Solvent extraction studies of rhodium(III) by using n-octylaniline from malonate media: Analysis of synthetic mixtures and alloys

Figures & data

Table 1. Comparison of the proposed method with previously reported solvent extraction methods

Reagent	Conc.	pH/acidity	Solvent	Strippant	Determination	References
Alamine 336	0.17 M	HCl	Kerosene	–	ICP-AES	(4)
Alamine 336	–	HCl	Toluene	–	ICP-OES	(5)
Trioctylamine	0.23 M	HCl	Toluene	8 M HNO3	ICP	(9)
Aliuqot 336	0.5 M	HCl	Kerosene	–	ICP-OES	(11)
Tri iso octylamine	0.2 M	HCl	Kerosene	HCl/Thiourea	ICP-OES	(12)
N-n-Octylaniline	0.1 M	0.025 M Malonate pH = 9.5	Xylene	1 M HCl	Spectrophotometer	(15)
Trinbutylphosphate	–	HNO3/trichloroacetate pH = 3	–	8 M HClO4	FAAS	(17)
Trinbutylphosphate	–	HCl	–	4 M HCl/NaCl	Spectrophotometer	(18)
Cyanex 921	0.75 M	HCl	Toluene	5 M HNO3	Spectrophotometer	(20)
Cyanex 923/Cyanex 471X	0.15 M/0.8 M	HBr	Toluene	4 M HCl + 2 M HNO3	Spectrophotometer	(23)
Cyanex 923	0.05 M	HCl	Toluene	3 M HNO3	Spectrophotometer	(24)
n-Octylaniline	0.1 M	0.03 M Malonate pH = 9.0	Xylene	1 M HCl	Spectrophotometer	PM

Note: Conc. = Concentration.

Figure 1. (A) Plot of pH vs. percentage extraction of rhodium(III). Condition: Rhodium(III) = 200 μg, sodium malonate = 0.03 M, n-octylaniline = 0.1 M in toluene, shaking time = 3 min. (B) Extraction of rhodium(III) as a function of n-octylaniline concentration. Condition: Rhodium = 200 μg, pH = 9.0, sodium malonate = 0.03 M, shaking time = 3 min. (C) Extraction behavior of rhodium(III) as a function of weak organic acid concentration. Condition: Rhodium(III) = 200 μg, pH = 9.0, n-octylaniline = 0.1 M in toluene, shaking time = 3 min.

Table 2. Extraction behavior of rhodium(III) as a function of diluents

Solvent	Dielectric constant (∈)	Percentage extraction (% E)	Distribution ratio (D)
Benzene	2.27	100	∞
Xylene*	2.30	100	∞
Toluene	2.38	100	∞
Chloroform	4.80	41.1	1.74
Methyl isobutyl ketone	13.10	42.7	1.86
n-Butyl alcohol	17.80	No extraction	–
Amyl alcohol	13.90	No extraction	–
Amyl acetate	13.90	No extraction	–
1,2-Dichloroethane	10.50	No extraction	–

Condition: Rh(III) = 200 μg, pH = 9.0, aq: org = 2.5:1, sodium malonate = 0.03 M, equilibrium time = 3 min, strippant = 1 M Hydrochloric acid (2 × 10 mL).

^* Recommended for general extraction procedure.

Table 3. Extraction behavior of rhodium(III) as a function of equilibrium time

Time in min	Percentage extraction (% E)	Distribution ratio (D)
10 s	60.5	3.82
30 s	72.6	6.62
1	100	∞
2	100	∞
3*	100	∞
4	100	∞
5	100	∞
6	100	∞
7	100	∞
8	100	∞
9	100	∞
10	100	∞
15	90.1	22.75
30	62.1	4.09

Condition: Rh(III) = 200 μg, pH = 9.0, sodium malonate = 0.03 M, n-octylaniline = 0.1 M in xylene, strippant = 1 M hydrochloric acid (2 × 10 mL), aq:org = 2.5:1.

^* Recommended for general extraction procedure.

Table 4. Extraction behavior of rhodium(III) as a function of stripping agents

Strippant	Mol/L	Percentage extraction (% E)
Ammonia	1–10	No stripping
HCl*	1–3	100
H2SO4	1–3	100
HNO3	1–3	100
HBr	1–3	100
Water	–	31.9

Notes: Ammonia buffer = pH-10, No stripping.

NaCl = 1–5%, No stripping.

Condition: Rh(III) = 200 μg, pH = 9.0, sodium malonate = 0.03 M, n-octylaniline = 0.1 M in xylene, aq: org = 2.5:1, equilibrium time = 3 min.

^* Recommended for general extraction procedure.

Figure 2. (A) Log–log plot of Log D_[Rh(III)] vs. Log C_[malonate] at fixed n-octylaniline concentration. (B) Log–log plot of Log D_[Rh(III)]] vs. Log C_{[n-octylaniline]} at fixed malonate concentration.

Table 5. Effect of foreign ions on the extraction of 200 μg rhodium(III) at pH 9.0 in 0.03 M sodium malonate with 0.1 M n-octylaniline in xylene

Rhodium:ion	Mass tolerated, mg	Foreign ion
2:500	50	Iodide
2:250	25	Zn(II), oxalate.
2:150	15	Ni(II), Te(IV), Tl(III), Mo(VI), Se(IV), Ba(II), Ce(IV)
2:100	10	Mg(II), Cd(II), Sb(III), V(V), Pb(II), Sn(II), Bi(III), luoride, thiourea, Nitrate
2:50	5	Cu(II), Co(II), Fe(III)
2:20	2	Fe(II), Hg(II), Cr(VI)
2:1	1	Ag (I), Pt(IV),OS(VIII), Au(III), Pd(II)
2:0.5	0.5	Ru(III), Ir(III)^a

^a Masked with oxalate.

Table 6. Separation of rhodium(III) from binary mixtures

Metal ion (μg)	Mass taken (μg)	Average (%) Recovery*	Chromogenic ligand	References
Rh(III)	200	99.0	Stannous Chloride-Hydrobromic acid	(37)
Ir(III)^a	100	97.4
Rh(III)	200	99.0	Stannous Chloride-Hydrochloric acid	(37)
Pt(IV)	300	99.4
Rh(III)	200	98.8	4′-ChloroPTPT	(38)
Pd(II)	200	98.4
Rh(III)	200	98.8	SnCl2	(37)
Au(III)	200	97.1
Rh(III)	200	99.0	4′-BromoPTPT	(39)
Se(IV)	200	97.0
Rh(III)	200	98.8	4′-BromoPTPT	(40)
Te(IV)	200	98.9
Rh(III)	200	98.0	Thiourea	(37)
Os(VIII)	200	99.3
Rh(III)	200	99.0	Thiocyanate	(37)
Fe(III)	500	98.8
Rh(III)	200	99.0	Thiocyanate	(37)
Co(II)	500	98.7
Rh(III)	200	99.0	DMG	(36)
Ni(II)	1,000	98.9
Rh(III)	200	99.2	4′-ChloroPTPT	(38)
Ru(III)	200	98.9
Rh(III)	200	99.0	4′-ChloroPTPT	(41)
Cu(II)	1,500	98.7

^* Average of five determinations.

^a Masked by 20 mg oxalate.

Table 7. Separation of rhodium(III) from ternary mixtures

Metal ion	Amount taken (μg)	Average recovery of rhodium(III)* (%)
Rh(III)	200	99.0
Pt(IV)	100
Pd(II)	100
Rh(III)	200	98.6
Fe(III)	150
Ni(II)	100
Rh(III)	200	98.6
Cu(II)	150
Ni(II)	100
Rh(III)	200	99.0
Pd(II)	200
Cu(II)	150
Rh(III)	200	99.0
Pd(II)	200
Au(III)	100
Rh(III)	200	98.6
Ir(III)^a	100
Pd(II)	200

^* Average of five determinations.

^a Masked by oxalate.

Table 8. Separation of rhodium(III) from synthetic mixtures

Composition (μg)	Rhodium(III) found (μg)	Recovery* (%)	RSD (%)
Rh(III),200; Pd(II),200; Pt(IV),200; Ir(III)^a,100	197.2	98.6	1.4
Rh(III),200; Au(III),100; Pd(II),200; Pt(IV),100	197.0	98.5	1.5
Rh(III),200; Pd(II),200; Pt(IV),100; Ru(III),200	198.0	99.0	1.0
Rh(III),200; Pd(II),200; Pt(IV),100; Ru(III),200; Ir(III)^a,100	197.2	98.6	1.4
Rh(III),200; Pd(II),200; Pt(IV),100; Ru(III),200; Ir(III)^a,100; Os(VIII),100	197.0	98.5	1.5

Note: RSD = relative standard deviation.

^* Average of five determinations.

^a Masked by 20 mg oxalate.

Table 9. Determination of rhodium(III) from synthetic mixture corresponding to alloys

Alloys	Rhodium(III) taken (μg)	Rhodium(III) found (μg)	R* (%)	RSD (%)
Pseudo-palladium Rh(III),50%; Ag(I),50%	200	198.0	99.0	1.0
Iron–rhodium alloys Rh(III),74.98%; Fe(III), 25%	148	145.9	98.6	1.4
Rh(III),67.71%; Fe(III) 32.28%	135	133.1	98.6	1.4
Platinum–rhodium alloy Pt(IV) 87% Rh(III)13%	174	172.2	99.0	1.0

Notes: R = % recovery of rhodium(III). RSD = relative standard deviation.

^* Average of five determinations.

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