Solvent extraction, separation and recovery of thorium from Korean monazite leach liquors for nuclear industry applications

Journal Pre-proof Solvent extraction, separation and recovery of thorium from Korean monazite leach liquors for nuclear industry applications Kyeong Woo Chung, Ho-Sung Yoon, Chul-Joo Kim, Jin-Young Lee, Rajesh Kumar Jyothi

PII:

S1226-086X(19)30605-7

DOI:

https://doi.org/10.1016/j.jiec.2019.11.014

Reference:

JIEC 4856

To appear in:

Journal of Industrial and Engineering Chemistry

Received Date:

6 September 2019

Revised Date:

5 November 2019

Accepted Date:

10 November 2019

Please cite this article as: Chung KW, Yoon H-Sung, Kim C-Joo, Lee J-Young, Jyothi RK, Solvent extraction, separation and recovery of thorium from Korean monazite leach liquors for nuclear industry applications, Journal of Industrial and Engineering Chemistry (2019), doi: https://doi.org/10.1016/j.jiec.2019.11.014

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Solvent extraction, separation and recovery of thorium from Korean monazite leach liquors for nuclear industry applications Kyeong Woo Chung1, Ho-Sung Yoon1, Chul-Joo Kim1, Jin-Young Lee2 and Rajesh Kumar Jyothi2* 1

Resource Recovery Research Center, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 34132, Korea 2

*Corresponding author

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E-mail address: [email protected] (R. K. Jyothi)

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Convergence Research Center for Development of Mineral Resources (DMR), Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 34132, Korea

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Graphical abstract

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Highlights

 Extraction, separation and recovery of thorium from Korean monazite was studied

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 Phosphorous and nitrogen based commercial extractants were examined  It was concluded that, Prieme JM-T proved as best extractant followed by D2EHPA > PC-88A  To minimize cerium co-extraction with thorium, cerium oxidation sate was changed from +4 to +3  Process was developed for thorium recovery and separation from rare earths 2

Abstract The technology for extraction and recovery of the thorium from its source is one of the significant areas of research Present investigation deals on development of a process for extraction of thorium and its separation from the uranium and rare earths contained Korean monazite leach liquor. In the preliminary study, sulfuric acid treatment of monazite concentrate followed by water leaching was carried out. Furthermore double salt precipitation

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and acid leaching lead to produce thorium rich leach liquor. Various commercial extractants accomplishing D2EHPA, PC88A, Amine and Primene JM-T were tested and optimized for selective separation of thorium. The effective extraction behavior of thorium followed the

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order as; Primene JM-T > D2EHPA > PC88A and high separation factor was resulted at high

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acidity (2.5 mol/L) of leach liquor, ensuring on high selectivity of Primene JM-T towards loading of Th. The co-extraction of cerium was prevented by changing thorium oxidation

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state using Fe2+ and H2O2 and reported. The co-extraction of other associated rare earths was scrubbed with sulfuric acid solutions. Subsequently, stripping studies were carryout with two

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different types of mineral acids and it was quantitative using high acid concentration (5 mol/L).

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Keywords: Thorium, Extraction, Separation, Korean Monazite, Stripping

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Introduction

Monazite mineral is the one of the major sources for thorium including the rare earth

elements (REEs) and uranium. The extraction and possible separation of thorium from other associated elements (rare earth elements (REEs) and uranium) are essentially needed exclusively in nuclear industry processes. Thorium deposit is comparatively higher than 3

uranium in the natural resources. Presently, most of the global nuclear reactors are being run by uranium, and the future prospective mainly is focused on thorium reactors. The projected worldwide thorium resources by International Atomic Energy Agency (IAEA), the total amount is ~6 355 300 to 6 372 300 tonns (in situ) [1, 2]. On the other hand in specific, a very limited amount of thorium (0.02 to 0.1% of ThO2) is also present in monazite or bastnasite ore other than the rare earth oxide (0.5 to 12% of REO) and uranium

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(0.002 to 0.004% of U3O8). Developed world is implementing the 4th industrial revolution whereas un-developed societies are still suffering with no electricity at urban areas. Therefore, thorium recovery could be the supplement for full filling all above needs as well as for its

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numerous industrial applications.

The demand of thorium is increasingly high in these days. However, its extraction process

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mainly for its separation from associated metals such as uranium and rare earths is again a

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challengeable task for the metallurgists. Hydrometallurgy is the most promising in metal extraction process which not only imparts on development of sustainable technology but also

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address the environmental concern while treating radioactive element(s) deposit in the earth up to significant extent. Environmental pollution and remediation is most noteworthy subject

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[3-6]. To recover thorium from monazite, solvent extraction (also called as liquid-liquid extraction) process [7-16] is the one of the strategic method and utmost reliable technique to

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reach out on target metal recovery with enrichment factor. Moreover, it is the most reliable method to reach target metal recovery while minimizing the generation of waste(s). Four well-known developed flowsheets were extensively discussed in which the process

has been adopted based upon hydrometallurgical methods for recovering REEs from concern 4

ore concentrates. Usually, thorium has the chance to be obtained as by-product in these processes. Bayan Obo concentrate [17] has processed for rare earth elements (REEs) extraction using roasting followed by leaching process. In this process, thorium-pyrophosphate (ThP2O7) was obtained in radioactive waste disposal step. And hence further, radioactive treatment was adopted to produce thorium as the products. On the other hand, o\in another study, bastanasite concentrate having 60 to 70% of rare earth oxides (REO), was

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initially roasted at 500oC followed by hydrochloric acid leaching. The leach residue resulted thus contains cerium with thorium which was further treated with hydrochloric acid dissolution study in presence of reductant to generate the enriched cerium solution. Through this approach, the separated residue contains the thorium compound in the form of Th(OH)4

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[17].

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A process flow sheet was developed for Kvanefjeld rare earth concentrate (Bastnasite) having ~14% of REO. In a first step leaching was carried out with weak acid (pH 1.9) to

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separate the U, Th content along with other and heavy rare earths (HREs) metals in the leach liquor. The remaining residue was further treated with strong acid leaching (110 g/L H2SO4)

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at 95oC temperature. The generated residue was further treated RE double salt processing followed by caustic conversion (with NaOH). The RE, Th and U contained residue was

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reacted with HCl to obtain a selective dissolution of thorium and later on it was subjected to

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prepare RE product(s) [17].

A systematic flow sheet for processing of the Nolans rare earth concentrate was

developed and reported [17]. This concentrate having ~5% of REO, pre-acid leaching was carried out with sulfuric acid in presence of hydrogen peroxide followed by sulphation at 230 to 250oC. The further step followed as water leaching and then double salt precipitation with 5

sodium sulfate. After S/L separation, aqueous solution was treated for possible recovery of U and P then rest solution having thorium rich (Th(OH)4) compound. The solid from double salt precipitation was further treated with caustic conversion and selective dissolution to process for RE product. As solid phase extraction of thorium using multi-walled carbon nanotubes from the ore sample and its spectroscopic determination was reported by Kandrro et.al [18]. In another study [19], cloud point extraction coupled to Uv-Vis spectroscopy was adopted for

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pre-concertation recovery and determination of Th from the rock sample. In downstream stages, separation and purification of Th was investigated by solvent extraction (SX) method. As of now, in most SX based separation processes, various nitrogen

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based extractants such as amine (and quaternary ammonium salt have been utilized for extraction of thorium. In summary of a SX study, Th extraction using Primene JM-T),

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stripping with base reagents such as sodium chloride (or) sodium carbonates followed by recovery study was described and reported [20]. In another study, anion exchanger AV-17-8

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was used for thorium recovery from uranium hydrochloric acid solutions [21]. Thorium (IV) was extracted from solutions formed in sulfuric acid breakdown of perovskite by using di-2-

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ethylhexyl hydrogen phosphate (HDEHP), octonal (OCL) and TBP. At about 40% of HDEHP-OCL extracted 98.9% of Th(IV) with 81 % of Ln(III) (Here, Ln = sum of RE’s

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oxides) [22]. By counter current extraction (CCE) process, thorium (IV) was recovered from

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leached monazite solutions [23]. Primary study on acidity conditioning it indicated that 6.0 mol/L of nitric acid concentration is optimum for thorium extraction. Aliquat 336 was diluted in three different diluents such as kerosene, benzene and xylene and then used for thorium extraction. Various stripping reagents were used and off these, H2O could able to strip 79.3% of thorium from loaded organic phase (LO) and 5.0 mol/L of HCl strip 84.2% of thorium [24]. 6

2-Ethyl-hexyl-phosphonic acid, mono (2-ethyl hexyl) ester (PC88A) diluted in n-dodecane was used as an extractant for thorium separation and recovery [24]. The thorium (IV) extraction processing can be represented by following equation (1) [24]: Th4+(aq) + nNO3-(aq) + mH2A2(org) = Th(NO3)n (H2-(4-n)A2)m(org) + (4-n)H+(aq)

(1)

High nitric acid (4 mol/L) leach liquor contained thorium was also processed using TBP (30%) and Aliquat 336 (10%) and substantially, thorium nitrate was recovered from loaded

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organic phases [21]. Up to 96% of thorium could be extracted with 10% TBP and more than 99% of thorium has been done with 10% of Aliquat 336, whereas the back extraction (stripping) of the loaded thorium was achieved by distilled water [25]. Schiff base was also

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utilized as an extractant for extraction and possible separation of thorium (IV) from chloride

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solutions [26].

The other hydrometallurgical methods like adsorption have also been applied for thorium

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removal from aqueous solutions using magnetic nanoparticles [27]. Regeneration and reuse capacity of the proposed adsorbent was tested with the following experimental conditions

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were optimized for adsorption process: pH is 4.5, adsorbent concentration was 1.0 g/L, initial thorium feed was 250 mg/L and contact time was required 140 min. and in this study the

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desorption was carried out using 0.1 mol/L HCl with 120 min contact time [27]. In an another study, poly(2-hydroxyethylmethacrylate-expanded perlite) [P(HEMA-EP)], prepared and

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used as an adsorbent for uranium and thorium adsorption was performed [28]. Thorium was adsorbed more effective than uranium at pH 3 to 6; lower pH conditions (1 to 3) are favorable to uranium. This study concluded that, ion selectivity shoed the above said adsorbent highest affinity towards sorption of thorium over uranium [28]. 7

It is well known that, selectivity is a key and significant parameter in liquid-liquid extraction (solvent extraction) processing. Selectivity is mainly depending upon nature of the extractant, speciation of the metal ion at studied pH range and periodic chemical properties of the element [29]. In specific H+ are usually, extracted in to the sites of organic phase of the extractant-diluent system and the differences in ion affinities leads to the specific selectivity of the metal ions. In addition, having a low pH hydrolysis of metals is suitable for favorable

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extraction of thorium at low pH condition. The present study accomplishes thorium extraction and its possible separation from monazite leach liquors, which was examined and established to ensure possible separation of thorium in presence of uranium and rare earths (REs). The close resemblance chemical property of thorium with uranium further ascertains

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its effective extraction with amine based on the results of our previous studies [30-33].

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In the above literature survey mostly the thorium recovery from its ores was based on hydrometallurgical routes, however the major issues was encountered as its high purity

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separation and recovery from the corresponding leach solution. Therefore, this paper was intended to develop a suitable thorium extraction process from Korean monazite ore leach

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liquors using three different reagents such as Primene JM-T, D2EHPA and PC-88A and reported. The possible separation of the thorium from rare earths (REEs) were calculated by

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measuring of separation factors and subsequently, the recovery of thorium from loaded

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organic of Primene JM-T, D2EHPA and PC-88A was established. The significant role of these solvent reagents as well as stripping reagents for recovery of thorium were systematically investigated and described. Experimental

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Apparatus and reagents The thorium and other rare earth elements content in aqueous solution(s) were analysed by ICP-OES (iCAP 6000 Series, Thermo Scientific, USA). The commercial-grade amine-based extractant; Primene JM-T amine (mixture of highly-branched C16 to C22 tertiary alkyl primary amine isomers) was supplied by The DOW Chemical Company (Rohm and Hass) and was used without further purification. The diluent A150 (commercial name) used for

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preparation of different extractant concentration was supplied by Samsung, Korea. The other reagent like D2EHPA (di(2-ethyl-hexyl) phosphoric acid) used for the present study has been supplied by Sinochem Limited, China. Alamine 336 (tri-octyl/decyl amine), Aliquat 336

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(quaternary ammonium salt) was procured from Cognis Company. The other extractant PC88A (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) was supplied by Daihachi

chemical names were presented in Table.1.

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Solvent (liquid-liquid) extraction procedure

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Chemical Industry Co. Ltd., Osaka, Japan. The details of the type of extractant(s) and their

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To determine the distribution ratio, equal volumes of aqueous and organic phases were equilibrated in a glass-stoppered separating funnel for 5 minutes using a mechanical shaker at

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25±0.5oC. Preliminary time experiments (not shown) study demonstrated that thorium extraction equilibrium is reached within 5 minutes of contact time. After equilibration, the

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respective samples were allowed for phase disengagement. The concentration of thorium and other metals in the aqueous phase were determined by ICP-OES and the extracted metal concentration at the organic phase was determined by mass balance between the phases (extraction procedure as followed in earlier our own studies) [34-37]). The distribution ratio is expressed ads ‘D’ which was defined as the ratio of concentration of metal in the organic 9

phase to the concentration of metal in the aqueous phase (D = metal in organic phase / metal in aqueous phase). The percentage extraction (% E) was calculated by the following equation: % E = (D x 100 / D+1) A:O. The general error agreement between the distribution ratios values obtained was within ± 3%. Results and discussions Pretreatment of Korean monazite

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Korean monazite concentrate was pretreated by several experimental steps such as sulphation by sulfuric acid, followed by water leaching, then double salt precipitation, caustic conversion and acid leaching (HCl). The detailed pretreatment procedure was given in Fig. 1.

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At 250oC temperature with sulfuric acid sulphation was carryout then followed by water leaching and double salt precipitation (by using Na2SO4). The solid and liquid was separated

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and was confirmed that there is no rare earth elements (REEs) reported in the aqueous solution. The solid was treated with sodium hydroxide (caustic conversion) followed by

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hydrochloric acid leaching. The solid and liquid separated majority of REEs were at acid leach liquor and the residue having thorium with minor REEs concentration. Further, this

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residue was dissolved in 0.5 mol/L sulfuric acid solutions, generated the thorium rich leach liquor and solution contains the metals: Th-426, La-83, Ce-379, Nd-242, Pr-25, Sm-36 mg/L

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±2. This leach liquor was further processed for thorium solvent extraction and possible

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separation from associated REEs present in it. Selection of extractant Phosphorous based extractants such as D2EHPA and PC-88A as well as nitrogen based

extractants such as Primene JM-T, Alamine 336 and Aliquat 336 were used for primary test of 10

thorium extraction and possible separation behavior from associated REEs. The results obtained data were presented in Fig. 2. It was evident that the Primene JM-T is better extractant for thorium extraction than other reagents in this investigation in context of extraction efficiency and they followed the order as: Primene JM-T > D2EHPA > PC-88A > Aliquat 336 > Alamine 336. From the above experimental studies, the separation factors (SFs) were determined and

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presented in the Table 2. As can be seen at lower concentration (0.05 mol/L) of Primene JM-T a complete separation (CS) of Th was attained in presence of other REEs (lanthanum, praseodymium and samarium REEs). Nevertheless, using 0.1 mol/L Primene JM-T the SF

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was further improved and highest SF was observed with 1.0 mol/L Primene JM-T. Whereas, phosphorus based extractants such as D2EHPA and PC-88A extracted all these three REEs

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(lanthanum, praseodymium and samarium) at the entire studied extractant concentration ranges (0.05 to 0.2 mol/L) rather than Th. The above observation was well ascertained the

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REEs exist as +3 oxidation state and follows cation exchange mechanism while getting extracted with organophosphorus reagents unlike the speciation of Th which is predominantly

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found as +4 oxidation form and hence it was poorly extracted with D2EHPA/PC88A from the acidic medium. Thus, this study concludes that Primene JM-T would be suitable for selective

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separation of thorium REEs bearing monazite leach liquor.

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Sulfuric acid influence on thorium extraction The sulfuric acid effect was tested in the range of 0.5 to 2.5 mol/L using three different

types of extractants such as Primene JM-T, D2EHPA and PC-88A. The other experimental condition such as phase ratio (A/O=1), temperature 25oC and extractant concentration 0.1 11

mol/L, were kept constant for all the above three extractant system. As shown in Fig. 3, Primene JM-T system showed constant thorium extraction trend, whereas the other two P based extractants; D2EHPA (or) PC-88A followed decreased Th extraction trend at the entire studied acidity range of the leach liquor. Overall, the thorium extraction efficiency found to be is in the increasing order as: Primene JM-T > D2EHPA > PC-88A, at lower acidity concentration (at 0.5 mol/L H2SO4) of leach liquor.

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The co-extraction of all these REEs was significantly decreased while increasing acidity of solution with either of extractants. Especially in the PC-88A system, other REEs were not extracted entire study range of acidity except cerium and in case of D2EHPA system, both

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cerium and neodymium were co-extracted and other REEs extractions were not reported. From this study, it was noticed that the Primene JM-T seems less selective exclusively at mild

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acidic range (0.5 mol/L H2SO4) as co-extraction of associated REEs is taking place at that range and at strongly acidic condition; Ce extraction was reportedly ~20%. Thus, the

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optimum acidity of the leach liquor of 2.5 mol/L was kept fixed for further experimental

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investigations.

Effect of extractant concentration on thorium and REEs extraction

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The concentration extractant is one of the important factors on in this study while estimating the loading ability of the respective extractant towards the extraction of Th. In this

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study the three extractants such as D2EHPA, PC-88A and Primene JM-T concentrations were increased from 0.05 to 0.2 mol/L at fixed A/O of 1 and temperature 25oC. The results obtained were presented in Fig. 4. As expected, the thorium extraction was increased with increasing in the concentration of either of the extractants (Primene JM-T (or) D2EHPA (or) 12

PC-88A). In contrast, REEs extraction behavior was reversed with Primene JM-T system. This assures on selective and effective separation of thorium rather than REEs from the acidic monazite leached liquor. In other two cases lanthanum and samarium was not extracted at the studied extractant concentration ranges. The extraction of Cerium and neodymium was increased with increasing extractant concentration by using D2EHPA (or) PC-88A. From this study it was ascertained on more selective and efficient extraction (99.9%) of Th while using

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higher concentration of Primene JM-T and in which the co-extraction of Ce and Nd were up to 20%. The co- extraction of Ce along with Th may be due to the exhibition of same oxidation state (+4) to that of Th which was minimized by reducing +4 to +3 oxidation state

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as described below. Oxidation state conversion of the cerium

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To minimize (or) or to prevent the co-extraction of cerium with thorium to the reduction

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of cerium oxidation state i.e. from +4 to +3 was investigated. This study was carried using Fe2+ and H2O2 as the reducing reagents and the results obtained are as shown in Fig. 5. It was

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presumed that ~12 equivalent ratio of H2O2 could completely reduce the Ce from +4 to +3 oxidation state and which was confirmed by based upon the percentage of cerium observed

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resulted in solvent extraction of reduced leach liquor with Primene JM-T. As can be seen from the results, almost no thorium was extracted leaving thorium extraction unaffected.

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Moreover, the adoption of this change in oxidation state of Ce was equally effective for solvent extraction separation study of rare earth as well as other metals from the numerous aqueous solutions. Scrubbing studies 13

After extraction the resulted loaded organic (LO) for corresponding three extractants were subjected to the scrubbing using sulfuric acid. Two different (low and high) concentrations of acid i.e 1.0 mol/L and 5.0 mol/L of H2SO4 were tested for scrubbing study. The obtained results were presented in Fig. 6. It was seen that the LOs of D2EHPA and PC-88A were quickly reacted with sulfuric acid leading to scrub out Th with REEs. On the other hand, while scrubbing the LO of the extractant Primene JM-T, initially scrubbing of thorium was

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affected <5% and other three REEs (La, Pr, Sm) were scrubbed out up to 90% .The scrubbing of Nd was found to be 79.6% of whereas Ce was of 61% as observed in the above study.. After scrubbing out the respective REEs, the LO was used for stripping study to separate the

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enriched content of Th with minim trace amount of other trace amount of REEs. Striping studies

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The REEs free LO of respective organic extractants (D2EHPA, PC88A and Prmene JM-T)

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was utilized for stripping study using hydrochloric acid and H2SO4. As per the literatures , amongst mineral acids, both H2SO4 and

HCl are being exclusively utilized for stripping of

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Th or REEs for its high stripping ability and quick regeneration ability of the organic extractants. Two different acid concentrations i.e. 1.0 and 5.0 mol/L was used for stripping of

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Th from the LO phase As shown in the Fig.7, more than 89% of the thorium was stripped at lower acidity (1.0 mol/L) of solution, n\but the stripping was quantitative with all the three

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loaded organics while stripping with higher acid concentration (5.0 mol/L HCl/H2SO4). The experimental outcome of the present investigation has been consistent with earlier

reported works [28, 38-47].The details of the findings-cum-comparative results of our work as well as the previous studies are summarized and as presented in Table 3. 14

Conclusions The present research paper was drawn following conclusions. Korean monazite was processed using hydrometallurgical techniques such as water leaching, sulphation, double salt precipitation by using Na2SO4, caustic conversion and acidic leaching by HCl. The leach liquor containing thorium with REEs such as La, Ce, Nd, Pr and Smwas subjected to the separation of either of these metals using Phosphorous and nitrogen based extractants such as

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Primene JM-T, Alamine 336, Aliquat 336, D2EHPA and PC-88A. The extractants are screened based upon better extraction of thorium as well as possibility of the separation from REEs. It was concluded that, Primene JM-T shown to be suitable extractant followed by

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D2EHPA > PC-88A. The other two extractants Alamine 336 and Aliquat 336 was not fitted well for this study. Sulfuric acid effect, given good acidic condition information for thorium

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extraction and possible separation of the associated REEs; and this study concluded that, 2.5 mol/L acidic conditions was suitable for present study. The extractant effect asertained that on

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increasing the extractant concentration, the % of metal extraction increased ,excepting the Primene JM-T case. In this case the reverse behavior was observed due to thorium extraction

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tendency was predominately more as compared with REEs extraction with Primene JM-T system. To minimize cerium co-extraction with thorium, cerium oxidation sate was changed

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from +4 to +3 resulting no co-extraction of cerium. On adoption of scrubbing stage in present

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study could successfully remove the REEs with minute loss of thorium. The La and Nd was scrubbed up to 99.9% whereas cerium: 61%, Nd: 79.6%, and Sm: 90.5%. Two mineral acids such as HCl and H2SO4 were tested for recovery of the thorium and the former one showed better results over later one. Subsequently high molar HCl (5 mol/L) appears to be suitable for thorium recovery for stripping it from loaded organic phase. The proposed technology 15

ensures for clean recovery of thorium for its utilizing in nuclear fuel applications.

Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Acknowledgements The research was supported by the Basic Research Project (GP2017-025) of the Korea Institute of Geoscience and Mineral Resources (KIGAM), funded by the Ministry of Science,

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ICT and Future Planning of Korea.

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[29] Michael L. Free, Hydrometallurgy: Fundamentals and Applications, ISBN 978-1-11823077-0, John Wiley & Sons, Inc., Hoboken, New Jersey, USA, 2013. [30] J. S. Kim, K. S. Han, S. J. Kim, S. D. Kim, J. Y. Lee, C. Han, J. R. Kumar, Journal of Radioanalytical and Nuclear Chemistry, 307 (2016) 843.

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[31] J. S. Kim, S. D. Kim, H. I. Lee, J. Y. Lee , J. R. Kumar, Monatshefte fur ChemieChemical Monthly, 144 (2013) 1589. [32] C. J. Kim, J. R. Kumar*, J. Y. Lee, J. S. Kim, H. S. Yoon, Journal of the Brazilian Chemical Society, 23 (2012) 1254. [33] J. R. Kumar, J. Y. Lee*, J. S. Kim, H. S. Yoon, Journal of Radioanalytical & Nuclear Chemistry, 285(2010)301. [34] C. J. Kim, J. R. Kumar, J. S. Kim, J. Y. Lee, H. S. Yoon, J. Braz. Chem. Soc. 23 (2012) 1254. [35] K. J. Reddy, J. R. Kumar, M. L. P. Reddy, A. V. Reddy, Sep. Sci. Technol. 44 (2009) 2022. [36] J. R. Kumar, H. I. Lee, J. Y. Lee, J. S. Kim, J. S. Sohn, Sep. Purif. Technol. 63 (2008) 184. [37] J. Y. Lee, J. R. Kumar, J. S. Kim, H. K. Park, H. S. Yoon, J. Hazard. Mater., 168 (2009) 18

424. [38] M. Singh, A. Sengupta, Sk. Jayabun, T. Ippili, J. Radioanal. Nucl. Chem. 311 (2017) 195. [39] S. Priya, A. Sengupta, Sk. Jayabun, V. C. Adya, Hydrometallurgy, 164 (2016) 111. [40] Q. H. Tran, V. T. Le, V. C. Nguyen, J. Chem-NY, 5078462 (2016) 1. [41] H. Huang, S. Ding, D. Su, N. Liu, J. Wang, M. Tan, J. Fei, Sep. Purif. Technol. 138 (2014) 65.

ro of

[42] M. Shaeri, M. Torab-Mostaedi, A. R. Kelishami, J Radioanal Nucl Chem. 303 (2015) 2093. [43] M. E. Nasab, Fuel, 116 (2014) 595. [44] Y. Wang,

Y. Li, W. Liao, D. Li, J. Radioanal. Nucl. Chem. 298 (2013)1651.

-p

[45] L. He, Q. Jiang, Y. Jia, Y. Fang, S. Zou, Y. Yang, J. Liao, N. Liu, W. Feng, S. Luo, Y. Yang, L. Yang, L. Yuan, J. Chem. Technol. Biotechnol. 88 (2013) 1930.

re

[46] P. Hu, L. Qian, Y. He, H. Wang, W. Wu, J. Radioanal. Nucl. Chem. 297 (2013) 297.

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lP

[47] X. Zhong, Y. Wu, J. Radioanal. Nucl. Chem. 292 (2012) 355.

19

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Figure 1. Flow sheet for synthesis of thorium rich residue associated with minor quantities of rare earth elements (REEs).

20

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Figure 2. Influence of various extractants on thorium extraction from monazite leach liquors (JM-T = Prieme JM-T, E = % Extraction, A/O = 1, Temperature = 25oC, Acidity = 0.5 mol/L H2SO4, Extraction time = 10 min and De = Distribution ratio for extraction).

21

22

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-p

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lP

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ur

Jo

Jo

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lP

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-p

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Figure 3. Extraction of Th and REEs from sulfuric acid solution with the variation of H2SO4 using (a) Prieme JM-T, (b) D2EHPA and (c) PC88A (A/O=1, Extractant concentration = 0.1 mol/L, Temperature = 25oC and Extraction time = 10 min).

23

24

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-p

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lP

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ur

Jo

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-p

Figure 4. Extraction of Th and REEs from sulfuric acid solutions with the variation of extractant concentration (a) Prieme JM-T, (b) D2EHPA and (c) PC88A (A/O=1, Temperature = 25oC, Extraction time = 10 min and Acidity = 2.5 mol/L of H2SO4).

Figure 5. Oxidation state conversion of cerium by using Fe2+ and H2O2 ( RL = Rest liquor, OL = Original liquor). 25

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Figure 6. Scrubbing of the thorium and rare earth elements (REEs) from loaded organic phase by using sulfuric acid.

26

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Figure 7. Stripping of LO’s of Prieme JM-T, D2EHPA and PC-88A by using mineral acids.

27

Table 1. Various extractants used for present study Reagent class

Di-(2ethylhexyl)phosphoric acid

Phosphonic acid

PC-88A

2-ethylhexyl phosphonic acidmono-2-ethylhexyl ester

Primary amine

Prieme JMT

Tertiary amine

Alamine 336

Quaternary ammonium salt

Aliquat 336

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D2EHPA

Mixed t-alkyl primary amines Tri-octyl/decyl amine N-Methyl-N,N,N-trioctyl-ammonium chloride

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Anionic exchanger

Phosphorous acid

-p

Cation exchanger

Commercial name of Chemical name of the the extractant extractant

28

Table 2. Separation factors data drawn from effect of various extractants Separation factor Extractant concentration (SF) = DTh / DREE With Prieme JM-T 0.05 mol/L

0.1 mol/L

0.2 mol/L

CS*

128.3

97.3

DTh / DCe

106.9

34.3

31.9

DTh / DNd

281.1

42.6

38.3

DTh / DPr

CS*

234

91.8

DTh / DSm

CS*

52.3

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DTh / DLa

46.6

With D2EHPA

0.1 mol/L

CS*

CS*

DTh / DCe

2.1

18.8

DTh / DNd

6.6

DTh / DPr

CS*

DTh / DSm

CS*

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DTh / DLa

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0.05 mol/L

0.2 mol/L

CS* 73.2 181.6

CS*

CS*

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50.9

CS*

CS*

With PC-88A

na

0.05 mol/L

DTh / DCe DTh / DNd

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DTh / DPr

DTh / DSm

0.2 mol/L

CS*

CS*

CS*

0.3

3.3

20.3

2.5

21.5

61.3

CS*

CS*

CS*

CS*

CS*

CS*

ur

DTh / DLa

0.1 mol/L

DTh = Distribution ratio of thorium, DREE = Distribution ratio of rare earth element, CS* = Complete separation is possible

29

Media

Schiff base extractant,(E)-4-(2hydroxy-ethyl-imino) pentan-2-one (AcEt)

Methylene chloride

Chloride

Cyanex 923 (tri-n-alkyl phosphine Oxide), Cyanex 272 (Bis(2,4,4trimethyl) pentyl phosphinic

Xylene

Remarks

Reference

pH 6.5 is optimum condition for thorium extraction with 0.012 mol/L AcEt and 0.5 mol/L nitric acid is good resulted for stripping (98.5% of Th back extracted from loaded organic phase)

[26]

eNitrate

Thorium extraction efficiency was followed by the following order: Cyanex 923 > Cyanex 272 > DHOA > TBP

[38]

Cation exchange’ mechanism was followed the thorium and species reported as: [Th(NO3).3SO]3+ and the extraction efficiency followed APSO > BMSO > DHSO > DISO

[39]

Pr

na l

Acid), TBP (tri-n-butyl phosphate), DHOA (di-n-hexyl octanamide) in C8mimNTf2 (1-octyl-3-methylimidazolium bis(tri-fluoro-methanesulfonyl) imide)

Bis-(tri-fluoro-methylsulfonyl) imide lithium salt (LiNTf2), 1-butyl1-methyl-piperidinium bis

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Benzyl-methyl sulphoxide (BMSO), allyl phenyl sulphoxide (APSO), di isobutyl-sulphoxide (DISO), di hexyl sulphoxide (DHSO)

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Diluent

pr

Extractant

f

Table 3. Summary of the thorium extraction systems [10, 15-24]

Nitrate

(tri-fluoro-methylsulfonyl)imide and 1ethyl-2,3-dimethylimidazolium 30

Sulfonated kerosene

oo

N,N,N ,N ,N,N-hexa-octyl-nitrilotri-acetamide (NTAamide(C8)) and N,N,N,N,N,N-hexa-butyl-nitrilotri-acetamide (NTAamide(C4))

Nitric acid Higher acidity condition i.e 10 mol/L HNO3 is the best condition for thorium as much as possible separation from uranium and rare earth elements. Sodium carbonate (2.0 mol/L) is the best stripping reagent for thorium back extraction from loaded organic phase

Pr

Kerosene

Nitrate

na l

Tri-butyl phosphate (TBP) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex272)

pH 1 to 10 98% of thorium was extracted with TEAC range

pr

CH3OH

Kerosene

HNO3, HCl and H2SO4

Kerosene

HNO3

Jo ur

Tri-butyl-phosphate (TBP), trioctyl-amine (TOA), and tricaprylyl methyl ammonium chloride (Aliquat 336)

Di-(2-ethyl-hexyl) 2-ethylhexyl phosphonate (DEHEHP)

[40]

[41]

e-

5,11,17,23-Tetra[(2-ethylacetoethoxyphenyl)(azo)phenyl]cal ix[4]arene (TEAC)

f

bis (tri-fluoro-methylsulfonyl)imide

Optimum pH condition is 3.0 and maximum synergistic enhancement factor 3.86 with 1:4 molar ratio of the Cyanex 272 and TBP was reported

[42]

Aliquat 336 at 5.0 mol/L HNO3 concentration

[43]

Various salting-out agents such as LiNO3, NaNO3, NH4NO3 and KNO3 tested for thorium extraction process. And lithium nitrate proved the best salting-out reagent. The extracted species reported as: Th(NO3)4 . 2DEHEHP

[44]

31

Lower acidic condition (~0.5 mol/L HNO3) is the favorable for thorium extraction and it was possible to increase extraction efficiency in presence of the salting-out reagent (NaNO3). Up to 72% thorium was stripped with 0.64 mol/L HNO3

[46]

HCl and HNO3

~95% of Thorium was extracted by this method and recovery was 86% reported

[47]

H2SO4

Prieme JM-T is better extractant for thorium extraction. And the orders of extraction efficiencies were as follows: Prieme JM-T > D2EHPA > PC-88A > Aliquat 336 > Alamine 336. Sulfuric acid used as a scrubbing agent to recovery the co-extracted rare earths, finally 5.0 mol/L HCl is most suitable reagent for quantitative recovery of the thorium.

Present method

1, 2-Di-choloro-ethane

HNO3

f

[45]

HNO3

Purified aliphatic diluent (A150)

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Primene JM-T (mixture of highlybranched C16 to C22 tertiary alkyl primary amine isomers), D2EHPA (di(2-ethyl-hexyl)phosphoric acid) and PC 88A (2-ethyl-hexyl phosphonic acid mono-2ethylhexyl ester)

Kerosene

Pr

Di(1-methyl heptyl) methyl phosphate ( P350)

e-

pr

N,N-di-ptolylpyridine2,6-dicarboxamide (DTPDA)

Thorium as much as maximum extracted at pH 3.97 (~90%). Thorium separation with various rare earth elements are as follows: La-28.3, Ce23.8, Nd-22.8

CH2Cl2

oo

Polyaramide

32