Particles in clays

Erebs, m. cancer crayfish grain, hard particle (in clay, etc.) knot (in ore, etc.) wart canker crab crustacean. 

FIGURE 35.2 The electrochemical effect on a fine particle in clay-water system. 

Figure 12. Electron micrographs of some allophanic clays separated from New Zealand soils, (a) Clay dispersed in sodium carbonate at pH 9 from Kaharoa soil (b) clay dispersed in sodium carbonate at pH 9 from Egmont Ash soil (c) fibrous clay dispersed with acid from Egmont Ash soil (d) coarse glassy particles in clay dispersed with alkali from Egmont Ash soil.

Size reduction (qv) or comminution is the first and very important step in the processing of most minerals (2,6,10,20—24). It also involves large expenditures for heavy equipment, energy, operation, and maintenance. Size reduction is necessary because the value minerals are intimately associated with gangue and need to be Hberated, and/or because most minerals processing/separation methods require the ore mass to be of certain size and/or shape. Size reduction is also required in the case of quarry products to produce material of controlled particle size (see Size measurement of particles). In some instances, hberation of valuables or impurities from the ore matrix is achieved without any apparent size reduction. Scmbbers and attritors used in the industrial minerals plants, eg, phosphate, mtile, glass sands, or clay, ate examples. 

Most surface waters contain varying amounts of suspended solids, including silt, clay, bacteria, and vimses and it is necessary to remove these before to distribution to the domestic or industrial consumer. Suspended soHds not only affect the acceptabiUty of the water but also interfere with disinfection. The principal treatment processes are sedimentation (qv) and filtration (qv). Sedimentation alone is rarely adequate for the clarification of turbid waters and is of htde or no value for the removal of such very fine particles as clay, bacteria, etc. Table 1 shows the effect of particle size on the sedimentation rate of a soHd having a specific gravity of 2.65 in water at 20°C. 

Deflocculants. Deflocculants (34), dispersants (qv), or anticoagulants are added to slurries to improve dispersion and dispersion stabiHty. Dispersants break up floes in a slurry by lowering van der Waals interparticle forces. Deflocculants adsorb on particle surfaces and prevent the approach of particles either by electrostatic or steric stabilization. Deflocculation by electrostatic stabilization is common in clay slurries, as weU as with ceramic particles dispersed in polar Hquids such as water. 

Talc and Pyrophyllite. Talc (qv) and pyrophjlhte are 2 1 layer clay minerals having no substitution in either the tetrahedral or octahedral layer. These are electrostatically neutral particles (x = 0) and may be considered ideal 2 1 layer hydrous phyUosiHcates. The stmctural formula of talc, the trioctahedral form, is Mg3Si402Q(0H)2 and the stmctural formula of pyrophylUte, the dioctahedral form, is Al2Si402Q (OH)2 (106). Ferripyrophyllite has the same stmcture as pyrophylUte, but has ferric iron instead of aluminum in the octahedral layer. Because these are electrostatically neutral they do not contain interlayer materials. These minerals are important in clay mineralogy because they can be thought of as pure 2 1 layer minerals (106). 

Clays are composed of extremely fine particles of clay minerals which are layer-type aluminum siUcates containing stmctural hydroxyl groups. In some clays, iron or magnesium substitutes for aluminum in the lattice, and alkahes and alkaline earths may be essential constituents in others. Clays may also contain varying amounts of nonclay minerals such as quart2 [14808-60-7] calcite [13397-26-7] feldspar [68476-25-5] and pyrite [1309-36-0]. Clay particles generally give well-defined x-ray diffraction patterns from which the mineral composition can readily be deterrnined. 

Plasticity in clay—water systems is caused by a bonding force between the particles and water which acts as a lubricant and permits some movement between the particles under the apphcation of a deforming force. The bonding force is in part a result of the charges on the particles (see Clays, survey). 

Fig. 2. (a) Brightness improvement obtained by the use of kaolin as a filler in paper and (b), opacity improvement obtained as pulp fibers are replaced with various kaolins. In both cases, A represents fine-particle calcined clay B, high brightness No. 1 kaolin C, coarse-particle water-washed kaolin and D,... 

The term electrophoresis refers to the movement of a soHd particle through a stationary fluid under the influence of an electric field. The study of electrophoresis has included the movement of large molecules, coUoids (qv), fibers (qv), clay particles (see Clays), latex spheres (see Latex technology), basically anything that can be said to be distinct from the fluid in which the substance is suspended. This diversity in particle size makes electrophoresis theory very general. 

In the production of clay, talc, cement, chalk, etc., an emission of particulate matter will usually accompany each process. These processes may involve grinding, drying, and sieving, which can be enclosed and controlled to prevent the emission of particles. In many cases, the recovered particles can be returned to the process for a net economic gain. 

Natural colloid particles in aqueous systems, such as clay particles, silica, etc. may serve as carriers of ionic species that are being sorbed on the particulates (pseudocolloids). It seems evident that the formation and transport properties of plutonium pseudocolloids can not yet be described in quantitative terms or be well predicted. This is an important area for further studies, since the pseudocolloidal transport might be the dominating plutonium migration mechanism in many environmental waters. 

The physical transport of particles in a river occurs by two primary modes bedload and suspended load. Bedload consists of material moved along the bed of the river by the tractive force exerted by flowing water. Bedload may roll or hop along the bottom, and individual particles may remain stationary for long periods of time between episodes of movement. Suspended load consists of material suspended within the flow and that is consequently advected by flowing water. Rivers and streams are naturally turbulent, and if the upward component of turbulence is sufficient to overcome the settling velocity of a particle, then it will tend to remain in suspension because the particles become resuspended before they can settle to the bottom of the flow. Suspended load consists of the finest particles transported by a river, and in general is composed of clay- and silt-sized... 

Quartz on filter media in a clay matrix is also available from NIST. The SRM 2679a is certified for quartz at three levels 30.8, 80.2 and 202.7 [xg/filter respectively. Respirable silica in powder form is also issued by NIST SRMs 1878a and 1879a are crystalline silica materials with particles in the respirable range and they are intended for use in X-ray diffraction and infrared spectroscopy. 

Topsoil should have a loose and open structure so that it drains fast to keep the ground surface dry. At the same time, it must be able to retain enough moisture in order that plants growing in it are not constantly subjected to drought stress. The properties of interest include particle gradation, clay content, nutrient content, and retention capacity. 

Other studies use soil or sediment samples for a more accurate indication of microbial activity in natural environments. In these samples, organic matter and clay particles play a role in metal toxicity.76112113 Both organic material and clay particles in soil can bind metals and reduce their bioavailability. For example, Pardue et al.87 demonstrated that much less solution-phase cadmium was required to inhibit trichloroaniline (TCA) dechlorination in a mineral-based soil than in a soil containing a higher concentration of organic matter. Other studies have shown that adding clay minerals to a medium mitigates toxicity. Clay minerals, such as kaolinite, montmorillonite, bentonite, and vermiculite, can bind to metals to decrease the amount that is bioavailable.112 115... 

It is possible for complex metals ions that are adsorbed onto very small particles of clay to migrate as metal-clay particles. Laboratory experiments found that radioisotope-clay particles at a low salinity were retained in a sand core, but passed through it at a high salinity.44 Clay-metal particles would not be expected to travel long distances in deep-well reservoir rocks because the pores would be too small. 

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