Study on the efficient precipitation of germanium by Fe(OH)3 colloid generated by neutralization precipitation method

This study delves into the reaction mechanism of neutralization precipitation and the kinetics of precipitation, as well as the equilibrium of adsorption of germanium. The investigation examines the impact of various experimental parameters, including reaction temperature, reaction duration, iron-germanium mass ratio, and the final pH of the reaction, on the rate of germanium precipitation. The findings suggest that optimal precipitation conditions are attained at a reaction temperature of 60 °C, a precipitation duration of 120 min, an iron-germanium mass ratio of 40:1, and a pH of 5.5 at the reaction endpoint. Under these conditions, the precipitation efficiency can achieve 99.42%. Kinetics and adsorption equilibrium were analyzed, revealing that the germanium precipitation reaction adhered to the pseudo-second-order model for kinetics and the Freundlich adsorption isothermal model for adsorption equilibrium. Based on theoretical analysis and detection of precipitate, the precipitation reactions can be divided into three parts: (1) GeO₂ reacts with water to form small amounts of germanic acid, which then hydrolyzes to form colloidal precipitates; (2) colloidal ferric hydroxide, adsorbing germanium, precipitates spontaneously; (3) due to the addition of NaOH to adjust pH both at the outset and during the experiment, a portion of the solution will have a high pH region for a certain period of time, leading to the presence of germanium in the forms of HGeO₃⁻ and GeO₃²⁻ within these localized areas. The HGeO₃⁻ and GeO₃²⁻ at this point will form a small amount of colloid in the reaction.