Fibre Chemistry, Vol. 28, No. 6, 1996

F I B R E S O R B E N T S F O R L O C A L R E M O V A L O F H E A V Y M E T A L

C O M P O U N D S F R O M W A S H I N G S O L U T I O N S

S. V. Burinskii UDC 677.494.745.32.005

Reactive fibres are fabricated by incorporating functional groups capable of reversibly entering into ion-exchange,

complexing, and redox reactions with the ions or molecules in close contact with them in the structure of the starting nitron

fibre. The major advantage of these fibres in comparison to similar materials in the form of granules or beads is the much

higher (by 15-20 times) density of functional groups on the developed active surface, which allows conducting mass-exchange

or redox processes with a very high intensity [1]. Practically, more intense mass or energy exchange in media allows miniaturizing the apparatus used and conducting

technological processes with significantly lower consumption of energy and chemicals [2]. In addition, fibre sorbents in the

form of nonwoven cloth with high reactivity and low gas or liquid flow resistance allow for efficiently conducting these

processes even with a very low concentration of substance to be extracted. In addition to significant savings of materials and power, the use of reactive fibre materials makes it possible to

organize closed water cycles, saving up to 90-95% of the water used for washing and its local purification not in purification

installations, but directly in the shops. This solves several problems simultaneously: it makes it easier to avoid dumping highly

toxic substances in fishing waters, including in the form of burst emissions, decreases the volume of emissions with a high

concentration of salts, decreases the total cost of waste purification, and eliminates fines. These problems are fully solved not

only by using local methods of purification of aqueous solutions with fibre sorbents, but also by implementation of the entire

spectrum of modern technologies, primarily methods of intense washing of the fibres [3]. One of the most complex problems of environmental protection is making technologies involving wastes contaminated

by heavy metals ecologically safe. Hexavalent chromium, copper, cadmium, and zinc compounds are stable chemical pollutants

having a cumulative effect and specific toxic properties. Wastewaters and emissions from electroplating plants are the basic

sources of entry of these substances into air and water. The so-called reagent methods used here do not solve the problem, since

the volumes of water consumed and dumping of polluted wastewaters are not decreased. Attempts to use membrane

technologies and methods of electrodialysis and heterocoagulation have not produced positive results, since the necessary

cleaning of the wastes is not attained for high costs and low productivity. Specialists are now becoming increasingly convinced

that there is essentially only one way to solve these problems -- to organize waste-free and low-waste schemes based on local

cleaning of washing and technological solutions using a new generation of ion-exchangers [2]. Sorption of chromium(VI), copper, and zinc from aqueous solutions of their salts with different ion-exchangers has

been investigated repeatedly [4-6]. However, as established in [6-8], fibre ion-exchangers have the highest sorption and

desorption efficiency.

The products of chemical modification of graft copolymers of nitron fibre containing epoxy groups (AN-1 anion-

exchanger) with diethyl- and trimethylamine and Ampan polyampholyte, also obtained by chemical modification of nitron fibre

by incorporation of weakly basic aliphatic amine groups in its structure, were used as fibre ion-exchangers with sorption activity

for chromium(VI) ions [9]. The AN-1 anion-exchanger contains tertiary amine groups and has an exchange capacity of 3

mmole/g. The total static exchange capacity (SEC) of Ampan fibre is 4 mmole/g.

The sorbents selected for the study were resistant to hexavalent chromium compounds (monochromates in basic and

bichromates in acid medium), which are strong oxidants. The studies of the sorption capacity of these fibres with respect to

chromium(Vl) ions in sorption--desorption cycles showed that their exchange capacity, swellability, shrinkage, and physico-

St. Petersburg University of Technology and Design. Translated from Khimicheskie Volokna, No. 6, pp. 16-19.

November-December, 1996.

374 0015-0541/96/2806-0374515.00 '~1997 Plenum Publishing Corporation

TABLE 1. Sorption of Copper by Fibre Ion-Exchangers

SEC, mmole/g Amount of absorbed copper at different pH, mmole/g

Fibre sorbent for for basic carboxyl groups groups

L _ _ _ - - _ . . . . .

Kopan - I 0 3,2 I. 2

Kopan -60 2. I 3.6 Kopan -90 2.0 3.9 Kopan 150 , 1,7 4,3 Karpan i 0.3 5, I Ampan 4 , 0 0 , 2

3 4

1,2 1.6 1.8 2,0 2.7 2.q I,O 2.0 3,1 1,8 3.(1 3.3 0,~ 2.5 2.5 I.O 1,4

5 ,~ 9 I0

_,.i . . . . . . . . . . . . . . . . . 2.3 2.4 2.0 2.8 2.4 2,6 2,6 2.9 2.7 2,8 2,9 3.0 2.8 3,1 3.4 2.0 1.6 1.7 1.8

1,4 1.2 0,1 0.6 0.4

c, rag/liter

210

t 2

150

90

J 0

d 1 0 V r l i t e r

Fig. 1. Output curves of sorption of

chromium(VI) ions by Ampan (1) and AN-1

(2) fibre ion-exchangers.

mechanical indexes vary insignificantly. The SEC of AN-1 ion-exchanger in the pH range of 2 to 5 is 0.93 mmole/g.

Equilibrium arises during sorption between the active groups of the ion-exchangers and solution containing chromium ions after

2-3 min of contact. The ion-exchangers exhibited selectivity for chromium ions even in the presence of significant amounts Gf

sulfate ions. The distribution coefficient of the chromium between AN-1 sorbent and the sulfuric acid solution was 1.3.103.

Both ion-exchangers were tested in 300 sorption--desorption cycles in dynamic conditions. The dynamic exchange capacity

(DEC) for a rate of passage of the working solutions through the column of 3 m/h was 131 and 125 mg/g, respectively, for

AN-1 and Ampan 131.

As the output curves of sorption of chromium ions show (Fig. 1), both fibres have a long-lasting protective effect. After

saturation, the ion-exchangers are easily regenerated with solutions of sodium hydroxide. The degree of regeneration is 80-92 %.

The degree of concentration of chromium ions in the eluates can attain 3.5-8.0.

Ion-exchange fibres fabricated by polymer-analog transformations of nitron fibre were used for the study of sorption

of copper ions: Ampan (SEC = 4 mmole/g), Karpan with carboxyl groups (SEC = 5 mmole/g), and Kopan fibre with

carboxyl, amine, imine, and hydrazine groups (Kopan-10, Kopan-60, Kopan-90, Kopan-150). Absorption of copper ions by

the fibre ion-exchangers was investigated by varying the concentration, temperature, and pH of aqueous solutions of copper

sulfate [10]. For most of the fibres, a decrease in sorption was observed when the concentration of the working solutions was

decreased from 2-3 to 1.0-0.2 g/liter. The fibres retained relatively high sorption capacity even with minimum concentrations of copper in the working solutions.

The data characterizing sorption of copper ions as a function of the pH of the solutions are reported in Table I. In the

pH 3-4 region, absorption of copper increases markedly with an increase in the proportion of carboxyl groups in the ion-

exchanger. This type of sorption is observed in absorption of copper from aqueous solutions of the copper--ammonia complex formed in ammonia etching of copper from printed circuit boards.

In the basic medium, the sorption capacity of Kopan-150 polyampholytes is 1.5-2.0 times higher than for Karpan

cation-exchangers. As the concentration of carboxyl groups in the ampholyte increased, sorption of copper increased markedly

when the pH changed from 8 to 11. Absorption of copper ions by Kopan polyampholytes is complex in nature, since it takes

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TABLE 2. Diffusion Coefficients D of Copper Ions in

Fibre Ion-Exchangers

I Fibre

!

t Kopan.10

!i Kopan. 150

] Karpan

[hmP

i D.I 09, cm2/sec, for a concentration l of copper, g/liter

. . . . 1 !1 0.25 1.20 2.50 6,00 :

0.056 O.O85 ! 0 .140 0.200:1

0.121 0.420 i i 'i i 1,046 1,331 ,I 0,095 0,410 1,016 I I 1,160

TABLE 3. Basic Technical Characteristics of

Installations for Local Purification of Washing

Solutions from Electroplating Plants

Data for installations

Indexes LPI/ LPI / ~ LPI /

Output, liter/h

Concentration of extracted substance, rag/liter, no greater than

at inlet

at outlet

Working filtra- tion cycle, h i

Volume of regenerat- ! ing solutions, liter

Area occupied, m 2

Chrom- ium

25O

I

,: 50

' 0,07

17

200

I 2

Cad- Zinc mium

150 250

i 100 I

I 0,01

i 8 I

200 I

I 2

LPI / Copper

250

100 100

0,5 0,05

8 20

150 200

I - 2 1 2 2

I t Guaranteed working I I time without changing ', sorbent, year

Power consump- I , I 0.5- 1 ,0 ' 0 .5 - 1,0:! tion, kwh/m 3 . . . . . . . . . . = v _ _ _ ~ l

place by a minimum of two mechanisms: on exchange and complexation. The pH of the medium, together with the nature of

the ionogenic groups, affect the mechanism of sorption.

Sorption is low in the acid region due to weak dissociation of carboxyl groups and the presence of protonated amine

groups which prevent formation of the N --, Me coordination bond. When the acidity of the medium is decreased, the degree

of protonation of the basic groups decreases and dissociation of carboxyl groups is potentiated. Up to 200 mg of copper per

I g of fibre is sorbed at pH 34.

The degree of saturation of ionogenic groups as a function of the duration of contact with solutions of copper sulfate

of different concentrations was investigated. The experimental data indicate a higher rate of absorption of copper ions by Kopan

and Karpan fibres, and the rate of the exchange processes is a function of the ratio of carboxyl and basic groups in the ion-

exchanger in this case. In particular, it is much higher for Kopan-150 fibres than for Kopan-60 and Kopan-10 fibres. The linear

character of the dependence of the degree of saturation on the square root of the duration of sorption for low degrees of

exchange indicates that diffusion of absorbed ions inside the fibre is the stage that determines the kinetics of the processes. Total

saturation of the ionogenic groups in the fibres takes place after 15-20 rain, and they are 80% saturated after the first 1-5 rnin

of contact. The values of the calculated diffusion coefficients are reported in Table 2. The important increase in these values

with an increase in the concentration of the starting solutions indicates the intradiffusion character of the kinetics of the sorpti0n

processes.

In studying sorption of copper in dynamic conditions, the rate of feeding in the working solutions was 4-7 mlh. Kopa~"

150, Kopan-60. and Karpan fibres exhibited the maximum absorption of copper ions, and the DEC before breakthrough was

376

not very dependent on the concentration of copper in the working solutions, while the total DEC increased markedly with an

increase in the concentration of copper. Maximum absorption of copper (up to 240 mg/g) took place when Kopan fibres were

used. In studying the effect of the working solution feed rate on the character of the sorption output curves, it was found that increasing the rate from 1 to 7 m/h decreased the DEC before breakthrough by a total of 25-30%.

Solutions of sulfuric acid in the concentration of 1/2 M were used for elution of copper from the fibres. It was found

that when the sulfuric acid solutions were heated to 80~ the degree of desorption increased from 85-90 to 96-98%. A similar

effect was obtained in increasing the concentration of sulfuric acid to 1 M. A high degree of regeneration was also obtained

by repeatedly using the same regenerating solution until the concentration of copper ions in it was 8-10 g/liter. The duration

of the elution process did not exceed 10-20 min.

The results of the systematic studies conducted at the SPGUTD described above allowed Ekopolymer Co. and SPGUTD

to conduct engineering calculations, develop the technology, and create the equipment for local purification of washing solutions

from chrome-plating, passivation, cadmium-plating, and zinc-plating deparmaents of electroplating plants and washing waters

from production of copper--ammonia complex printed circuit boards.

The technical characteristics of the installations are reported in Table 3. The individual types of equipment passed

comprehensive industrial tests and are being used successfully in a number of enterprises.

Introduction of water-recycling cycles will save approximately 90% of the water used for washing, decrease the load

on purification installations, decrease consumption of chemicals, and eliminate frees.

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1.

2.

3.

4.

5.

6.

7.

8. 9.

10.

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Processing, Metrology, Ecology, Safety-96 [in Russian], St. Petersburg (1996), p. 336.

K. E. Perepeikin, M. D. Gluz, and V. M. Lishevich, Mass-exchange Processes in Processing of Chemical Fibres [in

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A. M. Garbar, Zh. Prikl. Khim., 59, 657-658 (1986).

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