Surface Acidity of Amorphous Aluminum Hydroxide

Abstract

The surface acidity of synthetic amorphous Al hydroxide was determined by acidhase titration with several complementary methods including solution analyses of the reacted solutions and XRD characterization of the reacted solids. The synthetic specimen was characterized to be the amorphous material showing four broad peaks in XRD pattern. XRD analyses of reacted solids after the titration experiments showed that amorphous Al hydroxide rapidly transformed to crystalline bayerite at the alkaline condition (pIb10). The solution analyses after and during the titration experiments showed that the solubility of amorphous aluminum hydroxide, K ' p = , was 10'0*3.The amount of consumption of added acid or base during the titration experiment was attributed to both the protonatioddeprotonation of dissolved Al species and surface hydroxyl group. The surface acidity constants, surface hydroxyl density and specific surface area were estimated by FITEQL 4.0.aH'

Adsorption and co-precipitation behavior of arsenate, chromate, selenate and boric acid with synthetic allophane-like materials

“…These PZC values were similar to synthesized amorphous aluminum hydroxide with PZC value of 9.1 in which the variable positive charge was also attributed to the surface aluminol groups [20]. It can be seen from the figure that the surface charge of the precipitates generate a variable positive charge at the acidic pH range up to the point of zero charge (PZC) value and a negative charge at the pH condition above the PZC value.…”

Basic aluminum sulfate@graphene hydrogel composites: preparation and application for removal of fluoride

“…XRD pattern of BAS shows four broad peaks at the locations of 8 o , 20 o , 40 o and 65 o , characteristic of amorphous BAS. 34 GHG has a broader peak centered around 25 o , corresponding to the interplanar distance of 35 stacked CCG sheets. 30 In the XRD patterns of the BAS@GHG composites, no obviously peak related to BAS is found, except for the broad peak inherited from GHG.…”

Influences of pH value on the microstructure and phase transformation of aluminum hydroxide

“…Furthermore, the wet chemical precipitation is one of the commonest methods to obtain hydroxide powders due to its simplicity, easy operation, and uniform product in batches. Recently, Fukushi et al [5] reported that pH value during the precipitation step was an important factor for the successful formation of active phase in the preparation of aluminum hydroxides and the amorphous aluminum hydroxide rapidly transformed to crystalline bayerite under alkaline conditions (pH N10). This implies that pH value in the preparation of aluminum hydroxides by chemical precipitation can serve as a key factor for determining the microstructures of aluminum hydroxides and phase transformation of aluminum hydroxides in the dehydrogenation process.…”