EI-Tohamy, S.A ( 2012). Removal of selenium from polluted soil, goethite and Zerovalent iron by using some extratantsJ. Biol. Chem. Environ. Sci., 2012, Vol. 7(1):433-453 www.acepsag.org
Abstract: This work was carried out in laboratory experiments to investigate the removal of selenate from soil, goethite and zerovalent iron (ZVI) by using some extracting such as phosphate, sulphate, molybdate and DTPA as procedures to reduce its amounts in soil, goethite and zerovalent iron. Selenium was equilibrated with soils at 10-100 μg Se mL-1 surface coverage and extracted by 0.005M DTPA. On the other hand, it was equilibrated with goethite and zerovalent iron at 10 μg Se mL-1 and pH values of 5 and 9 as well as it was extracted by phosphate, sulphate and molybdate solutions at a ratio of 1 : 100 = Se : each solution and pH values ranging from 3 to 12. Regarding soils, desorbed Se (VI) from both the studied loamy and clay loam soils by DTPA gradually increased with increasing initial Se (VI) concentration. A slight increase in the desorbed Se from the loamy soil was observed with increasing its initial concentration
from 10 to 20, 30 to 40 and 50 to 100 μg Se mL-. Concerning goethite, the values of Se (VI) desorbed by using phosphate (at pH 5) depended on the pH values, where the relative increase percentages of Se(VI) desorbed from goethite reached 37.3, 67.0 and 84 % at pH values of 3,7 and 12, respectively. The corresponding relative increase percentages of Se (VI) desorbed in case of phosphate (concentration of 100 times as selenate and at pH 9) were greatly affected and reached 42, 80 and 94 %, respectively. In case of sulphate, the relative increase in Se (VI) desorbed was negligible either at pH 3 or with increasing its value up to 7, where the relative increase percentage was 2.04,2.94 % at both pH values, and REMOVAL OF SELENIUM FROM POLLUTED SOIL, GOETHITE 434 then greatly increased to 66.6% at pH 12. At initial concentration
ratio of 100 : 1 of MoO4 : Se), MoO4 had a great effect on Se(VI), where the relative increase percentages of Se (VI) desorbed reached 46% at pH 3, and then decreased to 39.2 % with increasing pH up to 7. Above pH 7, the relative increase percentages of Se (VI) desorbed increased again to 48 % at pH 12. With respect to zerovalent iron, phosphate (at concentration ratio of 100 phosphate : 1 Se and pH 5) had a moderate effect on Se (VI) desorbed at pH 3, where the relative increase percentage was 12.0 %, and it tended to inecrease with increasing pH value up to 7 (14.2%). Above pH 7, the increase percentage of Se (VI) reached 19.01% at pH 12. In case of phosphate (at initial adsorption pH of 9), the relative increase percentages were 6.2, 6.1 and 9.08% at pH values of 3, 7 and 12, respectively. Sulphate (at initial ratio of 100: 1 Se and pH 5) exhibited quantity of Se (VI) desorbed at pH values of 3 and up to 9 as its relative increases were 10.12 and 16.6 %, respectively. Above pH 9.0,. the relative increase of Se (VI) greatly increased to 19.2% at pH 12.Sulphate at initial pH 9 showed a very less relative increase percentages in Se (VI) desorbed at pH values of 3 up to 8 reached only 5.44 and 5.24%,respectively.Above pH8 the relative increase of Se (VI) greatly increased to 10.5% at pH 11. Se (VI) desorbed as a result of molybdate (at initial adsorption pH 5) with increasing pH value 7, and then a pronounced increase occurred (20.22%) at pH 10. In case of molybdate (at a ratio 100 MoO4: 1 Se and pH 9), the relative increase was achieved for Se (VI) desorbed at pH 3 (5.7%), and then it
inecreased to 6.3% with increasing pH up to pH 7. Above pH7, Se (VI) desorbed tended to increase again (9.02%) at pH 12.
Keywords: (Desorption process, selenate, goethite, zerovelant iron, phosphate, sulphate, molybdate pH value)
