Process and installation for producing alumina trihydrate by alkaline digestion of bauxite ore

A process for producing alumina trihydrate comprising an digestion step (26), a separation step (70), and a precipitation step (52) the separation step including: b1) pretreating a slurry from the digestion step by adding a fiocculant to said slurry and mixing the fiocculant and the slurry, b2) settling the resulting flocculated slurry in a gravity settler vessel, b3) determining a measured value representative of the concentration of solid particles in the resulting clarified liquor, b4) comparing the measured value with a predetermined threshold, b5) feeding said clarified liquor directly to the precipitation step (52), while the measured value is less than said predetermined threshold, and b6) redirecting said clarified liquor to the pre-treatment step b1), when the measured value is more than said predetermined threshold. An installation for operating said process.