hydroxyindoles to stabilize them against auto-oxidation ( I O , 12, 13). The fact that ascorbic acid. cysteine, and glutathione can actually react with OPT t o form fluorescent products (Table I) and can have either an enhancement or diminishing effect on the fluorescence of a given 5-hydroxyindole compound (Table 11) indicate that caution should be exercised in the use of these compounds in assays for 5hydroxyindoles. The diminishing effect on fluorescence observed in the case of ascorbic acid is in agreement with the findings of Thompson e t al. (26) and the enhancement on fluorescence of 5-HIAA by cysteine is in confirmation with the findings by Korf and Valkenburgh-Sikkema 120). We have found that working in a dimly lit room, and keeping the samples in the dark as much as possible, is sufficient to prevent significant losses of 5-HT or 5-HTP from auto-oxidation and eliminates the need for the use of any antioxidants in the analyses of these two compounds.
LITERATURE CITED Zimmerman, 2.Physiol. Chem., 189,4 (1930). (2)G. Klein and H. Linser, 2.Physiol. Chem., 205, 251 (1932). (3)A. R . Patton. J. Biol. Chem., 108,267 (1935). (4)G. Curzon and J. Giltrow, Nature (London), 173,314 (1954). (5) R . P. Maickel and F. P. Miller, Anal. Chern., 38, 1937 (1966). (6)J. H. Thompson, C. A. Spezia, and M. Angulo, Experientia, 25, 927 (1) W.
(1969). (7)J. H. Thompson, C. A. Spezia. and M. Angulo, lr. J. Med. Sci., 3 , 197 (1970). (8)J. H. Thompson, C. A. Spezia, and M. Angulo, Experientia, 26, 327 (1970). (9)N. N. Komesu and J. H. Thompson, Eur. J. Pharmacol., 16,248 (1971). (IO) J. Korf and T. Valkenburgh-Sikkema, Clin. Chim. Acta, 26, 301 (1969). (1 1) C. Atack and M. Lindqvist, Naunyn-Schmiedebergs Arch. Pharmakol. Exp. Pathol., 279,267 (1973). (12)C. A. Marsden, Comp. Gen. Pharmacol., 3, l(1972). (13)G. Curson and A. R. Green, Brit. J. Pharmacol., 39,653 (1970). (14)R. H. Cox, Jr., and J. L. Perhach, Jr., J. Neurochem., 20, 1777 (1973). (15)K. H. Tachiki and M. H. Aprison, manuscript submitted for publication. (16)J. H. Thompson, C. A . Spezia, and M. Anguio, Anal. Biochern., 31, 321 (1969).
RECEIVEDfor review May 2, 1974. Accepted September 9,
ACKNOWLEDGMENT The authors gratefully acknowledge the excellent technical assistance of Roger Jackson.
1974. This investigation was supported by Research Grant MH-03225-15 from the National Institute of Mental Health, U S . Public Health Service.
Determination of Mercaptobenzothiazole (MBT) in Flotation Liquors by Solvent Extraction and Ultraviolet Spectrometry Michael H. Jones and James T. Woodcock CSlRO Division of Mineral Chemistry, P.O. Box 124, Port Melbourne, Victoria, Australia 3207
2-Mercaptobenzothiazole (MBT) is a constituent of some flotation collectors and there is a need to determine residual MBT in plant liquors and effluents. MBT can be determined by UV spectrometry at 329 nm in a chloroform extract obtained after acidifying the liquor to less than pH 2 or after adjusting the pH to 7-8 with ammonium acetate. MBT in chloroform has a molar absorptivity of 28100 f 200 liter mole-‘ cm-‘ and obeys Beer’s law up to 9 mg/l. At pH 1, with an aque0us:organic ratio of 1:1, 99% of the MBT is extracted in one stage, and the absorbance of the chloroform extract is directly proportional to MBT concentration in the original aqueous solution (MBT concentration (mgll.) = 5.95 X absorbance in 1-cm cells). The nominal detection limit is 0.1 mg/l. but this can be extended to 0.01 mg/l. by using higher aqueous:organic ratios. Few compounds interfere, although cuprocyanide interfered with extraction from acid solution but not from ammonium acetate solution. Ore slimes in the aqueous phase did not interfere with extraction.
A knowledge of residual reagent concentrations in a flotation pulp may give a better understanding of the process and may be a guide to reagent addition rates. Anti-pollution measures may also require a knowledge of residual reagent concentrations in flotation plant effluents. 2-Mercaptobenzothiazole (MBT) or 2(3H)-benzothiazolethione is widely used as a flotation collector. I t is marketed under such names as MBT, Captax, and Flotagen, and is a major constituent of reagents in the 400 series of the American Cyanamid Company.
In a previous paper ( I ) it was shown that direct UV spectrometry of an aqueous filtrate from a flotation pulp could be used to measure MBT concentrations up to 12 mg/l. using a 1-cm cell. Cuprocyanide interfered when more than 20 mg/l. was present. Suspended matter in the liquor also interfered. Because MBT is more soluble in organic solvents than in water, it was thought that it should be possible to extract M B T from aqueous solution and measure the absorbance of the extract. Koch (2) studied the UV absorbance of rubber accelerators in chloroform and benzene, and Kress ( 3 )applied this information to the analysis of accelerator-rubber mixtures by measuring the UV absorbance in chloroform. In this work, the main effort was directed to the use of chloroform which seemed to be the most suitable solvent.
EXPERIMENTAL Equipment. Spectral scans were obtained with a Unicam SP800A recording spectrophotometer using stoppered 1-cm quartz cells and linear wavelength and absorbance presentation. Instrument calibration was checked using holmium oxide glass and aqueous solutions of potassium dichromate and nitrate ( 4 ) . Mercaptobenzothiazole. For much of the work, pure 2-mercaptobenzothiazole prepared for the previous study ( I ) was used. This contained C, 50.02; H, 2.99; N, 8.22; S, 38.5; melting point 180 “C (calculated for C7HsNS2: C, 50.27: H, 3.01: N, 8.38; S, 38.34). A second batch, prepared 12 months later, analyzed C, 50.25; H, 3.05; N, 8.09; S, 38.5. Other Reagents. AR chloroform was used without purification. Flotation chemicals were used “as received.” Reagents that were not completely soluble in water were made up a t 500 mg/l., filtered. and the filtrate was used.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 1, JANUARY 1975
11
I
I
I
I
I
I
~
_
_
Table I. Values of Molar Absorptivity for MBT maxt
€ 9
Solvent
nm
liter mole-’ cm-1
Authms
CHC1,
32O.ga 329 329 333 329
24500b 2576ObSC 28100 200 28700 25000
K o c h (2) Kress (3)
cc1, CBH,
*
This work T h i s work K o c h (2)
aProbably an error; should be 329.0 nm. bLow value because commercial M B T used. Converted from specific extinction coefficient.
Wavelength, nm
Figure 1. UV absorbance spectrum of 10 mg/l. MBT in chloroform using 1-cm cells
Ore slimes and flotation liquors were obtained from laboratory tests or operating plants. Procedure. Most extractions were conducted at an aqueous: organic ratio of 1:l by shaking for 2 min. Ratios of 1 O : l and 0.25:1, and shake times of 30 min were used in some tests. Extractions were conducted after adjusting the p H of the aqueous solution to less than 2 (usually by adding 1 ml of concentrated HC1 to 25 ml of solution). In the presence of cuprocyanide, extractions were also conducted after adjusting the p H to 7-8 by adding solid ammonium acetate. In addition, the effect of p H on extraction was studied over the p H range 0-13 using NaOH or HC1 for pH adjustment. Disengagement of the phases was usually rapid and the phases were usually clear enough to add to the cell without filtration. UV absorbance spectra of the organic and/or the aqueous phases were determined over the wavelength range 250-450 nm. Two types of calibration curves were obtained in this work. These were concentration of MBT in chloroform us. absorbance a t 329 nm, and concentration of M B T in aqueous solution us. absorbance at 329 nm of a chloroform extract obtained from the aqueous solution. Calibration curves were obtained for extraction a t pH 1, 7.3, and 8.3. The MBT concentrations used were 0, 5 , or 10 mgil. Although the absorbance for 10 mg/l. is just off the straight line part of the calibration graph, it was convenient to use this Concentration. Plant solutions were spiked with MBT by adding 10 ml of M B T solution to 90 ml of plant solution. A blank was prepared by adding 10 ml of water to 90 ml of plant solution. The selection of substances investigated for possible interference was based partly on those thought reasonably likely to be present in a flotation solution and partly on data given in a detailed study on determination of xanthate in flotation liquors ( 5 ) . No particular approval or otherwise is to be inferred for the reagents chosen.
RECOMMENDED METHODS Solutions Containing 0-9 mg/l. MBT and No Cuprocyanide. Take 25.0 ml of aqueous solution in a 100-ml separating funnel, add 1.0 ml of concentrated HC1 (or sufficient to give pH less than 2), and let stand for 1 min. Add 25.0 ml of chloroform and shake for 2 min. After disengagement of the phases, filter the chloroform if necessary to remove entrained water or solids. Measure the absorbance of the chloroform extract a t 329 nm. Determine the original MBT concentration from a calibration graph prepared in a similar way or from Equation 1for 1-cm cells.
where Caq,1= concentration of MBT in mg/l. in the original aqueous solution; extraction a t p H 1. A 3 2 9 = absorbance of chloroform extract at 329 nm. Solutions Containing 0-9 mg/l. MBT and up to 700 mg/l. Cuprocyanide. Take 25.0 ml of aqueous solution and add ammonium acetate to give a known, slightly alkaline pH (this may be typically 7.3 or 8.3 depending on the alkalinity of the original solution). Add 25.0 ml of chloroform and proceed as above. Determine the original MBT concentration from a calibration graph prepared 12
at a specific p H from a similar matrix, or from Equations 2 and 3 for 1-cm cells. For accurate results, the p H should be known to 0.1 unit.
The symbols have a similar meaning t o those given above. Other Solutions. For solutions containing less than 1 mg/l. M B T when greater accuracy than that obtainable above is required, it is suggested that 200 ml of aqueous solution and 20 ml of chloroform can be taken.
RESULTS AND DISCUSSION The UV absorbance spectrum of 10 mg/l. MBT in chloroform in a 1-cm cell is shown in Figure 1. Both batches of MBT made for this work gave the same spectrum. Replicate determinations of the absorbance a t 329 nm for 10 mg/l. MBT gave 1.645 f 0.01. A plot of absorbance a t 329 nm us. MBT concentration in chloroform gave a straight line (not shown here) up to 9 mg/l. A linear regression analysis of 42 pairs of figures from four separate calibrations gave Equation 4. =
cICor~
-
(4 )
where A329 = absorbance a t 329 nm in 1-cm cells. a = constant, and at 99% confidence limits = 0.168 f 0.001. Corg = concentration of MBT in mg/l. in chloroform. b = constant = 0.005 f 0.005. A Student’s t test applied to this constant showed that it did not differ significantly from zero. I t was calculated from Equation 4 that the molar absorptivity, e , was 28100 f 200 liter mole-l cm-l. This value is compared in Table I with previous values. Extraction of MBT. A 2-min shake time gave 99% extraction from acid solution and there was therefore no need to investigate shaking times in detail. MBT is ionized in aqueous solution; the degree of ionization is pH-dependent (6, 7 ) with a pK, value of about 7.0. The effect of pH on extraction of 5 and 10 mg/l. MBT into chloroform using an aqueous:organic ratio of 1:l is shown on Figure 2. Calibration Curves. A plot of the MBT concentration in aqueous solution us. the absorbance of a chloroform extract a t p H 1 was a straight line (not shown here) up to 9 mg/l. MBT. A linear regression analysis of 36 pairs of figures from four calibrations gave Equation 5 .
where A 3 2 9 = absorbance of chloroform extract a t 329 nm using 1-cm cells. a = constant, and a t 99% confidence limits = 0.168 f 0.002. Caq,l = concentration of MBT in mg/l. in original aqueous solution; extraction a t pH 1. b = constant = 0.005 f 0.008. A Student’s t test showed that this constant did not differ significantly from zero.
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO. 1, J A N U A R Y 1975
100
t
s
20
-
t t 0
100
0
200
300 400 Cu(tN)f; agll
500
600
700
Figure 3. Effect of cuprocyanide and cuprocyanide plus thiocyanate on extraction of MET with chloroform from hydrochloric acid and ammonium acetate solution
By putting the second constant in Equation 5 equal to zero, and rearranging to give a form more suitable for estimation of unknown M B T concentrations, Equation 1 was obtained. About 0.1 mg/l. MBT was detected in the aqueous raffinate when the original aqueous solution contained 10 mg/l. MBT. Hence, the first constant in Equation 5 , for acid extraction, could be expected to be 1% lower than that in Equation 4, for MBT dissolved directly in chloroform. However, except for slightly wider limits, Equation 5 has the same numerical constants as Equation 4. The cause of this apparent discrepancy was.not resolved. Replicate measurements showed that the absorbance of the extract obtained from an acidified solution containing 10 mg/l. MBT was 1.65 i 0.01. Calibrations obtained for extraction in the presence of ammonium acetate also showed straight line relationships u p t o 9 mg/l. MBT in the original aqueous phase. Equations 2 and 3 were calculated from the results. The actual absorbance values indicated that a t pH 7.3 about 98% of the M B T was extracted t i e , rather more than would be inferred from Figure 2 ) . At p H 8.3, about 86% of the MBT was extracted. O t h e r Conditions The standard procedure covered the expected range of MBT concentrations in flotation solutions. However, when an aqueous solution containing 40 mg/l. M B T was extracted a t 1:l ratio, the aqueous raffinate Contained 0.7 mg/l., indicating that 98.3% of the MBT had been extracted. When 100 ml of solution containing 0.1 mg/l. MBT was extracted with 10 mi of chloroform a t p H 1, about 88% of the M R T was extracted. Carbon tetrachloride also extracted 99% of the MBT a t p H 1 and phase ratio 1:1, but was thought to be less desirable than chloroform for general usage. Cyclohexane, which can be used for determination of 0-isopropyl ethylthiocarbamate in flotation liquors ( 8 ) ,extracted only about 30% of the M B T a t pH 1 using standard conditions. This was so inferior to extraction with chloroform that no more work was done with cyclohexane. Hack Extraction. Back extraction of MBT into aqueous sodium hydroxide solution was briefly investigated because the need might arise to strip MBT from chloroform if MBT concentrations were being monitored continuously. Hack extraction of chloroform containing 5 and 10 mg/l. M B T with 0.1M or 1M NaOH and measurement of the absorbance confirmed that no M B T was left in the chloroform. However, the absorbance of the aqueous phase was a t least 4% lower than expected. I t appeared that M B T was
0 10 mg/l. MET, zero NH4SCN, HCI solution, pH 1; 0 10 mg/l. MBT, zero NHISCN, NH40Ac solution, pH 7.3; A 10 mg/l. MET, 500 mg/l. NH4SCN, HCI solution, pH 1: A 10 mg/l. MBT, 500 mg/l. NH4SCN. NH40Ac solution, pH 7.3
decomposing in the presence of chloroform and sodium hydroxide. Effect of Inorganic Acids and Salts. Hydrochloric acid additions of 1 ml and 10 ml to 25 ml of solution t i e . , 0.46M or 3.43M) gave the same MBT extraction (Table 11) confirming the results of Figure 2. Lower additions than 1 ml, especially to highly alkaline solutions, may not give a sufficiently low p H for complete extraction. Most anions, when used alone in the concentrations shown in Table 11, which were greater than those expected in a flotation liquor, had no effect on MBT determination. However, it was necessary to use the close cell position when silicate was present since precipitated silicic acid transferred to the chloroform. Thiosulfate may precipitate sulfur on acidification, but, as shown previously ( 5 ) ,it usually takes several minutes for sulfur to form. Extraction was usually complete within this time, but, even when sulfur did form, no adverse effects were noted. Cuprocyanide interfered with MBT extraction from acidified solution, and the greater the amount of cuprocyanide present, the less MBT extracted (Figure 3). When a solution containing M B T and cuprocyanide was acidified, a white precipitate formed and this formed a skin around the chloroform during extraction. I t was suggested previously (1 ) that this precipitate contained MBT Cu and CuCN. However, X-ray and infrared examination showed that the precipitate contained MBT Cu but only a trace or no CuCN. I t is now suggested that the reaction in Equation 6 occurs.
-
-
-
H t 3H' C,H,NSS * CU i4HCN (6) Some MBT Cu or another compound was extracted into the chloroform as shown by the shoulder on the absorbance curve in Figure 4. This compound increased the total absorbance a t 329 nm, but low results for MBT were still obtained. MBT extraction was not improved by an increase in shaking time to 30 min, an increase in acid addition to 10 ml, or by making the solution 10% in sodium chloride. In the presence of thiocyanate as well as cuprocyanide, which is a common situation when cyanide is used in a plant, results by extraction from acid solution were very poor (Figure 3). By using ammonium acetate to buffer the solution a t p H 7-8 for extraction, a high proportion of the M B T was extracted over a wide range of cuprocyanide plus CU(CN),~- -I- C,H,NSS
*
A N A L Y T I C A L C H E M I S T R Y , VOL. 47,
NO. 1,
J A N U A R Y 1975
13
~
_ _ _ _ _ ~ ~
~~~
~
Table 11. Effect of Selected Reagents on Determination of MBT by Extraction into Chloroform at pH 1 M E T , mg/l.
Reaqent Name
Type
Acid Anion
Cation
Frother
Collector
HCl Na2C0, NaCl CU(CN),~-
AR AR AR This work
Cyanide Nickelocyanide Nitrate Silicate Sulfate Sulfide Sul f i t e Thiocyanate Thiosulfate
KCN Ni (CN),'KN03 NazSiO, Na2S0, NazS-9Hz0 NaZSO3.7H20 NHdSCN Na,S,03*5Hz0
AR This work AR AR AR AR AR AR AR
Copper Lead Zinc
AR AR AR
mg/l.c' Concn
40,000 10,000 100.000 350 3 50 100 250 1,000 1,000 10,000 100 1,000 200 1.000 1,000
FeS0,*7Hz0 MnS0,*4Hz0 NiS0,.7Hz0
AR AR AR
A e r o f r o t h 65 B a r r e t t No. 634 Creosote C r e s y l i c Acid TD MIBC TEB
Glycols N e u t r a l oil
Cyanamid Supplied by D e n v e r
100 50 50
Cresols Methyl isobutyl carbinol 1.1.3 -triethoxybutane
Union C a r b i d e Shell Nat. C h e m . P r o d .
100
Aerofloat, Sodium
Sodium diethyl dithiophosphate A r y l dithiophosphoric acid
Cyanamid Cyanamid
Dixanthogen Oleate Xanthate
Dixanthogen Sodium oleate P o t a s s i u m ethyl xanthate
This work B.D.H. This w o r k
z -200
0 -isopropyl ethylthiocarbamate
Dow
Cellofas B300
Sodium c a r b o x y m e t h y l cellulose Sodium lignosulfonate
IC1
Quebracho T a n n i c acid
78% Tannin, 15% non tannin T a n n i c acid
Copper o r e (oxidized)
Nickel o r e (sulfide) Nickel o r e ( l a t e r i t e ) Q u a r t z (-10 p m )
SiOz
Crown - Z e l l e r b a c h Quebracho B.D.H
Added
Fomd
10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 0.0 10.0
10.0 10.0 10.0 8.4 9.4d 10.0 9.9 9.9 10.oe 9.9 9.9 9.6' 10.1
0.0 10.0
Under c e r t a i n condi tions t h e s e m e t a l s r e a c t with MBT t o f o r m insoluble p r e cipitates. Any MBT r e m a i n i n g in solution is readily d e t e r m i n e d . 1,000 10.0 8.8E 9.59 1,000 10.0 1,000 10.0 9.5%
Iron I1 Manganese I1 Nickel
Orzan S
O r e s and minerals
Manufacturer b
Hydrochloric Carbonate Chloride Cuprocyanide
Aerofloat 25
Others
Principal component a
100 100 10 10 10 10
10.0 0.0 10.0 10.0 10.0 10.0
10.0 0.2 10.4 10.0 10.0 10.0
0.0 10.0
0.0 9.9
0.0
0.0 9.8 9.9
10.0
l o * 10.0 100 10 10 7.5 7.5
10.0 0.0 10.0 0.0 10.0
10.0 0.0 10.0
100
10.0
10.1"
50 50 50 50 50
0.0 10.0 0.0 10.0
0.0 10.0 0.0 9.9 9.9'
500 500 10,000 500 500 500 500
10.0 0.0 10.0 0.0 0.0 0.0
0.0 10.0
0.0 9.9
0.0 9.9 0.0 0.0 0.0 0.0 10.0
0 From Jones and Woodcock ( 5 ) and manufacturers' reagent literature. b AR = Analytical grade reagent; B.D.H. = British Drug Houses Ltd.; Crown-Zellerbach = Crown-Zellerbach Co.; Cyanamid = American Cyanamid Co.; Denver = Denver Equipment Co.: Dow = The Dow Chemical Co.; IC1 = Imperial Chemical Industries Ltd.; Nat. Chem. Prod. = National Chemical Products Ltd.; Quebracho = Quebracho Institute; Shell = Shell Chemical (Aust.) Pty Ltd; Union Carbide = Union Carbide Australia Ltd. c Concentrations by weight of original reagent. d Result for ammonium acetate extraction a t pH 7.3. e Close cell position. f After 5-min contact. g After filtration. h Using a suspension of the reagent in water.
14
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO, 1, J A N U A R Y 1975
2'o
9 I------
250
2'o
275
300 325 350 Wavelength, nm
400
-2 5 0
4%
275
300 325 350 Wavelength, nm
400
450
Figure 4. UV absorbance spectra in 1-cm cells of chloroform extracts from aqueous solution containing 10 mg/l. MBT and 350 mg/l.
Figure 5. UV absorbance spectra in 1-cm cells of chloroform extracts from acid solution
CU(CN)~~-
a. 1000 mg/l. Na2S03. 7H20; b. 1000 mg/l. Na2S03. 7H20
a. Extraction from HCI solution, pH1; b. Extraction from NH40Ac solution, pH 7.3
thiocyanate concentrations (Figure 3). No precipitate was observed except a t very high cuprocyanide levels. The absorbance curve of the chloroform extract was a normal MBT-in-chloroform curve (Figure 4). In contrast to cuprocyanide, nickelocyanide did not interfere with M B T extraction from acid solution. Sulfite a t the 1000 mg/l. level in alkaline solution reacts with MBT ( I ) , but when such a solution is acidified the reaction stops. Chloroform extraction of such solutions extracts SO2 and M B T as shown in Figure 5 . However, the absorbance curve of SOz, or sulfite, does not interfere with M B T determination. For a solution containing initially 1000 mg/l. NaZS03 7H20 and 10.0 mg/l. MBT, values of M B T found by extraction were 96% after 5-min standing (the minimum practical time), 93% after 30 min, and 92% after 2 hr. Cations such as copper, lead, and zinc form insoluble precipitates with MBT over a wide range of p H values. After removal of the precipitate, residual MBT can be determined by the standard technique. Iron 11. manganese 11, and nickel do not readily form M B T compounds, although hydroxide precipitates form in alkaline solution and may absorb MBT. As shown in Table 11, when such metals were added to an alkaline solution of MBT and the resultant precipitate filtered off, low results were obtained. However, the absorbance curves showed no unusual features and it was concluded that the method accurately determined MBT present. Effect of Frothers. Five typical frothers of different types were used (Table 11).The level of 100 mg/l. used was greater than that expected in a plant. Aerofroth 65, MIBC, and T E B had no detectable effect on M B T determination. Cresylic acid was partly extracted into chloroform and had an absorbance peak a t about 280 nm. However, there was no absorbance a t 329 nm and therefore no interference with MBT determination, Barrett No. 634 Creosote is completely soluble in chloroform and gives a rich absorbance spectrum. The reagent is not completely soluble in water, but the soluble fraction gives an appreciable absorbance spectrum ( 5 ) .The waterinsoluble part was filtered off in this work before contacting the solution with chloroform, but care could be needed with a plant pulp containing undissolved creosote. With the nominal 50 mg/l. creosote level in aqueous solution the chloroform extract had an appreciable absorbance below 300 nm and 0.03 absorbance a t 329 nm, leading to a small positive error for MBT determination (Table 11).
+ 10 mg/l.
MET
Effect of Collectors. Six commonly-used collectors were investigated (Table 11). None of the collectors, when added alone, had any effect on MBT determination. Aerofloat 25 contains cresylic acid which was extracted but had no effect a t 329 nm as noted above. 0-Isopropyl ethylthiocarbamate, which is the main constituent of 2-200, was also extracted into chloroform but had no absorbance a t 329 nm. Xanthate had no effect on MBT determination if the standard procedure of standing for 1 min between acidification and extraction was followed. If extraction was commenced immediately after acidification, then an unstable compound with an absorbance peak a t 271 nm was extracted. This was thought to be xanthic acid ( 9 ) , but it did not interfere with M B T determination. In the simultaneous presence of xanthate, cuprocyanide, and thiocyanate, very poor results for MBT estimation were obtained by the acid extraction procedure. In the ammonium acetate procedure, however, accurate results were obtained. Dixanthogen, which can be added as a reagent or can form from xanthate, was extracted into chloroform giving a broad absorbance band with a peak a t 290 nm. With 10 mg/l. of dixanthogen there was no interference with MBT determination. When sodium oleate was present, oleic acid precipitated on acidification but this had no effect on MBT determination. Effect of O t h e r Reagents. Flocculants, organic colloid depressants, dispersants, filter aids, wetting agents, and surface active agents in general may also be present in a flotation solution. Many of these reagents have no UV absorbance above 275 nm a t the 500 mg/l. level in aqueous solution (51, and there was no reason to suppose that they would have a UV absorbance a t 329 nm in chloroform. Use of the standard acid extraction technique in the presence of Orzan S, quebracho, and tannic acid showed that the reagents did not interfere (Table 11), provided the determination was made within a few minutes of preparing the solution. However, on standing in aqueous alkaline solution, tannic acid and MBT reacted in some way. Determination of MBT 5 min after mixing with tannic acid showed that 99% of the MBT was recovered. After 1 hr, 91% was recovered; after 3 hr, 69% was recovered. Effect of O r e Solids. With pulps that are naturally or deliberately dispersed during flotation, it is sometimes difficult to obtain a perfectly clear solution for analysis. Results for MBT determination in the presence of various dis-
ANALYTICAL C H E M I S T R Y , VOL. 47, NO. 1 , J A N U A R Y 1975
15
Table 111. Results in Some Actual Flotation Solutions MRT after spiking with 5 . 0 mq/l,
Type of flotation
A. Plant flotation of Cu- Pb-Zn sulfide o r e (pH 9.5) B. Plant flotation of copper sulfide o r e (PH 10) C. Laboratory flotation of oxidized copper o r e (pH 9.8)' D. Laboratory flotation of nickel sulfide o r e (pH 8.3)"
LIBT found in solut'on, rng1l.b
Expected, Ingll.
Found mg/l.
0.15
5.15
5.1
0.05
5.05
5.0
Sodium metasilicate. sodium sulfide. Aerofrotli 65. Aero P r o m o t e r 42Sd
1.35
6.35
6.45
Sodium hexameta phosphate, copper sulfate. Aero P r o m o t e r 412d
0.45
5.45
5.4
Reagents used in flotation'
Lime. sodium sulfite. ethyl xanthate. s e c ondary butyl xan thate. 2 -200, copper sulfate. M300 Lime, Aerofroth 65, z -200
a These reagents m a y have been consumed during flotation. A f t e r m i x i n g 90.0 ml of test solution w i t h 10.0 ml of water for ease of comparison w i t h spiked solutions. e Solution cloudy w i t h ore slimes. This reagent contains MBT.
persed solids are shown in Table 11. None of the solids used had any effect in concentrations up to a t least 500 mg/l. (which is a turbid solution) and the chloroform disengaged readily from the aqueous phase. Plant and Laboratory Solutions. Application of the extraction technique to two solutions from operating plants where MBT was not used and two laboratory tests where MBT was used gave the results in Table 111. Compounds derived from the reagents, from recycled solutions, and from interactions between ore, water, and air were present in unknown amounts. Solution A contained sulfite and thiosulfate but these did not interfere. There was a small absorbance in the chloroform extract which led to a slight overestimate of MBT for the solution alone and after spiking with MBT. Solution B contained 2-200 but this did not interfere. Solutions C and D from the laboratory tests, in which MBT-containing reagents were used, contained residual MBT a t the end of flotation. Both solutions were slightly cloudy with ore slimes, and direct UV determination by the previous method ( I ) gave high results. However, the extraction technique gave an accurate recovery of the spike addition of MBT.
CONCLUSION MBT can be determined in a wide range of flotation liquors by the solvent extraction technique discussed here. Advantages of the solvent extraction technique over the previously-developed method of direct UV measurement are that it is more sensitive, can be more readily applied to
16
measure low concentrations, can overcome interference from cuprocyanide and certain other reagents, and can be applied to solutions containing ore particles. The main disadvantage is that an extra step is needed, and this makes development of an on-stream technique more difficult. For general purposes, it is suggested that the technique of acidification before extraction be used. This is the simplest procedure for solutions with a variable alkali content because any pH between 0 and 2 after acidification gives the same result. When acidification leads to difficulties, as in the presence of cuprocyanide, then extraction from a solution buffered with ammonium acetate should be used. Although any pH between 7 and 8.3 can be used, the pH needs to be known to 0.1 unit so that the correct calibration curve can be applied.
LITERATURE CITED (I) (2) (3) (4) (5) (6) (7) (8)
(9)
M. H. Jones and J. T. Woodcock, Can. Met. Quart., 12, 497 (1973). H. P. Koch, J. Chem. SOC., 401 (1949). K. E. Kress, Anal. Chem., 23, 313 (1951). J. R. Edisbury, "Practical Hints on Absorption Spectrometry," Hilger and "Watts,London, 1966, pp 176-179. M. H. Jones and J. T. Woodcock, "Ultraviolet Spectrometry of Flotation Reagents with Special Reference to the Determination of Xanthate in Flotation Liquors," The Institution of Mining and Metallurgy, London, 1973. K . L. Sutherland. J. Phys. Chem., 63, 1717(1959). 6.Stanovnik and M. Tisier, Vestn. Slov. Kern. Drus., lO(1-2), 1 (1963). M. H. Jones and J. T. Woodcock, Australas. Inst. Mining Met. Proc.. 231 11 (1969). A . Pomianowski and J. Leja, Can. J. Chem., 41, 2219 (1963).
RECEIVEDfor review April 8, 1974. Accepted August 19, 1974.
A N A L Y T I C A L C H E M I S T R Y , VOL. 47, NO. 1. J A N U A R Y 1975
