January, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
79
Study of the Floc Produced b y Chlorinated CopperaslS2 Edward S. Hopkins with Eugene R. Whitmore BUREAU OF WATER SUPPLY, BALTIMORE, MD.
ONSIDERABLE interest is being shown in the use of sulfate adsorption in the precipitate will occur under cerchlorinated copperas (ferrous sulfate) as a coagulant. tain conditions and tend t o neutralize additional positive The work described by Mohlman and Palmer (9) with charges. activated-sludge coagulation and the results obtained by Another interesting result was the maximum precipitation Hedgepeth and Olsen (3)with a highly colored water indicate of floc in acid water as shown in Table 111. the value of this material. Enslow (2) has recently presented These results show that the reagent is an efficient practical data relating to the operating economic value of this co- coagulant. With an excellent turbidity removal and pracagulant and also concerning the reactions involved. tically complete precipitation of iron a t all hydrogen-ion conLaboratory experiments under simulated plant conditions, centrations less than pH 3.5,8 p. p. m. concentration excepted, as explained in a previous article (d), and using the same use may be made of it to an extent not possible in the narrow method of procedure, show alkaline range (pH 9.4+) of that this reagent is a satist h e u s u a l i r o n and lime factory coagulant for turbid coagulation. The relative The practical use of chlorinated copperas as a water economic value of this or water, being comparable to coagulant is presented, using simulated plant cona l u m in this respect. A any other coagulant will deditions. It is an efficient coagulant for turbid waters compact, easily settling floc pend entirely upon its cost at any pH value above 3.5. Removal of organic coloring is obtained at any p H value a t the point of application. material from swamp water may be accomplished by above 3.6. This is in sharp Several years ago Miller it. Manganese is not adsorbed by the floc produced contrast to the value found ( 8 ) showed that the floc below pH 9.4 as is true for iron and lime coagulation. efficient for ferric hydroxide p r o d u c e d from potassium A discussion of the theoretical composition of the floc floc (4) when using the usual ferric alum is almost comis given. iron and lime treatment. pletely precipitated near a p H value of about 3.5, but Coagulation Data that with ferric chloride the Mohlman and Palmer (9) compared the coagulating value floc does not appear until about pH 5.0. Krause (?), studying of chlorinated copperas, alum, and ferric chloride upon a ferric hydroxide floc formation in air from ferrous sulfate by weight basis and also upon the value of the anions, finding the addition of sodium hydroxide, found that the oxidation of ferric salts superior to aluminum salts when corresponding ferrous hydroxide is dependent upon the H ion in solution. reagents were used. Their curves show that ferric chloride If the ratio of ferrous sulfate to sodium hydroxide is less than is a better coagulant for activated sludge than the other 1, the final product always contains Fe++ ions. His sulfate salts. This relation applies to turbid Gunpowder River ratio is a t variance with that obtained in other investigations water. Comparison of these coagulants using a fairly clear (4, 8), but his theory-that a portion of the iron is not oxiwater (25 p. p. m. turbidity) with practically all particles in a dized below a definite alkalinity ratio-would explain the colloidal state is shown in Table I. high p H required for complete oxidation of ferrous sulfate by lime as it is usually employed, which is unnecessary for the Table I-Quantity of Various Coagulants Necessary to Produce an highly oxidized chlorinated copperas. This is substantiated Easlly Settling Floc 6H P. b. m. by a consideration of the precipitating p H value of the ferric Chlorinated copperas 6.8 17.6 chloride solution-5.5. It seems logical, as a result of the 6 . 7 12.0 FeCla.6HiO 6.6 17.1 Fer(SOda work of Thomas and Frieden (IO), to expect a precipitation a t AI?(SOi)s.18HzO 6.8 12.0 about this point, since their stabilized oxide hydrosol acting Mixture FeCla.6H10 and Fea(S03:a 6.6 17.6 a Concentration of mixture proportionate to chlorinated copperas. as a solution link was obtained a t a hydrogen-ion concentration of Therefore a greater alkalinity should produce These figures show that chlorinated copperas compares favor- precipitation due to complete coagulation of the sol. ably with alum as a coagulant for turbid water and that ferric chloride has a superior precipitation value. Table 11-Comparison of Actual a n d Theoretlcal Ferric-Ion Coagulating Values Since the ferric ion and hydrous ferric oxide sol carry posiVARIATION EFFICIENCY tive charges, comparison of their theoretical electronic coaguTHEORETICAL PROM RATIOTO Ft COAGULATINGACTUALCHLORINATED lating values with that actually obtained by experiment is COAGULANT CONTENT VALUE EXPT. COPPERAS of interest. Using the reaction formula
C
6FeSOc7Hz0
+ 3 C l ~= 2Fe2 (SO&.7H10 + 2FeCL
Table I1 presents this relationship. The results explain in part the repressive action of the sulfate ion when comparison is made of the coagulating value of ferric sulfate and ferric chloride. It is also known, as will be shown later, that
* Received November 1, 1929. Presented by E. S. Hopkins before the Division of Water, Sewage, and Sanitation at the 78th Meeting of the American Chemical Society, Minneapolis, Minn., September 9 to 13,1929. * Submitted by Edward S. Hopkins in partial fulfilment of the requirements for the degree of doctor of philosophy in the Graduate School of Georgetown University.
Chlorinated copperas FeCla.6H10 FedSOS:
2.2 3.5
2.4
Table 111-Characteristics CHLORINATED COPPERAS PH P . d . m.
s
17 34 86
iik 1710
7.4 3.6
3.2 3.6
!::3.6
1
17.1 11.1 16.2
-0.5 -0.9 -0.9
1.0 1.4 1.1
of Initial Coagulation Giving an Easily
Settling Floc ----TURBIDITY-Fe IN Raw Removed SETTLED water Removed a t p H 0 . 4 WATER P.d.m. P.6.m. P.6.m. P.6.m. 10 7 8 0.1 12 10 10 0.3 30 27 27 0.5 600 490 498 0.9 Excessive concentration for coagulation
INDUSTRIAL A,VD ENGINEERIhTG CHEMISTRY
80
These results clearly indicate that when the iron is completely oxidized to the ferric state coagulation will occur regardless of pH value above a definite minimum. This theory gives a satisfactory explanation of the ability of chlorinated copperas to produce a compact floc in acid water. I n sharp contrast alum, being amphoteric, may be considered as having an isoelectric point (1, 12),but since hydrous ferric oxide does not redissolve, maximum precipitation is governed only by complete oxidation and is not a function of the hydrogen-ion concentration, as is true for hydrous aluminum oxide or ferric oxide obtained by alkali precipitation. Is it not time to discard the old designation “ferric hydroxide” and substitute the colloidal term “hydrous ferric oxide” in the daily technical discussion of this floc? Manganese Removal Manganese was not completely removed by chlorinated copperas below a pH value of 9.4. Progressive reduction was obtained a t values above neutrality, using lime to produce the required alkalinity. “Split” applications of coagulant and alkali were tried, but were not successful below the maximum pH value. The results are given in Table IV. Table IV-Manganese PH
Removal Data Using a Solution Containing 0.5 P. p. m . M n COAGULANT MANGANBSR RRMOVBD
P . p. m.
P . p . m.
Per cent
Chlorinated comeras
0
6.6 6.8 7.0 7.3 7.4 7.5 7.6 8.1 9.1 9.2 9.3 9.6 9.6
28 40 50 30 56 62 100 100 66 100
8.7 9.0 9.3 9.5
22 44 60 100
8.7 9.1 9.3
0 0
sulfate
21 21 21
0.40 0.42 0.46
agulant and type of ferric salt used, a certain pH value (9.0) is necessary for complete removal of manganese. Weiser (11) states that “low concentration of positive hydrous ferric oxide precipitates the negative manganese dioxide sol.” This would indicate an adsorption by the oxide obtained from chlorinated copperas which does not take place. As a high alkalinity is necessary to produce a colloidal oxide from a manganese solution, it is obvious that only in this state will adsorption occur. Color Removal The highly colored water from Knobbs Creek, Elizabeth City, S.C., was used in this study.3 It is from the same source as reported by Hedgepeth and Olsen (S), having the characteristics noted in Table V. Table V-Analysis
Using simulated plant procedure, coagulation was obtained with a n initial dosage of 34 p. p. m. chlorinated copperas, stirring 5 minutes, and then adding, more or less simultaneously, 17 p. p. m. of lime and an additional 34 p. p. m. chlorinated copperas, with subsequent stirring for a further 10 minutes. The color of the filtered water so treated was reduced to 10 p. p. m., with practically no iron in solution. It is to be noted that this floc gave every indication in appearance, color, and ease of settling of being hydrous ferric oxide comparable with that obtained from turbidity coagulation. Analysis of this floc indicates that it is a n organic iron complex with a formula of Fez03.3Hz0.2SiO2.4X, X being the organic constituent. The relation of 4X was determined by its ratio to the mineral components, or the organic relationship is four times that of the added coagulant and turbidity present. This analysis confirms the belief that definite adsorption and chemical combination with the negatively charged colloidal color particles occur. Composition of Floc
Hydrated ferric oxide floc obtained as previously described (.5) was washed free of sulfates by centrifugation and subsequent decantation with water, care being taken to break up the floc a t each washing. Adsorption of sulfate did not occur with normal plant operating concentration of chlorinated copperas, except a t the initial precipitation point, pH about 3.5. Sulfates were present in the floc formed between p H 3.6 and 6.6 when the concentration of coagulant was 1710 p. p. m., as given in Table VI. This is in agreement with previous work (C), but their absence below p H 9.4 in such a concentration is in striking contrast to it.
of Knobbs Creek Water as Received in Baltimore P . p. m. 5.6 PH 1s Alkalinity Fe 2.0 Soap hardness 30 Turbidity 8 Carbon dioxide 22.0 Color 300
8 This water was obtained through the courtesy of L. H. Enslow. Chlorine Institute, and T. R. McCrea, Elizabeth City Filtration Plant.
of Sulfate Adsorption in Floc a n d Alkali Concentration SULFATE ALKALI ADSORPTION Fe PH OF PPTN. EQUIVALENT IN FLOC Mols N o per mol Fe Mol per liter 0.0003” 3.8 2.0 Present 6.3 2.3 Absent 0.0006 3.8 1.5 Present 6.2 1.6 Absent 0.0015 3.6 0.8 Present 6.4 1.1 Absent 7.3 1.2 Absent 9 4 1.3 Absent 0.0061 3.6 0.3 Present 6 6 0.4 Present 8.1 0.5 Absent 9.4 0.6 Absent 0.0003 mol Fe is equivalent to 85 p. p. m. chlorinated copperas.
Table VI-Relation
80 84 92
It is clearly shown that, regardless of concentration of co-
Vol. 22, No. 1
5
The floc was washed free of sulfates and chlorides when less than the stoichiometric quantity of alkali to react according 3(OH)- = Fe(OH), was used. As to equation Feff+ would be expected, the precipitate gave negative chloride reaction even when sulfates were present. The relation between ferric oxide and sulfate content of the floc is practically constant regardless of concentration of salts or of precipitating pH value. This indicates that, similar to alum floc (.5), a definite formula of Fe2O3.SO3would be correct for this material. This agrees with the one assigned by Krause ( 6 ) for similar floc obtained from ferric sulfate solutions and alkali. The formation of a basic sulfate in floc precipitated from fairly strong acid solution is due, as stated above, to the presence of a stabilized hydrosol acting as a solution link. The absence of sulfate adsorption in the floc when less than stoichiometric quantities of alkali were used as a precipitant is due to the complete coagulation produced with the highly pre-oxidized ferric salt, a t low Concentration of electrolyte, in the presence of sufficient alkalinity to neutralize all the positive charges on the ion. Where excessive concentration of coagulant is used (1710 p. p. m.) below neutrality, it is believed that there are set free a number of positive charges
+
Jaiiuary, 1930
lNDUSTRIAL A N D ENGINEERING CHEMISTRY
which require a definite quantity of negative ions for neutralization in excess of that furnished by the clays and other inaterials found in normal ivaters. These charges are therefljrc tieUtra1iZed by thc sulfates present in the precipitating c::ectrolytc and produce a solution link. Above neutrality t1ici.c is sufficient alkalinity to produce complete coagulation. 111 tlic study n i t h iron and lime ( 4 ) it was shown that invompicte oxidation will accoulit for t,he formation of thc ;olutioli link. With chlorinated copperas solutions below iicutrality, incomplete ncutra1izatio:i of the positive charges on t,lx Fc ion accounts for the sulfate adsorption.
81
Literature Cited Baylis,
J.
A m . il'ater
Assocll,,
303 (,323),
(2) Enslow, itfunic. H e w s Ii'o/rr ri.s7i;,, 76,227 (1020). (3) Hedgepeth and Olsen. J. A n i . 1C'c:rr Il'orks .-lssorn., 20. 467 (1928).
it;
~ ~ ~ N ~ ~ ~ ~f s ~r ~ G ~ l 'IOB ~~ , ~(1924). ~ ) ; .2 , ; ~ ~ ; n. !6) Krause, Roczniki Ciicm,, 6, (7) Krause, z. anorg. al/ge,n. C h e m , 174, 146 (1928). ( 8 ) hliller, U.S. Pub. Health Service, Pub.Heall/: Regts. 40, 1413 (1925)
(::i" , : ~ a h ~ ~ : n , ~ ~ " , ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ e ; ~ : " . . 4 b 9 0 ~ : ~ ~ (11) lveiscr, r , f l y d r o u s
p,
(1926).
(12) WVo!nian antl Ifannari, Chem. M e t . Eng., 24, 728 (1921).
Cracking of High-Boiling Coal-Tar Acids' C. E. Senseman
a
High-boiling coal-tar acids were fractionated to o v e n . T h e g a s e s are led remove all material boiling under 207' C. The pora w a y a n d condensed, and scarcli here rcportccl tion of the acids boiling above this temperature was tlie tar acids are removed by w a s t o c o n v e r t the run through a cracking apparatus to determine whether 11 i gli -boi 1 i n g phcnols, frctlie usual processes. These or not any would be converted into the more useful a c i d s a r c somewhat more cliiciitly rcferrcd t o as conllower boiling phenols. Following each run the contar acids, d i i c h occur abunconiples than the domestic densate was fractionated until all material boiling o n e s , b u t they were more d a n t l y in t a r s rcceivcd below 207" C. was removed. Water, benzene, xylenes, readily availnble at thc time tlirougli the low-tenipcrature cresols, and much smaller quantities of phenol and coking of coals, to tl:c more thc investigation was started. coumarone derivatives were identified as products KOanalysis was inadc in this useful Ion--boiling pl3cnols. formed in the process. For t h c s c m o r e y o l a t i l e laboratory to dctcrminc the Studies were made of the effect of temperature, plicnols t l m e is already a constitucnts, but Warnes (3) charging rate, and pressure. Tables are given to show great dcnmnd in the innking aiid othcrs report tlic presthe influence of the first two variables. Pressure was cncc of a small amount of of mir.s, disinfectants, and not found to be a significant factor in producing the p h c no1 , crcsol s , xylenols, tiicrcsyl pliosphatc. L a r g e lower boiling acids. quantitics of t l x high-boiling pseuclocumcnol, n n p h t h o l s , Tests were made o n the cresols formed to determine acids are annually imported and prohab!y phcnol cthcrs. their usefulness in the manufacture of resins. by the Gnited States. The ~)!ivsicalDromrtics of the It lias long been k n o w n mntiriils uset~ ncrc as folthat tile quality, as well as the quantity, of any conl tar lows: s2ccific grayity a t 26' C., 1.021; phcnols boiling rincler 207" C., 32 per cciit; boiling range of rcsiduc, 207-290" C. J L tiependent upon a large number of factors, such as tlx As the principal objective in this rwcarch was to protlucc source of tlie coal, the temperature of coking, the rate of licating, tlie compactness of the charge, the shape and size from tlie higher acids those plicnols which could bcst be used in the manufacture of resin.. . any phenol or cresols present in of the retort, aiid the method of removing the volatile matter. Of tlie 200 or more compounds (3) present in the crude had first to bc rcmoved. 7'llis was done by fractar Irom 1;igli-temperature coking processes it is generally tionating in a Henipel column pac~licdwith glass beads antl n g m t l that ninny arc formed through the decomposition, well insulated from draft uiitil 3 teinpcrature of 207" C. was crr ci,ncl;ing, of compounds formed during low-temperature reached. The portion boiling above this temperature was h i t n.hich subsequently undergo this change before used for cracliing purposes. S o practical method for the t1.c rcturt during the high-temperature coking proc- separation of these various constituents is known. Hence tlie €59. In fact, Parr ( 2 ) quotes Gentry as defining tcmpera- group separation through fractional distillation. turc c8::rbonization as "the destructive distillation of coal a t Apparatus or I;clon. the clacking temperature of the hydrocarbons in primary tar." Thc apparatus used (Figure 1) is basically the same as that This linowledge, together with tlic results on thc cracking of vxi.ims hydrocarbons, both aliphatic and aromatic, ob- used by Dean and Jacobs ( I ) . Some modifications of the tained tluring tlie last two decades, led to a belief that tlie original set-up m r e made, and others m r e introduced as the clacking of the high-boiling acids from lowtemperature coking investigation progressed. Briefly, the apparatus consists of a iiiiglit be effected so as to yield more useful materials, par- reservoir for holding tlie tar acids, which is equipped with a pressure equalizing tube, a needle valve, and a t the base, a ticularly for the making of resins. sight feed, permitting a regulated flow of material through Material Used the drip tube to the center of the top of the cracking chamber. The cracking chamber consists of an electrically-heated 1.25T1:c work here reported was done on coal-tar acids pro- inch extra heavy steel pipe 30 inches long. The lower end of iluccd i n Scotland from blast furnace gases. The splint coal the clianiber has a clean-out plug, iirinicdiately above which o f Scotland servcs very well for blast furnace purposes, tlie a condenser tiii~rl01 0.75-inrti extra heavy steel pipe takes off. upper part of the furnace serving as a low-temperature coke Tlie loner end of tlle condenser is supplied with a drain cock, ICcceived September 1.1, 1920. which liad to be kept closed when a pressure greater than at-
HE purpose of the re-
I
.
