El-Sayed, M., Abd El-Haleem, A., El-Tohamy, S. (2008). COMPETITIVE ADSORPTION OF ARSENATE WITH PHOSPHATE, MOLYBDATE, SELENATE, AND SULFATE ON GOETHITE AND ZEROVALENT IRON (ZVI).. Journal of Soil Sciences and Agricultural Engineering, 33(10), 7663-7674. doi: 10.21608/jssae.2008.200384
M.H. El-Sayed; A. A. Abd El-Haleem; S. H. El-Tohamy. "COMPETITIVE ADSORPTION OF ARSENATE WITH PHOSPHATE, MOLYBDATE, SELENATE, AND SULFATE ON GOETHITE AND ZEROVALENT IRON (ZVI).". Journal of Soil Sciences and Agricultural Engineering, 33, 10, 2008, 7663-7674. doi: 10.21608/jssae.2008.200384
El-Sayed, M., Abd El-Haleem, A., El-Tohamy, S. (2008). 'COMPETITIVE ADSORPTION OF ARSENATE WITH PHOSPHATE, MOLYBDATE, SELENATE, AND SULFATE ON GOETHITE AND ZEROVALENT IRON (ZVI).', Journal of Soil Sciences and Agricultural Engineering, 33(10), pp. 7663-7674. doi: 10.21608/jssae.2008.200384
El-Sayed, M., Abd El-Haleem, A., El-Tohamy, S. COMPETITIVE ADSORPTION OF ARSENATE WITH PHOSPHATE, MOLYBDATE, SELENATE, AND SULFATE ON GOETHITE AND ZEROVALENT IRON (ZVI).. Journal of Soil Sciences and Agricultural Engineering, 2008; 33(10): 7663-7674. doi: 10.21608/jssae.2008.200384
COMPETITIVE ADSORPTION OF ARSENATE WITH PHOSPHATE, MOLYBDATE, SELENATE, AND SULFATE ON GOETHITE AND ZEROVALENT IRON (ZVI).
1Soil, Water and Environment Research Inst., Agricultural Research Center, Giza, Egypt.
2Soil Department, College of Agriculture, Benha University.Egypt
Abstract
A laboratory experiment, was carried out on synthetic goethite and zerovalent iron (ZVI) to study the competition between AsO43-(10µg As mL-1)and PO43-, SeO42-, SO42- and MoO42- at different ratios (1:0, 1:1, 1:2 and 2:1) on the adsorption surfaces of the selected minerals. Obtained data showed that, at pH 7.0 a quantity of 2891 µg As g-1 goethite was adsorbed from the added As(V) (AsO43-), with increasing the pH above 9.0 the adsorbed AsO43- was decreased to be 1662 and 945 µg As g-1 goethite at pH 11.0 and 11.8 , respectively. On the other hand, the amount of adsorbed As(V) on ZVI recorded 23590 µg As g-1 at pH 4.0 and decreased to be 15620 and 983 µg As g-1 ZVI at pH 9.5 and 12.0, respectively. Adsorption of As(V) on both goethite and ZVI was decreased with increasing pH when As(V) was added alone or with PO43- at As :P ratios of 1:0, 1:1 and 1:2.
However, more pronounced increases in AsO43- adsorption was noticed when AsO43- was added at 2:1 ratio as compared to PO43- with all tested pH values. The adsorption affinity of goethite and ZVI to AsO43-was affected largely by pH and arsenate concentration in the equilibrium solution. It could be mentioned that PO43- could not compete well with arsenate on the specific sites of AsO43- if its ratio to AsO43- was less than 2:1. These results indicate that the preference of adsorption sites to AsO43- was mainly affected by pH values and the concentration of associated oxyanions.
With respect to the competition between AsO43-and SeO42-,MoO42- and SO42-, obtained data also indicated that the adsorbed AsO43-on both goethite and ZVI was decreased more at As:Se ratio of 1:2 as compared with other ratios.Selenate (SeO42-) had competed with AsO43-on the adsorption sites of both goethite and ZVI, and reduced the amount of adsorbed AsO43- .Increasing the initial concentration of adsorbed As comparing with selenate or any other oxyanions alleviated the effect of competing oxyanions as indicated with As:Se ratio of 2:1. More than 95% of As(V)was adsorbed on both goethite and ZVI below pH 4.0 in single AsO43-anion and binary with MoO42-anion systems.
These data suggested that MoO42- occupies a fraction of the pH- dependent As(V) adsorption sites on the studied minerals and there was another distinct fraction of sites had higher affinity for As MoO42- at low pH. Obtained data also indicated that, the preference of the adsorbents to AsO43-over SO42- was declared when they added together.