Study on the various factors affecting the quality of precipitated non-metallurgical alumina trihydrate particles

Processes for production of superfine white alumina trihydroxide (ATH) powders from actual plant Bayer liquor have been developed for use in non-metallurgical applications. The specialty grade hydroxides suitable for non-metallurgical application should conform to certain qualities such as fineness, purity, brightness, etc. The effect of a number of parameters such as precipitation temperature, amount of seed, seed surface area, precipitation time, soda content of pregnant liquor, modifier/additives, etc. on the precipitation of ATH were studied to achieve the required fineness. At higher temperatures, a purer product (with respect to soda) is obtained and particle size is increased, whereas at lower temperatures particle size is reduced and the soda quantity in the product is increased. The effect of seed surface area and seed quantity are found to have marked effects on the productivity and particle size of precipitated ATH. Higher seed specific surface area and higher seed quantity favoured productivity and finer particle size. Increased soda content in the pregnant liquor also enhanced productivity and finer size particles. The single most important parameter that influenced the precipitation process with respect to productivity, particle size and purity is the effect of a modifier, namely aluminium sulfate. ATH productivity is doubled when a modifier is added and the particle size is also reduced to ~1 mu m. An improvement in yield and finer size is also observed when organic additives are used.