High Concentrations Of Sodium Aluminate Solution Seeded Precipitation Process,

Alumina production in china using difficultly soluble diaspore not only has a higher production cost than that of the foreign alumina production, but also it is very difficult to produce sandy alumina product by traditional process arrangement, especially under the condition of high sodium aluminate concentration. Therefore, in terms of our current production situation and process characteristics, it is necessary to investigate the effect of varied precipitation conditions on solution precipitation rate and product quality, and find its precipitation mechanism, which can provide alumina production with theoretic instruction.Firstly, the paper studies dynamics of the seed precipitation and calculates apparent activity energy of precipitation reaction in different solutions on the base of the established dynamic equation, and then a new finding of the precipitation mechanism is put forwarded by the fact that low molecular ratio brings about the high apparent activity energy of the precipitation reaction and the precipitation speed is mainly controlled by the chemical precipitation reaction largely influenced by the temperature; In contrast, high molecular ratio leads to low apparent activity energy, the precipitation speed is mainly controlled by dispersion process, temperature has a small influence on the precipitation reaction. Meanwhile, the way to intensify the precipitation process is given as the following: in the beginning of precipitation, increases gradient of temperature drop, but in the mid and end, raises the speed of agitation to disperse the mass transfer rapidly.Employing the trial liquor after separation and settlement prepared with the seed from the precipitation workshop and industrial sodium hydrate, effect of molecular ratio of the precipitation green liquor, the concentration of the liquor after separation and settlement, the seed, temperature system and other process conditions on the precipitation process has been studied. Consequently, it reveals the effect law of the above-mentioned process conditions on the precipitation productivity,particle size and strength of the product hydrate. Optimum conditions are described as the following: temperature drop system:65-50°C; moderate seed addition is ks=2.0; suitable particle size (mean particle size:30-40um) including some fine seed.The production operation system of high concentration and one-stage precipitation technology specially used for the ore-dressing Bayer process of Zhongzhou Branch has been concluded. It will play an important role in China's sandy alumina production.