COMPETITIVE ADSORPTION OF ARSENATE WITH PHOSPHATE, MOLYBDATE, SELENATE, AND SULFATE ON GOETHITE AND ZEROVALENT IRON (ZVI). | ||||
| Journal of Soil Sciences and Agricultural Engineering | ||||
| Article 6, Volume 33, Issue 10, October 2008, Page 7663-7674 PDF (727.16 K) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/jssae.2008.200384 | ||||
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| Authors | ||||
| M.H. El-Sayed1; A. A. Abd El-Haleem2; S. H. El-Tohamy1 | ||||
| 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. | ||||
| Keywords | ||||
| arsenate; competition; adsorption; pHospHate; molybdate; selenate; goethite and iron metal | ||||
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