Precipitation-filtration process

Because the brine is recirculated, solid salt is required for resaturation. The brine, which must be quite pure, is first dechlorinated and then purified by a straightforward precipitation - filtration process. 

Precipitation softening processes are used to reduce raw water hardness, alkalinity, siHca, and other constituents. This helps prepare water for direct use as cooling tower makeup or as a first-stage treatment followed by ion exchange for boiler makeup or process use. The water is treated with lime or a combination of lime and soda ash (carbonate ion). These chemicals react with the hardness and natural alkalinity in the water to form insoluble compounds. The compounds precipitate and are removed from the water by sedimentation and, usually, filtration. Waters with moderate to high hardness and alkalinity concentrations (150—500 ppm as CaCO ) are often treated in this fashion. 

Toxic pollutants found in the mercury cell wastewater stream include mercury and some heavy metals like chromium and others stated in Table 22.8, some of them are corrosion products of reactions between chlorine and the plant materials of construction. Virtually, most of these pollutants are generally removed by sulfide precipitation followed by settling or filtration. Prior to treatment, sodium hydrosulfide is used to precipitate mercury sulfide, which is removed through filtration process in the wastewater stream. The tail gas scrubber water is often recycled as brine make-up water. Reduction, adsorption on activated carbon, ion exchange, and some chemical treatments are some of the processes employed in the treatment of wastewater in this cell. Sodium salts such as sodium bisulfite, sodium hydrosulfite, sodium sulfide, and sodium borohydride are also employed in the treatment of the wastewater in this cell28 (Figure 22.5). 

In addition to the heavy metals stated in Table 22.10, ferro- and ferricyanide are also part of the pollutants in the wastewater generated in a chrome pigment plant. These wastes are generally combined and treated through reduction, precipitation, equalization, and neutralization to be followed by clarification and filtration processes. Most of the heavy metals are precipitated using lime or caustic soda at specific pH. Chromium is reduced by S02 to a trivalent form, wherein it is precipitated as chromium hydroxide at specific pH. Sodium bisulfide is also employed to precipitate some of the metals at a low pH. The treated water is recycled for plant use while the sludge is sent to landfills (Figure 22.7). 

Sodium hydrosulfite is produced through the Formate process where sodium formate solution, sodium hydroxide, and liquid sulfur dioxide reacted in the presence of a recycled stream of methanol solvent. Other products are sodium sulfite, sodium bicarbonate, and carbon monoxide. In the reactor, sodium hydrosulfite is precipitated to form a slurry of sodium hydrosulfite in the solution of methanol, methyl formate, and other coproducts. The mixture is sent to a pressurized filter system to recover sodium hydrosulfite crystals that are dried in a steam-heated rotary drier before being packaged. Heat supply in this process is highly monitored in order not to decompose sodium hydrosulfite to sulfite. Purging is periodically carried out on the recycle stream, particularly those involving methanol, to avoid excessive buildup of impurities. Also, vaporized methanol from the drying process and liquors from the filtration process are recycled to the solvent recovery system to improve the efficiency of the plant. 

After the electrochemical reaction, or after the desired amount of time has passed, remove the power source, and then filter-off the precipitated brick-red copper-I-oxide (contained submerged under water in a beaker), and then wash the filtered-off mass with three 250-milliliter portions (three 8.4 fluid oz. portions) of warm water, and then vacuum dry or air-dry the washed solids. Note do not use heat to dry the copper-I-oxide as it is easily oxidized to copper-II-oxide. Now, for the copper-I-chloride, carefully extract the small submerged beaker (placed under the copper anode to collect the flaky precipitate of copper-I-chloride), using a suitable utensil or equivalent, and then carefully filter-off the white mass, using preferably vacuum filtration. After the filtration process, wash the filtered-off copper-I-chloride with three 50-milliliter portions (three 1.6 fluid oz. portions) of cold alcohol, and then vacuum dry or air-dry the washed copper-I-chloride. Note copper-I-chloride is rather unstable and tends to change colors when exposed to air and moisture. 

The exact mechanism of pentamidine renal toxicity is unknown. Early on, Makula et al suggested that renal toxicity may result from the ability of pentamidine to react with and form insoluble precipitates with nucleotides, leading to depletion of the nucleotide pool (e.g. ATP) necessary for various energy-dependent functions inhibition of DNA, RNA and protein synthesis. In addition, the complexes could be deposited in the kidney impairing the normal filtration process [172]. 

An extraction is frequently more attractive than a precipitation method for separating inorganic species. The processes of equilibration and separation of phases in a separatory funnel are less tedious and time consuming than conventional precipitation, filtration, and washing. 

A simple centrifugation or MF step in the primary clarification may directly be succeeded by a secondary clarification or an enrichment step, such as extraction, precipitation, or adsorption. The concentrated product may then be subjected to membrane filtration processes. Ultrafiltration might be done earlier and then followed by extraction or precipitation with salts. Diafiltration units can subsequently be used to remove the... 

The newly invented polystyrene-supported palladacycle catalyst was prepared in six steps with high yields. The simple precipitation and filtration process to recycle the catalyst after model reactions for Heck, Suzuki, and Sonogashira reactions is noteworthy.[1]... 

At the lower dosage of 25 mgL , FeClj floes are visible. These floes were observed to break up during the filtration process. Restabilisation of the precipitate occurred at 100 mgL FeCl.v... 

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