Acid Waste Treatment with Lime WILLEM RUDOLFS New Jersey Agricultural Experiment Station, New Brunswick, N. J. Expansion of chemical industries on account of several days. I n some cases HE treatment and dispH variations were within war work has made the problem of acid waste disposal of relatively diposal more acute. The wastes studied caused sewer rather narrow limits, whereas lute acid wastes produced in others intermittent discorrosion, interference with biological sewagetreatby chemical industries has charges of alkalies caused mament processes, and stream pollution, and affected been, in many instances, a terial fluctuations. The wastes aquatic life. The wastes consisted primarily of considerable problem for a consisted primarily of sulfuric mixtures of sulfuric, nitric, and hydrochloric acids, number of years. Expansion acid mixed with nitric and/or with some alkalies, solvents, and poisons present. of these industries on account hydrochloric acid. Cooling The character and volumes fluctuated materially. of war work has made the water and wash water were Methods of treatment were developed, and deproblem more acute. Although present in all cases, while wastes pended upon the type of acids, volume of flow, the wastes produced vary in 2, 4, and 5 contained relatively materials in the waste, and purpose of treatment. composition and strength, they small amounts of domestic sewNeutralizing agents used for experimental purposes consist mainly of mixtures of age. were calcium and magnesium hydrates, quick acids or mixtures of acids limes, limestones, soda ash, caustic soda, and their and alkalies discharged interThe flow of the various combinations. mittently with or without some wastes fluctuated in most cases During experimentation with nitrocellulose waste materially. salts, solvents, and poisons it was found that neutralization with calcium present, hydrate proceeded gradually until about 90 per The problems created by Methods of Treatment cent of the total acids was destroyed, followed by a the discharge of these wastes sharp break. The contact time required and pertain mainly to corrosion The neutralization agents amounts of sludge formed varied with the type and in sewers and equipment at used for experimentation were concentration of lime used. A combination of dolosewage treatment plants, secalcium and magnesium hymitic hydrate with soda ash was preferable over vere effects on biological sewdrate, soda ash, caustic soda, lime, soda ash, or caustic soda alone. The dry age treatment processes, interand combinations of the variweight of sludge decreased with increasing quantiference with fish life and selfous neutralization agents. ties of soda ash, but the volume of sludge increased purification of receiving waters. After considerable experiand the ease of dewatering decreased. The reacThis paper is primarily mentation the most effective tion time required for complete neutralization inconfined to a discussion of the and most economical methods creased with increasing quantities of soda ash. characteristics of the wastes, of treatment for the various their variations in strength and wastes were as follows: fluctuations in flow, and the Waste 1, Neutralization of the mineral acidity by filtering presentation of laboratory results pertaining to treatment of through a bed of calcium limestone with a contact time of 5 the wastes to prevent difficulties. minutes. The wastes studied were produced by: Waste 2. Equalization and neutralization to pH 6.0 with high calcium hydrate. Waste 3. Neutralization with high magnesium hydrate and 1. ,A large chemical laboratory and pilot plant causing sewer soda ash to any desired pH value. corrosion. Waste 4. Equalization and neutralization of mineral acidity 2. Plant waste causing sewer corrosion and interference with with high ma nesium hydrate. sewage treatment processes. Waste 5. aeutralization with dolomitic limestone and aera3. Plant waste causing Dollution and interference with tion. aquatic life. 4. Plant waste causing stream pollution. It is evident that the method of neutralization to be used 5. Plant waste causing sewer corrosion. depends not only on the type of acid and volume of flow, but also upon other ingredients in the wastes and the purpose to The character of the wastes from different sourcw varied be served by the treatment. A more detailed discussion of materially, both within each plant and among the different one of the wastes and a description of the treatment plant plants, as shown in Table I. The variations given were constructed will be published in the future. obtained by frequent sampling during 8-24 hour periods on
T
TABLE I. VARIATIONIN CHARACTER OF WASTIDS AND FLOWS Waste
No.
Principal Ingredients
Acidityo,
P. P. M.
227
Alkalinit
do'
P.'P.
T
e of gids
-Flow,
Minimum
Gd./DayMaximum
INDUSTRIAL AND ENGINEERING CHEMISTRY
228
During the course of experimentation a number of questions \\?ereraised pertaining to the behavior of t'he various neutralization agents, Results on part of the work' are presented t o illustrate the action of the neutralization agents and indicate some of the more important factors involved. The particular waste used for illustration, discharged from a nitrocellulose process, consisted essentially of a mixture of
6
I
a4
8
I2
THOUSANDS P.P.M.
FIGURE 1. EFFECT OF LINE CONCENTRATION ON pH OF ACID
TIME I N MINUTES
FIGURE 2. EFFECTOF CONTACT TIME
sulfuric and nitric acids, some solvents, and a very small amount of nitrocellulose floc. The total acidity of the waste, expressed as CaC03, mas 11,810 p*P* m'? with 3660 P* P' nitric and 8150 p. p. m. sulfuric acid. The procedure of the general method employed for neutralization consisted of placing 100-cc. samples in beakers equipped with a stirring device and the electrodes of a pH apparatus placed stationary in the liquid. Various types of lime used were added dry while the waste was rapidly stirred. m%en the dosage necessary to complete neutralization was found, the sludge produced was dewatered, dried, and weighed. Observations were made regarding the character of the sludge formed, its rate of formation, the rate and completeness of settling, ease of dewatering, and amounts of cake produced. Effect of Lime TYPE OF LIME, Keeping the contact time between the various types of lime a,nd acid waste constant a t 30 minutes, the quantities of neutralizing agent were determined. The theoretical amounts of lime, actual quantities, and resulting p H values are sammarized in Table II. Calcium and cloiomitic quick lime were unsuitable, because the lime balled in the waste on account of a coating of calcium sulfate formed before complete hydration could take place. The dolomitic limestone was unsatisfactory, because with this material, even when dosages far in excess of the theoretical amounts were employed, neutralization could not be completed in 30 minutes. Calcium limestone liberates considerable carbon dioxide. &lost of t.his is removable by aeration for 15 minutes and by paddle mixing for an appreciably longer time. When paddle mixing is employed, only part of the carbon dioxide is removed after 30 minutes, giving a final pH value of 4.7. Removal of carbon dioxide with air produces considerable foaming. Calcium hydrate addition required larger quantities and produced more sludge than dolomitic hydrate. CONCENTRATION. Series of experiments were made with a wide range of hydrate lime dosages to determine the effect 1 P a r t of t h e laboratory work was performed under t h e fellowship grant from t h e National Lime Association.
TABLE 11.
Vol. 35, No. 2
QUANTITIES OF LIMEREQUIRED TO RAISE I X 8O-hfISUTE CONTACT TINE
T y p e of Lime High-calcium hydrate Dolomitic limestone High-calcium quick lime Dolomitic quick lime
PH VALUES
Theoretical, P. P. Ll.
P . P.M.
Final pH
9,200 7,020 12,240 10,930 6,900 6,000
Actual, 9,250 7,750 13,000 15,000 9,000 8,000
8.6 8.5 4.7 1.4 3.4 3.3
of lime concentration on the resulting pH values. The contact time was kept constant a t 20 minutes, with vigorous stirring to remove the carbon dioxide formed as much as possible. A typical example, using calcium hydrate, is illustrated in Figure 1. Neutralization proceeded gradually until about 90 per cent of the total acids was destroyed. There was then a sharp break in the curve, giving evidence of the unbuffered character of the waste. Acid wastes containing appreciable quantities of salts in solution may behave differently. CONTACT TIME. The effect of contact time varies with the type and concentration of lime used. Employing quantities of lime sufficient to raise the p H values to 8.6, the rate of neutralization with increasing time is illustrated in Figure 2, for high calcium and magnesium hydrate and limestones. In all cases the mixtures were vigorously stirred. The dolomitic hydrate reacts most rapidly, followed by calcium hydrate, the reactions being completed in 20 minutes. w i t h calcium limestone the pH was raised rapidly during the first minutes and gradually tapered off, while the dolomitic limestone required several hours to raise the pH to 5.5.
i
80
0
L
m
o m
"3 z3
60
6
01
r
or 'e
$9
0
40;
4
n
I < a c
-
2 C
d o m
0 20
2
'
1 -I
2
W PI 0
0
2 4 6 8 THOUSAND P.PM DOLCMITIC H Y D R A T E
FIGURE 3. SLUDGE FORbIATION WITH VARYING DEGREES OF NEUTRALIZATION
SLUDGEFORXATION. The quantities of sludge formed by the different types of lime varied mat,erially. This is indicated by the following figures, showing the amounts of lime added and quantities of sludge formed per 1000 gallons of waste: Type Calcium h y d r a t e Dolomitic hydrate Calcium limestone
Pounds Added 76.8 64.0 1 0 s ,0
Pounds D r y Sludge 55 21 67
T y p e of
Sludge Plastic Plastic Granulai
and be vacuumdewatered filtered. The rate of sludge formation, employing increasing
February, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
229
cost, the intense foam formation with soda ash alone made i t undesirable for this purpose.
t J
\
Combination of Lime and Soda Ash
2.0
3 4
7
1.2
W
0 3
d
0.4
0
20 40 60 eo 100 Te N E U T R A L I Z A T I O N BY SODA A S H
FIGURE4. WEIGHT OF SLUDGEPRODUCTION WITH VARYINGPERCENTAGES OF MAGNESIUM HYDRATE AND SODA ASH
To complete neutralization of the waste with lime alone 7750 p. p. m. of dolomitic hydrate were necessary, but large volumes of sludge were formed. Experiments were performed particularly to determine whether the quantities of sludge could be reduced without interference with dewatering. Amounts of lime and soda ash were calculated to give the neutralization effect of lime alone. The technique used was to add the materials dry, stir vigorously for 6 minutes, and then add the other material. The sludge formed was dewatered and the dry weight determined. I
quantities of dolomitic hydrate, increases rapidly with a decrease of acidity remaining until about 90 per cent of the acidity is neutralized. With further neutralization the volume of sludge decreases, although the total dry weight increases slightly. The maximum amount of sludge formation varied between 8 and 9 per cent of the total volume of waste. The relation between sludge volume, the degree of neutralization, and the resulting p H values is graphically shown in Figure 3. The greatest volumes of sludge were produced when the liquor had pH values between 2.5 and 5.7 with a maximum a t about pH 3.5. The decrease in sludge volume with higher p H values appears to be related to the physical character of the sludge. In this connection, it is of interest that completely neutralized waste does not contain water of hydration.
100
I
a
I
I
F I G U R 6E. R E L A T I O N BETWEEN NEUTRALIZATION AGENT REQUIRED AND RATIOOF LIMEAND SODAASH
I
% D O L . 40 %SODA 60
60 40
80
20
100 0
Addition of lime first appeared to give slightly better results than partial neutralization with soda ash followed by lime. When soda ash is added first, large amounts of carbon dioxide are liberated. Most of this is immediately expelled as long as the pH is below 4.5. The carbon dioxide remaining, however, may cause carbonization of the lime when added later.
p C
u)
E
0
rn
OF CHEMICALS TABLE 111. CHANGEIN pH VALUESON ADDITION TO ACIDWASTE
Dolomitic Hydrate,
%
51.5 64.5 77.5 90.3 100
FIGURE5. VOLUME OF
I
l-rL4-4
C
I5 eo
10.000
SLUDGE
PRODUCED AFTER %HOUR SETCLING COMPARED WITH DRYWEIGHT
Of the various limes used for treatment of this acid waste, dolomitic hydrate was found best for neutralization, but it produced considerable quantities of sludge. Soda Ash and Caustic Soda Considerable experimentation with soda ash and caustic soda for neutralization showed that soda ash was preferable because of the tendency of intense color formation with caustic soda. Aside from the question of availability and
NsaCOs.
Total Neutralizing Agent,
48.5 36.5 22.5
10,050 9,430 8,820
9.7 0
8,180
%
P.P. M.
7,750
-pH 3 1.3 1.5 1.7 2.2 3.1
0
1.3 1.5 1.7 2.6 5.0
after 9 4.7 6.5 5.7 7.5 6.2
Minutes:12 15 18 0.3 6.9 7.0 6.7 7.1 7.2
... ... ...
6:7
f : i i:8
The weight of sludge produced when varying percentages of magnesium hydrate and soda ash are added is illustrated in Figure 4. With less than 50 per cent dolomitic hydrate added to complete neutralization, the weight of dry sludge is very small, increasing rapidly with the percentage increase of lime. It is possible, therefore, to balance the cost of sludge treatment against the cost of two-stage treatment. With increasing quantities of soda ash, however, the sludge becomes increasingly lighter, more voluminous, and more difficult to dewater. The fluffiness of the sludge produced with the larger percentages of soda ash increases with time of settling, so that after 18 to 24 hours the sludge volume is three to four times larger than sludge produced with dolomitic hydrate alone. The volume of sludge formed after %hour settling is illustrated in Figure 5. Neutralization with 90 per cent dolomitic hydrate and 10 per cent soda ash produced about the same amount of sludge as ne’utralization with magnesium hydrate alone. The smallest volume and lowest dry weight
230
INDUSTRIAL AND ENGINEERING CHEMISTRY
were obtained when the acids were neutralized with about 80 per cent lime and 20 per cent soda ash. This sludge, however, did not settle so well as that produced by dolomitic lime alone. The moisture content of the filter cakes produced with different treatments varied, but the filter yields decreased with increasing quantities of soda ash. Complete neutralization with lime and soda ash required a larger quantity of chemical than lime alone. As an example, some results obtained are illustrated in Figure 6. In this respect the rate of neutralization in a given time is of particular interest. When soda ash is added following the addition of lime, the higher the sodium carbonate percentage, the longer i t takes before neutralization is accomplished. Some results
Vol. 35, No. 2
given in Table I11 illustrate this. Bfter addition of lime vigorous stirring was continued for 6 minutes, the sodium carbonate was added, and stirring was continued until neutralization was completed. With abont 10 per cent soda ash added, the time required for complete neutralization was less than half that required when about 50 per cent sodium carbonate was used. The probable reason is that large quantities of carbon dioxide are formed with the soda ash addition, and even vigorous stirring does not release the carbon dioxide fast enough to prevent carbonization and coating of the lime. PRESENTED before the Division of W a t e r , Sewage, and Sanitation Chemistry CHEMICAL SOCIETY,Buffalo, N Y. a t t h e 104th Meeting df t h e AVERICAN Journal Series Paper, N.J Agricultural Experiment Station, Rutgers University, D e p a r t m e n t of Water and Sewage Research.
Stabilizing Zein ispersions against Gelation' CYRIL D. EVANS AND RALPH H. _MANLEY Northern Regional Research Laboratory, U. S. Department of Agriculture, Peoria, Ill.
Z
E I N disperses readily in a large number of single and mixed solvents such as diethylene glycol, the lower mono ethers and esters of the glycols, the lomer mono and diesters and ethers of glycerol, aqueous mixtures of methyl, ethyl, and isopropyl alcohols, aqueous acetone, and numerous organic acids, amides, and amines, as shown by Swallen (4), Evans and Manley ( I , S ) , and others. I n all of these solvents zein tends to set spontaneously with time to a solid gel which is useless for most commercial purposes. The stability of such zein bols may be increased by storage a t low temperatures, by the use of substantially anhydrous solvents, by the addition of certain reagents, or by keeping the concentration of zein a t a practical minimum. Effective control of temperature is usually not practical, as summer room temperatures are frequently high enough t o cause commercially usable concentrations of zein to gel in a few days. Thus, a dispersion of 20 grams of dry commercial zein dissolved in 100 ml. of 85 per cent aqueous ethyl or isopropyl alcohol may be expected to set t o a useless gel in 4 or 5 days if stored a t 38" t o 40" C. Swallen (4) pointed out that alcoholic zein dispersions containing a low concentration of water are, in general, more resistant to gelation than are those in the more highly aqueous alcoholic solvents. This is illustrated by the observation that 20 grams of dry zein dissolved in 100 ml. of aqueous 90 per cent ethyl alcohol will not set to a gel in 2 weeks a t 40" C., whereas 20 grams of dry zein in 100 ml. of aqueous 70 per cent ethyl alcohol will usually gel in less than 1 dag a t the same temperature. The stabilization of zein dispersions by the simple addition of small amounts of gelation retarders a t room temperature has thus far proved unsatisfactory. Addition of 20 grams or more of acetaldehyde to alcoholic solutions of zein containing 20 grams of protein in 100 ml. of 85 per cent ethyl alcohol may, however, postpone gelation as long as several months. Amounts in the range of 2 to 5 grams of the aldehyde added to 1 A p a t e n t applicatlon covering t h e results of this work has been filed in t h e U. S. P a t e n t Officeand assigned t o t h e Seoretary of Agrioulture.
100 nil. of similar dispersion have little stabilizing effect. Benzene, morpholine, the nitroparaffins, and the chlor onitroparaffins also stabilize zein dispersions under proper conditions but to a lesser extent than the aldehydes. The rate of gelation of aqueous alcoholic dispersions of zein containing less than 10 per cent of the protein is very slow, but the viscosities of such dilute solutions are so low as t o limit their industrial usefulness. It would be desirable for some purposes to use zein concentrations as high as 40 per cent, but this is usually impractical because of the rapid rate a t which such dispersions gel a t room temperatures. IT HAS been found that zein dispersions may be stabilized against gelation to a limited extent simply by heating for 15 minutes or longer a t a temperature above 100" C. and belon the point where destruction of the protein occurs; that their stability may be further improved by heating the dispersion, followed by adding 1 t o 5 per cent of an aldehyde; and that much more stable dispersions may be prepared by heating in the presence of a small percentage of an aldehyde a t a temperature above 100" C. and below the point where destruction of the protein occurs. This last stabilizing treatment also improves materially the color and flexibility of films formed from such dispersions. Heat treatment of aqueous alcoholic zein dispersions containing as little as 1 or 2 per cent of an aldehyde and as much as 50 per cent of water increases their resistance t o gelatiori many fold as shown in Table I. Simple addition of such small amounts of aldehyde without heat treatment has little stabilizing effect. Films and coatings produced from the aldehyde heattreated zein dispersions are made insoluble in the ordinary zein solvents by baking, and are also made strongly resistant to the discoloring and softening action of water to which untreated zein films are so sensitive (a). For example, 20 grams or more of commercial zein may be dispersed in 90 ml. of 85 per cent ethyl alcohol and 10 ml. of 37 per cent formaldehyde and the dispersion then heated in a sealed container a t ap-
