WO2024180258A1 - Method for upgrading the black mass of alkaline and salt batteries, coke produced according to this method and method for using the coke - Google Patents

Abstract

The invention relates to a method for upgrading the black mass of spent alkaline and salt batteries mainly comprising manganese and zinc, and also potassium hydroxide and carbon, which is characterized in that it comprises the following steps: - incorporating the black mass in coking coal or in a mixture of coking coals, the amount of black mass incorporated being less than 10% by weight of the mixture, - pyrolytic coking of the mixture obtained in the previous step, and - obtaining a composite coke comprising manganese. The invention also relates to a composite coke comprising manganese obtained by such a method. . Lastly, the invention relates to the use of this composite coke in a metal melting furnace such as a blast furnace or a cupola furnace.

Description

Process for recovering the black mass of alkaline and saline batteries, coke produced by this process and process for using the coke

The invention relates to a process for recovering the black mass of used alkaline and saline batteries, a composite coke produced by this process and a process for using this composite coke in a metal manufacturing furnace.

The most widespread process for the recovery of used alkaline and saline batteries consists, after sorting them from other portable accumulators, in carrying out a crushing operation to obtain:

• a steel metal fraction from the battery casing after magnetic separation,

• a fraction containing plastics and paper after sorting by a densimetric process,

• and finally a black powder called black mass BM, the latter containing 33% manganese in oxidized form MnO2, 27% zinc partly in oxidized form ZnO, 5% carbon, and a maximum of 6% potassium in KOH form.

The quantities of alkaline and saline batteries placed on the European market each year are of the order of 170,000 tonnes and the objective defined at European level requires recycling at least 45% of this volume since 2016. Thus, 70,000 to 80,000 tonnes of used batteries are therefore processed and recovered each year in Europe.

European regulations require that at least 50% of the solid materials contained in batteries be recovered. This percentage is called Recycling Efficiency, RE. High RE processes are therefore sought as a priority in order to recycle the maximum amount of materials contained in batteries.

The grinding process, although very widespread, because it is also used for other types of used accumulators, unfortunately only has an RE at the limit of the regulatory value, i.e. 50% to 55%, because only steel, carbon and zinc are validly recovered. The manganese and zinc contained in the black mass are treated in Waelz furnaces, but only zinc is recovered in the form of zinc oxide at a purity level of 60% to 65%. As for manganese and residual elements such as nickel and copper, they are found in the form of oxide in the slag from the Waelz furnace and are therefore lost. Manganese present in large quantities, and whose market value is between €1,000/t (2020) and €1,800/t (January 2022) is therefore lost and not recovered, which is not relevant and desirable from an environmental point of view.

There are also hydrometallurgical processes that can be used to recover manganese, but their implementation is expensive and the product obtained is more difficult to use because it is obtained in a powder form. These processes have therefore not been developed on a large scale. The invention aims to propose a technology to overcome the drawbacks of the state of the art.

For this purpose, the process for recovering black mass, mainly comprising manganese and zinc, as well as potash and carbon, is essentially characterized in that it comprises the following steps:

- incorporation of black mass into coking coal or into a mixture of coking coals, the quantity of black mass incorporated being less than 10% by weight of the mixture,

- coking by pyrolysis of the mixture obtained in the previous step, and

- obtaining a composite coke comprising manganese.

Advantageously, from waste from the crushing of used alkaline and saline batteries, the manufacture, for example in a coking plant, of composite coke from a mixture of coking coals and black mass makes it possible, on the one hand, after coking, to obtain a composite coke composed of carbon and a certain percentage of manganese integrated into the composite coke, and on the other hand to separate and recover the zinc contained in the black mass. This composite coke can then be used in cupola and blast furnace type metal melting furnaces for its specific function as a coke (supply of heat, carbon), but also to supply and recover manganese in the cast iron produced. The chemical reaction of reduction of manganese oxide by carbon in the cupola furnace or blast furnace will be facilitated by the fact that the manganese oxide will be transported by the composite coke into the high temperature zone of the furnace (1500 °C to 1800 °C) where the chemical reaction of reduction to manganese metal can take place, which will be dissolved in the cast iron. In addition, since the few percentages of manganese oxide are intimately trapped in the coke, manganese losses will be reduced.

The process according to the invention makes it possible to recover zinc at a purity level of between 80% and 100% (depending on the method of separation from other gases) instead of 65% in the prior art, as well as manganese. It therefore contributes to the preservation of manganese, a metal classified as strategic in Europe and contributes to a reduced exploitation of manganese ore mines.

The process of the invention may also include the following optional features considered in isolation or in all possible technical combinations: the coking step is carried out in a coke oven. This makes it possible to avoid any modification of existing coke oven processes and devices. the amount of black mass added to the coking coal mixture is between 1% and 10% by weight.

This low black mass content in the coking coal mixture means that the properties of the composite coke obtained after pyrolysis are not modified, particularly in terms of mechanical resistance. the percentage by weight of manganese in the composite coke is between 0.5 and 5%, preferably between 1 and 4%. the percentage by weight of black mass in the mixture formed with the coking coal or the mixture of coking coals is evaluated according to the percentage by weight of manganese in the composite coke. the percentage by weight of black mass in the mixture formed with the coking coal or the mixture of coking coals is evaluated, according to the percentage by weight of manganese targeted in the composite coke, from the chart presented in figure 4. the zinc contained in the black mass incorporated in the coking coal is vaporized in the form of metallic zinc during the pyrolysis operation, entrained in the volatile coke oven gas vapors leaving the coke oven, separated from the other volatile materials and recovered after cooling in solid metallic form or in the form of solid zinc oxide of purity between 80 and 100%. During pyrolysis, the sulfur present in the coking coal or the mixture of coking coals is partly eliminated by the zinc in the black mass. At least part of the acid gases of the SO2 type released during pyrolysis is neutralized by the potash in the black mass.

The invention also relates to a composite coke obtained by the process as previously described.

Advantageously, the composite coke comprises between 0.5 and 5%, preferably between 1 and 4% of manganese.

Preferably, the composite coke does not contain zinc.

The invention finally relates to a method of using the composite coke as previously defined in a metal melting furnace, at least part of the coke introduced into the furnace being said composite coke.

Preferably, the metal melting furnace is a blast furnace, cupola furnace or manganese arc furnace for making cast iron.

Advantageously, to produce cast iron having a predetermined weight percentage of manganese, the weight percentage of manganese in the composite coke introduced into the furnace is adjusted. The invention will be better understood and other objects, characteristics, details and advantages thereof will appear more clearly in the explanatory description which follows, made with reference to the appended drawings given solely by way of example:

Figure 1 is a first schematic view illustrating the process for recovering black mass from used alkaline and saline batteries according to the invention;

Figure 2 is a schematic view illustrating a mode of recovery of zinc during the manufacture of composite coke according to the process of the invention;

Figure 3 is a second complete schematic view illustrating the process for recovering black mass from used alkaline and saline batteries according to the invention;

Figure 4 is a diagram illustrating the relationship between the weight percentage of manganese in the composite coke obtained according to the process of the invention as a function of the mass percentage of black mass in the coking coal mixture before pyrolysis;

Figure 5 is a diagram illustrating the percentage of manganese Mn in the composite coke obtained according to the process of the invention as a function of the percentage of coke to be introduced into a cupola furnace according to different percentages of manganese Mn in the cast iron to be produced by the cupola furnace, and

Figure 6 is a diagram illustrating the percentage of manganese Mn in the composite coke obtained according to the process of the invention as a function of the percentage of coke to be introduced into a blast furnace according to different percentages of manganese Mn in the cast iron to be produced by the blast furnace.

The process according to the invention makes it possible to overcome the drawbacks of the state of the art and to recover the manganese contained in the black mass, economically, thanks to the creation of a composite coke-manganese oxide product, containing a few percent of manganese, typically and in a non-limiting manner between 1% and 4%, while using for its manufacture already existing equipment for the manufacture of conventional coke.

Coke has long been used for the production of cast iron, in particular in blast furnaces and cupola furnaces. The invention provides for the use of the composite coke according to the invention as a replacement for the usual coke in blast furnaces and cupola furnaces, which makes it possible to valorize the manganese contained in the black mass as well as the copper and nickel residues directly in the cast iron produced. Since it is possible, as will be described later, to produce a coke with a desired manganese content, by appropriate dosing of the amount of the black mass in the coking coals before pyrolysis, the invention makes it possible to produce a cast iron whose manganese content is predeterminable. Coke is generally used at a rate of 12% to 15% of the weight of the metal charges in cupola furnaces and at a rate of 40% to 50% in the case of blast furnaces.

The recovery of manganese by this process thus makes it possible to greatly improve the RE which goes from 50/55% to 75/80%, which is an environmental advantage with a significant reduction in the carbon footprint thanks to the recovery of used batteries according to the invention in Europe and worldwide. Thanks to this recycling process, there is a saving of natural resources, a reduction in mining extraction and a reduction in the production costs of ferromanganese.

To better understand the process according to the invention, we will first explain how a coking plant works, and how the usual coke produced is then used in the metallurgical industries, namely in particular in cupola furnaces and blast furnaces.

Two main categories of coke are manufactured:

• small-sized metallurgical coke, approximately 20mm to 60mm, mainly intended for blast furnaces producing cast iron.

• Foundry coke of size 60mm to 250mm intended for cast iron foundries equipped with hot blast or cold blast cupolas.

The coking process mainly consists of carrying out a pyrolysis operation on a mixture of coking coals.

More precisely, it involves mixing different coking coals carefully selected for their physicochemical characteristics (swelling power, volatile matter, etc.) and weighed according to the recipe used, before being finely ground. Grinding with a maximum particle size of 2 mm is recommended in order to optimize the loading with a higher apparent density. In general, several coking coals are mixed according to different well-known recipes, with a majority of so-called coking coals with a low volatile matter content and 10% to 15% maximum of less expensive low-coking coals to optimize the cost of the load. In this mixture, 0.1% to 0.2% of fuel oil is generally introduced in order to form a paste which will either be loaded by gravity into the pyrolysis furnaces or pounded and compacted in order to produce a loaf which will be pushed into the furnaces.

The heating of the pyrolysis operation will be done away from the air thanks to the energy input by combustion of the combustible gases released during the pyrolysis of the coke. The heating time is 15 to 35 hours depending on the type of coke produced, this time being used to adapt the physico-chemical and mechanical properties of the coke to those sought. In general, metallurgical coke is heated for about fifteen hours, and for 30 hours for larger foundry coke. The chamber of the furnaces where the coking coal paste is introduced is parallelepipedal. with refractory brick walls, measuring 12 to 18m in length, with a height of 4m to 8m, and a width of 0.4 to 0.8m. Heating is carried out by the 2 vertical sides on the height and length of the cell. At both ends of the chamber, doors allow loading and unloading of the oven. In order to save energy and investments and increase the capacity of the coking plant, the ovens are placed side by side and constitute a battery that can include several dozen ovens.

The temperature of the furnaces is maintained between 1000°C and 1200°C, which allows, after loading the loads, pyrolysis to be carried out and the majority of the volatile substances contained in the coking coal to be vaporized. At the end of the operation, a very hard and mechanically resistant product is obtained in the form of pieces of up to 250mm. The operations on the product initially loaded into the furnace are carried out chronologically as follows:

• From 100°C to 150°C, water vaporization.

• From 350°C to 400°C softening of the coal and creation of a plastic phase.

• Obtaining a minimum viscosity around 450°C to 480°C.

• Re-solidification into “semi coke” from 470°C to 510°C with formation of porosities, the quantity of volatile materials released being at its maximum.

• Carbonization of semi-coke above 500°C and release of residual volatile materials.

The coke is then discharged incandescent at around 1000°C into a coke wagon which is then positioned under a water spray tower for rapid cooling, which allows fragmentation into pieces of up to 250mm. This spraying also removes some of the sulfur contained in the coke, which is then screened to obtain the desired particle sizes. Its typical composition is shown on the left side of Table 1 below, while the composition of the coke ash is shown on the right side.

Table 1

Coking coals contain volatile matter at a rate of 15% to 35%. These volatile matter will gradually be vaporized into gas at different temperatures during pyrolysis. The hot gases from the pyrolysis of coking coals exit at around 800°C above the ovens and undergo sudden cooling to around 85°C using recycled ammonia water. All gas, water and tars are sent to a collector called a barrel. Non-condensable gases such as hydrogen H2, methane CH4, nitrogen N2 and carbon monoxide CO will be partly recovered to provide heat to the coke ovens and the rest for recovery. The tars and benzols will undergo various washing and separation processes for their material recovery. Typically at the oven outlet, these gases contain 55% to 60% H2, 25% CH4, a little CO and N2 and various hydrocarbons.

In terms of the material balance, coke production is carried out with a yield of around 1,400, i.e. for 1,400 tonnes of coking coal entering, 1,000 tonnes of coke are obtained, the difference representing the gases, tars and volatiles emitted during the pyrolysis operation.

In terms of energy, 2,500 to 3,000 MJ/t of dry coal are required for the production of coke.

The coke produced will be used in blast furnaces to, on the one hand, provide the energy needed to melt the charges through its combustion with a supply of air and oxygen, and on the other hand, to reduce the ore or iron oxides. The presence of carbon in the coke will also make it possible to obtain cast iron with 3% or 4% carbon content, by dissolving the carbon in the cast iron. A coke rate of approximately 40% to 50% of the charges is used. These blast furnace cast irons can then be converted into steel or used directly in the steel industry and foundries. Their basic composition generally includes carbon between 3% and 4%, silicon between 2% and 3% and other alloying elements depending on demand, for example manganese at a rate of 0.5% to 1.0%, which is contained in the charges introduced into the furnace.

In the case of cupola furnaces, the charges of iron ore or oxide are replaced by charges of recovered steel, or cast iron already produced by the blast furnaces, or old cast iron, so that the coke is mainly used to provide fusion heat and carburize the steels, to give a cast iron enriched with 3% to 4% carbon. Since the iron oxide reduction operation is not necessary in this case, a rate of only 12% to 15% coke is generally used in relation to the metal charges.

Most cupola furnaces produce lamellar cast iron with the following composition: carbon around 3.5%, silicon around 2.0% to 2.5%, manganese between 0.50% and 1.0%, plus some alloying or residual elements depending on the final applications of the product such as chromium, copper, nickel, molybdenum, etc.

Thus, coke provides four main functions as follows:

Carbon (content of about 90%) to, during combustion in a blast furnace or cupola with air or oxygen, provide the heat necessary to melt the metal charges. Carbon to act as a reducer and transform iron ore into cast iron. This function is necessary for blast furnaces and less so for cupola furnaces because in the latter the steel and cast iron are directly charged and reduction coke is not necessary. This is the reason why a cupola furnace consumes only 10% to 15% of coke compared to a blast furnace which requires 40% to 50% of coke.

Carbon, a small part of which is recovered as material in cast iron, which generally contains 3% to 4% in the end. This carbon from coke carbides steel or iron ore which contains little or no carbon to provide cast iron with a carbon content of 3% to 4%.

Its particle size and mechanical resistance called MICUM are essential and necessary for its use in blast furnaces and cupolas. The coke in pieces is loaded at the bottom of the cupola or blast furnace. This pile is called a "laminate". The metal or ore charges are stacked several meters or tens of meters above this lab which must support tens or hundreds of tons without crushing. Because air and oxygen are blown into this lab to maintain combustion, and there must be gaps between the pieces of coke to allow the combustion gases (CO2 and CO and N2) and the liquid iron which flows to the bottom to pass. If the coke were crushed into powder, combustion could not take place and this equipment could not operate.

After this description of the process for manufacturing conventional coke and its application to the production of cast iron, the following description is given of the manufacture of composite coke according to the process for recovering black mass from used alkaline and saline batteries of the invention, namely manganese coke, for example in a standard coke oven.

As written above, black mass is a waste resulting from the grinding of alkaline and saline batteries whose manganese was not mainly recovered in current technology. This black mass comes in the form of a black powder, and its typical analysis is presented in Table 2 given below.

Table 2 It should be noted that direct incorporation of black mass into blast furnace and cupola charges has the disadvantage that the black mass is in powder form, so that direct loading into these furnaces would lead to entrainment by hot gases leaving the furnace and to very poor yields.

The process which is the subject of the invention therefore consists in recovering the manganese from the black mass of alkaline and saline batteries by producing a composite product, namely manganese coke, which can be loaded and used in cupola furnaces or blast furnaces, in particular to produce cast iron loaded with a given manganese content. The coke serves as a sort of vector for transporting the manganese.

For this, and in the first stage of the process of the invention, the black mass of used alkaline and saline batteries with an average manganese content of 33% is conveyed to a coking plant and, from a storage hopper and a weighing system, is incorporated according to a given percentage with the charges of the different coking coals, the whole being then crushed so as to constitute a homogeneous mixture.

Figure 1 illustrates as an example at 1, 2, 3 and 4 respectively three storage hoppers for three different coking coals CK1, CK2 and CK3 and a storage hopper for black mass. The contents of each hopper are weighed at 5 and, if necessary, dosed. Then the mixing and grinding are carried out at 6 to obtain the desired homogeneous mixture.

This crushed and homogenized product is then sent to the coke oven 7.

The quantities added in black mass can be variable between 1% and 10%, preferably between 2% and 10% by weight of the mixture, and a specific dosage can be carried out if necessary for the production of a composite coke with a desired manganese content. The quantity of black mass less than 10% in the mixture intended to undergo the pyrolysis operation is chosen so that the process of manufacturing the coke is not or only little affected by the incorporation of the black mass.

The mixture of coking coals and black mass then follows the classic coke manufacturing process, i.e. the pyrolysis coking operation, preferably in a classic coke oven.

After compaction and loading into batteries of air-tight furnaces in which the mixture of black mass and coking coals is maintained for between 15h and 35h (depending on the application of the coke in blast furnaces or cupolas) up to temperatures between 1000°C and 1200°C.

It has been found that the black mass incorporated homogeneously in the coking coal or in the mixture of coking coals will undergo several transformations: • First, just as with coking coal used alone, any residual water will be evaporated.

• The manganese dioxide MnO2 present in the black mass at approximately 50% will, during its temperature rise in the coke oven, decompose into intermediate compounds such as Mn2O3 at around 535°C then Mn3O4 at around 930°C to arrive at a stable form MnO above 1080°C. This partial reduction of MnO2 to MnO will be accompanied by a release of CO according to the reaction MnO2 + C >> MnO + CO.

• The KOH potash present at approximately 9% in the black mass will pass into liquid form at around 500°C at a temperature close to that of the softening of coking coals. This presence of potash remains limited in quantity, typically of the order of 0.5% of the mixture intended to produce this composite coke. Its presence could have beneficial effects on the neutralization of acid gases such as SO2, and possibly on the plasticity of the coking coal at around 500°C, according to the study by Christien A. Strydom in 2015 {Influence of various additions of potassium compounds on the plasticity of a South African coking coal with high swelling under pyrolysis conditions published in the "Journal of Analytical and Applied Pyrolysis". A disadvantage of this potash could be faster wear of the furnace refractories, but the low percentage of potash in the mixture, as well as tests conducted in cupola furnaces on equivalent percentages have not demonstrated any particular wear.

• Advantageously, the zinc present in the form of zinc oxide ZnO (with a little residual Zn metal) at a rate of 34% (ZnO form) reacts with the carbon of the black mass and/or coke above 910°C to be reduced to gaseous zinc metal which, mixed with the other pyrolysis gases, is recovered after cooling and separation of the other volatile gases originating from the pyrolysis of the coking coals. A separation is carried out between the vaporized zinc and the volatile organic substances. The zinc can be recovered in metallic form after sudden cooling of the gases or possibly be re-oxidized in air if necessary, but after separation from the other gases and recovered in the form of a very pure oxide (>80%) of high market value, which will be used for the electrolysis of zinc metal. Another technique, Figure 2, consists of reacting the zinc vapors at the outlet of the furnace with only part of the cooling water so as to reduce it to hydrogen, which allows the precipitation of zinc oxide, ZnO being solid at these temperatures.

[Zn] + [H2O] >>> <ZnO> + [H2]

As seen in this figure 2, hot gases with a temperature of the order of 800° leave the coke oven 7. They contain vaporized zinc as well as H2, CH4 and various other substances. These gases pass into a reactor 8 where the zinc vapors are made to react with water introduced at 9 in a stoichiometric quantity, which makes it possible to obtain zinc oxide ZnO in solid form at 10, then available for recovery. The gases leaving the reactor at 11 will be subjected to the usual treatment of cooling by water at around 85°C, then there is separation of the different materials. Note that the oxidation of zinc produces additional hydrogen in the gases. • The zinc oxide thus separated from the gases can be recovered and these gases continue their usual journey and treatment.

• These combustible gases are used to heat the ovens, and the other fractions, benzol, tars, etc. are recovered and recycled in the traditional way.

• The carbon contained in the black mass, approximately 5%, should theoretically provide a material supplement to the carbon in the coke, but the chemical reactions of reduction of Mn02 to MnO and that of ZnO to Zn gas will consume all of this carbon supply from the black mass plus a small additional carbon from the coking coals.

• Some of the sulphur present in coking coal is eliminated thanks to the presence of zinc, which gives a better quality of coke, as sulphur is not sought.

• Similarly, part of the acid gases such as SO2 released during the pyrolysis of coking coals are neutralized thanks to the presence of potash provided by the black mass.

• Coking coal pyrolysis gases, typically composed of hydrogen H2, methane CH4 and carbon monoxide CO to name only the gases present in larger quantities (see § 2.1), will be enriched with additional CO from the reduction reactions of MnO2 to MnO and ZnO to Zn gas. For a pyrolysis mixture typically comprising 5% of black mass from batteries with a mileage of 1400, the additional quantity of CO in the gases should be of the order of 4.7%.

Finally, there remains a product that has become hard and resistant: coke with, enclosed in its structure, manganese oxide MnO at a rate of 1 to 4% by mass, and a little residual potash KOH. This composite coke rich in manganese is then removed from the furnace, then treated in the same way as a classic coke. It is then sent to foundries and steelworks requiring coke and a share of manganese for their cast iron production.

The recovered zinc or very pure zinc oxide (at least 80%) is valorized and allows to increase the added value of the coking plant as well as its margins. The price of pure zinc is currently around €3,000/t. Thus, composite coke brings additional added value to the coking plant, at marginal cost, which allows it to improve its profit margins.

From waste from the crushing of used alkaline and saline batteries, the production in a coking plant, for example, of composite coke from a mixture of coking coals and a few percentages of this black mass makes it possible on the one hand to separate and recover the zinc contained in the black mass, and on the other hand, after coking for 15 to 35 hours, to obtain a composite coke composed of carbon and a certain percentage of manganese. This composite coke can then be used in cupola furnaces and blast furnaces for its own function as a coke (supply of heat and carbon), but also to supply and recover manganese in the cast iron produced. The applications of the composite coke according to the invention are numerous, including in particular the use in blast furnaces, in hot blast and cold blast cupolas, or in arc furnaces for the production of manganese cast iron.

Cast irons produced from cupola furnaces are mainly lamellar gray cast irons requiring a manganese content of around 0.5% to 1.0%.

The metal fillers which can be recovered steels from the automobile industry generally provide part of the necessary manganese but there are losses on ignition, so that in general additions of 0.2% to 0.5% of manganese from ferromanganese or briquettes loaded with manganese are necessary. The composite coke according to the invention will then fulfill two functions, the usual one, necessary for the production of cast iron, and that of a particular contribution of manganese, replacing the ferro manganese usually used. Advantageously, the few percentages of manganese oxide present in the composite coke being intimately trapped in the coke, the manganese losses will be reduced.

Composite coke containing little or no zinc has a very clear advantage in the case of cold blast cupolas that do not have a combustion chamber. The latter have significant manganese requirements but can hardly use batteries or black mass containing zinc, because the absence of a combustion chamber will not contribute to oxidizing the gaseous zinc into solid zinc oxide and there is a risk of fire at the filter that collects the fusion dust, since powdered zinc metal is pyrophoric. Composite coke from which the zinc has been completely or almost completely eliminated in the coking plant will be able to be used safely in this type of cupola to provide this additional manganese in addition to the coke.

The same applies to blast furnaces which wish to produce cast iron containing manganese of the order of 0.5% to 1.0% and which do not tolerate zinc in their charges.

Another advantage that can be provided by the potash present in this composite coke is the neutralization of acid gases and the possibility of reducing the level of dioxins and furans in atmospheric discharges.

The use of a composite coke according to the invention is therefore interesting for these applications, and the tonnages produced in coke are sufficiently large to allow the recovery of all the black mass generated in the world with this process, the global production of coke being 700 million tons for approximately 1 million tons of black mass from alkaline and saline batteries in the event that they would all be recovered by the grinding sector. Typically only 30 million tons of coke out of 700 million would allow the recovery of all the black mass generated on a global scale. Figure 3 schematically summarizes and as an example the recovery according to the process of the invention of the black mass, as described above. Box 14 symbolizes the sorting of used alkaline and saline AS batteries and to be recovered, other accumulators, after having been crushed in 13. In 15 the sorted batteries are subjected to the separation of iron, plastic and black mass. The black mass is transported in 16 to the coking plant, while the iron and plastic are transported in 17 to a recovering user.

In the coking plant, in 20, the black mass is mixed with the coking coals to obtain a homogeneous mixture which will be subjected to coking to produce the composite coke according to the invention. Box 21 indicates the sale of zinc or zinc oxide for electrolysis and obtaining zinc metal.

Regarding the composite coke, it will be transported in 22 to metal manufacturing furnaces, coke users, in particular cupolas and blast furnaces. Box 23 symbolizes the operation of using the composite coke for the manufacture of a cast iron, where appropriate specific, by appropriate dosage of the black mass and the composite coke in the manner which will be described below as examples. It should be noted that the invention ensures a recycling efficiency RE of 75% to 80% for the battery crushing sector.

Referring to Figures 4 to 6, certain essential and advantageous features of the invention will be described below.

The diagram in Figure 4 illustrates the dosage of the amount of black mass to be added to the coking coals in accordance with Figure 1, before pyrolysis of the mixture in a coke oven, to obtain a composite coke according to the invention, which has a desired and therefore predeterminable manganese content.

Line L of the diagram represents the relationships between the percentage by weight of manganese in the composite coke obtained, indicated on the ordinate, and the percentage by weight of black mass to be mixed with the coking coals, indicated on the abscissa. This relationship is not exactly proportional. Also, it is not possible to put this relationship into an equation and only the comparison with this abacus makes it possible to evaluate the percentage by weight of black mass to be added to the mixture formed with the coking coals according to the percentage by weight of manganese targeted in the composite coke after pyrolysis.

The diagram in Figure 4, carried out on the basis of a 1400 thousand setting in the coking plant, allows, for a desired percentage by weight of manganese in the composite coke, to determine the percentage by weight of black mass of alkaline and saline batteries to be introduced in a mixture with the coking coals before pyrolysis in the coking plant. Thus, if a foundry or steel plant wants a composite coke loaded with 2% by weight of manganese, the coke plant will have to charge 4.3% by weight of black mass from alkaline and saline batteries in its coking coal charges.

To demonstrate how the straight line expressing the percentage by weight of manganese in the composite coke is established as a function of the percentage by weight of the black mass to be added to the coking coals, the following mixture is chosen as an example: 50 kg of black mass and 950 kg of coking coals are mixed, i.e. 5% by weight of black mass. The 50 kg therefore include a quantity of manganese of 16.5 kg, because the black mass contains 33% manganese.

But after coking, the coking coal loses its volatile matter. In the case chosen of a setting per thousand of 1400, the 950 kg of coal become, after coking, 678 kg (950 / 1.4). Similarly, the 50 kg of black mass lose the zinc which is vaporized, the oxygen of the coal and the initial mass is divided by two in the end, i.e. 50/2. Thus there remains 25 kg of black mass and a total coke weight of 678 + 25 = 703 kg. The manganese, itself, remained in the coke, which gives 2.34% (16.5 kg / 703 kg). This value is in good agreement with figure 4.

Figures 5 and 6 show how a composite coke can be prepared for use in a cupola and a blast furnace respectively.

A cupola furnace typically requires 10% to 15% coke usage relative to the weight of cast iron. As an example, let's take the case of a cupola furnace that consumes 13% coke and 0.3% manganese must be added to its cast iron, a fairly standard value for common lamellar cast irons. The composite coke to be ordered from the coking plant must have a manganese Mn composition of 0.3 x 100 / 13 = 2.31%. The quantity of black mass to be introduced into the coking plant in the coking coals will be approximately 5%, as shown in Figure 4.

Generally, the manganese percentage composition of the composite coke to be ordered from the coke plant is A% x 100 / B% coke, where A is the desired weight percentage in the cast iron and B is the weight percentage of coke consumed in the cupola or blast furnace relative to the weight of cast iron. The curves shown in Figure 5 were calculated from this formula for manganese additions to the cast iron, A ranging from 0.2% to 0.6%, and for coke consumptions between 10% and 15%. Compositions of 10 to 13% are more for the case of hot blast cupolas, while cold blast cupolas generally consume slightly more coke between 13 and 15%.

It should be noted that most cupola furnaces only need an addition of 0.2% to 0.4% manganese in their cast iron because the charged steels and the recycled cast iron returns contain a portion of manganese, so that a composite coke will in the majority of cases only need a maximum weight content of 4% manganese, figure 5, or a maximum addition of 8.3% black mass in the coking coal charges, figure 4.

In the event that the coking plant cannot produce mixtures that are too varied in black mass in its coals due to its operating rate per campaign, the foundry using a cupola furnace will order a standard composite coke, with a black mass value just lower than that desired by the foundry, and will then supplement the missing value by adding a reduced amount of ferro manganese.

Concerning a blast furnace, this requires 40% to 50% of coke in its charges for the production of its cast iron.

The abacus shown in Figure 6 is calculated in the same way as for the cupola, but with higher coke consumptions of between 40 and 50% of the weight of cast iron produced. In the case of a requirement of 45% of coke, if the requirement for the addition of manganese in his cast iron is 0.6%, he will have to order a composite coke loaded with 1.3% (0.6*100/45) of manganese Mn, Figure 6. This composite coke will be manufactured with an addition of only 2.8% by weight of black mass in the coking coal charges, Figure 4.

The invention has considerable environmental and societal benefits.

Let us estimate that the tonnage placed on the world market each year in alkaline and saline batteries represents a value close to 2 million tonnes, with considerable stocks of used batteries built up over time, because many of these batteries sometimes remain for years in an electrical device. Despite the new rechargeable accumulators placed on the market in recent years, this market for alkaline and saline batteries continues to grow by around 3% per year. Many of these batteries are also unfortunately landfilled. More and more countries are sorting these batteries and accumulators with a view to recycling them. In Europe, this recycling approaches 50% of the quantities placed on the market, but in some countries they are still landfilled.

These stored or unstored batteries represent a veritable mine of metals.

Without considering the stocks accumulated over time, these 2 million tonnes of batteries placed on the market annually contain a significant value in metals and chemical elements which can be estimated at:

• 460,000 tonnes of manganese.

• 360,000 tonnes of zinc.

• 400,000 tonnes of iron.

• 100,000 tonnes of carbon. 40,000 tons of expensive metals such as nickel and copper.

Given the current price of metals, €1,700/t for manganese, €3,000/t for zinc, €400/t for iron, €1,000/t for carbon, and at least €10,000/t for copper and nickel, the total value contained is of the order of €2.5 billion at the current price of metals.

There are processes that allow the majority of these elements to be recycled locally with good yields, of the order of 75% to 80%, but they are not yet very developed and the grinding process, although the yield is generally lower, around 50% to 55%, remains to this day the most common process used at around 90%.

The process according to the invention offers a very satisfactory yield by improving that of the most widespread grinding process and provides major environmental and societal benefits.

The invention also brings considerable economic benefits to users of the invention.

Let us take as an example a coking plant producing 300,000 tonnes per year of coke which would incorporate 5% of black mass from alkaline and saline batteries in its charges, i.e. 21,000t/year for charges of 400,000t in different coals and which will increase to 295,000t of composite manganese coke after pyrolysis (setting to mile # 1400).

After pyrolysis and separation, 295,000t of composite coke were obtained, comprising 6,930t of Mn and 5,670t of Zn metal, presented either in oxidized form or in metallic form.

The manufactured composite would be loaded with 2.3% Mn and would provide 0.35% Mn in addition in the cast iron with a loading of 15% of composite coke, which is the case of a cold blast cupola.

The investment in such a process would be very minimal, the operating cost requiring little energy, without additional labor or fixed costs, since it involves a marginal addition of only 5% of black mass in the coking plant charges.

In terms of materials, the black mass currently has a negative value estimated between -80€/t and -120€/t (processing costs) including transport from the crusher site to the zinc recycler.

The manganese portion added to the composite can be sold to the foundry or steel industry at a reduced price of around €1,000/t of Mn instead of €1,700/t which is the current price of this metal.

Zinc recovered in metallic form or as a high purity oxide of between 80 and 100% can be resold at a discount, at least between €1,000/t and €2,000/t of Zn, knowing that the current price is around €3,000/t.

In terms of balance, the carbon supplied by the black mass is completely consumed by the reduction reaction of ZnO to Zn gas. For the reduction of MnO2 to MnO, the necessary quantity of carbon The additional heat consumed must be taken into account for a value of 350€/t on coking coal. Finally, the additional heat required to heat the 5% additional black mass is taken into account.

With the assumptions seen above, Table 3 gives a rough idea of the possible additional gains for the coking plant that would manufacture and sell this composite coke. It is not a question of calculating an exact value but of giving an approach to the possible gain to show the interest of such a process. Even taking into account large discounts on the resale of manganese in this composite coke, just as for the resale of zinc, the result shows a gain of several million additional euros which will be added to the own results of the coking plant which are generally rather modest in this type of activity.

Table 3 below shows the case of a coking plant integrating 5% of black mass for 300,000 T/year of composite coke.

CASE OF A COKING PLANT INTEGRATING 5% BLACK MASS FOR 300,000 T/year OF COMPOSITE COKE

Table 3

Thus for 21,000t/year of recovered black mass, a minimum additional income of at least €10 million (to keep only a very conservative value compared to the €12.4 million calculated) is conceivable for the coking plant.

This gain makes it possible to quickly amortize the few investments which could prove necessary, in particular for the safe recovery of zinc dust. Profit margins in coke plants are generally very low and the addition of this product with the creation of a composite coke could allow them to be multiplied by a factor of 2 with a single addition of 5% in the raw material charges of the coke plant.

Thus the four user factors of the invention concerned, "the battery crusher, the coking plant, the foundry or steel industry using the composite and the zinc manufacturer" can each find a remarkable advantage:

• The battery crusher with a less negative cost selling price of the black mass, than what it is today with the Waelz zinc furnace recycler, therefore an additional margin.

• The coking plant, as indicated with reference to Table 3.

• The foundry or steel industry which will benefit from a discounted purchase price for manganese (taken at €1,000/t compared to €1,800/t).

• The manufacturer of pure zinc who will benefit from a discount on the price of zinc and who will be able to obtain supplies directly from the coking plant, rather than going through the Waelz furnaces as is currently the case (priced at €1,000/t against a pure zinc value of €3,000/t).

On the environmental level, in addition to improved yields, the carbon footprint is significantly reduced and logistics circuits and intermediaries will be reduced, which is also a plus for reducing the carbon footprint.

Claims

Claims 1. Process for recovering black mass from used alkaline and saline batteries, mainly comprising manganese and zinc, as well as potash and carbon, characterized in that it comprises the following steps: - incorporation of black mass into coking coal or into a mixture of coking coals, the quantity of black mass incorporated being less than 10% by weight of the mixture, - coking by pyrolysis of the mixture obtained in the previous step, and - obtaining a composite coke comprising manganese. 2. Method according to claim 1, characterized in that the coking step is carried out in a coke oven. 3. Method according to any one of the preceding claims, characterized in that the quantity of black mass added to the mixture of coking coals is between 1% and 10% by weight. 4. Method according to the preceding claim, characterized in that the percentage by weight of manganese in the composite coke is between 0.5 and 5%, preferably between 1 and 4%. 5. Method according to any one of claims 3 and 4, characterized in that the percentage by weight of black mass in the mixture formed with the coking coal or the mixture of coking coals is evaluated according to the percentage by weight of manganese in the composite coke. 6. Method according to the preceding claim, characterized in that the percentage by weight of black mass in the mixture formed with the coking coal or the mixture of coking coals is evaluated, according to the percentage by weight of manganese targeted in the composite coke, from the chart presented in Figure 4. 7. A method according to any one of claims 2 to 6, characterized in that the zinc contained in the black mass incorporated in the coking coal is vaporized in the form of metallic zinc during the pyrolysis operation, entrained in the volatile coke oven gas vapors leaving the coke oven, separated from the other volatile materials and recovered after cooling in solid metallic form or in the form of solid zinc oxide of purity between 80 and 100%. 8. Method according to any one of the preceding claims, characterized in that during pyrolysis, the sulfur present in the coking coal or the mixture of coking coals is partly eliminated by the zinc of the black mass. 9. Method according to any one of the preceding claims, characterized in that at least part of the acid gases of the SO2 type released during the pyrolysis is neutralized by the potash of the black mass. 10. Composite coke, characterized in that it is obtained by the process according to one of the preceding claims. 11. Composite coke according to claim 10, characterized in that it comprises between 0.5 and 5%, preferably between 1 and 4% of manganese. 12. Composite coke according to one of claims 10 and 11, characterized in that it does not contain zinc. 13. A method of using the composite coke according to any one of claims 10 to 12 in a metal melting furnace, at least a portion of the coke introduced into the furnace being said composite coke. 14. Method according to the preceding claim, characterized in that the metal melting furnace is a blast furnace, a cupola furnace or an arc furnace for producing manganese cast iron. 15. Method of use according to any one of claims 13 and 14, characterized in that to produce cast iron having a predetermined percentage by weight of manganese, the percentage by weight of manganese in the composite coke introduced into the furnace is adjusted.