Electrodialytic recovery process of metal finishing waste water

Des&nation, 32 (1980) 383-389 8 Ekevier Scientific Publishing Company, Amsterdam-RintedinTheNetherlands

ELECTFUJDIAL.Y!FIC RECOVERYPRCCESS

s. ITDI, I. NAKAMURAAWD

OFMETALFIWISHIWGWASTEWA'I.ER

T.KAWABARA

Chemicals Division of Asahi Glass Company, Ltd., Tokyo (Japan)

SUMMARY

Astudy nickel

for electrodialytic

electroplating process.

recovery of waste water was made in the Ey the use of the electrodialysis

equipment.

rinsing waste water is desalted and reused for rinsing, while nickel salt is concentrated and recovered to the plating bath. electrodialysis

Although conventional

equ.ipmMt is able to apply in this process. proper pretreat-

ment and suitably designed operation condition of the electrodialysis

unit

are needed for a long term stable o_Deration.

Electrodialysis

technique , which was developed mainly for sea water

concentration and water desalination, has long developing history of over a qnarter century and has been worldwidely

commercialized.

Recently,

there

are many commercial scale applications in waste water treatment and one of the tYpical example is the treatment of metaI finishing waste water, Special features of the electrodialysis

technique are summar ized as

foU.ows. l

Electrolyte solution is concentrated to 20% or more, according to the

l

Electrolyte solution is desalted to 100-200

Condition of

feed solution.

*Concentration

ppm or less.

ratio of the concentratestreamanddiluate

streamis

attain-

ed to 100 in an electrodiaIyzer. l

Electrolyteis

separated from organic nonelectrolyte

in aqueous solution.

* In neutral, acidic or slightly basic condition ,ion-exchangemembraneis durable for a long Period without any change of electrochemical properties. By these properties, dilute waste water of the electroplating process is advantageously rinsingwaterandto

treated by the electrodialysis recovervaluable 383

technique to reuse as the

constituents.

384

IT01 ET BL

Above all, nickel cially,

because

the waste

and

recovery

electroplating ously

of water

and

pollution

ELECTRDDIALYSIS

Outline

On sewage salt

salt

stage

the

other

after

the

from

hand,

salt

In nickel

to be economical.

containing is quite

is fairly

is considerably

nickel

salt

essential

is continu-

for

the

preven-

WASTE

rinsing

final-stage applied

plating

of

the bath

liquor.

rinsing

In this

and

I

more larger

Pretreat-

Then

of the

waste

water

higher

also

above

._

-e,

bath,

bath.

control

to improve

1

nickel

volume

rinsing

.te=

the

to the plating

rinsing

t

in

fed back

bath,

for the

bath

is used is

final-stage

first-stage

rinsing

nickel

metal

water

treatment.

to the plating

suitably

PLATING

waste

of holding-up

in the

liquor

and

commer-

Process

rinsing

adjustment

acidic

to recover

problem-

plural-stage

first-stage

water

treatment

is able

or nickel

is supposed

waste

water

OF NICKEL

of the

Usually

rinse

water

compound

of nickel

waste

waste

is slightly

nickel

factory,

exhausted

tion

water

Furthermore,

dissociated. expensive

electroplating

the

efficient the the

mentioned

Electrmdialys~s

of

feed-back loss

of Ni-ion

disposal

unit

and

the

is discharged

electrodialysis

concentration

for

concentration the

amount

process

bath

to the of nickel

of

the

of nickel technique in the

problem.

I

Exchange

Exchange

Collmm

COlUmn

i

ment

& ,K

lst-stacre

Fig_

1

Electrodialysis Process

Nickel

Electroplating

is first-

Waste

Water

Recovery

IT01

ET AL As

the

preferable

electroplating for

is connected

with

Although

the

desalination

ing

precautions

*Current

model

are

is lower

moreover

nickel

than

salt

hydroxide

by

the

important

to prevent

the

in

has

slight

the

is shown

design

which for

density

tendency

of

hydrolysis

of pH

value.

SO,

scale

formation

in

organic

cases,

the

for

follow-

conditionr sulfate

or nickel

chloride

to form

current

liquor

and

nickel

density

originated causes

Topreventorganic

pretreatment

for

purpose,

is very

electrodialyzer-

matter

bath

pretreatment

is designed

or sodium

the

is

unit

1,

this

of nickel

sulfate

raise

membrane-

designed

required in Fig,

to apply

operation

electrodialysis

of operation

of sodium

electroplating

anion-exchange

with

electrodialyzer is able

current

that

In some

Antifouling

bath

the

Limiting

density

specially

for

the

rinsing

water

needed

and

process

of the

of brackish

chloride

additives

of the

continuous

continuously,

equQanent,

first-stage

scheme

standard

the

is operated

electrodialysis

General

equipment.

l

the

fouling

the

removal

was

performed

from

organic

some

fouling the

of

of organic

of

membrane.

electrolyte

is required.

operation

of Electrodialysis

First waste

liquor

unitwas 1.5

batchwise from

and

commercial

process

of

voltage

the plating

line. and

final

-positions

scale

equipment

an automobile

in two-stage

from

operation

the plating

in constant

Initial

Nextly,

formed out

taken

oprated

A/dm'.

ting

of all,

Equipment

method bath

and

parts

Laboratory initial of

was

factory.

In

together

with

use

of rinsing

electrodialysis

are

shown

set at

in the

in Table

nickel

the process,

l.lkg/hr

plated

the

scale

currentdensitywas

liquor

operated

approximately

by

product

rinsing

of Ni-ion

was

in normal

1.

electroplawas

taken

operation.

TABLE1

Chemical Composition of &.wr Nickel Electroplating

by Batchwise

Eleclxodialysis

of

Rinsig

in

Component

NiSO

4

NiC12 E3Bo3

Feed Stream

(g/l)

Concentrate Stream

12.47

133.4

( " 1

1.81

29-7

( " 1

<3_I8)

TotalNi("

1

S-2

Dilute Stream

1.27 0.039 (2.87)

69.1

0.50

Waste

per-

ITOI~AL

386 Outline

of

This stage

that

"as

bath

desalted

the

was

of

operated

water

had a role

water

having

was

5 g/l

less but

of the

when

It was

than

0.5

rinsing

observed

in the

of Ni-ion

operation

of the

reaSon,

curr ent

density

of 1.0

between

the

rinsing

the plat-

made

level

throughout

while

bath

TABLE

Equiment

and

Model

Electrodialyzer Ion-Exchange Size

electrodialysis

O-49

of Membrane Membrane

Installed

No.

Membrane

Area

of Membrane

in Automobile

DU-III

Selemion

Membrane

Effective

Flow

Installed

CMV

& Selemion

m x 0.98

0.336

AMV

m

m2/sheet

40 pairs

PtirS

2.0 mm

Distance

Velocity

3.0

cm/set A/dm2

Current

Density

1.0

Maximum

Voltage

50 v

Feed

to

ED

3 m3/hr

Concentrated Stream [To Plating Bath] 12.4 l/hr (Ni2+ 83 g/l) Fig.

2

(Ni2+

5 g/l)

Diluted

Stream

3 m3$$2+

-2-k ion and water Balances NI Continuous Electrodialysis

in ProCeSS

the

rinsingwaste

2. of Electrodialysis Plant

to

equipment

unit.

Main Specifications Parts Electroplating

test

by batchwise

be preferable

electrodialysis

A/dm2

first-

of

preliminary

was

would

in desired

by

in

content

this

By

continuously

specifications

concentration

bath

process.

recirculated

main

Ni-ion

g/l

continuous

the plating constant

1 and

2.

ofmaintainingNi-ion

84 g/l.

operation,

i+ Fig.

in Table

approximately

concentration

operation

is shown

is shown

approximately

electrodialysis keep

process

equipment

rinsing

ing bath

the

unit

electrodialysis

4-65

g/l)

IT01

El! AL

387

Material.

balances

the

operation,

the

concentrated

without unit

any

was

over

of

90%

80%

and

salt

anddiluted

As

and

volume

of nickel

liquor

trouble.

over

liquor

was

Ni-ion recovered

liquorwas

a whole,

current

electricity

are

efficiency was

in Fig.

to the plating

reused

consumption

shown

By

bath

as

rinsing bath

in the of the

2.

electrodialysis

approximately

2 kWh/kg

Ni-ion. For ment

originated ed

that

for

term stable

along

eguipment

for

from

main

DESIGN

in the

AND

density

in Table

TABLE

3.

ion

Current

amount

bath

electrodialyzer

Relation between BathLiquor

Main

Concentration

for

plating

commercial

of Ni-ion

bath,

pretreat-

matter

and

it was

had

to be

is kept

Current

witbin

of

Density

in lst-stage

the plating

In the

is determined the

and

nickel

5 -7 on

the

.2+ ion _

Specifications

Take-out

Rate

FG.nsing Bath

basis

test shown

Concentration

(kg/m2-day)

concentration

applied

of are

(g/l)

of Electrodialysis

Eguimt

of NiS04

ion

results

Electrodialysis

Effective

Model

Unit

InstalledNo.

ofmembrane Membrane

%urrentBensity

Area

Rinsing

Bath

4,

in Rinsing

3-5

5-7

0.8

1.0

0.92

1.47

1.84

89 kg/day

in First-stage

as

in Table

0.5

90 %

Concentration

current

2-3

in Conceptual

RecoveryFiateofNiB04 Ni2+

studied

is approximately

Ni-ion

g/l , and

equipment

Ni-ion

bath

plant,

TABIJX 4. Main

consider-

electroplating

(A/dm2)

BecoveryBateofNr

the

organic

eguipment

scale

from

condition.

specifications

Applied

Density

to the

to install basic

ESTIMATION

operation

rinsing

3_

needed

of weakly

of the pretreatment

is made

take-out

to the

sh-

Ni2+

chemicals

COST

in s tandard

first-stage

of a kind

proce&_

design

in which

34 kg/day

dosing

plating

Conceptual plant

the

it was

operation,

removal

specifications

individual

CONCEPTDAI.

the

5-7

g/l

DU-III sopairs 16.8

aI2

1.0

A/am2

Design

IT01

388

BY ion

tie

operation

is recovered

4.6 m3/hr

of rinsing

In addition profit

plant

wwo the

water

salt

recovery

are

3,460

purchase

electrodialysis bath,

in

of water Table

this

process, and

in a month.

equipment, at

tie

same

to the

rinsing

reuse,

there

over

30 kg/day

time, bath.

is another additional

5 shows

approximate

evaluation

In this

estimation,

working

monthly

of Ni-

approximately

recovery

of

days

of

salt is

of nickel

saving of the cost As the result, 6H 0. 4 2 in this pl&nt is approximately Y892,810 in a

kg as NiSO

of nickel

and

is recycled

recovery,

20 days

ximately

the

to the merit

of nickel

nickel. salt the

of

to the plating

ET AL

salt

l

for

month.

NICKEL

SALT

RECOVEXY

In spite rinsing

T3BLE

IN FINAL-STAGE

of water

bath

reuse

as mentioned

and

RINSING

WAS!IE

nickel

salt

small

amount

above,

recovery

in the

of nickel

first-staqe

salt

is taken

out

5.

Cost Estimation Electroplating

of Electrodialytic Process

Recovery

of

Ffinsing Waste

Water

Nickel Recovery Rate (as NiSO4 - 6H20) Electricity

Consumption

(

"

in Nickel

3,460

)

kq/month

0.7

kWh/kg

_________________-_-__--__-_-______~~~___--_-~~~--~~~----------------Equipment

Installation

Electricity Purchasing

Unit

cost

Y15 Million

Cost

@lO

Price of Nickel

(as NiSO * 6H20) ____--__-_----------_------__-----_------_--------------Profit

Salt

@360

s/kWb g/kg

of Nickel Salt Recovery

360 g/kg x 3.460 kg/month = 1,245,600 gfmonth Funning cost Electricity Maintenance

10 FfkWh x 0.7 kWh/kg h Consumable

Item

c15,000,000 Amortization

kg/month

=

24,220

*/month

f 12 month

=

37,500

g/month

x 3,460

(Annually

3%)

x 0.03

(7 years) ~15,000,000 4 7 Year e-12 month = 178,570 Y/month

Interest

(Annually 9%) Y15,000,000

x O-09 +- l2 month

Running cost Profit

lbt.iiL

= 112,500

V/month

352,790 #F/mona 892,810 s/month

IT01 to

389

ET AL the

final-stage rinsingbath

togetherwiththeplatedproduct.

Nickel

salt contained in the final-stage waste water is able to remove by means of conventional ion-exchange technique as shown in Fig. 1.

Demineralized water

is reused as rinsing water, and removed Ni-ion is exhausted from cationexchange column by the regeneration of the resin.

To recover Ni-ion frcm

acidic regeneration waste liquor, dialysis technique is suitably applied to separate excess sulfuric acid from nickel sulfate solution.

Lleacidified

nickel sulfate solution is used in the plating bath to keep the holding-up volume of the bath against the evaporation of water from the bath liquor.