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NATURAL ZEOLITES AS MULTIFUNCTIONAL ENVIRONMENTAL FRIENDLY MATERIALS

THEIR APPLICATION FOR REMOVAL OF Pb AND Zn FROM

BINARY SOLUTIONS

Marina TrgoFaculty of Chemistry and Technology

University of SplitCroatia

2nd Slovenian-Croatian Symposium on ZeolitesLjubljana, 2009

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natural aluminosilicate minerals with crystal three-dimensional structure hydrated cations are located inside framework structure and weakly bound

with structure advantages of these natural minerals are their large deposits on the Earth,

easiness of exploitation and mostly unnecessary treatment for practical application

the most important deposits are in the United States, Mexico, Ukraine, Slovakia, Italy, Greece, Turkey, Russia, Serbia, Romania, Bulgaria, Georgia, Armenia, Cuba and Croatia

discovered more than 260 years ago by the Swedish mineralogist A.A.F. Cronstedt, commercial exploitation started ~30 years ago

the end of 70-ties is proclaimed as "new discovery" of natural zeolites about 50 different minerals of zeolites are discovered in nature, but some

of them have commercial valuable currently, the world’s annual production of natural zeolite is about 4 million

tons

NATURAL ZEOLITES - deposits and properties

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NATURAL ZEOLITES - physical and chemical properties

many natural zeolites are synthesized in laboratory difference between natural zeolite minerals is manifested in content of

hydrated cations which occupied pores and channels, ratio of Si/Al in structure and number of water molecules

zeolites have different dimensions of pores and channels responsible for their physical and chemical properties

each examined sample is mineralogical heterogeneous, and quantification of its mineralogical composition in mostly complex procedure.APPLICATION of natural zeolites is based on or more of the following properties:

- cation exchange- adsorption and related molecular sieving- dehydration and rehydration- biological activity- catalytic

All of these properties have been intensively investigating.

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Cation exchange

- the ability to exchange inherent cations for other cations on a basis of ion selectivity

- high cation exchange capacity for heavy metal cations that can be removed from liquid effluents through the process of ion-exchange. These cations include lead, silver, cadmium, cobalt, zinc, copper, mercury, magnesium, iron, aluminium, chromium and others. Some natural zeolites are applicable in industries such as mining, electroplating and electronics. Giant industrial houses, like IBM, have deployed this application for treatment of wastewater containing heavy metals.

-selectivity for ammonium cations, the natural zeolites lower the level of ammonium in wastewaters and sewages to non-toxic, acceptable levels. The zeolite beds can be regenerated and recycled indefinitely.

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Adsorption and related molecular sieving

The adsorption on molecular sieves is therefore dependent

on the following physical molecular properties:

- Size and Shape; molecules or ions larger than the pore

opening of the zeolite can not be adsorbed, smaller

molecules or ions can.

-Molecular Polarity; due the charge on outer and inner

zeolitic surface particle, molecules with large polarity or

polarisability can be adsorbed preferentially under identical

conditions.

The adsorption process is fully reversible and of purely physical nature. The structure of the zeolite is unchanged during the adsorption process and its later regeneration.

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- this property is used for selective absorption of organic

molecules and for absorption of radioactive ions (absorber of Sr

and Cs radioisotopes in the nuclear industry and for clean up of

nuclear accidents - applied in the Chernobyl disaster).

Adsorption and related molecular sieving

- adsorption process on zeolite is used to remove polar H2O, H2S,

and CO2 from natural gas and developed a zeolite-adsorption

process for purifying methane produced in a landfill.

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Dehydration and rehydration

Natural zeolites may hold water up to 60% of their weight due to a high porosity of the crystalline structure. Water molecules in the pores could be easily evaporated or reabsorbed without damage to such structures.

Zeolites assure a permanent water reservoir, providing prolonged moisture during dry periods; they also promote a rapid rewetting andimprove the lateral spread of water into the root zone during irrigation. This results in a saving in the quantity of water needed for irrigation.

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Biological activity

- natural zeolite has been shown to exhibit diverse biological activities and has been used successfully for the treatment in medical therapy- promotes better plant growth by improving the value of fertilizer, helps preventing the plant from burning, that can be caused by over use of fertilizer, by trapping and slowly releasing valuable nutrients

- as additive in concentrated animal growing facilities improve feed conversion, reduce airborne ammonia up to 80%, act as a mycotoxin binder, and improve bone density, it can be used in general odour elimination for all animal odours

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- modifying the surface of clinoptilolite with long-chain quaternary amines allowed it to adsorb benzene, toluene, and xylene in the presence of water

-surface modified natural zeolites remove toxic compounds from animal food

- natural zeolite can be treated further with additional amine to produce anion exchangers capable of taking up chromate, arsenate, selenate, and other metal oxyanions from aqueous solutions

Surface modification of natural zeolites

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Physical characteristics of some naturally occurring zeolites

Natural zeolite - clinoptilolite

- is one of the most investigated natural zeolites

- unit cell formula is (Na, K)6Si30Al6O72 · 20H2O

- high silica zeolite, Si/Al≥4, HEU type framework topology- Croatia has deposits of natural zeolite with content of 30-50% of clinoptilolite- recent investigations in Croatia have done with Serbian zeolite which contain ~80% clinoptilolite

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Clinoptilolite Examinations on Faculty of Chemistry and Technology University of Split

- removal of Cu, Zn and Pb on natural and pre-treated zeolite

using batch

method

- study of kinetic and thermodynamic of Zn on natural zeolite

- removal of Pb or Zn on natural and pre-treated zeolite using

column

method

- removal Pb and Zn from binary solution on natural and pre-

treated

zeolite using column method

-recent examinations are directed on removal of metal ions on

iron coated zeolite

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Removal Pb and Zn from binary solution on zeolite-clinoptilolite using column method

SERVICE CYCLE- experiments were performed in glass columns, d=12mm, H=40mm- binary aqueous solutions of lead and zinc ions have been prepared by

dissolving of Pb(NO3)2 and Zn(NO3)2 in doubly distilled water

- flowrate was 1 ml/min Concentrations of metal ions in binary solutions for each service cycle.

Concentration ratio

co(Pb)/co(Zn)

co(Pb+Zn)mmol/l

co(Pb)mmol/l

co(Zn)mmol/l

0.19 1.031 0.165 0.866

0.71 1.149 0.478 0.671

0.95 1.062 0.516 0.546

1.37 1.060 0.612 0.448

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0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 200 400 600 800BV, -

c/c o

,-

Pb/Zn=0.19Pb/Zn=0.71Pb/Zn=0.95Pb/Zn=1.37

c/co =c(Pb+Zn)/co(Pb+Zn) Pb/Zn= co(Pb)/co(Zn)

Removal Pb and Zn from binary solution on zeolite-clinoptilolite using column method

exhaustion points

breakthrough points

BV=V/VS

14c/co =c(Pb or Zn)/co(Pb or Zn)

Pb/Zn=0.19

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 200 400 600 800 1000BV,-

c/c o

, -ZnPbPb+Zn

Pb/Zn=0.71

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 200 400 600 800 1000BV,-

c/c o

, -

ZnPbPb+Zn

Pb/Zn=0.95

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 200 400 600 800 1000BV,-

c/c o

,-

ZnPbPb+Zn

Pb/Zn=1.37

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 200 400 600 800 1000BV,-

c/c o

, -

ZnPbPb+Zn

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Concentration ratio Pb/Znin influent

VB,BV

VE,BV

qB, mmol/g

qB(Pb)/qB(Zn)qE,

mmol/g

qE(Pb)/qE(Zn)

0.19218.9

564.0

Pb+Zn 0.336

0.189

0.545

0.174Pb 0.053 0.080

Zn 0.281 0.460

0.71206.8

583.9

Pb+Zn 0.337

0.714

0.521

1.012Pb 0.140 0.260

Zn 0.196 0.257

0.95221.2

614.8

Pb+Zn 0.336

0.942

0.509

1.980Pb 0.163 0.396

Zn 0.173 0.200

1.37

209.0

572.8

Pb+Zn 0.312

1.364

0.581

2.010Pb 0.180 0.388

Zn 0.132 0.193

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Removal Pb and Zn from binary solution on zeolite-clinoptilolite using column method

REGENERATION CYCLE- experiments were performed in glass columns, d=12mm, H=40mm- regeneration solution has been prepared by dissolving of NaNO3 in doubly distilled water - flowrate was 1 ml/min

0

5

10

15

20

25

0 40 80 120 160BV, -

c(Z

n+P

b), m

mol

/l

.

Pb/Zn=0.19Pb/Zn=0.71Pb/Zn=0.95Pb/Zn=1.37

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REGENERATION CURVES for particular ions

Regeneration was completed with 100 BV of solution.

0

5

10

15

20

25

0 40 80 120 160BV, -

c(P

b), m

mol

/l .

Pb/Zn=0.19Pb/Zn=0.71Pb/Zn=0.95Pb/Zn=1.37

0

5

10

15

20

25

0 40 80 120 160BV,-

c(Z

n), m

mol

/l

.

Pb/Zn=0.19Pb/Zn=0.71Pb/Zn=0.95Pb/Zn=1.37

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Removal of lead and zinc on zeolite using column method is applicable in practice.

CEC of zeolite doesn't depend of concentration ratio in feeding solution.

The quantity of regenerated zinc is significantly lower compared to the lead. The only exception is the binary solution with a small Pb/Zn ratio.

This confirms that lead was mostly bound onto zeolite, possible due to replacement of zinc ions with lead ions during the service cycle.

This replacement is due to higher selectivity of natural zeolite for lead ions. Lower radius of the hydrated Pb2+ ion in comparison to Zn2+ provides for its better mobility through the framework structure.

Advantage of column method is regeneration of zeolite what enables unlimited use of the same bed.

CONCLUSIONS

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Presented investigations are part of the scientific project

"Natural zeolites in water protection"

which has been financing by Ministry of Science, Education and Sports of the Republic of Croatia

Researchers on the project:

Jelena Perić, full professor - senior researcher

Marina Trgo - assistant professor

Nediljka Vukojević Medvidović- assistant professor

Ivona Nuić - assistant

Marin Ugrina - assistant

Thank you!

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Thank you!