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Extraction into methyl isobutyl ketone of metal complexes with ammonium pyrrolidine dithiocarbamate formed in strongly acidic media
Analytica Chimica Acta, 217 (1969) 165-170 Elsevier Science Publishers B:V., Amsterdam -
EXTRACTION COMPLEXES CARBAMATE
165 Printed in The Netherlands
INTO METHYL ISOBUTYL KETONE OF METAL WITH AMMONIUM PYRROLIDINE DITHIOFORMED IN STRONGLY ACIDIC MEDIA
ROBERT R. BROOKS*, MAKI HOASHI, SHANE M. WILSON and RUI-QI ZHANG Department of Chemistry and Biochemistry, Massey University, Palmerston North (New Zealand) (Received 13th July 1988)
SUMMARY It is shown that stable metal complexes with ammonium pyrrolidine dithiocarbamate (APDC) are formed in strongly acidic (0.5-6 M) solutions and can be extracted into methyl isobutyl ketone (MIBK 1,although APDC is normally used for extractions from solutions at pH 2-12. Percentage extraction curves are presented for 24 elements (Ag, As, Au, Bi, Cd, Co, Cu, Fe, Ga, Ge, Hg, In, Ir, Ni, OS, Pb, Pd, Pt, Rh, Ru, Sb, Sn, Tl and Zn) from solutions of hydrochloric or nitric acid with and without addition of APDC. Some elements (e.g., Fe, Ga, Ge, In and Au) show identical extractions as their chloro complexes in hydrochloric acid with or without APDC. Others (e.g., Ni, Cu, Pd, As, Ag, Sb, Ir, Hg and Bi) are strongly extracted (Z&> 20), from 2 M hydrochloric or nitric acid in the presence of APDC. Palladium (& = 8000)) Sb ( Kd = 10 000)) and Bi ( Kd = 3500 ) are particularly easily extracted. The potential of the extraction system was tested by extraction and quantification of palladium from the CANMET standard ore PTC-1; the mean value found was 12.55 m gg’ (ppm) palladium with a relative standard deviation of 7.6% (n=12) and a relative error of 1.2% from the recommended value of 12.70 pg g-i.
The analytical significance of ammonium pyrrolidine dithiocarbamate ( APDC ) as a ligand for metal complexes extractable into methyl isobutyl ketone (MIBK ) was first suggested by Malissa and Schijffmann [ 11. After this early report, numerous other workers applied extraction of APDC-metal complexes into organic solvents (usually MIBK) for the determination of trace elements in brines [ 21, and sea water [ 31. There have, however, been very few examples of the use of an APDC extraction system for samples other than natural waters, although there has been a report of its use at pH 2.4 for determining heavy metals in fish samples [ 41 and at pH 3 for precipitation of heavy metals directly on to a graphite furnace prior to electrothermal atomic absorption spectrometry [ 51. Although extraction of metal-APDC complexes from aqueous solutions in the pH range 2-14 has been considered the standard procedure, it has not previously been appreciated that some metal-APDC complexes can be ex-
0003-2670/89/$03.50
0 1989 Elsevier Science Publishers B.V.
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tracted from strongly acidic (i.e., l-6 M) solutions of hydrochloric and nitric acids. The significance of such extractions, which have recently been investigated, lies in their obvious potential for extracting trace elements from solutions of silicate rocks which normally require hydrochloric or nitric acids at a strength of at least 2 M. The extraction of metal-APDC complexes of 24 elements into MIBK from hydrochloric and nitric acid solutions with concentrations in the range 0.5-6 M is reported in this paper. Above 6 M acid, the increased miscibility of MIBK with the aqueous phase causes significant problems and experiments were therefore not conducted at these higher concentrations. Extractions from hydrochloric acid solutions (0.5-6 M) without added APDC were examined because many elements form chloro complexes which are also extractable into MIBK [6]. It was thereby possible to establish the degree to which chloro complexes rather than those with APDC were responsible for extraction in specific cases. The elements studied in this work were the transition elements Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ru3+, Rh3+, Pd2+, Ag+, Cd2+, OS*+, Ir*+, Pt*+, Au3+, and Hg2+ In addition, elements of Groups 3b, 4b and 5b were studied, these were Ga3+: In3+, TP+, Ge*+, Sn2+, Pb2+, As3+, Sb3+, and Bi3+. All of the above elements were selected on the basis of their known formation of complexes with APDC [ 11, and because of their importance as trace elements (except for iron) in silicate rocks. EXPERIMENTAL
The extractability of metal-APDC complexes was determined by equilibrating equal volumes of organic and aqueous phases and determining the concentrations of the metal ions in the aqueous phases before and after equilibration. When the percentage extraction was not excessively great or small, it was possible to conduct these determinations by flame atomic absorption spectrometry with an IL457 instrument. When percentage extractions were very high so that the concentrations in the aqueous phases were very low, or very low (low concentrations in the organic phase), the metal concentrations were determined by graphite-furnace atomic absorption spectrometry with a GBC-1000 furnace coupled to a GBC-902 double-beam instrument. From the ratio of absorbances in the two phases, values of the distribution coefficient (&) were obtained and were related to the percentage extraction (E), where E = {I& [&/ + ( VJ V,) ] } 100 and V, and V, are the respective volumes of the aqueous and organic phases. Extractions were examined on 5-ml aliquots of three sets of solutions prepared as follows: (i) 0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 M hydrochloric acid; (ii) as (i) but with the addition of 0.01 g of APDC to each aliquot; (iii) nitric
167
acid solutions of the same strengths as (i) and with addition of 0.01 g of APDC to each aliquot. The original metal ion concentrations in the aqueous phases ranged from 10 to 200 ,ug ml-’ (ppm) depending on the analytical sensitivity of the metals concerned. The oxidation state of each metal was chosen to represent the state most likely to be found in a rock solution prepared under oxidizing conditions (e.g., Fe3+ rather than Fez+ ). This was in order to approximate the actual conditions likely to be encountered in the course of silicate rock analysis. RESULTS AND DISCUSSION
Figure 1 shows the percentage extraction into MIBK of 24 metals as a function of concentrations of mineral acids, with and without addition of APDC. Table 1 gives values of Kd for the extraction of each ion from 2 M solutions of nitric and hydrochloric acid with and without addition of APDC. Solutions of this strength were chosen because they represent the most likely acid concentration in a rock solution prepared for trace analysis. The curves in Fig. 1 demonstrate that the extractability of the metal ions can be divided into four classes as follows: (i) the extraction is not affected by Fe3’
Co2’
Ni”
Cd+
Zn2’
Ga3*
G&’
As3’
Fig. 1. Curves for the extraction of metal-APDC complexes into MIBK from hydrochloric and nitric acid solutions with and without addition of APDC; (-) HNO,+APDC; (- - -) HCl + APDC; ( ***) HCl only.
166 TABLE 1 Values of the distribution coefficient (&) for extraction of metal ions into MIBK from 2 M acid solutions with and without addition of APDC” Ion
W As”
2MHCl
+
Au”+ Bi” + Cd’+ co2+ cl?+ Fe”+ Ga”+ Ge*+ Hg*+ In”+ Ir4 + Ni2+ os4+ Pb2+ Pd2+ Pt4+ Rh:‘+ Ru:’+ Sb”+ Sn2+ TP+ Zn2+
0.06 10 000
2 M HCl/ APDC
53 10 000 1250 co.01 0.05
78
0.74 0.51 0.04 642 0.51 3.00 20 co.01
2 M HNOJ APDC
41
0.01 3.40 3500 0.10 0.50 co.01 0.22
24
CO.01 co.01 0.12 3.00 0.06 0.40 1.50
“Valuesof Kd> 20 correspond to a percentage extraction of 95.2% for a 1:l organic/aqueous phase ratio, have potential for analysis and are underlined in the Table.
addition of APDC and depends solely on the formation of chloro complexes in hydrochloric acid solutions; (ii) the extraction is dependent on the presence of APDC and the Kd values are sufficiently high in 2-3 M acid to be advantageous for their separation and subsequent quantification; (iii) the extraction is dependent on the presence of APDC but the Kd values are too low to be of use for their separation and quantification; (iv) ions which are not extracted under any circumstances. Each of the above classes will now be discussed. In class (i) are Fe3+, Ga3+, Ge4+, In3+, TP+, and Au3+. There is no advantage in using APDC to extract any of these elements from solutions of silicate rocks because they are extracted equally well as their chloro complexes from hydrochloric acid solutions. In such cases, however, only gold and thallium lend themselves to extraction from 2 M hydrochloric acid; the other elements require higher acid concentrations for high percentage extraction.
169
The elements of class (ii) include Ni2+, Cu2+, Pd2+, As3+, Ag+, Sb3+, Ir4+, Hg2+, and Bi3+. In 2 M hydrochloric or nitric acids, values of Kd> 20 (95.2% extraction) were as follows: Ni2+, 20 (2 M HCl); Cu2+, 78 (2 M HCl); Pd2+, 8000 (2 M HCl); As3+, 53 (2 M HCl); Ag+, 41 (2 M HNO,); Sb3+, 10 000 (2 MHC1);Ir4+,24 (2MHN03);Hg2+,642 (2MHN03);Bi3+,1250 (2MHCl) and 3500 (2 M HN03). It is clear that, in general, the HCl-APDC system is preferable to HNO,-APDC. It may be that the nitric acid has some oxidative effect on the APDC, particularly at higher acid concentrations. The ions of class (iii) include Co2+, Zn2+, Ru3+, Rh3+, Cd2+, Sn2+, Pt4+, and Pb2+. Many of these ions (i.e., all except Ru3+, Rh3+, and Pt4+ ) are extracted strongly under relatively neutral or weakly acidic conditions (pH 212 ), but not under the strongly acidic solutions needed to stabilize a rock digest. under any Only Os4+ falls into class (iv) where there is no extraction conditions. A practical application of the APDC extraction system Apart from Au3+, which is extracted very easily from hydrochloric acid solutions without the need for APDC, Bi3+, Pd2+, and Sb3+ are extracted very strongly from mineral acid solutions containing APDC (Kd> 1000). The potential of the extraction system was tested by determining palladium in the CANMET standard ore PTC-1 [7]. Samples (0.5 g) were digested in teflon beakers with 10 ml of a 1:l:l mixture of nitric, hydrofluoric and perchloric acids. After fuming to dryness, the residues were redissolved in 5 ml of aqua regia and evaporated down to about 1 ml giving effectively 6 M constant-boiling hydrochloric acid. The volume was adjusted to about 5 ml with 6 M hydrochloric acid and the iron was removed by shaking with an equal volume of MIBK. The volume of the residue was adjusted to 50 ml with acid to give a final strength of 2 M hydrochloric acid. Aliquots of 3 ml (corresponding to 0.03 g of rock) were then shaken with 1 ml of aqueous 0.05% APDC and 3 ml of MIBK. After about 3 min, palladium was determined in the organic phase by flameless atomic absorption spectrometry with the equipment listed above. The heating cycle was as follows: drying, 10 s at 120’ C; charring, 5 s at 500 oC; atomisation, 1 s at 2500 oC. The absorption line used was 247.6 nm. Twelve replicate analyses gave a mean value of 12.55 pg g-l (ppm) palladium with a precision of 7.6% and relative error of only 1.2% from the recommended value of 12.70 pg g-’ [ 71. Conclusions It is concluded that extension of the use of APDC-metal complexes to the extraction of several heavy metals from acidic solutions into MIBK will have important applications in the future as was shown above in the case of palladium. It is probable that elements such as bismuth and antimony can also be determined in silicate rocks after only a single extraction from acidic solutions.
170
There are several other elements which have sufficiently high distribution coefficients (i.e., > 5) to provide essentially complete extraction by two or more separate operations. This work has demonstrated the very wide application of the APDC extraction system for determination of several elements in silicate rocks where this was not thought previously to be possible.
REFERENCES H. Malissa and E. Schoffmann, Mikrochim. Acta, 1 (1955) 187. S. Sprague and W. Slavin, At. Absorpt. Newsl., 20 (1964) 11. R.R. Brooks, B.J. Presley and I.R. Kaplan, Talanta, 14 (1967) 809. I. Okuno, J.A. Whitehead and R.E. White, J. Assoc. Off. Anal. Chem., 61 (1978) 664. J.A. Nichols and R. Woodriff, J. Assoc. Off. Anal. Chem., 63 (1980) 500. C.R. Boswell and R.R. Brooks, Mikrochim Acta, 5-6 (1965) 814. R.C. McAdam, Sutarno and P.E. Moloughney, Dep. Energ. Mines. Res. Mines Branch tawa), Tech. Bull., TB176, 1973.
(Ot-
EXTRACTION COMPLEXES CARBAMATE
165 Printed in The Netherlands
INTO METHYL ISOBUTYL KETONE OF METAL WITH AMMONIUM PYRROLIDINE DITHIOFORMED IN STRONGLY ACIDIC MEDIA
ROBERT R. BROOKS*, MAKI HOASHI, SHANE M. WILSON and RUI-QI ZHANG Department of Chemistry and Biochemistry, Massey University, Palmerston North (New Zealand) (Received 13th July 1988)
SUMMARY It is shown that stable metal complexes with ammonium pyrrolidine dithiocarbamate (APDC) are formed in strongly acidic (0.5-6 M) solutions and can be extracted into methyl isobutyl ketone (MIBK 1,although APDC is normally used for extractions from solutions at pH 2-12. Percentage extraction curves are presented for 24 elements (Ag, As, Au, Bi, Cd, Co, Cu, Fe, Ga, Ge, Hg, In, Ir, Ni, OS, Pb, Pd, Pt, Rh, Ru, Sb, Sn, Tl and Zn) from solutions of hydrochloric or nitric acid with and without addition of APDC. Some elements (e.g., Fe, Ga, Ge, In and Au) show identical extractions as their chloro complexes in hydrochloric acid with or without APDC. Others (e.g., Ni, Cu, Pd, As, Ag, Sb, Ir, Hg and Bi) are strongly extracted (Z&> 20), from 2 M hydrochloric or nitric acid in the presence of APDC. Palladium (& = 8000)) Sb ( Kd = 10 000)) and Bi ( Kd = 3500 ) are particularly easily extracted. The potential of the extraction system was tested by extraction and quantification of palladium from the CANMET standard ore PTC-1; the mean value found was 12.55 m gg’ (ppm) palladium with a relative standard deviation of 7.6% (n=12) and a relative error of 1.2% from the recommended value of 12.70 pg g-i.
The analytical significance of ammonium pyrrolidine dithiocarbamate ( APDC ) as a ligand for metal complexes extractable into methyl isobutyl ketone (MIBK ) was first suggested by Malissa and Schijffmann [ 11. After this early report, numerous other workers applied extraction of APDC-metal complexes into organic solvents (usually MIBK) for the determination of trace elements in brines [ 21, and sea water [ 31. There have, however, been very few examples of the use of an APDC extraction system for samples other than natural waters, although there has been a report of its use at pH 2.4 for determining heavy metals in fish samples [ 41 and at pH 3 for precipitation of heavy metals directly on to a graphite furnace prior to electrothermal atomic absorption spectrometry [ 51. Although extraction of metal-APDC complexes from aqueous solutions in the pH range 2-14 has been considered the standard procedure, it has not previously been appreciated that some metal-APDC complexes can be ex-
0003-2670/89/$03.50
0 1989 Elsevier Science Publishers B.V.
166
tracted from strongly acidic (i.e., l-6 M) solutions of hydrochloric and nitric acids. The significance of such extractions, which have recently been investigated, lies in their obvious potential for extracting trace elements from solutions of silicate rocks which normally require hydrochloric or nitric acids at a strength of at least 2 M. The extraction of metal-APDC complexes of 24 elements into MIBK from hydrochloric and nitric acid solutions with concentrations in the range 0.5-6 M is reported in this paper. Above 6 M acid, the increased miscibility of MIBK with the aqueous phase causes significant problems and experiments were therefore not conducted at these higher concentrations. Extractions from hydrochloric acid solutions (0.5-6 M) without added APDC were examined because many elements form chloro complexes which are also extractable into MIBK [6]. It was thereby possible to establish the degree to which chloro complexes rather than those with APDC were responsible for extraction in specific cases. The elements studied in this work were the transition elements Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ru3+, Rh3+, Pd2+, Ag+, Cd2+, OS*+, Ir*+, Pt*+, Au3+, and Hg2+ In addition, elements of Groups 3b, 4b and 5b were studied, these were Ga3+: In3+, TP+, Ge*+, Sn2+, Pb2+, As3+, Sb3+, and Bi3+. All of the above elements were selected on the basis of their known formation of complexes with APDC [ 11, and because of their importance as trace elements (except for iron) in silicate rocks. EXPERIMENTAL
The extractability of metal-APDC complexes was determined by equilibrating equal volumes of organic and aqueous phases and determining the concentrations of the metal ions in the aqueous phases before and after equilibration. When the percentage extraction was not excessively great or small, it was possible to conduct these determinations by flame atomic absorption spectrometry with an IL457 instrument. When percentage extractions were very high so that the concentrations in the aqueous phases were very low, or very low (low concentrations in the organic phase), the metal concentrations were determined by graphite-furnace atomic absorption spectrometry with a GBC-1000 furnace coupled to a GBC-902 double-beam instrument. From the ratio of absorbances in the two phases, values of the distribution coefficient (&) were obtained and were related to the percentage extraction (E), where E = {I& [&/ + ( VJ V,) ] } 100 and V, and V, are the respective volumes of the aqueous and organic phases. Extractions were examined on 5-ml aliquots of three sets of solutions prepared as follows: (i) 0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 M hydrochloric acid; (ii) as (i) but with the addition of 0.01 g of APDC to each aliquot; (iii) nitric
167
acid solutions of the same strengths as (i) and with addition of 0.01 g of APDC to each aliquot. The original metal ion concentrations in the aqueous phases ranged from 10 to 200 ,ug ml-’ (ppm) depending on the analytical sensitivity of the metals concerned. The oxidation state of each metal was chosen to represent the state most likely to be found in a rock solution prepared under oxidizing conditions (e.g., Fe3+ rather than Fez+ ). This was in order to approximate the actual conditions likely to be encountered in the course of silicate rock analysis. RESULTS AND DISCUSSION
Figure 1 shows the percentage extraction into MIBK of 24 metals as a function of concentrations of mineral acids, with and without addition of APDC. Table 1 gives values of Kd for the extraction of each ion from 2 M solutions of nitric and hydrochloric acid with and without addition of APDC. Solutions of this strength were chosen because they represent the most likely acid concentration in a rock solution prepared for trace analysis. The curves in Fig. 1 demonstrate that the extractability of the metal ions can be divided into four classes as follows: (i) the extraction is not affected by Fe3’
Co2’
Ni”
Cd+
Zn2’
Ga3*
G&’
As3’
Fig. 1. Curves for the extraction of metal-APDC complexes into MIBK from hydrochloric and nitric acid solutions with and without addition of APDC; (-) HNO,+APDC; (- - -) HCl + APDC; ( ***) HCl only.
166 TABLE 1 Values of the distribution coefficient (&) for extraction of metal ions into MIBK from 2 M acid solutions with and without addition of APDC” Ion
W As”
2MHCl
+
Au”+ Bi” + Cd’+ co2+ cl?+ Fe”+ Ga”+ Ge*+ Hg*+ In”+ Ir4 + Ni2+ os4+ Pb2+ Pd2+ Pt4+ Rh:‘+ Ru:’+ Sb”+ Sn2+ TP+ Zn2+
0.06 10 000
2 M HCl/ APDC
53 10 000 1250 co.01 0.05
78
0.74 0.51 0.04 642 0.51 3.00 20 co.01
2 M HNOJ APDC
41
0.01 3.40 3500 0.10 0.50 co.01 0.22
24
CO.01 co.01 0.12 3.00 0.06 0.40 1.50
“Valuesof Kd> 20 correspond to a percentage extraction of 95.2% for a 1:l organic/aqueous phase ratio, have potential for analysis and are underlined in the Table.
addition of APDC and depends solely on the formation of chloro complexes in hydrochloric acid solutions; (ii) the extraction is dependent on the presence of APDC and the Kd values are sufficiently high in 2-3 M acid to be advantageous for their separation and subsequent quantification; (iii) the extraction is dependent on the presence of APDC but the Kd values are too low to be of use for their separation and quantification; (iv) ions which are not extracted under any circumstances. Each of the above classes will now be discussed. In class (i) are Fe3+, Ga3+, Ge4+, In3+, TP+, and Au3+. There is no advantage in using APDC to extract any of these elements from solutions of silicate rocks because they are extracted equally well as their chloro complexes from hydrochloric acid solutions. In such cases, however, only gold and thallium lend themselves to extraction from 2 M hydrochloric acid; the other elements require higher acid concentrations for high percentage extraction.
169
The elements of class (ii) include Ni2+, Cu2+, Pd2+, As3+, Ag+, Sb3+, Ir4+, Hg2+, and Bi3+. In 2 M hydrochloric or nitric acids, values of Kd> 20 (95.2% extraction) were as follows: Ni2+, 20 (2 M HCl); Cu2+, 78 (2 M HCl); Pd2+, 8000 (2 M HCl); As3+, 53 (2 M HCl); Ag+, 41 (2 M HNO,); Sb3+, 10 000 (2 MHC1);Ir4+,24 (2MHN03);Hg2+,642 (2MHN03);Bi3+,1250 (2MHCl) and 3500 (2 M HN03). It is clear that, in general, the HCl-APDC system is preferable to HNO,-APDC. It may be that the nitric acid has some oxidative effect on the APDC, particularly at higher acid concentrations. The ions of class (iii) include Co2+, Zn2+, Ru3+, Rh3+, Cd2+, Sn2+, Pt4+, and Pb2+. Many of these ions (i.e., all except Ru3+, Rh3+, and Pt4+ ) are extracted strongly under relatively neutral or weakly acidic conditions (pH 212 ), but not under the strongly acidic solutions needed to stabilize a rock digest. under any Only Os4+ falls into class (iv) where there is no extraction conditions. A practical application of the APDC extraction system Apart from Au3+, which is extracted very easily from hydrochloric acid solutions without the need for APDC, Bi3+, Pd2+, and Sb3+ are extracted very strongly from mineral acid solutions containing APDC (Kd> 1000). The potential of the extraction system was tested by determining palladium in the CANMET standard ore PTC-1 [7]. Samples (0.5 g) were digested in teflon beakers with 10 ml of a 1:l:l mixture of nitric, hydrofluoric and perchloric acids. After fuming to dryness, the residues were redissolved in 5 ml of aqua regia and evaporated down to about 1 ml giving effectively 6 M constant-boiling hydrochloric acid. The volume was adjusted to about 5 ml with 6 M hydrochloric acid and the iron was removed by shaking with an equal volume of MIBK. The volume of the residue was adjusted to 50 ml with acid to give a final strength of 2 M hydrochloric acid. Aliquots of 3 ml (corresponding to 0.03 g of rock) were then shaken with 1 ml of aqueous 0.05% APDC and 3 ml of MIBK. After about 3 min, palladium was determined in the organic phase by flameless atomic absorption spectrometry with the equipment listed above. The heating cycle was as follows: drying, 10 s at 120’ C; charring, 5 s at 500 oC; atomisation, 1 s at 2500 oC. The absorption line used was 247.6 nm. Twelve replicate analyses gave a mean value of 12.55 pg g-l (ppm) palladium with a precision of 7.6% and relative error of only 1.2% from the recommended value of 12.70 pg g-’ [ 71. Conclusions It is concluded that extension of the use of APDC-metal complexes to the extraction of several heavy metals from acidic solutions into MIBK will have important applications in the future as was shown above in the case of palladium. It is probable that elements such as bismuth and antimony can also be determined in silicate rocks after only a single extraction from acidic solutions.
170
There are several other elements which have sufficiently high distribution coefficients (i.e., > 5) to provide essentially complete extraction by two or more separate operations. This work has demonstrated the very wide application of the APDC extraction system for determination of several elements in silicate rocks where this was not thought previously to be possible.
REFERENCES H. Malissa and E. Schoffmann, Mikrochim. Acta, 1 (1955) 187. S. Sprague and W. Slavin, At. Absorpt. Newsl., 20 (1964) 11. R.R. Brooks, B.J. Presley and I.R. Kaplan, Talanta, 14 (1967) 809. I. Okuno, J.A. Whitehead and R.E. White, J. Assoc. Off. Anal. Chem., 61 (1978) 664. J.A. Nichols and R. Woodriff, J. Assoc. Off. Anal. Chem., 63 (1980) 500. C.R. Boswell and R.R. Brooks, Mikrochim Acta, 5-6 (1965) 814. R.C. McAdam, Sutarno and P.E. Moloughney, Dep. Energ. Mines. Res. Mines Branch tawa), Tech. Bull., TB176, 1973.
(Ot-