CYANEX 272 ExtractantSolvent Extraction Reagent Selective for cobalt over nickel from sulfate and chloride media. Selective for zinc in the presence of calcium and cobalt. Extracts other metal cations.

CONTENTSINTRODUCTION Chemical Structure Typical Properties Stability Solubility Losses Toxicity Suitability of Construction Materials COBALT RECOVERY Cobalt-Nickel Selectivity Sulfate Solution (Table 1) Chloride Solution (Table 2) Calcium Rejection Cobalt Extraction Isotherm Cobalt Loading Scrubbing Isotherm Stripping Isotherms Using H2SO4 (Table 7) Using HCl (Table 8) Continuous Separation of Cobalt from Nickel in Sulfate Solution Effect of Process Variables on Cobalt-Nickel Separation Factor Effect of Temperature (Table 9) Effect of Equilibrium pH (Table 10) Effect of Diluent Aromaticity (Table 11) Effect of Phase Modifier (Table 12) OTHER POTENTIAL APPLICATIONS Diluent Oxidation and Prevention Recovery from Ammoniacal Solutions (Table 13) Extraction from Single Metal Sulfate Solutions (Table 14) Extraction from Single Metal Chloride Solutions (Table 15) ANALYTICAL METHODS In Organic Solvents In Aqueous Solutions TECHNICAL PAPERS AND PATENTS Technical Papers Patents HEALTH AND SAFETY 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 6 6 7 8 8 8 8 9 9 9 10 13 15 16 31 35

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INTRODUCTIONCYANEX 272 extractant has proven to be the reagent of choice for the separation of cobalt from nickel from both sulfate and chloride media. It is now being used to produce a major portion of the world's cobalt. Since the active component of CYANEX 272 extractant is a phosphinic acid, metals are extracted through a cation exchange mechanism. Although CYANEX 272 extractant is selective for cobalt in the presence of nickel, a variety of other cations can also be extracted depending upon the solution pH. CYANEX 272 extractant is totally miscible with common aromatic and aliphatic diluents, and is extremely stable to both heat and hydrolysis.

Chemical StructureThe active component of CYANEX 272 extractant is bis(2,4,4-trimethylpentyl)phosphinic acid.

Typical PropertiesCH3 CH3 C CH3 P CH3 CH3 C CH3 CH2 CH CH3 CH2 OH CH2 CH3 CH CH2 O

CAS Number: 83411-71-6

Bis(2,4,4-trimethylpentyl)phosphinic acid : 85% Appearance : Colourless to light amber liquid : 0.92 Specific Gravity at 24oC : 142cp Viscosity, Brookfield at 25oC : 37cp 50oC Solubility in distilled H2O at pH 2.6 : 16 g/ml pH 3.7 : 38g/mL Boiling Point : >300oC Pour Point : -32oC Flash Point, closed cup : >108oC o : 0.48 cal/gm/oC Specific Heat @ 52 C Thermal Conductivity : 2.7 x 10-4cal/cm/sec/oC

StabilityThe hydrolytic stability of CYANEX 272 extractant was examined in several tests which involved equilibrating the reagent with aqueous cobalt-nickel sulfate solutions at pH 5 and 50oC. The experimental procedure involved contacting the aqueous and organic phases in a stirred vessel for one week and then stripping the organic phase with sulfuric acid. The solvent was subsequently returned to the vessel for a further one week contact with a fresh aqueous solution. The procedure was repeated for a total contact time of four weeks. Analysis by titration and 31P NMR failed to detect any degradation of the reagent, nor were any statistically significant changes in cobalt-nickel selectivity observed. Furthermore, no degradation has been detected in plants which have been operating continuously for as long as ten years.

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Solubility LossesLosses of CYANEX 272 extractant by distribution to aqueous cobalt-nickel sulfate solutions were determined in a number of shake-out tests. The effect of two variables, pH and aqueous phase salt concentration, was studied. Aliquots of the organic and aqueous phases were contacted for 5 minutes at 50oC and A/O = 1. After coalesence, the aqueous phases were analyzed for CYANEX 272 extractant using a gas chromatographic procedure. The solvent was composed of 12 v/o CYANEX 272 extractant in Kermac* 470B diluent. Ammonium hydroxide was used for pH adjustment. The results of the extractant solubility (truly dissolved data) are given below.Aqueous Composition (g/l) Ni Co Total Salt Conc. 100 25 5 2 25 5 300 133 27 Equilibrium pH 3-5 4.6 5.3 6.2 4.6 5.5 6.5 CYANEX 272 Extractant Solubility (g/ml) 0.5-1.5 2 2 2 3 8 25

Suitability of Construction MaterialsMetals: Samples of stainless steel (304 and 316), mild steel and aluminum in the form of coupons (approximate dimensions 50mm x 20mm x 3mm) were immersed in capped jars for 8-1/2 months at 50oC (temperature was maintained only during working hours). No corrosion was observed in the three steel samples but aluminum exhibited minimal corrosion at a rate of 1 mil/year. Plastics and Rubbers: Samples of various plastics and rubbers were immersed in CYANEX 272 extractant and kept at 50oC for a total of 424 hours. The following observations were made:Material Butyl Rubber Teflon Fluorocarbon Film** Polypropylene Natural and Black Latex PVC Laboratory Grade PVC Solvent Grade Red Gum Rubber Remarks Unsuitable. Increase in dimensions and softening. Suitable. No measured effect. Suitable. No measured effect. Unsuitable. Complete dissolution in less than 192 hours Short term suitability. Loss of plasticity in less than 192 hours. Suitable. Only small change in dimensions observed. Unsuitable. 100% increase in weight and dimensions and softening. Suitable. No measured effect. Unsuitable. Disintegrated after 56 hours. Unsuitable.

The solubility losses follow the general pattern expected of an acidic extractant. Distribution to the aqueous phase was found to be proportional to pH and inversely proportional to salt concentration. As can be seen, the losses are not excessive and this is corroborated by operating plant experience where total annual losses from both solubility and entrainment are approximately 10-15% of the solvent inventory. Toxicity The acute oral (rat) and acute dermal (rabbit) LD50 values for CYANEX 272 extractant are >3.5 g/kg and >2.0 g/kg, respectively. The product produced only limited to mild eye and ski irritation during primary irritation studies with rabbits. The acute LC50, (96 hr) for the bluegill sunfish and rainbow trout are 46 mg/L and 22 mg/L, respectively. When CYANEX 272 extractant was assayed for mutagenic potential in the Ames Salmonella Test, it was determined to be nonmutagenic. CYANEX 272 extractant is considered as a non-toxic material.

Viton Fluoroelastomer** Silicon EPDM

** Dupont Dow Elastomers* A product of Kerr McGee Refining Corp.

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COBALT RECOVERYCobalt-Nickel Selectivity The results of batch shake-out tests showing the effect of pH on Co-Ni selectivity from both sulfate and chloride media are given in Tables I and 2, respectively.TABLE 1 - SULFATE SOLUTION

Solvent (v/o) Aqueous (g/l) Temperature Contact Time A/O pH Control

: : : : : :

12% CYANEX 272 extractant, 5% isodecanol in Kermac 470B diluent 1.96 Co, 98.0 Ni as sulfates 50oC 5 minutes 1 NH4OH Equilibrium pH 3.8 4.2 5.3 5.7 6.1 Separation Factor 700 1000 2000 2700

% Extraction Co Ni 21.5 0.04 43.7 0.08 88.0 0.37 96.7 1.05 100 1.81

TABLE 2- CHLORIDE SOLUTION

Solvent (v/o) Aqueous (g/l) Temperature Contact Time A/O pH Control

: : : : : :

10% CYANEX 272 extractant, 5% isodecanol in Kermac 470B diluent 0.88 Co, 1.76 Ni as chlorides 50oC 5 minutes 1 NaOH

% Extraction Co Ni 2.9 0.1 54.2 0.3 98.1 7.0 99.7 30.0 99.9 72.9

Equilibrium pH 3.2 4.0 5.1 5.5 6.2

Separation Factor 40 370 680 680 650

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Calcium RejectionUnlike other organophosphorus cobalt extractants, CYANEX 272 extractant will extract cobalt preferentially to calcium when both are present in the same feed stream. This performance characteristic is demonstrated in Table 3 and Figure 1.TABLE 3- CALCIUM REJECTION IN THE PRESENCE OF COBALT AND NICKEL

TABLE 4

Solvent (v/o) Aqueous (g/1) Temperature Equilibrium pH pH Control

: : : : :

12% CYANEX 272 extractant, 5% isodecanol in Kermac 470B diluent. 5 Co as sulfate 50oC 5.00.1 1N NaOH

Solvent (v/o) Aqueous (g/1) Temperature Contact Time A/0 pH ControlCo 3.1 17.2 54.3 91.7 98.3 100

: : : : : :

15% CYANEX 272 extractant, 10% p-nonylphenol in Kermac 470B diluent 1.60 Co, 77 Ni, 0.31 Ca as sulfates 50oC 5 minutes 1 NH4OHCa 0.95 1.24 3.33 12.0 25.7 5.16 Equilibrium pH 1.99 3.34 3.85 4.84 5.72 6.63

Equilibrium Cobalt Concentration (g/l) A/O Solvent Aqueous 10 6.32 4.68 5 6.13 4.13 2 5.54 2.58 1 2.72 0.06 The actual loading capacity of this solvent was 6 g/l cobalt, whereas the stoichiometric capacity is approximately 10 g/l cobalt.

% Extraction Ni 0 0.04 0.17 1.03 3.95 13.4

Cobalt LoadingLoading studies were carried out at 50'C and pH 6.0 0. 1. The pH was controlled by the addition of ammonia. Other details and results are shown in Table 5. Solvent (v/o) : TABLE 5 30% CYANEX 272 extractant in Kermac 470B diluent 10 Co as sulfate Approximately 24 5 minutes Co in Solvent (g/l) 5 10 15 23* 23* % of Theoretical Maximum 21 42 63 96 96

Aqueous (g/l) : Theoretical Maximum (g/l) : Contact Time :

A/O 0.5 1.0 1.5 3.0 5.0

Cobalt Extraction IsothermProcedural details and results of our extraction studies are given in Table 4.

*At this loading the solvent was judged to be too viscous for practical use. The 15 g/l solvent did not exhibit this viscosity problem. The maximum practical loading for the conditions cited is probably about 65-75 % of theoretical. (39) This would correspond to a CYANEX 272 extractant:cobalt ratio of 6:2.

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It should be noted that the loading capacity of CYANEX 272 extractant will vary depending upon several parameters, notably pH, temperature, and extractant concentration, and may be more or less than the figure cited. For example, with a 15% CYANEX 272 extractant solution at 50oC and pH 5-5 the solvent can be loaded to 100% of the theoretical maximum while remaining sufficiently mobile for practical use.

TABLE 7 -USING H2SO4 Solvent (v/o) Solvent Loading (g/l) Temperature Contact Time Strip Feed (g/1) : : : : : 12% CYANEX 272 extractant, 10% p-nonylphenol in Kermac 470B diluent 3.26 Co (2 g/ml Ni) 40oC 5 minutes 20.5 Co (as sulfate), 24.5 H2SO4

Scrubbing IsothermAs can be seen from the results in Table 6, even if a high quantity of nickel is co-extracted with the cobalt, it can be successfully scrubbed from the loaded solvent.

Solvent (v/o)

:

Solvent Loading (g/1) : Scrub Feed (g/1) : Temperature :

TABLE 6 12% CYANEX 272 extractant, 5% isodecanol in Kermac 470B diluent 1.9 Co, 1.9 Ni 30 Co (as sulfate), initial pH 3.7 50oC

O/A 6.67 5 4 3.33 2.86 2

Equilibrium Cobalt Conc. (g/l) Organic Aqueous 0.58 38.4 0.22 35.7 0.19 32.5 0.03 31.3 0 29.8 0 27.0

TABLE 8 - USING HCl

Solvent (v/o) Equilibrium Concentration in Scrubbed Solvent (g/ml) O/A 10 5 2 1 Co 3820 3790 3740 3730 Ni 4.5 2.2 1.3 1.1 Co-Ni Ratio 850 1720 2900 3400 Solvent Loading (g/1) Temperature Contact Time Strip Feed (g/1)

: : : : :

12% CYANEX 272 extractant, 10% p-nonylphenol in Kermac 470B diluent 9.26 Co 50oC 5 minutes 19.4 Co (as chloride) 100 HCl

Stripping IsothermsStripping from a solvent modified with isodecanol tended to produce hazing. Substituting p-nonylphenol or TBP for the isodecanol essentially eliminated this problem. Tables 7 and 8 show stripping isotherms obtained with a pnonylphenol modified solvent.

O/A 2 3 5 7.5 10

Equilibrium Cobalt Conc. (g/l) Organic Aqueous 0 37.9 0 47.1 0 65.7 0.01 88.8 0.35 108.5

Continuous Separation of Cobalt from Nickel in Sulfate SolutionIn continuous countercurrent tests (four extraction and two scrub stages) carried out at Warren Spring Laboratory (Stevenage, U.K.), more than 99.5% of the cobalt in the feed was recovered as a product containing a Co-Ni ratio of greater than 1000 to 1.

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The experimental conditions are shown below. A circuit flowsheet and the relevant assays are given in Figure 2. Solvent (v/o) Aqueous Feed (g/l) Scrub Feed (g/l) Temperature Phase Ratios Mixer Residence Time : 20% CYANEX 272 extractant (NH4 salt)*, 10% p-nonylphenol : 2 Co, 100 Ni as sulfates, 20 (NH4)2O4, pH 5 : 40 Co as sulfate, pH 3 : 50oC : Extraction A/O = 2 Scrubbing O/A = 32 : 3.5-4 minutes (Based upon total liquid flow)

Effect of Process Separation Factor

Variables

on

Cobalt-Nickel

The effect of pH, temperature and diluent aromaticity on the cobalt-nickel separation factor in sulfate solutions was measured in a series of statistically designed tests and the data fitted to the following mathematical model: log10S = 1.8827 + 0.0332T + 0.01249A + 0.0033PT 0.002151PA - 0.0003405T2 Where: S = Co-Ni Separation Factor T = Temperature (oC) A = % Aromatics in diluent P = Equilibrium pH

*The phosphinic acid contained in the solvent was converted 70% to the ammonium salt by reaction with concentrated ammonium hydroxide solution (S.G. = 0.88). A phase modifier was used since converting more than 50% of the free acid to a salt (NH4+ or Na+) usually requires a modifier to prevent third phase formation. ** A product of Shell Chemical Co.

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The effect of these process variables on the separation factor is shown in Tables 9 through 11. TABLE 9 - EFFECT OF TEMPERATURE Solvent (v/o) Aqueous (g/l) pH A/O : : : : 22% CYANEX 272 extractant in the diluent (95% MSB 210* diluent, 5% Aromatic 150** diluent). 2 Co, 100 Ni as sulfates 5.5 1 Temperature o C 30 35 40 45 50 55 60

TABLE 11 -EFFECT OF DILUENT AROMATICITY

Temperature Diluent (v/o) pH Other Conditions

: : : :

50oC 100% MSB 210 (aliphatic) to 100% Aromatic 150 5.5 See Table 9 Aromaticity v/o 0 10 20 30 40 50 60 70 80 90 100

Co-Ni Separation Factor 1320 1850 2480 3220 4000 4790 5510 * A product of Shell Chemical Co. **A product of Exxon Co., USA.

Co-Ni Separation Factor 3970 4030 4090 4160 4220 4280 4350 4420 4480 4550 4620

The effect of the phase modifiers TBP, p-nonylphenol, isodecanol and TOPO (tri-n-octylphosphine oxide) on the separation factor is shown in Table 12. TABLE 12 -EFFECT OF PHASE MODIFIER Extractant (v/o) Modifier Aqueous (g/l) A/O Temperature Equilibrium pH Contact Time Diluent : : : : : : : : 22% 10 v/o (TBP, isodecanol, pnonylphenol) 10 w/o TOPO (solid) 10 Co, 100 Ni as sulfates 1 55oC 5.5 5 minutes MSB 210 Co-Ni Separation Factor 6700 3400 1800 1000 1000

TABLE 10 - EFFECT OF EQUILIBRIUM pH Temperature : Diluent (v/o) : Other Conditions : 50oC 95% MSB 210, 5% Aromatic 150 See Table 9

Co-Ni Separation Factor 2810 3010 3230 3470 3730 4000

pH 4.5 4.7 4.9 5.1 5.3 5.5

Modifier None TBP p-Nonylphenol Isodecanol TOPO

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OTHER POTENTIAL APPLICATIONSDiluent Oxidation and PreventionHydrocarbon diluents oxidize readily to carboxylic acids in the presence of a cobalt (Co2+) catalyst (24,90). The formation of carboxylic acids, which are active nickel extractants, can seriously reduce the cobalt-nickel selectivity obtained with CYANEX 272 extractant. However, inhibitors such as BHT can be used to prevent this oxidation. Plants following this practice have run for many years without loss of selectivity. Although CYANEX 272 extractant is designed primarily for cobalt-nickel separations, the data in Tables 14 and 15, and Figures 3 and 4 show that it will extract a variety of metal cations and indicate its potential for other selective separations.

Recovery from Ammoniacal SolutionsCYANEX 272 extractant can be used to recover cobalt from ammoniacal as well as acidic solutions. The data in Table 13 show that it outperforms other organophosphorus extractants. TABLE 13 - EXTRACTION FROM AMMONIACAL SOLUTIONS Solvent (v/o) Aqueous (g/L) Temperature pH Control Contact Time A/0 : : : : : : 20% extractant, 5% isodecanol in Kermac 470B diluent 0.97 Co3+, 0.95 Ni2+, (NH4)2O4 for a total SO42- concentration of 16 50oC 11.6 with NH4OH 5 minutes 1 Solvent

TABLE 14 - EXTRACTION FROM SINGLE METAL SULFATE SOLUTIONS : : : : : : 0.6 M CYANEX 272 extractant, 10 v/o p-nonylphenol in Kermac 470B diluent 0.015 M metal as sulfate 50oC NH4OH or H2SO4 as appropriate 5 minutes 1

Aqueous Temperature pH Control Contact Time A/O

Metal Fe3+

Extractant CYANEX 272 PC-88A D2EHPA

% Extracted Co Ni 91.5 15.6 91.4 22.0 90.4 46.9

Co/Ni Separation Factor 58 18 7

Zn2+

Cu2+

Co2+

Ca2+

Cd2+

% Ext. 8.8 23.6 61.2 88.1 98.7 14.6 24.2 53.3 87.7 99.4 6.4 17.7 21.7 73.9 85.7 94.8 9.2 19.0 70.8 99.8 3.4 20.4 81.7 99.6 4.2 19.7 63.1 91.0 99.5

Final pH 0.25 0.85 1.33 1.75 2.31 0.90 1.42 1.88 2.40 3.08 1.73 2.64 2.90 3.56 3.84 4.08 1.78 3.34 4.11 5.98 4.15 4.53 5.38 6.52 2.00 3.00 3.51 4.00 5.00

Metal Ni2+

Mg2+

Al3+

% Ext. 27.6 36.0 52.3 84.0 92.8 14.5 29.7 67.1 82.0 97.4 23.9 41.9 87.5 97.2 42.3 86.1 99.8 7.9 21.1 46.5 85.1

Final pH 6.33 6.59 6.72 7.22 7.47 3.00 4.20 4.76 4.99 5.81 1.11 2.50 2.92 3.14 3.40 3.96 5.66 1.11 1.34 1.44 1.81

Mn2+

V4+

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TABLE 15 - EXTRACTION FROM SINGLE METAL CHLORIDE SOLUTIONS Solvent Aqueous Temperature pH Control Contact Time A/O : : : : : : 0.6 M CYANEX 272 extractant in Exxsol D-80 0.015 M metal as chloride 50oC NH4OH or HCl as appropriate 5 minutes 1

Metal Ca2+

Co2+

Ni2+

Mg2+

% Ext. 0.0 25.7 48.9 91.9 99.4 1.9 48.0 86.7 95.9 100.0 0.0 19.3 44.7 84.8 95.1 99.7 1.2 41.2 66.2 89.1 99.0 99.9

Final pH 3.33 4.36 5.00 5.90 6.45 2.8 3.5 4.1 4.4 5.5 3.6 4.9 5.2 5.9 6.3 7.0 3.4 4.4 5.0 5.4 6.4 6.6

Metal Fe3+

Cu2+

Zn2+

% Ext. 32.6 35.2 66.4 95.2 99.0 0.0 8.5 51.9 86.2 97.6 12.6 22.6 54.2 67.9 76.2 92.9

Final pH 0.2 0.3 0.7 1.1 1.4 2.0 2.6 3.1 3.5 3.9 0.9 1.2 1.6 1.7 1.8 2.1

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FIGURE 3 - EXTRACTION OF METALS BY CYANEX 272 EXTRACTANT FROM SULFATE SOLUTIONS

100 80 % Extraction 60 40 20 0 0 1

Fe

3+

Zn+

2+

Cu

2+

Mn

2+

Ca

2+

Ni

2+

V4

Al

3+

Co

2+

Mg

2+

2

3

4 pH

5

6

7

8

11

FIGURE 4 - EXTRACTION OF METALS BY CYANEX 272 EXTRACTANT FROM CHLORIDE SOLUTIONS

100 % Extraction 80 60 40 20 0 0

Fe

3+

Zn

2+

Cu

2+

Co

2+

Ni

2+

Mg

2+

Ca

2+

2

4 pH

6

8

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ANALYTICAL METHODSAnalysis for Active Component in CYANEX 272 Extractant in Organic Solvents by Titration The active component of CYANEX 272 extractant is bis(2,4,4-trimethylpentyl)phosphinic acid. Its concentration in an organic solvent is determined by titration with standard caustic solution. 4. Note the initial pH and begin to titrate with 0.1N NaOH. Record the pH as a function of the volume of NaOH added. Three endpoints should be observed. As each endpoint is approached, the incremental addition of NaOH should be reduced to 0.1 ml to facilitate calculation of the titer by the method of second differences. Calculation A typical potentiometric curve is as follows:

O R2POH + NaOH

O R2PONa + H2O

The extractant contains small quantities of a dibasic impurity (2,4,4-trimethylpentyl phosphonic acid) which also titrates with caustic.

O RP(OH)2 + 2NaOH

O RP(ONa)2

The endpoints are detected potentiometrically. Apparatus pH meter Magnetic stirrer Standard laboratory glassware Reagents 75 v/o 2-propanol in distilled water 0.1N Standard NaOH solution in 75 v/o 2-propanol 100 g/l H2SO4 All reagents are AR grade. Procedure 1. Contact approximately 50 ml of the solvent to be analyzed with 50 ml of 100 g/l H2SO4 for 5 minutes at 50oC. Separate the phases and allow to stand for 15-30 minutes. Centrifuge the solvent or filter through PS paper* to remove entrained aqueous. 2. To prepare the analyte solution, pipette a 25 ml aliquot of the solvent and dilute to 200 ml in a volumetric flask with the appropriate diluent (Escaid**, Kermac*** etc.). Alternatively, the 75 v/o solution of 2-propanol may be used for volume make-up. 3. Pipette 25 ml of the analyte solution into a 150 ad tall-form beaker. Dilute to approximately 50 ml with the 2-propanol solution. Insert the pH electrodes and begin stirring. * Phase separation paper available from Whatman Inc., Clifton, NJ. ** A product of Exxon Chemical Co., USA *** A product of Kerr McGee Refining Corp.

The titer T1 corresponds to the neutralization of sulfuric acid dissolved in the solvent. T2 represents the neutralization of the phosphinic acid plus the reaction of the first of two replaceable hydrogen ions associated with the phosphonic acid. The phosphonic acid is totally neutralized at T3.

0.1N NaOH (ml) 9.8 9.9 10.0 10.1 10.2 10.3

pH 7.50 8.00

First Differential 50

Second Differential +40

90 8.90 180 10.70 50 11.20 10 11.30 = Then, T2 = (10.0 + 0.1) x 90 10.04 ml 90 + 130 13 -40 -130 +90

T1 and T3 may be calculated in an analogous manner. When all three titers are known, the concentration of bis(2,4,4-trimethylpentyl)phosphinic acid may be determined. bis(2,4,4-trimethylpentyl) phosphinic acid (g/1) = [T2 (T3 T2) T1] x N(NaOH) x 290 x 1000 1000 x 25 x 25 200 Similarly the concentration of the phosphonic acid and dissolved sulfuric acid may also be calculated. 2,4,4-trimethylpentyl phosphonic acid (g/1) = T2 T2 x N(NaOH) x 194 x 1000 1000 x 25 x 25 200 H2SO4 (g/l) = T1 x 49 x N(NaOH) x 1000 1000 x 25 x 25 200 NOTES 1. A minimum net titer, i.e. [T2 (T3 T2) T1], of 10 ml is recommended to obtain reproducible results. In this procedure, 10 ml of 01N NaOH is equivalent to approximately 100 g/l concentration of phosphinic acid. Where necessary, the size of the aliquots and dilutions may be varied to ensure a sufficient volume of titrant is consumed. 2. Approximate pH's corresponding to the T1, T2 and T3 endpoints are 4, 9 and 11, respectively. However these values may vary depending upon the composition of the solvent. After gaining experience with a system, the NaOH may be added rapidly until the particular endpoint pH is approached and then added in 0.1 ml increments to define the point of inflexion in the curve. 3. The concentrations of sulfuric and phosphonic acids in the solvent are usually small and these endpoints may not be observed. In this case T1 and T3 should be assigned a value of zero in the calculations. Typically, T1 and T3 - T2) will be < 0.2 and < 0.1 ml of 0.1N NaOH, respectively, corresponding to