The invention provides methods and compositions for inhibiting the accumulation of DSP scale in the liquor circuit of Bayer process equipment. The method includes adding one or more GPS-surfactant based small molecules to the liquor fluid circuit. These scale inhibitors reduce DSP scale formation and thereby increase fluid throughput, increase the amount of time Bayer process equipment can be operational and reduce the need for expensive and dangerous acid washes of Bayer process equipment. As a result, the invention provides a significant reduction in the total cost of operating a Bayer process.

The invention provides a method of inhibiting the accumulation of DSP scale in the liquor circuit of Bayer process equipment. The method includes adding one or more particular silane based small molecules to the liquor fluid circuit. These scale inhibitors reduce DSP scale formation and thereby increase fluid throughput, increase the amount of time Bayer process equipment can be operational and reduce the need for expensive and dangerous acid washes of Bayer process equipment. As a result, the invention provides a significant reduction in the total cost of operating a Bayer process.

There are provided processes for treating red mud. For example, the processes can comprise leaching red mud with HCl so as to obtain a leachate comprising ions of a first metal (for example aluminum) and a solid, and separating said solid from said leachate. Several other metals can be extracted from the leachate (Fe, Ni, Co, Mg, rare earth elements, rare metals, etc.). Various other components can be extracted from solid such as TiO.sub.2, SiO.sub.2 etc.

A process for producing alumina trihydrate includes a digestion step, a separation step, and a precipitation step the separation step including: b1) pretreating a slurry from the digestion step by adding a flocculant to said slurry and mixing the flocculant 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, 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 may be configured for operating said process.

A settler for decanting mineral slurries includes a tank having a side wall, a bottom and a top, an outlet for a thickened slurry at the bottom of the tank, a first overflow outlet for withdrawing an overflow stream of a clarified liquid, a slurry inlet means for introducing fresh slurry into the tank, the slurry inlet means having a slurry opening through which fresh slurry joins a body of slurry in the tank, and a stirrer having a vertical axis around which the stirrer rotates or reciprocates, in said settler the slurry opening is displaced laterally relative to said vertical axis of the stirrer and said slurry inlet means comprises mixing means. A separation installation includes the above settler and a method for separating a clarified liquid from a thickened slurry of a mineral slurry.

A washing method of red mud that is produced when an alumina-containing ore having a goethite to hematite mass ratio of 60/40 (goethite/hematite) or more in the iron component thereof is heat-treated with an alkaline solution at a temperature of 110 C. to 160 C. to obtain an aluminate liquor, including: mixing the red mud with a diluting fluid to obtain suspension that has an aluminum concentration of 95 g/L or less in terms of Al.sub.2O.sub.3; adding a flocculant to the suspension, wherein, the flocculant includes a polymer having a repeating unit derived from (meth)acrylic acid or a salt thereof and being substantially free from a repeating unit derived from vinylhydroxamic acid compound or a salt thereof; and settling and separating the red mud so as to wash the red mud.

A washing method of red mud that is produced when an alumina-containing ore having a goethite to hematite mass ratio of 60/40 (goethite/hematite) or more in the iron component thereof is heat-treated with an alkaline solution at a temperature of 110 C. to 160 C. to obtain an aluminate liquor, including: mixing the red mud with a diluting fluid to obtain suspension that has an aluminum concentration of 95 g/L or less in terms of Al.sub.2O.sub.3; adding a flocculant to the suspension, wherein, the flocculant includes a polymer having a repeating unit derived from (meth)acrylic acid or a salt thereof and being substantially free from a repeating unit derived from vinylhydroxamic acid compound or a salt thereof; and settling and separating the red mud so as to wash the red mud.

Disclosed herein are methods and compositions for increasing the alumina content of a bauxite ore prior to alumina extraction by an extractive process, such as the Bayer process. By adding a beneficiation agent to an aqueous ore slurry, then applying a gravitational force to separate, or partition, the slurry into a beneficiary and a gangue, a number of quantifiable benefits are observed. These include increased alumina content and reduced silica content in the beneficiary solids as compared to the starting ore. These benefits are in excess of those observed by pre-extraction gravitational separation of ore slurries without the addition of a beneficiation agent. Beneficiation agents include DADMAC polymers, and combinations of DADMAC polymers with dextrans. The beneficiary is collected and applied to an extractive process, such as the Bayer process.