Kinetics of phosphate sorption to polygalacturonate-coated goethite

• Published in: Soil Science Society of America journal Vol. 70; no. 2; pp. 541 - 549
• Main Authors: Mikutta, C, Lang, F, Kaupenjohann, M
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.03.2006; Soil Science Society of America; American Society of Agronomy
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Carbon dioxide; Chemical, physicochemical, biochemical and biological properties; Coatings; desorption; diffusion; Earth sciences; Earth, ocean, space; electrophoresis; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; galacturonic acid; Geochemistry; goethite; immobilization in soil; Kinetics; mathematical models; Mineral components. Ionic and exchange properties; Mineralogy; Minerals; Non silicates; Organic matter; Phosphates; Physics, chemistry, biochemistry and biology of agricultural and forest soils; polygalacturonates; Rhizosphere; Soil adsorption; Soil and rock geochemistry; Soil science; Soil sciences; Soils; Sorption; Zeta potential; oxides; Uronide polymer; Inorganic element; sorption; goethite; inorganic materials; Non silicate mineral; Soil science; porous materials; Chemical diffusion; Adsorbent; Soil chemistry; sugars; geochemistry; Polyanion; Oside; Earth science; Chemical reaction kinetics; Coated material; hydroxides; Organic anion; Inorganic anion; physicochemical properties; Pore; phosphates; Carboxylate; organic materials; Phosphorus compound; Iron III Hydroxides oxides; Polysaccharide
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2005.0250

Biogenetic polysugars may affect the sorption characteristics of soil mineral particles in the rhizosphere. We hypothesized that polygalacturonate [PGA, (C6H7O6)n(-)] coatings on goethite reduce the diffusion of phosphate into the pores of the adsorbent. Goethite was preloaded with PGA (0-10 mg C g(-1)). The samples were characterized by N2 and CO2 adsorption, electrophoretic mobility measurements, and scanning electron microscopy/energy dispersive X-ray analysis (SEM-EDX). The phosphate sorption kinetics was studied with batch experiments over 2 wk at pH 5 and an initial phosphate concentration of 250 micromolar. Pore volume and specific surface area of the goethite samples declined after PGA addition. The PGA coatings reduced the zeta-potential of goethite from 42.3 to -39.6 mV at the highest C loading. With increasing PGA-C content and decreasing zeta-potential the amount of phosphate sorbed after 2 wk decreased linearly (P < 0.001). Sorption of phosphate to pure and PGA-coated goethite showed an initial fast sorption followed by a slow sorption reaction. At the smallest C loading (5.5 mg C g(-1)) the portion of phosphate retained by the slow reaction was smaller than for the treatment without any PGA, while at higher C loadings the fraction of slowly immobilized phosphate increased. Our results suggest that at low C-loadings PGA impaired the intraparticle diffusion of phosphate. In contrast, the slow step-by-step desorption of PGA (<52% within 2 wk) or the diffusion of phosphate through PGA coatings or both are rate limiting for the slow phosphate reaction at C loadings > 5.5 mg C g(-1).