The effect of 3,4 dihydroxy benzoic acid (3,4 DHBA) on the precipitation of alumina trihydrate

In this study, a second order rate equation was used successfully model the rate of nucleation and crystal growth during the precipitation of alumina trihydrate. In unseeded liquors, 3,4 DHBA reduces the rate of nucleation and crystal growth significantly. It hinders the agglomeration of nuclei and crystals, producing less dense products compared to those precipitated from pure liquors. It was also found that alumina hydroxide nuclei need to crystallise before crystal growth occurs, and 3,4 DHBA delays the crystallisation process. In seeded liquors, 3,4 DHBA causes an exponential increase in the number of secondary, nuclei and a decrease in the rate of crystal growth. It also causes an increase in induction time. Provided this induction time is known the whole system can be characterised by the second order equation. Accumulated kinetic and induction time data can be used for the simulation of the precipitation process.