R

Weak h2so4

Caustic soda storage

Off gas

Liquefaction

To tank caps

Tank cap wash to waste treatment

Deionized Noncontact water waste cooling

Holding tank

^ discharge

FIGURE 22.4 Flow diagram of a typical plant production of chlor-alkali indicating water use and wastewater generation.

TABLE 22.9

Summary of Raw Waste Loadings Found in Verification Sampling of Unit Product of Chlor-Alkali (Mercury Cell and Diaphragm Cell Processes)

Maximum Raw Waste Loadings (10-3 kg/Mg)

TABLE 22.9

Summary of Raw Waste Loadings Found in Verification Sampling of Unit Product of Chlor-Alkali (Mercury Cell and Diaphragm Cell Processes)

Maximum Raw Waste Loadings (10-3 kg/Mg)

Pollutant

Mercury Cell

Diaphragm Cell

Antimony

0.77a

Arsenic

1.1

2.1

Cadmium

0.23

0.0061

Chromium

0.4

4.6

Copper

0.6

1.1

Lead

0.7

1.5

Nickel

0.7

1.8

Mercury

48

0.014

Thallium

5.4

BDL

Selenium

BDL

Beryllium

BDL

Silver

0.83

0.0007

Zinc

10

2.1

Source: U.S. EPA, Treatability Manual, Technical Report EPA-600-/2-82-001, U.S. Environmental Protection Agency,

Washington, DC, 1982. a 0.77 (10-3 kg/Mg) = 0.00077 Kg/106 g. BDL, below detection limit.

Source: U.S. EPA, Treatability Manual, Technical Report EPA-600-/2-82-001, U.S. Environmental Protection Agency,

Washington, DC, 1982. a 0.77 (10-3 kg/Mg) = 0.00077 Kg/106 g. BDL, below detection limit.

22.3.311 Chrome Oxide

Chrome oxide is produced by mixing sodium dichromate and sulfur with water and the resultant mixture is heated in a kiln. The kiln products are slurred with water, filtered, washed, dried, ground, screened, and packaged.

22.3.31.2 Chrome Yellow

Chrome yellow pigment is made up of lead chromate, and it is formed as a precipitate of the reaction involving lead nitrate, caustic soda, and sodium dichromate. The precipitate is filtered, treated with

Cell water -

Process water

Treatment

^-Scrubber

Press

Solids to

landfill -

Treated effluent

FIGURE 22.5 General wastewater treatment process flow diagram at a mercury cell plant for the production of chlor-alkali.

Brine process water

Brine process water

Discharge

FIGURE 22.6 General wastewater treatment process flow diagram at a diaphragm cell plant for production of chlor-alkali.

Discharge

FIGURE 22.6 General wastewater treatment process flow diagram at a diaphragm cell plant for production of chlor-alkali.

chemicals to develop the desired pigment properties, dried, milled, and packaged. Chrome orange is produced in the same process and shares many characteristics with chrome yellow.

22.3.3.1.3 Chrome Green

Chrome green is produced by mechanically mixing chrome yellow and iron blue pigments in water. An iron blue, [Fe(NH4) (FeCN6)], is an oxidized precipitate product of the reaction between an aqueous solution of iron sulfate and ammonium sulfate with sodium hexacyanoferrate.

22.3.3.1.4 Molybdenum Orange

This type of pigment is the precipitate formed when molybdic oxide is dissolved in aqueous sodium hydroxide with the addition of sodium chromate. The resulting mixture is reacted with a solution of lead nitrate. The precipitate formed is further processed through filtration, washing, drying, milling, and packaging.

22.3.3.1.5 Zinc Yellow

The reaction of zinc oxide, hydrochloric acid, sodium dichromate, and potassium chloride produced zinc yellow as a precipitate, which is a complex compound of zinc, potassium, and chromium. The complex compound is further subjected to filtration, washing, drying, milling, and packaging for use.

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