Environmental II Session F Pickling Acid Recovery with Bipolar Membrane Technology Michael Prescott Lancy International, Inc. 181 Thorn Hill Road Warrendale, PA 15086-7527

American Electroplaters and Surface Finishers Society, Inc.

75th Annual Technical Conference - Los Angeles Environmental II

§ession F

Acid Purification and Recovery Using Resin Sorption Technology-A Review Mike Ceiakand Kevin Munns Eco-Tec Limited 925 Brock Road, South Pickering, Ontario L1W 2x9

A Comparison of Vacuum and Atmospheric Evaporative Recovery Equipment Raymond A. Baker Applications Engineer Corning Process Systems Big Flats. NY 14814

F.1

F-2

Absolute Reclamation of Water and Bath Through Use of New Reverse.Osmosis.Based System.. . , , . . , . . F.3 Ronald R. Rich, CEF Water Technologies Inc. -Minneapolis, MN

Source Reduction of Chlorinated Solvents: Aerospace Applications.. . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . F.4 Dr. Kathleen Wolf Source Reduction Research Partnership Los Angeles, CA

No Paper Available

Pickling Acid Recovery with Bipolar Membrane Technology Michael Prescott Lancv International. Inc. 181 iho rn Hill Road Warrendale, PA 15086.7527

Some 'Unsolved' Problems in Closed Loop Nickel Recovery Lyle Kirman Kinetic0 Inc. 10845 Kinsman Road 1 Newbury, OH 44065

A New Technology for Wastewater Treatment Using immobilized Algae Patrick M. Nelis and Dennis W. Darnall BioRecovery Systems, Inc. 4200 S. Research Drive P.O. Box 3982 Las Cruces, NM 88003

.. ; . . . . . F-6 ' ~'

'2

F.7

Mr. Michael Prescott Lancy International, Incorporated

18 1 Thorn H i l l Road Warrendale, PA 15086-7527 TeleDhone: (31 2) 772-0033

T i t l e : Pickl ing Acid Recovery w i t h Bipolar Membrane Technology

ABSTRACT

Bipolar membrance technology of fers an ef f ic ient and economical approach Tor the recycle of spent industr ia l acids. The recovery system nucleus Is a Datented membrane stack which provldes v i r tua l ly complete regeneration o f spent acids.

TRls waste acid recovery system i s part icular ly applicable in specialty sr?ei rilanufact.iirinq lor recovering spent pickle l iquor acids (such as h~drof iuor ic /n i t r ic 'ac id mixtures) fo r reuse; providing an environmentally sound al ternat ive to \"e treatment and/or disposal o f spent acids, resul t ing in the reduction of long-term l iab i l i t y .

*This paper i s an Edited Version of !'Aquatech Systems: An Economic and Environmentally Sound Commercial Process to Recycle Spent Pickle Liquor", By Carolyn Hutter-Byszewski, Andrew Bogeatzes of Al l ied Signal Corporation and Harold Moore of Washington Steel Corporation

-1-

INTRODUCTION

An electrodialytic membrane process has been developed which

economically separates salt solutions into their constituent acids and

bases.

regeneration offers an economic, environmentally sould alternative to

dumping.

disposal and the ever growing contraints being imposed on dumping.

This technology when applied to waste pickling acid

The steel industry is keenly aware of the soaring costs of

Resource recovery and waste minimization technology is the practical

solution.

essentially closed loop process with minimal chemical makeup

requirements and potentially no disposal costs.

It transforms the once-thru pickling process into an

The technology has been successfully piloted at the Washington Steel

facility in Washington, Pennsylvania, for over two years, resulting in

the design and construction of the first ccmmercial plant. This plant

will regenerate over 1.5 million gallons o f spent pickle acid per year

into reuseable HF/HNO3 acid as well as eliminate the threat of the

ever increasing disposal cost - now estimated at $0.55/gal. ($0.86

million dollars annually).

We will provide a brief background on the Bipolar Membrane technology

as it applies t o waste acid recovery, as well as review pickling

-2 .

chemistry t o more c l e a r l y r evea l t h e b e n e f i t s of b i p o l a r membranes

over competi t ive d i f f u s i o n d i a l y s i s or ion exchange adsorpt ion

technologies .

performance and f i n a l l y , a complete review of t h e Commercial P lan t

design and process flow c a p a b i l i t i e s concluding with an economic

a n a l y s i s w i l l be presented.

We w i l l touch on h i g h l i g h t s of t h e p i l o t p l a n t

TECHNOLOGY BACKGROUND

The b ipo la r membrane technology is an e l e c t r i c a l l y dr iven membrane

process , s i m i l a r t o e l e c t r o d i a l y s i s i n t h a t it employs conventional

ion exchange membranes t o s e p a r a t e i o n i c a l l y charged spec ie s i n

s o l u t i o n , bu t d i s t i ngu i shed by t h e unique water s p l i t t i n g c a p a b i l i t i e s

of t h e b i p o l a r membrane.

Under an e l e c t r i c a l p o t e n t i a l , conventional monopolar ion exchange

membranes a r e capable of s e l e c t i v e l y t r anspor t ing charged spec ie s

ac ross t h e i r boundary, t hus e f f e c t i n g separa t ion . Cation membranes

have f ixed negat ive charges which al low t h e t r a n s p o r t of p o s i t i v e l y

charged ions (cations) such as K+ t o pass a c r o s s them, whi le r e j e c t i n g

negat ive ions (F igure 1). Conversely, anion membranes have f ixed

p o s i t i v e charges which al low t h e t r a n s p o r t of nega t ive i o n s (anions)

such a s F- or NO3 t o pass ac ross them, whi le r e j e c t i n g p o s i t i v e l y

charged ions.

'3'

Electrodialysis For Concentrating KF

Water 1.1 r+ Concentrated KF

0

Anode ' @

i-

@ Allied Cation Membrane 0 AMV Anion Membrane

@ Cathode

Figure 1

The b i p o l a r membrane is a unique ion exchange membrane i n t h a t i t is

composed of two d i s t i n c t l a y e r s o f oppos i te ly charged ion exchange

ma te r i a l (Figure 2 ) .

Unlike conventional monopolar membranes, t h i s novel membrane is

capable of d i s s o c i a t i n g water i n t o hydrogen (H+) and hydroxyl (OH-)

i ons under t h e in f luence of an e l e c t r i a l po ten t i a l .

c a p a b i l i t i e s o f both monopolar and b ipo la r ion exchange membranes

g ives t h e system unique advantages (Figure 3).

s o l u t i o n t o t h e s t ack along with M: c u r r e n t t o t h e e l e c t r o d e s r e s u l t s

i n t h e conversion o f an aqueous s a l t so lu t ion such a s KF/KN03 into t h e

base KOH and t h e mixed ac id HF/HNO3.

Combining t h e

Supplying s a l t

.

RECYCLING SPENT PICKLING ACID

Conventional d i sposa l of spent acids gene ra l ly inc ludes n e u t r a l i z i n g

t h e waste ac id with lime (Ca(OH2), p r e c i p i t a t i n g and f i l t e r i n g ou t an

i n s o l u b l e CaF2 s a l t complexed with Fe(OH)3 cake for l a n d f i l l and

d ischarg ing a Ca(N03)2 s a l t s o l u t i o n to the.waterways.

producers must pay h igh costs t o d ispose o f va luable resources l i k e F-

and NO3- as well a s burden themselves with t h e l i a b i l i t i e s of

t r anspor t ing and d ispos ing of l i q u i d hazardous wastes - a t r i p l e c o s t

s i t u a t i o n .

Here steel

Bipolar Membrane Construction and Operation

-+H+

Figure 2

Waste Pickling Acid Application Three Compartment Cell

Depleted KFIKNO,

I

H20 KFIKNO, Hi0 SOLN

Legend 0 Bipolar Membrane @ Callon Membrane Q Anton Membrane

Figure 3

Alternatively, incorporating the bipolar membrane process with a

potassium hydroxide (KOH) neutralization results in a virtually closed

loop resource recovery scheme as illustrated in Figure 4.

neutralization to pH 10 differs fran Ca(OH12 neutralization in that it

results in a metal hydroxide precipitate free of fluoride canplexes,

while the fluoride and nitrate values are retained in solution as the

soluble salts KF and KNO3.

yields a metal hydroxide cake of Fe, Ni, Cr hydroxides which with

further drying and processing is suitable for recycle to the smelter.

The filtrate is suitable for feed to the bipolar membrane.

through the driving force of a direct current, the KF/KNO3 salt is

converted to 8-10 w t . % (1.5N) KOH and a mixed acid HF/HNO3 of similar

canposition as the waste acid (typically 2.5 - 4N) (Figure 5). KOH base in recycled to the neutralization step while the fresh

product acid is sent to the pickling tubs.

The KOH

Conventional plate and frame filtration

Here

The

PILOT PLANT PERFORMANCE

In October 1984, Washington Steel Corporation piloted this technology

for waste acid reclamation.

intermittently since March 1985, for over two years testing various

facets of the process including: resource recovery efficiency,

operating conditions, membrane life expectancy, system performance,

filtrate and produGt quality and energy consumption.

The pilot plant has been in operation

x -

STAINLESS STEEL PICKLE LIQUOR REGENERATION

CLEAN HF/HNO, * STAIHLESS STEEL PlCKLlND

OPEIIATIOt4

PICKLE L i a u o n

S P E N T

PICKLE LIQUOR --P 1 - - t i A Z A R D O U S

WASTE D I S P O S A L

r/

.

FIGURI? 4

3 0

m 0 L[:

4-

N

To v e r i f y t h e recovery r a t e s of f l u o r i d e s , n i t r a t e s and potassium by

our process , a material balance was performed around t h e p i l o t p l an t .

A s shown i n Figure 6 , t h e streams en te r ing t h e b a t t e r y limits a r e

waste ac id , makeup water and KOH, whi le those e x i t i n g inc lude product

ac id and f i l ter cake. The r e s u l t s of t h e o v e r a l l ma te r i a l balance

show t h a t t h e system c o n s i s t e n t l y recovered:

93% of a l l f l u o r i d e va lues both complexed and free 99+% of a l l n i t ra te va lues 96+% of a l l potassium va lues

The ma te r i a l balance i n Table 1 a l s o i l l u s t r a t e s t h e very s u b s t a n t i a l

reduct ion i n waste mass.

approximately 10,000 l b s . of hazardous l i q u i d waste.

One thousand ga l lons o f p i c k l e l i q u o r is

With t h e b i p o l a r

membrane system, t h e cake byproduct reduced t o a 2640 l b s . cake

i n i t i a l l y a t 40 wt .% s o l i d s .

i n a r ecyc lab le iron hydroxide cake of 660 lb s .

reduct ion i n waste mass o r a 15 f o l d volumetric reduct ion, a s well a s

t ransformation of waste in to a more e a s i l y managed form s u i t a b l e for

r ec ycl ing .

Further drying t o 90 wt.% s o l i d s results

This r ep resen t s a 94%

Optimal opera t ing condi t ions are l i s t e d i n Table 2 a long with normal

ope ra t ing ranges f o r each c r i t i c a l parameter.

parameters such a s c u r r e n t dens i ty , temperature , and vol tage provide

ex tens ive system f l e x i b i l i t y and 25% turndown c a p a b i l i t i e s , with

l i t t l e effect on c u r r e n t e f f i c i ency .

Varying process

L

I I I I -

W

The p i l o t p l an t operated cont inuously for a 170 day per iod t o allow a

comparative s tudy o f membrane performance.

performance tests were performed on t h e membrane samples a t zero, 90

and 170 days. The results of t h e tests t abu la t ed i n Table 3 show an

expected p red ic t ab le rise i n membrane vol tage over time with no

s i g n i f i c a n t effect on membrane permselec t iv i ty or e f f i c i ency .

on t h i s 0.3 vo l t /6 month rise i n membrane vol tage , a one year l i f e was

projec ted .

Q u a l i t y con t ro l

Based

P la te and frame f i l t r a t i o n c o n s i s t e n t l y produced a feed q u a l i t y

acceptab le t o t h e c e l l s t ack with Cr, Fe and N i i o n s less than 3 wppm.

Product ac id composition and s t r e n g t h were maintained i n r a t io s

propor t iona te t o t h e waste a c i d provided.

t o produce one ton HF/HNO3 (4/8 w t . % ) plus corresponding co-product

1.5 ton KOH was measured a t 2000 KWH/Ton HF/HNO3

F i n a l l y t h e power requi red

BIPOLAR MEMBRANE ADVANTAGES

To f u l l y apprec i a t e b ipo la r membrane's advantage over t h e

a l t e r n a t i v e s , such a s d i f f u s i o n d i a l y s i s , ac id r e t a r d a t i o n techniques

and ion exchange adsorpt ion methods, a review of p ick l ing ba th

chemistry is required.

environment with s o l u b i l i t y limits, concent ra t ion swings and phase

changes.

i n p i ck l ing , it is t h e F- ion t h a t i s t h e aggress ive p i ck l ing agent

The p i c k l e b a t h is a ccmplex chemical

It is widely agreed t h a t whi le both F- and NO3- va lues a i d

- 1.3

TABLE 1

Washington Steel Corporation 100 Day Pilot Run - Overall Material Balance

Lbs. Material Handled, Lbs. - + Stream Gallons - F- N 03- K +

1 Waste Acid 1000 520 800 2 Recycle Base 2450 190 1750 3 . Acid Product 1800 486 800 4 Cake 2640 34 0 70

Overall Recovery F- 93% N 0,- 99+% K + 96%

TABLE 2

operatinu Parameters

Optima 1

80 2 Current, AMPS/FT

volts/Cell Initial Final

Products Acid, Normality Base, Normality Salt , Normality

2.0

3.0 1.5 0.1

Average Efficiency, % E O

Temperature, DEG F 90

Range

60-90

2.0-3.0 4 . 0

2.5-3.5 1.0-2.0

0.01-0.2

70-90

75-110

TABLE 3

Washington Steel Corporation Pilot Test Review

Membrane Analysis

Manu- Type facturer Unlts Nominal 100 Days 170 Days -

( w m w ) Bipolars Allied Volls 1.1 1.29 1.4

Anlon. RAI 4035 ohm-cm2 2.3 2.7 2.2

@I 1 OmA/cm2 Cation Allled ohm-cm2 6.0 6.9 6.8

which removes oxide fi lms and conver t s them to complexed metal

f l uo r ides .

moderating agent which retards p i t t i n g o f metal under layers .

n i t r a t e s a l t s remain i n so lu t ion a s d isso lved s a l t s .

then has t h r e e key ing red ien t s ; t h e d i s soc ia t ed n i t r a t e s whether s a l t s

o r ac ids , t h e d i s soc ia t ed free a c i d i c f l u o r i d e s and t h e complexed

metal f l uo r ides .

dep le t ion , t h e complexed metal f l u o r i d e s can r ep resen t 50 up t o go+%

of t h e f l u o r i d e values.

The n i t r i c ac id functions p r imar i ly a s a f a c i l i t a t i n g

The

The spent ba th

Depending on t h e ba th composition and t h e extent o f

Diffusion Dia lys i s , ion exchange adsorp t ion or a c i d r e t a r d a t i o n

techniques recover only t h e free n i t r a t e s and f l u o r i d e s and a r e unable

to recover t h e ma jo r i ty of t h e f l u o r i d e s which are t i e d up a s

complexed metal s a l t s .

n e u t r a l i z i n g r e a c t i o n s t e p breaks t h e ccmplex f l u o r i d e salts t o form

so lub le sal ts . F luor ide and n i t r a t e anions and metal c a t i o n balance

a n a l y s i s of waste ac id using I C P methods confirm t h i s .

is 6-7 times more va luable than t h e ni t ra tes , t h i s recovery process

r e a l i z e s p ropor t iona l ly h igher savings.

With t h e b ipo la r membrane process , through its

Since f luor ide

F i n a l l y , F igure 7, research publ ished by Dr. Albert Krepler show t h e

increased metals s o l u b i l i t y a t t a i n a b l e a t lower excess HF

concentrat ion. F igure 7 f u r t h e r i l lustrates how inc reases i n ac id

concent ra t ion v i a a c i d sp ik ing midway through t h e p i ck l ing process

17

I 7 0 0 0 0

c 0 e4 -t M

0 0 (D In

0 0 m b

0 - 0 r

':

0 0

' W

w w [I: 3 I-

W 0- I W I-

0 9

2

O f

0 N

results i n s ludge formation.

concent ra t ion lowers s o l u b i l i t y limits r e s u l t i n g i n ion f l u o r i d e

complexes p r e c i p i t a t i n g .

t o d e l i v e r a d i l u t e mixed ac id product t o t h e p i ck l ing tubs should

s u b s t a n t i a l l y reduce s ludge formation.

Sudden inc rease i n excess a c i d

The a b i l i t y of t h e b ipo la r membrane system

Minor ba th concent ra t ion adjustments can b e accomplished with

a d d i t i o n s of HF and HNO3 still requi red due t o drag ou t and vapor

lo s ses .

COMMERCIAL PLANT PROCESS FLOW

Figure 8 is a block diagram showing t h e commercial process f o r t h e

recovery o f spent p i c k l e ac id . Step 1 c o n s i s t s of t r e a t i n g t h e used

ac id (metal s a l t s p lus small amount of free n i t r i c /hydro f luo r i c ac id )

with potassium hydroxide t o form t h e potassium n i t r a t e / f l u o r i d e s a l t s .

A t t h i s po in t t h e meta ls ( i ron , c h r m e , n i c k e l , etc.) present i n t h e

spent p i c k l e ac id are p r e c i p i t a t e d ou t a s metal hydroxide s o l i d s .

s o l i d s (stream 3) a r e removed from t h e s a l t s o l u t i o n using a f i l ter

p r e s s ( s t e p 2) before treatment o f t h e s a l t solution i n t h e b i p o l a r

membrane cel l s t ack system.

The

I n t h e b ipo la r membrane system ( s t e p 4) t h e potassium n i t r a t e / f l u o r i d e

s a l t s a r e converted back t o t h e i r r e s p e c t i v e ac id and base components

- HF/HN03 (5) and KOH (6).

-19 -

T3-l - 0 D 3-a e-

n h m

A

I

- sr-

d

P n a

7 I n

D- d 1 r

m -I

CI 7 . * R

0

2 6-

wl A

Ln Wash Water a 4 ~ r m -h m o -3 . d

n ' Concentrated Salt 5 :

. d m E 7 -

VI R

The b i p o l a r membrane process is e s s e n t i a l l y a c losed loop system. The

depleted s a l t so lu t ion from t h e b ipo la r membrane (s t ream 7 ) is t r e a t e d

i n an e l e c t r o d i a l y s i s (ED) system containing monopolar membranes t o

upgrade i t s concentrat ion.

b ipo la r membrane c e l l s t acks f o r f u r t h e r ac id and base recovery.

water recovered i n the ED system is used t o wash t h e f i l t e r p res s cake

(stream 9 ) .

s o l i d s and b r i q u e t t i n g , is s u i t a b l e f o r recyc le .

The concentrated s a l t i s re turned t o t h e

The

The metal hydroxide cake, w i t h further drying t o 90 wt.%

Small amounts of water (stream 10) and KOH (s t ream 11) a r e added a s

make-up for t h e KOH and water l o s t i n t h e wet filter cake.

Small amounts of hydrogen (12) and oxygen (13) gases form a t t h e

cathodes and anodes a s a r e s u l t o f the e l e c t r o l y t i c r e a c t i o n s tak ing

place. An e l e c t r o d e rinse s o l u t i o n is pumped through t h e e l e c t r o d e s

to sweep up t h e gases which a r e vented off .

EQUIPMENT DESIGN BASIS

The b a s i s used f o r t h e p l a n t design is shown a s Table 4.

mi l l i on g a l l o n s of waste ac id w i l l be recycled, recovering 90 - 95% of

the f l u o r i d e va lues while consuming less than 428 kw of energy.

Over 1.6

The major equipment f o r t h e process i s l i s t e d on Table 5.

l a r g e s to rage tanks and n e u t r a l i z a t i o n tank a r e loca ted outs ide .

The t h r e e

0 PLANT CAPACITY - 1.65 M I L L I O N GALLONS OF W E N 1 PICKLE ACID PER YEAR

0 POWER REQUIREMENT - MAXlflUM OF 128KW FOR MEMBRAI~E CELL STACKS

0 ACID RECOVERY - 90 - 95%

0 FILTER CAKE - 70 CU. FT. PER SHIFT

0 WATER MAKEUP - I GAL./MIN

0 UASE MAKEUP - 200 LBS./DAY (45% KOH)

TASLE: 5

Commercial P l a n t

Mai o r E a u i D m e n t

a THREE STORAGZ TANKS - 10,000 TO 15,000 GAL.

0 TWO STORAGE TANKS - 3,000 GAL. EACH

0 NINE PROCESS TANKS - 200 TO 600 GALMNS

a NEUTRALIZATION TANK/AGITATOR - 8,000 GALLONS

0 HEAT EXCFLANGE2 - 500 FT2

a CHILLER - 1,000,000 BTU/HR.

0 FILTER PRESS - 82 CU. FT.

TWO MEMBRANE STACK PRESS FRAMES - 3' X 13' EACH

0 ONE K E M B W E STACK PRESS F R U I - 3' X 10'

0 TWO POWER SUPPLIES - 227 KW EACX

0 POWER SUPPLY - 26 XW

0 SIXTEEN PUMPS - 1 GPM TO 120 GPM

The smaller s to rage tanks and t h e o the r remaining equipment a r e

housed i n a 70 f t . x 32 f t . bui lding. The total p l a n t a r ea is

approximately 3500 ft2.

With t h e except ion of t h e f i l t r a t i o n s t e p , the process i s h ighly

automated.

batch-volume of spent ac id feed and a pH c o n t r o l l e r for the add i t ion

of t h e base.

The n e u t r a l i z a t i o n s t e p i s a batch process and inc ludes a

The b ipo la r membrane and ED systems and assoc ia ted equipment a r e

semi-continuous and a r e ccmputer process cont ro l led . An automatic

t i t r a t o r is used t o c o n t r o l t h e concentrat ion of t h e product ac id .

conduct iv i ty c o n t r o l l e r is used i n t h e ED sys t en , which upgrades t h e

concentrat ion of t h e depleted sa l t from t h e b ipo la r membrane cell

s t a c k system.

A

I t i s expected t h a t t h e present ope ra to r s fran the exisitng adjacent

water t reatment p l an t p lus one add i t iona l operator will be used t o

ope ra t e the p l a n t which w i l l normally be operated s i x days per week.

BENEFITS SUMMARY

Bipolar Membranes o f f e r s many advantages i n waste ac id regenerat ion.

Table 6 itemizes p l a n t economics spec i f i ed for the Washington Steel

Pro jec t . Key b e n e f i t s inc lude 93% f l u o r i d e recovery inc luding both

-2.q -

TABLE 6

Pickle Liauor Recovem Caoital and Ooeratina Costs

Basis :

1.6 x lo6 Gals/ Yr. of Spent - Pickle Liquor Containing 5 wt% F-, 10 wt% NO3 8000 Hrs./Yr. One Year Life for Cell Assembly Acids Recovered (Net): 350 T/Yr. of HF

740 T/Yr. Of HN03

Total Battery Limits Capital for Plant Aug. ' 87 Costs ~ l l costs in US Dollars

Ooeratina Cost Summarv

Raw Materizls

Makeup KOH @ $540/Ton Filter Aid @ $3OO/Ton cell Maintenance Electricity @ 5 /KwII Cake Processing @ $11O/Ton Other Maintenance Labor & Supervision Depreciation @ 10% Taxes & Insurance @ 2% Total Operating Costs

Product Credits

HF @ $1,365/Ton HNO @ 205/Ton Was2e Material @ $0.55/Gal. Total Credits

Savings RO I

6 2.2 x 10

36,000 14,000 300,000 128 I 000 229,000 78,000 40,000 220,000 44,000

I, 089 I 000

480,000 152,000 880,000

1,512,000

432 I 000 19%

3.2 Yrs. Payback

\

free and complexed fluorides, 99+$ recovery of nitrates, a 94%

reduction in waste mass which is transformed into a solid hydroxide

cake suitable for recycle and the elimination of liquid waste

handling.

can potentially save about $650 per 1000 gal/P.L. above operating

costs by taking credit for only disposal cost savings and recovered

resource values.

On a basis of 1000 gallons of pickle liquor, the process

Some of the more subtle benefits such as increased plant safety by

minimizing concentrated acid handling and eliminating liquid waste

disposal must also be considered.

- ,Ab-