Reactivity with phosphate and phytotoxicity of hydroxyaluminosilicate ions synthesized by instantaneous mixing of aluminum chloride and sodium orthosilicate solutions

Abstract

Hydroxyaluminosilicate ions are important as precursors of imogolite in synthetic systems and as less toxic aluminum-bearing species in natural aquatic systems. Despite their importance, their structures and properties have not been fully elucidated. We prepared a solution of hydroxyaluminosilicate ions by instantaneous mixing of solutions of sodium orthosilicate and aluminum chloride and carried out phosphatebinding experiments and phytotoxicity testing. To avoid possible alteration by drying, phosphate binding was measured in hydroxyaluminosilicate solutions contained in dialysis bags. The amount of phosphate bound to hydroxyaluminosilicate ions linearly increased as the equilibrium phosphate concentration increased up to 0.7 mmol L -1 . The amounts of bound phosphate were lower than those of imogolite and allophanes at relatively low phosphate concentrations; however, phosphate binding by hydroxyaluminosilicate ions surpassed binding by allophane and imogolite at equilibrium phosphate concentrations > 0.4 mmol L , at which concentration the hindrance by hydroxyaluminum and aluminum ions was 80 -85%. These results suggest that hydroxyaluminosilicate ions have very low biological activity in natural waters.

Mineralogy of Laterite Samples from Viet Nam and Their Use as Flocculating Agents for the Removal of Clay Suspensions

“…However, negative effects on the environment have been found by the use of some agents. Aluminum salts and synthetic polymers cause possible physiological effects on organisms (Nakanishi and Wada, 2007) as well as aluminum accumulation in the environment and its connection with Alzheimer disease (Stauber et al, 1999). Some natural substances such as chitosan and carboxymethyl cellulose are nontoxic to environment, available from renewable resources and very effective for pollutant removal (Divakaran and Pillai, 2001) but they are not stable against microbial attack during storage (Tripathy and De Rajan, 2006;Zhang et al, 2010) and may increase the biological oxygen demand of processed water if high dose is used.…”

Response to Comment on “Avoidance of Aluminum Toxicity in Freshwater Snails Involves Intracellular Silicon—Aluminum Biointeraction”

“…(i) We have used hydroxyaluminosilicate (HAS) as a term to indicate that Al is coordinated to OH groups as well as O−Si groups, including Al bound to the surface of polysilicate in aqueous environments, and with evidence of some imogolite-like configuration. In a recent paper , Nakanishi and Wada (the latter of whom is credited with encouraging wider spread use of the term “HAS” from 1980 , although this definition has been in use since at least the 1960s – ) stated: “In all these studies, the structure, stability and reactivity of HAS ions have not been well elucidated. Some consensual results are that they are cationic, their Si/Al ratios are variable depending on those of the starting solutions (Wada & Wada, 1980), and the configuration of one silicon in HAS ions is essentially the same as that in imogolite” .…”

“…In a recent paper , Nakanishi and Wada (the latter of whom is credited with encouraging wider spread use of the term “HAS” from 1980 , although this definition has been in use since at least the 1960s – ) stated: “In all these studies, the structure, stability and reactivity of HAS ions have not been well elucidated. Some consensual results are that they are cationic, their Si/Al ratios are variable depending on those of the starting solutions (Wada & Wada, 1980), and the configuration of one silicon in HAS ions is essentially the same as that in imogolite” . We support this view, as opposed to a more narrow interpretation of HAS, based on its preparation route rather than its structure, as supported by Dr. Exley.…”