Waste water caustic soda

Disposal of waste or spilled caustic soda must meet all federal, state, and local regulations and be carried out by properly trained personnel. Accidental spills of dry caustic are shoveled and flushed with water caustic soda solutions must be diluted and neutralized with acid before discharging into sewers. Dilute acetic acid may be used to neutralize final traces of caustic. 

Soda-ofen, m. soda furnace, black-ash furnace, -riickstande, m.pl. soda residues, tank waste (in the Leblanc process), -salz, n. soda salt (sodium salt), specif, sodium carbonate, -schmelze, /. black ash. -see, m. soda lake, -seife, /. soda soap, -stein, m. caustic soda, -wasser, n. soda water, -zahl, /. soda number. 

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). 

Historically, a classic example of an evaporation process is the production of table salt. Maple syrup has traditionally been produced by evaporation of sap. Concentration of black liquor from pulp and paper processing constitutes a large-volume present application. Evaporators are also employed in such disparate uses as desalination of seawater, nuclear fuel reprocessing, radioactive waste treatment,preparation of boiler feed waters, and production of sodium hydroxide. They are used to concentrate stillage waste in fermentation processes, waste brines, inorganic salts in fertilizer production, and rinse liquids used in metal finishing, as well as in the production of sugar, vitamin C, caustic soda, dyes, and juice concentrates, and for solvent recovery in pharmaceutical processes. 

Derivation (1) Leaching of bauxite with caustic soda followed by precipitation of a hydrated aluminum oxide by hydrolysis and seeding of the solution. The alumina hydrate is then washed, filtered, and calcined to remove water and obtain the anhydrous oxide. (2) Aluminum sulfate from coal mine waste-waters is reduced to alumina. 

What became known as the Leblanc process was actually several interrelated processes. Salt was first reacted with sulphuric acid in a cast-iron pan, then in a reverberator furnace (in which heat was apphed from a flame blown from a separate chamber, not in direct contact with the salt), to produce saltcake (sodium sulphate), with hydrochloric acid released as a waste gas. Saltcake was used to make sodium carbonate, or roasted with limestone (calcium carbonate) and coal or coke to produce black ash. This mixture of sodium carbonate, calcium sulphide, sodium sulphide, hme, salt, carbon, and ash could be treated further with hot water to produce impure sodium carbonate in solution, evaporated into soda crystals (washing soda), or heated to yield anhydrous sodium carbonate. The latter, in turn, could be reacted with lime to made caustic soda (sodium hydroxide), the strongest commercial alkali then available. 

A strongly acidic pharmaceutical waste, = 10 M, is to be neutralized to pH 6 prior to discharge. Continuous neutralization with M percent caustic soda, NaOH, resulted in an effluent pH that varied widely in the range 4 to 11 because of the low buffer intensity of the water, A laboratory study showed that the addition of sodium bicarbonate, NaHCOs, or soda ash, NaaCOa, could be used to increase the buffer intensity of the solution so that the desired final pH could be... 

The exhaust air, saturated with water vapor, is first treated in an absorption unit for removal of HjS by routing it through two successive j et scrubbers working with dilute caustic soda solution. Downstream of these, a centrifugal scrubber is installed as an entrainment separator. The sulphide-containing solution rejected from the scrubbers is used to precipitate zinc in the waste water treatment system of the production plant. By products adsorbed on the activated carbon, such as sulphuric acid and elemental sulphur, are removed periodically by water and alkaline extraction. 

---