Morphology control of goethite acicular particles during aging by nitrogen bubbling and subsequent reactive aeration

Conditions for synthesizing acicular fine particles of goethite with high aspect ratio were devised by oxidizing mixed slurry comprising ferrous carbonate and hydroxide after neutralizing by alkali carbonate. By bubbling N₂ after neutralization into the slurry containing FeCO₃ and Fe(OH)₂, dissolved CO₂ is ejected. As a consequence, the relative concentration of CO₃²⁻ decreases and that of hydroxide increases. These favor the increase of the aspect ratio of the goethite particles via two factors, i.e., (1) decrease in the critical size of the nuclei and (2) suppression of growth inhibition at the tip of needle-like particles due to CO₃²⁻ adsorption. We propose a reaction scheme for the entire processing.