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STUDIA UNIVERSITATIS BABEŞ-BOLYAI, CHEMIA, LIV, 3, 2009 HEAVY METAL IONS REMOVAL FROM MODEL WASTEWATERS USING ORAŞUL NOU (TRANSILVANIA, ROMANIA) BENTONITE SAMPLE ANDRADA MĂICĂNEANU a , HOREA BEDELEAN b , SILVIA BURCĂ a , MARIA STANCA a ABSTRACT. A bentonite sample from Oraşul Nou deposit, (Transilvania, Romania), was used to remove heavy metal ions (Zn 2+ , Pb 2+ , Cd 2+ ) from model monocomponent wastewaters. A representative sample of bentonite (ON) was characterised using, wet chemical analyses, XRD, BET and FTIR. The bentonite deposit from Oraşul Nou formed by alteration of rhyolites and perlites. Mineralogically, they contain clay minerals (montmorillonite, and subordinately kaolinite, illite), cristobalite, carbonates, zeolites (clinoptilolite), iron oxi-hydroxides and relics of primary minerals such as quartz and feldspar.The bentonite sample was used as powder, (d < 0.2 mm), without any chemical treatment. We studied the influence of the working regime, static and dynamic, concentration, and solid : liquid ratio over the process efficiency. We used monocomponent synthetic wastewaters containing zinc, lead and cadmium ions. The bentonite sample proved to be efficient for the removal of the considered heavy metal ions, removal efficiencies up to 100% (lead and zinc removal) were reached. First-order, pseudo- second-order and Elovich models were used to study the adsorption kinetic of zinc ions on the bentonite sample. Keywords: bentonite, montmorillonite, zinc, lead, cadmium, removal INTRODUCTION Heavy metals such as Cd, Pb and Zn are usually found in Earth’s crust mainly as minerals and are mobilised by soil erosion, volcanic activities and forest fires (natural sources). Heavy metals concentration in the environment increased drastically due to intense human activities (anthropogenic sources). Cadmium, lead and zinc can be found in air (eroded particles), water (in ionic form, from wastewaters insufficient treated or mobilised from polluted soils) and soil (adsorbed on soil particles) in different combinations. Heavy metals exposure can take place by inhalation (contaminated air, cigarette a Universitatea Babeş-Bolyai, Facultatea de Chimie şi Inginerie Chimică, Str. Kogălniceanu Nr.1, RO-400084 Cluj-Napoca, România, andrada@chem.ubbcluj.ro b Universitatea Babeş-Bolyai, Facultatea de Biologie şi Geologie, Str. Kogălniceanu Nr. 1, RO-400084 Cluj-Napoca, România, bedelean@bioge.ubbcluj.ro
128 ANDRADA MĂICĂNEANU, HOREA BEDELEAN, SILVIA BURCĂ , MARIA STANCA smoke, working exposure), ingestion (water and contaminated food) and dermal (contact with contaminated soil, heavy metal compounds) exposures. With exception of Zn, which in small quantities is nutritive elements, heavy metals are toxic to humans, animals and plants. Heavy metal ions have the tendency to accumulate in living organisms causing a variety of disorders [1-3]. Heavy metal ions can be removed from the environment using a variety of methods such as precipitation, solvent extraction, vacuum evaporation, membrane technologies, adsorption or ionic exchange, the selection of a method depending mainly upon the heavy metal ion concentration. Adsorption is used when concentration of heavy metal ions is small, but is higher that the allowable concentration according to environmental legislation. Low-cost adsorbents such as natural zeolites, clay minerals (kaolinite, montmorillonite), chitosan, peat moss, fly ash, coal, natural oxides (aluminium oxide, ferric oxide), industrial waste (waste slurry, iron (III) hydroxide, lignin, furnace slag, sawdust, activated red mud, bagasse fly ash, brewery waste biomass), rice husk, coconut shell, agricultural waste, etc. were all considered as adsorbents for heavy metal ions (cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel, zinc) removal from wastewaters [4,5]. Due to their availability and low costs, natural materials such as zeolites and clay minerals became object of many research papers in the last years. In Romania, most studies related to the identification of new materials used in environmental protection, concerned natural zeolites (zeolitic volcanic tuffs), which were used in various applications based on their properties [6]. Clays, especially bentonite clays, are present in large amounts in Romania. Bentonite collected from Transilvanian deposits, Petreşti, Oraşul Nou and Valea Chioarului were considered for heavy metal ions (Petreşti), ammonium ions (Petreşti, Valea Chioarului, Oraşul Nou) and organics (Petreşti, Oraşul Nou) removal from wastewaters [7-9]. Clay minerals are aluminium hydrosilicates, crystallized in monoclinic system, characterized by planar reticular structures. Stratified structure of mineral clays is determined by the combination in one reticular plan (structural unit) of two cationic layers, one layer in which silicon is coordinated tetrahedric with O⋅OH (tetrahedric level Te) and one layer in which aluminium is coordinated octahedric with O⋅OH (octahedric level Oc). These layers are bonded between them with van der Waals bonds forming the structural unit. According to the numbers of Te and Oc layers, clay minerals are classified in 1Te:1Oc (e.g. kaolinite), 2Te:1Oc (e.g. montmorillonite) and 2Te:2Oc (e.g. chlorite). The layered structure of the clay minerals and presence of isomorphous replacement of Si 4+ with Al 3+ (negative charge compensated by Na + , K + , Ca 2+ and/or Mg 2+ ) determines their main properties: swelling, water and organic compounds adsorption and ionic exchange capacity [4,10].
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ANA-MARIA CORMOS, JOZSEF GASPAR, AN
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Studia Universitatis Babes-Bolyai C
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MARCELA ACHIM, DANA MUNTEAN, LAURIA
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STUDIA UNIVERSITATIS BABEŞ-BOLYAI,
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STUDIES ON WO3 THIN FILMS PREPARED
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