ITBR20130002A1 - "PROCEDURE FOR THE PRODUCTION OF HOMOGENOUS BLENDS OF LEAD AND METALLIC LEAD MONOSSID, USED FOR THE PREPARATION OF PASTE FOR ACID LEAD BATTERY ELECTRODES, BEGIN FROM LEAD-FREE OXIDE WITH HIGH PURITY THROUGH A REDUCTION - Google Patents

Description

"PROCEDURE FOR THE PRODUCTION OF HOMOGENEOUS MIXTURES OF LEAD MONOXIDE AND METALLIC LEAD, USED FOR THE PREPARATION OF PASTES FOR LEAD ACID BATTERY ELECTRODES, STARTING FROM LEAD OXIDE WITH HIGH PURITY THROUGH A REDUCED GAS REDUCTION.

Description

The present invention relates to a process for the production of homogeneous mixtures of lead monoxide and metal lead, usable for the preparation of pastes for lead acid battery electrodes, starting from high purity lead oxide through a controlled reduction with reducing gases.

The reduction of metal oxides with gaseous reducing agents is a fairly common industrial practice. Currently, metal oxide reductions are carried out especially for compounds such as Tungsten, Molybdenum, Nickel, Germanium, etc. often the reducing agent is not represented by hydrogen but by methane, carbon monoxide or, in more sectoral studies and limited to laboratory investigations, by molecular hydrogen. For these processes there is an abundant literature supporting their practical feasibility.

There are several scientific works dating back to the early 1900s and mid-century that deal with the use of hydrogen for the reduction of lead oxide.

In particular, Brislee et al., Have reported studies relating to this topic in various publications. They highlighted the formation of Lead Suboxide when the monoxide of the same metal is treated with hydrogen. In the same work they stated that at temperatures between 211 ° C and 235 ° C in the presence of hydrogen, two simultaneous reactions take place: the first starting from lead oxide to form lead suboxide and water, the other starting from suboxide of lead to form metallic lead and water. In these situations the reaction with a higher yield, according to the authors, should be that which leads to the formation of lead suboxide (1908. F.J. Brislee, J.Chem, Soc ,, London) (1903, Gluser, Z. anorg. Chcm .).

Subsequently John et al., Demonstrated that already at 185 ° C there is an appreciable reduction of lead oxide to metallic lead in the presence of hydrogen (1 929, J, L. St. Jhon, J.Phys. Client).

Further confirmation can be found in a paper published by Gallo et al., Who report that the conversion of PbO to metallic lead occurs starting from 160 ° C but that it is necessary to reach 240 ° C to obtain appreciable kinetics (1951, G, Gallo, M. Del Guerra, Ann. Chini. Appi ,, Rome). The presence of lead suboxide previously hypothesized by Brislee et al. and subsequently postulated by Dunnoyer et al. (1951, J. M, Dunnoyer, Ann, Chim.), Was later denied by David et al., Who showed in their publication that lead suboxide is actually a mixture of Pb and PbO not necessarily in equimolar proportions (1955, R. David, Acad. Sci. Paris, Paris).

In a publication of '61 by Culver et al., The study on the kinetics of reactions involved in the reduction of lead oxide with hydrogen at temperatures between 400 ° C and 800 ° C, as the size of the pcllets varies. of PbO and the composition of the reducing gas (1961, R.V. Culver, The kinetics of the veteran fon of lead mouoxide hy hydrogen).

In addition to popular scientific publications, there are currently no patents or application examples of the aforementioned processes.

Currently in the industrial practice for the production of mixtures of lead oxide and metallic lead used for the preparation of pastes for the construction of electrodes for lead acid bacteria, two processes are used (Attrition process and Burton process) which use lead as raw material metallic.

The Applicant has found a very flexible process, alternative to the two industrially used processes, which, starting from high purity lead oxide, allows to obtain mixtures of lead and metallic lead with a variable stoichiometric Pb / O ratio, including in particular those with composition similar to that of the oxides used for the construction of lead acid battery electrodes.

This process makes it possible to achieve a uniformity of distribution of the metallic lead among the PbO powder which guarantees the uniformity of the product which will thus have better characteristics for the target market.

The process, object of the present invention, essentially comprises making the high purity lead oxide react in a reactor with hydrogen or with a mixture of hydrogen and other reducing gases, such as CO, CH4, etc. and / or inert gases , such as N2Ar, etc., at a temperature comprised between 150 and 320 ° C, preferably between 250 and 300 ° C. obtaining after cooling a homogeneous mixture of lead monoxide and lead.

By high purity lead oxide we mean a lead oxide of purity equal to or greater than 99% by weight.

The claimed process, for partial reduction of lead oxide using, as reducing agent, molecular hydrogen or mixtures of hydrogen and other reducing gases, takes place according to the reactions (1, 2 and 3);

The reaction takes place preferably at atmospheric pressure.

The reactor can be operated in batch or continuous mode.

In order to obtain a final product having a desired particle size and as uniform as possible, it is advisable that the pure lead oxide used as raw material is suitably broken down and sieved before undergoing the reduction treatment with hydrogen, preferably to a particle size between 0.01 and 100 μ, preferably between 0.1 and 10 μ.

The gaseous stream leaving the reactor, containing unreacted hydrogen and water vapor produced by the reaction in addition to any inert gases used, can preferably be recirculated to the reactor, after cooling and separation by condensation of the water vapor formed as a result of the reaction. when the stream containing hydrogen is readmitted back into the reactor, it is preferably heated up to the operating temperature.

The liquid separated by condensation can be collected in a container. The measurement of the quantity of water collected, in the case in which pure hydrogen is used as reducing gas, allows to evaluate the degree of progress of the reaction as it is directly proportional to the quantity of reduced lead oxide.

In batch mode, upon reaching the desired degree of conversion, the reactor is emptied of residual hydrogen (possibly mixed with other reducing gases and / or inert gases) and cooled by blowing in inert gas, for example nitrogen.

After cooling, a mixture of oxide and metal having a practically uniform composition is obtained. In the case of preparation of mixtures having a final composition equal to that of the oxides used in the production of batteries, this mixture can be directly used in the preparation of electrode pastes for the construction of batteries. lead acid.

More particularly, the claimed process can be preferably carried out by means of the following steps:

• grind and sift the high purity lead oxide to the desired particle size;

• feeding said lead oxide, ground and sieved to a reactor, possibly previously luxated with inert gas and heated to the reaction temperature;

• inject a stream of hydrogen or hydrogen mixed with other reducing gases and / or inert gases, previously heated to operating temperature, causing the ground and sieved lead oxide to react;

• empty the reactor, once the desired conversion degree is reached, from a gaseous stream containing unreacted hydrogen.

water vapor produced and any other reducing gases and / or inert gases used;

• cooling the reactor by blowing in inert gas, obtaining a mixture of lead monoxide and metallic lead having a practically uniform composition.

The flexibility of the process according to the invention also allows the possibility of:

• operate the reaction in packed bed or fluidized bed mode by varying the quantity of powders loaded into the reaction chamber and increasing the recirculation speed of the gaseous stream, so as to allow the PbO powders to expand under the effect of the hydrogen in order to reduce the external resistances to the transport of matter and to improve the reaction kinetics;

• produce mixtures of lead oxide and metal lead powders having the desired composition or Pb / Q ratio, suitably varying the quantity of oxide loaded into the reaction chamber, the recirculation flow rate, the operating temperature or the reaction time

Preferably, the reactor used in the process according to the invention can substantially comprise a vertical tube, inside which a reaction chamber is formed between two supports into which the pure ground and sieved lead oxide is fed, which reactor is possibly housed inside a thermostatic chamber / oven.

The high purity lead oxide can be that obtained from the pastel treatment of spent lead batteries, after desulfurization,

In particular, said lead oxide can be obtained with i! STC process for the production of pure oxides (described in the application EP-1728764 of the same applicant), which allows to obtain very high purities of the final products with submicronic particle sizes, starting from materials and / or residues containing lead in the form of sulfals and possibly oxides and / or of other compounds, such as pastel coming from spent acid batteries, essentially comprising the following stages:

• desulphurization of the material and / or residue containing lead sulphate in aqueous suspension with a suitable carbonate or hydrate in order to obtain the conversion of the lead sulphate into carbonate or hydrate; • calcination of said material and / or desulphurized residue so as to obtain impure lead monoxide which is followed by cooling and grinding;

• leaching of the impure lead monoxide by means of an aqueous solution of acetic acid followed by filtration separating a solid residue, essentially consisting of unconverted lead sulfate, from a solution of lead acetate;

• precipitation from the lead acetate solution by means of an alkaline or alkaline-earth hydroxide, which can give soluble acetates, so as to obtain, by carrying out said precipitation at boiling temperatures, a precipitate in the form of lead oxide, followed by filtration of the precipitate obtained by separating a solution thereof, at least one washing and subsequent separation of the washing liquid; • drying and possible calcination of the filtered and washed precipitate in order to obtain high purity lead oxide by operating at a drying temperature preferably between 130 and 150 <°> C.

Further characteristics of the obtaining process can be found in the same patent application cited above.

A batch mode embodiment of the present invention is now provided by FIG. 1 which should not be considered a limitation of the invention itself.

In a reactor {R). preferably consisting of a vertical stainless steel tube inside which a reaction chamber is formed between two porous supports, the PbO powders to be treated are loaded. This reactor can optionally be housed inside a thermostatic chamber (or oven). The supports, made for example of ceramic frit, should have a porosity such as to allow the passage of the reducing gas without excessive pressure losses and able to prevent any dust entrainment. The reactor can be equipped at both ends with a system of flanges and counter-flanges between which, during tightening, a sealing o-ring made of a material suitable to withstand the required operating temperatures is positioned; the inlet and outlet connections for the gaseous stream are inserted on the counter-flanges. In addition, appropriate measures can be made to the reactor, for example by providing two rotary valves, one at the top for the lead oxide inlet, one at the bottom for the discharge of the partially converted mixture.

A stream (FI) of hydrogen or hydrogen mixed with other reducing and / or inert gases, heated up to the operating temperature, is injected into the reaction chamber through a porous septum placed in the lower part of the reaction chamber, recreating a situation of packed bed, i.e. by increasing the flow rate of circulating gas, of fluidized bed. From the reactor (R) a gaseous stream (F2) comes out, containing unreacted hydrogen, the water vapor formed and any other reducing gases and / or inert gases, which is cooled in a condenser (E), for example a trap condensing, consisting of a counter-current coil exchanger in which a refrigerant solution circulates. At the outlet of the condenser (E) the cooled current (F3) flows into a container (T), which acts as an expansion vessel to favor the complete separation between the non-condensable gases (F4), to be recycled, and the condensate obtained by cooling .

The measurement of the current temperature (F4), using a temperature transducer, allows you to adjust the amount of cooling by acting on the flow of refrigerant to the exchanger.

A make-up of the reducing gas (F7), hydrogen or a mixture of hydrogen with other reducing gases and / or inert gases, consumed by the reaction, allows the desired operating pressure to be maintained within the system.

Through a three-way valve (VI), it is possible to interrupt the supply of the reducing gas (F7), to insufflate nitrogen and / or other inert gases (F8), inside the reactor during the washing and heating phases. lead oxide and cooling the mixture produced at the end of the experiment. According to the phases of the process and the type of gas used (for example if the reducing gas is pure hydrogen), a second three-way valve (V2), allows to short-circuit the supply to the reactor and the discharge after cooling and separation of the condensation or expel the gases (F6) coming out of the collection container. During the reaction the stream (F5) containing the dehumidified reducing gas is recirculated in tcsLa to the reactor (R) by means of the fan (PI). A regulation valve (V3), downstream of the fan, allows to vary the flow rate fed to the reactor and, therefore, the recirculation speed, in order to maintain a high partial pressure of the reducing gas throughout the bed of powders to be reduced. . In particular with high recirculation ratios, when the gas velocity in the bed exceeds the minimum fluidization velocity, it is possible to operate the system as an expanded bed. In this operating mode, due to the effect of fluidization, in addition to reducing the resistance to transport at the interface between the phases, with obvious benefits for the reaction kinetics, the radial and axial temperature gradients in the reactor itself are reduced

Examples are now provided according to the invention, in order to better illustrate the present invention, carried out according to the scheme of Fig. - 1.

Example 1

1000 grams of lead oxide, having a purity of 99.9% by weight, previously disintegrated and sieved, were loaded into the reaction chamber between the two porous supports in the tubular reactor. All the system volumes were washed with nitrogen, in order to remove (valve V2 in the "purge" position (E6)) all the oxygen in the air initially present and the traces of residual moisture. After washing, heating of the reactor was started.

When the temperature of 180 ° C was reached, acting on the valve V I the nitrogen supply was interrupted and hydrogen was fed into the system. After about 15 minutes the entire volume of the system was filled with hydrogen (the nitrogen was washed away). By acting on the three-way valve V2, the cold current discharge exiting the trap was short-circuited with the supply side in order to create a closed circuit. At the same time, the gas recirculation fan was started. In these conditions, the regret is full of hydrogen and the working pressure of the system equals the delivery pressure of hydrogen (-1 alni), which continuously supplies the amount of hydrogen consumed by the reaction. In fact, the water vapor produced by the reaction condensing, by cooling in the cold trap, tends to produce a decrease in the total pressure compensated by the hydrogen make-up. After an hour, the reaction was interrupted by acting on the two three-way valves. switching the supply from the hydrogen cylinder to the nitrogen one and purging the washing stream to the outside. At the same time, the thermostating system and the recycling fan were turned off. The measurement of the weight variation between the initial charge and the Pb-PbO mixture recovered from the reaction chamber at the end of the experiment allowed to determine a conversion of about 35%.

Under the same conditions as in Example 1 a mass of lead oxide of 2000 grams was heated up to 240 ° C in a nitrogen stream and, at this point, reacted with hydrogen while maintaining the temperature at 240 <°> C for one hour, obtaining a final conversion of 25%,

Claims (9)

CLAIMS 1 Process for the production of homogeneous mixtures of lead monoxide and metallic lead, starting from high purity lead oxide through a controlled reduction with reducing gases, essentially comprising reacting said lead oxide in a reactor with hydrogen or with a mixture hydrogen and other reducing gases and / or inert gases at a temperature between 150 and 320 <D> C, obtaining after cooling a homogeneous mixture of lead monoxide and lead. 2. Process according to claim 1 where the temperature is between 250 and 300 ° C. 3. Process according to claim 1 where the high purity lead oxide has a particle size between 0.01 and 100 μ, preferably between 0, 1 and 10 µ. 4. Process according to claim 1 comprising the following steps: * grind and sift the pure lead oxide to the desired particle size; * feeding said ground and sieved lead oxide to a reactor, possibly previously fluxed with inert gas and heated to the reaction temperature; * injecting into the reactor a stream of hydrogen or hydrogen mixed with other reducing and / or inert gases, previously heated up to the operating temperature, causing the ground and sieved lead oxide to react; * emptying the reactor, upon reaching the desired degree of conversion, of a gaseous stream containing unreacted hydrogen, water vapor produced and any other reducing and / or inert gases used; * cooling the reactor by blowing inert gas, so as to obtain the mixture of lead monoxide and metal lead having a substantially uniform composition. 5. Process according to claim 4 wherein the gaseous stream emptied from the reactor is recirculated to the reactor itself, after cooling and separation by condensation of the water vapor formed. 6. Process according to claim 1 wherein the reactor substantially comprises a vertical tube, inside which a reaction chamber is formed between two supports into which the ground and sieved high purity lead oxide is fed. 7. Process according to claim 6 where the reactor is housed inside a thermostatic chamber / oven. 8. Process according to one of the previous claims where high purity lead oxide is obtained from exhausted lead acid batteries. 9. Process according to claim 8, where the high purity lead oxide is obtained from materials and / or residues containing lead in the form of sulphates and possibly oxides and / or other compounds, such as pastel from exhausted acid batteries , characterized by the fact that it includes the following stages: • desulphurization of the material and / or residue containing lead sulphate in aqueous suspension with a suitable carbonate or hydrate in order to obtain the conversion of the lead sulphate into carbonate or hydrate; • calcination of said material and / or deoxidized residue so as to obtain impure lead monoxide which is followed by cooling and grinding; • leaching of the impure lead monoxide by means of an aqueous solution of acetic acid followed by filtration, separating a solid residue, essentially consisting of unconverted lead sulphate, from a solution of lead acetate; • precipitation from the lead acetate solution by means of an alkaline or alkaline-earth hydroxide, which can give soluble acetates, so as to obtain, by carrying out said precipitation at boiling temperatures, a precipitate in the form of lead oxide, followed by filtration of the precipitate obtained by separating a solution thereof, at least one washing and subsequent separation of the washing liquid; • drying and possible calcination of the precipitate, filter it and washed in order to obtain high purity lead oxide by operating at a drying temperature preferably between 130 and 1 50 <°> C.