F. Kovanda, E. Kovácsová and D. Koloušek
Department of Solid State Chemistry, Institute of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic ; e-mail kovandaf@vscht.cz
Abstract
The removal of arsenate, chromate, and vanadate from water solutions by hydrotalcite calcined at 350 - 550 °C was studied. The initial anion concentration was 0.002 mol l-1. The sorption isotherms were measured at 20 °C and neutral pH solutions. The Langmuir adsorption isotherm was used for the sorption capacity evaluation. The ability of calcined hydrotalcite for the anion removal from solution decreased in order of vanadate - arsenate - chromate. The sorbed anions were released by anion exchange in a carbonate containing solution and the hydrotalcite after next calcination was used again for the removal of anions. The repeating cycles of calcination - rehydration - anion exchange gradually reduced the absorption capacity of calcined hydrotalcite. The sorption capacity decreased by 50 % after the first two cycles but it did not change significantly in the further cycles. When chromate anions were absorbed, the decrease of sorption capacity was not observed during repeated calcination - rehydration - anion exchange cycles. The change of the sorption capacity was influenced by the ability of calcined hydrotalcite to regenerate the layered crystal structure during the rehydration process.