Adsorption of fluoride on synthetic iron (III), zirconium(IV) and binary iron(III)-zirconium (IV) oxides: comparative assessment on pH effect and isotherm.

Fluoride is an accumulative poison at high dose of intake for humans and animals. In the present study, the sorption of fluoride from aqueous solution has been investigated on synthetic hydrous ferric oxide (HFO), hydrous zirconium oxide (HZO) and hydrous zirconium(IV)-iron(III) oxide (HZFO) by batch mode experiments. Both HFO and HZFO were crystalline and HZO was amorphous in nature. The parametes studied were the effect of pH and sorption equilibriums. The results showed increase in fluoride-sorption with increasing pH from nearly 2.0 to 5.0, 4.6 and 6.8 for HFO, HZO and HZFO, respectively. Analysis of temperature dependent sorption data obtained at equilibrium solution pH 6.8 (+/- 0.2) has been described by the Langmuir, Freundlich, Temkin and Redlich-Peterson isotherm model equations. The present sorption data fit, in general, found very well with the Langmuir and Redlich-Peterson models; and the data fit for HZFO and HFO found to increase, but for HZO the data found to decrease with increasing temperature. The computed thermodynamic parameters such as deltaG0, delltaH0 and deltaS0 from the Langmuir equilibrium constant (b, L/Umg) values show that the fluoride-sorption on HZFO was more spontaneous and endothermic process compared to HFO. The deltaH0 value obtained for fluoride adsorption on HZO indicates exothermic nature.

Removal of trace chromium (VI) from contaminated water: bio-sorption by Ipomea aquatica.

Ipomea aquatica is a wetland plant, which floats in water bodies and is being used as a vegetable. This plant has ability to remove Cr(VI) from the contaminated water by transforming Cr (VI) to Cr (III). This adsorption of Cr(VI) basically takes place in roots of this plant. The contact time required to bring down Cr(VI) concentration below the permissible level (0.05 mg/1) is 30 to 40 days for this plant, and that varies with varying initial concentration. The lower level of contamination requires greater contact time than the higher one to bring down Cr(VI) below the permissible level. Recovery (94 +/- 1%) of chromium from the treated plant has been reported in this paper, and at the same time disposal problem also dose not arise. The study revealed that the plant Ipomea aquatica adsorbs Cr(VI) from the contaminated water very slowly compared to the other reported plants.