ELSEVIER Desalination 180 (2005) 163-172

DESALINATION

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Development of an ion exchange system for plating wastewater treatment

Tae-Hyoung Eom a, Chang-Hwan Lee a, Jun-Ho Kim b, Choul-Ho Lee a* aDepartment of Chemical Engineering, Kong ju National University, Kong ju, 314-701 South Korea

Tel. +82 (41) 8528638; Fax +82 (41) 8582575; e-mail: chlee@kongju.ae.kr bRR C/NMR, Kong ju National University, Kong ju, 314- 701 South Korea

Received 13 July 2004; accepted 29 November 2004

Abstract

Ion exchange technology was applied to this study to treat nickel ion from plating wastewater which contains heavy metal, bringing environmental problems such as chromium, zinc, copper, and lead. To separate nickel ion from wastewater, the nickel recovery unit (NRU) used a column packed with strongly acidic cation resin. The leak of the ion appeared when rinse water that has a concentration of 1.8 g-Ni/L-distilled water flowed into the NRU as much as 20 times the bed volume. At this time, the capacity of resin packed in the column was 1.7 meq/ml and over 99% nickel ion was removed. Sulfuric acid was employed with a reagent in order to regenerate nickel ion from the resin adsorbed. Nickel ion recovered by sulfimc acid was obtainable up to 120 g-Ni/L. The concentration of sulfuric acid was 2N and space velocity was 2/h. Acid retardation unit (ARU) experiment could be accomplished by deacidification to control the pH of the solution to recycle in the plating process. The composition was 30 g-Ni/L and the pH maintained was over 3.0.

Keywords: Ion exchange technology; Plating waste water; Nickel recovery unit; Acid retardation unit; Ion ex- change system

1. Introduction

Wastewater discharged from industries like plating processes contains many heavy metals. They, such as copper, lead, chromium, nickel, iron, and zinc etc., have a fatal effect on the human body as well as causing environmental pollution. Especially, nickel that has been used in plating processes, nickel batteries, alloys, and steels. To be produced from rinse water to elec-

*Corresponding author

trolyte after plating is a major source that ex- hausts nickel ion in the middle of them [1-5]. The nickel concentration contained in rinse water is about from 500 ppm to 2000 ppm.

In environmental pollution, plating com- panes focussed on the removal of toxic ma- terials in the past, but recently researchers have been studying a technology to hold back pollutants at least and recycle them [4].

In order to choose the method to recycle the metals in the plating process, there are some

0011-9164/05/$- See from matter 2005 Elsevier B.V. All rights reserved doi: 10.1016/j.desal.2004.11.088

164 T.-I-L. Eom et al. / Desalination 180 (2005) 163-172

points to consider like using the solution con- centrated from the process, treatment for by- product sludge, regeneration and recycling of process water and recycling for treated waste- water [3,4].

Technologies to separate ions from waste- water have been physical adsorption using an adsorbent such as silica gel, activated carbon and activated alumina, etc. These physical methods, however, are limited in selective re- moval of organic materials and other metals containing high concentration in the rinse water from the plating line. To overcome the problem of physical methods and to efficiently separate pollutant ions, many methods have been used such as oxidation/reduction, precipitation, ion exchange, reverse osmosis, adsorption, electro- winning, electrodialysis and so on. Of the above methods, the performance of electro-dialysis and reverse osmosis has some advantages over the others. But even though both methods have an advantage in efficiency, they have some problems such as installation charges and operation costs. Also, there is the need to secondarily treat the recovered solution and there are difficulties in treating large volumes and high concentration due to the pressure drop [4-6,8].

Comparing the technology of ion exchange with others, ion exchange technology has the advantage that it can treat a large volume at once and directly recycle the metals in a plating bath. It can recover over 97% [6,7].

Ion exchange is a phenomenon that is re- versibly exchanged between counter ion on bead surface and ion in the solution by the dif- ference of electrostatic force. In the process, ca- tion, such as nickel, copper, sodium etc., is ex- changed with hydrogen ion. Also, anion, as sulfates, chromates and chlorides etc., is ex- changed with hydroxyl ion [ 10-13].

This technology has been mainly applied to pharmaceutical purification, water softening pro- cesses, separation and purification in the food industry, catalyst and manufacture of ultra-pure water used in semiconductor processes etc.

Technology recovering nickel ion-by-ion ex- change uses a column that packed beads. At the present, to separate nickel ion, ion exchange resins use cation resins that are able to selec- tively exchange the nickel ion with hydrogen ion in wastewater. While the solution flows into the column until its capacity is reached to break- through point, the resin separates nickel ion from the solution. After adsorbing nickel ion, the resin is regenerated by acid [11-13]. Be- cause the pH of the solution recovered through the column packed with cation is too low to re- cycle directly in the plating bath, it requires other treatment to be able to use the solution in it. To accomplish this requirement, acid retard- ation also was used in this study. That is the technology that high concentration acid is ad- sorbed on the anion resin and metal salts are excluded by passing through the resin. This is a reversible process and acid adsorbed on the resin could be easily regenerated by distilled water [14,15].

This study was carried out to confirm and sel- ect operational conditions and ways that need to develop ion exchange system (IXS). It was com- posed with a nickel recovery unit (NRU) to con- centrate the concentration of nickel ion from rinse water as salt and acid retardation unit (ARU) to control the pH of the salt solution to be recycled in the bath. Experiments were con- ducted on each unit, NRU, ARU, and IXS inte- grating them in order to build up operational variables as space velocity (SV) of solutions flowing into column, H2SO4 concentration and volumes of distilled water used in regeneration of the ARU column.

2. Experiment

Before the experiment was carried out, the resin had to be selected and its characteristic un- derstood. In selecting apt ion exchange resin, although weakly acidic cation and weakly basic anion resins have greater affinity than each strong resin for counter ion, the strong resins were used because they especially have an advantage for pH range.

2.1. Materials

T.-H. Eom et al. / Desalination 180 (2005) 163-172

The resin used in this experimental work was of the DIAION series, made by Mitsubishi Kasei Co., Japan. It is a strongly acidic cation resin that separates nickel ion from rinse water, contains PK 228 that has an Na form as the exchange group and a strongly basic anion resin does PA312. It has the C1- form and is used to control the pH of the solution recovered by the cation resin in order that nickel ion may be recycled in the plating bath without other treat- ment. Both the cation resin and the anion resin are porous type. Table 1 shows characteristics of each resin, strongly acidic cation and strong- ly basic anion resin, used in this experiment [11].

To manufacture model rinse water, nickel (II) sulfate (NiSO4, 6H20) and nickel (II) chloride (NiC12,'rH20) used an extra pure grade made by Junsei Chemical Co. In order to pre- treat ion exchange resin to be used in the experi- ment, an extra pure grade sodium chloride, manufactured by Junsei Chemical Co., and sulfuric acid manufactured by Dong Woo Fine Chemicals for the electronic grade was em- ployed.

The size of the column composed in each unit, nickel recovery unit (NRU) and acid re-

165

tardation unit (ARU), had a diana of 25 mm and length of 500 ram. This is bench scale. The column was packed with PK 228 and PA 312. In the mini-pilot plant scale test, the diam and length of the column was each 34 mm and 570 ram. At this time, all of each column, bench scale and mini-pilot plant scale, were packed by using a measuring cylinder and packed more volume than column volume. The model rinse water was fed into the units with a peristaltic pump made by Masterflex Co., model No. 7523-47.

2.2. Pre-treatment of ion exchange resins

Before the test was carried out, the resin had to be pre-treated. After the resin was packed in the column, a particle was removed through backwash below 300 grn. In general, the con- ditioning method is to provide HC1 (4-8%) and NaOH (4%) by turns. At this time, reagent and rinse water flowed into the column by repeti- tion. The procedure of pre-treatment, however, is different for the goal of experiment and ionic form.

In this experiment, pre-treatment process was comprised with supplying 2N NaOH solu- tion into the column excessively and, after that, washing ions remained on beads, and 5 vol %

Table 1 Properties of ion exchange resins

Grades PK 228 PA 312

Resin type Porous Porous Matrix Polystyrene + DVB Polystyrene + DVB Functional group -SO3-, sulfonate -N(CH3)3CI-, Trimethyl ammonium Ionic form Na ~ C1- Specific gravity 1.35 1.1 0-1.16 Total capacity, meq./ml 2.05 1.3 Operating temp., C 120, Na, H form 60, OH form, 80 C1 form Moisture content, % 37-43 49-55 pH range 0-14 0-14

166 T.-H. Eom et aL / Desalination 180 (2005) 163-172

sulfuric acid and distilled water did so. Through this step, strongly acidic cation resins packed in NRU column substituted Na + form to H + form and strongly basic anion resins used in ARU column exchanged C1- form to SO42- form.

2.3. Continuous experiment

2.3.1. Nickel recovery unit (NRU)

The NRU experiment, bench scale and mini- pilot scale, used strong cation exchange in order to recover nickel salt from rinse water. It was exchanged Na + form with H + form through pre- treatment. Model rinse water used in this test was made by dissolving nickel sulfate (NiSO4,'6H20) 6.2 g and nickel chloride (NiC12,-6H20) 1.6 g in 1 L distilled water. The nickel ion concentration of this solution is 1.8 g-Ni/L. This is the average concentration of nickel ion contained in wastewater.

To confirm the working capacity of the strong resin, nickel-loading test employed the NRU column of bench scale. Model rinse water was provided into the column upward to pre- vent a drift in the space velocity of 50/h. After finding out the capacity, the experiment pro- gressed to obtain optimal operational conditions as the change of space velocity. At this time, the volume was supplied in 10, 25, 50 and 75/h. The regeneration of the NRU column used sul- furic acid solution. In the first place, the sulfuric acid solution of 2 N concentration was run into the NRU column adsorbing nickel ion to fred out the composition of solution regenerated for the

change of the flow rate of sulfuric acid with 2, 3, 4, and 5/h. To examine the concentration change of nickel salt recovered by H2SO4, the flow rate of reagent fixed in 2/h and the con- centration of H2SO4 was changed with 1 N (2.8 vol %), 2 N (5.3 vol %), 3 N (8 vol %), 4 N (10.7 vol %) and 5 N (13.3 vol %) concentration. At this time, nickel salt concentration of eluted solution in each step was measured by using ICP-AES (Perkin Elmer Co. Model name - Op- tima 2000DV) and the pH and ion conductivity of solution eluted from the column did the same way. The conditions are exhibited in Table 2.

2.3.2. Acid retardation unit (ARU)

ARU experiment used strongly basic anion exchange resin (Diaion PA312) which substi- tutes C1- form to SO42- form to control the pH of nickel solution regenerated from NRU through de-acidification. The concentration of model solution was 37.3 g-Ni/g and it was manufactured based on the composition of nickel salt recovered from NRU. At this time, because the pH of the solution from NRU was 1 below, 5 vol % sulfuric acid was added into the model solution to adjust the pH. While it was provided into ARU column in SV2, 5 and 10/h, the concentration of nickel ion was measured on flow rate change.

Regenerating the anion resin in ARU column used ultra pure distilled water (DI water). The flow rate was changed with 10, 20 and 30/h. Solutions supplied in ARU loading and regene-

Table 2 The condition of nickel recovery unit test

Feed Class Concentration

Space velocity, h Resin type

Loading Regeneration

6.2g NiSO4"6H20 + 1.6g NiC12.6HzO 1.8 g-Ni/L 10, 25, 50, 75 Strongly acidic cation -- PK 228

SulNricacid 1,2,3,4,5N 2,3,4,5

T.-H. Eom et aL / Desalination 180 (2005) 163-172 167

ration selected the direction to be upward to prevent a drift.

The nickel salt concentration of eluted solu- tion in each step was measured by using ICP- AES (Perkin Elmer Optima Co., Model 2000DV) and pH and ion conductivity did so. Table 3 shows the experiment conditions of ARU.

2.4. Ion exchange system (IXS) experiment

A systematic experimental apparatus was designed with bench scale and pilot plant scale. The experiment was performed to systemize NRU and ARU through applying the opera- tional condition gotten by column test for re- covery and recycling of nickel salt.

In the case of the bench scale, model rinse water was supplied into the NRU of system in order to recover concentrated nickel salt with space velocity 10, 50/11. The regeneration of NRU used 3.8 N (10 vol %) H2SO4 solution and it was run into the column upward with 2/h. The solution regenerated from NRU flowed straight to the ARU column with the same direction of NRU. When the solution was pro- vided to ARU, the hydrogen ion concentration of the solution was controlled and to supply sulfuric acid was broken as the pH got ready up to the concentration that enabled its use in the plating bath. After stopping the provision of HzSO4, solution that existed between beads of NRU and ARU columns was removed by air blowing-down. Reagent employed ultra pure DI

water to regenerate nickel ion adsorbed on strongly basic anion resin. The flow rate changed space velocity 10, 50/h. At this time, because the solution regenerated by DI water contained high nickel ion concentration, it made nickel ion re-adsorbed and used to wash beads of NRU. The system experiment of bench scale was operated in a co-current way. In the case of the mini-pilot plant, the operation manner employed was counter current and did not carry out air blowing in each step. The results of the mini-pilot plant scale were compared with the bench scale. Apparatus of IXS, mini-pilot plant scale, is exhibited in Fig. 1.

3. Results and discussion

3.1. Continuous experiment

3.1.1. Nickel recovery unit ~RU)

In the NRU loading test, the leak of nickel ion appeared when model rinse water, 1.8 g-Ni/L, flowed into the column as much as 20 times the resin volume with SV 10, 25, 50 and 75/h. At this breakthrough point, the strongly acidic cation resin, PK 228, could con- fu'rn to have a working capacity of 85 mg-Ni/rnl- resin, 1.7 meq/ml. Nickel ion concentration was found out to be detected as 22 ppm and it was removed over 99%. Ion conductivity of solution eluted from the column had increased from 6.57 mS/cm to 30.7 mS/cm. Also, the pH was decreased from 5.5 to 2 below because hydro- gen ion in the solution increased through ex-

Table 3 The condition of acid retardation unit test

Feed Class

Concentration Space velocity, h Resin type

Loading

178g NiSO4'6H20 + 5 vol % Hz SO4

37.3 g-Ni/L, pH 1.0 below

2, 5, 10 Strongly basic anion - - PA 312

Regeneration

Distilled water

10, 20, 30

168 T.-H. Eom et al. / Desalination 180 (2005) 163-172

1.2

1,0

o o 0.8 0 g 0.6. O -o 0.4

iTi 0.2

0.0

it-St t~m- =~-=t,= =~

/ f l! ' ~ A 1 ,' sv = 10in

':' SV = 2~lh A / AI~ ,A SV=50~

. . . . . . . . . . . . . . . . . . *

2000 4000 6COO 8000 10000 12000 14000

Acc. feed volume [ml]

Fig. 2. The effect of space velocity on eluted nickel ion, Ni 2+, concentration in case of NRU loading as initial nickel concentration of rinse water is 1,800 rng-Ni/L.

Fig. 1. Apparatus of ion exchange system of mini-pilot plant scale, 500ml.

changing selectively between nickel ion and I-I + on the resin.

In this case, the capacity of strongly acidic cation resin which was packed in NRU was not influenced in the flow rate. Fig. 2 shows the breakthrough curve on the SV change of rinse water supplied into NRU.

When aqueous H2504 was supplied with space velocity 2/h and the sulfuric acid com- position was 2 N to regenerate NRU, the nickel ion concentration obtained was 72 g-Ni/L as the highest concentration.

Although the flow rate of H2SO4 solution increases, the concentration of nickel ion re- covered from the column was not increased. It seems to be taken place dilution of the ion by H2SO4 at the desorption process. To examine the effect of reagent concentration, when the feed rate of H2SO4 was fixed with 2/h and the concentration of H2SO4 was changed with 1 N (2.8 vol %), 2 N (5.3 vol %), 3 N (8 vol %), 4 N (10.7 vol %), and 5 N (13.3 vol %), the con-

centration of aqueous H2SO 4 could be gained up to as much as about 120 g-Ni/L. This is considered as the composition of nickel ion recovered from regeneration process depends on H2SO4 concentration. The results are shown in Figs. 3 and 4.

3.1.2. Acid retardation unit (ARU)

It is possible for the solution regenerated by sulfuric acid to be used using in plating bath except having very low pH. To recycle nickel salt regenerated by HzSO4, the solution needs to be controlled pH with treatment by using strongly basic anion resin. ARU maintained over 30 g-Ni/L until the concentrated solution sup- plied was as much as 400 ml and recovered over 3.5 while it flowed into the column about 300 ml. These results had no connection with the flow rate. In aqueous solution, the dissoci- ation constant (Ka) of sulfuric acid is 103 and the dissociation constant of bisulfate is 10 -2. Be- cause the pH of solution employed to ARU is 1.0 below, H2SO4 existing in model solution fed to ARU has bisulfate form and hydrogen ion after it passes the first dissociation step. Contact-

T.-H. Eom et al. / Desalination 180 (2005) 163-172 169

80

6O

"O

~. 2o

0

sv = 2fn [ ] SV : 3fn SV = 4/h

,' ~ SV = 5/h

0 108 200 300 400

Acc. reagent feed volume [ml]

Fig. 3. Nickel ion, Ni 2+, concentrations on space velo- cities in the case of NRU regeneration by sulfuric acid solution.

1.0

8 0,8

=d 0.6

8 o.4

0.2

o.o

/

/ /m / sv=10~

100 200 300 400 500

Feed volume [roll

Fig. 5. Space velocity effects on the nickel ion, Ni 2+, concentration of mixed solution in case of ARU load- ing.

120 1 ~ 1NH=SO, 1 0.030

11 ~1'0 ' ~H,SO, / 0.025

40 ]:

0 ; - ~-~2~ - - TZ: 0.005

0 1130 20O 300 40O 0,000

Acc. reagent feed volume [m0

Fig. 4. Nickel ion concentrations in eluted solution re- generated by each sulfuric acid concentration at space velocity 2/h.

ting with the resin having SO4 2- group by pre- treatment, hydrogen ion remaining excessively in the solution is adsorbed on the strongly basic resin and SO4 2- on the resin is substituted with HSO4- .

While this sorption is advanced between bi- sulfate ion existed in concentrated model solu- tion and sulfate ion on the resins, HSO4- in the solution is dissociated with H and SO4 2- again. This sorption is dominated by Le Chateliers principle.

k SV= 2tn SV= 5in U SV=l~ /

/

1 [ /

/

0 100 200 300 480 Feed vam-~ [ra]

Fig. 6. H concentration change of mixed solution on space velocity in case of ARU loading.

It seems to raise the pH of solution re- covered from NRU as a result of being di- minished hydrogen ion by this process. But, at this time, nickel ion was adsorbed on the resin with I-I +. The changes of the concentration and the pH of solution recovered from ARU on the change of flow rate are exhibited in Figs. 5 and 6.

In process regenerated nickel ion which is adsorbed in ARU, desorption of nickel ion was

170

easily carried out through feeding DI water and had no connection with flow rate of DI water. This shows that the separation technology by acid retardation is a reversible process. The re- sults from the ARU regeneration process are shown in Fig. 7.

3.1.3. Mini-pilot plant experiment

In order to get a systemized operational con- dition of the ion exchange system (IXS), a mini-pilot scale, 500 ml, was operated with space velocity of 50/h that was selected through a bench scale test.

It is was found that the breakthrough point of nickel ion occurs when model rinse water was fed into the mini-pilot column as much as 25 times. Fig. 8 exhibits the results. The con- centration of regenerated solution was 80 g-Ni/L. The results comparing with bench scale are shown in Fig. 9.

In the ARU experiment, ARU column could recover more volumes of solution than bench scale of which nickel concentration is 30 g-Ni/L over and its pH is 3.0 over by deacidification.

Figs. 10 and 11 exhibit each of the results comparing ARU bench scale and mini-pilot scale.

300O0

-d

d 20000

8 z

~ 100t70 3 LU

T.-H. Eom et al. / Desalination 180 (2005) 163-172

SV= 104q

- - I - - sv = 2o~ - -4k - - sv: 3~ . . . . . . . , ~ . . . . . . 5V = 40 ,~h

- " -0 .... S,,,' = ,50,h

500 1000 1500 2000 2500

water vdume [~]

Fig. 7. The concentration change of eluted solution on space velocity change in case of ARU regeneration by DI water.

1,0

"~" o.e

0 ~ 0.6 ~: 0.4

[] 0.2

0.o',

m . . . . .

~ Bench scale (200ml) Mini pilot (500ml)

20 40 60

Volume fraction (ml-feed/ml-resin)

Fig. 8. Breakthrough curve change for bench scale and mini-pilot scale in the case of the IXS experiment.

120

100

0

~ 40 3 rn

20.

0.0

Bench scale (200 rnl)

, , , . . . . , . . . . , . . . . ,

0.5 1.0 1.5 2.0

Volume fraction (rnl-reagentlrnl-resin)

I !

Fig. 9. Nickel ion concentration of NRU regeneration by sulfuric acid, 3.8 N, for bench scale and mini-pilot scale.

The working capacity of ion exchange resin relies on variables as resin capacity, the com- position of model rinse water and void volume etc. For all that, in this experimental work, the ion concentration and the resin capacity are con- stant but the void volume of the column of mini-pilot plant scale is diminished due to being compactly packed with resin/unit volume. Therefore working capacity for treating nickel

1.0

0.8

0~0.6 v

8 0,4

0.2

0.0 ~,~ . . . . . . . . . , . , 0,0 0.2 0.4 0.6 0.8 1.0 1,2

Vol~'ne fraclJon (ml-feedtml-resin)

T.-H. Eom et al. / Desalination 180 (2005) 163-172

=

/t t"~/0 ,.///~ Benchscale(2OOml) ..~ M~ni pilot scale (500 rnl)

Fig. 10. Nickel ion concentration of solution recovered from ARU of bench scale and mini-pilot scale.

171

solution has high concentration as the H2804 concentration is high and its flow rate is low. By basing on these, the space velocity of re- agent fed with 2/h and the concentration was 3.8 N (10 vol. %). At this time, the highest concentration of recovered solution was 83 g-Ni/L. To control pH of the solution, the solution recovered from NRU was supplied continuously to ARU until the mixed pH of solution from ARU was holding up 3.0 over. Finally, IXS could recover nickel salt solution that the concentration of the mixed solution was 30 g-Ni/L over and its pH 3.0 over. The volume of the recovered solution was the same as the volume of resin packed in the column and the

0.010

0.008

d 0.006

"~ 0.004 X

0.002

Bench scele(2OOml) ~t[~l b4ni pilot scale (500 mb

J

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Volume fraction (ml-feedtml-resin)

iL-- . -4

Fig. 11. H + concentration of solution recovered from ARU for bench scale and mini-pilot scale.

ion was enhanced and the ARU column could treat greater volume than the bench scale.

highest mixed concentration of nickel ion was 38 g-Ni/L.

To examine the effect on operation ways, bench scale IXS, 200 mi, was carried out with co-current and in each step, the solution was removed with air blowing down after pausing to feed solutions. However, mini-pilot plant scale, 500 ml, applied counter current way without air blow down. The result had not many differ- ences between bench and mini-pilot scale. Only, it needs to give back what is eluted from NRU regeneration and ARU regeneration to keep from dilution to NRU feed tank in counter current operation though the solutions contain nickel ion of very low concentration. The com- position of the solution was 30 g-Ni/L and its pH was 3.0 over and recycled volume was 1.3 times the resin volume. Fig. 12 shows the concentration recovered through counter current way.

3.2. Ion exchange system (IXS) experiment

In the IXS experiment systemized NRU and ARU mini-pilot scale through integrating operational condition, model rinse water was fed into NRU column until breakthrough point. The NRU loading test could find out treating same volume, 25 times of packed resin volume, with continuous test. While NRU resins are regenerated by aqueous H2SO4, the recovered

4. Conclusion

In the continuous test, NRU treated the solu- tion of which model rinse water concentration is 1.8 g-Ni/L as much as 20 times of strongly acidic cation resin. In this case, working capa- city was 1.7 meq/ml resin and it was used about 80%. Nickel ion in rinse water was removed above 99%. Mini-pilot was operated until 25 times of resin volume. In case ofNRU regen-

172 T.-H. Eom et al. / Desalination 180 (2005) 163-172

30

25

20 o

15 z ,~ 10

5

1 0.0004 I ~ Feed w ~d i~ cone. i - - I - - Feedvs rni=d I. ~onc. ~ [

',, / f -, ',, / /I / /f

100 200 300 400 500 600

Regenerated solul~on reed [ml]

Fig. 12. Nickel ion concentration and H + concentration of solution recovered from ARU in case of IXS mini- pilot scale experiment with counter current.

eration, the highest composition of nickel ion recovered by H2504 was obtained as H2804 flow rate is 2/h and H2SO4 concentration is high.

It is possible for ARU to control the pH of the model concentrated solution of NRU main- tains 3.0 or more and the concentration is more than 30 gNi/L by acid retardation.

Bench scale IXS systemized by continuous operational condition could recycle model rinse water as much as resin volume and mini-pilot scale treated 1.3 times. Also, operational way of IXS was selected with counter current.

Acknowledgement

The authors wish to acknowledge with thanks the Ministry of Science and Technology, Industrial Waste Recycling R&D Center at KI- GAM, and the Regional Research Center for new material by recycling (RRC/NMR) in Kong Ju National University for financial support.

References

[1] S.W. Kim and J.G. Chung, Hwahak Konghak, 4(8), 37 (1999) 575.

[2] J. Choong, J.Y. Park and Y.J. Yoo, Korean J. Chem. Eng., 18(6) (2001) 955.

[3] C.J. Brown and M. Sheedy, Novel ion exchange kidney for mill closure, Paper presented at Engi- neering Technologies Symposium, Florida, 1997.

[4] A. Mohammad, R.A.K. Rao, R. Abroad and J. Ahmad, J. Hazardous Materials, B79 (2000) 117.

[5] H. Leinonen, Report Series in Radio Chemistry, 13 (1999) 1.

[6] R.P. Gouthro and L. Vaz, Recovery and purifica- tion of nickel salts and chromic acid using the Recoflo system, Paper presented at Eco-Tech 99, Metal Fisher's Assoc. of India, Mumbai, 1999.

[7] F. DeSilva, Chem. Eng., July (1994) 86. [8] C. Giorgia, M.S. Saunders, J.P. DeCarli II and J.B.

Vierow, AIChE Symposium Series, No. 264, 84 (1988) 54.

[9] F.G. Helfferich and Y.L. Hwang, AIChE Sympo- sium Series, No. 242, 81 (1985) 17.

[10]H.J. Michael, P.M. Nelis and M.D. Mayne, Metal Finishing, 8 (1988) 67.

[11]Mitsubishi Kasei Co., Diaion-ion Exchange Manu- al I, 1992, pp. 6, 28, 153.

[ 12] Mitsubishi Kasei Co., Diaion-ion Exchange Manu- al II, 1992, p. 65.

[13]F.G. Helfferich, Ion Exchange, Dover Publica- tions Inc., 1995, p. 5.

[14] K. Dorfner, Ion Exchangers Properties and Appli- cations, Ann Arbor Sci. Publishers Inc., 3 (1977) 117.

[15] P. Pajunen and J. Harrison, Anodizing acid purifica- tion using resin sorption technology at pioneer metal finishing, Paper presented at AESF Com- pliance Week '97, Orlando, 1997.

[16]V.M. Bhandari, T. Yonemoto and V.A. Juvekar, Chem. Eng. Sci., 55 (2000) 6197.

[17]V.M. Bhandari, V.A. Juvekar and S.R. Patward- han, Ind. Eng. Chem. Res., 32 (1993) 200.

[18] R.A. Alberty and R.J. Silbey, Physical Chemistry, John Wiley & Sons Inc., 2 (1996) 155.

[19]P.W. Atkins, Physical Chemistry, Oxford Univer- sity Press, 7 (2002) 234.

[20] V.L. Snoeyink and D. Jenkins, Water Chemistry, John Wiley & Sons Inc., 1980, p. 125.