Sorbent and Leachate Characteristics of Fly Ash - ACS Symposium

27 Sorbent a n d Leachate Characteristics o f F l y Ash 1

1

1

1

John W. Liskowitz, Richard B. Trattner, James M. Grow, Mung S. Sheih, James A. King , John Kohut, and Melvin Zwillenberg 2

3

3

1

Industry/University Cooperative Center for Research in Hazardous and Toxic Substances, New Jersey Institute of Technology, Newark, ΝJ 07102 Lincoln University, Lincoln, PA 19352 Public Service Electric & Gas, Newark, NJ 07101

Downloaded by MONASH UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: September 18, 1986 | doi: 10.1021/bk-1986-0319.ch027

2

3

Coals from ten different mines were burned under monitored conditions in three different types of coal fired utility boilers in order to determine the influence of coal com position and boiler combustion conditions on the leaching and sorbent characteristics of the fly ash produced. The leaching and removal exhibited by the fly ashes with regard to pH, Cd, Sn, Ni, Pb, Mo, Cu, Fe, Cr, Zn, Mn, As and organics were examined. Results indicate that the leachable elements are contained to some extent within a water soluble component in low and high fusion fly ashes. The leachable amounts of each element are in general related to the bulk composition of the elements in the coal from which the fly ash is produced and the size of the fly ash particles. Boiler temperatures also influence the leachable amounts of elements in low fusion fly ashes. Aqueous washing of the fly ash provides a sorbent with the capacity to remove the elements in amounts in excess of that originally leached. The sorbent charac teristic of fly ash is favored by combustion temperatures that lead to the fusion of the fly ash during its forma tion and the time it remains in the fused state. No correlation could be established between the sorbent characteristic of the fly ashes and their bulk major , minor, trace elemental compositions and the particle size of the fly ash particles. Only the carbon content of the fly ash could be related to its organic removal properties. Increased reliance on coal combustion can give rise to significant fly ash storage or disposal problems. Most fly ash is presently used as a low cost material for construction purposes and also as cover material for landfills. Other, more economically advantegeous, uses for this inexpensive material would be desirable. One such use for fly ash could be to treat ash pond effluent for reuse by power plants as cooling tower makeup water. Another application could be as 0097-6156/86/0319-0332$06.00/ 0 © 1986 American Chemical Society

In Fossil Fuels Utilization; Markuszewski, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


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333

s o r b e n t s f o r t h e t r e a t m e n t o f t h e heavy m e t a l s , t o x i c a n i o n s and o r g a n i c s u b s t a n c e s commonly found i n l e a c h a t e s emanating from l a n d fills. Over t h e p a s t s e v e r a l y e a r s , o u r l a b o r a t o r y has d e v e l o p e d , under EPA Grant R803-717 a method u t i l i z i n g f l y a s h a l o n e o r i n c o m b i n a t i o n w i t h o t h e r i n e x p e n s i v e s o r b e n t s f o r t h e removal o f heavy m e t a l s , t o x i c a n i o n s and o r g a n i c s from i n d u s t r i a l s l u d g e l e a c h a t e s and i n d u s t r i a l waste stream e f f l u e n t s . D u r i n g t h e c o u r s e o f t h e s e i n v e s t i g a t i o n s , two t y p e s o f f l y a s h were r e p e a t e d l y c o l l e c t e d a t d i f f e r e n t t i m e s from t h e same e l e c t r o s t a t i c p r e c i p i t a t o r a t a c o a l burning b o i l e r of a l a r g e east coast e l e c t r i c u t i l i t y . These f l y ashes e x h i b i t e d d i f f e r e n t l e a c h i n g and sorbent c h a r a c t e r i s t i c s . A l t h o u g h b o t h f l y ashes i n i t i a l l y l e a c h e d b o t h c a t i o n s and a n i o n s , t h e l e a c h i n g e v e n t u a l l y ceased and removal of t h e s e s p e c i e s o c c u r r e d . F o r example, one f l y a s h whose e f f l u e n t was i n i t i a l l y a c i d i c l e a c h e d copper (0.69 micrograms/gram o f f l y ash) and z i n c (0.32 micrograms/gram o f f l y ash) when t h i s m a t e r i a l was p l a c e d i n a l y s i m e t e r and e l u t e d w i t h i n d u s t r i a l s l u d g e l e a c h a t e . A f t e r a p e r i o d o f t i m e t h e l e a c h i n g ceased and b o t h copper and z i n c i n t h e t r e a t e d e f f l u e n t were reduced from about 2.5 mg/L and 0.4 mg/L, r e s p e c t i v e l y , t o 0.01 mg/L ( 1 ) . S i n c e each f l y a s h t y p e e x h i b i t e d d i f f e r e n t s o r b e n t c h a r a c t e r i s t i c s , a m i x t u r e o f b o t h t y p e s was found t o be more e f f e c t i v e i n t h e t r e a t m e n t of i n d u s t r i a l s l u d g e l e a c h a t e s . Up t o t h i s p o i n t , t h e a v a i l a b i l i t y o f t h e d i f f e r e n t t y p e s o f f l y a s h from t h e power p l a n t c o u l d n o t be p r e d i c t e d . One s i m p l y had t o c o l l e c t what was a v a i l a b l e and d e t e r m i n e i t s c h a r a c t e r i s t i c s by t e s t i n g . T h i s l a c k of an adequate s u p p l y o f f l y ashes w i t h t h e d e s i r e d s o r b e n t c h a r a c t e r i s t i c s i n h i b i t e d t h e f u r t h e r development of t h i s low c o s t t e c h n o l o g y f o r t h e t r e a t m e n t o f i n d u s t r i a l waste e f f l u e n t and l e a c h a t e from i n d u s t r i a l l a n d f i l l s . Therefore, t h i s i n v e s t i g a t i o n was c a r r i e d out t o c o r r e l a t e t h e s o r b e n t and l e a c h i n g c h a r a c t e r i s t i c s o f f l y a s h produced w i t h t h e c o m p o s i t i o n o f t h e c o a l and t h e combustion c o n d i t i o n s t h a t e x i s t e d d u r i n g t h e p r o d u c t i o n o f t h e s e f l y ashes. E x p e r i m e n t a l B o i l e r Types Three d i f f e r e n t t y p e s o f c o a l f i r e d b o i l e r s were u t i l i z e d i n t h i s s t u d y . One t y p e (A) was a d r y bottom b o i l e r w i t h d i r e c t f i r e d b u r n e r s l o c a t e d on o p p o s i t e w a l l s . The second t y p e (Β), wet bottom b o i l e r s #11 and #12, was o p e r a t e d i n p a r a l l e l w i t h t h e same c o a l stream s p l i t t o f e e d b o t h b o i l e r s s i m u l t a n e o u s l y . The t h i r d b o i l e r t y p e s (C & D) were d r y bottom, t a n g e n t i a l l y f i r e d b o i l e r s . Samples and T h e i r A n a l y s i s S i x h i g h - f u s i o n c o a l s and f i v e l o w - f u s i o n c o a l s were burned i n t h e t h r e e d i f f e r e n t b o i l e r t y p e s under c l o s e l y m o n i t o r e d c o n d i t i o n s . W e l l d e f i n e d combustion c o n d i t i o n s were f o l l o w e d t o i n s u r e u n i f o r m i t y i n t h e e v a l u a t i o n o f t h e t e s t c o a l s ( 2 ) . T a b l e I g i v e s a l i s t i n g of t h e s e e l e v e n c o a l s by mine name and l o c a t i o n .


FOSSIL FUELS UTILIZATION: ENVIRONMENTAL CONCERNS

334

C o a l s burned under t e s t c o n d i t i o n s

Table I .

Locat i o n

Mine


High Fusion Coal Militant Deep H o l l o w Upshur Badger Mine Mouth C Mine Mouth D

Pennsylvania West V i r g i n i a West V i r g i n i a West V i r g i n i a Pennsylvania Pennsylvania

Low F u s i o n C o a l Wellmore Cactus Wellmore A c k i s s Ellsworth Nora Blend

Virginia Virginia Pennsylvania Pennsylvania Not Known

D u r i n g t h e combustion of each c o a l , samples were c o l l e c t e d a t t h e e n t r a n c e t o each p u l v e r i z e r j u s t p r i o r t o b e i n g burned. The c o l l e c t i o n o f f l y a s h was timed t o correspond t o t h e c o a l b e i n g burned. D i f f e r e n t s i z e d i s t r i b u t i o n s o f t h e f l y a s h were o b t a i n e d by t h e c o l l e c t i o n o f samples from b o t h t h e f r o n t and back row of e l e c t r o s t a t i c p r e c i p i t a t o r s . The c o a l s and t h e i r ashes were a n a l y z e d f o r p e r c e n t C, S, S i 0 , AI2O3, CaO, K 0 , N a 0 , and MgO, and ppm o f T i , Cd, Cu, C r , Pb, Zn, Sn, N i , and Mn, a s h c o n t e n t and a s h f u s i o n temperatures a c c o r d i n g t o ASTM p r o c e d u r e s . 2

2

2

A l l b o i l e r temperatures were measured j u s t p r i o r t o and a f t e r t h e c o l l e c t i o n o f t h e c o a l samples and t h e i r r e s p e c t i v e f l y ashes, s i n c e i t was p h y s i c a l l y i m p r a c t i c a l t o c o l l e c t t h e samples and measure t h e temperatures a t t h e same t i m e s . I n a l l c a s e s , t h e temperatures remained e s s e n t i a l l y c o n s t a n t . An o p t i c a l pyrometer was used t o measure flame t e m p e r a t u r e s , and w a t e r - c o o l e d j a c k e t e d thermocouples were used t o m o n i t o r t h e b o i l e r t e m p e r a t u r e s . The w a l l e f f e c t s on t h e temperature measurements were m i n i m i z e d by i n s e r t i o n o f t h e thermocouple, i n t o t h e b o i l e r u n t i l temperatures remained c o n s t a n t w i t h d i s t a n c e upon f u r t h e r i n s e r t i o n o f t h e thermocouple i n t o t h e b o i l e r . Surface A n a l y s i s The s u r f a c e c o m p o s i t i o n o f t h e f l y a s h samples was o b t a i n e d u s i n g a V a r i a n I.E.F. spectrometer o p e r a t i n g a t around 1x10"^ t o r r . The powder samples were mounted on t h e probe u s i n g two s i d e d t a p e . The r e l a t i v e c o m p o s i t i o n s were c a l c u l a t e d u s i n g W e i n g l e ' s p h o t o e l e c t r i c c r o s s s e c t i o n s a s a measure o f r e l a t i v e i n t e n s i t i e s (3). Lysimeter

Studies

L y s i m e t e r s were used t o e v a l u a t e t h e l e a c h i n g and removal of Cd, Sn, N i , Pb, Mo, Cu, C r , Zn, Mn, F e , A s , and COD u s i n g 500 grams o f f l y a s h under c o n t i n u o u s f l o w c o n d i t i o n s .



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335

L a b o r a t o r y l y s i m e t e r s were c o n s t r u c t e d o f p l e x i g l a s s t u b i n g (6.2 cm i . d . ; 0.6 cm w a l l t h i c k n e s s ; 90 cm l e n g t h ) , s u p p o r t e d i n a v e r t i c a l p o s i t i o n . A 164 m i c r o n pore s i z e corundum d i s c (6.10 cm d i a m e t e r ; 0.6 cm t h i c k n e s s ) was p l a c e d i n each column d i r e c t l y over the d r a i n h o l e i n o r d e r t o support t h e f l y a s h sorbent and t o p r e v e n t clogging of t h e o u t l e t . The l e a c h i n g c h a r a c t e r i s t i c s of t h e f l y ashes g e n e r a t e d under the v a r i o u s combustion c o n d i t i o n s were e v a l u a t e d as t o t h e e x t e n t t h a t each f l y a s h l e a c h e s Cd, Sn, N i , Pb, Mo, Cu, C r , Sn, Mn, and Fe. D e i o n i z e d water was added t o t h e l y s i m e t e r s c o n t a i n i n g 500 grams of t h e f l y a s h and s p e c i f i c volumes o f e f f l u e n t l e a c h a t e s were c o l l e c t e d and a n a l y z e d f o r t h e above elements u n t i l 4 l i t e r s had passed t h r o u g h each a s h sample. I t was observed t h a t 500 grams of f l y a s h g e n e r a l l y ceased t o l e a c h a f t e r passage o f 4 l i t e r s o f water t h r o u g h t h e column. The packed columns were t h e n s l o w l y wetted w i t h a s h pond e f f l u e n t t o a l l o w t o t a l s a t u r a t i o n and t o f o r c e a l l t h e a i r t r a p p e d i n t h e v o i d s o u t o f t h e column p a c k i n g . The column was then f i l l e d w i t h a s h pond e f f l u e n t t o t h e l e v e l o f an o v e r f l o w i n g d r a i n , i n o r d e r to p e r m i t a c o n s t a n t head c o n d i t i o n . The a s h pond e f f l u e n t was f e d to t h e t o p of t h e column t h r o u g h a v a l v e d m a n i f o l d w h i c h d i s t r i b u t e d the e f f l u e n t t o a l l l y s i m e t e r s , s i m u l t a n e o u s l y , from a c e n t r a l r e s e r v o i r . The c e n t r a l r e s e r v o i r , a 100 l i t e r p o l y e t h y l e n e c a r b o y , d e l i v e r e d t h e a s h pond e f f l u e n t t o t h e m a n i f o l d system by means of a g r a v i t y s i p h o n f e e d arrangement. Any o v e r f l o w from t h e c o n s t a n t head d r a i n s was c o l l e c t e d and pumped back t o t h e c e n t r a l r e s e r v o i r . A l l t u b i n g i n t h e system was made o f Tygon ( 3 / 8 " i . d . ) . Tygon was used because a n a l y s i s o f a s h pond e f f l u e n t samples passed t h r o u g h t h i s t u b i n g r e v e a l e d no l e a c h a b l e c o n s t i t u e n t s . A c o n s t a n t h y d r a u l i c head was m a i n t a i n e d i n t h e l y s i m e t e r s a t a l l t i m e s and t h e volumes o f e f f l u e n t p a s s i n g t h r o u g h t h e columns were c o n t i n u o u s l y m o n i t o r e d . Samples of t r e a t e d a s h pond e f f l u e n t were c o l l e c t e d a t i n t e r v a l s and a n a l y z e d t o d e t e r m i n e t h e c o n c e n t r a t i o n o f a l l measurable c o n s t i t u e n t s r e m a i n i n g i n t h e e f f l u e n t a f t e r a known volume had passed t h r o u g h t h e column. T h i s was c o n t i n u e d u n t i l b r e a k t h r o u g h had o c c u r r e d f o r a l l measurable c o n t a m i n a n t s o r e x c e s s i v e l y low perme a b i l i t i e s were encountered. B r e a k t h r o u g h i s d e f i n e d a s t h a t c o n d i t i o n when t h e c o n c e n t r a t i o n s o f t h e s p e c i e s o f c o n c e r n i n t h e l y s i m e t e r e f f l u e n t sample approached o r exceeded t h a t i n t h e pond e f f l u e n t samples. R e s u l t s and D i s c u s s i o n s The t e m p e r a t u r e p r o f i l e s m o n i t o r e d i n t h e c o a l f i r e d b o i l e r s d u r i n g the c o l l e c t i o n of t h e c o a l and f l y a s h samples a r e l i s t e d i n T a b l e I I f o r d i f f e r e n t power o u t p u t s . The l i m i t e d t e m p e r a t u r e r e s u l t s ob t a i n e d f o r t h e M i l i t a n t and Deep H o l l o w f l y ashes was t h e r e s u l t of our thermocouple probes b e i n g u n a v a i l a b l e f o r t h e s e t e s t b u r n s . The t h r e e d i f f e r e n t t y p e of b o i l e r s used i n t h i s s t u d y were found t o e x h i b i t d i f f e r e n t t e m p e r a t u r e p r o f i l e s . The f l a m e and b o i l e r t e m p e r a t u r e s m o n i t o r e d i n B o i l e r A, when measured, were observed t o be w e l l below t h e i n i t i a l d e f o r m a t i o n t e m p e r a t u r e o f t h e ash ( s e e T a b l e I I ) . On t h e o t h e r hand, t h e f l a m e t e m p e r a t u r e s e n c o u n t e r e d i n t h e Β and D b o i l e r s were above t h e i n i t i a l d e f o r m a t i o n p o i n t o f t h e a s h , and i n some c a s e s above t h e t e m p e r a t u r e a t w h i c h the a s h becomes f l u i d . I n a d d i t i o n , t h e temperatures monitored i n



B o i l e r C: B o i l e r D:

B o i l e r B:

B o i l e r A:

Mine mouth Mine mouth

Wellmore Ackiss Wellmore Ackiss Wellmore Cactus (2) Ellsworth

Wellmore Cactus (1) Nora

Upshur Badger Back Blend

Deep H o l l o w

Deep H o l l o w

Deep H o l l o w

Militant

Militant

Militant

Ash Militant

Source Front Back Front Back Front Back Front Back Front Back Front Back Front Back Back Front Full No. 11 No. 12 No. 11 No. 12 No. 11 No. 12 No. 11 No. 12 No. 11 No. 12 No. 11 No. 12 No. 11 No. 12 Full Full Full Full Full Full Full Full Min. Min. Full Full Full Full Full Full

Power Full Full Full Full Int. Int. Min. Min. Full Full Int. Int. Min. Min. Full Full

2650

3100 3100 3150 3150 3100 3250 3050 2950 2870 2950 3125 2970 3100 3100

2470 2550 1815 1737 1620 1530 1850 1700 1900 1725 1590 1620 1400 1400 1815 1740 2600 2700

1590 1750

1450

1550

2700

2250 1835 2080 1480 2175 1700 2180 1500 1780 1500 1680 1320 2240 1820

1565 1440

B o i l e r Temp °F Above Flame Arch Basket

2325 2325 2285 2310 2230 2265 2330 2265

2400 2215 2235 2275 2520 2503

2190 2155 2150 2155 2183 2125

2700+ 2700+

2700

2143 2188 2120 2135 2130 2145 2135 2110

2700+ 2700+

2605

2695 2510 2445 2470 2700+ 2700+

2665 2353 2570 2555 2330 2480 2625 2440

2700+ 2700+

2700+

Ash F u s i o n op Init. Def Fluid Soft 2555 2700+ 2700+

T a b l e I I : R e l a t i o n s o f B o i l e r C o n d i t i o n s t o L e a c h a t e pH


pH range 3.5- 6.6 3.8-6.8 4.2-6.7 3.6- 6.9 3.8-7.2 3.8-5.9 3.7- 6.9 3.7-7.3 3.7- 5.1 3.8- 5.5 4.0-6.1 3.6-4.7 3.8-5.6 6.3-7.0 2.7-4.5 2.8-5.5 3.6-4.6 7.7-9.1 7.3-7.5 8.3-9.3 6.9-7.9 9.4-9.8 4.1-6.4 7.3-8.6 5.1-6.8 7.2-9.1 5.6-5.8 9.8-11.5 8.2-9.0 10.5-12.3 8.5-9.4 6.6-8.1 7.1-10.0


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the a r c h o f b o i l e r #11 was s i g n i f i c a n t l y h i g h e r than t h a t measured at t h e a r c h i n b o i l e r #12 even though t h e y were b u r n i n g t h e same c o a l . A l s o , t h e C and D b o i l e r t e m p e r a t u r e s above t h e f l a m e basket were observed t o be g r e a t e r t h a n t h e s o f t e n i n g t e m p e r a t u r e s of t h e ash. The r e s u l t s of m o n i t o r i n g t h e temperature p r o f i l e s and a s h f u s i o n t e m p e r a t u r e s of t h e a s h r e s u l t i n g from t h e t e s t c o a l s burned i n t h e d i f f e r e n t b o i l e r s i n d i c a t e d t h a t t h e e f f e c t of b o i l e r t e m p e r a t u r e and a s h f u s i o n c h a r a c t e r i s t i c s of t h e c o a l on t h e l e a c h i n g and s o r b e n t c h a r a c t e r i s t i c s s h o u l d be examined. T h i s c o u l d be c a r r i e d out t h r o u g h a comparison of t h e l e a c h i n g and sorbent c h a r a c t e r i s t i c s of t h e f l y a s h produced i n t h e #11 b o i l e r w i t h t h a t produced i n #12 b o i l e r and t h e f l y a s h produced i n t h e A b o i l e r w i t h t h a t produced i n t h e C and D B o i l e r s , r e s p e c t i v e l y . Leaching F a c t o r s I n f l u e n c i n g L e a c h a t e pH The pH f o r t h e f l y a s h l e a c h a t e s i n d i c a t e t h a t t h e ashes produced b a s i c and a c i d i c l e a c h a t e s . The pH's o f low f u s i o n f l y a s h produced i n t h e wet bottom Β b o i l e r s i n g e n e r a l range from a minimum of about 4.1 up t o a maximum o f about 12.3 ( s e e T a b l e I I ) . H i g h b o i l e r t e m p e r a t u r e s accompanied by f u s i o n o f t h e a s h appears t o f a v o r t h e f o r m a t i o n of f l y a s h t h a t g e n e r a t e s an a l k a l i n e l e a c h a t e . I n a l l c a s e s , t h e f l y ashes g e n e r a t e d i n b o i l e r #11 a r e s i g n i f i c a n t l y more a l k a l i n e than t h o s e produced i n #12 even though t h e r e i s no s i g n i f i cant d i f f e r e n c e i n t h e major and minor element c o n t e n t s o f t h e s e ashes ( s e e T a b l e I I I ) . Table I I I .

Ash

R e p r e s e n t a t i v e amounts of major and minor ( i n %) Source

Wellmore Cactus (1) No.11 No. 12 Badger Front ppt. Back p p t . Mine Mouth B o i l e r C: Mine Mouth B o i l e r D:

CaO

K 0

MgO

Si0

2.84 3.36 2.04 2.14

3..59 3..39 1.,94 2..08

1.02 0.94 0.44 0.44

1.40 1.50 0.63 0.80

49.6 48.1 38.3 46.2

25.8 26.1 32.9 33.6

13.8 14.6 11.8 12.1

0.28 0.63 0.25

1.65

3,.18

0.58

0.93

52.7

26.4

11.5

0.27

2.18

2..76

0.58

0.81

46.4

29.7

18.3

0.20

2

Na 0

constituents

2

2

A1 0 2

3

Fe 0 2

3

S

The b o i l e r t e m p e r a t u r e s i n t h e #11 b o i l e r were observed t o be 400-600 degrees h i g h e r t h a n t h o s e measured i n #12 b o i l e r . The d i f f e r e n c e i n t e m p e r a t u r e was e s p e c i a l l y pronounced i n t h e a r c h r e g i o n o f t h e b o i l e r s . These t e m p e r a t u r e s i n d i c a t e t h a t t h e f l y a s h i n t h e #11 b o i l e r was exposed t o h i g h e r t e m p e r a t u r e s f o r l o n g e r p e r i o d of t i m e i n t h e f u s i o n s t a t e than t h e f l y a s h i n #12 b o i l e r . A comparison o f f l a m e t e m p e r a t u r e s encountered i n b o t h t h e #11 and #12 b o i l e r s and t h e a s h f l u i d t e m p e r a t u r e s e x h i b i t e d by t h e f l y ashes i n d i c a t e s t h a t t h e f l a m e t e m p e r a t u r e s a r e some 500°F h i g h e r t h a n t h a t r e q u i r e d t o melt the ash.



338


S i m i l a r e v e n t s a l s o seem t o have o c c u r r e d w i t h t h e b o i l e r C and D f l y ashes. B o t h f l y ashes a l s o g e n e r a t e a l k a l i n e l e a c h a t e s (see T a b l e I I ) . A comparison o f t h e b o i l e r t e m p e r a t u r e s t h a t produced t h e b o i l e r C and b o i l e r D f l y ashes and t h e i r ash f u s i o n t e m p e r a t u r e s suggest t h a t t h e b o i l e r t e m p e r a t u r e s were h i g h enough t o cause f u s i o n of t h e i r r e s p e c t i v e f l y ashes w i t h i n t h e b o i l e r s . Temperatures o f 2600 and 2700°F were measured above t h e f l a m e b a s k e t i n t h e b o i l e r C and b o i l e r D, r e s p e c t i v e l y . T h i s i s some 200° above t h e s o f t e n i n g t e m p e r a t u r e s o f t h e f l y ashes. A p p a r e n t l y , t h e h i g h t e m p e r a t u r e s encountered by t h e f l y ash i n t h e Β b o i l e r s , b o i l e r C and b o i l e r D, have r e s u l t e d i n f u s i o n r e a c t i o n s t h a t have l e d t o a l k a l i n e p r o d u c t s t h a t can be d i s s o l v e d upon c o n t a c t w i t h w a t e r t o form a l k a l i n e leachates. I t can be seen from T a b l e I I t h a t t h e f l y ashes produced i n t h e A b o i l e r e s s e n t i a l l y f o r m a c i d i c l e a c h a t e s even though t h e major element c o m p o s i t i o n o f t h e s e f l y ashes were comparable t o t h e amounts found i n t h e b o i l e r C and b o i l e r D f l y ashes ( s e e T a b l e I I I ) . The M i l i t a n t , Deep H o l l o w , Upshur and Badger f l y ashes produced i n t h i s b o i l e r encountered f l a m e and b o i l e r t e m p e r a t u r e s t h a t a r e below even t h e i n i t i a l d e f o r m a t i o n t e m p e r a t u r e s o f t h e f l y a s h . Hence, t h e f u s i o n r e a c t i o n s p r o b a b l y d i d not o c c u r t h a t might have l e d t o f o r m a t i o n o f p r o d u c t s t h a t g e n e r a t e an a l k a l i n e l e a c h a t e . F a c t o r s I n f l u e n c i n g Leachate Composition The d i f f e r e n t amounts o f l e a c h i n g e x h i b i t e d by t h e f l y ashes suggest t h a t t h e l e a c h a b l e elements a r e c o n t a i n e d w i t h i n a water s o l u b l e component w h i c h i s e v e n t u a l l y removed when t h e f l y a s h i s brought i n c o n t a c t w i t h s u f f i c i e n t q u a n t i t i e s of w a t e r . I n most c a s e s , t h e l e a c h a b l e elements i n 500 grams o f f l y ash ceased t o appear a f t e r 4 l i t e r s o f water was passed t h r o u g h t h e f l y ash samples. The d i f f e r e n c e s i n l e a c h i n g o f Cd, Sn, Mo, Pb, Cu, C r , Zn, and Mn from t h e f l y a s h e s , w i t h t h e e x c e p t i o n o f N i and F e , were found t o be dependent upon t h e d i f f e r e n c e s i n t h e amounts o f t h e s e elements p r e s e n t i n t h e f l y ash. A l s o , t h e d i f f e r e n c e s i n b o i l e r t e m p e r a t u r e s encountered by t h e f l y ashes d u r i n g combustion were observed t o i n f l u e n c e t h e l e a c h i n g o f t h e above elements. A c o r r e l a t i o n between t h e d i f f e r e n c e s i n t h e amount o f N i and Fe p r e s e n t i n a m a j o r i t y o f t h e s e ashes and t h e i r l e a c h a b i l i t y was n o t o b s e r v e d . T h i s l a c k o f c o r r e l a t i o n s u g g e s t s t h a t t h e s e elements a r e i n a m a t r i x t h a t i s not r e a d i l y s o l u b i l i z e d by t h e water used t o generate the leachate. Hansen and F i s h e r (4) have shown t h e i r o n t o be p r i m a r i l y i n t h e i n s o l u b l e s i l i c a t e m a t r i x and n i c k e l appears t o be a s s o c i a t e d w i t h an a c i d i n s o l u b l e phase. However, f o r a l l o f t h e o t h e r e l e m e n t s , t h e d i f f e r e n c e s i n amounts leached from t h e f l y ashes were c o r r e l a t e d w i t h t h e b u l k d i f f e r e n c e s found i n t h e f l y ashes. The d i f f e r e n c e i n t h e amounts o f Cd, Sn, Mo, Pb, Cu, Zn, and Mn, measured i n t h e h i g h f u s i o n ashes can be r e l a t e d t o t h e i r c o n c e n t r a t i o n s i n t h e c o a l and t h e s i z e o f t h e f l y a s h p a r t i c l e s . The s m a l l e r f l y ash p a r t i c l e s i n g e n e r a l c o n t a i n e d g r e a t e r amounts o f a g i v e n element t h a n t h e l a r g e r p a r t i c l e s . I n c o m p a r i s o n , t h e d i f f e r e n c e s i n t h e amount o f s p e c i f i c e l e ments found i n t h e low f u s i o n f l y ashes were not o n l y observed t o be r e l a t e d t o t h e c o n c e n t r a t i o n o f t h a t element i n t h e c o a l and i t s



27.

LISKOWITZ ET AL.


339

p a r t i c l e s i z e , but a l s o b o i l e r temperatures. The s m a l l e r l o w f u s i o n f l y a s h p a r t i c l e s and/or lower b o i l e r t e m p e r a t u r e s , when compared t o t h e l a r g e r p a r t i c l e s and/or h i g h e r b o i l e r t e m p e r a t u r e s , c o n t a i n e d t h e g r e a t e r amounts of t h e m a j o r i t y o f t h e above elements. B o i l e r temperatures p r o b a b l y i n f l u e n c e t h e l e a c h i n g c h a r a c t e r i s t i c s o f t h e f l y ashes by f i x a t i o n o f t h e l e a c h a b l e elements. The d i f f e r e n t l e a c h i n g r e s u l t s o b t a i n e d w i t h t h e low f u s i o n f l y ashes produced from t h e same c o a l a t t h e same t i m e , b u t i n two b o i l e r s operated i n p a r a l l e l a t d i f f e r e n t t e m p e r a t u r e s , i n d i c a t e d t h a t o p e r a t i o n of t h e b o i l e r s a t temperatures above t h e a s h f u s i o n temper a t u r e s , a l o n g w i t h t h e ash produced i n t h e h o t t e r b o i l e r r e m a i n i n g i n t h e f u s e d s t a t e f o r l o n g e r l e n g t h s o f t i m e may e x p l a i n t h e s e d i f f e r e n c e s . A p p a r e n t l y , t h e h i g h temperatures a l o n g w i t h t h e a s h remaining i n the f u s e s t a t e f o r d i f f e r e n t lengths of time l e a d t o some f i x a t i o n o f t h e s e elements i n t o a n o n - s o l u b l e p o r t i o n o f t h e f l y ash. F a c t o r s I n f l u e n c i n g Sorbent P r o p e r t i e s o f F l y A s h Four s e p a r a t e ash pond samples were used t o e v a l u a t e t h e e f f e c t i v e n e s s o f t h e f l y a s h i n t r e a t i n g f l y a s h pond e f f l u e n t . R e s u l t s o f t h e a n a l y s e s o f t h e s e ash pond samples a r e p r e s e n t e d i n T a b l e I V . T a b l e IV.

Element Cadmium Tin Molybdenum Nickel Lead Copper Chromium Zinc Manganese Iron Arsenic COD

E l e m e n t a l C o n c e n t r a t i o n o f A c t u a l A s h Pond Samples Used i n F l y A s h Sorbent C h a r a c t e r i z a t i o n .

Sample A mg/1. N.D.* 0.90 3.0 0.26 1.80 0.01 0.48 0.16 0.24 0.22 0.16

Sample Β mg/1. N.D.* 2.07 2.70 0.11 0.35 0.01 0.18 0.06 0.24 0.05 0.15

Sample C mg/1. 0.02 1.01 0.41 0.09 0.62 0.09 0.09 1.48 0.40 0.10 0.13

Sample D mg/1. 0. 02

0. 30 0. 07 0. 56

0. 10 12. 8 * N.D. =below measurable l i m i t s

Sample D, w h i c h was p r i m a r i l y used t o measure COD removal by t h e f l y ashes, was c o l l e c t e d from a d i f f e r e n t ash pond than t h o s e a s h ponds w h i c h p r o v i d e d Sample A, Sample Β and Sample C. The COD i n t h e l a t t e r a s h ponds c o u l d not be determined because o f h i g h c h l o r i d e i n t e r f e r e n c e s r e s u l t i n g f r o m s a l t water c o n t a m i n a t i o n o f t h e a s h pond effluent. The r e s u l t s show t h a t f l y a s h c a n be used f o r t r e a t m e n t o f Cd, Sn, Mo, N i , Pb, Cu, Zn, Mn, Fe, As and o r g a n i c s i n t h e s e ash pond e f f l u e n t s . Removals o f g r e a t e r t h a n 75 p e r c e n t were a c h i e v e d f o r a l l o f t h e above elements w i t h t h e e x c e p t i o n o f Mo where r e m o v a l s of o n l y 43% were o b t a i n e d . F o r example, F i g u r e 1 shows t h a t t h e c o n c e n t r a t i o n o f l e a d i n t h e t r e a t e d ash pond sample remained below d e t e c t a b l e


340



l e v e l s w i t h no i n d i c a t i o n of b r e a k t h r o u g h even a f t e r p a s s i n g 36 l i t e r s of a s h pond sample t h r o u g h t h e f l y a s h g e n e r a t e d from t h e Nora c o a l s . These r e m o v a l s were a c h i e v e d even though t h e c o n c e n t r a t i o n o f l e a d i n t h e a s h pond sample was i n c r e a s e d t o 3.0 mg/1 ( s e e d o t t e d l i n e i n F i g u r e 1 ) . The maximum a l l o w a b l e p r i m a r y d r i n k i n g s t a n d a r d f o r l e a d i s 0.05 mg/1. The e x c e p t i o n a l r e m o v a l o f l e a d does not appear t o be due t o p r e c i p i t a t i o n s i n c e t h e c o n c e n t r a t i o n o f l e a d i n t h e a s h pond sample was kept below t h e maximum s o l u b i l i t y o f t h e l e a d a s measured a s a f u n c t i o n o f pH ( s e e F i g u r e 2 ) . A l s o , t h e pH measured i n t h e t r e a t e d a s h pond e f f l u e n t ranged f r o m an a l k a l i n e v a l u e o f 10 down t o an a c i d i c v a l u e o f 6 d u r i n g t h e removal o f l e a d from 36 l i t e r s o f a s h pond sample ( s e e F i g u r e 3 ) . The g e n e r a l s o r b e n t c h a r a c t e r i s t i c s o f t h e f l y a s h e s a r e f a v o r e d by low a s h f u s i o n t e m p e r a t u r e s , combustion t e m p e r a t u r e s t h a t f a v o r t h e f u s i o n of t h e f l y a s h d u r i n g f o r m a t i o n and t h e t i m e t h a t t h e f l y a s h remain i n t h e f u s e d s t a t e . No c o r r e l a t i o n c o u l d be e s t a b l i s h e d between t h e s o r b e n t c h a r a c t e r i s t i c o f t h e f l y ashes and t h e i r b u l k major, minor and t r a c e e l e m e n t a l c o m p o s i t i o n s n o r w i t h t h e i r major and minor e l e m e n t a l c o m p o s i t i o n s . A l s o , no c o r r e l a t i o n c o u l d be e s t a b l i s h e d between t h e a d s o r b t i o n a c h i e v e d w i t h t h e f l y ashes and s i z e o f t h e f l y a s h p a r t i c l e s . Only the carbon content of t h e f l y a s h c o u l d be r e l a t e d t o i t s o r g a n i c removal p r o p e r t i e s . The amount o f c a r b o n r e m a i n i n g i n t h e f l y ashes which have undergone f u s i o n a p p e a r s t o be a f a c t o r i n COD r e m o v a l . The amount o f c a r b o n r e m a i n i n g i n t h e Mine Mouth D, B l e n d and Nora f l y ashes on a d r y b a s i s was 2.5%, 1.8% and 1.0%, r e s p e c t i v e l y . The d e c r e a s i n g amounts o f c a r b o n r e m a i n i n g i n t h e f l y ashes c o r r e l a t e d w i t h t h e removal o f COD a c h i e v e d . The Mine Mouth D, B l e n d and Nora f l y ashes r e d u c e t h e COD i n a s h pond Sample D f r o m 12.8 mg/L down t o 1.0 mg/L, 2.0 mg/L and 2.5 mg/L, r e s p e c t i v e l y . These r e s u l t s a r e i n agreement w i t h t h o s e r e p o r t e d by Johnson e t a l . (5) and Mancy et a l . ( 6 ) , who showed t h a t f l y ashes w i t h h i g h o r g a n i c c o n t e n t a r e b e t t e r a d sorbers. A p p a r e n t l y , t h e h i g h b o i l e r t e m p e r a t u r e s e n c o u n t e r e d by t h e s e f l y ashes i n t h e m o l t e n s t a t e may l e a d t o a c t i v a t i o n o f t h e c a r b o n p r e s e n t i n t h e f l y a s h . A c t i v a t e d c a r b o n i s r e g u l a r l y used f o r t h e removal o f o r g a n i c s from waste s t r e a m s . The sobent c a p a c i t i e s o f t h e f l y a s h e s , i d e n t i f i e d i n t h i s i n v e s t i g a t i o n t o p r o v i d e t h e b e s t t r e a t m e n t , a v e r a g e o v e r 80 yg/g f o r t h e Cu and Zn, 66 yg/gm f o r Cd, 3.4 yg/gm f o r As and about 700 yg/gm f o r t h e o r g a n i c s . Experimental evidence suggests that the s o r b e n t c a p a c i t y f o r As may be i n c r e a s e d w i t h f u r t h e r washing o f t h e f l y ashes. These s o r b e n t c a p a c i t i e s were independent o f pH i n t h e range f r o m about 6 t o 10. A l s o , t h e r e m o v a l s o f Cd, Cu, Pb, and Zn were independent o f t h e i r i n l e t c o n c e n t r a t i o n i n t h e r a n g e s from 0.52 mg/1 t o 2.0 mg/1, 0.52 mg/1 t o 3.5 mg/1, 0.30 mg/1 t o 3.0 mg/1 and 0.56 mg/1 t o 4.0 mg/1, r e s p e c t i v e l y . G r e a t e r t h a n 75 p e r c e n t r e m o v a l s o f t h e Cd, Cu and Zn p r e s e n t i n t h e a s h pond samples were a c h i e v e d w i t h i n 15 m i n u t e s o f c o n t a c t t i m e between t h e f l y a s h and t h e sample. In addition, the r e s u l t s i n d i c a t e t h a t removal o f t h e above elements i n a s h pond samples c a n be achieved w i t h t h e f l y ash that o r i g i n a l l y leached these elements. The washed f l y ashes were o b s e r v e d t o have a s i g n i f i c a n t e x c e s s o f s o r p t i v e c a p a c i t y beyond t h a t r e q u i r e d t o t r e a t t h e element o r i g i n a l l y l e a c h e d from t h e f l y a s h ( s e e T a b l e V ) .


27. LISKOWITZ ET AL.

341


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F i g u r e 2. I n f l u e n c e o f Treatment o f A s h Pond E f f l u e n t w i t h Nora F l y A s h on R e s u l t a n t T r e a t e d E f f l u e n t pH.


36



342


27. LISKOWITZ ET AL. Table V.

343

Representative Element Leaching and Removals Exhibited by Selected F l y Ashes.

Fly Ash Samples Militant Blend Nora Militant Blend Nora Downloaded by MONASH UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: September 18, 1986 | doi: 10.1021/bk-1986-0319.ch027


Leaching Cd 2 12 .2 Removals 41 66 56

(ug/gm) Cu 30 .04 .4 (ug/gm) 34 83 70

Zn 12 .2 1 51 86 60

Conclusion The sorbent and leaching c h a r a c t e r i s t i c s of f l y ash can be related to operating temperatures i n the b o i l e r and to coal ash compositions that provide low ash fusion temperatures. B o i l e r temperatures that favor the fusion of the ash and maintain the ash i n the fused state reduce the amount of trace elements leached from the f l y ash and improve the sorbent c h a r a c t e r i s t i c s of the f l y ash for removal of these elements from ash pond effluents. In a d d i t i o n , the leachable amounts of each of the elements analyzed i n t h i s study can be c o r related with the f l y ash p a r t i c l e area and with t h e i r bulk composit i o n s i n the o r i g i n a l c o a l . No c o r r e l a t i o n could be i d e n t i f i e d between the sorbent c h a r a c t e r i s t i c s of f l y ashes and t h e i r p a r t i c l e s i z e and bulk, major, minor and trace elemental compositions, with the exception of the carbon content. Only organic removals, as measured by COD from ash pond effluent; could be correlated with the carbon content of the f l y ash p a r t i c l e s . Acknowledgments F i n a n c i a l support for t h i s work was provided by the U . S . Department of Energy, U n i v e r s i t y Coal Research Programs PETC, P i t t s b u r g h , Pennsylvania under Grant No. DE-FG22-80PC30231. L i t e r a t u r e Cited 1.

2. 3. 4. 5.

6.

Chan, P., Dresnack, R, L i s k o w i t z , J . W . , Perna, A. and Trattner, R. "Sorbents for Fluoride Metal Finishing and Petroleum Sludge Leachate Contaminant Control", EPA 600/2-78-824. Match (1978) "Sorbate C h a r a c t e r i s t i c s of F l y Ash", Volume II, F i n a l Report, U.S. D.O.E. Grant DE-FG22-80PC30231, August, 1983, page 212. Swingle, R . S . and Riggs W.M. "ESCA" Critical Reviews i n A n a l y t i c a l Chemistry 5. 267 (1975) Hansen, R . D . , and F i s h e r , G . L . "Elemental D i s t r i b u t i o n in Coal F l y Ashes", Env. Sci. & Tech., 14, pp. 1111-1117, 1980. Johnson, G . E . , Kunka, L.M. and Field, J. H., "Use of Coal and F l y Ash as Absorbents for Removing Organic Contaminants from Secondary Municipal E f f l u e n t s " , I & EC, Process Design and Development 4, 323-327, 1965. Mancy, K. H., Gates, W . E . , Eye, J . D . and Deb, P. K., "The Adsorption K i n e t i c s of ABC on F l y Ash", Purdue U n i v e r s i t y Engineering Bulletin, Ext. Ser. 117, pt. 1, pp. 146-160, 1964.

RECEIVED April 9, 1986 In Fossil Fuels Utilization; Markuszewski, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Sorbent and Leachate Characteristics of Fly Ash - ACS Symposium

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