A novel method for speciation of chromium: coprecipitation without carrier element by using a triazole derivative.

A coprecipitation method has been established for speciation of chromium(III) and chromium(VI) in real samples. The procedure is based on the coprecipitation of Cr(III), by using a new organic coprecipitant, 3-phenyl-4-o-hydroxybenzyl-idenamino-4,5-dihydro-1,2,4-triazole-5-one, without adding any carrier element. After reduction of Cr(VI) by concentrated H2SO4 and ethanol, the method was applied to the determination of total Cr. The level of Cr(VI) was calculated by the difference of total Cr and Cr(III) levels. For optimum recovery of Cr(III), different analytical factors such as pH, amount of coprecipitant, centrifugation rate and time, and effect of sample volume, were investigated. The influences of some anions, cations, and transition metals on the recoveries were also investigated, and no significant interferences were observed. The preconcentration factor was 100. The detection limit based on 3 times standard deviation (sigma) of the blank (n = 10) for Cr(III) was 0.50 microg/L. In order to evaluate the accuracy of the method, certified reference materials (CRM-TMDW-500 Drinking Water and National Institute of Standards and Technology Standard Reference Material 1573a Tomato Leaves) were analyzed, and the results obtained were in good agreement with certified values. The presented procedure was applied for Cr speciation in various solid and liquid samples with successful results.

Removal of fluoride ions from aqueous solution by waste mud.

The present study was carried out to assess the ability of original waste mud (o-WM) and different types of activated waste mud which are acid-activated (a-WM) and precipitated waste mud (p-WM), in order to remove excess of fluoride from aqueous solution by using batch technique. The p-WM exhibited greater performance than the others. Adsorption studies were conducted as a function of pH, contact time, initial fluoride concentration, adsorbent concentration, temperature, etc. Studies were also performed to understand the effect of some co-existing ions present in aqueous solutions. Adsorption process was found to be almost independent of pH for all types of waste mud. Among the kinetic models tested for p-WM, pseudo-second-order model fitted the kinetic data well with a perfect correlation coefficient value of 1.00. It was found that the adequate time for the adsorption equilibrium of fluoride was only 1h. Thermodynamic parameters including the Gibbs free energy (DeltaG degrees ), enthalpy (DeltaH degrees ), and entropy (DeltaS degrees ) revealed that adsorption of fluoride ions on the p-WM was feasible, spontaneous and endothermic in the temperature range of 0-40 degrees C. Experimental data showed a good fit with the Langmuir and Freundlich adsorption isotherm models. Results of this study demonstrated the effectiveness and feasibility of WM for removal of fluoride ions from aqueous solution.

Carrier element-free coprecipitation with 3-phenly-4-o-hydroxybenzylidenamino-4,5-dihydro-1,2,4-triazole-5-one for separation/preconcentration of Cr(III), Fe(III), Pb(II) and Zn(II) from aqueous solutions.

A separation/preconcentration procedure, based on the coprecipitation of Cr(3+), Fe(3+), Pb(2+) and Zn(2+) ions using a new organic coprecipitant, 3-phenly-4-o-hydroxybenzylidenamino-4,5-dihydro-1,2,4-triazole-5-one (POHBAT) without adding any carrier element has been developed. The method, thus, has been called carrier element-free coprecipitation (CEFC). The resultant concentrated elements were determined by flame atomic absorption spectrometric determinations. The influences of some analytical parameters including pH of the solution, amount of the coprecipitant, standing time, centrifugation rate and time, sample volume and diverse ions were investigated on the quantitative recoveries of analyte ions. The validation of the present preconcentration procedure was performed by the analysis of two certified reference materials. The recoveries of understudy analytes were found in the range of 93-98%, while the detection limits were calculated in the range of 0.3-2.0 microg L(-1). The precision of the method evaluated as relative standard deviation (R.S.D.), was in the range of 3-7% depend on the analytes. The proposed method was successfully applied to environmental samples for the determination of the analytes.