Study Of Pd(ii) Adsorption On Powder Graphite
STUDY OF Pd(II) ADSORPTION ON POWDER GRAPHITE
AND ACTIVATED CARBONS
R. Dobrowolski
Analytical Laboratory, Faculty of Chemistry, Maria Curie Sklodowska University 20-031 Lublin, Poland
Palladium nitrate has been recently proposed as a generally applicable chemical modifier for trace elements determination by graphite furnace atomic absorption spectrometry (GFAAS). The physical mechanism of modification occurs when the solutions are proposed [1]. Probably the reduction of palladium on graphite wall takes place even at room temperature. Modification of Hg(II) by palladium nitrate at room temperature was observed [2,3]. The aim of this part of paper was to investigate the influence of the main parameters (pH value, ion strength, matrix effects, and companion ions) on Pd(II) adsorption from aqueous solution on the super pure powder graphite used for the graphite furnace AAS manufacture (SGL CARBON GmbH, Werk Ringsdorff). Based on experimental data the mechanism of Pd(II) adsorption on graphite was suggested.
For contrast the adsorption of Pd(II) on the activated carbon was studied too. The adsorption yield of the ion metals on the activated carbons depends on many parameters [4]. These parameters can be divided into the three groups: parameters describing the nature of carbon surface, specific ion properties and the solution components. Depending on the system investigated, the role of each group of parameters is different. The adsorption centers on the carbon surface are in conjugation with pH values of the bulk solution. The equilibrium between the surface functional groups and the solution depends on the pH value of the solution. Adsorption of ions is affected by the surface charge of the particles of activated carbon and some specific interactions between particular kinds of the surface groups and the ions. This effect plays a significant role in the case of the adsorption of multivalent cations. The strength of interactions between particular surface groups and the ions depends on both the kind and activity of the adsorption center and the ion properties. The most active adsorption centers are occupied firstly by the ions, then the adsorption on the
other centers takes place. Exhaustion of the most reactive adsorption centers causes the change of adsorption mechanism. Therefore the studies of the initial part of the ion adsorption isotherms on the activated carbon were carried out. In this study the powder activated carbons Nr 1860, manufactured by Merck, Germany and Medical Carbon (Carbo Medicinalis) produced by The Dry Destillation of Wood Plant in Hajnowka, Poland were studied. Application of activated carbons for a preliminary separation and concentration of trace amounts of the elements and further their determinations by atomic spectroscopy methods involves very fine purification of carbons from mineral additives. Commercially available carbons were leached by concentrated hydrochloric acid using a Soxhlet apparatus made of quartz and by hydrofluoric acid in the Teflon vessel. Then the studied carbons were modified using two different methods e.g. oxidation by 13% H2O2 or by concentrated nitric acid. The aim of this modification was obtain an adsorbent with well-defined nature of the carbon surface.
References
1. H. Qiao and K. Jackson, Spectrochim. Acta 46B, 1841 (1991).
2. P. Bermejo-Barrera, J. Moreda-Pineiro, A. Moreda-Pineiro and A.Bermejo-Barrera, Anal. Chem. Acta, 296, 181, (1994).
3. R. Dobrowolski and J. Mierzwa, Analyst, 121, 897 (1996).
4. R. Dobrowolski, Adsorption and its application in industry and enviromnetal protection, edyt. by A. Dąbrowski, Elsevire Science, Amsterdam, pp.777-805, (1999).
Related articles::