Alkalinity precipitation

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...

Where sodium sulfite is added as a component of multifunctional or one-drum products designed for smaller boilers, no cobalt catalyst is added because of the cobalt alkaline precipitation problem. Consequently, if the FW temperature is low this type of formulation is unsuitable because the sulfite requirement will be too high and the available reaction time too short. Probably a tannin-based, one-drum product would be more suitable (although here again there may be a problem because tannin-based products, unlike sulfite cannot be mixed with amines). 

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. 

Ferrimagnetic nanoparticles of magnetite (Fc304) in diamagnetic matrices have been studied. Nanoparticles have been obtained by alkaline precipitation of the mixture of Fe(II) and F(III) salts in a water medium [10]. Concentration of nanoparticles was 50 mg/ml (1 vol.%). The particles were stabilized by phosphate-citrate buffer (pH = 4.0) (method of electrostatic stabilization). Nanoparticle sizes have been determined by photon correlation spectrometry. Measurements were carried out at real time correlator (Photocor-SP). The viscosity of ferrofluids was 1.01 cP, and average diffusion coefficient of nanoparticles was 2.5 10 cm /s. The size distribution of nanoparticles was found to be log-normal with mean diameter of nanoparticles 17 nm and standard deviation 11 nm. 

Alkaline precipitation solution 0.6 M sodium acetate, 100 pg/mL tRNA (final concentrations). 

Alkaline precipitation solution (for 10 mL solution) 2 mL 3 M sodium acetate, 100 pg/mL tRNA solution, distilled water up to 10 mL. Store at -20°C. 

Transfer the upper phase to a new tube and ethanol precipitate add 1 volume of alkaline precipitation solution and 2.5 volumes of cold 100% ethanol (mix gently) and incubate for at least 20 min at -20°C. 

Alkaline Precipitation from Acidic Solution of Chloride at Boiling Point The heating was continued for 2 h, then the product was washed, dried and calcined at 200-800°C in oxygen. 

In some cases the precipitate was recovered by conventional filtration. Separation of the solid from the alkaline precipitate medium by this method was followed by repeated washings with hot distilled water. In other instances, the precipitated solid was freeze dried. When this method was employed, the precipitated solid was allowed to settle overnight, and the alkaline precipitation medium was removed by vacuum pipette, leaving behind only enough... 

With a view to optimizing the activity and selectivity of the Au/C catalyst, a short screening on deposition and activation methods was carried out. Comparing, in Table 3, three different deposition methods, namely alkaline precipitation (entry 1), absorption from diluted solution of HAUCI4 (entry 2) and incipient wetness impregnation (entry 3), followed by reduction of gold to metal, we observed that the first method performed the best. Although all the methods show... 

ChloropyrazoIe 744 Dry chlorine (10 g) is led into a solution of pyrazole (2.72 g) in CC14 at 0° in 60 min. The. precipitated hydrochloride (88 %) is filtered off and dissolved in water. Adding Na2C03 to weak alkalinity precipitates, 4-chloropyrazole, and the remainder is extracted in ether. The total yield is 55 % and, after recrystallization from light petroleum the m.p. is 76-77°. 

These metals form genuine hydroxides (not hydrous oxides) by alkaline precipitation from aqueous solution, obtainable in crystalline form by hydrothermal methods (crystallization from hot Ln2 03/Na0H under pressure). All have the nine-coordinate UCI3 structure, except for Lu(OH)3 which adopts the six-coordinate In(OH)s structure. Like the oxides, their basicity extends to reaction with atmospheric CO2, affording the carbonates. 

BIOLOGICAL PROPERTIES will persist until natural alkalinity precipitates as oxide attaches to small particulates in air and remains for many days most ends up in soil and attaches to particulates containing iron, manganese, or aluminum found in low levels in rivers, lakes, and streams 35 ppt of salinity 0.3 pg/L in seawater and at 1.1 pg/L in freshwater streams highly persistent in water with a half-life of longer than 200 days can be detected in water by atomic absorption 0.2 pg/L found in tap water found in some foods in the parts per million range... 

The answer to the effect of alkalinity is to use small amounts of low-alkalinity additives. Sodium bicarbonate or calcium carbonate contain low levels of alkalinity (precipitated calcium carbonate can sometimes contain high levels of residual calcium hydroxide). Sodium carbonate contributes to higher levels. 

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). 

Magnetite (Fe304) nanoparticles are prepared by alkaline precipitation of ferrous and ferric chloride (molar ratio 1 2) aqueous solution using Cabuil and Massart s method [15]. The resulting suspension is washed several times with water to remove excess salts. Afterwards the precipitate is treated with nitric acid (2 M), and stabilized in aqueous dispersion according to the method of Philipse et al. [16]. The slow addition of 0.01 M citric acid leads to particle flocculation followed by the redispersion through the addition of tetramethyl ammonium hydroxide in order to increase the pH of the dispersion to 7. 

BAT is to reduce Zn from the waste water by alkaline precipitation followed by sulphide precipitation (see Section 12.7.6)... 

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