V O L U M E 20, NO. 10, O C T O B E R 1 9 4 8 EXPERJMENTAL RESULTS
T o illustrate the effect of acidity on the electrodeposition of lead, three 10-gram samples of copper (0.03570 lead) were dissolved in 50 ml. of water and 40 ml. of nitric acid, then evaporated to dryness, cooled, and diluted with water. Then 10, 20, and 30 rnl. of nitric acid were added to the respective beakers, and the solutions were boiled, cooled, and electrolyzed at 1 ampere for 30 minutes. The amounts of lead recovered were as follows: 10 ml. of nitric acid, 0.03% Pb 20 ml. of nitric acid, 0.02% Pb 30 ml. of nitric acid, 0.0% Pb This amply illustrated the hindering effect of excess nitric acid. A series of check samples was run by the colorimetric and electrodeposition methods (Table I ) . Polarographic examination of the impurities of the lead dioxide deposits is not within the scope of this paper (1). The techniques described cannot be considered original, as these general methods have been in use for many years. The
909 author invites comment on the discussions and takes this opportunity t o thank associates for assistance rendered. LITERATURE CITED
Cholak, J., and Bambach, K., IND. ENG.CHEW,AXAL.ED.,13, 583 (1941). Classen, A., “Quantitative Analysis by Electrolysis,” tr. from 5th German ed. by W. T. Hall, pp. 108-11, Iiew York, John Wiley & Sons, 1913. Fischer, H., 2. angew. Chem., 42, 1025 (1929); 50. 919 (1937). ENG.CHEM., ANAL.ED.,9, 943 (1937). Hubbard, D. M., IND. Rosin, Joseph, “Reagent Chemicals and Standards,” New York, D. Van h’ost.rand Co., 1937. Schoonover, J. C., S a t l . Bur. Standards, Research Paper 836,,377 (1935). Silverman, L.,IND. ESG. CHEM.,ANAL.ED.,17, 270 (1945). Ibid., 19, 698 (1947). Taylor, H. S., “Treatise on Physical Chemistry,” N e w York, 839, D. Van Nostrand Co. (1931). Wichmann, H. J., IND. ENG.CHEM.,ANAL. ED.,11, 66 (1939). Winter, 0 . B., Robinson, H. M.. Lamb, E. W., and Miller, E. J . Zbid., 7, 265 (1935). RH~CEIVBD November 12, 1947.
Analysis of Sulfite Waste liquor and lignosulfonates Determination of Neutralized Solids and Wet Oxidation f o r Determination of Total Sulfur and Cations .I. RICHTER SALVESEN
AND DAVID HOGAN, Muruthon Corporation, Rothschild, V i s .
A method is presented that allows a more complete determination of sulfite waste liquor components than the present total solids method. In the procedure described, neutralization of the sulfite waste liquor with caustic soda prior to drying prevents the loss of volatile organic acids and sulfur dioxide. A simple, rapid procedure for analyzing sulfite waste liquor and lignosulfonates involving oxidation of the organic matter by a nitric-perchloric acid mixture is described. This method may be used with either liquid or solid samples and it permits ready determination of all cations, silica, and total sulfur using the material from one digestion. The precision in the determination of sulfur is equal ta that obtained in the Carius method.
S
ULFITE waste liquor is the spent cooking liquor that drains from the cellulose pulp made by digesting wood chips a t elevated temperature and pressure with an aqueous solution of sulfurous acid and bisulfite. This waste liquor contains in soluble form the main part of the noncellulose components of wood. These components are mainly lignin, present as lignosulfonates, and hemicelluloses, present as partiallv or wholly hydrolyzed carbohydrate compounds. Because sulfite waste liquor organic matter usually comprises about 50% of the wood, it represents large amounts of organic matter which may give rise to objectionable pollution when passed into rivers and other waterways. Furthermore, this organic matter represents potential economic value. For these reasons sulfite waste liquor disposal and utilization procedures are being studied with increasing interest. Such studies have been handicapped by lack of suitable analytical procedures. Partansky and Benson (16) have published procedures which have been adopted as TAPPI Standard Methods (BO) and another set of standard methods has been adopted by the German Pulp and Paper Chemists and Engineers Association (3).
The procedures presented herex-ith have been used for a number of years. They have been found convenient and accurate for research as well as control in the field of sulfite waste liquor. One method is for the determination of “neutralized solids” in sulfite waste liquor. These neutralized solids are the
solids obtained upon drying sulfite waste liquor which has beak, previously adjusted to a pH in the range from to 8.5 to 9.G with sodium hydroxide. Another method is for the wet oxidation of either solid or liquid samples, whereby the organic matter is completely oxidized and the resulting solution can be used for determination of the inorganic sulfite waste liquor components such as total sulfur, silicon dioxide, ferric oxide, aluminum oxide, calcium oxide, magnesium oxide, and sodium oxide by known procedures. DETERMINATION OF NEUTR4LIZED SOLIDS FROV SULFITF WASTE LIQUOR
Sulfite waste liquor norniallv has a pH of from 1.5 to 3.0 and will therefore lose volatile acid components when evaporated to dryness. These acids are partly organic, such as acetic and formic, and partly sulfurous acid present in the original liquor as free sulfur dioxide, bisulfite, and “loosely oombined” (aldehydic) sulfur dioxide. By neutralizing the sample m-ith a knowi-r! amount of standard sodium hydrovide solution to pH 8.5 to 9.0 prior to the evaporation and drying, the loss of the volatile acids is prevented. Sulfur analyses by wet oxidation shoFv that no sulfur compounds present in the original sulfite waste liquor are lost by evaporation and drying with the neutrallzed solid. procedure. Analytical Procedure. Pipet 10 ml of sulfite waste liquor into 8, 2.50-ml. beaker containing 100 to 125 ml. of dlstilled water
910
ANALYTICAL CHEMISTRY
Titrate with 0.2 AVsodium hydroxide to a pH of 8.5 to 9.0 with she aid of a glass electrode pH meter. This titration is used to determine the sodium hydroxide required for neutralization. Weigh a ground glass-stoppered weighing bottle to 0.0001 gram Pipet another 10 ml. of sulfite waste liquor sample into the bottle and reweigh to 0.001 gram. Add the same amount of 0.2 iV aodium hydroxide as was used in the above titration and mix well. Dry the neutralized sample in a constant temperature oven a t 105" C., cool in a desiccator, and weigh to 0.0001 gram with cover on. For use in ordinary analysis 48 to 72 hours' drying is sufficient. After 96 hours there is virtually no loss in weight. From the dry weight subtract the tare weight of the dish plus the weight contributed by the sodium hydroxide added (milliliters of titration X normality of the sodium hydroxide solution X 0.022). Calculations. ;('
total solids =
corrected weight of dried sample x 100 Weight of sulfite waste liquor
corrected weight of driedsamDleX sp.gr.of sulfitewasteliquor X'IOOO Total solids, grams per liter = weight of sulfite waste liquor With ordinary sulfite waste liquor containing from 50 to 150 grams per liter of solids, this procedure will give results reproducible within 0.2 gram per liter or 0,027, solids. Analytical Data. Table I illustrates the difference obtained when solids are determined according to the present standard method (20) by drying the sulfite waste liquor for 24 hours at 105' C. as compared with the neutralized solids procedure.
Table I. Sulfite Waste Liquor Solids Sample
Total Solids us. Neutralized Salids Total Solids
Neutralized Solids
G./L
Q./L
94.9 94:i 96.4 88.6 96.2
99.4 100.9 103.0 101.1
99.2
Discussion. The sulfite waste liquor samples used in the solids determinations given in Table I were of average free sulfur dioxide content. Under these conditions there is a difference of 4.0 to 5.5% in solids content between the two procedures The true difference would be higher than shon-n, as the solids determined by the standard method do not come to constant weight in 24 hours. WET OXIDATION FOR DETERMINATION OF TOTAL SULFUR AND CATIONS
This procedure consists in digesting the sulfite waste liquor sample nith a mixture of nitric and perchloric acids until all organic matter is completely oxidized. Many analytical procedures, contributed mainly by Kahane (4) and Smith (18, 19), are based on the use of perchloric acid for the rapid dissolving of samples and oxidation of organic matter. Wolesensky applied this principle for the determination of total sulfur in rubber (23) in a procedure based upon one of Kahane's ( 5 ) . The authors' method is adapted from these published procedures. The method as described will conveniently eliminate the organic matter and will enable the use of well-known standard methods for determination of silica and the cations present in wlfite waste liquor. The authors have found also that the oxidation quantitatively converts all sulfur compounds to sulfate, which is readily determined in a suitable aliquot of the digested sample. The digestion procedure therefore gives a convenient way for determining total sulfur in sulfite waste liquor. The most generally accepted method for determining total sulfur, combined or mixed with organic matter, is the Carius method i21). This is limited to solid samples, is time-consuming, and requires special equipment and considerable skill in glass
blowing. However, because the Carius method is recognized for its accuracy, it was employed as a standard reference for the analysis of total sulfur in a number of solid sulfite waste liquor and lignosulfonate samples which had been analyzed previouslv by the nitric-perchloric acid oxidation procedure described here. The accuracy of the wet oxidation method has been demonatrated repeatedly when used for the analysis of aqueous solutions of sulfite waste liquor and lignosulfonates as well as of solid samples. This is a distinct advantage over procedures requiring a solid sample, as it eliminates the time required for drying and allows the use of a liquid sample, thereby simplifying precautions necessary to obtain a homogeneous sample. Reagents and Apparatus for Wet Oxidation. C.P. nitric acid (70%), C.P. hydrochloric acid (37 to 38%), C.P. perchloric acid (60%), 100-ml. Kjeldahl flasks (Pyrex), and micro-Kjeldahl digestion shelf. Analytical Procedure. If the sample is dried sulfite waste liquor, weigh 1 to 2 grams to the nearest 0.001 gram and introduce quantitatively into a 100-ml. Kjeldahl flask. If the sample is a liquid sulfite waste liquor, pipet out a 10.0-ml. sample into the Kjeldahl flask. In either case rinse down the neck of the flask with 10 to 15 ml. of distilled water. Next add 10 to 15 ml. of concentrated nitric acid and 5 ml. of perchloric acid. It is important in preventing explosions to have sufficient nitric acid present. Although the size of the sample used is the most important factor, the amount of nitric acid needed is dictated partially by the apparatus used and partially by the rate of digestion. If the digestion solution suddenly darkens after the main part of the excess nitric acid has boiled off, the digestion should be turned off immediately and more nitric acid added before the digestion is continued. This sudden darkening almost always indicates insufficient nitric acid. Until the worker is familiar with the apparatus and digestion procedure, maximum additions of the nitric acid are advisable. Place the flask on a steam bath. When the oxidation reaction has subsided (usually after 15 to 20 minutes, as indicated by absence of the red-brown nitrogen dioxide fumes), transfer the flask to the digestion shelf and heat over the burner with moderate heat until oxidation is complete, as evidenced by a colorless solution and evolution of dense white perchloric acid fumes. Allow the solution to cool to room temperature, then add 5 ml. of concentrated hydrochloric acid and again heat on the shelf until the white fumes appear. Akllowthe solution to cool to room temperature, add 50 to 60 ml. of distilled water, and place on the steam bath to bring all salts into solution. Piormally sulfite waste liquor contains only small amounts of silica which usually are not determined. If a silica determination is desired, it is better to carry out the digestion in a beaker, thereby facilitating the quantitative transfer of the silica. I n either case, filter off the silica on a filter paper and wash the precipitate with water. The silica is nongelatinous, owing to the dehydrating action of the perchloric acid, and can be determined either gravimetrically or colorimetrically (12, 2 2 ) . From the filtrate precipitate the ferric hydroxide and aluminum hydroxide with ammonia by the established procedures ( 7 ) and heat on the steam bath until the precipitate flocks. Filter and wash the precipitate with a hot 1%ammonium chloride sohtion. Ignite the precipitate and weigh as ferric oxide plus aluminum oxide, or if individual analyses are desired, redissolve the precipitate in dilute hydrochloric acid and make the resulting solution to 100 ml. in a volumetric flask. Determine ferric oxide and aluminum oxide individually from aliquots of this solution by known methods (8). Make the ammoniacal filtrate from the RZOi precipitate to 250 ml. in a volumetric flask. Pipet out 100 ml. of this solution for determination of sulfur, adjust the pH of this aliquot with dilute hydrochloric arid to be just acid to methyl orange, and precipitate the sulfate with barium chloride. Filter, ignite, and weigh the orecipitate according to the standard procedures (9) and cal&lace the sulfur. Use the remaining 150 ml. of the ammoniacal solution for determination of calzum oxide as oxalate, which is filtered, redissolved and titrated with 0.1 iV potassium permanganate. by the standard procedure (IO). Use the filtrate from the calcium oxalate precipitate for determination of magnesium oxide. This is carried out conveniently by the bromometric S-hydroxyquinoline method described in detail elsewhere (11, 16). Only certain types of sulfite waste liquor and lignosulfonates contain sodium ions. These can be determined conveniently after the digestion procedure described above.
911
V O L U M E 20, NO. 10, O C T O B E R 1948 It is best to take an aliquot for sodium determination from the filtrate after the removal of silica. Make this filtrate to 50 or 100 ml. in a volumetric flask and from this pipet 2 ml. or weigh approximately 2 grams into a 50-ml. beaker. Add 22 ml. of zincuranyl acetate reagent, stir, and let stand a t least 30 minutes in a water bath at 20 O * 1 C. Filter and transfer the precipitate into a glass filtering crucible. Wash the beaker and precipitate in crucible with 15 to 20 ml. of anhydrous isopropyl alcohol in small portions. After drawing air through the crucible for 3 to 5 minutes, dry in an oven at a temperature of 105” C. to constant weight, which is usually established in 15 to 30 minutes. This rapid method for sodium analysis has repeatedly given 99% of calculated values when samples with known sodium content have been used. For preparation of the reagent and addit,ional information upon the procedures see, ( 1 , 2 , 1 7 ) .
Table 11.
Determination of Total Sulfur NitricPerchloric Acid Method,
dample
-l”7-
4
Type of Sample Technical basic calcium lignosulfonate Technical sodium lignosulfonate Pure ammonium lignosulfonate Sulfite waste liquor solids
5
Sulfite waste liquor solids
NO. 1 2
3
1 4.61 Av. 6.97 Av. 7.44 Av. 7.46 Av. 9.74 Av.
Carius Method, V” 1 2 4.70 4.71 4.70 6.98 7.13 7.06 7.25 7.26 7.26 7.47 7.36 7.42 10.02 9.85 9.94 I”
2 4.61 4.61 7.03 7.00 7.46 7.45 7.46 7.46 9.75 9.74
Analytical Data. Dried and finely ground samples of sulfite waste liquor and lignosulfonates were used in the analysis for total sulfur, and the method described above was employed. The dried sulfite waste liquor samples were obtained by the neutralized solids procedure. The same samples were also used for total sulfur analysis by the Carius procedure. Analyses with both methods were carried out in duplicate for all samples. The results are given in Table 11. I n Table I11 is given a comparison of the values obtained from the determination of total sulfur by means of the wet oxidation method, in one case using samples from neutralized solids and in the other case, liquid samples from the same liquor. In the former case, the dried solids were dissolved in water and then introduced into the Kjeldahl flask. I n the latter, the analyses were made directly on a pipetted sample of 10.0 ml. Table 111. Total Sulfur-Sulfite Waste Liquor Solids us. Liquid Sulfite Waste Liquor
Sample
Total Solids G./1.
1 2 3 4
98.0 140.1 140.4 98.1
Sulfur in Sulfite Waste Liquor Solids % G./L 7.38 7.23 7.74 10.84 7.08 9.94 7.95 7.80
Sulfur in Liquid Sulfite Waste Liquor G./L
7.31 10.77 9.89 7.76
sulfur, sulfite waste liquor contains sulfurous acid, bisulfite, sulfate, and often small amounts of thiosulfate and elemental sulfur. With the wet oxidation method, all these sulfur compounds are oxidized quantitatively to sulfate, simultaneously with complete destruction of the organic matter. It is likely that many organic sulfur compounds other than the lignosulfonates can be analyzed for total sulfur by this relatively simple method. For example, S-benzyl thiuronium chloride has been suggested (14) as a standard for checking the analysis of organic sulfur. A carefully purified preparation of this compound w&o analyzed for total sulfur by the wet oxidation method. The analysis showed 15.82 and 15.8370 sulfur compared with 15.82% sulfur calculated for the pure compound. I n general, the wet oxidation procedure offers a simple, convenient, and rapid method for obtaining a solution of the inorganic constituents free from organic matter. Six digestion8 can be made simultaneously on the shelf; the oxidation occur6 smoothly and requires a minimum of supervision by the analyst. This digestion procedure has been used for years in the authors’ laboratory and no untoward incident has been experienced. However, because perchloric acid when incorrectly applied or handled can produce dangerous explosions, it is recommended that the literature be consulted (6, 13, 18, 19), particularly if its use is contemplated on organic material of a type different from that in sulfite waste liquor. ACKNOWLEDGMENT
911 the analyses by the Carius procedure were made at the Institute of Paper Chemistry, Appleton, Wis. The authors wish to express their appreciation to F. E. Brauns, research associate a t the Institute of Paper Chemistry, for his assistance in carrving out these analyses. LITERATURE CITED (1) Barber, H. H., and Kolthoff, I. AM., J . Am. Chem. SOC.,50, 182531 (1928). (2) Ibid., 51, 3233-7 (1929). (3) Fachausschuss, U. -A. fur Faserstoffanalysen, Yerein der. Zell.
stoff- und Papierchemiker und Ingenieur, Papier-Fabr., 35 Tech. Teil, 283-8 (1937). (4) Kahane, E., “L’Action de 1’Acide Perchlorique sur les Matibres Organiques, I, GQnBralitBs,11, Applications,” Paris, France Herman et Cie, 1934. ( 5 ) Kahane, E., Caoutchouc & gutta-percha, 24, 13549-50 (1927), (6) Kahane, E.,Z.anaZ. Chem., 111, 14-17 (1927). (7) Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” pp. 294-9, 303-7, New York, Macmillarr Co., 1937. (8) Ibid., pp. 306, 635-7. (9) Ibid., pp. 308-20. (10) Ibid., pp. 3 2 3 4 , 3 3 3 - 7 , 576-7. (11) Ibid., pp. 333-7, 351-2, 609-10. (12 IKnudson, H. W., Juday, C., and LMeloche, V. W., IND.ENG CHEM.,AXAL.ED.,12,270-3 (1940). Kuney, J. H., Chem. Ena. IYezcs, 25, 1658-9 11947). ogg, c . L., and lviilits,-c. IND. ESG. CHEM.,ANIL. ED., 18, 334 (1946). Partansky, A. AT., and Benson, H. K., Paper Trade J., 102, No 7. 29-35 (193fii. Redmond,J. C., and Bright, H. A., Bur. Standards J . Research, 6, NO.1, 119-20 (1931). Scott, W.W., “Standard Methods of Chemical Analysis,’’ 5th ed., N. H. Furman, ed.. Vol. I, pp. 878-9, New York, D. Van Nostrand Co., 1939.
o.,
~~~~~I
DISCUSSION
I t is evident from the analytical data presented in Table I1 that the nitric-perchloric acid digestion procedure here described permits the determination of total sulfur in sulfite waste liquor and lignosulfonates with a precision equal to or better than that obtained with the Carius method. Table I11 demonstrates that the same results for total sulfur in sulfite waste liquor and lignosulfonates are obtained when the sulfite waste liquor is used in either liquid or neutralized solids form. It is thereby established that no part of the sulfur in sulfite waste liquor escapes oxidation to sulfate in the digestion oxidation. The foregoing method for sulfur analysis was worked out for wlfite waste liquor and lignosulfonates. Aside from sulfonic
Smith, G. F., “Mixed Perchloric, Sulfuric, and Phosphoric Acids and Their Applications in Analysis.” 1st ed., Colum. bus, Ohio, G. Frederick Smith Chemical Co., 1935. Smith, G. F., “Perchloric Acid.” Val. I, 2nd ed., Columbus, Ohio, G. Frederick Smith Chemical Co., 1933. TAPPI Standard Methods T629m-45. Treadwell, F. P., and Hall, TV. T., “Analytical Chemistry.” T‘ol. 11. p. 326, New York, John Wiley 8: Sons, 1931. Willard, H. H., and Cake, IT7. E., J. A m . Chem. SOC.,42, 220812 (1920).
Wolesensky, E.,I n d . Eng. Chem., 20, 1234-8 (1928). RECEIVED October 13, 1947.
