Manufacture of spherical alumina from gibbsite

A method of manufacturing spherical alumina comprising the steps of:

• (a) digesting, at an elevated temperature and an elevated pressure, gibbsite with an aqueous hydrochloric acid solution to thereby form an aqueous basic aluminum chloride solution having an aluminum concentration in the range of from 9 wt.% to 11 wt.% and a weight ratio of aluminum to chloride in the range of from 0.4 to 0.6;
• (b) adding, at an elevated temperature, an aqueous ammonia solution to said aqueous basic aluminum chloride solution, and then dissolving metallic aluminum in the resulting mixture under conditions effective to form an alumina hydrosol containing ammonium chloride, said alumina hydrosol having an aluminum concentration in the range of from 7 wt.% to 14 wt.% and a weight ratio of aluminum to chloride in the range of from 0.6 to 1.3, wherein said weight ratio of aluminum to chloride is calculated on the basis of excluding the chlorine content of said ammonium chloride;
• (c) then commingling said alumina hydrosol with a gelling agent which hydrolyzes at an elevated temperature, thereby forming a mixture, and then dispersing said mixture as droplets in a suspending medium under conditions effective to transform said droplets into hydrogel particles;
• and
• (d) ageing said hydrogel particles first in said suspending medium and then in aqueous ammonia, and thereafter washing said hydrogel particles with water, then drying and calcining said hydrogel particles to obtain said spherical alumina particles.