WO2024259535A1

WO2024259535A1 - Process and system to extract rare earth from clay and convert residue in sustainable binder for concrete

Info

Publication number: WO2024259535A1
Application number: PCT/CA2024/050837
Authority: WO
Inventors: Joel Fournier; Najoua BADER
Original assignee: Clayson Ecomineral Inc
Current assignee: Clayson Ecomineral Inc
Priority date: 2023-06-22
Filing date: 2024-06-21
Publication date: 2024-12-26
Anticipated expiration: 2025-12-22

Abstract

The present description relates to a process that includes subjecting clay ore to pre- treatment; leaching the pre-treated clay to produce a leachate enriched in rare earth elements and a solid residue; calcining the solid residue to produce pozzolanic clay material suitable for use as a concrete binder; subjecting the leachate to precipitation to form precipitated rare earth element oxides (REEO) and a rare earth depleted solution; and calcining the precipitated REEO to form an REEO product mixture. Both REEO product and concrete binder material can thus be produced from clay ore.

Description

PROCESS AND SYSTEM TO EXTRACT RARE EARTH FROM CLAY AND CONVERT RESIDUE IN SUSTAINABLE BINDER FOR CONCRETE

TECHNICAL FIELD

[001] The technical field generally relates to the extraction of rare earth from clay and the conversion of residues. In particular, the technical field relates to an integrated process and system for rare earth extraction from clay based materials and conversion of resulting residues in a sustainable binder for concrete.

BACKGROUND

[002] In various technologies and applications, there is an increasing need for rare earth elements. In certain countries, efforts to re-establish mining of rare earth elements have been undertaken. Supplies of rare earth elements may considerably depend upon economic viability of the extraction and production processes and technological innovations requiring such rare earth elements. In addition, global demand for cement and concrete has increased significantly in recent years with global cement production having increased almost four-fold since 1990. This has led to the expansion of industries connected to concrete as one of the leading construction industry components, starting from raw material extraction and increased fossil fuel consumption for material processing and cement production. Improvements in concrete sustainability have become a notable concern. Most of the binding materials used in concrete are based on Portland cement, which is the hydraulic binder that hardens when combined with water and is produced through an energy intensive process. While there have been some improvements in the cement and concrete industry, such initiatives have been outpaced by the dramatic increases in demand, and further developments are required to reduce the environmental impacts and costs. To address the sustainability problems facing the concrete industry, there is a need to develop concrete compositions with reduced cement content.

[003] There is indeed a need for a technology that facilitates sustainable production of rare earth elements as well as concrete binder materials. SUMMARY

[004] In some implementations, there is provided a process comprising: subjecting clay ore to pre-treatment to produce a pre-treated clay material; leaching the pre-treated clay material to produce a leachate enriched in rare earth elements and a solid residue; separating the leachate from the solid residue; calcining the solid residue to produce pouzolanic clay material suitable for use as a concrete binder; subjecting the leachate to precipitation to form precipitated rare earth element oxides (REEO) and a rare earth depleted solution; separating the precipitated REEO from the rare earth depleted solution; and calcining the precipitated REEO to form an REEO product mixture.

[005] In some implementations, the pre-treatment comprises drying the clay ore to obtain a dried ore; the drying is performed at a drying temperature between 150°C and 250°C; the pre-treatment comprises milling the dried ore to obtain a milled ore that is subjected to the leaching; the milling is performed to a granulometric distribution (D50) between 5 and 30 microns, or between 10 and 25 microns; the separating of the leachate from the solid residue is performed by filtration; calcining the solid residue is performed at a residue calcining temperature of 700°C to 1000°C, 875°C to 1000°C, or 885°C to 950°C; the precipitation includes addition of a carboxylic acid to the leachate; the carboxylic acid comprises a dicarboxylic acid; the dicarboxylic acid comprises oxalic acid; separating the precipitated REEO from the rare earth depleted solution comprises filtration; calcining the precipitated REEO is performed at a REEO calcining temperature between 700°C and 1000°C; the process also includes recycling at least a portion of the rare earth depleted solution back into the leaching step as part of a leaching solution; the process also includes adjusting the rare earth depleted solution before recycling back into the leaching step; the adjusting comprises addition of a sulfate; the leaching is performed using magnesium sulfate; the leaching is performed at a solution pH of 3 to 5 or 1 to 3; the process also includes subjecting the REEO product mixture to dissolution in HCI and fractional solvent extraction to produce individual rare earther elements (REE); and/or the process also includes forming a concrete additive comprising the pouzolanic clay material as well as fly ash and/or silica fume.

[006] In some implementations, there is provided a system comprising: a drier configured to receive mined clay ore and produce a dried clay; a milling unit configured to receive the dried clay and produce a milled ore; a leaching unit configured to leach the milled ore to produce a leachate enriched in rare earth elements and a solid residue; a separation unit coupled to the leaching unit for separating the leachate from the solid residue; a clay calciner configured to receive and calcine the solid residue to produce pouzolanic clay material suitable for use as a concrete binder; a precipitation unit configured to receive the leachate and form precipitated rare earth element oxides (REEO) and a rare earth depleted solution; a separator configured for separating the precipitated REEO from the rare earth depleted solution; and an REEO calciner configured to receive and calcine the precipitated REEO to form an REEO product mixture.

[007] In some implementations, the milling unit is configured to mill to a granulometric distribution of at most D50 of 20 microns; the separation unit is a filtration unit; clay calciner is configured to operate at a residue calcining temperature of 700°C to 1000°C, 875°C to 1000°C, or 885°C to 950°C; the precipitation unit is configured to receive a precipitation solution that includes a carboxylic acid; the carboxylic acid comprises a dicarboxylic acid; the dicarboxylic acid comprises oxalic acid; the separator for separating the precipitated REEO from the rare earth depleted solution comprises a filter; the REEO calciner is configured for calcining the precipitated REEO at a REEO calcining temperature between 800°C and 1000°C; the system also includes a recycle system in fluid communication with the separator and configured for recycling at least a portion of the rare earth depleted solution back into the leaching unit as part of a leaching solution; the system also includes an adjustment unit coupled to the recycle system and the separator, and configured for adjusting the rare earth depleted solution before recycling back into the leaching unit; and/or the adjustment unit comprises a magnesium sulfate solution addition inlet.

[008] In some implementations, there is provided a use of a clay ore feedstock for extraction and co-production of rare earth element oxides (REEO) and a clay-based concrete binder. The use of the clay can include one or more features described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[009] The attached figures illustrate various features, aspects and implementations of the technology described herein.

[0010] Fig 1 is a graph and table of cumulative distribution versus particle size. [0011] Fig 2 is a graph of weight versus temperature.

[0012] Fig 3 is a process flow diagram of a process for extracting rare earth elements and producing a concrete binder from the clay residues.

[0013] Fig 4 shows an X-ray diffraction graph and compositional information of a sample of Grande Vallee material.

[0014] Fig 5 is a bar graph of extraction percentage versus different elements.

DETAILED DESCRIPTION

[0015] Techniques described herein relate to systems, devices and methods for extracting rare earth elements from clay based materials and producing a concrete binder from the clay residues. In some implementations, the clay based material can be obtained from mining a clay deposit, pre-treating the clay ore which can include drying and milling, leaching the milled clay ore to produce a leachate enriched in rare earth elements and a solid residue, filtering or otherwise separating the leachate from the solid residue, calcining the solid residue to produce pouzolanic clay material, subjecting the leachate to precipitation to form precipitated rare earth element oxides (REEO), separating the precipitated REEO from the rare earth depleted solution, adjusting and recycling the solution back into the leaching step, and calcining the precipitated REEO to form an REEO product mixture. The process and system will be described in more detail further below.

[0016] The following provides additional context for the present technology. Rare-earth elements are incorporated in accessory minerals in various rocks, but the most commercially significant sources are:

(1) Bastnasite, is a fluorocarbonate mineral containing 65-75 wt.% light rare earth oxides (REO). They account for more than 80% of global REO production. The two major sources in the world for lanthanides are bastnasite deposits at Mountain Pass, California (USA, owned by Molycorp Inc. devoted solely to REE production, and Bayan-Obo, Inner Mongolia (China) - mined primarily for iron ore and REE as a by-product (also containing monazite). (2) Monazite, is a LREE phosphate containing 55-65 wt.% REO, associated with granites and beach sands in Australia, Brazil and India; the Mount Weld deposit in Western Australia, owned by Lynas Corp., contains one of the highest grades REE deposits in the world. Until about 1965 monazite was the main REE source; since then, the use of monazite has been considerably reduced due to radioactivity caused by thorium and radium.

(3) Xenotime, is an yttrium-rich phosphate containing 25-60 wt.% Y2O3 and other heavy REE. It is recovered mainly as a byproduct of mining for titanium, zirconium and tin in Malaysia, Indonesia and Thailand.

(4) Weathered crust elution-deposited rare earth ores (ion-adsorption ores) are aluminosilicate minerals (e.g. kaolinite, illite and smectite) containing 0.05-0.3 wt.% REEs physically adsorbed at sites of permanent negative charge. The ionadsorption clay deposits are the result of in situ weathering of host rocks (mainly granitic), which, over geological timescales, results in the formation of aluminosilicate clays.

[0017] Clay minerals are part of the phyllosilicate class, containing layered structures of shared octahedral aluminium and tetrahedral silicon sheets, allowing water molecules and hydrated cations to move in and out of the interlayer spaces. Very commonly, isomorphous substitution of one cation with another (of similar size but with lesser charge, e.g., Al³⁺ for Si⁴⁺ or Mg²⁺ for Al³⁺) within crystal structures leads to a charge imbalance in silicate clays, which accounts for the permanent negative charge on clay particles, and thus the capability of adsorbing lanthanide ions released/dissolved from precursor REE- bearing minerals during weathering. Warm tropical and sub-tropical climates present ideal conditions for this process to occur. The best example of this formation process exists in Asia, where many such deposits are known to exist.

[0018] Regardless of the low grades, ion-adsorption clays account for ~35% of the China’s total REE output and ~80% of world’s HREE production. Some important deposit has recently been found in Canada in an area named Gaspesie (Quebec). [0019] Carbonate and phosphate sources, of high grade, are associated with elevated recovery costs due to separation, beneficiation and need for aggressive conditions to dissolve the REE. For example, bastnasite is generally leached with concentrated H2SO4 or HCI, whereas monazite/xenotime concentrates need to be baked either in 98% H2SO4 or 70% NaOH to render the REE soluble. Other REE deposits in North America in addition to bastnasite consist of the so-called “hard-rock” peralkaline ores including zircon, titanate, niobate, allanite, eudialyte, gadolinite; these deposits are enriched in HREE but require harsh conditions to break down the mineral matrix (e.g. caustic bake followed by acid leaching); the processing of these ores is directed mainly towards extraction of niobium, tantalum, and zirconium.

[0020] The route followed by ion-adsorption type deposits are substantially lower grade than other types of lanthanide sources, nominally requiring higher costs for REE extraction and recovery. However, this disadvantage is largely offset by the easier mining and processing costs, and the relatively low content of radioactive elements such as thorium and uranium. These deposits are mined by open-pit methods and no ore beneficiation is required. A simple leach using monovalent sulfate or chloride salt solutions at ambient temperature can produce a high-grade REO product. Because of their abundance in surface layers in nature, ease of mining and processing, these clays warrant a detailed study as important sources of rare earths.

[0021] In terms of Portland cement production for concrete, the process emits large amounts of greenhouse gases, an estimated 5-8% of the world’s anthropogenic CO2. This trend is expected to increase in the coming decades as the countries continue to increase their concrete demand. It is predicted that cement production could represent 10% to 15% of global CO2 emissions by 2030. The cement industry has made substantial development in improving its production efficiency as well as reducing its environmental impact. Automation of the manufacturing of lime in modern cement kilns and increased use of alternative and sustainable fuel sources are the key improvements in the cement industry for reducing energy consumption and associated CO2 emissions. However, these initiatives have been outpaced by the dramatic increases in demand, and further developments are required to reduce the environmental impacts and costs. [0022] To address the sustainability problems facing the concrete industry, there is a need to develop concrete compositions with reduced cement content. Recent advancements in packing optimization and the development of water-reducing superplasticizers have already contributed to more sustainable concrete use. Furthermore, the cement industry has already achieved impressive improvements by developing supplementary cementitious materials (SCMs) and naturally sourced blending materials, such as silica fume (SF), natural pozzolan, fly ash, and limestone, to reduce the required cement content in concretes. Pozzolanic and filling effects are the two essential characteristics of these mineral admixtures. To date, a large variety of products have been used as cementitious materials, with a wide range of chemical compositions, which are placed in a CaO-SiCh-AhCh ternary phase diagram. Although industrial by-products or waste (e.g., fly ashes and blast furnace slags) are widely used to replace part of the cement clinker, the availability of these SCMs is limited by their production as by-products of power plants or blast furnace industries. Furthermore, their efficiency to replace clinker has been studied by various researchers who have concluded that they cannot be considered a global alternative to cement. Thus, there is a growing tendency to find new alternative inorganic binders from local sources for replacing cement in concrete structures. Raw earth based materials are promising options for low-cost and environmentally friendly building materials. Among such materials, clays are an abundant option that can be effective as mineral additives or in blended concrete in many places of the world. Clays are a source of alumina and silica, which can cause a pozzolanic reaction under the proper conditions. Clays have already been shown to have excellent pozzolanic properties under specific calcination conditions or surface modifications.

[0023] The present technology relates to a new process and system to extract rare earth from clay while improving the pozzolanic activity of the resulting by-product material. Fig 3 illustrates one implementation of the process.

[0024] The clay mineral can be challenging to directly mine and introduce into a milling stage and thus can be subjected to pre-treatment. The typical composition of clay is present in Table 1. The REE and REEO content in the clay ore is presented in Table 2. The humidity content would generate a sticky mud. It is thus first passed through a drying step, which may be an air-drying step at 200C for 1 hr. The resulting loss in weight of this drying step is present in Table 3.

Table 1

Table 2

Table 3

Average lost% 9,7 lost% 1,2

[0025] After drying, the dried clay material can be subjected to a size-reduction stage, such as a milling step, to reduce the particles size, e.g., to a D50 of 20um (see Figure 1). A weight loss of average 1 .2% is related to the fine particles passing into the air filtration system (see Table 3).

[0026] The physisorbed REE ions can be readily displaced from the clay surface by monovalent cations (e.g., Na⁺ and NH₄ ⁺) following the below reaction mechanism:

(1) Clay - REE³⁺ + 3NH₄ ⁺ Clay - (NH₄ ⁺)₃ + REE³⁺

[0027] An ammonium sulfate solution is typically employed for the ion-exchange leaching and the solution pH is maintained at between 3 and 5 or 1 to 3 to prevent the hydrolysis of REE³⁺ ions and minimize the dissolution of impurities such as aluminum- and iron-bearing minerals. The temperature of the leaching step could vary from 25°C to 85°C with a preference around 40°C to 60°C or at 50°C. It is noteworthy that in the current invention it is preferred to use magnesium sulfate instead of ammonium sulfate for the leaching step, although other leaching agents are possible. For example, leaching agents can include calcium sulfate, sodium sulfate, and ammonium sulfate can be used, and mixtures of two or more of such leaching agents can be used in combination. Magnesium based leaching agents can be preferred as it has been found that they can facilitate pouzolanic properties of the clay residue after calcination. The use of magnesium sulfate for leaching of ion-adsorption clays has the dual aim of replacing ammonium-based lixiviants to avoid environmental concern related to the next calcination step of the residue and improve the pozzolanic activity of this material. An additional benefit of using MgSC t instead of (NH^SC is the 10-15% decrease in aluminum desorption, which translates into a lower solution impurity content to be processed or eliminated downstream.

[0028] There are other leaching agents and processes that can be used. For example, HCI, H2SO4 and HNO3 can be employed in leaching steps and processes as described in WO 2012/149642 (Boudreault et al.), the contents of which are incorporated herein by reference, can be used in combination with techniques described in the present document. Processes described in WO’642 related to rare earth separation can also be used in combination with techniques described herein to separate rare earth compounds from each other, e.g., where rare earth oxides produced according to processes herein are dissolved (e.g., using an HCI solution) and then introduced into the rare earth separation process.

[0029] The dissolved REE are usually selectively precipitated with a carboxylic acid, such as oxalic acid, to form oxalates (see Equation 2) that are subsequently converted to REEO via calcination or roasting at 900°C.

(2) REE ₂(SO₄)₃ + 3 C2O4H2 + 10 H₂O REE 2(C₂O4)3*10H₂O + H₂SO₄

[0030] Thermal decomposition of these oxalates gives the oxides, which is the most commonly marketed form of these elements.

(3) REE 2(C₂O4)3*10H₂O REE2O3 + 3CO + 3CO₂ + 10H₂O

[0031] Finally, the mixed REEO can be separated into individual REE by dissolution in HCI and fractional solvent extraction.

[0032] Turning to the clay reside treatment, the solid residue from the leaching stage can be conveyed to a calcination stage for processing. The calcination of clay minerals means the process of dehydroxylation of ultrafine clay by thermal activation in high temperature in a calciner kiln, which results in driving off the chemically bound water, breaking down the crystal structure, and changing the material into a highly reactive transition phase. Different temperatures are possible for the process of calcination and the preferred temperature can be between 700°C and 1000°C although others are possible and as disclosed herein. Below shows an example of dihydroxylation of kaolinite:

Schematic representation of kaolinite dehydroxylation producing increased disorder in the alumina sheet

[0033] Calcination temperature can affect the fresh/wet and hardened properties of cementitious material. One of the most applicable products of kaolinite (AhSi2O5(OH)4) calcination is metakaolin as an anhydrous alumino-silicate (AhSi2O7). Metakaolin is a dehydroxylated form of the clay mineral kaolinite obtained by calcination. This reaction liberates water instead of CO2 for a clinker.

Kaoli nite — melakaol in: AI₂Si₂( iOH

— Al₂Si₂()₇ - 2H₂( ) |

[0034] The major constituents of residual clay are silica oxide (SiO2) and alumina oxide (AI2O3). SiO 2 reacts with Ca(OH)2 in concrete to produce secondary calcium silicate hydrate (CSH) gel at ambient temperature. Apart from that, the alumina in residual clay reacts with calcium hydroxide to produce additional alumina-containing phases, including C4AH13, C2ASH8, and C3AH6. MgO can be obtained by decomposition of MgSC However, at 1500K, the temperature where this decomposition occurs, the pozzolanic properties of clay is strongly reduced. The thermodynamic study suggests that in the presence of reducing agents, such as carbon, hydrogen gas, aluminum or magnesium scrap, a decreased decomposition temperature is obtained for the MgSC t making the formed oxide (MgO) good for this use. Analyses performed with the variables of excess reducing agent (charcoal) and temperature showed that temperature is the variable that most influences the decomposition of MgSO4. Experiments at 1173K and 20, 25 and 30 min were the conditions that indicated the best experimental results of conversion, reaching a conversion close to 100%. [0035] MgO subjected to calcination temperatures (e.g., light burned MgO calcined at 700 - 1000°C) presents a great reactivity and early age expansion of concrete. Hydration reaction of MgO, which leads to the formation of Mg(OH)2, is as follows :

MgO + H₂O = Mg²⁺ + 2 OH' = Mg(OH)₂

[0036] Since the volume of hydration products is higher than that of the reagents, the hydration of MgO leads to an expansion, which, if properly controlled, can be used to compensate the shrinkage typically observed in cementitious composites and their deformation due to creep as well. The compatible chemical nature of MgO with that of cement may produce beneficial expansive components capable of reducing the number of microcracks and contribute to strength gain under certain circumstances. Similar to that observed in the hydration of cement, after the formation of Mg(OH)2, ensuing pozzolanic reactions can lead to the formation of magnesium silicate hydrates (e.g., MgO-SiO2-H2O or M-S-H) capable of presenting considerable strength gain, if in the presence of amorphous silica-bearing mineral additions, such as fly ash or silica fume. Another practical feature of using reactive MgO-based cementitious composites is their ability to capture a considerable amount of CO2, thereby further decreasing the material’s environmental impact throughout its life cycle.

[0037] It is noted that various REEs can be extracted from the feedstock using the methods described herein. For example, in the context of the present description, REEs include the lanthanides as well as yttrium and scandium. For certain feedstocks, such as ion-adsorption clay materials, there is a higher concentration of heavy rare earth elements compared to conventional mineral deposits, and thus the process can be provided accordingly to obtain such REEs.

[0038] It is also noted that various integration techniques can be employed in the context of the present technology. For example, heat and material can be recycled at certain parts of the process to enhance efficiency, energy use, and sustainability. In one example, at least a portion of the vapors released from one or more of the calcination stages can be reused for preheating at least a portion of the material in the drying stage. The preheating can be done by direct contact of the hot vapours or using indirect heating. In addition, the partially cooled vapours that are withdrawn from the drying stage can be used to for heating purposes in the leaching stage (e.g., used to maintain the leaching temperature in the desired range or at around 50°C). It is also possible to use one of the calcination vapour streams for drying and the calcination vapour stream for leaching step heating.

[0039] Regarding the feedstock, it is noted that feedstock materials that are particularly suited to processing via this technology are high in degraded clay and high in clay mineral phases of kaolin, illite, and montmorillonite. Such clay materials can lead to better REE adsorption and kaolin rich materials can facilitate enhanced performance and properties after calcination for use in concrete. For example, analysis of the Grande Vallee clay has shown a composition containing a majority of Kaolinite, lllite/Mica muscovite and Quartz. See Fig 4 for X-ray diffraction of a sample of Grande Vallee material. It is preferred to have a composition of combined Kaolinite and lllite/Mica muscovite over 40% to have desired pozzolanic activity. For the concrete industry, the pozzolanic activity of the material after calcination should ideally have a minimum of 5 Mpa according to the CSA A3004 E1 test and obtain a score of 5g/100g of dried paste in the bound water measurements according to the ASTM C1897-20 Standard Test Methods. Of course, various other feedstocks and compositions are also possible in certain embodiments.

EXPERIMENTATION

[0040] Various tests were performed to assess materials and the technology described herein. Three samples of mortars were prepared with clays processed based on the present technology and calcined at different temperatures and lime according to standard CSA A3004-E1 , Appendix A and the samples were tested after 7 days of curing. The composition of the mortars with the clays calcined at temperatures of 800°C, 850°C and 900°C, their fresh state, and their compressive strength after 7 days of curing are presented in Table 1 below:

Table 4

[0041] The CSA A 3001 :23 standard requires that the minimum strength of the mortar tested at 7 days, according to the A3004 — Annex 4 standard, be at least 5 MPa. The analysis of the results showed that the three clays studied have very good potential as cementitious additions. The reactivity of the three clays was maximum at a calcination temperature of 900°C. The pozzolanic reactivity test, Canadian test CSA A3004-E1 , Appendix A, shows results above the threshold necessary to consider cementitious additions as reactive.

[0042] It is noted that calcination temperatures between 875°C and 1000°C, optionally between 885°C and 950°C, can be used to provide a mortar strength of at least 5 Pa for the tested materials. It is also noted that the temperature and calcination conditions could be modified depending on clay composition and source as well as processing features such that the calcination results in a mortar strength of at least 5 Pa at other calcination operating conditions.

[0043] Referring now to Fig 5, leaching tests were performed to assess rare earth extraction. In such tests, the pH was approximately 2.57 (between 1 to 3) and the leaching solution was (NH^SCUwith a leaching time of 30 minutes.

[0044] Several alternative implementations and examples have been described and illustrated herein. The implementations of the technology described above are intended to be exemplary only. A person of ordinary skill in the art would appreciate the features of the individual implementations, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the implementations could be provided in any combination with the other implementations disclosed herein. It is understood that the technology may be embodied in other specific forms without departing from the central characteristics thereof. The present implementations and examples, therefore, are to be considered in all respects as illustrative and not restrictive, and the technology is not to be limited to the details given herein. Accordingly, while the specific implementations have been illustrated and described, numerous modifications come to mind.

Claims

1. A process comprising: subjecting clay ore to pre-treatment to produce a pre-treated clay material; leaching the pre-treated clay material to produce a leachate enriched in rare earth elements and a solid residue; separating the leachate from the solid residue; calcining the solid residue to produce pozzolanic clay material suitable for use as a concrete binder; subjecting the leachate to precipitation to form precipitated rare earth element oxides (REEO) and a rare earth depleted solution; separating the precipitated REEO from the rare earth depleted solution; calcining the precipitated REEO to form an REEO product mixture.

2. The process of claim 1, wherein the pre-treatment comprises drying the clay ore to obtain a dried ore.

3. The process of claim 2, wherein the drying is performed at a drying temperature between 150°C and 250°C.

4. The process of claim 2 or 3, wherein the pre-treatment comprises milling the dried ore to obtain a milled ore that is subjected to the leaching.

5. The process of claim 4, wherein the milling is performed to a granulometric distribution (D50) between 5 and 30 microns, or between 10 and 25 microns.

6. The process of any one of claims 1 to 5, wherein the separating of the leachate from the solid residue is performed by filtration.

7. The process of any one of claims 1 to 6, wherein calcining the solid residue is performed at a residue calcining temperature of 700°C to 1000°C, 875°C to 1000°C, or 885°C to 950°C.

8. The process of any one of claims 1 to 6, wherein calcining the solid residue is performed at a residue calcining temperature of 875°C to 1000°C.

9. The process of any one of claims 1 to 8, wherein the precipitation includes addition of a carboxylic acid to the leachate.

10. The process of claim 9, wherein the carboxylic acid comprises a dicarboxylic acid.

11. The process of claim 10-, wherein the dicarboxylic acid comprises oxalic acid.

12. The process of any one of claims 1 to 11 , wherein separating the precipitated REEO from the rare earth depleted solution comprises filtration.

13. The process of any one of claims 1 to 12, wherein calcining the precipitated REEO is performed at a REEO calcining temperature between 700°C and 1000°C.

14. The process of any one of claims 1 to 13, further comprising recycling at least a portion of the rare earth depleted solution back into the leaching step as part of a leaching solution.

15. The process of claim 14, further comprising adjusting the rare earth depleted solution before recycling back into the leaching step.

16. The process of claim 15, wherein the adjusting comprises addition of a sulfate.

17. The process of any one of claims 1 to 16, wherein the leaching is performed using magnesium sulfate.

18. The process of any one of claims 1 to 17, wherein the leaching is performed at a solution pH of 3 to 5 or 1 to 3.

19. The process of any one of claims 1 to 18, wherein the leaching is performed at a solution pH of 1 to 3.

20. The process of any one of claims 1 to 19, further comprising subjecting the REEO product mixture to dissolution in HCI and fractional solvent extraction to produce individual rare earther elements (REE).

21. The process of any one of claims 1 to 20, further comprising forming a concrete additive comprising the pouzolanic clay material as well as fly ash and/or silica fume.

22. A system comprising: a drier configured to receive mined clay ore and produce a dried clay; a milling unit configured to receive the dried clay and produce a milled ore; a leaching unit configured to leach the milled ore to produce a leachate enriched in rare earth elements and a solid residue; a separation unit coupled to the leaching unit for separating the leachate from the solid residue; a clay calciner configured to receive and calcine the solid residue to produce pouzolanic clay material suitable for use as a concrete binder; a precipitation unit configured to receive the leachate and form precipitated rare earth element oxides (REEO) and a rare earth depleted solution; a separator configured for separating the precipitated REEO from the rare earth depleted solution; an REEO calciner configured to receive and calcine the precipitated REEO to form an REEO product mixture.

23. The system of claim 22, wherein the milling unit is configured to mill to a granulometric distribution of at most D50 of 20 microns.

24. The system of claim 22 or 23, wherein the separation unit is a filtration unit.

25. The system of any one of claims 22 to 24, wherein clay calciner is configured to operate at a residue calcining temperature of 700°C to 1000°C, 875°C to 1000°C, or 885°C to 950°C.

26. The system of any one of claims 22 to 24, wherein clay calciner is configured to operate at a residue calcining temperature of 875°C to 1000°C.

27. The system of any one of claims 22 to 26, wherein the precipitation unit is configured to receive a precipitation solution that includes a carboxylic acid.

28. The system of claim 27, wherein the carboxylic acid comprises a dicarboxylic acid.

29. The system of claim 28, wherein the dicarboxylic acid comprises oxalic acid.

30. The system of any one of claims 22 to 29, wherein separator for separating the precipitated REEO from the rare earth depleted solution comprises a filter.

31. The system of any one of claims 22 to 30, wherein the REEO calciner is configured for calcining the precipitated REEO at a REEO calcining temperature between 700°C and 1000°C.

32. The system of any one of claims 22 to 31 , further comprising a recycle system in fluid communication with the separator and configured for recycling at least a portion of the rare earth depleted solution back into the leaching unit as part of a leaching solution.

33. The system of claim 32, further comprising an adjustment unit coupled to the recycle system and the separator, and configured for adjusting the rare earth depleted solution before recycling back into the leaching unit.

34. The system of claim 33, wherein the adjustment unit comprises a magnesium sulfate solution addition inlet.

35. Use of a clay ore feedstock for extraction and co-production of rare earth element oxides (REEO) and a clay-based concrete binder.

36. The use of claim 35, further including one or more features of any one of claims 1 to

34 and/or as disclosed herein.