RISTIC Mira Rudjer Boskovic Institute

Spoluautoři OPACAK Ivana, MUSIC Svetozar

Influence of gum arabic (GA) on the precipitation of goethite in highly alkaline medium was investigated using XRD, 57-Fe Mössbauer, FT-IR and FE-SEM. In absence of GA long goethite rods with nanosize width (~30nm), as a single phase, were produced. The lateral aggregation of two or more goethite rods is visible. A very strong effect of GA on the precipitation of goethite in a highly alkaline medium was noticed. At a prolonged time of autoclaving time the ferrihydrite-like phase transformed to goethite and hematite. The formation of hematiteas the end product of this precipitation process was controlled by the dissolution/recrystallization mechanisms. The effect of GA addition to the precipitation system of Fe(ClO4)3 salt in highly alkaline medium was assigned to the surface interactions of GA with nuclei and crystallites (particles) formed during the kinetics investigated. It was assumed that a thick layer of GA biopolymers suppressed the formation of goethite from the ferrihydrite-like phase, which is generally a fast process in the absence of GA. In such a way the conditions for nucleation and crystal growth of hematite are created and with a prolonged autoclaving time the reactions were shifted to the formation of hematite as end-product.