resulting from the waste of active mass, not formed, with the composition of table 1, having, for example, the humidity: u = 20%, the paste is loaded in a vertical chemical reactor, provided with an axial agitator, with the capacity of 125 kg dry paste. This amount of dry paste contains 15 kg PbS0 ₄ , 85 kg PbO and 25 kg Pb. From the stoichiometry of the reaction (4), an amount of 3,957 kg NaOH is required, in order to obtain 11,930 kg Pb (0H) ₂ and 7,027 kg NaS0 ₄ (anhydrous). At the humidity of the paste: u = 20%, the water content of the paste is 31.25 kg, the weight of the wet paste being 156.250 kg. The NaOH concentration of the aqueous reagent solution is chosen so that, together with the 31.25 kg water in the paste, about 25 v% (volume percent) solid phase is introduced into the reactor, the remainder being liquid phase.

The volumetric proportion of water insoluble particles results from the ratio between the mass of the insoluble particles and their density. Thus, for: 15 kg / (6.2 kg / dm ³ ) = 2,419 dm ³ ; PbSO ₄ ; 85 kg / (8kg / dm ³ ) = 10.625 dm ³ PbO and 25 kg / 11.34 = 2.205 dm ³ Pb, it turns out that in total 15, 249 dm ³ by volume is occupied by the solid phase, insoluble in water. Using an aqueous NaOH solution of 216.24 g / l (grams / liter) and density of 1.2 kg / dm ³ , 10 salts are needed: 3957 g / (216.24 g / l) = 18.3 I solution. By diluting this solution with 31,250 kg water from the moisture of the paste, the concentration of the aqueous solution decreases to 89.243 g / l NaOH, corresponding to the density of 1.09 g / cm ³ .

The initial volume ratio between the solid phase of 15.249 dm ³ and the liquid phase, of 18.300 + 31.250 = 49.550 dm ³ , is 23.5 v% solid phase and 76.5 v%, liquid phase.

By converting PbSO ₄ , insoluble in water, into soluble Na ₂ SO ₄ , the volume proportion of the liquid phase increases.

From 125 kg wastes in the form of dry paste, with 12% PbS0 ₄ , the following products can be obtained stoichiometrically, by means of the hydrometallurgical process presented in Fig. 1: 11,930 kg Pb (0H) ₂ , of which results from the reaction (5), 11,040 kg PbO, and as salable by-products, 15,930 kg Na _of SO ₄ with 10H ₂ 0 (by crystallization from the concentrated aqueous solution by boiling) or 11,540 kg BaS0 ₄ , precipitated and dried at 105 ° C, by treatment with Ba (0H ] ₂ .

The 125 kg desulphate paste, which results after drying and final heating at 150 ° C, contains: 85+ 11,040 = 96,040 kg PbO and 25 kg Pb, (total = 121,040 kg), in the form of cubic sizes of sizable quantities obtained on metal pallets.

Working with a single reactor of the capacity given in the previous example, a number of 83 hydrometallurgically desulfated batches is required for loading a short rotary furnace of 10 t minimum economic capacity.

The batch of 10 ta of the total carbothermal reduction furnace contains 6800 kg PbO of the paste composition and 883.2 kg PbO converted hydrometallurgically from PbS0 ₄ and another 2000 kg Pb. The carbon requirement for reduction, (relation (3)], is 413.1 kg for reducing the amount of 7683.2 kg PbO to 7132.4 kg Pb, which with the 2000 kg Pb initially existing in the paste reaches 9132.4 kg Pb.

As a carbothermal reducing agent, it is possible to use: coal, which contains 79% C and 1% ash and has humidity

RO 114351 Bl 5%, or metallurgical coke with 87.3% C, 8% ash and 2% humidity.

The flow, which is the architect of the NaOH - Na ₂ C0 _{3 system} , is used in a proportion of 1% of the mass of the batch when working with the coal and 2% when working with metallurgical coke.

In the short rotary oven, with the capacity of 10 t and a temperature of 8OO ° C, the order is introduced: half the quantity of flow composed of 37 kg caustic soda in the form of blocks or scales and 63 kg calcined soda. The required quantity of coke of (413.1 / 0.873) (1 + 0.1) = 520 kg is then loaded. The batch of PbO-containing dry fillers is loaded, over which 37 kg of caustic soda and 37 kg of calcined soda are loaded. Similarly, the coal is used.

The batch of crude liquid Pb is transferred by pumping into the refining pot, (fig. 2), pre-heated to 500 ° C, where 0.25% of the mass of the batch (25 kg) is introduced, a flow consisting of 18.6 kg Na OH and 6.4 kg Na ₂ CO ₃ , which can be used successively in several batches.

In order to eliminate below the permissible limit of one of the elemental impurities dissolved in lead, ([As] _Pb , [Sb] _Pb or [Sn] _Pb - reactions (7), (8) and (9)), it is partially introduced into the pot a Harris refining device for crude lead, (fig. 3), at a liquid lead temperature of 45O ... 42O ° C. The Harris device, cylindrical and vertical, is provided with a funnel 1, a stirrer with blades 2 and a recirculation pump of Pb 3 through a liquid eutectic salt mixture, composed of 29.8% NaCl, the rest Na OH, ^with ^ melting = 358 ° C. By continuous feeding with Na NO ₃ through funnel 1, it decomposes thermally into the liquid stream, (reaction (6)) and the three impurities oxidize, turning into arsenate, antimony or sodium tin, substances that remain in the stream, where it is recovered after its saturation.

The removal of zinc is done at a bath temperature of Pb of 400 ... 35 ° C by introducing hexachlorethane pills, coated in Pb thin sheet, by means of an immersion alloying device (fig. 4). The device, which is partially inserted in the bath of Pb, is provided with a funnel 1 for continuous feeding with pills or by preloading with a stirrer with propeller 2 ', which pushes the liquid lead downwards and with four intake windows 4, arranged on the circumference working cylinder.

The tablets are compressed by pressing in portions of 100 g. The need for pills results from the reaction stoichiometry (10).

The copper is removed from the bath at 34o ... 33o Pb ° C by fine blanking, in the form of bark ₂ S, which is formed on the bathroom mirror, having _topjre T = 1130 ° C. For alloying with S, the stoichiometry of the reaction (11) is taken into account. The sulfur is introduced by means of the immersion alloying device (fig.4), the copper sulphide bark being collected from the bath mirror with perforated spoons.

Bismuth is removed from the Pb bath also at 34O ... 33O ° C, by precipitation with magnesium pre-alloy with 30% calcium (Mg Ca 30), by reaction (12). The pre-coating is introduced in the form of granules, using the immersion alloying device (fig. 4). In molten lead, insoluble compounds precipitate, which rises on the bath mirror, such as: Bi ₃ Ca, Bi ₂ Ca ₃ , Bi ₂ Mg ₃ with T _top , _e = 507, 928 and 715 ° C, respectively.

The barks, collected separately, are processed for the extraction of useful substances.

The refined lead, thus obtained, has a purity according to the tolerances allowed for impurities in the lead intended for the production of active masses (pastes), for the batteries of accumulators.

Claims (5)

claims 1. Process for recycling lead from active masses of waste and lead batteries, comprising a pre-hydrometallurgical desulfurization phase at ambient temperature, a carbothermal reduction phase at 800 ° C and a RO 114351 Bl pyrometallurgical refinery phase in a "duplex" system at 5OO ° C, characterized in that, in the carbothermal reduction phase, a mass of PbO is derived partly from the composition of the initial waste mass and the rest, from desulphatation PbS0 ₄ from the mass - waste with NaOH and dehydration Pb (0H] ₂ resulting in the preheated carbothermal reduction furnace, with a protective reactive flow from the system: Na OH - Na ₂ C0 ₃ . 2. Process according to claim 1, characterized in that, for the accomplishment of an ecological mechanical processing, of dismantling, grinding and sifting of the lead active masses, a humidity of about 25% of it is allowed, at the beginning of the first processing phase. Process according to Claim 1, characterized in that the reactive flow of NaOH - Na ₂ CO ₃ is added to the lead bath in a proportion of up to 2% of it in the carbothermal reduction phase and in a proportion up to 0.5 %, in the refining phase, with the initial composition corresponding to the architectural point having 63% Na ₂ C0 ₃ and T _topjre = 480 ° C, first adding the amount of NaOH and then the corresponding amount of Na ₂ CO ₃ , at the characteristic operating temperature, without prior melting. 4. Process according to claims 1 and 3, characterized in that, at a greater number of charges, proportional to the increase of the viscosity of the reactive flow of protection and refining by including the ash of the reducing agent and the impurities, the relative NaOH content is gradually increased up to to the eutectic composition of the system NaOH - Na ₂ C0 ₃ with 25% Na ₂ C0 ₃ and T _{top, re} of 288 ° C, and after the reaction becomes unusable for the process flow, it is dissolved in hot water to recover chemical components. 5. Process according to claims 1, 3 and 4, characterized in that the removal of zinc impurities from the lead bath in the refining phase is accomplished by introducing in it a stoichiometric quantity required by hexachlorethane pills, by means of an alloying device. by immersion, with agitator.