Silicate, sodium Subject

Powdered, particulate MCM-41 molecular sieves (Si/Al = 37) with varied pore diameters (1.80, 2.18, 2.54 and 3.04 nm) were synthesized following the conventional procedure using sodium silicate, sodium aluminate and C TMAB (n = 12, 14, 16 and 18) as the source materials for Si, A1 and quaternary ammonium surfactants, respectively [13]. Each sample was subjected to calcination in air at 560 °C for 6 h to remove the organic templates. The structure of the synthesized material was confirmed by powder X-ray diffraction (XRD) and by scanning/transmission electron microscopy. Their average pore sizes were deduced from the adsorption curve of the N2 adsorption-desorption isotherm obtained at 77 K by means of the BJH method (Table 1). 

In this procedure the soil sample (spiked with isotopic marker compounds) is processed in a two-part enrichment procedure (Fig. 5.3). In part I, a mixture of the sample and sodium sulphate is subject to solvent extraction, and the extract is, in the same process, passed through a series of silica-based adsorbents and then through the carbon/glass fibre adsorbent. The extract passes through the adsorbents in the following order potassium silicate, silica gel, cesium or potassium silicate, silica gel and finally an activated-carbon... 

Sodium silicate cemcnl does not withstand bases, bui is resistant to acids except hydrofluoric. This cement sets lo a very rigid solid, so lhal when subjected to mechanical shock or lo temperature change il is liable to crack. 

Regardless of the t)q)e of soluble metal silicates used, they are subject to the same molecular speciation in aqueous solution resulting in a mixture of monomeric tetrahedral ions, oligomeric linear or cyclic silicate ions, and polysilicate ions. Sodium metasilicate, an example of a soluble metal silicate, can be prepared in anhydrous form or in the presence of water of crystallization as the penta- or nona-hydrate. It is readily soluble in water [8]. 

Tuber slices (338 kg) (1.5-2,0 mm thickness) of Ri cultivar Rishiri were inoculated with a zoospore suspension (250000-500000 zoospores/ml) of incompatible race of Phytophthora infestans (Mont.) de Bary, race 0 and incubated at 18-20°C for two days. The inoculated slices were stored in an ice-box (-30°C) for a week and then immersed in methanol (250 1) for a week. The supernatant was separated by decantation and the process was repeated twice with methanol (2 x 150 ml). The methanol extracts were combined and concentrated under reduced pressure below 30°C. The concentrate was extracted with chloroform and evaporated to yield oily residue from which a solid material was precipitated on treatment with acetone and was then removed by filtration. The filtrate w as c oncentrated to yield an o ily residue which w as treated with hexane. The hexane solution was concentrated, extracted with ether and washed with aqueous sodium carbonate (10%) and hydrochloric acid (0.1 M) to remove acidic and basic components. The ether extract was washed with water, dried and evaporated. The residue, which contained many c ompounds (by tlc) w as subjected toehromatographic p urification over silicic acid (Mallinckrodt, AR-100) and celite. Benzene ether (1 1 and 1 2) afforded crude rishitin which showed an almost single spot on tic. This was chromatographed over silica gel (Merck). Ether eluted pure rishitin (40) (3.9 g, from 338 Kg tuber slices), m.p. 65-67°C, [ai]-35.1°, max s, 3060,1640 and 890 cm 1 1HNMR 51.12 (3H, d, J=6 Hz), 3.12 (1H, t, J=9Hz),3.55 (lH,br,do,d, J=9and7 Hz), 4.18 (2H, br, s, 2 OH) C,3NMR 148.9 (Cn), 129.0 (C5), 124.9 (C10), 10.9 (C12), 79.2 (C8), 71.5 (C2), 41.6 (C7), 40.4 (C4), 38.3 (C8), 31.1 (C6), 29.7 (C9), 26.5 (C,), 21.0 (C13), 16.4 (Cm).22... 

During the process, the aqueous silicate solution is introduced into the upper portion of the gas-fired spray dryer and passes through a spray nozzle or a disk atomizer (see Figure 22.5). The speed of the spray wheel may be about 11,000 rpm. The finely and evenly dispersed liquid comes into contact with upwardly directed hot air. Typical spray tower tanperatures are about 180°C [21] with inlet temperatures of about 260-300°C and outlet air temperatures of above lOO C. The resultant spray-dried droplets adopt the form of hollow microspheres. The silicate particles are collected at the spray dryer s bottom and are withdrawn by a screw conveyor. The amorphous sodium silicate may have a bulk density on the order of 250-500 g/L, an SiOjiNajO molar ratio of 2.04 1, and an ignition loss on the order of 19-20%. Its mean particle size can be on the order of 100-200 pm. The material may be subjected to further milling to modify the form and density of the powder [51,63]. 

Process modifications may include producing granules from quartz flour, soda ash, and sodium silicate solution, the latter to act as a binder, by roll compaction, and subjecting them to calcination [78]. 

Alternative Process Aids. Numerous substitute process aids have been evaluated for possible use in the hot water flotation process. Indeed, this is probably the subject of the majority of patents directed at oil sand processing. It should be fairly obvious that if sodium hydroxide is a suitable process aid then other alkaline agents could be used as well. Research by many investigators has borne this out over the years. Other bases, including silicates and phosphates have been studied in some detail [122]. Some of these alternative alkalis have performance advantages over NaOH. The main reason NaOH has remained in commercial use over three decades has been economic. 

Silicic acid from sodium silicate has long been used as a coagulant in water treatment, and the subject has been well summarized by Vail (192). 

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