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THE POTENTIAL APPLICATIONS OF ALUMINOSILICATES FOR METALS REMOVAL FROM WATER PowerPoint PPT Presentation


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Technical University of Czestochowa Institute of Environmental Engineering Czestochowa, Poland. THE POTENTIAL APPLICATIONS OF ALUMINOSILICATES FOR METALS REMOVAL FROM WATER. M agdalena Zabochnicka-Świątek. Heavy metal pollution . TOXICITY human health living resources

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THE POTENTIAL APPLICATIONS OF ALUMINOSILICATES FOR METALS REMOVAL FROM WATER

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The potential applications of aluminosilicates for metals removal from water l.jpg

Technical University of Czestochowa

Institute of Environmental Engineering

Czestochowa, Poland

THE POTENTIAL APPLICATIONS OF ALUMINOSILICATES FOR METALS REMOVALFROM WATER

Magdalena Zabochnicka-Świątek


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Heavy metal pollution

TOXICITY

  • human health

  • living resources

  • ecological systems


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HEAVY METALS IN THE ENVIRONMENT

1. ARSENIC (As)

  • controlled by adsorption (iron and manganese oxides) and precipitation

    2.COPPER (Cu)

  • adsorption and ion exchange (inorganic and organic materials)


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HEAVY METALS IN THE ENVIRONMENT

3.LEAD (Pb)

  • may be immobilized by adsorption (organic matter), ion exchange (hydrous oxides) or by chelation (humic or fulvic acids)

    4. NICKEL (Ni)

  • Adsorption (organic matter), ion exchange, chelation, precipitation and coprecipitation (hydrous iron and manganese oxides)


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Aluminosilicates

Aluminium (Al)

Silicon (Si)

Oxygen (O)

  • many naturally occurring aluminosilicates

  • hydrated aluminosilicate minerals – zeolites


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The most important properties of zeolites

  • adsorption ability for a number of compounds (metal-ions, vapours and gases)

  • high chemical-, temperature- (500 - 10000C) and radiation stability

  • low density and large void volume of dehydrated samples (900 m2/g)

  • reversible water absorption - 1 do 25%


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Schematic structure of natural zeolite - TETRAHEDRON

The cells:POLYHEDRONS inside of which there are voids of different sizes dependent on the zeolite type A- 0.4 nm i type X- 0.9 nm

sodalite faujasite


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Zeolites

CATION EXCHANGE

  • The size and shape of intrinsic canals determines which cations and molecules can enter or remain outside the crystal structure.

    ADSORPTION CAPACITY

  • Cations present in the canals in the zeolite structure readily undergo the process of exchange (exchangeable cations). Ions of heavy metals can be replaced with Na, Ca, Mg and K.


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Cation Exchange Capacity

Differences:

  • particle density

  • cation selectivity

  • molecular pore size


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Heulandite Analcime Gmelinite

Mordenite Chabazite


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Clinoptilolite

  • adsorption capacity

  • ion exchange selectivity

  • molecular-sieves ability

  • catalytic properties

  • high thermal stability

(Na, K, Ca)4Al6Si30O72•24H2O


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Clinoptilolite

  • Modifications: physical and chemical methods - increases the content in a single cation = homoionic form

  • Regeneration: would enable the recovery of both

    the sorbent and metal

  • Sythetic zeolites: controlled and known physico-chemical

    properties

    0,125 mm


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The maximum values of ion exchange capacity for clinoptilolite


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Arsenic removal from water

Studies on both non-activated and activated zeolites, as well as on zeolites hydrogenated or modified with iron:

  • sorption of arsenic takes place more slowly on zeolites in comparison to ferrihydrite

  • removal of arsenite by some of the iron-modified zeolites is comparable with the amount removed by iron


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Competition processes influence the selectivity series

Natural:

Pb2+ > Cd2+ > Zn2+ ≥ Cu2+ > Ni2+ > Hg2+

Pb2+> Fe2+> Cr2+ ≥ Cu2+

Pb2+> Cu2+> Cd2+> Ni2+

Synthetic:

Pb2+ > Cd2+ > Cu2+ > Ni2+


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The process has three stages

  • Fast adsorption on the zeolite microcrystal surfaces.

  • The inversion stage: short-time prevalence of the desorption process connected with the diffusion flow from the clinoptilolite microcrystal’s interior.

  • The moderate adsorption in the microcrystal’s interior.


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The application of zeolites provide an economical means of removing mixed heavy metals from water.

Each metal has a tendency to form specific compounds in water and they can be removed by different mechanisms – adsorption or/and ion exchange.

The removal of heavy metals from water because of their toxic effects on living species is extremely important.

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Conclusions


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The differences in the ion exchange selectivity of clinoptilolite are probably caused by competition processes.

Sorption of arsenic on zeolites requires further research.

Modifications of clinoptilolite enhance its ion exchange ability by optimising the selectivity and sorption efficiency.

Clinoptilolite may be used, as a low-cost, nontoxic and abundant source, for the removal of heavy metals from water.

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Thank you very much for your attention

Magdalena ZABOCHNICKA-ŚWIĄTEK


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