1. Introduction
1.1. Background of the study
Over the last decade, rare earth elements (REEs) have gained international attention due to their multiple usages [1]. Because of their unique properties, the elements play a vital role in electronics, defense, aerospace, transportation, agriculture, and communications technology [2,3]. They are also critical to the high technology and low carbon economy [1]. These applications drive demand for rare earth products and promote the steady development of the rare earth industry [4].
Production of REEs is increasing tremendously. Demand for REEs is expected to increase more than 3 to 7 times between 2020 and 2040 [5]. China has the major share of REE production globally. With increasing global demand, a significant amount of energy, chemicals, and water are used for the processing of REEs, including many challenges [6]. Historically, the crisis of REEs in 2010, caused by China's monopoly over the majority of production, posed a challenge to change the industry rules worldwide, and various organizations contributed to this issue. Including lower prices, opening new mines, curtailing black markets, reducing environmental and social harm, and ensuring supply chain security are major steps that have been attempted after the crisis [7].
The use of rare earth elements in industrial settings is rapidly increasing, with serious consequences for the environment and human health in the form of compounds or metals. These anthropogenic compounds end up in the soil and water through waste disposal, mining operations, wastewater treatment, and emissions into the atmosphere [8]. The process of separating rare earth elements (REEs) is challenging, and the increasing use of technological devices has raised concerns about sustainability, which has recently received more attention [9].
Global demand for rare earth elements (REEs) is expected to rise, requiring increased production and recycling efforts. Financial constraints, inefficient collection systems, high costs, and a lack of efficient techniques, on the other hand, prevent widespread recycling of REEs from used consumer goods and industrial waste [10-12]. REE recycling from end-of-life (EOL) consumer goods or industrial wastes is currently very limited, largely because of the challenging economics [3]. The most effective recycling strategy of REEs involves minimizing waste generation, reusing minimized materials through recycling and energy recovery processing, and disposing of waste properly with appropriate treatment [13].
This paper presents a global literature review covering the current scenario, impacts, challenges, recycling, and development related to Rare Earth Elements (REEs). Building on the insights from the global literature, we will subsequently discuss the situation in Bangladesh concerning the impacts of REE issues, suggestions for recycling processes from the recent literature, and recommendations for the future.
1.2. Overview of REEs
The most significant components in today's world, which are essential to science and technology, are rare earth elements. The International Union of Pure and Applied Chemistry (IUPAC) classifies 15 lanthanide elements, along with Y and Sc, as rare earth elements in the periodic table. Table 1 contains a list of the rare earth elements with abundance. They share similar physical and electrical characteristics despite not being members of the same group (Y and Sc).
All of the REEs are found in nature, though not in their pure metal form. However, the rarest one, promethium, is only present in very minute quantities in natural materials because it lacks stable or long-lived isotopes [20]. As the atomic number rises in the lanthanides series, the 4f orbitals in lanthanide atoms gradually fill up, but the arrangement of the valence electrons in the outermost shell is constant across all elements. The screening of the 4f orbitals led to the incredibly similar physical and chemical characteristics of the elements [21]. Another related effect is the so-called “lanthanide contraction” (Figure 1), which is characterized by a gradual decrease in the ionic radius from La3+ (1.06) to Lu3+ (0.85) [22]. REEs typically exist in the trivalent oxidation state and have similar chemical properties, with the exception of two special REEs such as cerium and europium, which occur as Eu2+ and Ce4+, respectively [23]. The two main categories into which the REEs are divided are the light rare earth elements (LREEs) and the heavy rare earth elements (HREEs). The LREEs are the elements with atomic numbers between 57 (Lanthanum) and 63 (Europium), while the HREEs are those with atomic number between 64 (Gadolinium) and 71 (Lutetium) plus Y. Yttrium (39) is included as HREE due to its chemical similarities, where Scandium (21) forms a group in itself as its properties cannot be classified as either a LREE or HREE [136].
REEs are found in different kinds of mineral forms such as oxides, carbonates, silicates, phosphates, and halides, and the 169.1 ppm total REE abundance found in the Earth's crust is made up of 31.3 ppm of HREEs and 137.8 ppm of LREEs [25]. So REEs are not as uncommon as their name might suggest. When compared to other commonly used elements and their respective chondritic abundances, the estimated average concentration of REE in the Earth's crust, which ranges from about 130 μg/g to 240 μg/g, is actually significantly higher [26]. The abundance of some LREEs is comparable to that of some of the most used industrial metals, such as Lead, Tungsten, Chromium, Nickel, Copper, or Zinc. For instance, the abundance of Ce (60–70 ppm) is nearly equivalent to the abundance of copper in the Earth's crust [27].
2. Applications of REEs
Rare Earth Elements (REEs) are increasingly vital in the development of modern technology, especially as global industrialization continues to rise. These elements are key to advancing technology and ushering in a new era in electronics. REEs are widely used as catalysts and play crucial roles in ceramics, glass production, and polishing, among other applications (Figure 2 and Figure 3).
Many everyday items (Table 2), such as computer memory, DVDs, rechargeable batteries, cell phones, and solar panels, contain rare earth metals or their alloys. In electronics, their strong magnetic properties make them essential for producing magnets used in hard drives, speakers, and electric motors, with elements like neodymium, praseodymium, and dysprosium being particularly important [22,28,29]. In defense and aerospace technology, REEs are incorporated into communication devices, night-vision goggles, radar systems, and precision-guided weapons [30]. In agriculture, the concentration of REMs in the soil is further increased by the use of REEs as fertilizers to increase crop growth and yield. Low concentrations have beneficial effects on agriculture, while higher concentrations have harmful effects on terrestrial plants [31,32].
3. Rare earth elements from global view
3.1. Current Production Scenario
Rare earth elements (REEs), valuable strategic mineral resources as well as essential manufacturing raw materials, are widely used in industries that require high-precision manufacturing on a global scale [33]. The estimated 130 million metric tons of rare earth resource reserves worldwide are primarily located in China, the United States, Russia, Brazil, Thailand, Burma, Madagascar, India, Vietnam, and other nations (2023, USGS [34],). The production of rare earths is clearly unevenly distributed around the world, with China emerging as the main producer. The production of Rare Earth Oxides (REOs) increased from approximately 29,000 to 300,000 tons when comparing the years 2021 to 2022 [34]. China maintains its dominant position, accounting for 70% of the market, followed by the United States (14%) and Australia (6%) (Figure 4). The largest consumer, china holds the highest global share of REOs (>80%) [35]. The current estimates indicate an increasing trend in global demand for REEs (Figure 5).
3.2. Processing of REEs and challenges
The processing of rare earth elements (REEs) is a resource-intensive process that involves considerable energy input, chemical use, and water consumption. Mining and processing operations require significant land allocation, particularly for tailings dams and long-term radioactive waste storage facilities. The physical beneficiation method for minerals containing rare earth elements is determined by the deposit's mineralogy. Since the deposits are typically made of hard rock, the ore must first be ground up in order to release the valuable mineral grains [36-38]. Key separation techniques in REE beneficiation include gravity separation, magnetic separation, electrostatic separation, and froth flotation [39]. Gravity separation is effective in concentrating RE minerals with high value, as many gangue minerals have low specific gravities. Magnetic separation is commonly employed to isolate individual paramagnetic rare earth minerals and ferromagnetic gangue minerals [40].
The mining of REE-rich rocks involves a complex, multi-stage separation process that drives growth in the sector. Figure 6 depicts the technology used to produce REEs. First, various types of separation methods are used to collect the REEs that are contained in minerals. Then, by adding with solution, the cracking process is introduced for chemical leaching. Hydrometallurgical methods like solvent extraction and ion exchange are used to selectively remove the individual elements from the combined REE solution. Depending on the desired end use, the precipitated products can either be sold as pure metal oxides or reduced to pure metal products [36,38].
One of the primary challenges with rare earth elements is their chemical similarity, which makes it difficult to distinguish them both from the surrounding materials and from each other [41,42]. Current manufacturing processes require large quantities of ore and produce significant amounts of toxic waste to extract even small amounts of rare earth metals. This waste often includes harmful substances like radioactive water, toxic fluorine, and acids [43]. Figure 7 highlights the major challenges in REE production.
Geological formation and the rarity of REEs, which indirectly relate to the location of ore deposits, present the greatest challenges for mining and extraction [44]. Furthermore, the use of acid leaching during extraction leads to various environmental issues. The complexities of the supply chain can also introduce geopolitical risks, which, in turn, contribute to energy sensitivities, higher greenhouse gas emissions, and further environmental degradation [45].
3.3. Impact of REEs on Global Perspective
Due to its multiple stages of application in various sectors, REEs are being used more and more frequently around the world. Over the following few decades, it is anticipated that the areas contaminated by REEs deposits will keep growing as REEs exploration, production, and use increase, having a significant negative impact on the environment, animal health, and human health [46].
3.3.1. Mining pollution
Rare earth mining generates a large amount of waste and radioactive pollution, which contributes to environmental instability and has the potential to have a greater impact on biodiversity. According to statistics, the mining process generates 13 kg of dust, 9,600-12,000 cubic meters of waste gas, 75 cubic meters of wastewater, and one ton of radioactive residue for every ton of rare earth produced. In total, 2,000 tons of toxic waste are generated for every ton of rare earth [47]. The challenges of handling this enormous mining waste load can result in economic inflation.
3.3.2. Radioactive waste generation
More radioactive mineral resources include zircon, rare earths, and niobium/tantalum. Their respective average external gamma doses are 5709, 3263, and 1592 nGy/h. These mineral resources contain more than 1000 Bq/kg of U-238, Ra-226, and Th-232 on average [48]. For instance, the Inner Mongolian mine Baiyun Obo has a deposit of rare earth and iron ores. The largest rare earth deposit in China is there. With a concentration of ThO2 of 0.01-0.05% and a concentration of U3O8 of 0.0005-0.002%, the ore is abundant in radioactive elements. Rare earth alloys contain 0.04–0.24% Th, rare earth chlorides contain approximately 0.045% Th, and rare earth oxides contain 0.0069% Th [48,49]. Table 3 shows the natural level of radioactivity in Rare earth elements. Proper disposal of radioactive waste can lead to long-term health risks, including cancer, due to chronic exposure.
3.3.3. Deforestation
Due to the clearing of land for processing in the mining operations and infrastructure, the production of rare earth has significant indirect effects on deforestation. Additionally, the use of chemicals in mining and processing may have an impact on nearby forests or areas, which contributes to environmental degradation [50]. To illustrate, according to a report by the NGO Global Witness, highly toxic rare earth mining has rapidly increased in northern Myanmar, contributing to environmental contamination, deforestation, and violations of human rights [51].
3.3.4. Air pollution
The mining and processing of rare earths can cause air pollution through a number of different mechanisms. Different types of dust, airborne particulate matter, and harmful gases are released into the atmosphere during extraction and processing. In addition to this, the scenario of booming development and transportation also contributes to air pollution. Shen, Yi-Wen, et al. investigated rare earth elements in PM2.5 over a five-year period in an inland Chinese city. Their research revealed that Ce and La contributed the most to the population's overall intake of REEs in PM2.5, followed by La and Nd. The total REE concentration increased over the course of five years, rising from 46.46 ± 35.16 mg/kg (2017) in 2017 to 81.22 ± 38.98 mg/kg in 2021 which is a great concern for cities [52].
3.3.5. Water scarcity and groundwater contamination
The mining, extraction, and refining processes required to produce rare earths demand a large amount of water.The scarcity of water sources can lead to increased demand, worsening the issue and negatively impacting ecosystems. The use of hazardous chemicals, such as acidic compounds and fluorides, can also contaminate groundwater and surface water [53]. Heavy metals, radioactive waste, and other pollutants may be present in the waste produced by these chemicals, which presents a serious risk to the environment and water resources. At the São Domingos mining complex, researchers found that mining mainly rare earth elements increased the pH of neutral freshwaters by 1-2 orders of magnitude. With maximum values of 221.8 and 166.9 μg/L, Y and Ce can also be distinguished at higher concentrations. Generally, concentrations increase as the pH of the water decreases [54].
3.3.6. Soil erosion and contamination
The bioavailability, toxicity, and deficiency of any element are influenced by its unique properties, as well as the soil's capacity to release it from the mineral phase or colloidal fraction. Some rare earth materials, including La, Y, Pr, and Gd, are adsorbed differently depending on the pH scale and CEC. And as pH and redox potential decrease, their availability rises [55,56,57].
Various studies investigated that concentration levels of REEs have impacts on soil erosion. Because of their low mobility, REEs have been found to continuously accumulate in surface soil through a variety of pathways, including atmospheric deposition, sewage irrigation, mining operations, and application of REE fertilizers [58,59,60]. For example, due to integrated industries in metallurgy, rare earth production, and machinery manufacturing, as well as the increasing use of REE salvolatile compound fertilizer and REE-phosphate fertilizer on farmland in Baotou, China's Baiyun Obo, the soils there were seriously contaminated by REEs [61,62].
3.3.7. Impacts on health
REEs have a significant impact on modern technology, but they also have a detrimental effect on people because they release a variety of toxic gases, compounds, and other pollutants during processing and disposal, which contaminate the soil, water, and air and have a negative impact on people's health in the vicinity of the release sites [63,64]. Although the chemicals that are released do not have a significant level of toxicity, their long-term effects can lead to cancer or lung diseases. For instance, researchers investigated that Crystal silica; fine particulate dust has been linked to lung cancer and irreversible interstitial pulmonary disease as an occupational hazard in miners or communities near mining fields [65]. Yin, Xiangbo, et al. reported a list of the main health risks associated with the REE industry and the groups involved as well as planning and control measures [66]. Besides, due to inhalation and dermal contact with REEs that release radioactive exposure such as (U, Th, etc.), there is a risk of pneumoconiosis and neurological effects for workers, nearby residents, and uninformed individuals [67]. Furthermore, snowfall has the potential to accumulate more dust increase the rate of dermal contact pose serious risks for the workers and nearby people [68]. Through a process known as bioaccumulation, rare earth elements are absorbed and retained by aquatic organisms more quickly than they can be excreted. This is frequently brought on by the constant presence of these elements in their surroundings. According to studies, sugar beets and potatoes absorb more REEs from contaminated soil than other vegetables which can affect the human body through bioaccumulation [69]. Special attention should be paid to these and other food items with a higher REE bioaccumulation capability as the output of REE in the global industrial sector develops.
3.3.7. Impacts on animal
REEs have been shown in several studies to increase enzyme activity, improve protein metabolism, suppress bacterial growth, promote the secretion of digestive fluids in the stomach, increase cell proliferation, increase ruminal feed degradability, modulate digestive microorganisms and enzymes, inflammation, and the immune system, improve animal growth, among other things [70-73]. Initially, when farm animals were given rare earth elements to aid in their growth, the result was more milk from cows and more eggs from laying birds. However, it was found that the animals' health gradually deteriorated as rare earth elements (REEs) accumulated significantly within their bodies over time. This included various problems like restricted movement, epileptic seizures, tissue decay in the liver, increased activity of lymphoid follicles, damage to the kidney system, and the progression of lung fibrosis [74-75]. For animals exposed to REEs, toxicity (Table 4) is the main cause for concern, and numerous studies have offered insight into REE effects and considerations. More long-term research is required to observe the effects of REEs on animals because the study gap has only been partially filled up to this point.
To address these concerns, it is crucial to develop new methods for mining and utilizing rare earth elements in ways that minimize harm to both the environment and human health. Customers of rare earth products can contribute by properly disposing of their electronics and buying goods from environmentally conscious producers.
5. Rare earth elements in Bangladesh
5.1. Current status of REE deposit distribution, mining, and policies in Bangladesh
Mineral sands or ‘heavy minerals’ having high specific gravity include commercially important minerals content rich in titanium, zirconium and rare earth minerals. Significant heavy mineral sand deposits can be found in Bangladesh's offshore islands, coastal shorelines, and the “char lands” of the Brahmaputra and Padma rivers. Exploration for heavy minerals in the country is limited but there are encouraging findings of commercial deposits of valuable heavy mineral sand. The Bangladesh Atomic Energy Commission (BAEC) is actively involved in searching for these sands and has initiated a pilot project to extract valuable components from sands found along the Cox's Bazar coastline. In the south-eastern coastal belt area and on the beaches of Cox's Bazar, Inani, Silkhali, Teknaf, Sabrang, Badarmokam, and Kuakata along the main coastlines, as well as in the offshore islands of Moheshkhali, Matarbari, Kutubdia, and Nijhumdwip, BAEC has identified 17 commercially viable high grade heavy mineral sand deposits. Approximately 4.35 million tonnes of heavy minerals are present in these mineral sand deposits, of which 1.76 million tonnes are economic deposits of magnetite (81,000 tonnes), zircon (158,000 tonnes), garnet (223,000 tonnes), rutile (70,000 tonnes), leucoxene (97,000 tonnes), monazite (17,000 tonnes), kyanite (91,000 tonnes), and ilmenite (10,25,000 tonnes) [138,139,140].
For more than 40 years, the Bangladesh Atomic Energy Commission has been conducting exploration work on the heavy mineral sands that line Bangladesh's southeast coast. Reports have been made available regarding the exploration findings, mineral grade, technical features, and mining potential of the found deposits. Within the parameters of the exploration permissions they had received from the government, a few foreign companies also conducted exploration work in the coastal and Brahmaputra river Char areas. Primer Minerals Limited Bangladesh (PML,B), a mineral development company based in Singapore, submitted an application for the mining of heavy mineral sands from the prospective deposit blocks of the Teknaf-Cox's Bazar area based on the results of their exploration and a feasibility study. In the char areas of the Brahmaputra river areas, Carbon Mining Pty Ltd, another mineral development company, conducted exploration for heavy mineral sands and applied for a few mining leases for the extraction of heavy mineral sands. Unfortunately the applications for mining leases for mineral sands are pending for several years [138,141].
The government of Bangladesh has implemented certain mining policies that are essentially effective for coal mining. There are several pertinent government policies that are related to environmental conservation and the exploration and mining of minerals, in addition to the main laws and regulations governing these activities. They are: National Conservation Policy 1991; Industrial Policy 1991; National Environment Policy 1992; National Energy Policy 1996; National Policy for safe water supply and sanitation 1998; National Agricultural Policy 1999 National Biodiversity Strategy and Action Plan 2004 etc [138,142,143]. However, Bangladesh does not currently have any effective policies for mining and extracting rare earth elements.
5.2. Current imports scenario in Bangladesh
Bangladesh, despite its small size and large population, is rapidly adopting technological advancements, but faces challenges like lack of skilled labor and financial constraints. Hence, the country relies on international partners for exports and imports of unmanufactured goods. Bangladesh also depends on other nations for Rare Earth Elements (REEs), but the complexities of mining, processing, and related procedures make international imports a logical choice. According to recent data from INDEXBOX, in 2021 (Figure 8), Bangladesh imported $88.8k in REE compounds, becoming the 62nd largest importer country in the world [82]. In contrast to historical data, the import rate has increased, owing to the wide range of applications involving Rare Earth Elements (REEs). Between 2020 and 2021, the fastest growing import markets for Rare-Earth Metal Compounds in Bangladesh were India ($57.6k), the United Kingdom ($4.21k), and France ($1.87K) [82].
5.3. Secondary sources of REEs in Bangladesh
The industry for extracting and processing REEs ores is not well developed in Bangladesh. The only way to satisfy public demand is to import. In addition, there are many secondary sources of REEs. They can be found in coal combustion byproducts such as fly ash, bottom ash, and incinerator ash, industrial byproducts such as slags, dross, phosphogypsum, and red mud, and electronic wastes such as nickel-metal hydride batteries, hard drives from laptop and desktop computers, cellular phones, and speakers [83]. This study uses secondary data sources (Table 5) like government archival materials, news media, official reports, and academic articles to analyze the potential consequences of Rare Earth Elements (REEs) in Bangladesh, relying on the synthesis and interpretation of these sources in the absence of primary data.
5.4. Probable REEs impacts in Bangladesh
The use of REEs is increasing in Bangladesh due to the expansion of certain facilities such as achieving 100% electricity coverage, greater opportunities for importing goods, enhance international relationships with other companies, and certain governmental initiatives. Figure 8 represents that between 2020 and 2021, there was a notable increase in the importation of rare earth elements and their demands. It can be inferred that in the near future, this situation will undergo a transformation, and production will experience growth. With the increasing usage of REEs, waste generation in Bangladesh is expected to rise.
Bangladesh's open dumping of waste, despite ineffective regulations, poses significant environmental, human health, and animal health risks due to the presence of heavy metals, radioactive waste, and REEs. Electronic waste, generated from secondary sources like electronics and appliances, is an increasing issue in Bangladesh, with an average annual production of 2.7 million metric tonnes [90]. To reduce this, the country must take action and raise public awareness.
Unregulated mining practices in Bangladesh, particularly coal mining, are causing significant environmental damage, including soil erosion, aquatic ecosystem pollution, and deforestation. This interaction can endanger plants and animals, allowing harmful compounds to enter the food chain. The unchecked coexistence of contaminants, including heavy metals, radioactive waste, and REEs, increases the toxic web of biodiversity. Air pollution from mining operations may worsen respiratory conditions and have long-term health effects. Therefore, it is crucial to regulate mining practices in Bangladesh to protect the environment [91-93].
5.5. Recycling of REEs in Bangladesh from the global view
The majority of end-products that contain these elements only use a small amount of REEs, and since collecting, processing, and recovering these elements from the end-product present a significant challenge, REE recycling has become more challenging to date [94]. The demand for rare-earth elements, particularly those closely linked to permanent magnets like Dy, Pr, Nd, and Tb, is expected to increase significantly due to the growing demand for electric and green energy systems [85]. To meet these demands, more primary production will be required, but in the mean time, robust recycling of rare earth elements can be a significant source of supply. Recycling offers a number of benefits over primary production because it can avoid the expensive steps of separating low-value REEs and co-existing radioactive waste [94,95]. Rare earth elements (REEs) manufacturing processes in Bangladesh are less well-established than those for heavy metals and radioactive elements. In comparison to monitoring processes for REEs, heavy metals and radioactive elements are subjected to stricter regulations. Jowitt, Simon M., et al. [96] provided an extensive analysis of the comprehensive landscape of recycling processes for rare earth elements (REEs) derived from sources such as magnets, catalysts, fluorescent lamps, and Ni-MH batteries. Recycling REEs from industrial waste is taking great attention among researchers. In this work, our attention will be focused on examining the recycling scenario in Bangladesh, centered around these sources, and suggest effective ways of recycling REEs from the available literature in the global review.
5.5.1. Recycling REEs from Batteries
According to Bangladesh import data by Volza (2023), the import shipments of batteries in Bangladesh amounted to 87.5K units. These were brought in by 2,919 importers in Bangladesh from a total of 3,722 suppliers [97]. Heavy metals like Cd, Pb, and Hg are frequently found in the waste produced by batteries. However, metal alloys with Ni, Co, Fe, and other elements are primarily found in Ni-MH rechargeable batteries. These metal hydride alloys are significant because of their high content of Rare Earth Elements (REEs), which account for more than 10% of the composition. The key elements for a Ni-MH battery include, among others, REEs, La,Pr, Nd, and Ce [3,98]. Bangladesh is one of the largest importers of Ni-MH batteries. According to a recent survey, China is the leading country for exporting Ni-MH batteries to Bangladesh. Furthermore, the use of various other electronic devices including Ni-MH batteries, contributes significantly to the spread of electronic waste. Despite being treated like lead batteries, there is currently no effective policy in place against Ni-MH batteries in Bangladesh. That is why recycling is a burning question for Bangladesh, and practical, affordable solutions can have a greater impact on developing nations like Bangladesh.
Up until recently, the most advanced industrial recycling of NiMH batteries consisted of using them to produce stainless steel as a cheap source of nickel, with the rare earth elements being lost in the slags of the smelter [99]. According to Binnemans, Koen, et al. [100], the rare earth elements (REEs) in these batteries may be recyclable via hydrometallurgical or pyrometallurgical methods. Both of these methods, however, are still relatively new and are not widely used. Filip [101] investigated the recovery of Co, metallic Ni, and REEs from NiMH batteries. They found that it is possible to selectively remove REE(OH)3 corrosion products using acetic or citric acid. Yuxiang et al. [102] developed a process that relies on supercritical fluid extraction utilizing CO2 as the solvent. They concluded that this process is very effective because it requires low temperature, doesn't produce hazardous waste, and can recover almost 90% of REEs. Jha, Manis Kumar, et al. [103] described a feasible hydrometallurgical method of recovering the REEs and found that over 90% dissolution of rare earth metals (REEs) such as Nd, Ce, and La was achieved in 60 minutes using 2M H2SO4 at 75°C, aided by the presence of 10% H2O2. Then, using 10% PC88A in kerosene and a two-stage counter-current extraction procedure at an equilibrium pH of 1.5 and an organic-to-aqueous (O/A) ratio of 1:1, Nd and Ce were successfully recovered from the leach solution.
5.5.2. Recycling REEs from permanent magnets
Permanent magnets are important parts for data storage, transducers, and many other applications in contemporary electronic gadgets. Notably, due to their remarkable magnetic properties, neodymium iron boron (NdFeB) magnets have become increasingly popular. Other Rare Earth Elements, besides neodymium, such as praseodymium, dysprosium, and terbium, may be used in NdFeB magnets. While addressing supply chain issues, the use of these REEs aims to enhance magnet performance [104].
Bangladesh's NdFeB magnet market faces production challenges due to high demand, heavily reliant on imports from India, Germany, Belgium, and China, alongside other global suppliers. As the electronic devices are responsible for e-waste, magnets have partially contributed to it in Bangladesh. Khuda, Kudrat-E [105] investigated the scenario and impacts of e-waste in Bangladesh and found that Bangladesh produces about 2.7 million metric tonnes of electronic waste annually. Only 20-30% percent of this waste is recycled, and the remaining 80-90% percent is dumped in landfills, rivers, canals, and open areas, endangering human health and the environment but information on recycling REEs was absent in this investigation.
Several researchers proposed many alternative solutions for recycling waste from permanent magnets including REEs [96]. reports three techniques that are very practical to use, including conventional hydrometallurgical recovery techniques, pyrometallurgical recovery techniques, and gas phase extraction techniques. David et al. [106] reported an innovative model for recycling of REEs from NdFeB magnet using carboxyl-functionalized ionic liquid and with high separation factors, the valuable elements (Nd, Dy, Co) are thus separated from the iron. Vander Hoogerstraete, Tom, et al. [107] proposed a recycling process that only uses oxalic acid, water, air, and electricity has been developed to recover rare earths from NdFeB magnets with extremely high purity. Nighat et al. [108] presented a novel method for dissolving REEs in NdFeB magnet swarf using copper nitrate and recovering about 97% of those REEs as mixed rare-earth oxides (REOs) with purity levels above 99.5% which is eco-friendly.
End-of-life REE-containing magnets can be found in WEEE (waste electrical and electronic equipment), which includes mobile phones and computer hard drives. Automatic sorting of NdFeB magnets used in pre-processing WEEE may draw crushed parts to ferrous metal scrap. This can separate REE into a single output stream, but it could also contaminate the stream and prevent recovery [98,109].
5.5.3. Recycling REEs from Catalyst
Rare earth elements (REEs) such as cerium, lanthanum, praseodymium, and neodymium are important for catalytic applications (Table 2). Despite their prominence, rare earth elements (REEs) are rarely extracted through mining in Bangladesh, resulting in a relatively limited focus on the recycling of these elements from catalysts. However, it is significant to proactively address this problem and take the necessary steps from a global perspective. Although the rare earth elements found in these catalysts are of relatively low value, it is unclear whether recycling these components from the catalysts will be profitable in the near and long term [110,96]. Goujian et al. [111] found a way of recovering REEs from spent fluid catalytic cracking (FCC) catalysts using H2O2. The process of hydrochloric leaching was used to obtain rare earth elements. They found that this process of reduction and leaching offers a highly effective way to recover valuable REEs from used catalyst.
5.5.4. Recycling REEs from Fluorescent lamps
Fluorescent lamps are widely regarded as more energy-efficient than traditional incandescent bulbs. This effectiveness is owing to the inclusion of Rare Earth Elements in their phosphor coatings, which help convert ultraviolet radiation into visible light [112]. As the form of phosphor, these lamps contain a significant amount of REEs such as Y,Ce,Eu,Tb. Typical fluorescent lamp waste is made up of phosphors in the colors of white, red, green, and blue that range in size and contain more than 20% REEs by weight [113]. Fluorescent lamp manufacturing in Bangladesh is well developed, and they also import it from other countries. According to Volza, Bangladesh imports most fluorescent lamps from China, India and HongKong. Baqer et al. [114] investigated the effects of fluorescent lamps over normal lamps in Bangladesh but didn’t explore the REEs. They also discussed how the increasing use of fluorescent lamps has greater effects on human beings, the environment, and the power supply. According to the most recent government report from 2022 [115], Bangladesh has achieved nationwide complete electricity coverage. As access to electricity grows, there is a likely scenario in which the prevalence of fluorescent lamps will increase significantly. However, the difficulty of implementing efficient recycling measures is the main source of concern regarding the impending rise in fluorescent lamp usage in Bangladesh.
Fluorescent lamps can carry various types of hazardous waste in addition to REEs. Utilizing a variety of techniques and methods, it is essential to recycle these wastes for sustainable development. Here, we present a few strategies from recent research that can be used to cut down on waste production in Bangladesh.
Kumari et al. [94] mentioned three methods for recycling REEs from secondary sources: direct reuse, individual separation of phosphor components, and chemical attack for REE recovery. The majority of the literature focuses on recycling Y and Ce because these elements are present in greater quantities in fluorescent lamps than others. As a result, it is critical to develop feasible methods for recovering REEs from fluorescent lamps. The most recent processes for recycling REEs from fluorescent lamps reported by researchers are shown in Table 6.
5.5.5. Recycling REEs from industrial waste
Despite having a high REEs content and the scarcity of end-of-life resources, it is difficult to recycle directly, which results in the production of industrial wastes like red mud, coal fly ash, and wastewater. Even though waste streams contain a smaller amount of REE, recovery options are constantly being investigated [94].
Industries hold significant importance in the economic growth of developing countries like Bangladesh. The majority share of Bangladesh's industries (approximately 82%) comes from the textile sector. Besides this, the growth rate of other sectors is also satisfactory [121]. With the increasing number of industries, the amount of waste produced is expected to rise proportionally. In 2008, a study by Waste Concern and the Asian Development Bank revealed that seven industries in Bangladesh produce three types of waste: solid waste (26,884 tons/year), wastewater (109.47 million cubic meters/year), and sludge (0.113 million ton/year). By 2025, the estimated volume of industrial solid waste, wastewater, and sludge would be 53,874 tons/year, 2472.07 million cubic meters/year, and 2.81 million tons/year [122]. Various planned and unplanned industries contribute to pollution, with a major concentration in certain areas. Therefore, safely managing waste from different types of industries poses a considerable challenge. In this context, REEs play an important role in industry waste. Coal fly ash, waste water, and red mud are the common industrial waste sources that contain REEs. To date, the government of Bangladesh has taken numerous steps to implement the 3R and 4R policies for waste reduction. These policies aim to eliminate waste disposal into floodplains, rivers, and open dumps while also promoting waste recycling practices through source-based waste separation and financial rewards for recycling efforts [90]. However, no effective separation method is currently available in Bangladesh for extracting REEs from waste. Globally, researchers proposed various methods (Table 7) for extracting REEs from industrial waste. These methods can be used in any developing country to achieve long-term development.
Besides, limited research is also a challenge for recovering Rare Earth Elements (REEs) from industrial waste globally. Thus, in this study, various recent methods are mentioned concerning how industrial waste can be easily recycled when compared with the previously available methods due to their high efficiency, low cost, and easy usability. To create a sustainable environment, choosing high-efficiency methods for recovering REEs would be a logical way for developing countries like Bangladesh.
6. Future development, new technology and sustainability for REE recycling
Future developments for REE recycling will involve the advancement of new technology, which will be the best option to recover the REEs. A significant amount of research-based work has been undertaken to develop new methods that will be feasible and enable controlling waste generation. However, to achieve a more efficient process, the lack of infrastructure, economic conditions, and other factors must be considered.
Some recent advanced research provides great importance, but the study gap is still an issue. For example, various methods have been established to combat REEs. Among them, the lack of a cost-effective method to recover the REEs is not too common, such as WEEE. Another concerning parameter, the supply side and demand side have many possible responses to understanding the supply risks [98].
Microbial electrochemical systems (MES) are innovative technologies that leverage microorganisms to convert chemical energy into electrical energy, and vice versa. These novel systems utilize microbial electrochemical phenomena to generate bioenergy or produce valuable chemicals, offering a promising alternative to fossil fuels for electricity generation and reducing reliance on hazardous substances in chemical production. Also, MES can be used for gathering rare earth elements from waste streams [144,145]. MES includes various systems such as microbial fuel cells (MFC), sediment microbial fuel cells (SMFC), microbial electrolysis cells (MEC), microbial desalination cells (MDC), microbial reverse-electrodialysis cells (MRC), and microbial electrosynthesis cells (MESC), among others.
Microbial fuel cells (MFCs) are bioelectrochemical fuel cell systems that generate electricity by diverting electrons from reduced compounds to oxidized compounds. They can be used to extract energy from waste streams and aid in recovering REEs by integrating electricity generation with recovery processes. SMFCs is an additional type of MFC that functions inside sediments. SMFCs are especially intriguing for in-situ applications where power generation and the recovery of rare earth elements (REEs) from sediment-based waste streams can be combined [144,146,147].
Another novel technology related to MFCs is Microbial electrolysis cells (MECs). MECs utilise an electric current to partially reverse the process of producing hydrogen or methane from organic material, whereas MFCs produce an electric current from the microbial breakdown of organic compounds. The generated hydrogen could be utilised in processes that isolate and concentrate REEs, allowing for the adaptation of this system for REE recovery [148,149]. Apart from these technology, Microbial Desalination Cells (MDCs) offer a potential method of recovering rare earth elements (REEs); by utilising saline waste streams, the desalinated stream generated promotes REE concentration and separation. For the production of power, Microbial Reverse-Electrodialysis Cells (MRCs) depend on salinity gradients and that makes their variety an electrochemical state capable for extraction/isolation of REEs from mixed waste streams. Microbial Electrosynthesis Cells (MESCs) have the potential to selectively capture rare earth elements through specialized electrode design or tailored biochemical pathways that bind these useful metals during the electrification process. Nevertheless, further research is required to refine this early-stage technology [150,151,152].
Increasing resource demand, scarcity of primary resources, environmental pollution, and rising waste production are the primary barriers to sustainable urban development caused by urbanization and industrialization. Urban mining could be another option for the sustainable recovery of REEs. Some concepts, such as industrial ecology, industrial metabolism, and sustainability, are the major supporting parameters of understanding urban mining, which improves mining efficiency [129,130]. Urban mining provides an environmentally friendly way to reuse and dispose of these materials as well as a way to reduce the mining of rare earths. The waste is considered a recyclable source. Developing urban mining processes can be a blessing not only for consumers but also for future development.
Establishing a resource-circulation society is a critical component for rare earth production, helping to overcome challenges such as enlargement, quality assurance, efficiency enhancement, energization, and public awareness. Additionally, the sustainability of REEs is greatly impacted by major principles such as resource circulation, waste reuse, and waste reduction [131].
Industrial Symbiosis is a widely discussed concept in eco industries, aiming to maximize resource conservation and emission reductions by exchanging by-products between industries. The initiative promotes collaboration and resource sharing across REE industries and businesses in order to create a more sustainable and efficient industrial ecosystem [83,132].
Considering how new technologies for recycling REEs can be incorporated into Bangladesh's industrial landscape is the first step towards applying global perspectives on REE recycling and sustainable urban development to the nation. Bangladesh can recover rare earth elements (REEs) from local waste streams through urban mining initiatives. Resource- circulating policies promote reuse, recycling, and responsible management, reducing waste. Collaboration with government agencies, industry stakeholders, and academic institutions is crucial for sustainable resource management practices. Industrial symbiosis among REE-related industries optimizes resource utilization and minimizes waste. Prioritizing capacity-building, training p rograms, technology transfer partnerships, and research collaborations enhances local expertise in REE recovery and recycling techniques. Therefore, Proper strategies can promote sustainable development of REEs in Bangladesh.
7. Findings and Implications
Bangladesh, a South Asian country, achieved 100% electricity coverage in 2020. In 2011, around 55–58% of Bangladesh's population had access to electricity [135]. By 2020, the country achieved 100% electricity coverage, nearly doubling the previous rate within 10 years. This increase is mainly attributed to rural areas gaining access to electricity. As these areas were previously without electricity, there is now a growing demand for new gadgets and electronic devices. The increase in electronic gadget usage, partially influenced by improved electricity coverage, contributes to the rising demand for rare earth elements [14]. This milestone, coupled with import opportunities, international relationships, and government initiatives, has led to a surge in the use of rare earth elements. With 38% of the population living in urban areas, this rapid urbanization is also a result of the increasing use of Rare Earth Elements (REEs), particularly in large cities [15]. REEs generate different kinds of waste that can harm health, the environment, aquatic systems, and animals. Until now, many policies have been established in Bangladesh to combat and recycle various types of waste, such as heavy metal waste, solid waste, and radioactive waste [16,17]. However, no policy has been established for managing REEs, their waste, and recovery. The current situation in Bangladesh is causing significant concern and apprehension.While the global implications of REE shortages are significant, Bangladesh is expected to experience similar challenges, though with less severe consequences. Traditional mining techniques yield significantly higher amounts of REEs compared to secondary sources, but concentration issues could still arise, leading to potential environmental, ecological, and human health impacts.
Another critical aspect is the exploration of mining opportunities, which is essential for tapping into REE deposits. However, the lack of an established policy in Bangladesh remains a concern. Adopting international policies could be a favorable option for guiding mining activities and ensuring safety precautions. Additionally, Bangladesh does not yet have a well-established recycling policy for REEs. Implementing globally available policies could help in collecting and recovering REEs from gadgets, which is key to reducing environmental pollution.
Introducing with newer technology for recyling and recovering the REEs is the anoter aspiration of minimizing the cost and to ensure the resource security, support economic growth, and reduce environmental impact. This drives technological progress, boosts global competitiveness, and supports sustainable development, enabling the country to participate in emerging industries.
Understanding the challenges in REE deposits and mining is important because they affect not just coal mining but also REEs. Skilled workers and international collaboration are needed to help overcome these issues and support growth. This study aims to explore these key challenges.
8. Recommendations for Bangladesh
The country lacks proper regulations and monitoring, making it crucial to develop methods to accurately determine REE levels, analyze potential dangers, evaluate ecosystem effects, and suggest technical strategies and policy directions. Future research should also focus on waste disposal and controlling mining complexity and processing to reduce REEs. Specifically, focusing on coal urban mining in Bangladesh could significantly reduce REEs impacts. Recycling REEs from e-waste is not practiced but is controlled by the informal sector [133]. Therefore, Bangladesh will face difficulties in dealing with e-waste unless an efficient recovery and management system is established. The recommendations to address the challenges linked to REEs, specifically in Bangladesh, include:
1. Enhancing sustainable mining practices: Encourage the use of eco-friendly practices (Coal mining) such as waste reduction, water conservation, and the use of renewable energy sources. This can assist in developing an approach to reducing waste with recovery.
2. Evaluation of Resources: Conducting a comprehensive assessment of REE sources aids in gaining a feasible idea about geological surveys and studies, which are critical for understanding the quality and quantity of REEs.
3. Enhancing research and innovation: More investment in research and innovation favors the development of new instruments, methods, and ideas for extracting, processing and recycling REEs. According to the UGC report of 2020, only 2% of the total budget spent for research is inadequate [134].
4. Regulatory framework: Develop strict guidelines for all types of mining and waste generation, as well as for the extraction, processing, and recycling of REEs. Make sure these guidelines ensure the safety of the public, the impact on the environment, and ethical mining practices.
5. Establishing transparency and accountability: Increase transparency make sure the entire supply chain mechanism. This must include ensuring that local communities are effectively involved and their rights are protected.
6. Recycling practices: Develop new methods and technology for recycling e-waste and recovering REEs. It contributes to waste reduction and helps to achieve the SDGs.
7. Promoting environmental issues: Reduce pollution and protect various types of plants and animals to keep the environment safe and ecosystems healthy. This may help mitigate the negative effects of REE on both human and animal health.
8. International collaboration: Collaborate with other nations and organizations to share information, resources, and knowledge about REE production. This can contribute to understanding the policies better and receiving support from them.
9. Long-term planning: Create a long-term policy and recycling system. This will help to achieve the Sustainable Development Goals (SDGs) and promote economic growth.
10. Raising awareness: Education and promoting knowledge about REEs are the most important components to lessen e-waste, recover REEs, and raise awareness. Educated consumers may stimulate the market for environmentally friendly products.
9. Conclusions
The increasing demand for rare earth elements (REEs) due to green technologies presents significant challenges in extraction and processing. Extracting Rare Earth Elements (REEs) globally leads to environmental issues such as mining-related pollution, the generation of radioactive waste, water scarcity, soil contamination, and deforestation, impacting human populations and wildlife. Sustainable exploitation schemes for REE ore deposits are critical to preventing environmental damage and ensuring long-term, cost-effective, and meticulously followed development. Alternative sources like coal fly ash, red mud, and electronic recycling initiatives are being recognized as promising ways to meet future REE demands, instead of new mining operations. Although more primary production is projected, strong recycling of rare earth elements may be able to cover the demand shortly. In Bangladesh, many of these challenges, including mining facilities, exploration methods, extraction and processing operations, sustainable recycling, etc., have been addressed based on secondary sources, but ineffective policies could worsen the situation. To mitigate these concerns, Bangladesh should focus on recycling REEs from secondary sources using established global methods. Therefore, modern technologies need to be more developed to overcome the recycling issue.
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