Barium Sulphate Precipitation in a double-feed semi-batch stirred reactor

A study of barium sulphate precipitation in a double-feed, semi-batch mode was conducted. Experiments were carried out in a 101 reactor stirred by a Rushton turbine. The effects of addition mode (feed together or apart), feed location (near the impeller or the surface), feed molar ratio [1:1, 15/1 (Ba in excess) or 1/15 (SO4 in excess)] and stirrer speed on the precipitate characteristics were investigated. It was found that stirrer speed had only a limited effect. The most important parameter was the local, initial molar ratio of reactants, hence the local supersaturation, which also particularly depended-on the overall feeding strategy. These initial conditions then had a controlling effect for the rest of the feeding period. The change in morphology, mean size and size distribution as a function of time in relation to feed strategy was also clearly observed. In general, small sizes were obtained when feeding the two streams close together with either component in stoichiometric excess.