Calcium sulfate complexing

Lime-Sulfuric. Recovery of citric acid by calcium salt precipitation is shown in Figure 3. Although the chemistry is straightforward, the engineering principles, separation techniques, and unit operations employed result in a complex commercial process. The fermentation broth, which has been separated from the insoluble biomass, is treated with a calcium hydroxide (lime) slurry to precipitate calcium citrate. After sufficient reaction time, the calcium citrate slurry is filtered and the filter cake washed free of soluble impurities. The clean calcium citrate cake is reslurried and acidified with sulfuric acid, converting the calcium citrate to soluble citric acid and insoluble calcium sulfate. Both the calcium citrate and calcium sulfate reactions are generally performed in agitated reaction vessels made of 316 stainless steel and filtered on commercially available filtration equipment. 

A. N,N-Dimeihyljormamide-dimelhyl sulfate complex. In a 500-ml. four-necked flask equipped with mechanical stirrer, reflux condenser with calcium chloride drying tube, dropping funnel, and thermometer is placed 73 g. (1.0 mole) of dimethyl-formamide, and 126 g. (1.0 mole) of dimethyl sulfate is added dropwise with stirring at 50-60° (Note 1). After the addition is complete, the mixture is heated for another 2 hours at 70-80°. The dimethylformamide complex forms as a viscous, colorless or pale yellow ether-insoluble oil. 

Other physical phenomena that may be associated, at least partially, with complex formation are the effect of a salt on the viscosity of aqueous solutions of a sugar and the effect of carbohydrates on the electrical conductivity of aqueous solutions of electrolytes. Measurements have been made of the increase in viscosity of aqueous sucrose solutions caused by the presence of potassium acetate, potassium chloride, potassium oxalate, and the potassium and calcium salt of 5-oxo-2-pyrrolidinecarboxylic acid.81 Potassium acetate has a greater effect than potassium chloride, and calcium ion is more effective than potassium ion. Conductivities of 0.01-0.05 N aqueous solutions of potassium chloride, sodium chloride, potassium sulfate, sodium sulfate, sodium carbonate, potassium bicarbonate, potassium hydroxide, and sodium hydroxide, ammonium hydroxide, and calcium sulfate, in both the presence and absence of sucrose, have been determined by Selix.88 At a sucrose concentration of 15° Brix (15.9 g. of sucrose/100 ml. of solution), an increase of 1° Brix in sucrose causes a 4% decrease in conductivity. Landt and Bodea88 studied dilute aqueous solutions of potassium chloride, sodium chloride, barium chloride, and tetra-... 

Fig. 1. Schematic flowsheet of uranium processing (acid leach and ion exchange) operation. Numbers refer to the numbers that appear in the boxes on the flowsheet. Operations (3), (6), (9), and (11) may be done by thickening or filtration. Most often, thickeners are used, followed by filters. The pH of the leach slurry <4) is elevated to reduce its corrosive effect and to improve the ion-exchange operation on the uranium liquor subsequently separated, In tile ion exchange operation (7), resin contained in closed columns is alternately loaded with uranium and then eluted. The resin adsorbs the complex anions, such as UC fSO 4-. in which the uranium is present in the leach solution. Ammonium nitrate is nsed for elution, obtained by recycling the uranium filtrate liquor after pH adjustment. Iron adsoibed with the uranium is eluted with it. Iron separation operation (8) is needed inasmuch as the iron hydroxide slurry is heavily contaminated with calcium sulfate and coprecipitated uranium salts. Therefore, the slurry is recycled to the watering stage (3). Washed solids from 1,6). the waste barren liquor from (7), and the uranium filtrate from (11) are combined. The pH is elevated to 7.5 by adding lime slurry before the mixture is pumped to the tailings disposal area. (Rio Algom Mines Limited, Toronto)...

The dry product is ground to a powder and then a little calcium sulfate (CaS04) is added to slow down the setting rate of the cement. When water is added to the mixture, slow complex chemical changes occur, resulting in the formation of a hard interlocking mass of crystals of hydrated calcium aluminate and silicate. 

An official procedure [10,11] describes a method for the determination of chloride in a saturated calcium sulfate extract of soil. The extract is acidified and the concentration of chloride is determined by titration with mercuric nitrate using diphenylcarbazone as indicator. Mercuric ion in the presence of chloride forms mercuric chloride, which, although soluble, provides insufficient mercuric ion to form the mercuric-diphenylcarbazone complex. When all of the chloride has been removed in this way, addition of further mercuric ion produces the violet complex. 

Multivalent ions in starch dispersions, particularly those of aluminum, calcium, sulfate and oxalate, will induce retrogradation due to complexation or competition for water of hydration. The ions can be introduced by hard process water or accumulate by leaching from paper during surface sizing or coating. The destabilizing effect of ions follows the Schulze-Hardy rule. 

As pointed out earlier in this review, increasing the level of dietary calcium decreases the zinc bioavailability from phytate-containing foods. Presumably the mechanism is through the formation of chemical complexes containing zinc, phytate and calcium which are insoluble at intestinal pH and nonabsorbable (24). Recently, our laboratories used slope ratio techniques to compare the bioavailability of zinc contained in calcium sulfate-and in magnesium chloride-precipitated soybean curd (Tofu) to that of zinc added as the carbonate to egg white diets by slope ratio techniques (25). Total dietary calcium level in all diets was adjusted to 0.7% with calcium carbonate. The results (not shown) indicated that the relative availability of zinc from both tofu preparations was 51% as measured by weight gain and 36-39% for bone zinc. These results are similar to those reported for full fat soy flour (16) in Table I. 

A question must be raised as to why the tap water and the calcium bicarbonate washing treatments give such different results. The alkaline pH of the tap water suggests that calcium carbonate or bicarbonate is present and that the final product deposited in the fiber should be similar to that obtained with the pure bicarbonate solution. However, the chemical makeup of any city tap water is very complex and must contain a number of components that could affect the stability of cellulose. For example, the municipal treatment plant in Ottawa adds large amounts of alum (aluminum sulfate) to the water to settle particulate matter. Because alum makes the water very acidic, lime is then added to raise the pH. The result is that a large amount of calcium sulfate is present in the tap water and must affect the overall chemistry of the salts deposited in the fibers. One may further speculate that the anions present can influence the stability of cellulose as much as the cations. Any comprehensive understanding of the factors involved must include aH parameters. 

Moles of carbon dioxide per unit volume of flow required to bring the pH of water to the saturation pH Sulfate complex of calcium ion... 

The mechanism by which dietary protein induces an increase in urinary calcium is not clear, The effect has been attributed, in part, to the catabolism of sulfur-containing amino acids to yield sulfate. Elevated levels of plasma sulfate can form a complex with calcium. The complex passes into the renal tubule, where it is poorly reabsorbed, resulting in its excrehon in the urine. The mechanism by which phosphate reverses the hypercalciuric effect of protein is also not dear. 

In the presence of moisture, calcium salts may be incompatible with amines, amino acids, peptides, and proteins, which may form complexes. Calcium salts will interfere with the bioavailability of tetracycline antibiotics. It is also anticipated that calcium sulfate would be incompatible with indomethacin, aspirin, aspartame, ampicillin, cephalexin, and eryth-romycin " " since these materials are incompatible with other calcium salts. 

Dilution with lanthanum-HCl reduces interference from protein, phosphate, citrate, sulfate, and other anions. Phosphate causes the greatest interference because calcium-phosphate complexes are not dissociated readily by the air-acetylene flame. Lanthanum-HCl dissociates complexes, ensuring that all fractions of calcium (free, protein-bound, and complexed) are measured. Dilution effectively reduces the viscosity, which can also interfere by reducing the aspiration rate and atomization of the specimen. 

Many physiological anions, including protein, phosphate, citrate, lactate, sulfate, and oxalate, form complexes with calcium ions. Although these anions reduce the concentration of free calcium by complex formation, they do not directly interfere with the measurement of the calcium that is free. Protein deposits on the electrode may act as a divalent cation exchanger, resulting in positive interference with high concentrations of Mg. Older electrodes were sensitive to the concentration of protein in the sample. The newer electrodes use a dialysis membrane or neutral carrier to reduce or eliminate this protein effect. Investiga-... 

This work represents an attempt to elucidate the complex nature of proper drying and its effect on the composition of gypsum containing various calcium sulfate phases. 

The main source of sulfate in automobile poultices from aggressive northern sites is acid deposition. Road salts introduce both sodium chloride and calcium chloride. However, because of wet/dry cycles, the chemistry of the poultices is complex, involving the formation of calcium sulfate and the depletion of nitrate and chloride ions with a reduction in acidity. Thus corrosion tests based on the analysis of solubles within a poultice at any one time may not reproduce field results the history of the poultice is important. 

High levels of sulfate (in excess of about 500 mg/1) cause the water to be aggressive towards concrete. Lime can be used to precipitate calcium sulfate, but the residual sulfate concentration in solution may still be too high. Treatment with sodium aluminate and lime at pH 9.5 to 10.0 precipitates a Ca Al S04 0H complex and reduces the sulfate level to well below 500 mg/1 [28.2]. 

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