Sedimentation time, effect

Figure 5.2. Effect of various stabilizing oonditions on the sedimentation time of lead slurries. ( ) 5% nitric acid + 0.1 % TritonX-100, (m) 0.5% nitric acid + 0.1 % TritonX-100, (a) 5% nitric acid and (x) 0.5% nitric acid. Each slurry was subjected to US radiation only before injeotion of the first aliquot. (Reproduced with permission of Elsevier, Ref [26].)...

Figure 5.2 illustrates the effect of various stabilizers on the slurry sedimentation time after stopping US application in the determination of lead from lake sediments in particle sizes < 2 mm [26], The presence of nitric acid has the twofold effect of stabilizing slurries and increasing analyte leaching. The latter effect is a function of both the acid concentration and the nature of the target analyte [10]. 

Sedimentation Techniques. Other techniques that effect a physical separation include gravitational or centrifugal sedimentation, in which particles or emulsion droplets are separated on the basis of size and density. The separation that occurs can be quantified by monitoring X-ray or light absorbance as a function of position. Stokes law then can be used to determine the particle size distribution from the absorbance data as a function of the sedimentation time (73, 74). 

O Day PA, Carroll SA, Waychunas GA (1998) Rock-water interactions controlling zinc, cadmium, and lead concentrations in surface waters and sediments, U.S. Tri-State Mining District. I. Molecular identification using X-ray absorption spectroscopy. Env Sci Tech 32 943-955 O Reilly S, Strawn DG, Sparks DL (2001) Residence time effects on arsenate adsorption/desorption mechanisms on goethite. Soil Sci Soc Am J 65 67-77... 

The herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and trifluralin are mineralized or degraded at slower rates under anaerobic conditions. Pronounced differences in degradation rates of added, labeled 2,4-D as affected by sediment redox potential were observed (DeLaune and Salinas, 1985). Degradation of 2,4-D was approximately six times faster under aerobic conditions (+500mV) as compared to anaerobic conditions (-200 mV) in sediments. The effect of redox... 

By repeating those surveys at certain time intervals, time lapse data will be provided. From this one can carry out mapping of static and dynamic parameters such as rate of corrosion, drift, sedimentation, leakage, effects on the marine fauna and flora and dispersion of pollutant. Armed with such accurate information, which is not available to the relevant marine... 

Many suspensions (particularly those that are weaMy flocculated or structured to reduce sedimentation) show time effects during flow. At any given shear rate, the viscosity of the suspension continues to decrease with increasing the time of shear on stopping the shear, the viscosity recovers to its initial value. This reversible decrease of viscosity is referred to as thixotropy. 

One more obvious example illustrates strong influence of particle s sedimentation upon the sensitivity threshold. Assume that we have to ensure the detection of the cracks with the depth 10 > 2 mm in the case when the same product family indicated above is applied and h = 20 pm. The calculation using formula (1) shows that in the absence of sedimentation only the cracks with the width H > 2 pm could be detected. But when the effect of sedimentation results in the reduction of the value of developer layer thickness from h = 20 pm to h = 8 pm, then the cracks of substantially smaller width H > 0,17 pm can be revealed at the same length lo = 2 mm. Therefore we can state that due to the sedimentation of developer s particles the sensitivity threshold has changed being 12 times smaller. Similar results were obtained using formula (2) for larger particles of the developers such as kaolin powder. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

Geochemical Stage. The conversion of peat to bituminous coal is the result of the cumulative effects of temperature and pressure over a long time. The sediment covering the peat provides the pressure and insulation so that the earth s internal heat can be appUed to the conversion. The temperature increase is about 4 to 8°C for each 100 m of depth. The changes in plant matter are termed normal coalification. 

The most commonly used physical method for long-term eutrophication control in lakes is that of artificial destratification. This method is well tried and understood and uses either jetted water or compressed air bubbles to break down the lake stratification in the summer months. Algal growth is also affected by an increase in circulation. This is due to the artificial shading effect which results from the algae spending less time near the surface and consequently less time in the light. This technique also reduces the redox-dependent phosphorus release from sediments because the sediment surface remains aerobic. 

---