400417 Overcoming Kinetic Limitations of Cr(VI) Adsorption Onto Biosorbents: Biomas-Magnetite Bionanocomposite

Monday, April 27, 2015
Exhibit Hall 5 (Austin Convention Center)
Agnes Pholosi, Chemistry, Vaal university of Technology, Vanderbiljpark, South Africa, Augustine E. Ofomaja, Chemistry, Vaal university of Technology, Vanderbiljpark, WV, South Africa and E.B Naidoo, Chemistry, Vaal University of Technology, VanderbiljPark, South Africa

OVERCOMING KINETIC LIMITATIONS OF Cr(VI) ASORPTION ONTO BIOSORBENTS: BIOMAS-MAGNETITE BIONANOCOMPOSITE

Pholosi A., Ofomaja A.E., Naidoo E.B.

Biosorption and Water Treatment Research Laboratory, Department of Chemistry,

Faculty of Applied and Computer Sciences, Vaal University of Technology, P. Bag X021,

Vanderbijlpark, 1900 South Africa.

 


INTRODUCTION

Biosorbents are a promising class of adsorbents discovered in the last decade for their potential application in water and waste water treatment (Abdolali et al., 2014). One class of biosorbents are the lignocellulosic materials obtained from plant wastes or by-products (Ngah and Hanafiah, 2008). Lignocellulosic materials are composed of macromolecules such as lignin, cellulose and hemicellulose compounds† which are known to contain groups that exhibits exchange and complexating properties (Ofomaja and Ho, 2007). The lignin portion of lignocellulosics acts a binding agent holding the celluloses fraction to the hemicellulose fraction and keeps the plant materials erect and firm. As a result particles of biosorbents materials applied as adsorbents possess very low porosity and internal surface causing restriction of fluid flow.

This feature of biomasses, as they are called generally leads to several challenges when during application of biomasses as adsorbents and these includes (i) low diffusion rates of pollutants within the adsorbent particles during adsorption (Thinh et al., 2013), (ii) high operating pressures when applied in packed columns (Yavuz et al., 2006), low adsorption rates and capacities (Thinh et al., 2013). To overcome these shortcomings researchers have resorted to reducing the sizes of the biomass materials by crushing or grinding them to smaller particles sizes. Small particle sized materials for adsorptions are also known to come with its challenge, which is the separation of the adsorbent particles from the treated solution at the end of contact (Safarik et al., 2007).

Currently researchers have turned to the use of bio-nanocomposites consisting biomaterials coated with magnetic nanoparticles to overcome these limitations. Although much success have been achieved in applying these novel biomaterials composites yet little is known about how and to what extent these limitations are dealt with. This paper therefore seeks to study how and to what extent to which kinetic limitations are avoided when pine biomass coated with magnetite is applied as adsorbent for Cr(VI) from aqueous solution.

METHODS:

Pine cone was treated with 0.15 mol/dm3 NaOH and the 1.0 g of the product added to a solution containing a mixture of Fe2+/Fe3+ of molar ratio 2:1. Magnetic was then precipitated onto the pine surface using NH4OH. The biocomposite and the raw pine biomass were characterized. Batch kinetic adsorption studies of Cr(VI) from aqueous solution was performed using both materials from a 150 mg/dm3 solution at 26, 31, 36, 41 and 46 oC. Three nonlinear kinetic and three diffusion models were applied to test the kinetic data.†

RESULTS:

FTIR spectra for the NaOH treated and MNP-Pine composite are shown in Figs. 1 and 2. The presence of Fe-O and Fe-OH bonds in the composite confirms that presence of magnetite in the bio-nanocomposite.

Fig. 1: FTIR of NaOH treated pine

Fig. 2: FTIR of MNP-Pine Composite.

Surface characteristics of the NaOH treated and the bio-composite are shown in Table 1. The results shows that an increase of BET surface from 2.67 m2/g to 68.91 m2/g in the bio-composite. The external surface and pore width were also increased drastically with the composite. The small size of the magnetite coating as well as the possibility of magnetite formation within the pores of the pine causing expansion and breakup of the pine particles may be responsible for this happening.†

The kinetic data for the adsorption of Cr(VI) onto NaOH and MNP-Pine composite were fitted to the intraparticle diffusion model in Fig. 3. The results indicate the while the metal uptake per square-root of time profile for the NaOH treated pine can be broken into two sections, the MNP-Pine composite profile can be broken into three sections.

†Fig. 3: Intraparticle Diffusion plots for NaOH treated pine and MNP-Pine.

The implication of this is the decrease in kinetic restriction by the creation of increased internal surface in the composite. The intraparticle diffusion constants were found to be higher for the bio-composite than for the NaOH treated pine signifying free flow of aqueous solution through the internal surface of the material. The relationship between intraparticle diffusion constant and temperature is shown in Table 2. Also it was observed that the constants increased with increasing solution temperature. Increasing solution temperature increases the rate of migration which is responsible for the increased diffusion of the pollutant through the adsorbent material.

CONCLUSION:

Kinetic limitations associated with the use of biomaterials as adsorbents can be eliminated by coating of biomaterials with nanoparticles. The resulting bio-composite processes better surface properties and improved diffusion properties for pollution removal from aqueous solution.

References

Safarik, I., Lunackova, P., Mosiniewicz-Szablewska, E., Weyda, F., Safarikova, M. Adsorption of water-soluble organic dyes on ferrofluid-modified sawdust. Holzforschung 61 (2007) 247-253.

Yavuz, H., Denizli, A., GŁngŁnes, H., Safarikova, M., Safarik, I. Biosorption of mercury on magnetically modified yeast cells. Separation and Purification technology 52 (2006) 253-260

Abdolali, a., Guo, W.S., Ngo, H.H., Chen, S.S., Nguyen, N.C., Tung, K.L. Typical linocellulosic wastes and by-products for biosorption process in water and wastewater: Bioresource Technology 160 (2014) 57-66.

Ngah.,W.S.W., Hanafiah, M.A.K.M. Removal of heavy metal ions from wastewater by chemically modified plant waste as adsorbents: A review. Bioresource Technology 99 (2008) 3935-3948.

Table 1: Surface Properties

Properties††††††††††††††††††††††††††††††† NaOH treated Pine ††††††††††††††† MNP-Pine Composite

Surface area (m2/g)††††††††††††††††† 2.67†††††††††††††††††††††††††††††††††††††††† 68.91†††

Pore volume (cm3/g)††† †† †††††††† 0.002†††††††††††††††††††††††††††††††††††††† 0.153††††††††††††††††††††††††††††††††††††††

External surface (m2/g)†††††††††† 2.25†††††††††††††††††††††††††††††††††††††††† 48.79

Ave. pore width (nm) ††††††††††††††††††††††† 8.89†††††††††††††††††††††††††††††††††††††††† 33.10

Table 2: Diffusion parameters for Cr(VI) adsorption onto NaOH treated and MNP-Pine at different temperatures

Temp. (oC)†††††† ††††††††††††††††††††††† Intraparticle diffusion rate constant (mg/g min0.5)

††††††††††††††††††††††††††††††††††† NaOH Treated Pine††††††††††††††††††††††††††† MNP-Pine Composite

††††††††††††††††††††††††††††††††††† ki1††††††††††††††††††††††††††††††††††††††††††††††††††††††† ki1††††††††††††††††††††††††††††††† ki2

26††††††††††††††††††††††††††††††† 0.1465†††††††††††††††††††††††††††††††††††††††††††††††† 0.1404†††††††††††††††††††††††† 0.6828

31††††††††††††††††††††††††††††††† 0.1994†††††††††††††††††††††††††††††††††††††††††††††††† 0.2192†††††††††††††††††††††††† 0.8464

36††††††††††††††††††††††††††††††† 0.2450†††††††††††††††††††††††††††††††††††††††††††††††† 0.2662†††††††††††††††††††††††† 1.0963

41††††††††††††††††††††††††††††††† 0.2690†††††††††††††††††††††††††††††††††††††††††††††††† 0.3142†††††††††††††††††††††††† 1.3046

46††††††††††††††††††††††††††††††† 0.3110†††††††††††††††††††††††††††††††††††††††††††††††† 0.3789†††††††††††††††††††††††† 1.7028†††††††††††††††††††††††††††††††††††† ††††††††††† ††††††††††††††††††††††††††††††††††† †††††††††††††††††††††††

 


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