Alkalinity precipitation processes

The pulp and paper industry and potable and wastewater treatment industry are the principal markets for aluminum sulfate. Over half of the U.S. aluminum sulfate produced is employed by the pulp and paper industry. About 37% is used to precipitate and fix rosin size on paper fibers, set dyes, and control slurry pH. Another 16% is utilized to clarify process waters. The alum sold for these purposes is usually Hquid alum. It is frequendy acidic as a result of a slight excess of H2SO4. Aluminum sulfate consumption by the pulp and paper industry is projected to remain constant or decline slightly in the near term because of more efficient use of the alum and an increased use of alkaline sizing processes (13). 

Alkaline Coupling Process. Orange II [633-96-5] (21) (Cl Acid Orange 7 Cl 15510) a monoazo dye discovered ia 1876, serves as an example of the production of an azo dye by alkaline coupling. A suspension of diazotized sulfanilic acid (0.1 mol) is added to a solution (cooled to about 3°C) of 14.4 g 2-naphthol dissolved ia 15 g 30% sodium hydroxide, 25 g sodium carbonate, and 200 mL of water. The temperature should not be allowed to rise above 5°C. The reaction is heated until solution occurs and the dye is precipitated with 100 g sodium chloride. The mixture is cooled and filtered, and the product is dried. 

Fig. 13. Flowsheet of medium pressure synthesis, fixed-bed reactor (Lurgi-Ruhrchemie-Sasol) having process conditions for SASOL I of an alkaline, precipitated-iron catalyst, reduction degree 20—25% having a catalyst charge of 32—36 t, at 220—255°C and 2.48 MPa (360 psig) at a fresh feed rate of...

The choice of phosphate is inextricably linked to the FW alkalinity in order to control the precipitation process. A minimum BW hydroxide alkalinity (hydroxyl, OH, O, or P2 alkalinity) must be maintained. A maximum total alkalinity (M or T alkalinity), as well as a control range for phosphate (usually given as ppm or mg/1 P04) also must be maintained. These various control parameters change not only with the level of FW hardness, but also with boiler pressure. 

Prominent among the heavy metals found in the wastewater generated in the copper sulfate industry are copper, arsenic, cadmium, nickel, antimony, lead, chromium, and zinc (Table 22.11). They are traced to the copper and acids sources used as raw materials. These pollutants are generally removed by precipitation, clarification, gravity separation, centrifugation, and filtration. Alkaline precipitation at pH values between 7 and 10 can eradicate copper, nickel, cadmium, and zinc in the wastewater, while the quantity of arsenic can be reduced through the same process at a higher pH value. 

Wastewater treatment in the copper sulfate industry can further be improved, particularly the removal of the toxic metals, through sulfide precipitation, ion exchange, and xanthate processes. Addition of ferric chloride alongside alkaline precipitation can improve the removal of arsenic in the wastewater. 

Hexavalent chromium and metals such as zinc and nickel that are present as impurities in the chromites ore are predominant pollutants associated with the sodium dichromate plant. They are generally removed through alkaline precipitation, clarification, filtration, and settling processes. The wastewater is treated with sodium sulfide to reduce hexavalent chromium to trivalent chromium,... 

Common pollutants in a titanium dioxide plant include heavy metals, titanium dioxide, sulfur trioxide, sulfur dioxide, sodium sulfate, sulfuric acid, and unreacted iron. Most of the metals are removed by alkaline precipitation as metallic hydroxides, carbonates, and sulfides. The resulting solution is subjected to flotation, settling, filtration, and centrifugation to treat the wastewater to acceptable standards. In the sulfate process, the wastewater is sent to the treatment pond, where most of the heavy metals are precipitated. The precipitate is washed and filtered to produce pure gypsum crystals. All other streams of wastewater are treated in similar ponds with calcium sulfate before being neutralized with calcium carbonate in a reactor. The effluent from the reactor is sent to clarifiers and the solid in the underflow is filtered and concentrated. The clarifier overflow is mixed with other process wastewaters and is then neutralized before discharge. 

The analysis was made on the assumptions that the differences in gaseous-precursor fission products resulted in a potential fractionation of the three alkaline-earth radionuclides and the radioaerosols participating in the precipitation processes in the Pacific cyclones over the... 

The basic framework and procedures to simulate alkaline-related processes are presented in Example 10.4. When a particular case is specified, the details of the reaction chemistry and input data set required must conform to that particular case. This section briefly provides one more case that includes clay and silica dissolution/precipitation based on the description by Bhuyan (1989). This section presents only the elements, species, reactions, and equilibria that are not listed or different from those in Example 10.4. We add this case because clay and silica dissolution or precipitation is a common problem. For more cases, see Mohammadi (2008). 

The fines fiction, consisting mainly of zinc and manganese oxides and carbon, are leached in a sodium hydroxide bath. This selectively dissolves the zinc. Any amalgamated mercury present in the zinc precipitates out at this time and settles at the bottom of the reactor. This is periodically tapped off and sent for specialist treatment. After filtration, the zinc rich filtrate is allowed to cool naturally, then dendritic zinc is deposited by electrolysis. This is potentially a high value material used within the paint industry. The sodium hydroxide is recycled back into the alkaline leaching process. 

It is essential to preserve the integrity of the sample between the time of collection and the time of analysis. There are, however, several processes that can cause changes in the chemical composition. Examples of these include biodegradation (e.g., of nitrogen- and phosphorus-containing compounds), oxidation (e.g., of Fe(II) and organic compounds), absorption (e.g., of CO2 which affects pFl and alkalinity), precipitation (e.g., removal of CaC03, Al(OH)3), volatilization (e.g., loss of NH3, HCN), and adsorption (e.g., of dissolved metals on the walls of the container). 

These simple facts are the basis of many precipitation processes for silica. They all involve neutralizing sodium silicate solution with an acid so that colloidal particles will grow in weakly alkaline solution and be flocculated by the sodium ions of the resulting soluble sodium salt. However, there is the further factor of reinforcement or strengthening of the aggregate structure that must also be taken into account. 

Because the lanthanide and actinide metal ions are readily hydrolyzed (and precipitated) in alkaline solutions, these studies require the presence of water-soluble com-plexants. Both solvating and chelating extractants have been used in these studies. Primary and quaternary amines, alkylpyrocatechols, /J-diketones, pyrazolones, and N-alkyl derivatives of aminoalcohols are the extractants indicated as useful for alkaline extraction processes. A variety of diluents have been used, but their nature seems to have little effect on the extraction efficiency or separation factors. 

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