Field of Invention

The present invention generally relates to a method for recycling spent lithium-ion batteries. More particularly, it relates to a method for removal of impurities from a leaching solution of spent lithium-ion batteries.

Background

Lithium-ion batteries contain valuable precious metals which would go to waste when the batteries are spent and discarded. With the rising use of lithium-ion batteries, the recovery of precious metals from spent lithium-ion batteries have become an important industry.

Typically, spent lithium-ion batteries are dismantled, crushed, or shredded to form a black mass to prepare them for recycling. Current lithium-ion battery recycling efforts are often primarily focused on recovering the precious metals cobalt and lithium from lithium cobalt oxide cathodes. However, there are many other types of cathode materials used in lithium-ion batteries. A significant portion of these cathode materials include other precious metals such as nickel and manganese. Conventional recycling methods do not adequately handle the recycling of different types of lithium-ion battery cathode materials and fail to sufficiently address the extraction of these other precious metals.

Further, black mass, especially those derived collectively from different types of lithium-ion batteries contains many types of impurities. Failing to effectively remove them adversely affects the purity of precious metals recovered from recycling. Present efforts of impurity removal involve numerous steps requiring many reactors and filters. Not only does this lengthen the entire recycling process, but with each reactor or filter, valuable material is lost along the way resulting in a severe reduction in the amount of precious metals available for recovery.

Thus, there exists a need for a lithium-ion battery recycling process which can better handle the removal of impurities in black mass, especially that derived collective from different types of lithium-ion batteries. There also exists an associated need to remove impurities in a more efficient way that requires less equipment and results in less reduction in the amount of precious metals available for recovery.

The invention seeks to answer these needs. Further, other desirable features and characteristics will become apparent from the rest of the description read in conjunction with the accompanying drawings.

Summary

In accordance with the present invention, a method of treating a leaching solution derived from a black mass is provided. The method comprises setting pH of the leaching solution to about pH 1 .2 to 2.15, adding iron powder to induce copper cementation, adding lime after copper cementation, and after adding lime, transiting pH of the leaching solution to about pH 6 to extract calcium fluoride, titanium hydroxide, aluminium hydroxide, iron hydroxide, and iron phosphate. Preferably, about 2.5g of iron powder is added for each litre of the leaching solution. More preferably, the iron powder may be added over a period of about 15 minutes. Preferably, the lime is calcium oxide and about 20-40g of calcium oxide is added for each kg of black mass. Alternatively, the lime is calcium hydroxide and about 30-60g of calcium hydroxide is added for each kg of black mass. Preferably, the leaching solution is derived from the black mass by leaching the black mass with sulfuric acid and hydrogen peroxide. Preferably, the sulfuric acid is 4M sulfuric acid, and about 6 litres of sulfuric acid is added for each kg of the black mass. Preferably, about 50ml of hydrogen peroxide (30% concentration) per litre of solution is added. Preferably, the sulfuric acid and hydrogen peroxide are added in consecutive order. The method may further comprise agitating the black mass, sulfuric acid, and hydrogen peroxide for a period of 1 hour. The method may further comprise diluting the sulfuric acid to 2M by adding deionised water after the period of 1 hour.

In another aspect, a black mass recycling system is provided. The black mass recycling system comprises an impurity removal reactor configured to receive a sodium hydroxide feed, an iron powder feed, and a lime feed. Preferably, the black mass recycling system may fiirther comprise a leaching reactor configured to receive a sulfuric acid feed, a hydrogen peroxide feed, and a deionised water feed, and a first valved outlet associated with the leaching reactor providing fluid communication between the leaching reactor and the impurity removal reactor. More preferably, the black mass recycling system may further comprise an impurity removal agitator provided within the impurity removal reactor, and a leaching reactor agitator provided within the leaching reactor.

Brief Description of Drawings

Fig. 1 is a process flow diagram of a process of leaching and removal of impurities.

Detailed Description

In the following detailed description, reference is made to the accompanying drawings which form a part hereof. The processes and systems described in the detailed description and drawings are for illustrative purposes and are not meant to be limiting. Other embodiments can be utilised, and other changes can be made, without departing from the scope of the disclosure presented herein. In the present disclosure, the depiction of a given element or consideration or use of a particular element number in a particular Fig. or a reference thereto in corresponding descriptive material can encompass the same, an equivalent, or an analogous element or element number identified in another Fig. or descriptive material associated therewith.

Black mass is poured from its holding container 100 into a first reactor, namely a leaching reactor, 102. The black mass may collectively include lithium-ion batteries with cathodes made from lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), lithium nickel cobalt aluminium oxide (NCA), and lithium titanate (LTO). As a result, the black mass comprises impurities of iron, copper, fluorine, phosphorous, titanium and aluminium.

In the first phase of leaching, an inorganic acid, preferably sulfuric acid (H ₂ S0 ₄ ), provided from an inorganic acid source 110 is added to the black mass in the first reactor 102, forming a solution. Preferably, a proportion of about hydrochloric acid subject to adjustments to quantities of the reagents described below which should be apparent to a skilled person.

Hydrogen peroxide (H ₂ 0 ₂ ), preferably about 50 ml of hydrogen peroxide (30% concentration) per litre of the solution, is provided to the contents of the first reactor 102 from a hydrogen peroxide source 112 to facilitate leaching as a co-digestant. The contents of the first reactor 102 undergoes agitation by an agitator 132, preferably for about 1 hour. During the first phase of leaching, the sulfuric acid increases the availability of sulfate ions (SO ^2- ) which react with iron present in the black mass to form ferrous iron (Fe ²⁺ ). The hydrogen peroxide then oxidises the ferrous iron (Fe ²⁺ ) to ferric iron (Fe ³⁺ ). The ferric iron then reacts with the sulfate ions to produce iron sulfate (Fe ₂ (S0 ₄ ) ₃ ).

In the second phase, deionised water is added into the first reactor 102 from a deionised water source 114 to dilute the sulfuric acid in the first reactor 102, preferably to about 2M. Agitation of the contents of the first reactor 102 is maintained by the agitator 132 for about 30 minutes.

During both the first and second phases of leaching, the temperature of the contents in the first reactor 102 should be maintained at 70-90°C. A skilled person should readily understand that the amount of sulfuric acid, hydrogen peroxide and deionised water may be adjusted according to the amount of black mass processed.

After the first and second phases of leaching, the leaching solution from the first reactor 102 is released via an outlet valve 136 and transferred into a second reactor 104 by way of a pump 142. The following describes the processes of removing the impurities copper, fluorine, phosphate, iron, titanium, and aluminium from the leaching solution in the second reactor 104, during which the contents of the second reactor 104 are continually agitated by an agitator 134.

Sodium hydroxide (NaOH) from a sodium hydroxide source 116 is added to the leaching solution in the second reactor 104 to set the pH of the leaching solution at a value of about pH 1.2 to 2.15. Iron (Fe) powder is added from an iron powder source 118, preferably about 2.5 g of iron powder per litre of leaching solution, to the leaching solution over about 15 minutes while maintaining the temperature of the contents of the second reactor at about 60°C. Capitalising on the reductive capacity of ignoble metals on noble metal ions according to the electromotive force series (i.e., voltage gap between two half-cell reactions corresponds to higher propensity of reaction from a thermodynamic and electrochemistry standpoint), the iron powder will react favourably with copper in the leaching solution, leading to the cementation of copper:

Fe + Cu ²⁺ -» Fe ²⁺ + Cu

Graph 1. The effect of pH on copper cementation over time.

Graph 1 records the effect of copper cementation over a period of 60 minutes as a result of setting the pH of the leaching solution at 1.2, 2.15 and 3.07 respectively. The concentration of copper in the leaching solution is taken and computed to give a copper removal percentage during the period of 60 minutes as follows:

Initial concentration of copper — final concentration of copper Initial concentration of copper

It is observed that setting a pH of 1.2 or 2.15 results in the cementation of about 90% of copper in the leaching solution, that is, copper removal. When the pH is set at 3.07, cementation of copper in the leaching solution drops to below 80% over the same period.

The sulfuric acid and hydrogen peroxide added from the first phase of leaching in the first reactor 102 forms part of the contents of the second reactor 104. The hydrogen peroxide oxidises the ferrous iron (Fe ²⁺ ) formed during copper cementation to ferric iron (Fe ³⁺ ). The ferric iron reacts with the sulfate ions to produce iron sulfate (Fe ₂ (S0 ₄ ) ₃ ).

Some fluoride may be removed during the leaching process in the first reactor 102, but sufficiently undesirable and toxic amounts which may result in capacity attenuation of lithium-ion batteries that may eventually be produced will remain as fluoride ions in the leaching solution transferred to the second reactor 104. Lime is added from a lime source 120 to the contents of the second reactor 104, preferably about 20-40g of calcium oxide or about 30-60g of calcium hydroxide per kg of the black mass previously added into the first reactor 102. After the addition of lime, the contents of the second reactor 104 is left to rest (with continued agitation) for a period of about 30 minutes at about 40°C. Lime should be added only after the iron powder has completed the cementation of copper from the contents of the second reactor 104 to avoid the lime interfering with the capacity of the iron powder to induce copper cementation.

After the rest period of about 30 minutes, more sodium hydroxide is added to the second reactor 104 to transition the pH of its contents to about pH 6. The pH transition triggers precipitation of the other impurities (fluorine, iron, phosphorus, titanium, and aluminium) in the leaching solution transferred from the first reactor 102 to the second reactor 104. From about pH 2.2, fluoride starts to precipitate as calcium fluoride (CaF ₂ ):

CaO + 2HF -» CaF ₂ (s) + H ₂ 0

Graph 2. The effect of pH on fluoride concentration in solution.

Graph 2 records the concentration of fluoride in the leaching solution that started at an initial concentration of 650 mg/1 after 60 minutes at pH 2.27, 3.12, 4.06 and 5.24 respectively. It is observed that the concentration of fluoride is reduced consecutively and significantly at pH 3.12, 4.06 and 5.24, while the concentration of fluoride is not as significantly reduced at pH 2.27.

As the pH of the contents of the second reactor 104 rises to about pH 3, the sodium hydroxide causes iron ions, whether originally in the leaching solution or added for copper cementation, to precipitate as iron hydroxide. The remaining iron that is not precipitated as iron hydroxide reacts with phosphate ions ( P0 ₄ - ) in the contents of the second reactor 104 to precipitate as iron phosphate (FeP0 ₄ ).

Table 1. The effect of pH on iron (Fe) and Phosphorus (P) precipitation

Table 1 records the percentage of iron and phosphorus originally existing in the leaching solution which were precipitated as iron phosphate at pH values between pH 2.5 to 4.5 over 60 minutes. It is observed that precipitation occurred from pH 3 and increases at each pH value observed through to pH 4.5 where essentially all iron and phosphorus which existed in the leaching solution were precipitated.

As the pH of the contents of the second reactor 104 rises to and exceeds pH 4, the hydrogen peroxide which was added in the first reactor 102 and transferred in the leaching solution to the second reactor 104 pushes the oxidative states of titanium and aluminium to titanium (V) and aluminium (III) respectively, thus initiating precipitation of their hydroxides Ti(0H) ₄ and A1(OH) ₃ .

Once the pH reaches about pH 6, the contents of the second reactor 104 is left to rest (with continued agitation) for about 60 minutes at about 60°C. After the period of 60 minutes, the contents of the second reactor 104 is released from the second reactor 104 by an outlet valve 138 and is passed through a filter 148 to remove copper and the precipitates (calcium fluoride, iron phosphate, iron hydroxide, titanium hydroxide, and aluminium hydroxide), thereby removing a significant amount of the impurities that originally existed in the black mass. Graph 3. The effect of pH on the iron, aluminium and titanium concentration.

Graph 3 records the concentration of aluminium, iron and titanium in the leaching solution that started at an initial concentration of 2.26, 0.2, and 1.1 g/1 respectively after of a period of 30 minutes at pH 3.21, 4.16, 5.08 and 6.12 respectively. The concentration of aluminium, iron and titanium in the leaching solution is taken and computed to give a removal percentage after the period of 30 minutes as follows:

/ Initial concentration — final concentration \ ( \ - 7 I-n^itia-l; - concentrati : -on / I X 100

It is observed that the concentration of aluminium, iron and titanium reduced significantly at pH 4.16, 5.08 and 6.12 compared to pH 3.21.

The leaching process in the first reactor 102 and precipitation reactions in the second reactor 104 take about 3-4 hours in total, at the end of which less than 10mg/l of impurities from the black mass remains in the contents of the second reactor 104.

While various aspects and embodiments have been disclosed herein, it will be appreciated by a person skilled in the art that several of the above-disclosed structures, parameters, or processes thereof, can be desirably modified, adapted and combined into alternative structures, processes and/or applications. It is intended that all such modifications, alterations, adaptations, and/or improvements made to the various embodiments that are disclosed come within the scope of the present disclosure. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope of the disclosure being indicated by the following claims.