W IL L E M R U D O L F S
New Jersey Agricultural Experiment Station, New Brunswick, N. J.
T HE treatment and dis
presentation of laboratory results pertaining to treatment of the wastes to prevent difficulties.
The wastes studied were produced by:
1. A large chemical laboratory and pilot plant causing sewer corrosion.
2. Plant waste causing sewer corrosion and interference with sewage treatment processes.
3. Plant waste causing pollution and interference with aquatic life.
4. Plant waste causing stream pollution.
5. Plant waste causing sewer corrosion.
Waste 2. Equalization and neutralization to pH 6.0 with high calcium hydrate.
Waste 3. Neutralization with high magnesium hydrate and soda ash to any desired pH value.
Waste 4. Equalization and neutralization of mineral acidity with high magnesium hydrate.
Waste 5. Neutralization with dolomitic limestone and aera
tion.
It is evident that the method of neutralization to be used depends not only on the type of acid and volume of flow, but also upon other ingredients in the wastes and the purpose to
posal more acute. The wastes studied caused sewer corrosion, interference with biological sewage treat materials in the waste, and purpose of treatment.
Neutralizing agents used for experimental purposes were calcium and magnesium hydrates, quick limes, limestones, soda ash, caustic soda, and their combinations.
During experimentation with nitrocellulose waste it was found that neutralization with calcium hydrate proceeded gradually until about 90 per cent of the total acids was destroyed, followed by a sharp break. The contact time required and amounts of sludge formed varied with the type and concentration of lime used. A combination of dolo
mitic hydrate with soda ash was preferable over lime, soda ash, or caustic soda alone. The dry weight of sludge decreased with increasing quanti
ties of soda ash, but the volume of sludge increased and the ease of dewatering decreased. The reac
tion time required for complete neutralization in
creased with increasing quantities of soda ash.
T a b l e I. V a r i a t i o n i n C h a r a c t e r o f W a s t e s a n d F l o w s
228 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 35, No. 2 During the course of experimentation a number of questions
were raised pertaining to the behavior of the various neutrali
zation agents. Results on part of the work1 are presented to illustrate the action of the neutralization agents and indi
cate some of the more important factors involved. The particular waste used for illustration, discharged from a nitrocellulose process, consisted essentially of a mixture of
Ta b l e I I . Q u a n t i t i e s o fL i m e Re q u i r e d t o Ra i s ep H Va l u e s amount of nitrocellulose floe. The total acidity of the waste, expressed as CaCCh, was 11,810 p. p. m., with 3660 p. p. m.
nitric and 8150 p. p. m. sulfuric acid.
The procedure of the general method employed for neutrali
zation consisted of placing 1 0 0-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.
When 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 com
pleteness of settling, ease of dewatering, and amounts of cake produced.
E ffect o f L im e
T y p e o f L i m e . Keeping the contact time between the
various types of lime and acid waste constant at 30 minutes, the quantities of neutralizing agent were determined. The theoretical amounts of lime, actual quantities, and resulting pH values are Summarized in Table II. Calcium and dolo
mitic 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. Most of this is removable by aeration for 15 min
utes 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 con
siderable foaming. Calcium hydrate addition required larger quantities and produced more sludge than dolomitic hydrate. 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 con
taining appreciable quantities of salts in solution may behave differently.
C o n t a c t T i m e . The effect of contact time varies with
the type and concentration of lime used. Employing quantities of lime sufficient to raise the pH values to 8.6, the rate of neutralization with increasing time is illustrated in Figure 2, for high calcium and magnesium hydrate and lime
stones. In all cases the mixtures were vigorously stirred.
The dolomitic hydrate reacts most rapidly, followed by cal
cium hydrate, the reactions being completed in 2 0 minutes.
With calcium limestone the pH was raised rapidly during the first 5 minutes and gradually tapered off, while the dolo
mitic limestone required several hours to raise the pH to 5.5.
O
Fi g u r e 3 . Sl u d g e Fo r m a t i o nw i t h Va r y i n g De g r e e s o f Ne u t r a l i z a t i o n
. . ^ ? G E F o r m a t i o n . The quantities of sludge forme«
the different types of lime varied materially. This is indie y e ollowing figures, showing the amounts of lime at
February, 1943 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 229
% N E U T R A L I Z A T I O N BY S O O A A S H
Fi g u r e 4 . We i g h t o f Sl u d g e Pr o d u c t i o n' w i t h Va r y i n g Pe b c e n t a g e s o f Ma g n e s i u m
Ht d r a t e a n d So d a As h
cost, the intense foam formation with soda ash alone made it undesirable for this purpose.
C o m b in a tio n o f L im e a n d S o d a A sh
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 deter
mined.
quantities of dolomitic hydrate, increases rapidly with a de
crease 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 forma
tion 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 pH values is graphically shown in Figure 3 . The greatest volumes of sludge were produced considerable quantities of sludge.
S o d a A sh a n d C a u s t ic S o d a
Considerable experimentation with soda ash and caustic soda for neutralization showed that soda ash was preferable as long as the pH is below 4.5. The carbon dioxide remaining, however, may cause carbonization of the lime when added
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, Hie 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 treat
ment against the cost of two-stage treatment. With increas
ing quantities of soda ash, however, the sludge becomes in
creasingly lighter, more voluminous, and more difficult to dewater. The fiuffiness 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 2-hour settling is illustrated in Figure 5. Neutralization with 90 per cent dolomitic hydrate and 1 0 per cent soda ash produced about the same amount of sludge as neutralization with magnesium hydrate alone. The smallest volume and lowest dry weight
10.000
a o o o
a. 4000
230 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 35, No. 2 were obtained when the acids were neutralized with about 80
per cent lime and 20 per cent soda ash. This sludge, how
ever, did not settle so well as that produced by dolomitic lime alone.
The moisture content of the filter cakes produced with dif
ferent 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 it takes before neutralization is accomplished. Some results
given in Table III illustrate this. After addition of lime vigor
ous stirring was continued for 6 minutes, the sodium carbonate was added, and stirring was continued until neutralization was completed. With about 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 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 ( 1 , 3 ) , and others. In 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 sols may be increased by storage at low temperatures, by the use of substantially anhydrous solvents, by the addi
tion of certain reagents, or by keeping the concentration of zein at a practical minimum. Effective control of tempera
ture is usually not practical, as summer room temperatures are frequently high enough to cause commercially usable con
centrations 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 to a useless gel in 4 or 5 days if stored at 38° to 40° C.
Swollen (4 ) pointed out that alcoholic zein dispersions con
taining 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 at 40° C., whereas 20 grams of dry zein in 100 ml. of aqueous 70 per cent ethyl alcohol w’ill usually gel in less than 1 day at the same temperature.
The stabilization of zein dispersions by the simple addition of small amounts of gelation retarders at 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 a p p l i c a t i o n c o v e r i n g t h e r e s u l t s o f t h i s w o r k h a s b e e n file d in t h e U . S . P a t e n t O ffic e a n d a s s i g n e d t o t h e S e c r e t a r y o f A g r i c u l t u r e .
1 0 0 ml. of similar dispersion have little stabilizing effect.
Benzene, morpholine, the nitroparaffins, and the chloro- nitroparaffins also stabilize zein dispersions under proper con
ditions but to a lesser extent than the aldehydes.
The rate of gelation of aqueous alcoholic dispersions of zein containing less than 1 0 per cent of the protein is very slow, but the viscosities of such dilute solutions are so low as to 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 at which such dispersions gel at room temperatures.
IT HAS been found that zein dispersions may be stabilized