Calcium aggregates

Factors that affect fouling with NOM-calcium complexes include permeate flux and cross flow rate (see Chapters 3.3 and 9.4). At higher flux though the membrane, the concentration of calcium increases in the concentration polarization boundary layer at the membrane surface, as described above. Lower cross flow rates also increase the concentration of calcium in the boundary layer. The increases concentration of calcium at the membrane surface enhances the fouling of the membranes by the NOM-calcium aggregates.5... 

Further development of these methods will allow the examination of structural effects of systems, such as iron oxyhydroxides or natural organics, on filtration behaviour. In this thesis it was shown that there are structural effects, but their quantification for these systems (that is, oxyhydroxide floes and organic-calcium aggregates) was not possible. 

Hei and coworkers found that Tan-IIA reduced the hypoxic ischemic brain damage (HIBD)-caused downregulation of phosphor-NRl S879 and the HIBD-caused [Ca. The neuroprotective effect of Tan-IIA may be related to influencing NMDA receptor expressimi and decreasing intracellular free-calcium aggregation [92]. 

A salt originally called sodium hexametaphosphate, with n believed to be 6, is now thought to contain many much larger anion aggregates. It has the important property that it sequesters , i.e. removes, calcium ions from solution. Hence it is much used as a water-softener. 

The calcium sulfate [7778-18-9] discharged from the furnace can also be recovered. This is less the practice in the United States where natural gypsum is plentiful and inexpensive than in Europe, where CaSO recovery for use in cement (qv) and self-leveling floors is common. Some CaSO is recovered in the United States, primarily for lower end uses such as road aggregate. 

Low Cement, Ultra-Low Cement, and No-Cement Castables are classified on the basis of calcium oxide content. These are 1—2.5, 0.2—1.0, and 0.2% CaO maximum, respectively. In the latter case the lime content is not a result of a hydrauHc setting cement constituent but comes from aggregate impurities. The insulating class is also subdivided. This division is shown in Table 14. Refractories used in steel-pouring pits are classified under ASTM C435 (Table 15). 

Roadbed Stabilization/Dust Control. One of the earliest uses of calcium chloride was for dust control and roadbed stabilization of unpaved gravel roads. Calcium chloride ia both dry and solution forms are used both topically and mixed with the aggregate. When a calcium chloride solution is sprayed on a dusty road surface, it absorbs moisture from the atmosphere binding the dust particles and keeping the surface damp. Calcium chloride does not evaporate, thus this dust-free condition is retained over along period of time. 

If aggregate is mixed with dry calcium chloride or a calcium chloride solution and then compacted, the presence of the calcium chloride draws ia moisture to biad the fine particles ia the aggregate matrix. This process leads to a well compacted, maximum deasity gravel road. This appHcatioa for calcium chloride was reviewed ia 1958 (27). More receat pubHcatioas are also available (28—30). 

Calcium siHcate hydrate is not only variable ia composition, but is very poody crystallised, and is generally referred to as calcium siHcate hydrate gel or tobermorite gel because of the coUoidal sizes (<0.1 fiva) of the gel particles. The calcium siHcate hydrates ate layer minerals having many similarities to the limited swelling clay minerals found ia nature. The layers are bonded together by excess lime and iatedayer water to form iadividual gel particles only 2—3 layers thick. Surface forces, and excess lime on the particle surfaces, tend to bond these particles together iato aggregations or stacks of the iadividual particles to form the porous gel stmcture. 

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystalforming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) can be selected for specific chemical exposures. 

Figure 6.25 Dependence of calcium oxalate aggregation rates on power input (Zauner and Jones, 2000a)...

Bramley, A.S., Hounslow, M.J. and Ryall, R.L., 1996b. Aggregation during precipitation from solution. Kinetics for calcium oxalate monohydrate. Chemical Engineering Science, 52, lAl-lSl. 

Collier, A.P. and Hounslow, M.J., 1999. Growth and aggregation rates for calcite and calcium oxalate monohydrate. American Institute of Chemical Engineers Journal, 45, 2298-2305. 

Hartel, R.W., Gottung, B.E., Randolph, A.D. and Drach, G.W., 1986. Mechanisms and kinetic modelling of calcium oxalate crystal aggregation in urine-like liquor Part I mechanisms. American Institution of Chemical Engineers Journal, 32, 1176-1185. 

Mumtaz, H.S., Hounslow, M.I., Seaton, N.A. and Paterson, W.R., 1997. Orthokinetic aggregation during precipitation A computational model for calcium oxalate monohydrate. Transactions of the Institution of Chemical Engineers, 75, 152-159. 

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