a novel approach for toxicity removal through tailor-made sorbent

8/3/2019 A Novel Approach for Toxicity Removal Through Tailor-Made Sorbent

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A Novel Approach for Toxicity Removal through Tailor-made Sorbent

Document by:Bharadwaj

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ABSTRACT

Chelate co-ordinating resin having a) hydrophilic macro-pores, containing b) functional

moiety, with (c) tailor-made property has been designed. The macro-porous hydrophilic base (a) is

prepared by the addition polymerization process of a homogeneous mixture of acrylamide and (b) a

separate emulsion (based semi-interpenetrating structure) containing hydroxyl and carboxylic acid

group has been synthesized. The emulsion (b) was soaked in the slab of polyacrylamide (a) to make a

tailor-made (c) coordinating chelating resin. Tailor-made concept includes the incorporation of the

metal extraction reagent (ligand) by a physical/chemical impregnation technique. The uptake

performance of the sorbent has been evaluated by equilibrating a known weight of dry sorbent in

contact with solution containing toxic elements such as Pb, Cd along with U. The developed resin can

be used for the removal of contaminants from the effluent/waste water or for the purification ofaquifers water. More than that it is worth mentioning that it has a great immobilization factor which

follows the trend Cd>Pb>U>Cu, that shows a separation of toxic elements for the recovery of

Uranium.

Key Words :- Tailor-made Sorbent, uranium, contamination, recovery, interfering metals,

elution

1. Introduction

Geological distribution of uranium and its migration in environment is of great interest because

uranium is having environmental concerns around uranium mining areas. Toxic pollutants originate

from uranium mill tailings can become a substantial source of contamination in water. The long term

environmental impact of mill tailings leachate have increasingly raised public concern and posing a

potential risk to human beings and eco-systems The various forms in which the heavy metals exist,

influences the toxicity level accordingly. In most of the cases Cu, Mn and natural uranium contributes

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more that 70% of the total metal present as leachable fraction in water, whereas Pb, Cd are also

present but in less concentration.

The recovery/removal of heavy metals from waste water has become a major topic of research

in environment. During the last decade, considerable effort has been directed toward the development

of resins applicable to the separation of these metal ions from different nuclear effluents. The

economical viability of the process depends on the selection of low cost and efficient sorbent and also

on the mode of application. The lining of the duct (through which effluent passes) with these resin or

in the form of sheet for covering the pipe should possess some properties like i) low swelling, ii)

without change of shape or negligible deformities and iii) highly stable in applied condition and iv)

moreover it should sorb the metal ions which is present in the leached solution (such as rain water or

natural calamities like flood etc.). In this paper, A) the development of a tailor-made sorbent and B)

experimented on i) Tailing Pond (TP) run-off samples and ii) inlet effluent of Effluent Treatment Plant

(ETP) and C) their tabulated results have been presented.

2. Experimental

2.1 Materials and preparation:- Materials such as acrylamide, N, N methylene

bisacrylamide, acrylic acid, polyvinyl alcohol, methanol, acetone, sodium hydroxide were procured

from different indigenous sources.

Methodology for sorbent preparation: - Tailor-made sorbent has been prepared in three

steps;

A) Addition polymerization of a homogeneous mixture of acrylamide and cross-linker reacted

to give a gelled product which ultimately sliced to a shape of slab.

B) A separate emulsion (based semi-interpenetrating structure) containing hydroxyl and

carboxylic acid group has been synthesized. Polyvinyl alcohol as a base matrix and in its presence

acrylic acid had been co-polymerized with acrylonitrile to give a better stability in acidic condition, as

tailing pond leachate are acidic in nature (pH 3-4). Sodium lauryl sulfate was used as emulsion

stabilizer and redox initiator was used to initiate addition polymerization. The reaction carried out at

60C for 4 hrs and the reaction product was a stable mass.

C) The emulsion (A) was soaked (for a day) in the slab of polyacrylamide (B) to make a tailor-

made (C) coordinating chelating resin. Tailor-made concept includes the incorporation of the metal

extraction reagent (ligand) by a physical/chemical impregnation technique, which can be shaped by

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changing the shape in step (A). Product (B) is very much site specific. Therefore, according to the

requirement it can be applied and step (C), i.e., ultimate curing is essential to exhibit the stability of

the resin.

2.2 Sorption procedure: - The uptake performance has been evaluated by equilibrating a

known weight of dry sorbent in contact with particular concentration. The uptake of metal ions by the

sorbent was calculated according to the mass balance on the metal ions expressed as

q = [(C0 Ce).V]/m (1)

Here, q is the amount of metal ions sorbed on to the dry sorbent (g/gm), C 0 and Ce are the

concentrations of the metal ions in the initial solutions and in the aqueous phase at equilibrium,

respectively (g/l); V is the volume of the aqueous phase and m is the mass of the dry sorbent used

(gm).

2.3 Distribution coefficient: The sorption equilibrium expressed by the distribution coefficient

Kd (ml/g) is given by

Kd = [(C0 Ce).V] / Ce m ------ (2)

Where, C0 and Ceare the concentrations of stable element ( g/ml) at the beginning of the

experiment (i.e. at time t = 0) and at equilibrium condition (i.e. at time, t = 24 hrs), respectively in the

sample solution. V is the volume of the liquid phase in ml and m is the weight of the sorbent (polymer)

in gm.

2.4 Extraction procedure: - The sorbent loaded with metal ion was placed in the elutionmedium of certain volume and stirred for 3 hrs at room temperature.

Amount of metal ion eluted to the elution medium

Elution percent = ------------------------------------------------------------- x 100 --(3)

Amount of metal ions sorbed on the sorbent

For all the experiments around 0.5 gm dried sorbent was taken, in 25 ml solution, kept for 1

day. Then it was filtered, the filtrate was collected. The residue was dried and after extracting with

25ml 1 (N) HCl, leached solution (eluent) was collected. Analysis of both manganese and uranium has

been carried out in filtrate, as well as in eluent.

2.5 Immobilisation factor :- Metal ion Immobilisation of a resin is the act of limiting

movement or making incapable of movement if the metal ions by trapping or rather chelating it with

the functional groups of resin, can be caluclated as

immobilisation factor = (1- Elution factor)

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2.6 Sample Collection and Analysis: For the application of this polymer in field conditions,

the effluent treatment plant inlet sample and uranium tailings samples disposed in tailings pond were

collected from Jaduguda. These samples were containing high concentration of Mn, U as well as other

radionuclides and stable elements. Uptake studies were carried out by adding 0.5 gm of dried polymer

in about 25 ml of treated effluent and tailings leachate sample in neutral pH, (i) for 1 day, (ii) after

filteration, (iii) elution of the loaded sorbent with 1 (N) HCl .

2.7 Instrumentation : The estimation of manganese and uranium in the original feed sample (

i.e., before the sorption experiment), the filtrate and eluent obtained after the experiments were carried

out by flame atomic absorption spectrophotometry using GBC-Avanta atomic absorption spectro-

photometer and differential pulse adsorptive voltammeter, respectively.

3. Results and Discussion:-

Application to field samples

Field sample collection:- Uranium mining and milling effluent plant inlet sample and

the uranium tailings leachate containing toxic heavy metals such as Pb, Cd present in significant

concentration, which later on enters into the aquifers by the run-off water. Manganese and uranium,

also present at higher concentration in the aquifer surrounded by the tailing pond compared to any

normal ground water or surface water sample. There may be innumerous interferences at significant

concentration in tailing leachate (actually, 6 gm soil samples were taken and digested with HNO 3 and

HF in the ratio of 2:1 of 25 ml sample volume. From this, 2 ml aliquot was taken and diluted to 25 ml

to achieve better analytical accuracy) and in ETP inlet (was taken directly as it was in the liquid form).

In this regard, the prepared solution required to be processed and analyzed for the total metal content

(of manganese lead, cadmium and uranium) in them.

Application to field samples: - Most common mode of occurrence of natural uranium in the

tailings is in association with exchangeable form. The substantial amount of these toxic metals, which

is present in the aquifers, may be possibly a soluble fraction of TPL or ETP inlet samples, which

enters through the pores of soil. To purify the ground water it can be contacted with sorbent much

before the contamination stage is reached by applying the resin on the outside covering of the duct of

ETP or barrier of the reservoirs (TP). Uptake of contaminated metal ions from this effluent is

characterized by calculating distribution coefficient (Kd) in ml/g and immobilization of the metals by

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elution ratio, as per the equations given in equation (2) and (3), respectively and presented in Table 3.

TPL results signify high distribution co-efficient for Mn and Pb, and Cd is fully chelated in the

sorbent, which is difficult to elute. The result implies a high immobilization of metal ions, especially

Cd and Pb which are toxic. Although manganese and uranium can be sorbed substantially and a higher

elution can also be achieved with these two metal ions

For ETP inlet samples, sorbent signifies a satisfactory uptake and immobilization (by low

elution) of uranium even from low level compared to uranium present in TPL. Manganese, which is

integrally associated with all elements and present in much higher level, shows highest distribution co-

efficient (898.49 ml/g) values conducted so-far. The distribution co-efficient (119.72 ml/g) of Lead

implies significant sorption with the tailor-made sorbent can be achieved. However, the discrimination

of some Kd and elution characteristics can be attributed to the huge amount of other impurities present

in the soil, as well as medium pH and the specific choice of functional groups and their resisted

swelling characteristics, the chemical form/cluster formation of metal ions and the diffusion of metal

moieties/cluster inside the porous matrix/resin.

4. Conclusion:-

Macromolecular polymeric hydrogel chelating tailor-made resin has been prepared in the

laboratory by varying three step method depending on the situation of the site as well as application

devices. It was also taken into consideration that what kind of metal ion is present and the power of

immobilization so that it should not enter into aquifers. The sorbent can be spread in granular form or

in can be used on the barrier of well-wall to restrict the diffusion into the drinking water. The in-house

developed sorbent shows a promising result in both the purpose i.e., i) chelating the metal ions and ii)

in immobilization. However the discrimination of some Kd and elution characteristics can be

attributed to the huge amount of other impurities present in the soil, as well as medium pH and the

specific choice of functional groups and their resisted swelling characteristics, the chemical

form/cluster formation of metal ions and the diffusion of metal moieties/cluster inside the porous

matrix/resin.

For sample preparation and analysis Mr. Dilip Choudhury (EAD); and in procurement and

preparation of resin material, help from Mr. Chunu Soren (DD) is acknowledged.

References:

1. Sangita Pal, V. Ramachandhran, S. Prabhakar, and P.K. Tewari, Recovery of valuables

from sea water, Trombay Symposium on Desalination and Water Reuse (TSDWR 07), Feb 7-9, 2007.

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2. S. Mishra, Sangita Pal, G.G.Pandit, P.K.Tewari and V.D.Puranik, Use of Polymeric

Sorbent for the Uptake of Heavy Metals and Radionuclides from Different Effluents,

Proceedings of 16th National Symposium on Environment on Ground Water Resources,Conservation and Management, pp-161-165, held at Hisar, Hariana, during 16th-18th July 2008.

3. Sangita Pal, S. Mishra, G.G.Pandit, K.L. Thalor, P.K.Tewariand V.D.Puranik.Potentiality

of Polymeric Sorbents for Immobilization and Recovery Aspect of Contaminants from NuclearEffluents accepted for CHEMCON 2008.

4. Sangita Pal, S. Mishra, G.G.Pandit, K.L. Thalor, P.K.Tewari and V.D.Puranik.

Performance of In-House Resin for Recovery of Uranium along with otherValuables poster presentation for Homi Bhabha Centenary DAE-BRNSConference on 50 years of nuclear grade uranium metal production,31.01.2009.

5. Slavik D., Dev V., Yoram K., Doloressa G., David F., Ting K.C. and Burt E. (1997).Removal of Uranium from water using terrestrial plants. Environ. Sci. Technol. 31, 3468-3474.

6. Fischer J and Lieser K.H (1993), Cellulose exchangers with tailor made chelating groups for

selective separation of uranium, Fresenius Journal of Analytical chemistry, volume 346, pages

10-11.

TABLE 1

Uptake and elution characteristics of uranium with other metal ions in tailing pond leachate

(TPL) and inlet of effluent treatment plant (ETP)

Sample Element Initial conc.(C0)

(g in 25 ml)

Equilibrium

Conc. ( Ce)(g in 25 ml)

Distribution-

efficient (Kd)

(ml/g)

Elution

ratio (%)

Tailingsleachate

U 24.86 10.72 63.77 52.47

Mn 240 43.5 218.39 47.22

Pb 3.51 0.409 366.56 10.74

Cd 0.789 Nil 13.9

ETP inlet

in contactU 3.55 Nil 6.19

Mn 53.75 2.73 898.49 57.6

Pb 0.267 .0765 119.72 47.77

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a novel approach for toxicity removal through tailor-made sorbent

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