Natural Silts

Ruggiero et al. (1989) investigated the ability of a natural silt loam soil and the clay minerals, montmorillonite (Mte) and kaolinite (Kte), to immobilize laccase. They compared the catalytic abilities of the soil-enzyme and clay-enzyme complexes to degrade 2,4-dichlorophenol. They found that the immobilized laccase remains active in removing the substrate even after 15 repeated cycles of substrate addition (Figure 2.24). However, Claus and Filip (1988) found that the activity of tyrosinase, laccase, and peroxidase is inhibited by immobilization on bentonite. The type of saturating cations on clay surfaces also substantially influences enzymatic activity (Claus and Filip, 1990). 

With the above model, Wu and Gschwend (1986) also assumed that the entire surface area is available for mass flux and the path length of diffusive transfer is half the particle diameter. The authors introduced a correction factor f(ps, t) for >eff for natural silts, which is a function of intraaggregate porosity or tortuosity (tor), that is,... 

Ottawa Sand / Silt Ratio by weight Natural Silt ... 

Figures 2a-h shows cyclic shear induced pore pressure ratio r (= shear induced pore pressure Au/o ) versus normalized number of cycles N/N, where N=number of cycles applied andN =number of cycles to reach liquefaction, for a number of specimens at different silt contents. The specimen notations are as follows 25-408 = Ottawa sand/silt mix at 25% silt content and e=0.408 and NS(NJ)-785 = Natural silt from New Jersey at e=0.785. Also shown in these figures are the best-fit envelope curves for clean sands proposed by Seed et al. (1976) and the envelope curves proposed by El Hosri et al. (1984) for clayey silt with plasticity index of 8 to 15.

Natural Silts The non-plastic natural silt from New Jersey with a high silt content of 89% behaved similar to that of sil-co-sil 40 silt (Figure 2g). The natural silt from Los Angeles, CA with fines content of 53% and 8% particles smaller than 2pm with plasticity index of 7% showed a pore pressure response similar to that of non-plastic Ottawa sand silt mixtures at 40 to 60% silt content. The silt from San Fernando, CA had a fines content of 54% and 15% particles smaller than 2pm with plasticity index of 8%. It reached a high level of 5% of double amplitude axial strain in 9 cycles, but the pore pressure ratio did not build up beyond 65% (Shenthan 2001). No further tests were done on this soil. 

A number of tests are recommended to determine the dredgeability of soils and their behavior in placer mining or slurry mixing (Table 1-7). In nature, silts may be found in association with clays thus, the parameters for both silts and clays should be assessed. The following testing parameters are accepted by the industry. 

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

High Water Velocities. The abiUty of high water velocities to minimize fouling depends on the nature of the foulant. Clay and silt deposits are more effectively removed by high water velocities than aluminum and iron deposits, which are more tacky and form interlocking networks with other precipitates. Operation at high water velocities is not always a viable solution to clay and silt deposition because of design limitations, economic considerations, and the potential for erosion corrosion. 

Slime is a network of secreted strands (extracellular polymers) intermixed with bacteria, water, gases, and extraneous matter. Slime layers occlude surfaces—the biological mat tends to form on and stick to surfaces. Surface shielding is further accelerated by the gathering of dirt, silt, sand, and other materials into the layer. Slime layers produce a stagnant zone next to surfaces that retards convective oxygen transport and increases diffusion distances. These properties naturally promote oxygen concentration cell formation. 

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... 

Waterway Designs that do not narrow, block or accelerate natural flows, causing erosion or silting of channels. 

For compacted, low-permeability soil liners, the U.S. EPA draft guidance recommends natural soil materials, such as clays and silts. However, soils amended or blended with different additives (e.g., lime, cement, bentonite clays, and borrow clays) may also meet the current selection criteria of low hydraulic conductivity, or permeability, and sufficient thickness to prevent hazardous constituent migration out of the landfill unit. Therefore, U.S. EPA does not exclude compacted soil liners that contain these amendments. Additional factors affecting the design and construction of CCLs include plasticity index (PI), Atterburg limits, grain sizes, clay mineralogy, and attenuation properties. 

Sorption. Capture of neutral organics by non-living particulates depends on the organic carbon content of the solids (9). Equilibrium sorption of such "hydrophobic" compounds can be described by a carbon-normalized partition coefficient on both a whole-sediment basis and by particle size classes. The success of the whole-sediment approach derives from the fact that most natural sediment organic matter falls in the "silt" or "fine" particle size fractions. So long as dissolved concentrations do not exceed 0.01 mM, linear isotherms (partition coefficients) can be used. At higher concentrations, the sorptive capacity of the solid can be exceeded, and a nonlinear Freundlich or Langmuir isotherm must be invoked. 

Petroleum is formed under the earth s surface by the decomposition of organic material. The remains of tiny organisms that lived in the sea and, to a lesser extent, those of land organisms were carried down to the sea in rivers along with plants that grow on the ocean bottoms combined with the fine sands and silts in calm sea basins. These deposits, which are rich in organic materials, become the source rocks for the formation of carbon and hydrogen, i.e., natural gas and crude oil. 

Properties and extraction processes Oil-sand or tar-sand deposits are naturally occurring mixtures of quartz sand, silt and clay, water and natural bitumen (also called crude or natural bitumen), along with minor amounts of other minerals. Each particle of oil sand is coated with a layer of water, which is surrounded by a thin film of bitumen. 

Biological. A bacterial culture isolated from the Oconee River in North Georgia degraded 3-nitroaniline to the intermediate 4-nitrocatechol (Paris and Wolfe, 1987). A Pseudomonasstrain P6, isolated from a Matapeake silt loam, did not grow on 3-nitroaniline as the sole source of carbon. However, in the presence of 4-nitroaniline, all of the applied 3-nitroaniline metabolized completely to carbon dioxide (Zeyer and Kearney, 1983). In the presence of suspended natural populations from unpolluted aquatic systems, the second-order microbial transformation rate constant determined in the laboratory was reported to be 4.6 + 0.1 x 10 L/organism-h (Steen, 1991). 

CASRN 51235-04-2 molecular formula C12H20N4O2 FW 252.30 Soil/Plant. Degrades in soil and natural waters releasing carbon dioxide. The reported half-life in soil is 1 to 6 months (Hartley and Kidd, 1987). Rhodes (1980) found that the persistence of hexazinone varied from 4 wk in a Delaware sandy loam to 24 wk in a Mississippi silt loam. 

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