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Mining and recycling of metals
Raw materials criticality
In his very recent study, Guillaume Pitron alarms us that the world will have to double the production of rare metals every 15 years to support the change in our energetic model. This will imply the extraction of more ores during the next 30 years than during the past 70 000 years.7 Furthermore, the variety of metals used in technologies is highly increasing. While only seven metals were used between ancient history and Renaissance (Au, Cu, Pb, Ag, Sn, Hg and Fe), about 20 were extracted during the XXth century. Nowadays, the entire 84 primordial elements of the Mendeleïev table are part of the manufacture of modern technologies.7,31 Similarly to most of all natural resources, the tremendous increase in the production of metals already creates some geopolitical conflicts. 32 In order to identify the risks many countries were facing regarding specific pivotal systems using metals (e.g. energy supply, defense, communication…), the notion of criticality was introduced. Several methodologies33,34 were used to calculate the criticality of metals. They have been nicely reviewed by Erdmann and Graedel.35 According to seven academic papers on the subject, they were able to define the criticality rate as the number of criticality designation on the number of studies. This diagram is displayed in Figure I.8.
On the eight different metals used in NiMH battery electrodes (Ni, Mn, Co, Al, La, Ce, Pr, Nd), all of them have been described at least once as a critical element. Furthermore, cobalt and rare earth elements are described by 50 and 100 % of the studies respectively as being critical metals.
In 2010, the European Commission identified that the availability of metals was under pressure and asked a college of experts to build a report on “Critical raw materials for the EU”.36 This report stands as a warning towards European governments and a manifest for the need to build strong policies to tackle this issue. Depending on the economic importance and the supply risk of each element, they pointed out a list of 14 so-called critical raw materials:
Table I.3. List of critical raw materials from the EU level 2010. Platinum Group Metals: platinum, palladium, iridium, rhodium, ruthenium and osmium. Rare Earth Elements: yttrium, scandium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.
Following this work, the European experts expressed eight recommendations. The first one was to have an update of those data every five years maximum. A report was thus published in 201437 excluding tantalum and adding borates, cocking coal, chromium, magnesite, phosphate rock and silicon metal to the list. Very recently, in 2017 the last updated report from the EU38 added bismuth, hafnium, scandium and vanadium to the list.
Challenges for transition metals: the case of cobalt
Generalities
Transition metals were defined by IUPAC as: “an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub – shell.”39 They actually include most elements from group 3 to 11 of the Mendeleïev table excluding lanthanides and actinides. Manganese is the third most abundant transition metal after iron and titanium. Around 17 million tons of metal are extracted from the grounds of South Africa, China and Australia mainly. This element exists under several oxidation numbers, mainly (II), (IV) and (VII). The vast majority of manganese is used in alloys such as steel.40,41 Aluminum is widely used for its anti-corrosion and mechanical properties in transport manufacture, packaging, construction material, electronics… It is the third most abundant element in the earth’s crust. It can be oxidized to its third oxidation state. More than 50 % of the extraction of aluminum takes place in China.40,41 Nickel is used for a wide range of applications such as anticorrosion material, catalyst, coins, battery electrodes and in various alloys. The production is now over 2 million tons per year. The main producers are Philippines and Russia. It is however interesting to notice that France extracts about 7 wt. % of the nickel production thanks to its mines in New Caledonia.36,40,41 It mainly exists under the oxidation state (II).
Cobalt exhibits chemical properties similar to nickel. It exists under two main oxidation states, (II) and (III). Cobalt is a byproduct of the mining of nickel and copper. Extraction takes place at more than 60 % in the Democratic Republic of Congo. The world production is estimated to be close to 120 000 tons per year.40–42
According to data collected in Info Mine41 the price evolution within 4 years of these 4 transition metals is expressed in Figure I.9.
Figure I.9. Price of transition metals contained in NiMH battery electrodes from 2014 to 2018 expressed in US dollars per kilogram (USD/kg). The red and green curves express the decreasing or increasing price respectively within 4 years. A: manganese. B: Nickel. C: Aluminum. D: Cobalt. Manganese and aluminum are sold at prices 7 times lower than that of nickel and over 40 times lower than that of cobalt. Furthermore, the amount of Mn and Al in a NiMH battery is very low which makes them less interesting to recycle. Nickel being the major element in NiMH battery, it needs to be recovered, but no tension is to be seen on the market as its price seems stable within 4 years. This is not the case of cobalt which price has more than tripled from 2014 to 2018.
Extraction process of cobalt
Extraction techniques of cobalt depend on the nature of the ores processed. Co can be found under the form of arsenide (Morocco), oxide (New Caledonia) or more frequently sulphide in RD Congo. According to several books and reviews from Hannis et al.43 and Crundwell et al.44 the extraction procedure is performed in five main steps. (i) Ores are mined and crushed before being treated (ii) Leaching step is performed using concentrated sulphuric acid at high pressure (4.4 Million Pa) and temperature (250 °C). (iii) A washing and decanting step leads to metal concentration in the liquid phase. (iv) Copper and iron are precipitated out from the sulfuric medium with ammonia. (v) Nickel and cobalt are finally separated using solvent extraction techniques or electrowinning.
Tension towards cobalt mining
Defined as a critical material by the scientific community35–38, identified as having a very volatile price,41 cobalt is the center of numerous geopolitical tensions. Several parameters can explain this phenomenon.
First of all cobalt is used in many battery technologies, including NiMH electrodes and Li-ion cathodes21. The needs of cobalt for energy storage are thus dramatically increasing as expressed by the following figure.
As an example, the Li-ion battery developed by the famous brand Tesla weights 544 kg (data for Model S).45 This represents 25 wt. % of the car and about 80 kg of cobalt to get 500 km of autonomy.7 Furthermore, Elon Musk, the CEO from Tesla recently announced to the American channel CNBC that he will be able to reach an autonomy of 800 km with his new battery design (Millions of Teslas, 500-miles range coming) by consuming more raw materials.46 Recently, Nicolas Hulot, the French Minister of the ecological transition declared that he was aiming at the end of the diesel and oil cars on the market by 2040.47 Since more than 39 Million cars are used in France,48 the amount of cobalt needed to power these vehicles is already beyond comprehension.
Second, the mining industry is concentrated in one country. RD Congo is the center of many conflicts and the potential of war in the region strongly affects the supply chain of cobalt et vice versa42 As a result companies are stockpiling huge amounts of metal replacing the zero stock and just in time strategies by safer and more expensive economic models.49,50 Furthermore, even if RD Congo is the main country exploiting cobalt, more than 80 % of this metal is refined by China. Indeed, Chinese companies are strongly present in the eastern part of the country creating a new monopoly. As an answer, the Congolese government recently signed a new law in order to increase its mining royalties.51
Consequences of such policies lead to a strong volatility on the cobalt price and are already destabilizing the battery industry.
Despite the situation with cobalt, as described by the European commission in 2010,36 201437 and 201738 the most critical metals found in NiMH batteries are the Rare Earth Elements (REE).
Rare Earth Elements as highly critical raw materials
Hidden twins
Rare Earth Elements are defined by IUPAC39 as the 15 lanthanides elements (lanthanum to lutetium) as well as scandium and yttrium. They can be divided in two main categories: light REE (lanthanum to samarium) and heavy REE (europium to lutetium plus yttrium and scandium).52 The distinction between light and heavy REE varies from one review to another as no official definition exists. As far as we are concerned, our focus will be on the light Rare Earth Elements lanthanum, cerium, neodymium and praseodymium, present in NiMH batteries. Their names are either linked to the mythology (cerium was named from Ceres, the Roman Goddess of agriculture) or from their discovery. The origin of lanthanum is linked to the Greek etymology of the word “hidden” because La was considered to be cerium oxide for a long time. This confusion also existed with Pr/Nd. While, praseodymium stands for the “the green twin” because it exhibits a green color in a large range of salts, neodymium can be translated in “the new twin” because Pr/Nd were undifferentiated for years.
These designations are perfectly accurate to define light REE. They are present i n relatively high concentrations in the earth crust. Cerium is for example as abundant as copper ranging in a concentration of 48ppm.53 However, due to their close physicochemical properties, they are extremely difficult to extract and overall to isolate which justifies the denomination rare or hidden. All of them can be found under the third oxidation state except from cerium that can also be stable after oxidation in the fourth oxidation state. The coordination number for lanthanum(III), cerium(III), praseodymium(III) and neodymium(III) is similar between most light REE and reaches a value of 9 in water.54 A decrease of the ionic radius of elements from lanthanum to lutetium can be observed. This phenomenon is known as the lanthanide contraction. REE can be characterized by 4f electrons who present a small shielding effect of the nuclear charge. This shielding effect is decreasing within the following series: s > p > d > f. As a result, the higher the nuclear charge, the higher the attracting effect on electrons and the lower the ionic radius.55 However the difference in the ionic radius between the larger and the smaller cation, lanthanum and neodymium respectively is of 0.06 Å. This small difference can thus hardly be used for the separation of light REE and justifies the denomination of twins. Properties of La, Ce, Nd and Pr are described in Table I.4.
Nature of the ores
The nature and concentration of the main Light REE ores are depicted in of the total REE amount. The presence of actinides in monazite is a further huge issue as high amounts of radioactive wastes are produced during the ore processing. This is also the case for loparite. This ore is however lucrative because of the presence of niobium, another critical metal. Bastnaesite contain s lower but non-negligible amounts of thorium and uranium.
Generally, 1 ton of ore only produces between 10 and 80 kg of REE while it is consuming 200 m3 of water.7 It is important to point out that the variety of ores is large and some of them can be more concentrated in La, Ce or even Nd. For example, monazite-(Nd) is known to contain 30 wt. % of neodymium.
Applications of REE: the balance problem
Close to 30 kg of light REE can be found in a NiMH battery coming from a Toyota Prius HEV.56 26 wt. % of the production of lanthanum is devoted to the latter energy storage device. However, La is also used for catalytic converters (44 wt. % of the production) and in specific optical glasses57 found in microscopes or telescopes. This is not the case for praseodymium and neodymium which are mainly used for magnet production. 53 % in value of the whole REE industry is dedicated to magnets.56 They can be used to produce energy in wind turbines, to power cars in electric engines or even to store data in hard drives. 58 They can also be found in highly strategic applications such as guided missiles. 7
Table of contents :
INTRODUCTION
I. CHAPTER I STATE OF THE ART
I.1 PRESENTATION OF THE NIMH BATTERY
I.1.1 A historical overview of the energy sector
I.1.2 The battery devices, from performance to market
I.1.3 The NiMH technology
I.2 MINING AND RECYCLING OF METALS
I.2.1 Raw materials criticality
I.2.2 Challenges for transition metals: the case of cobalt
I.2.3 Rare Earth Elements as highly critical raw materials
I.3 IONIC LIQUIDS AS GREENER SOLVENTS
I.3.1 Definition
I.3.2 Structure
I.3.3 Properties and application
I.4 RECYCLING NIMH BATTERIES
I.4.1 Overview
I.4.2 Leaching and precipitation
I.4.3 IL-based Liquid-liquid extraction
I.4.4 IL-based Aqueous Biphasic Systems (ABS)
I.4.5 Electrodeposition in ionic liquids
I.5 SPECIFICATION OF THE STUDY
II. CHAPTER II SEPARATION OF TRANSITION METALS FROM RARE EARTH ELEMENTS
II.1 INTRODUCTION
II.2 PREPARATION AND MECHANICAL TREATMENT OF NIMH BATTERIES
II.2.1 Laboratory scale black mass production
II.2.2 Industrial scale black mass production
II.3 LEACHING
II.3.1 Preliminary tests with an ideal black mass
II.3.2 Leaching NiMH black mass produced at Recupyl®
II.3.3 Possibilities and limitations of using hydrophilic ILs in leaching process
II.4 SELECTIVE PRECIPITATION
II.5 CONCLUSION
III. CHAPTER III SEPARATION OF CERIUM, LANTHANUM, NEODYMIUM AND PRASEODYMIUM
III.1 INTRODUCTION
7 | Introduction
III.2 SEPARATION OF CERIUM FROM LANTHANUM, NEODYMIUM AND PRASEODYMIUM SULPHATE SALTS
III.2.1 Introduction
III.2.2 Oxidation of Ce(III) in alkaline conditions
III.2.3 Liquid-Liquid extraction of Ce(IV) by ILs
III.2.4 Conclusion
III.3 RECOVERY OF CERIUM FROM SPENT NIMH BATTERIES
III.3.1 Extraction of cerium in spent NiMH batteries
III.3.2 Electrodeposition of cerium in an ionic liquid: an alternative recovery strategy
III.4 TOWARDS THE SEPARATION OF NEODYMIUM FROM LANTHANUM
III.5 CONCLUSION
IV. CHAPTER IV SEPARATION OF COBALT, NICKEL, MANGANESE AND IRON
IV.1 INTRODUCTION
IV.2 DICYANAMIDE IONS AS COMPLEXING AGENT OF COBALT: FROM WEAK LIGANDS IN WATER TO STRONG ONE IN IONIC LIQUIDS
IV.2.1 Introduction
IV.2.2 Construction and fitting of a complexation model
IV.2.3 Co-DCA complexes in water
IV.2.4 Co-DCA complexes in ionic liquids
IV.2.5 Cobalt extraction by dicyanamide-based ionic liquids
IV.2.6 Conclusion
IV.3 NOVEL IONIC LIQUID-BASED ACIDIC AQUEOUS BIPHASIC SYSTEMS (ACABS): FROM FUNDAMENTALS TO METAL EXTRACTION
IV.3.1 Introduction
IV.3.2 Fundamentals of Acidic Aqueous Biphasic System
IV.3.3 Acidic Aqueous Biphasic systems for metal extraction
IV.3.4 Recovery of cobalt by electrodeposition in ABS-AcABS
IV.3.5 Conclusion
IV.4 SEPARATION OF TRANSITION METALS FROM SPENT NIMH BATTERIES
IV.4.1 Introduction
IV.4.2 Inducing an AcABS from leachate solutions: A versatile process
IV.4.3 Conclusion
IV.5 CONCLUSION
V. CONCLUSION AND PERSPECTIVES
VI. REFERENCES
VII. ANNEX
