Table 4 CCD experimental design for the leaching of REEs using citric acid.

From: Investigation on process optimization and kinetics for leaching of rare earth elements from red mud using citric acid

Expt. No.

A: Leachant Concentration (mol/L)

B: Reaction Temperature (K)

C: Leaching time (min)

Sc(mg/L)

La(mg/L)

Ce(mg/L)

Pr(mg/L)

Nd(mg/L)

Sm(mg/L)

⅀REE(mg/L)

REE Leaching efficiency(%)

1

0.75

343.0

240

2.909

3.022

0.559

0.429

3.174

1.015

11.108

44.50

2

1.375

320.5

165

2.691

4.254

0.229

0.335

3.527

0.998

12.034

48.21

3

2.43

320.5

165

4.086

6.689

0.883

0.802

4.248

1.993

18.701

74.92

4

0.75

298.0

90

1.579

2.142

0

0

2.231

0.438

6.390

25.60

5

1.375

320.5

165

3.264

3.997

0.256

0.389

3.654

0.854

12.414

49.74

6

1.375

320.5

165

2.994

3.884

0.257

0.415

3.224

1.005

11.779

47.19

7

0.75

343.0

90

2.173

2.597

0.165

0.246

2.836

0.836

8.853

35.47

8

2.00

343.0

90

3.745

6.142

0.231

0.201

4.349

1.447

16.115

64.56

9

1.375

320.5

291

3.781

4.408

0.449

0.411

3.983

0.997

14.029

56.21

10

1.375

320.5

165

3.012

3.884

0.257

0.415

3.224

1.005

11.797

47.26

11

2.00

298.0

90

2.716

5.229

0.23

0.075

3.219

0.788

12.257

49.11

12

1.375

320.5

165

2.784

3.657

0.221

0.409

2.891

0.884

10.846

43.45

13

1.375

358.3

165

4.364

5.019

0.627

0.561

4.125

1.354

16.05

64.30

14

0.32

320.5

165

1.418

1.306

0.318

0.164

1.372

0.615

5.193

20.81

15

0.75

298.0

240

1.785

1.949

0.226

0.12

1.965

0.507

6.552

26.25

16

1.375

320.5

39

2.34

2.219

0.516

0.556

2.916

1.186

9.733

38.99

17

1.375

320.5

165

3.187

3.487

0.338

0.428

2.891

1.005

11.336

45.42

18

2.00

343.0

240

4.784

7.954

0.848

0.724

5.748

2.447

22.505

90.16

19

2.00

298.0

240

3.234

5.238

0.315

0.319

4.119

1.452

14.677

58.80

20

1.375

282.7

165

1.143

1.879

0

0

1.883

0.784

5.689

22.79

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