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Journal of Agronomy
  Year: 2006 | Volume: 5 | Issue: 3 | Page No.: 406-417
DOI: 10.3923/ja.2006.406.417
 
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Surface Properties of Amorphous Al and Fe Hydroxides Formed in the Presence of Oxalate, Citrate and Tannate Ligands

M.I.D. Helal

Abstract:
Surface properties, point of zero salt effect (PZSE) and the remaining charge (σp) at the same pH, cation exchange capacity (CEC), sorption/desorption of P and oxalate sorption, are studied for amorphous Al and Fe hydroxides formed in absence and presence of low (oxalate and citrate) and high (tannate) molecular weight organic ligands. Co-precipitation of organic ligands with Al and Fe significantly shifted PZSE of the precipitation products to lower or higher pH values. As oxalate/(Al or Fe) molar ratio (MR) increased from 0 to 0.2, PZSE of Al precipitates significantly shifted to higher pH values (from 5.65 to 7.9), whereas, those of Fe ones shifted to lower pH values (from 6.4 to 5.95). In case of tannate ligand, PZSE of Al and Fe precipitates markedly shifted to lower pH values (from 5.65 to 3.6 and 6.4 to 2.96, respectively). Also, in the presence of citrate ligand, PZSE of Al and Fe precipitates shifted to lower pH values. In the presence of oxalate ligand, the remaining positive charge (σp) of Al and Fe precipitates increased, whereas, it reversed to be negative in the presence of citrate or tannate ones. Co-precipitation of organic ligands with Al or Fe significantly enhanced CEC values of the precipitation products from 32.9 to 62.4 and 58.9 to 68.0 Cmolc kg-1, pH 5.5, respectively. CEC values increased, as the molecular weight of co-precipitated ligand increased. All Al and Fe precipitation products had high capacity to sorb P (268 to 1413 mmol kg-1). Co-precipitation of oxalate ligand with Al or Fe considerably increased P sorption capacity of the precipitation products, whereas, co-precipitation of citrate or tannate ligands suppress P sorption capacity. A good harmony was observed between P sorption capacities of Al and Fe precipitates and PZSE values. The quantities of P desorbed from the previously sorbed varied widely between the precipitates and increased with sorption density. Fe and Al precipitates formed in the presence of oxalate ligand (Fe-Oxal, Al-Oxal) as well as those formed in absence of organic ligands (Fe-OH and Al-OH), which had a remaining positive charge at PZSE, had high ability to sorb and retain sorbed P. On the other hand, those formed in the presence of tannate or citrate ligands, which had a remaining negative charge, had limited one in this connection. Oxalate sorption capacity of Al and Fe precipitates are markedly lower than P. Co-precipitation of organic ligands with Al or Fe precipitates significantly reduced their capacity to sorb oxalate ions.
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How to cite this article:

M.I.D. Helal , 2006. Surface Properties of Amorphous Al and Fe Hydroxides Formed in the Presence of Oxalate, Citrate and Tannate Ligands. Journal of Agronomy, 5: 406-417.

DOI: 10.3923/ja.2006.406.417

URL: https://scialert.net/abstract/?doi=ja.2006.406.417

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