TECHNICAL FIELD

The present disclosure relates to the field of processing of slag generated during iron making. Particularly, the present disclosure relates to a method of extraction of rare earth elements from ground granulated blast furnace slag (GGBFS). The disclosure also relates to a method for preparing construction materials using GGBFS post extraction of rare earth elements.

BACKGROUND OF THE DISCLOSURE
Blast furnace slag (BFS) is a co-product formed in the process of iron making which comprises silicates, calcium oxide, alumina silicates (sometimes referred to as calcium-alumino-silicate matrix) as well as traces of rare earth elements. BFS constitutes about 20% by mass of iron production. Among the various types of blast furnace slag generated, granulated blast furnace slag is obtained by fast quenching of slag forming a crystalline structure. This crystalline structure renders it useful for preparing construction materials. There are not many reports on extraction of rare earths from iron bearing raw materials. Further, there has been no studies reported in literature on extraction of rare elements from granulated blast furnace slag. Extraction of rare earth elements from blast furnace slag with acids might destroy the amorphous nature of the slag, thus requiring less stringent and more amenable conditions to cause relinquishment of costlier rare earths from calcium-alumino-silicate matrix.

IN329474 discloses a process for selective extraction of lanthanum, cerium and neodymium from blast furnace slag as oxalates/oxides. The process comprises extraction of these metals from air cooled blast furnace slag as mixed oxides. However, the process does not involve separation of individual rare earth elements.

CN101768674B, US5015447, WO2012163200, and EP3449021 disclose extraction of rare earth elements from phosphate ores, not from iron ore slag.

US5030424, US10738369, US8968688, US20200048737, and CN103614563 disclose extraction of rare earth elements from red mud, coal, fly ash and titanium wastes.

WO2020191504 disclose recovery of iron from iron or steel slag but does not disclose recovery of rare earth elements.

In summary, there are no reports on extraction of rare earth elements from ground granulated blast furnace slag (GGBFS). The present disclosure provides for the first time a holistic process for recovering rare earth elements from GGBFS and using the extracted GGBFS (an acid leached residue) for preparing construction materials.

STATEMENT OF THE DISCLOSURE
The present disclosure relates to a method for extracting Ce, La, and Nd from GGBFS, comprising: a) reacting the GGBFS with a mineral acid to obtain a first residue and a first liquor containing Ce, La, and Nd; b) contacting the first liquor with a first solvent to obtain a first solvent-liquor mixture; c) stripping the first solvent-liquor mixture with a mineral acid to obtain a second liquor containing Ce, La, and Nd; d) contacting the second liquor with a first precipitant to obtain a cerium oxide precipitate and a third liquor containing La and Nd; e) contacting the third liquor with a second solvent to obtain a second solvent-liquor mixture; f) stripping the second solvent-liquor mixture with a mineral acid to recover neodymium oxide and to obtain a fourth liquor containing La; and g) contacting the fourth liquor with a second precipitant to obtain a lanthanum oxide precipitate.

The present disclosure also relates to a method for preparing a construction material comprising mixing the first residue (acid leached GGBFS) with cement and aggregates to prepare a dry mix; adding water to the dry mix to obtain a slurry; and setting the slurry to obtain concrete.

The present disclosure further relates to a construction material such as concrete comprising cement, acid leached GGBFS, and aggregates.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 shows an exemplary schematic of the steps involved in the extraction of Ce, La, and Nd from GGBFS and processing of the extracted GGBFS according to the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Reference throughout this specification to “some embodiments”, “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in some embodiments”, “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The term “about” as used herein encompasses variations of +/-10% and more preferably +/-5%, as such variations are appropriate for practicing the present invention.

The term “liquor” as used herein refers to a solution that remains after one or more components are removed from the precursor solution.

Methods of Extracting Rare Earth Elements
The present disclosure provides a method for extracting rare earth elements, namely, cerium (Ce), lanthanum (La), and neodymium (Nd), from GGBFS. Granulated blast furnace slag is ground and sized to obtain GGBFS. The method of extracting rare earth elements from GGBFS broadly comprises an acid leaching step followed by solvent extraction steps. In the acid leaching step, GGBFS is leached/treated with a mineral acid to obtain a residue (extracted GGBFS) and a liquor containing Ce, La, and Nd. The liquor containing Ce, La, and Nd is subjected to two solvent extraction steps to extract Ce, La, and Nd individually. The residue/extracted GGBFS is processed to prepare construction materials.

Figure 1 shows an exemplary schematic showing the method steps involved in the extraction of Ce, La, and Nd from GGBFS and processing of the extracted GGBFS according to the present disclosure. As shown in Figure 1, granulated blast furnace slag (GBFS) 1 is subjected to a grinding and sieving stage 2, to yield ground granulated blast furnace slag (GGBFS) powder 3. The GGBFS is leached 4 with acid 5 and the mixture is filtered 6 to yield PLS 7 (first liquor) and first residue 8. The PLS (first liquor) is subjected to first stage solvent extraction 9 to selectively load all rare earth elements and the loaded solvent is stripped 10. The stripped solution is subjected to first precipitation 11 and calcination 12 to yield cerium product 13. The raffinate/filtrate 14 from 11 is subjected to second stage solvent extraction 15 and stripped 16 to yield neodymium product 17. The raffinate 18 from step 15 is precipitated to obtain lanthanum product 19. The residue 8 is conditioned 20 in water and dried 21. The dried residue 21 is mixed with three aggregates and form a dry mix 22. The dry mix 22 is mixed with water 23 and allowed for setting 24 to form concrete product 25.

In some embodiments, a method for extracting Ce, La, and Nd from GGBFS comprises: a) reacting the GGBFS with a mineral acid to obtain a first residue and a first liquor containing Ce, La, and Nd; b) contacting the first liquor with a first solvent to obtain a first solvent-liquor mixture; c) stripping the first solvent-liquor mixture with a mineral acid to obtain a second liquor containing Ce, La, and Nd; d) contacting the second liquor with a first precipitant to obtain a cerium oxide precipitate and a third liquor containing La and Nd; e) contacting the third liquor with a second solvent to obtain a second solvent-liquor mixture; f) stripping the second solvent-liquor mixture with a mineral acid to recover neodymium oxide and to obtain a fourth liquor containing La; and g) contacting the fourth liquor with a second precipitant to obtain a lanthanum oxide precipitate. These steps are discussed below in detail.

GGBFS is reacted/leached with a mineral acid to obtain a first residue and a first liquor. In some embodiments, GGBFS is reacted with about 0.5-3M mineral acid at a temperature of about 40-90? for about 0.25-5 hours. In some embodiments, the mineral acid employed for acid leaching is selected from hydrochloric acid, nitric acid, sulphuric acid, or a combination thereof. In some embodiments, the strength of the mineral acid employed for leaching GGBFS ranges from about 0.5-3M, 0.5-2.5M, 0.5-2M, 0.5-1.5M, 0.5-1M, 1-3M, 1-2.5M, 1-2M, 1.5-3M, 1.5-2.5M, 1.5-2M, or 2-3M, including values and ranges therebetween. In some embodiments, the strength of the mineral acid employed for leaching GGBFS is about 0.5M, 0.75M, 1M, 1.25M, 1.5M, 1.75M, 2M, 2.25M, 2.5M, 2.75M, or 3M, including values and ranges therebetween.

In some embodiments, acid leaching of GGBFS is carried out at a temperature of about 40-90?, 40-85?, 40-80?, 40-75?, 40-70?, 40-65?, 40-60?, 40-55?, 40-50?, 45-90?, 45-85?, 45-80?, 45-75?, 45-70?, 45-65?, 45-60?, 45-55?, 50-90?, 50-85?, 50-80?, 50-75?, 50-70?, 50-60?, 55-90?, 55-85?, 55-80?, 55-75?, 55-70?, 55-65?, 60-90?, 60-85?, 60-80?, 60-75?, 60-70?, 65-90?, 65-85?, 65-80?, 65-75?, 70-90?, 70-85?, 70-80?, 75-90?, 75-85?, 75-80?, 80-90?, or 85-90?, including values and ranges therebetween.

In some embodiments, acid leaching of GGBFS is carried out at a temperature of about 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90?, including values and ranges therebetween.

In some embodiments, acid leaching of GGBFS is carried out at any one of the temperatures described herein for a duration of about 0.25-5 hours, i.e., for about 15 minutes to about 5 hours. In some embodiments, acid leaching of GGBFS is carried out for a duration of about 15 minutes to 4.5 hours, 15 minutes to 4 hours, 15 minutes to 3.5 hours, 15 minutes to 3 hours, 15 minutes to 2.5 hours, 15 minutes to 2 hours, 15 minutes to 1.5 hours, 15 minutes to 1 hour, 30 minutes to 5 hours, 30 minutes to 4.5 hours, 30 minutes to 4 hours, 30 minutes to 3.5 hours, 30 minutes to 3 hours, 30 minutes to 2.5 hours, 30 minutes to 2 hours, 30 minutes to 1.5 hours, 30 minutes to 1 hour, 45 minutes to 5 hours, 45 minutes to 4.5 hours, 45 minutes to 4 hours, 45 minutes to 3.5 hours, 45 minutes to 3 hours, 45 minutes to 2.5 hours, 45 minutes to 2 hours, 45 minutes to 1.5 hours, 45 minutes to 1 hour, 1 to 5 hours, 1 to 4.5 hours, 1 to 4 hours, 1 to 3.5 hours, 1 to 3 hours, 1 to 2.5 hours, 1 to 2 hours, 1 to 1.5 hours, 1.5 to 5 hours, 1.5 to 4.5 hours, 1.5 to 4 hours, 1.5 to 3.5 hours, 1.5 to 3 hours, 1.5 to 2.5 hours, 1.5 to 2 hours, 2 to 5 hours, 2 to 4.5 hours, 2 to 4 hours, 2 to 3.5 hours, 2 to 3 hours, 2 to 2.5 hours, 2.5 to 5 hours, 2.5 to 4.5 hours, 2.5 to 4 hours, 2.5 to 3.5 hours, 2.5 to 3 hours, 3 to 5 hours, 3.5 to 4.5 hours, 3.5 to 4 hours, 3 to 3.5 hours, 4 to 5 hours, or 4 to 4.5 hours, including values and ranges therebetween.

It is understood that acid leaching of GGBFS is carried out by employing any combination of the time, temperature, acid strengths, and the acids described herein. In an exemplary embodiment, GGBFS is reacted with a mineral acid at about 90? for about 2 hours.

In some embodiments, for acid leaching, about 5-30%, 5-25%, 5-20%, 5-15%, 5-10%, 10-30%, 10-25%, 10-20%, 10-15%, 15-30%, 15-25%, 15-20%, 20-30%, 20-25%, or about 25-30% w/v, including values and ranges therebetween, of GGBFS is reacted with about 70-90%, 70-85%, 70-80%, 70-75%, 75-90%, 75-85%, 75-80%, 80-90%, 80-85%, or about 85-90%, including values and ranges therebetween, of the mineral acid.

Treatment of GGBFS with a mineral acid extracts rare earth elements in the mineral acid. The residue of GGBFS left after extraction is referred to herein as a first residue/extracted GGBFS and the mineral acid phase enriched in rare earth elements is referred to herein as a first liquor.

In some embodiments, the first liquor has a lanthanum content in an amount of about 78-99.9%, including values and ranges therebetween, with respect to the total lanthanum content in the GGBFS; a cerium content in an amount of about 82-99.9%, including values and ranges therebetween, with respect to the total cerium content in the GGBFS; a neodymium content in an amount of about 89-99.9%, including values and ranges therebetween, with respect to the total neodymium content in the GGBFS. In other words, about 78-99.9% of lanthanum, about 82-99.9% of cerium, and about 89-99.9% of neodymium from GGBFS is extracted into the first liquor after acid leaching.

In some embodiments, the lanthanum content of the first liquor ranges from about 78-99.9%, 78-95%, 78-90%, 78-85%, 80-99.9%, 80-95%, 80-90%, 85-99.9%, 85-95%, 85-90%, 90-99.9%, 90-98%, 90-95%, 94-99.9%, or 95-99.9%, including values and ranges therebetween, with respect to the total lanthanum content in the GGBFS; the cerium content of the first liquor ranges from about 82-99.9%, 82-95%, 82-90%, 82-85%, 85-99.9%, 85-95%, 85-90%, 90-99.9%, 90-98%, 90-95%, 94-99.9%, or 95-99.9%, including values and ranges therebetween, with respect to the total cerium content in the GGBFS; and the neodymium content of the first liquor ranges from about 89-99.9%, 89-95%, 89-92%, 90-99.9%, 90-98%, 90-95%, 94-99.9%, or 95-99.9%, including values and ranges therebetween, with respect to the total neodymium content in the GGBFS.

The first residue/extracted GGBFS is processed to prepare construction materials as described in the later parts of this section. The first liquor containing rare earth elements extracted from GGBFS is subjected to solvent extraction step to isolate La, Ce, and Nd individually.

The first liquor is contacted with a first solvent to obtain a first solvent-liquor mixture. In some embodiments, the first liquor is contacted with the first solvent at a solvent:liquor ratio of about 1:1. The first solvent-liquor mixture is stirred for some time, for example, for about 30-40 minutes, 30 minutes, 20 minutes, 15-20 minutes, or about 15 minutes.

In some embodiments, the first solvent is selected from an amide, a phosphinic acid, a phosphorus based chelating agent, a phosphine oxide, or a combination thereof. In an exemplary embodiment, the first solvent is N,N,N,N Tetra (2 Ethylhexyl) Diglycolamide (TEHDGA). In another exemplary embodiment, the first solvent is a phosphorus based chelating agent or a phosphine oxide. In some embodiments, the first solvent is selected from the group consisting of dialkyl phosphinic acid, (2 Ethylhexyl) Diglycolamide, dialky1dithiophosphinic acid, trialkyl phosphine oxide, and a combination thereof.

In some embodiments, the first solvent and the first liquor are mixed in presence of an auxiliary solvent. In some embodiments, the auxiliary solvent is a dearomatized hydrocarbon solvent such as Exxsol ™ D80.

In some embodiments, the concentration of the first solvent is about 0.2-0.5M, including values and ranges therebetween, such as about 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5 M, or about 0.3-0.5 or 0.4-0.5 M. In some embodiments, the first solvent and the first liquor are contacted at a pH of about 0.5-3.0, including values and ranges therebetween, such as about 0.5-2.5, 0.5-2, 0.5-1.5, 1-3, 1-2.5, 1-2, 1.5-3, 1.5-2.5, 2-3, or about 0.5, 1, 1.5, 2, 2.5, or 3.

After stirring the first solvent-liquor mixture for about 15-40 minutes, the mixture is stripped with a mineral acid to obtain a second liquor containing Ce, La, and Nd. In some embodiments, the first solvent-liquor mixture is stripped with about 0.2-1N HCl for about 2 to 30 minutes (e.g., about 5, 10, 15, 20, 25, or 30 minutes) at room temperature (e.g., about 20-40?).

The second liquor is contacted with a first precipitant to obtain a cerium oxide precipitate and a third liquor containing La and Nd. In some embodiments, the first precipitant employed to precipitate cerium from the second liquor is an alkali or an alkali salt of peroxide. In some embodiments, the first precipitant is selected from ammonium oxalate, sodium hydroxide, or sodium peroxide.

In some embodiments, the second liquor is contacted with the first precipitant at a temperature of about 50-90?, 50-80?, 50-75?, 50-70?, 50-60?, 55-90?, 55-85?, 55-80?, 55-75?, 55-70?, 60-90?, 60-85?, 60-80?, 60-75?, 65-90?, 65-80?, 65-75?, 70-90?, 70-80?, 75-90?, or 80-90?, including values and ranges therebetween, for about 0.5-2 h, 0.5-1.5 h, 0.5-1 h, 1-2 h, 1-1.5 h, or 1.5-2 h, including values and ranges therebetween, to precipitate cerium oxide.

The cerium oxide precipitate is filtered and the filtrate containing La and Nd, referred to herein as a third liquor, is subjected to a solvent extraction step. For solvent extraction, the third liquor containing La and Nd is contacted with a second solvent to obtain a second solvent-liquor mixture. In some embodiments, the third liquor is contacted with a second solvent at a solvent:liquor ratio of about 1:1 or about 1.5:1 or more to obtain a solvent-liquor mixture (referred to herein as the second solvent-liquor mixture). In some embodiments, the second solvent-liquor mixture is stirred for about 15-20 minutes.

In some embodiments, the second solvent is selected from an organophosphorus that is a diester of a weak acid and alkanol. In an exemplary embodiment, the second solvent is a dialkyl phosphinic acid. In another exemplary embodiment, the second solvent is tetradecyltrihexylphosphonium bis(2,4,4-trimethylpentyl) phosphinate. In some embodiments, the second solvent is selected from the group consisting dialkyl phosphinic acid, (2 Ethylhexyl) Diglycolamide, dialky1dithiophosphinic acid, trialkyl phosphine oxide, and a combination thereof.

In some embodiments, the concentration of the second solvent is about 0.25-1M, such as about 0.25, 0.5, 0.75, or 1 M. In some embodiments, said contacting of the second solvent and the third liquor is carried out at a pH of about 3.0-4.0.

In some embodiments, the second solvent and the third liquor are mixed in presence of an auxiliary solvent. In some embodiments, the auxiliary solvent is a dearomatized hydrocarbon solvent such as Exxsol ™ D80.

Contacting of the third liquor with the second solvent extracts Nd in the solvent phase and the liquor phase contains La. The liquor phase is referred to herein as a fourth liquor or a raffinate. The solvent phase is separated from the liquor phase and is stripped with a dilute acid to recover neodymium oxide. In some embodiments, the solvent phase is stripped with about 0.2-1N HCl for about 2 to 30 minutes (e.g., about 5, 10, 15, 20, 25, or 30 minutes) at room temperature (e.g., about 20-40?).

The neodymium stripped in dilute acid is washed in deionised water and calcined at about 100-150?, including values and ranges therebetween, for about 0.5-1h to yield Nd oxide.

To precipitate La, the fourth liquor/raffinate is contacted with a second precipitant at a temperature of about 30-50?, 30-40?, 35-45?, or about 40-50?, including values and ranges therebetween, for about 0.5-2 h, 0.5-1.5 h, 0.5-1 h, 1-2 h, 1-1.5 h, or 1.5-2 h, including values and ranges therebetween.

In some embodiments, the second precipitant is selected from an oxalate salt of a hydroxide; an oxalate salt of a carbonate; a sodium salt of a hydroxide; a sodium salt of a carbonate; an ammonium salt of a hydroxide; an ammonium salt of a carbonate; or an ammonium salt of an oxalate. In exemplary embodiments, the second precipitant is selected from sodium hydroxide, sodium carbonate, sodium oxalate, ammonium oxalate, ammonium hydroxide, or ammonium carbonate.

The La precipitate is calcined at about 100-150?, including values and ranges therebetween, for about 0.5-1h to yield La oxide.

The method of the present disclosure isolates Ce, La, and Nd from GGBFS very efficiently. In some embodiments, the method extracts about 95-99.9% of Ce with respect to the total Ce content of the GGBFS, about 95-99.9% of La with respect to the total La content of the GGBFS, and about 95-99.9 % of Nd with respect to the total Nd content of the GGBFS. In an exemplary embodiment, the method extracts about 96-98% of Ce with respect to the total Ce content of the GGBFS, about 98% of La with respect to the total La content of the GGBFS, and about 99% of Nd with respect to the total Nd content of the GGBFS.

Methods for preparing construction materials
The first residue (extracted GGBFS) obtained after acid leaching of GGBFS is employed for preparing construction materials. The residue is conditioned prior to preparing the construction materials. The step of conditioning comprises washing the acid treated residue several times in water and filtering the washed residue to ensure its acid free before preparation of the construction materials. The conditioned residue is dried. This dry residue is processed to prepare a construction material. In some embodiments, the construction material is concrete.

In some embodiments, the method for preparing a construction material comprises mixing the dried conditioned residue with aggregates and cement to prepare a dry mix; adding water to the dry mix to obtain a slurry; setting the slurry to obtain concrete. Steps 20-25 shown in Figure 1 depict an exemplary method for preparing concrete.

In some embodiments, aggregates are materials such as sand, gravel, and crushed stone. In some embodiments, the size of the aggregate material ranges from about 100-150 micron, about 75-200 micron, or about 1-6 mm.

In some embodiments, the dried conditioned residue is mixed at a weight ratio of about 10-50% with respect to the weight of the dry mix.

In some embodiments, water is added to the dry mix at a ratio of about 2:5 to obtain the slurry.

The present disclosure also provides a construction material, for example, concrete comprising cement, the first residue (extracted GGBFS), and aggregates.

The methods of the present disclosure provide several advantages. The present disclosure is the first to provide methods that extract Ce, Nd, and La individually from granulated blast furnace slag. The combination of chemical leaching with stage-wise solvent extraction and selective precipitation provides a highly efficient process to obtain ultrapure metal salts of Ce, La and Nd and at the same time provides a complete utilisation of acid treated residue after metal extraction from ground granulated blast furnace slag. For example, about 85-99.9% of Ce, Nd, and La present in granulated blast furnace slag are extracted by the present methods there by providing a high yield of these elements. The rare earth elements obtained by the processes of the present disclosure can be used directly in low carbon technologies and the extracted granulated blast furnace slag is employed for making a construction material without further processing.

It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES

Example 1: Acid leaching of GGBFS using sulfuric acid:
GGBFS was reacted with 1M sulfuric acid at a temperature of 90? for 2 hours to obtain a leach residue (first residue) and a leach liquor (first liquor). The leach residue (first residue) and leach liquor (first liquor) were separated. The amount of metals at various stages of the process are shown in Table 1 below.
Table 1: Amounts of various metals at various stages of Example 1
Metals La Ce Nd Al Si Ca
Feed 90ppm 150ppm 70ppm 18.26% 32.80% 33.60%
Leach residue (first residue) 87ppm 130ppm 66ppm 15.23% 25.6% 19.88%
First liquor 1.95ppm 16.5ppm 3.99ppm 2.92g/L 6.56g/L 13.44g/L

Example 2: Acid leaching of GGBFS using hydrochloric acid:
GGBFS was reacted with 1M hydrochloric acid at a temperature of 90? for 2 hours to obtain a leach residue (first residue) and a leach liquor (first liquor). The leach residue (first residue) and leach liquor (first liquor) were separated. The amount of metals at various stages of the process are shown in Table 2 below.
Table 2: Amounts of various metals at various stages of Example 2
Metals La Ce Nd Al Si Ca
Feed 90 ppm 150 ppm 70 ppm 18.26% 32.80% 33.60%
Leach residue (first residue) 0.1 ppm 0.4 ppm 0.2 ppm 8.99% 31.30% 27.22%
First liquor 89.8 ppm 148.6 ppm 69.8 ppm 2.69g/L 0.9g/L 3.19g/L

Example 3: Acid leaching of GGBFS using nitric acid:
GGBFS was reacted with 1M nitric acid at a temperature of 90? for 2 hours to obtain a leach residue (first residue) and a leach liquor (first liquor). The leach residue (first residue) and leach liquor (first liquor) were separated. The amount of metals at various stages of the process are shown in Table 3 below.
Table 3: Amounts of various metals at various stages of Example 3
Metals La Ce Nd Al Si Ca
Feed 90 ppm 150 ppm 70 ppm 18.26% 32.80% 33.60%
Leach residue (first residue) 2.2 ppm 1.4 ppm 0.8 ppm 4.77% 24.70% 18.68%
First liquor 86 ppm 147 ppm 69 ppm 4.23g/L 3.69g/L 5.32g/L

Example 4: Separation of rare earth elements from the first liquor obtained from acid leaching of GGBFS
GGBFS was first reacted with 1M hydrochloric acid at a temperature of 90? for 2 hours to obtain a leach residue (first residue) and a leach liquor (first liquor). The first liquor was contacted with various solvent extraction reagents (in Exxsol™ D80) with organic/aqueous ratio of 1.0 and stirred for 15 minutes. The amounts of metals extracted in various solvents are shown in Table 4 below.
Table 4: Amount of metals loaded with various organic solvents of Example 4
Solution La Ce Nd Al Si Ca
First Liquor 86ppm 147 ppm 69ppm 4.23g/L 3.69g/L 5.32g/L
Cyanex 272 78ppm 73ppm 17ppm 1.09g/L 1.1g/L 1.99g/L
Cyanex 572 47ppm 86ppm 49ppm 1.22g/L 1.89g/L 3.12g/L
TEHDGA 85ppm 145ppm 67ppm 0.13g/L 0.09g/L 0.79g/L
Cyanex 301 39ppm 56ppm 59ppm 3.63g/L 2.23g/L 3.11g/L
Cyanex 923 84ppm 140ppm 32ppm 4.11g/L 3.32g/L 4.71g/L

Example 5: Process for separation of cerium from second liquor of ground granulated blast furnace slag
GGBFS was first reacted with 1M hydrochloric acid at a temperature of 90? for 2 hours to obtain a leach residue (first residue) and a leach liquor (first liquor). The first liquor was contacted with TEHDGA (in Exxsol™ D80) with organic/aqueous ratio of 1.0 and stirred for 15 minutes and stripped in HCl resulting in a second liquor. The second liquor was subjected to precipitation using various reagents (first precipitants), as shown in Table 5 below.
Table 5: Efficiency of various precipitation reagents for separation of cerium from Example 5
Solution La Ce Nd Al Si Ca
Second Liquor 85ppm 145ppm 67ppm 0.13g/L 0.09g/L 0.79g/L
Ammonium oxalate 64ppm 138ppm 60ppm 0.11g/L 0.09g/L 0.70g/L
NaOH 83ppm 140ppm 62ppm 0.13g/L 0.09g/L 0.79g/L
Sodium peroxide 0.4ppm 143ppm 1.19 ppm 0.02g/L 0.004g/L 0.02g/L

Example 6: Process for separation of lanthanum and neodymium from third liquor of GGBFS
GGBFS was reacted with 1M hydrochloric acid at a temperature of 90? for 2 hours to obtain a leach residue (first residue) and a leach liquor (first liquor). The first liquor was contacted with TEHDGA (in Exxsol™ D80) with organic/aqueous ratio of 1.0 and stirred for 15 minutes and stripped in HCl resulting in second liquor. The second liquor was subjected to precipitation by sodium peroxide and the filtrate (third liquor) rich in La and Nd was subjected to solvent extraction with various solvent extraction reagents (in Exxsol™ D80) with organic/aqueous ratio of 1.0 and stirred for 15 minutes resulting in a solvent phase enriched in Nd and a raffinate containing La. The raffinate was analysed as shown in Table 6 below.
Table 6: Concentration of La in raffinate after contacting with various solvents for separation of La from Nd of Example 6
Solution La Ce Nd Al Si Ca
Third Liquor 84ppm 2ppm 65ppm 0.11g/L 0.07g/L 0.77g/L
Cyanex 272 83ppm NIL 6.2ppm 0.03g/L 0.01g/L 0.2g/L
Cyanex 572 44ppm NIL 17ppm 0.06g/L 0.06g/L 0.5g/L
Cyanex 301 39ppm NIL NIL 0.07g/L 0.049g/L 0.45g/L
Cyanex 923 3ppm NIL 36ppm 0.08g/L 0.04 0.6g/L

Example 7: Process for synthesis of concrete from first residue of GGBFS
GGBFS was reacted with 1M hydrochloric acid at a temperature of 90? for 2 hours to obtain a leach residue (first residue) and a leach liquor (first liquor). The first residue was washed, conditioned and dried, before mixing with various ratios of river sand, clinker and aggregates, to form a dry mix, which was mixed with water and allowed for settling, as shown in Table 7 below.
Table 7: Mixing ratio and setting time for various ratios of first residue from Example 7
Sand (%) Clinker (%) Treated GGBFS (%) Initial Setting time (min) Final Setting Time (min)
70 20 10 75 140
60 20 20 65 135
70 15 15 130 450
70 15 15 165 580
65 15 20 60 130
IS Standard Not less than 30 min Not more than 10 h

Claims:

1. A process for the extraction of cerium (Ce), lanthanum (La), and neodymium (Nd) from ground granulated blast furnace slag (GGBFS), comprising:
a. reacting the GGBFS with a mineral acid to obtain a first residue and a first liquor containing Ce, La, and Nd;
b. contacting the first liquor with a first solvent to obtain a first solvent-liquor mixture;
c. stripping the first solvent-liquor mixture with a mineral acid to obtain a second liquor containing Ce, La, and Nd;
d. contacting the second liquor with a first precipitant to obtain a cerium oxide precipitate and a third liquor containing La and Nd;
e. contacting the third liquor with a second solvent to obtain a second solvent-liquor mixture comprising a solvent phase and a liquor phase (fourth liquor);
f. stripping the solvent phase with a mineral acid to recover neodymium oxide; and
g. contacting the fourth liquor with a second precipitant to obtain a lanthanum oxide precipitate.
2. The process as claimed in claim 1, wherein the mineral acid is selected from hydrochloric acid, nitric acid, and sulphuric acid.
3. The process as claimed in claim 1 or 2, wherein about 5-30% w/v of the GGBFS is reacted with about 70-90% w/v of the mineral acid.
4. The process as claimed in claim 1 or 2, wherein the GGBFS is reacted with about 0.5-3M mineral acid at a temperature of about 40-90? for about 0.25-5 hours.
5. The process as claimed in claim 4, wherein the GGBFS is reacted with the mineral acid at about 90? for about 2 hours.
6. The process as claimed in any one of claims 1-5, wherein the first liquor has a lanthanum content in an amount of about 78-99.9% with respect to total lanthanum content in the GGBFS; a cerium content in an amount of about 82-99.9% with respect to total cerium content in the GGBFS; a neodymium content in an amount of about 89-99.9% with respect to total neodymium content in the GGBFS.
7. The process as claimed in any one of claims 1-6, wherein the first liquor is contacted with the first solvent at a solvent: liquor (organic: aqueous) ratio of about 1:1 and the first solvent-liquor mixture is stirred for about 15-20 minutes.
8. The process as claimed in any one of claims 1-7, wherein the concentration of the first solvent is 0.2-0.5M and said contacting of the first solvent and the first liquor is carried out at a pH of about 0.5-3.0.
9. The process as claimed in any one of claims 1-8, wherein the first solvent is selected from an amide or a phosphinic acid.
10. The process as claimed in any one of claims 1-9, wherein the first solvent is N,N,N,N Tetra (2 Ethylhexyl) Diglycolamide (TEHDGA).
11. The process as claimed in any one of claims 1-9, wherein the first solvent is a phosphorus based chelating agent or a phosphine oxide.
12. The process as claimed in any one of claims 1-11, wherein the first solvent-liquor mixture is stripped with hydrochloric acid.
13. The process as claimed in any one of claims 1-12, wherein the second liquor is contacted with the first precipitant at a temperature of about 50-90? for about 0.5-2h.
14. The process as claimed in any one of claims 1-13, wherein the first precipitant is an alkali salt of peroxide to obtain cerium.
15. The process as claimed in any one of claims 1-13, wherein the first precipitant is selected from ammonium oxalate, sodium hydroxide, or sodium peroxide.
16. The process as claimed in any one of claims 1-15, wherein the third liquor is contacted with the second solvent at a solvent:liquor ratio of about 1:1, 1.5:1 or more and the second solvent-liquor mixture is stirred for about 15-20 minutes.
17. The process as claimed in any one of claims 1-16, wherein the concentration of the second solvent is about 0.25-1M and said contacting of the second solvent and the third liquor is carried out at a pH of about 3.0-4.0.
18. The process as claimed in any one of claims 1-17, wherein the second solvent is a dialkyl phosphinic acid.
19. The as claimed in any one of claims 1-18, wherein the second solvent is tetradecyltrihexylphosphonium bis(2,4,4-trimethylpentyl)phosphinate.
20. The process as claimed in any one of claims 1-19, wherein the second solvent-liquor mixture is stripped with hydrochloric acid.
21. The process as claimed in any one of claims 1-20, wherein the fourth liquor is contacted with the second precipitant at a temperature of about 30-50? for about 0.5-2h.
22. The process as claimed in any one of claims 1-21, wherein the second precipitant is ¬¬¬¬¬¬¬¬ selected from an oxalate salt of a hydroxide; an oxalate salt of a carbonate; a sodium salt of a hydroxide; a sodium salt of a carbonate; an ammonium salt of a hydroxide; an ammonium salt of a carbonate; or an ammonium salt of an oxalate.
23. The process as claimed in any one of claims 1-22, wherein the process extracts about 95-99.9% of Ce with respect to the total Ce content of the GGBFS, about 95-99.9% of La with respect to the total La content of the GGBFS, and about 95-99.9 % of Nd with respect to the total Nd content of the GGBFS.
24. The process as claimed in claim 1, wherein the first residue is mixed with cement and aggregates to prepare a dry mix; adding water to the dry mix to obtain a slurry; and setting the slurry to obtain concrete.
25. The process as claimed in claim 24, wherein said aggregates are selected from the group consisting of sand, gravel, crushed stone, and a combination thereof.
26. The process as claimed in claim 24 or 25, wherein the size of the aggregates ranges from about 100-150 micron, about 75-200 micron, or about 1-6 mm.
27. The process as claimed in any one of claims 24-26, wherein the first residue is washed with water prior to mixing with the cement and the aggregates.
28. The process as claimed in any one of claims 24-27, wherein the first residue is mixed at a weight ratio of about 10-50% with respect to the weight of the dry mix.
29. The process as claimed in any one of claims 24-28, wherein water is added to the dry mix at a ratio of about 2:5 to obtain the slurry.