Abstract
The purpose of the study described in this paper was to compare removal of Zn(II) from aqueous solutions by use of two adsorbents—alkali-modified fly ash (FAN) and alkali and dye-modified fly ash (FAN-MO). The effects of four conditions (solution pH, contact time, initial metal ion concentration, and dose of adsorbent) on removal of Zn(II) at 27 ± 5 °C were studied in batch mode. Adsorption of Zn(II) was greater at pH 4.0 for FAN (76.49 %) and at pH 5.0 for FAN-MO (24.72 %). Maximum adsorption of Zn(II) by FAN and FAN-MO was achieved after 50 min. The linear forms of the Langmuir, Freundlich, Tempkin, D–R, Harkin–Jura, and Frenkel–Halsey isotherms were used for experiments with different concentrations of the metals. Adsorption of Zn(II) ions satisfied the Langmuir isotherm model only. The adsorption capacity of both adsorbents was also investigated by column studies. Adsorption of Zn(II) ions on FAN in column studies (45.33 %) was lower than in batch mode studies. For FAN-MO, adsorption was 37.88 % in column studies, again lower than in batch mode studies. Fly ash modified by alkali had a higher adsorption capacity for Zn(II) ions than fly ash modified by alkali followed by addition of dye.
Highlights
Fly ash is an amorphous mixture of ferroaluminosilicate minerals generated by combustion of ground or powdered coal [1]
In this paper we report a comparative study of the efficiency of Zn(II) uptake on fly ash modified by treatment with alkali (4 M NaOH) (FAN) and on fly ash modified by treatment with alkali methyl orange (FAN-MO)
Adsorption of Zn(II) ions is pH-dependent, with maximum adsorption of 76.24 % occurring at pH 4 for FAN and of 24.7 % at pH 5 for FAN-MO
Summary
Fly ash is an amorphous mixture of ferroaluminosilicate minerals generated by combustion of ground or powdered coal [1]. The method most common and widely used for removing heavy metals from wastewater is chemical precipitation by use of caustic soda or lime [11] This method is not expensive but requires a large amount of chemicals and results in a large quantity of sludge that requires supplementary treatment. Replacing synthetic substrates with low-cost adsorbents has, been intensively studied, and there have been reports of the use of materials obtained from agriculture and from forest wastes, for example bagasse fly ash [12], sugar beet pulp [13], activated carbon derived from bagasse [14], maple sawdust [15], clay [16, 17], volcanic ash bone char [18], humus [19], or bituminous coal, for removal of heavy metals. Is correlated with surface structure (SEM and EDAX) by batch and column study
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