Abstract
Batch sorption system using two naturally occurring earth materials (EM) as adsorbents was investigated to remove fluoride ions from aqueous solution. The system variables studied include initial concentration of the sorbate, agitation time, adsorbent dose, pH, co-ions and temperature. The experimental data fitted well to the Freundlich isotherm. The amount of fluoride ions adsorbed per unit mass of the adsorbent was found to be 0.011 and 0.007 mg/g, at 30 °C from 4 mg/L fluoride solution, for EM1 and EM2 respectively. Thermodynamic parameters such as Δ H °, Δ S ° and Δ G ° were calculated which indicates that the removal of fluoride ions is an endothermic process. Kinetic studies reveal that the adsorption follows reversible first order kinetics. X-ray diffraction patterns of the adsorbents before and after adsorption and Dubinin-Radushkevick (D-R) isotherm indicate that the adsorption of fluoride ions onto these materials is a physisorption process. @ JASEM J. Appl. Sci. Environ. Manage . December, 2010, Vol. 14 (4) 90 - 95
Highlights
All the reagents used were of commercially available high purity analar grade (Merck or Sd-fine, India)
RESULT AND DISCUSSION Effect of contact time and initial concentration: The amount of fluoride adsorbed per unit mass of the adsorbent (Qe, mg/g) onto the two earth materials were studied and the results indicated that the amount of fluoride adsorbed increased with an increase in the initial sorbate concentration and with rise in temperature
Effect of co-ions: The effect of added co-ions viz. Cl, NO3, SO42- and HCO3- on the amount of fluoride adsorbed is studied and the results indicated that the addition of co-ions, in the concentration ranges investigated, has no appreciable effect on the amount of fluoride ions removed by these adsorbents
Summary
All the reagents used were of commercially available high purity analar grade (Merck or Sd-fine, India). Available earth materials were collected from Kanavilakku (EM1) and Bodidhasanpatty (EM2) of Andipatti block in Theni district, pulverized, sieved and used as adsorbents. These materials were examined by geologists and found as kankar, which is a deposit often nodules of CaCO3 formed in soils of semi aerid regions, similar to calcrete and cap rocks. Experimental variables considered were initial concentration of fluoride ions 2-10 mg/l; contact time between adsorbent and the fluoride solution 5-60 min; pH 311; dosage of the adsorbent 1-10 g/50 ml; temperature 30-500 C and co-ions viz. The goodness of fit was discussed using correlation coefficient, r, and standard deviation, sd
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