Abstract: A system for the preparation of a lime slurry and metering of the slurry, which prevents scaling and plugging of equipment and piping. The elimination of scaling and ease nof metering are achieved by a combination of process steps in an automated operating sequence. The system is particularly adaptable to the addition of lime to municipal water systems for reduction of the acidity of the water.

Abstract: A system for the preparation of a lime slurry and metering of the slurry, which prevents scaling and plugging of equipment and piping. The elimination of scaling and ease of metering are achieved by a combination of process steps in an automated operating sequence. The system is particularly adaptable to the addition of lime to municipal water systems for reduction of the acidity of the water.

Abstract: Fluoridic spent and waste materials, such as are generated in electrolytic aluminum reduction systems, are pyrohydrolyzed in a fluidized bed reactor. For fluidization of these materials, as well as for the combustion of carbon present in the materials, an O.sub.2 -containing gas stream, containing at least about 90% by volume O.sub.2, is employed. This results in the generation of an HF-containing offgas of significantly increased HF level, which can be employed for the manufacture of an AlF.sub.3 product of at least about 85% by weight AlF.sub.3 content from hydrated alumina. The offgas having the increased HF content can also be employed for the production of highly concentrated HF acid with significantly lower energy requirement needed for concentration than in conventional systems.

Abstract: An improved process is provided for the recovery of HF in increased yield from spent aluminum reduction cell linings. The spent linings are pyrohydrolyzed in a fluidized bed reactor and the generated Na-containing vapors and gases are then contacted with a relatively finely divided source of Al.sub.2 O.sub.3. Contacting is preferably accomplished in the close vicinity of the fluidized bed to obtain extended reaction between the Al.sub.2 O.sub.3 source and the vapors. This extended reaction allows conversion of the Na-containing compounds, such as NaF and Na.sub.2 O to HF and an Na.sub.2 OxAl.sub.2 O.sub.3 compound.

Abstract: A pyrohydrolysis system is provided for the recovery of valuable components from waste and spent materials generated in electrolytic aluminum reduction facilities. The pyrohydrolysis system employs a dense phase fluidized bed reaction zone for the pyrohydrolysis of coarse feed, a dilute phase fluidized reaction zone for pyrohydrolyzing fine feed, this zone being superimposed and interconnected with the dense phase zone. The offgases, after removal of the solids, are contacted in a dilute phase fluidized zone, with a source of Al.sub.2 O.sub.3 to remove residual Na values and to produce Na-free HF. The solids from the first dilute zone, having a desired high Na:Al atom ratio, can be combined with the product clinker from the dense bed zone. The offgas, containing the source of Al.sub.2 O.sub.3, is subjected to solids separation, the solids-free and Na-free HF is utilized, while the solids of low Na:Al mole ratio are recycled to the residual Na conversion step.

Abstract: A fully integrated process is provided for the recovery of valuable components from waste materials generated in electrolytic aluminum reduction systems. The waste materials, such as spent pot linings, channel and trench cleanings, floor sweepings and spent alumina from offgas purifying dry scrubbers, are combined, then pyrohydrolyzed at elevated temperature. Fluoridic values, such as NaF and HF can be recovered from the offgas generated by pyrohydrolysis, while alumina and Na.sub.2 O values, or if desired, sodium aluminate, is reclaimed from the solid residue of pyrohydrolysis.The fluoridic values from the pyrohydrolysis offgas can be used for the manufacture of both electrolytes for aluminum reduction cells and also for the production of anhydrous HF. The alumina from the pyrohydrolysis residue can be reclaimed by a Bayer process-type leach with a caustic solution and the recovered high purity alumina utilized, for example, as reduction cell feed and/or for scrubbing reduction cell offgases.

Abstract: Alkali metal hydroxide and chlorine are produced in a membrane-equipped electrolysis cell system in a staged manner wherein at least one cell of the system is used to generate a dilute caustic solution and wherein the subsequent cell(s) of the system are used to produce a more concentrated caustic solution by electrolysis of fresh brine and the dilute caustic produced in the first stage which is used in lieu of water in the subsequent stage(s). The stage-wise production of caustic of commercially acceptable concentration results in significant energy savings with corresponding increase in the average life of the membranes employed.