Homogeneous nucleation of Al(OH)3 crystals from supersaturated sodium aluminate solution investigated by in situ conductivity

• A homemade online conductance testing system was assembled to investigate the homogeneous nucleation of Al(OH)3 crystals.
• Induction period was verified by combination conductance and turbidity of sodium aluminate solution.
• Nucleation kinetics was achieved according to the homogeneous nucleation theory.
• Nucleation mechanism was discussed.

The homogeneous nucleation process of Al(OH)3 crystals from supersaturated sodium aluminate solution was investigated by a homemade online conductance testing system. Combined with the turbidity and equivalent circuit of conductometry, the conductance curve was divided into five regions, where the charge and discharge region, adsorption region and ionic polymerization region were identified as induction period in the decomposition process of sodium aluminate solution. According to the homogenous nucleation theory, the nucleation kinetics during the decomposition process was studied with the intermediate concentration solution at 333 K. The results showed that the solid–liquid interfacial energy was 26.1 mJ·m− 2, critical nucleation radius was 2.6–3.8 nm and the apparent reaction order was 2.9. Meanwhile, UV–vis spectra of sodium aluminate solution in homogeneous process were investigated with decomposition time, where three peaks were observed at 220, 260, and 370 nm, respectively. Combined with the conductance curve, the ionic structure change and nucleation mechanism have been discussed.