Quartz sand

After oxygen, silicon is the most abundant element in the earth s crust, It occurs extensively as the oxide, silica, in various forms, for example, flint, quartz, sand, and as silicates in rocks and clays, but not as the free element, silicon. Silicon is prepared by reduction of silica, Si02- Powdered amorphous silicon can be obtained by heating dry powdered silica with either powdered magnesium or a... 

Quartz sand IAEA-NBS127 Barium sulphate Carbonatite... 

Fig. 4. X-iay diffraction patterns using a Cu anode (a) ciystalline quartz sand, and (b) cristobalite.

Quarz-keil, m. (Optica) quartz wedge, -kiesel, m. quartz gravel, -kristall, m. quartz crystal, rock crystal. -lager, n. quartz deposit, -linse, /. quartz lens, -mehl, -pulver, n. quartz powder- -rohr, n., -rohre, /. quartz tube, -sand, m. quartz sand, -scheibe, /. 

Mortars of this system are prepared by blending ignited magnesium oxide, ADP and STPP with a filler, normally quartz sand. On mixing with water a cementitious mass is formed. The reaction has been studied by a number of workers Kato et al. (1976), Takeda et al. (1979), Neiman ... 

Abdelrazig, Sharp El-Jazairi (1988, 1989) prepared a series of mortars based on a powder blend of MgO and ADP with a quartz sand filler. They were hydrated by mixing with water. A mortar I (MgO ADP silica water = 17T 12-9 70-0 12-5), with a water/solid ratio of 1 8, formed a workable paste which set in 7 minutes with evolution of ammonia. The main hydration product, struvite, was formed in appreciable amounts within 5 minutes and continued to increase. Schertelite also appeared, but only in minor amounts, within the first 5 minutes and persisted only during the first hour of the reaction. Dittmarite appeared in minor amounts after 15 minutes, and persisted. 

In order to make scheelite decomposition irreversible, quartz sand is added to the charge in an amount sufficient to bind calcium as an insoluble silicate. Alternatively, scheelite concentrates are directly decomposed with hydrochloric acid according to the reaction ... 

Axenic cultures of dwarf spikerush (Eleocharis colorado-ensis) were established in 4 L aspirator bottles containing quartz sand and a synthetic culture medium. These were periodically drained and the effluent subjected to fractionation and bioassays. This crude leachate was passed through a C. cartridge to separate polar from nonpolar compounds. The nonpolar fraction was eluted from the cartridge with acetone and the solvent evaporated with gas. The polar fraction was lyophilized. Both... 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

Hybrid catalysts consisting of a zeolite (ZSM-5 or Beta) and bentonite as a binder were prepared and characterized by XRD, pyridine FTIR and nitrogen adsorption. The hybrid catalysts exhibited similar properties as the combined starting materials. Catalytic pyrolysis over pure ZSM-5 and Beta as well as hybrid catalysts has been successfully carried out in a dual-fluidized bed reactor. De-oxygenation of the produced bio-oil over the different zeolitic materials was increased compared to non-catalytic pyrolysis over quartz sand. 

Testing of the catalyst was performed in the dual-fluidized bed reactor, where in the first reactor pyrolysis of the biomass and in the second upgrading of the pyrolysis vapours through catalytic de-oxygenation occurred. The bed material in the pyrolysis section was 40 g of quartz sand with a particle size distribution of 100 - 150 pm. The particle size of the catalyst was 250 - 355 pm. The amount of zeolite used in each experiment was 1.75 g. The biomass raw material used in the experiments was pine... 

Biodegradation unacclimated aerobic aqueous biodegradation t,/2 = 48-192 h, based on a soil column study in which aerobic groundwater was continuously percolated through quartz sand (Kappeler Wuhrmann 1978 Howard et al. 1991) t,/2(aq. anaerobic) = 192-768 h, based on unacclimated aqueous aerobic biodegradation half-life (Howard et al. 1991). 

The groups are not exhaustive in representing all possible clay procurement and manufacturing localities for pottery sampled in the archaeological survey. Approximately one-third of the initially considered sherds - those characterized by medium to fine quartz sand - were not amenable to independent grouping or to membership in the established reference units. 

Many minerals have been found to dissolve and precipitate in nature at dramatically different rates than they do in laboratory experiments. As first pointed out by Paces (1983) and confirmed by subsequent studies, for example, albite weathers in the field much more slowly than predicted on the basis of reaction rates measured in the laboratory. The discrepancy can be as large as four orders of magnitude (Brantley, 1992, and references therein). As we calculate in Chapter 26, furthermore, the measured reaction kinetics of quartz (SiC>2) suggest that water should quickly reach equilibrium with this mineral, even at low temperatures. Equilibrium between groundwater and quartz, however, is seldom observed, even in aquifers composed largely of quartz sand. 

Further error is introduced if reactions distinct from those for which data is available affect the chemistry of a natural fluid. Consider as an example the problem of predicting the silica content of a fluid flowing through a quartz sand aquifer. There is little benefit in modeling the reaction rate for quartz if the more reactive minerals (such as clays and zeolites) in the aquifer control the silica concentration. 

In an example of a kinetic reaction path, we calculate how quartz sand reacts at 100 °C with deionized water. According to Rimstidt and Barnes (1980), quartz reacts according to the rate law,... 

Fig. 16.1. Results of reacting quartz sand at 100°C with deionized water, calculated according to a kinetic rate law. Top diagram shows how the saturation state Q/K of quartz varies with time bottom plot shows change in amount (mmol) of quartz in system (bold line). The slope of the tangent to the curve (fine line) is the instantaneous reaction rate, the negative of the dissolution rate, shown at one day of reaction.

To set up the calculation, we take a quartz sand of the same porosity as in the calculations in Section 26.1 and assume that the quartz reacts according to the same rate law (Eqn. 26.1). We let the rate constant vary with temperature according to the Arrhenius equation (Eqn. 26.7), using the values for the preexponential factor and activation energy given in Section 26.2. As in the previous section, we need only be concerned with the time available for water to react as it flows through the aquifer. We need not specify, therefore, either the aquifer length or the flow velocity. 

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