FI127830B - Procedure for processing the black mass in used alkaline batteries - Google Patents

Abstract

The present invention relates to a method for preprocessing an alkaline black mass (BM) of spent alkaline batteries which pre-processed alkaline black mass (56) is meant for a leaching process (C) to recover one or more metals from preprocessed alkaline black mass. The preprocessing (A) includes a heat treatment process (101.1, 202, 302) of the alkaline black mass. In addition, the invention relates to a method, device and system for processing a black mass of spent alkaline batteries.

Description

The invention relates to a method for processing a black mass of spent alkaline batteries, in which

- the alkaline black mass is pre-processed to reduce pH of the alkaline black mass for a leaching,

- the pre-processed alkaline black mass is leached with one or more acidic solutions in order to produce a leach solution,

- one or more products are made of the leach solution.

More specifically, the present invention relates to method for recovery and recycling of metals found in spent alkaline batteries.

Alkaline batteries make up about 80% of all collected spent batteries. Consequently, there is a need and interest of finding process for recovery of the metals used in spent alkaline batteries. Alkaline batteries are primarily batteries consisting mainly of zinc/zinc oxide and manganese dioxide (Zn I ZnO and MnO₂). In the alkaline battery, the anode (negative) is made of zinc powder, which gives more surface area for increased current, and the cathode (positive) is composed of manganese dioxide. In the alkaline battery cell (nominal voltage of a fresh alkaline cell is 1.5 V), there is an alkaline electrolyte of potassium hydroxide whereas zinc-carbon batteries have acidic electrolytes.

Many known methods of recovering the metals used in spent alkaline batteries either use electrolysis or use Zn powder making them commercially less interesting. Consequently, there is a need for an efficient, cost effective and safe method for recovery of metals present in alkaline batteries.

Current alkaline battery recycling facilities are based on high temperature smelting technology which does not allow the optimal recovery of valuable metals. One disadvantage of the smelting technology is its high cost by the use of energy, and relatively low recycling rate (-50%). Recently and partly as a consequence of this, some smelting plants have been shut down for environmental or safety reasons in the EU. Therefore, there is an urgent need for an environmentally benign and techno-economically more feasible recycling technology. Similarly, crushed alkaline battery powder is smelted, and also in this case, recycling efficiencies are low and process is not cost-efficient.

Additionally, international patent application publication number WO 2013/124399 A1 and

European patent application publication number EP 1 148 571 B1 discloses yet some other methods to process alkaline black mass of spent alkaline batteries. In these the alkaline black mass is first pre-processed and then leached with one or more acidic solutions. Washing of the alkaline black mass is a known method to pre-process the alkaline black mass. One of its intention is to reduce pH of the alkaline black mass for the leaching process. Water is an example of the washing liquid used in the washing. However, wasting of the solution being the result of the washing process is a problem in this preprocessing method which limits its use.

Some other references concerning the prior art are disclosed in international patent application publications WO2010102377 A1 and WO9320593 A1 and in EP-patent application publications EP1333522 A1 and EP2450991 A1.

An object of this invention is to provide method for processing a black mass of spent alkaline batteries, said method being simple and also safe as its implementation. The characteristic features of the method according to the invention are set forth in claims 1.

In the invention, the pre-processing of the alkaline black mass for leaching includes a heat treatment of the alkaline black mass. The heat treatment of the alkaline black mass performed before the leaching process of the alkaline black mass simplifies the total process and reduces the amount of substances which are useless or have minor significance. The heat treatment of alkaline black mass, for example, removes selected substances from the black mass and its alkalinity, too. In addition, by means of the heat treatment can be effected to the leaching process of the alkaline black mass and to the final product obtained from that. One particular advantage is that the amount of substances formed in the pre-processing is diminished owing to the heat treatment.

According to one embodiment the final product obtained from the leaching process may be applied in the liquid form. This also simplifies the implementation of the process because any kind of precipitation or cementation stages and also the need for chemicals for that have been avoided in the present invention. Additionally, the main water insoluble metals of the alkaline black mass i.e. manganese and zinc may be dissolved both in the same leaching process having together. Thus, there is no need for separate leaching processes for each metals.

In addition, owing to the method from the raw materials of the spent alkaline batteries are chemically achieved salts. This means that very big amount of the materials have been recovered and used. The leaching process may take place in room temperature (i.e. below 100 °C). That saves energy costs and simplifies also the implementation of the process. The process devices are also simple and the process may be run up very fast.

Owing to the invention the waste fractions have been minimized and metals have been recycled with high yield. The MnSO₄ and ZnSO₄ -solution that may be the sellable product of the process, can be used for micronutrients in fertilizers or as such to aid growth and health of plants, for example. Other additional advantages achieved with the invention become apparent from the description, and the characteristics are set forth in the claims.

The invention, which is not limited to the embodiments set forth below, is described in more detail by making reference to the appended drawings, in which

Figure 1 shows a basic principle of the method and system according to the invention in a simplified flow chart,

Figure 2 shows in greater detail an example of the stages of the method for preprocessing the alkaline black mass,

Figure 3 shows in greater detail an example of the stages of the method for processing the alkaline black mass,

Figure 4 shows in greater detail an example of the stages of the leaching process in another embodiment,

Figure 5 shows a basic principle of the method and system according to the invention in a simplified process chart,

Figure 6 shows an example of the heat treatment of the alkaline black mass and

Figure 7 shows an example of the separation of the leach solution from the solid residue of leaching.

Spent alkaline batteries are collected for the process of recovery of included metals. Prior to any actions they may optionally be sorted. Such a sorting process has the aim of separating alkaline batteries from any other kinds of batteries such as, for example, rechargeable lithium batteries and also trash in order to have alkaline batteries only as the starting material for preparation of the alkaline black mass BM. In this connection the accumulators and portable rechargeable batteries can also be understood as batteries as well as the conventional single use batteries. One sorting process that may be employed for this purpose is exemplified in WO 2011/113860 (A1). After the sorting the purity percentage concerning the alkaline batteries may be over 90%.

After sorting the alkaline batteries are crushed in a mechanical process in order to produce alkaline black mass BM. Alkaline black mass BM, that is the starting material i.e. a raw material for the method according to the invention, is produced in the recycling process of alkaline batteries. In the crushing the alkaline black mass BM has been produced, for example, through dismantling and magnetic separation of iron metals (or any ferrous material) prior to the pre-treatment and the leaching processes.

The alkaline black mass BM powder is typically a mixture of the cathodic (manganese oxide and graphite) and the anodic (zinc oxides and electrolytic solution) materials. In generally, it typically contains the following main metals; Al 1.2 %, Fe 0.6 %, Mn 30.0 % and Zn 21.8 % (vol%). However, it is to be clearly understood that any alkaline black mass can be used in the method according to the invention and in particular wherein the majority of metal content is mainly zinc and manganese. Thus, the present invention is mainly concerned with recovery of these metals. The average particle size of alkaline black mass is 250 - 500 pm. Metals are known to be concentrated on the smaller fractions, however the method presented herein is suitable of use on any particle sizes. However, any particle sizes even up to about 1.2 mm may be used in a process according to the invention.

In the method according to the invention it is beneficial to have a small particle size so as to speed up the reactions in pre-processing of the alkaline black mass and/or in the leaching of the metals present in the pre-processed alkaline black mass BM. Even though, the alkaline black mass BM may be used as is, the method may also involve any technique resulting in a smaller particle size, such as e.g. grinding of the alkaline black mass BM prior to the pre-processing step and/or leaching step of the metals.

The resulting material from crushing, dismantling, magnetic iron separation and possible grinding may also optionally undergo an optional pre-treatment step in order to remove any non-metallic coarse material present in the batteries. These may be e.g. plastic films, paper pieces, electric wires etc. from the dismantling operation non-woven cellulose or synthetic polymers. However, the material may also not be pre-treated in this sense any way before use or pre-processing stages, and hence the material may still contained plastic films, paper pieces, electric wires etc. from the dismantling operation. After crushing and possible other pre-treatment steps the hot alkaline black mass may be put in bags and transferred to the cooling room. Cooled bags are then stored and ready for the next phase.

The alkaline black mass BM is then subjected to different method steps to separate met als in the spent alkaline batteries. Figure 1 shows a principle of the method and also the system according to the invention as an example in a simplified flow chart. In that metals present in the alkaline black mass BM is recovered by means of the main steps of A) preprocessing, C) leaching and D) further processing to produce one or more products 17 from the substances resulting from the steps of pre-processing and leaching of the alkaline black mass BM. In generally, the pre-processing step A that is performed before the leaching C, includes the heat treatment 101.1 of the alkaline black mass BM. In the preprocessing A being now the heat treatment 101.1 has been reduced the alkalinity of the alkaline black mass BM i.e lowered its pH. In addition, in the heat treatment 101.1 has also been removed substances from the alkaline black mass BM. In the leaching process C metals like, for example, manganese and zinc have been dissolved from the preprocessed alkaline black mass.

According to the embodiment the alkaline black mass BM is transferred to feeding silo (not presented), which feeds alkaline black mass BM to the heat treatment 101.1. In generally, in the heating step 101.1 humidity, water ammonia, carbon, carbon dioxide, paper, board, and plastic components are removed from the alkaline black mass BM. Owing to that the pre-treatment (for example, screening or sieving) of the alkaline black mass BM in order to remove any non-metallic material present in the batteries after the crushing may not be needed which also simplifies the process. In addition, the heat treatment 101.1 of alkaline black mass BM drops the alkalinity of the black mass and improves its homogeneity. In other words, the pH of the alkaline black mass BM reduces in the heat treatment 101.1. Owing to the heat treatment 101.1 will not be formed such useless side flows as it takes place in washing, for example, but the amount of waste material is minimized.

Furthermore, the heat treatment 101.1 as a pre-processing A also speeds up the leaching reactions of zinc and manganese in the leaching process C. Owing to the heat treatment 101.1 zinc will be oxidized as zinc oxide. Zinc oxide leaches easily to sulphuric acid without forming great amounts of hydrogen gas. Owing to this the process is also simplified because the required atex classification of the process may be reduced.

Manganese will be in two different oxidizing level: +2 and +4. Oxidizing level +4 will not be leached to sulphuric acid without a reducing agent. By means of conditions of the heat treatment 101.1 it is possible to effect to the composition of the final product(s) 17 and/or upgrading of the leach solution 14. Specifically by means of conditions of the heat treatment 101.1 it is possible to change the formulation of the products relative to zinc and manganese. First it can be manufactured a product which contains zinc more than man ganese. After that from the residual sediment can be leached the manganese solution. Thus, the heating step 101.1 simplifies the process considerably in many different view. In the leaching process C manganese and zinc have been dissolved from the black mass 56.

Next in the optional step B the pre-processed alkaline black mass from the heat treatment step 101.1 is stored 102 before the leaching process C. This storing step 102 may also include the cooling of the black mass after the heat treatment 101.1. In other words, the pre-treatment A of the alkaline black mass i.e. heat treatment 101.1 may be proceed as its own independent process that is not tied to the leaching process C or to the further processing D of the pre-processed alkaline black mass 56. In other words, between the preprocessing A and the leaching process C of the pre-processed alkaline black mass 56 may be delay i.e. those need not to be continuous processes. This also means that the pre-processing A i.e. the heat treatment 101.1 may be performed another site than the leaching process C and further processing D performed after the leaching process C and there may be, for example, transportation of the pre-processed alkaline black mass 56 from the pre-processing site to the leaching processing site.

In process C the pre-processed i.e. heat treated alkaline black mass 56 from the preprocessing A is leached with one or more acidic solutions 12, 13, 24, 25, 26 in order to produce a leach solution 14. The leach solution 14 includes manganese and zinc in acidic solution.

Optionally the leach solution 14 may be purified of one or more heavy metals, such as, for example, nickel and/or copper (not shown). The leach solution 14 is then subjected to further processing D. Further processing D may include one or more steps 104. These steps 104 may include, for example, separation and/or filtering of the leach solution 14 to separate the solid substances from the acidic liquid and possible adjustment of pH of the liquid residue of the leach solution 14*, in generally, neutralization step.

Finally, one or more products 17 have been obtained from the leach solution 14. These are, for example, manganese and zinc containing product 17 (or a raw-material for such).

Figure 2 shows in greater detail the stages of the method for pre-processing A the alkaline black mass BM of spent alkaline batteries. Here the purpose of the pre-processing A is to prepare the alkaline black mass BM for the leaching process C in order to recover one or more metals from the pre-processed black mass in the leaching process C. Among oth ers, in the pre-processing A an alkalinity of the alkaline black mass BM is reduced i.e. its pH is lowered from high alkalinity level (pH = 12) towards neutral level.

Preparing stage 201 of alkaline black mass BM may include, for example, as stated already earlier, sorting of collected spent batteries, crushing of alkaline batteries, cooling of crushed alkaline batteries, removal of ferrous material from the crushed alkaline batteries and feeding of alkaline black mass to the pre-processing A. In addition, the preparing stage 201 may include one or more storing steps between the other steps.

The pre-processing A of the alkaline black mass BM of spent alkaline batteries includes a heat treatment of the alkaline black mass BM in step 202 after the preparing stage 201. Heat treatment 202 can be carried out, for example, in a furnace. Temperature of the alkaline black mass BM in the heat treatment 101.1, 202 is raised in the range 350 - 800 °C and more preferably in the range of 400 - 700 °C, for example, about 600 °C. The pH of the alkaline black mass BM in the beginning of the heat treatment 202 may be about pH = 11.

After the heat treatment 202 the black mass 56 is cooled in stage 203, screened in stage 204 and then stored in stage 205 and/or conveyed to the leaching process 206, (C) of preprocessed black mass 56 prior to the further processing 207, (D). In the heating step 202 carbon, paper, board and plastic components being in the alkaline black mass are removed from the mass and, for example, burned on step 202.2. Owing to that these substances can be used in energy production on stage 101.2. Another option is to scrubbing of the gases arising in the heat treatment 202 and/or burning process of the gases. This may be done by using a gas scrubber to purify gases arising in the heat treatment 202.

In the cooling stage 203 may be recovered the heat energy of the black mass. From the screening stage 204 solid coarse waste may be collected and the reject of the screening may be circulated back to the heat treatment stage 202.

Figure 3 shows in greater detail the stages of the method for processing the alkaline black mass BM of spent alkaline batteries. Stage 301 is preparing of alkaline black mass BM for the method. It may correspond the described and disclosed steps 201 of Figure 2.

The alkaline black mass BM is again pre-processed A. The heat treatment stage 302 as a pre-processing A of the alkaline black mass BM may also correspond the stage 202 already described and disclosed in Figure 2. The heat treatment 302 may be performed in oxidative conditions. One way to implement this is to feed air 92 to the heat treatment process 302.

The heat treatment 302 of the alkaline black mass BM may be performed in a reaction chamber, more generally, in a process device 51. The reaction chamber may be, for example, a furnace (or oven), a reel oven 20 or a heated screw 84. The reaction chamber may be, for example, a rotary type. In addition, the reaction chamber, more generally, the process device 51 in which the heat treatment process 101.1, 202, 302 of the alkaline black mass BM is performed may be indirectly heated. In that the alkaline black mass BM is not in direct contact with the heat source. In other words, for example in a furnace, the flames are not directed or contacted to the mass. Black mass BM mixing during the heat treatment 302 speeds up the process.

The residence time of the alkaline black mass BM in the heat treatment 302 may be 15 60 minutes, for example, 20 - 40 minutes. The residence time depends on, for example, the length of the process device 51. During the heat treatment 302 the humidity, ammonia, carbon, paper, board and plastic components, for example, are removed from the alkaline black mass BM. In addition, by the heat treatment 302 of the alkaline black mass BM, the alkalinity of that is dropped. After the heat treatment 302 the processed black mass will be cooled in stage 303 and stored in stage 304 for the next phase. Owing to the heating stage 302 the alkaline black mass BM may lose about 20 - 25 % of its mass as burned and/or evaporated compounds.

The heat treatment of the alkaline black mass BM may also be understood as black mass roasting. In other words, its purpose is not to burn the alkaline black mass BM. In stage 302 the alkaline black mass BM is roasted in elevated temperatures in oxidative conditions. In addition, in stage 302 the alkaline black mass BM is roasted in elevated temperatures in air atmosphere. Oxidative conditions are achieved by feeding air to the furnace or to corresponding reaction chamber in which the alkaline black mass is under the heat treatment. In oxidative conditions the oxygen level in the furnace is kept high enough to maintain oxidation process (i.e. C -> CO₂, Mn -> MnO₂, Zn -> ZnO, etc....) in the desired manner.

In the temperature ranges applied in the title invention the oxidative conditions have been achieved by feeding air 91 to the reaction chamber of the processing device 51. The cell reaction of the alkaline battery is Zn + 2MnO₂ # ZnO + Mn₂O₃. In other words, the crushed alkaline black mass BM includes metallic zinc, zinc oxide and manganese at dif ferent oxidation levels. Owing to the oxidative conditions i.e. by feeding air 91 to the reaction chamber next reaction equations will take place:

Zn + O₂ -> 2 ZnO

MnO + O₂ -> 2 MnO₂ C + O₂ -> co₂.

This means that owing to the oxidative conditions the oxidized compounds for zinc and manganese are formed. This also means that the reduction i.e. the formation of zinc may be avoided and also the melting of metallic zinc (and evaporation) which would otherwise take place in carbothermic reduction without extra air feeding. Without feeding of the air 91 to the heat treatment the only source of the oxygen for the carbon would be the oxygen included in the metals. Owing to the oxidative conditions zinc will be oxidized zinc oxide which leaches easily to sulphuric acid and does not form hydrogen at least in great amount.

Oxidation states of zinc and manganese can be altered by adjusting temperature and residence time. In the higher temperature the equilibrium part of manganese dioxide diminishes. In that case still larger part of manganese is in oxidation state +2 owing to which that leaches directly to sulphuric acid without reducing agent. This provides means for adjusting the zinc/manganese ratio of the final product 17 by means of the heat treatment 302. When producing final product with smaller manganese ratio unleached MnO₂ sediment is achieved as a byproduct. That can be leached by means of reducing agent, for example, citric acid to produce pure manganese product. In addition to the air also nitrogen may be feed to the heat treatment 302 in suitable ratios. Limiting the oxygen level may reduce the oxidation of manganese to manganese dioxide which is one way to effect to the zinc/manganese ratio of the final product. Other advantages of the heat treatment 302 are that paper, plastic and carbon contents are combusted during roasting reaction. These carbon containing substances may be used to produce additional energy 41 to the boiler system.

The alkaline black mass BM may be mixed during the heat treatment 302 in order to improve the oxidation reaction and mixing with the air 91. Some suitable heat chambers to implement this are the reel oven 20 and the heated screw 84. The oxidative reactions will be improved and the reactions speeded because the alkaline black mass BM mixes continuously with the air 91.

The black mass may be accepted to the leaching process C after most part of the ammo nium, paper, plastic and board have been removed from the mass. Practically already 400 °C with one hour reaction time about 15 % loss of mass is achieved. Different heat treatment conditions however make possible to adjust the ratios of the main metal components of the final product 17.

In stage 303 the resulting black mass from the heat treatment stage 302 may then be cooled. Cooling may take place, for example, in connection with a screw conveyer 54. In that the heat energy may be recover, for example, to the district heating system (return water) 55.1,55.2.

In stage 304 the black mass from the cooling stage 303 may then be screened. In other words, the pre-processed alkaline black mass 56 may be screened before the leaching process C. Screening 304 may include two-level screening (for example flat sieves 57.1, 57.2) and a crushing 75 between them. Heat treated and cooled black mass 56 from the cooling 303 will be fed by screw conveyor to the first sieve 57.1 (Figure 5) by which the most optimal size of the particle will be sorted for the leaching process C, 306 following the sieving. Size of the screen 57.1 may be 800 pm. Under size fraction of the heat treated black mass 56 is accept and that is transferred to leaching stage 306 by screw conveyor 58.1, for example. Over size fraction of the heat treated black mass 58.2 from the first screen 57.1 is transferred to crushing 75 for size reduction. Over size fraction may be about 15% of the mass of the heat treated black mass 56. Crushing 75 may be performed, for example, in a ball mill or roll crusher. After size reduction the crushed material is fed to second level screen 57.2. Again, size of the second screen 57.2 may also be 800 pm. Accumulating coarse material (mainly copper pins) 76 is removed from the process. The under size material is restored to the furnace, or more generally, to the heat treatment 302 I processing device 51.

After the screening stage 304 the under size fraction of the heat treated black mass is transferred to the leaching stage C, 306. Before the leaching C, 306 accept of the black mass will be analyzed. A reducing agent, for example, citric acid 13 may be added to the pre-processed black mass 56 in stage 305 i.e. between the pre-processing stage 304 and leaching stage 306. In the conveyor 58.1 transferring the under size fraction of the heat treated black mass to leaching 306 there may be an own connection 93 for the feeding of the citric acid 13 before the leaching process C. The citric acid 13 may be in solid form. In other words, the pre-processing of the black mass BM includes now also cooling and screening stages 303, 304 of the heat treated alkaline black mass between the heat treatment A, 302 and the leaching C, 306 and an adding of reducing agent, such as, for example, citric acid 13 to the heat treated black mass preferably before the leaching stage C, 306. Screening 304 before the addition of citric acid 13 improves the mixing of reducing agent to the pre-processed black mass 56.

The under size fraction of the heat treated black mass is lead to the leaching stage 306, (C). In other words, the pre-processed alkaline black mass 56 is leached C with one or more acidic solutions 12, 13 in order to produce a leach solution 14. According to the embodiment the leaching has been made in an acid resistant tank (reference number 62 in Figure 5) including heat treated and now also screened black mass with one or more acids 12, 13 (and possible water 94). In the disclosed embodiment the acids are sulphuric acid 12 as a leaching agent i.e. solvent and also citric acid 13. In this the citric acid 13 acts as a reducing agent. Other possible reducing agents are, for example, oxalic acid or isocitric acid.

The leaching process C, 306 is performed now in a single stage process i.e. as a batch, including at least two sub-stages. The leaching C can be performed as a batch process performed in one leaching tank 62. In a first sub-stage the pre-processed alkaline black mass 56 is leached in the presence of the reducing agent 13 and water 94. First substage in the leaching C, 306 is to add computational amount of fresh water 94 into the reactor 62 (Figure 5). After that black mass and citric acid 13 can be added to the reactor 62. The citric acid 13 acts now as reducing agent to manganese. Nitrogen purging may also be performed in order to avoid explosive conditions (hydrogen + oxygen). However, the amount of hydrogen is reduced owing to the heating process 101.1 and reactions taking place in the case of zinc.

In a second sub-stage the leaching process C, 306 is continued from the first sub-stage by adding a second leaching agent 12 to the leaching process C. This may be done in the same reactor 62 i.e. to continue by adding to the existing leaching process C second leaching agent 12. Second leaching agent 12 is now sulphuric acid. Second leaching agent is fed during 2 - 3 hours from the beginning of the first sub-stage. The temperature of the reaction solution is let to rise up to 80 ⁰ C. This is an exothermic reaction. Foam formation may be managed by entering the anti-foaming agent 22. The pH in the leaching process C, 306 is monitored. When the pH stabilizes the reaction is finished.

In the disclosed embodiment zinc and manganese dissolve in the leaching stage C, 306 according to following equations:

MnO + H₂SO₄ -> MnS0₄ + H₂O

Mn₂O₂ + H₂SO₄ -> MnO₂ + MnS0₄ + H₂O

Mn₂O₄ + 2H₂SO₄ -> MnO₂ + 2MnSO₄ + H₂O

ZnO + H₂SO₄ -> ZnS0₄ + H₂O

Zn + H₂SO₄ -> ZnS0₄ + H₂

The pre-processed alkaline black mass 56 contains some oxidized manganese (in the form of MnO₂). Therefore, a reducing agent 13 may be used in order to achieve complete dissolution of main metals (zinc and manganese) and also to reduce any insoluble metal oxides formed by reaction of the acid (such as e.g. sulphuric acid). Alkaline black mass contains also some other oxidized compounds of manganese, such as Mn₂O₃ and Mn₃O₄. These compounds are only slightly soluble and can form more MnO₂ to the process. An example of an appropriate reducing agent to be used in this step is, for example, citric acid 13. Reducing leaching of manganese oxide in the solution of sulfuric acid 12 and citric acid 13 is given by the following equation:

9MnO₂ + 9H₂SO₄ + C₆H₃O₂ 9MnSO₄ + 1377₂O + 6CO₂

The reducing leaching leads to the dissolution of metals from the pre-processed alkaline black mass 56. pH of the heat treated alkaline black mass 56 to be leached may be about in the range of pH = 7 to pH = 9, for example, or below pH = 7. In other words, the preprocessing A i.e. the heat treatment process 202, 302 drops the pH of the alkaline black mass BM down from about level pH = 12. Owing to this the amount acids 12, 13 needed in the leaching process C is less. pH in the leaching stage 306 including the leaching solution 12, 13 may be, for example, in the range of pH = 0,5 to pH = 1,2. By means of the leaching manganese and zinc have been changed to sulfate form from oxide and possible metal forms. Liquid/solid ratio at the beginning of the leaching for leaching agent 12 may depend on the size of the reactor 62. The concentration of the leaching agent 12 may be in the range of 15 - 20 M and more particularly, in the range of 16 - 18 M and for the reducing agent 13 in the range of 3 - 7 M and more particularly, in the range of 4 - 6 M. In the leaching the metals being still in the pre-processed alkaline black mass 56 are leached to the leach solution 14 being the result of the leaching stage 306.

After the leaching process C, 306 the leach solution 14 can be cooled to 50 °C at stage 307. This can be performed by means of cooling jacket built in the reactor 62, for example. The heat energy obtained from the cooling may also be recovered.

After leaching 306, (C) and also the cooling 307 leach solution 14 i.e. the mix of leached black mass and one or more acids 12, 13 with the leached substances is separated from the solid substances at stage 308. The solid residue 37 from the leach solution 14 is separated. According to the embodiment this has been performed by means of decanter centrifuge 63 by which insoluble material 37 is separated. The amount of insoluble material 37 may be about 10 % (w/w) from the pre-processed alkaline black mass 56 which was fed in to the leaching tank 62. One example of the separator is a decanter 63 marketed by Alfa Laval’s in the name of P2-305. The separation stage 308 removes from the solution 14 mainly carbon related substances and possible other insoluble materials 37. This remaining material 37 (mostly organic material from the batteries) after the reductive leaching C can be utilized in the energy production, e.g. by combustion.

The separated solution 14’ from stage 308 will continue from the decanter centrifuge 63 through a separate filter (not disclosed) to eliminate the lightest and the smallest solid particles 16. This takes place in stage 309. The filtrate i.e. the leach solution 14* from filtration stage 309 is then lead to adjustment of pH (i.e. neutralization) performed in stage 310 in which the pH of the separated and filtered leach solution 14* is adjusted.

After removing the solid substance 37, 16 the solution 14* will be transferred to storage tanks located in the hygiene area. In the pH adjustment stage 310 pH of the leach solution 14* is altered to higher level in the neutralization tanks. In that can be utilized one or several suitable neutralizing agent. Depending of the implementation of the leaching process C the neutralization step 310 may be optional. After the filtration stage 309 pH of the solution 14* may be in the range of pH = 0.5 to pH = 1,2. In the adjustment stage 310 pH of the leach solution 14* is adjusted to pH > 3.0, and more specifically to the range of pH =

3.5 to pH = 3.8, for example. In general, the pH is adjusted to the range of pH = 2 to pH = 4. pH level depends on product chosen to be processed. According to one embodiment in the adjustment of pH can be used KOH, NaOH or caustic soda, for example. Adjustment of pH is to minimize the precipitation of unwanted manganese and zinc hydroxides. The purpose of this is to achieve optimum pH to keep solubility of MnSO₄ and ZnSO₄ - product in which zinc precipitates first.

On the basis of the sample provides the solution will be adjusted, where appropriate, the strength of Mn and Zn in respect of the level of customer demand, using manganese sulfate and zinc sulfate. The purity of the product will be analyzed and returned to clean-up, if necessary. When the level of the solution is secured, so can it pass the IBC containers or the larger storage tank outside, for example, waiting for the delivery to the distributor for bottling or delivering to the customer.

Owing to the adjustment of pH one or more products 17 are made of the leach solution

14. This may be done in further processing step D, 104 presented in Figure 1 and may include stages 308 - 310, for example, presented in Figure 3. These are the products of manganese- and zinc-containing sulphate solution 17. These are suitable for micronutrients in fertilizers or as such to aid growth and health of plants, for example. The skilled person understands that the “product” meant in this connection may also be a rawmaterial for some special final product suitable for some specific purpose (for example, fertilizer).

Figure 4 shows in greater detail another embodiment to implement the leaching process C. The alkaline black mass pre-processed again by the heat treatment 101.1 is now leached in stage C, 306 by means of a counter-current leaching principle. Leaching process C is again used for the leaching of metals that remain in the pre-processed alkaline black mass BM: manganese, zinc (and also iron). Now the leaching process C includes at least two leaching stages C1, C2 being to implement counter-current leaching. The advantage of this is that best possible yield is achieved and metal levels have been kept minimum in the leaching residue and all metals in the process.

In a first leaching stage C1 is leached a solid residue 23 obtained from a second leaching stage C2. The leaching in the first stage C1 is carried out in the presence of a strong first acidic solution 25. Now the acidic solution 25 includes sulfuric acid 12 (H₂SO₄) in order to leach remaining metals i.e. zinc and manganese remained to the solid residue 23 of the second leaching stage C2. In addition, the acidic solution 25 includes also citric acid 13.1 as a reducing agent. pH of the leach solution 25 is in the first leaching stage C1 in the interval of pH = 0,1 to pH = 1, more specifically pH = 0,3 to pH = 0,7, for example, pH = 0,5. Thus, the acidic solution in the first leaching stage C1 can be said to be strong. Zinc and manganese dissolve again according to the equations presented already earlier.

Acidic solution 25 contains sulfuric acid 12 and citric acid 13.1. First leaching stage C1 is performed under elevated temperature from exothermic protonation reaction and exothermic leaching reaction. These may raise reaction temperature in insulated reactor to even 90 °C. In generally, the reaction temperature T in the first leaching stage C1 is in the range of 80 - 95 °C, more specifically 85 - 92 °C. There shouldn’t be need for additional heating as temperature rises due to release of chemical energy. Optimum leaching pro cess takes place in between 70 - 90 °C. Temperature in leaching reactors i.e. stages C1 and C2 can be controlled by circulating cold water or water vapour in heat exchange jacket.

In a second leaching stage C2 is leached the pre-processed alkaline black mass 56 from heat treatment 302 and cooling and screening stage 303, 304 added to acidic filtrate 24 obtained and pumped from the first leaching stage C1 and filtrated in stage 401 and a second acidic solution 26 added to the second leaching stage C2. The second acidic solution 26 used in the second leaching stage C2 includes antifoam agent 22 (for example, DST antifoam including an- and non-ionic surface-active agents) and citric acid 13.2. In addition, water may also be added to second leaching stage C2. During the second leaching stage C2 diluted antifoam agent 22 and citric acid 13.2 are added to leaching tank. Citric acid 13.2 used in the second leaching stage C2 stabilizes manganese product to suitable oxidize level (+2) in which that is liquid. In addition, one mole of citric acid may reduce nine mole of manganese which makes citric acid very effective in this connection. The concentration of the citric acid 13.2 used in the leaching stage C2 may be in the range of about 3 to 6 M. Amount of DST antifoam 22 is, for example, 15 ml of 1% solution per 285 ml of process solution.

The acidic filtrate 24 of the first leaching stage C1 is separated from a solid residue 28 by filtration (stage 403). Adequate amount of sulfuric acid 12 has been already added in first leaching stage C1. The pre-processed alkaline black mass 56 from heat treatment stage 302 is mixed in stage 402 to the acidic filtrate 24 of the first leaching stage C1 including sulfuric acid 12 and citric acid 13.1 which both were added in the first stage C1 to the solid residue 23 to be leached in that. The leach solution 14 to be fed to the further processing stage D, 104 is a filtrate 27 obtained from the filtration stage 404 after the second leaching stage C2. After second leaching stage C2 solids 23 are separated from liquid 14 by filtration 404. After filtration stage 404 filtrate 14 is pumped to storage tank. In this case the further processing D, 104 may include only the stage 310 of Figure 3 i.e. the adjustment of pH of the leach solution 14*. Solid residue 23 including zinc and manganese residues are conveyed to first stage of leaching C1 in which those have been leached in strong acidic conditions.

pH in the second leaching stage C2 raises and is in the interval of pH = 1 to pH = 2, more specifically pH = 1,3 to pH = 1,8. Temperature in second leaching (H₂SO₄) is lowered to 45 °C to improve manganese sulphate solubility. More generally, the reaction temperature T in the second leaching stage C2 is the range of 27 - 65 °C, more specifically 30 - 60 °C and particularly 45 °C. Temperature 45 °C is a compromise between highest manganese sulphate solubility (30 °C) and zinc sulphate solubility (60 °C).

The solid residue 28 from the first leaching stage C1 is separated by filtration and washed with adequate amount of water 29 in stage 403 and then filtrated. Filtrate i.e. the washing liquid 31 from stage 403 is lead to mixing stage 402 and the solid residue 30 is waste. That can be utilized in the energy production, e.g. by combustion, for example.

Both leaching stages C1, C2 are performed as a batch process. Batch volume increases from 10 m³ to 30 m³. The reaction time during the leaching process may be in the range of any time to completely or almost completely dissolve the metals of the pre-processed alkaline black mass 56. Such time ranges may be in the range of 2 - 5 hours per stage and more particularly 4 hours per leaching stage, for example.

At the completion of the leaching process C, the entire metal content is in solution 14 at least about 60%. It is to be clearly understood that of the metals present in the alkaline black mass, the dissolution percentages between the different metals may vary such that e.g. 85% of one metal may be in solution and 95% of another metal may be in solution after completion of the leaching process C. By means of the two-stage leaching process C described above the aim is to good yield and concentrated metal solution.

The stages after the leaching may correspond the presented stages in connection with Figure 3 without separation and filtering steps, particularly, if the result of the leaching process C of Figure 4 is the filtered leach solution 14*.

Figure 5 shows a basic principle of the method and a system according to the invention in a simplified process chart. The components/functions of the system have been presented in the sequential order.

A) Pre-processing: feeding of alkaline black mass BM, feeding of air 92, indirectly heated rotary furnace or reel oven 20, cyclone 52 to remove gases from heat treated alkaline black mass 56, gas scrubber 53, cooling conveyor 54 with cooling water inlet and outlet

55.1, 55.2, storage 21 of pre-processed alkaline black mass 56, screening 57.1, 57.2 of pre-processed alkaline black mass 56 with outlets for undersize (fine) and oversize (coarse) alkaline black mass 56.1, 56.2 and a crusher 75 between the screenings 57.1,

57.2.

C) Leaching process: storage 59 of pre-processed alkaline black mass 56, feeding silo 60, conveyer 18 with an inlet 93 of citric acid 13, inlet 61 of water 94 and leaching tanks with mixer 62.

D) Further processing: separation (stage 308; Figure 3): decanter separator 63 (with overflow gravity) having the components I functions: feed 64, feed tube 65, discharge port 66, conical end 67, inlet distributor 68, wall of the bowl 69, screw conveyor 70, gearbox 71, solids discharge 37 and liquid 14’ discharge by gravity. In generally, instead of decanter separator 63 can also be speak of solid-liquid separation.

Figure 6 shows one example to implement the pre-processing stage A i.e. heat treatment 202, 302, 51 of the alkaline black mass BM. This applies the heat boiler 82 of the heat power plant, for example, having power of 1,5 MW. The power plant may be district heat power plant, for example. The heating of the boiler 82 takes place now by feeding wood pellet or wood chips to the boiler by feeding means 90 and combusting them. To the combustion chamber 89 has been fitted screw conveyer 84 having canal form to which the alkaline black mass BM to be heated is fed from the feeding silo 81. By means of the conveyer 84 acting now as the heated screw the alkaline black mass BM is conveyed through the district heating power plant’s boiler system 83. Feeding takes place with air 91. The channel 84 may be open at the upper part in order to mix the gases discharging from the black mass BM during the heating to the combustion chamber 89 of the boiler 82. Fluegases formed during roasting operation are allowed to mix with flue-gases formed during wood chip combustion.

The length of the combustion chamber of the boiler 82 is about 4 meters and the normal combustion temperature is maintained at 700 - 800 °C in the boiler 82. The feeding velocity of the screw 84 is adjusted to be such that the temperature of the alkaline black mass BM is over 500 °C 15 to 20 minutes. Treatment time determination may be based on zero emission exhaust gas measurement, for example. In other words, when no emission from the black mass BM is determined the heat treatment 101.1, 202, 302 has been performed enough.

After heating the raw material 56 is supplied from the furnace to the cooling 85. In that its temperature is lowered to about 50 °C and it can be moved to further processing. After the reaction roasted black mass 56 still contains residual heat energy, which can be collected to district heating water 55.1, 55.2 with heat exchanging box 54 after mass exits screw conveyer 84. Due to the thermal expansion the channel being inside the boiler 82 can be a floating structure and closed from opposite ends in order to avoid the flow of air to the boiler 82 and so to keep the boiler 82 underpressurized. Exhaust gases of the oven 51 are extracted out using an injection flue gas fan allowing fresh air to flow in to the oven 51 from the opposite end relative to the feed of alkaline black mass BM. Free air flow into the oven 51 (air pressure 1013 hPa). This is one way to implement the oxidation process in air atmosphere.

Neutralised, i.e. pH adjusted manganese- and zinc-containing solution (MnSO₄ and ZnSO₄) can be stored in liquid form, precipitated as metal hydroxides by altering pH to higher level or crystallized as metal sulphate by evaporating by vacuum assisted heating. Solid hydroxide and sulphate products can be packed in tens of kilograms plastic bags. In liquid form content of manganese may be 150-80 g and zinc 100-40 g I one liter. pH of the solution can also be elevated in which case Mn- and Zn precipitates as an oxidic or OH form.

The manganese- and zinc-containing sulphate solution 17 can be utilized as micronutrients in fertilizers or used as such to aid growth and health of plants. The solution 17 may be mixed with plant-protective agent and spread to the field with that. Owing to that one extra work stage may be avoided. The suitable amount of the solution 17 in agriculture may be 2 to 5 liter per hectare.

In addition to the methods the present invention concerns also a device 51 for preprocessing alkaline black mass BM of spent alkaline batteries. An example of the device has been presented in Figure 6. The alkaline black mass 56 pre-processed with the device is suitable for a leaching process C to recover one or more metals from the preprocessed black mass 56. In the pre-processing A by means of the device an alkalinity of the alkaline black mass BM is reduced, among others. The device is a heat treatment device 51. The heat treatment device 51 and/or control means 11 of the heat treatment device 51 is arranged to implement one or more method steps described earlier in this application.

The present invention concerns also a system for processing alkaline black mass BM of spent alkaline batteries. An example of the system has been presented in Figure 5. The system includes pre-processing means of the alkaline black mass BM to pre-process alkaline black mass BM in a pre-processing stage A, leaching means 62 to leach the preprocessed alkaline black mass 56 with one or more acidic solutions 12, 13, 25, 26 in order to produce a leach solution 14 in leaching process C and further processing means 63 to produce one or more products 17 from the leach solution 14 in further processing D. The pre-processing means include a heat treatment device 51 of alkaline black mass BM described earlier in this application and applied in the pre-processing stage A.

The skilled person understands that the implementation of the system may be carried out by means of suitable tanks 62 and/or reactors 51, pumps and pipelines between the tanks and/or reactors arranged in a principle presented in Figure 1 and also in Figure 5.

Claims (11)

A method for processing black mass of spent alkaline batteries, wherein: - pretreating the black alkaline mass (BM) (A) to lower the pH of the alkaline black mass (BM) for leaching (C), - the pre-treated alkali mass (56) is dissolved (C) with one or more acidic solutions (12, 13, 24, 25, 26) to form a leach solution (14), one or more products (17) being prepared from a leach solution (14), characterized in that said pretreatment (A) comprises a heat treatment process (101.1, 202, 302) of alkaline black mass (BM) carried out under oxidizing conditions to oxidize the substances in alkaline black mass (BM). Method according to claim 1, characterized in that the heat treatment (101.1, 202, 302) is carried out by supplying air (91) to the heat treatment process (101.1,202, 302). Method according to one of the preceding claims, characterized in that in the heat treatment process (101.1,202, 302), the alkaline black mass (BM) is mixed with air (91). Method according to one of the preceding claims, characterized in that the process device (51), in which the heat treatment process (101.1, 202, 302) of the alkaline black mass (BM) is carried out, is a rotary kiln, a drum (20) or a heated screw (84). Method according to one of the preceding claims, characterized in that the process device (51) in which the heat treatment process (101.1, 202, 302) of the alkaline black mass (BM) is carried out is indirectly heated. Method according to one of the preceding claims, characterized in that the temperature of the alkaline black mass (BM) in the heat treatment process (101.1, 202, 302) is raised to a range of 350 to 800 ° C, and more preferably to a range of 400 to 700 ° C. Method according to one of the preceding claims, characterized in that the residence time of the alkaline black mass (BM) in the heat treatment process (101.1, 202, 302) is 15 to 60 minutes, for example 20 to 40 minutes. A process according to any one of the preceding claims, characterized in that the pretreated alkaline black mass (56) is screened (204, 304) before the leaching process (C) and a reducing agent such as citric acid (13) is added to the pretreated alkaline black mass (56). (C). Process according to any one of the preceding claims, characterized in that Process (C) is performed as a one-step process comprising at least two sub-steps in which - in the first sub-step, the pretreated alkaline black mass (56) is dissolved in the presence of a reducing agent (13) and water (94), - in the second sub-step, the dissolution is continued from the first step by adding the second solvent (12) to the dissolution process (C). Method according to one of the preceding claims, characterized in that - adjusting the pH of the leaching solution (14) in the range pH = 2 to pH = 4, - from the leaching solution (14 *) a manganese and zinc sulphate solution is prepared 15 (17), which is suitable as a trace element in fertilizers or as such to assist plant growth and health. Use of one or more products obtained by the process of any one of the preceding claims as trace elements in fertilizers or as such for plant growth and health. 20 help.