Formation of colloidal dispersions from supersaturated iron(III) nitrate solutions. III. Development of goethite at room temperature

Competing Interactions of As Adsorption and Fe(III) Polymerization during Ferric Coprecipitation Treatment

This study revealed the effect of As on the formation and dissolution of iron (hydr)oxides and its further impact on the As removal efficacy of FeCl₃ treatment. Adding 6.7 mg/L FeCl₃ into 325 μg/L As solution (coprecipitation) resulted in more As removal (99% As(V) and 75% As(III)) at 2 min than adding As into aged FeCl₃ solution (preaged, 52-87% As(V) and 7-42% As(III)) at pH 7. However, soluble As gradually increased in the coprecipitation system and decreased in the preaged system to give similar concentrations during 800 h aging. The particle size of the iron (hydr)oxides increased more slowly in the coprecipitation than in the preaged systems. These results suggest the rapid adsorption of As on Fe polymer during the initial polymerization process, which delays the growth of iron (hydr)oxides. Thermodynamically, quantum chemical calculations implied that iron ions adsorption on iron (hydr)oxide polymer was more stable than As adsorption, which is the main driving force for the As release during aging process. This study improved our understanding of the kinetic and thermodynamic processes of As adsorption and iron (hydr)oxide precipitation in the coprecipitation treatment of As, and the potential for As release during aging of sludge generated in the treatment.

Nucleation and Growth of Uniform m-ZRO2

Hydrothermal treatment of zirconyl salt solutions produces uniform m-ZrO2 powder on the order of 80 nm. This powder is porous, has a 3-nm crystallite size, and exhibits an unusually high degree of crystallographic alignment within particles. The generation of this powder occurs via a complex process involving nucleation, growth, and controlled agglomeration of primary particles. Particle formation, crystallographic alignment and particulate uniformity are explained in terms of solution reactions and colloidal behavior.