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URANUM EXTRACTION REFINING PROCESS ON THE BASE OF MINING METALURGICAL PLANT «STEPNOGORSK MINING –CHEMICAL COMBINATE»

Abstract

It is suggested the possible way of uranium and molybdenum quantitative separation at the stage of extracting when optimal рН meaning is chosen. It is derived that the process of uranium separation from molybdenum happens in the interval of рН = 5,5-6,5. To refine uranium solutions from mechanical impurities we have made preliminary procedure of zirconium ions’ sedimenting, where a non-solvent agent was liquid glass. Uranium liquids’ purification from emulsionizing impurities provides stableness of uranium extracting process and enhancement of the final product.

Keywords: uranium, refining process, extraction

1. Introduction

Starting from 2005 year the Institute for High Technologies is maintaining a process stage of extraction at Hydro-Metallurgical Plant of “Stepnogorsk’ Mining-Chemical Combinate” Ltd. (HMP “SMCC” Ltd.). As the subject is of high priority, we performed several research trials of different methods of uranium solutions refining from emulsionizing impurities and the ways of selective decomposition of uranium from molybdenum of different methods of clearing.

Today HMP “SMCC” Ltd. has 2 operating extraction lines, consuming different raw materials:

1. Ore extracting line – affinage of local raw material with extracting agents’ mixture di-(2-ethylhexsyl) phosphoric acid (Di2EHPA) + threealkylamin (ТАА) + threebutylphosphate (ТBPh) in diesel fuel;

2. Southern extraction line – affinage of uranium concentrates, supplied from South mining enterprises JS NAC “Kazatomprom” with extracting agents’ mixture Di2EHPA + ТАА in diesel fuel.

At Mining extracting line we affinage uranium solutions, derived from uranium ore refining delivered from deposits “Zvezdnoye” and “Vostok”. The uranium ore processing pass the technological scheme, including crack operation, fining, and autoclave sodium leach. Uranium is concentrated during the sorption process on strongly basic ionite, and regeneration is performed through soda-chloride solutions. Uranium extraction re-filtering is made by applying extracting agents based on Di2EHPA + ТАА + ТBPh. Re-extraction is performed by carbonate-bicarbonate solutions, resulting ammonium uranilthreecarbonate (AUTC), through its inciderating we got the end product – uranium protoxide-oxide.

2. Experimental

Laboratory research works were conducted to detect the factors, impacting on the forming the third phase, when uranium containing ores from deposits “Zvezdnoye” and “Vostok” are extracted. The derived results stated that uranium ores at abovementioned deposits contain water solving forms of zirconium, molybdenum, silicone, mineral organics and other concomitant dirts. Zirconium and mineral organics in uranium ores brings to form quite long third phase in the processes of uranium extraction-reextraction and contaminating the end product with zirconium. So as ore leaching is performed by soda liquids, the third phase forming also is caused by ferrous (Fe3+), aluminum (Al3+) ions and silicon acids in uranium solutions.

Average zirconium content in uranium ores of current developing fluctuate in-between 0,018 to 0, 03 %. Today the zirconium concentration in the ore is 0,022 %. Zirconium is readily soluble under pressure leaching by soda solutions in the processing environment of HMP. Having close chemical congeniality, zirconium ions accompany uranium along all technological process stages, impact on uranium refining, became the source of end product mudding.

3. Results and discussion

We conducted research works on zirconium concentration in different technological process stage of uranium extraction. It is proved that it takes place the process of gradual concentration of zirconium ions in desorption soda-chloride solutions and in the solutions of Na diuranate. Zirconium after autoclave carbonate leaching passes into anion form, and like (ZrO(CO3)3)2- sorbs onto anionite, than transmits into soda-chlorine reclaim (SCR). The results of the experiments carried out display, that the ionites, applied in processing lines of HMP “SMCC” Ltd. can not provide effective separation of uranil-ions from water solvent zirconium isosteric compounds. The most strong zirconium ion concentrations are detected in the re-extracting wombs, which brings to regular co-depositing with AUTC and dirt of the end product.

We have studied several methods of zirconium ions extraction from productive uranium solutions: boiling, thermo hydrolyze autoclaving, depositing by phosphoric acid, depositing by liquid glass, stabilizes applying (modificators), flocculants.

As the modificators descending emulsion we used high spirits (octyl, decyl), threebutylphosphate. Boiling was performed at 1000С during 2 hours with air agitation 120 l/h per liter of reagent. It results the convergence with zirconium content 8-25 %, silicon 50%, calcium-magnesium 12 % and ferrum about 1 %. The boiling helped to decrease the content of zirconium and silicon up to 75 %, however the concentration of mineral organics remained the same.

When using thermohydrolyze autoclaving we obtained the refining from emulsionizing impurities up to 95 %. But this method applying on the facilities of HMP “SMCC” Ltd. is not acceptable because of high costs. When zirconium ions were sedimented by phosphoric acid we reached the refining level to 75 %.

The most effective and processible in the mills’ lines method of refining uranium solutions from zirconium ions is sediment by liquid glass, when the level of refining gets 96 %.

Aiming to simplify technological scheme and exclude expensive procedures to prepare uranium solutions to re-refining extraction, we conducted researches on extracting separation of uranium from molybdenum in soda-chloride solutions in the interval рН = 2,0-7,0. The average molybdenum concentration in uranium ores in current exploration fluctuates in the frames of 0,02-0,04 %. Soda chloride reclaim is a transit product in the technological scheme of uranium ore processing, mined from “Zvezdnoye” and “Vostok”. All range of oncoming impurities: molybdenum, zirconium, silicon, aluminum, and mineral organics, concentrated in uranium ore in considerable proportions transmit to soda-chloride reclaim. Uranium concentration in soda-chloride reclaims balances between 5-10 g/l. To concentrate uranium and decontaminate it, the following procedures should be performed: Na diuranate depositing, deoxidization, thermohydrolyzes, rectification purification, filtering and residual matter. The mentioned way of SCR processing is multistage one, long and extravagant. After all abovementioned SCR stages are performed, however the third phase arises as considerable interval in the process of uranium extraction-reextraction.

In this connection we studied the possibility of refining soda-chloride uranium-molybdenum reclaims according to the scheme, anticipating their distillation from zirconium ions by liquid glass and selective uranium extraction applying extragents: Di2EHPA+TAA, Di2EHPA+TBPh, Di2EHPA+ TAA+ TBPh.

The derived figures of the research on uranium extraction from soda-chloride reclaim in the interval of рН = 2,0-7,0 by abovementioned extragents blends are displayed in Tables 1-3.

Table 1. Uranium extraction results made of SCR blend 0,25 mole/l Di2EHPA + 0,15 mole/l ТАА in diesel fuel

 

Content of extraction womb, g/l

Extraction in organic phase, %

The volume of third phase, %

рН

U

Mo

U

Mo

7,0

0,040

1,410

94,6

7,8

trace

6,5

0,045

1,470

99,6

3,9

trace

6,0

0,040

1,450

99,6

5,2

trace

5,5

0,040

1,450

99,6

5,2

trace

5,0

0,080

0,822

99,3

46,3

trace

4,0

0,090

0,010

99,2

99,3

1,5

3,5

0,036

0,010

99,7

99,3

1,5

3,0

0,050

0,011

99,6

99,3

1,5

2,0

0,150

0,005

98,7

99,7

2,5

Table 2. Uranium extraction results made of SCR blend 0,25 mole/l Di2EHPA + 0,25 mole/l TBPh in diesel fuel

 

Content of extraction womb, g/l

Extraction in organic phase, %

The volume of third phase, %

рН

U

Mo

U

Mo

7,0

0,860

1,360

92,3

11,1

Emulsion 10-15

6,5

0,200

1,400

98,2

8,5

1,0

6,0

0,028

1,490

99,7

2,6

trace

5,5

0,025

1,460

99,8

4,6

trace

5,0

0,030

1,430

99,7

6,5

trace

4,5

0,010

1,030

99,9

32,7

trace

4,0

0,025

1,340

99,8

35,0

0,5

3,5

0,003

0,850

99,97

44,4

0,5

3,0

0,015

0,694

99,9

54,6

2,0

2,0

0,020

0,192

99,8

87,5

5,0

When using extraction mixture 0,25 mole/l Di2EHPA + 0,15 mole/l ТАА (Fig.1) uranium extraction in acidic area reaches its maximum meaning 99,7 %. Molybdenum extraction in organic phase in emitting interval рН = 2,0-7,0 changes from 4% to 99,7 %, which provides quite effective uranium and molybdenum separation at the stage of uranium extraction. The volume of the third derived phase when extracting is insignificant (up to 2,5 %). So, for extragents blends 0, 25 mole/l Di2EHPA + 0, 15 mole/l ТАА best range of quantitative uranium separation from molybdenum at stage of extraction is the interval рН = 5,5-6,5.

Table 3. Uranium extraction results made of SCR blend 0,24 mole/l Di2EHPA 0,24 + 0,16 mole/l ТАА + 0,15 mole/l TBPh in diesel fuel

 

Content of extraction womb, g/l

Extraction in organic phase, %

The volume of third phase, %

рН

U

Mo

U

Mo

7,0

0,017

0,82

99,8

6,8

no

6,5

0,015

0,83

99,8

5,7

no

6,0

0,010

0,86

99,9

2,3

no

5,5

0,014

0,79

99,8

10,2

no

5,0

0,014

0,36

99,8

59,1

no

4,0

0,005

0,028

99,9

96,8

no

3,0

0,005

0,011

99,9

98,8

2,0

When uranium extracting through extragents blend 0,25 mol/l Di2EHPA + 0,25 mol/l TBPh (Fig. 2) extracted uranium content level is 92-99%, the third phase forming during extraction is minimal (excluding рН = 7,0, when volume is 10-15%, which is caused by ineffective activity of this blend of extragents within defined рН meaning). Molybdenum extracting in organic phase is 2,6-87,5 %. The increase of molybdenum extracting in organic phase happens in acidulous area of рН. It is shown that effective uranium separation from molybdenum possible in the interval рН = 5,0-6,0.

Fig. 1. Association of uranium and molybdenum with рН when uranium is extracted through extragents blend Di2EHPA +ТАА

When we extracted uranium through triple blend of extragents 0,24 mole/l Di2EHPA + 0,16 mole/l ТАА + 0,15 mole/l TBPh (Fig. 3) the third phase forming is not happen. Uranium extraction is on the level of 99,9 % along all studied interval of рН. Molybdenum extracting in organic phase reaches the point 98,8 % when рН indication is higher 4. Selective uranium separation from molybdenum happens in the period of рН = 5,5-6,5.

Fig. 2. Association of uranium and molybdenum with рН when uranium is extracted through extragents blend Di2EHPA + TBPh

So, we presented the possibility in principal of direct uranium extracting from soda-chloride reclaim through researched extragents blends with simultaneous separation of uranium from molybdenum in the interval рН = 5,5-6,5. When uranium extracted the most favorable condition is the fazes balance O:W = 1:1, extraction duration period 5-10 min. The important point in the process of uranium separating from molybdenum is preventive high purity filtering the soda-chloride reclaims from zirconium, whish provides minimal impact of mineral organics to form third phase.

Fig. 3. Association of uranium and molybdenum with рН when uranium is extracted through extragents blend Di2EHPA +ТАА+ TBPh

As a result of the researches conducted, we suggest to shorten technological scheme applying direct extraction refining of soda-chloride reclaim in optimal interval рН = 5,5-6,5 by extragents blend 0,24 mole/l Di2EHPA + 0,16 mole/l ТАА + 0,15 mole/l TBPh in diesel fuel; then to make preliminary purifying procedure from zirconium ions where the settling agent is liquid glass. Chemical analysis of protoxide-oxide of uranium, derived through suggested technology proves, that the end product completely meets requirements of ST NAC 02-2007 as per the impurities concentration and the molybdenum content which does not exceed 0,0001 %.

4. Conclusion

The simplification of soda-chloride reclaim refining scheme provides to decrease the procedures number, the period of preparing the uranium solutions for re-purifying extraction and the costs for reagents. The soda-chloride reclaim’ solution affinage from emulsionizing impurities will provide the stableness of the process of uranium extracting and advances the quality of protoxide-oxide of uranium.