Surface precipitates types

Surface runoff. Hydrologists have identified two processes for generating surface runoff over land. The first, saturated overland flow (SOF), is generated when precipitation (or snowmelt) occurs over a saturated soil since water has nowhere to infiltrate, it then runs off over land. SOF typically occurs only in humid environments or where the water table rises to intersect with a stream. Horton overland flow (HOF or infiltration-limited overland flow) occurs when precipitation intensity exceeds the infiltration capacity of the soil in a non-saturated environment. In this case, only the excess precipitation (that exceeding the infiltration capacity) runs off over the surface. Both types of overland runoff generate relatively rapid flows that constitute the surface water contribution to the hydrograph (Fig. 6-6). 

Table 4 summarizes some experimentally determined Ka values for a variety of apatites and contaminants. Some values are veiy large (> 10,000), indicating the propensity for apatites to sorb and/or induce surface precipitation reactions. These values are useful in terms of understanding the broad affinity that apatites have for various solutes. However, they reflect the operationally defined conditions particular to each partition study (pH, I, solid-to-liquid ratio, and apatite type). 

Wet removal processes are further controlled by precipitation types and rates. Dry deposition processes on surfaces are affected by atmospheric transport rates that mix fresh pollutant into the surface boundary layers and by the physical properties of particles. For the Eastern U.S., the approximate annual deposition rates of sulfate can be compared as follows (Table III), considering that deposition flux is the product of a concentration and a velocity of deposition (Vd) (20) ... 

The processes of adsorption, precipitation and coprecipitation are difficult to distinguish on that basis from the analysis of the diminution of the ions from the solution, changes of pH and kinetics. Only the spectroscopic investigations of the molecular interactions between adsorbent and adsorbate may help to distinguish a type of the process [146,147]. As an adsorption of the ions, is assumed process of the two-dimensional structure formation, whereas for three-dimensional structures precipitation or surface precipitation takes place. From this reason an AFM method may be useful at investigations of the morphology changes of the adsorbate surface [147]. 

The second form of precipitation cannot be understood from the thermodynamic properties of the solution the solution is undersaturated, even so, precipitation takes place on the surface. This process is called surface precipitation. In this case there are three possibilities. One of them is when the precipitate is formed in a monomolecular layer. The second possibility is coprecipitation, when a component in low concentration coprecipitates with another component in high concentration if it can be built into the crystal lattice (Section 1.2.4). In this case, the thickness can be higher than that in the monolayer. For example, cesium ions in very low concentration coprecipitate with iron and magnesium containing carbonates (Konya et al. 2005 Chapter 3, Section 3.1.2). These types of surface precipitation can quantitatively be described by the adsorption equations (Section 1.3.4.1). 

The adsorption of aqueous Pb(II) has been studied extensively. The following important factors have been studied solution pH [233,234,190,235-239], type of adsorbent [166,171,233,234,190,236,1981 and chemical surface modification [210,223,240], As in the case of many metallic cations, Pb- uptake increases with increasing aqueous solution pH, with a sharp increa.se ( adsorption edge") being observed in a narrow pH range, typically between 3 and 6 [ 171 ], depending on the pHpzc of the carbon used. Adsorption of Pb(II) as a function of solution pH for different initial concentrations is illustrated in Fig. 11. As the pH increases further, there is surface precipitation of the products of hydrolysis of Pb (see Table Al in the Appendix). 

Surfaces 2. Precipitant type 2. Ligands, inhibitors, effectors... 

The mechanism for the formation of metal hydroxide surface precipitates is not clearly understood. It is clear that the type of metal ion determines whether metal hydroxide surface precipitates form, and the type of surface precipitate formed (i.e., metal hydroxide or mixed metal hydroxide) is dependent on the sorbent type. The precipitation could be explained by the combination of several processes (Yamaguchi et al., 2001). First, the electric field of the mineral surface attracts metal ions (e.g., Ni) through adsorption, leading to a local supersaturation... 

The molecular models may predict at least two types of phase transitions Transitions leading to (i) two immiscible surface solutions, and (ii) surface precipitation. 

Three different types of nucleation products have been proposed formation or sorption of polymers (dimers, trimers, etc.) on the surface (polynuclear surface complexes) a solid solution or coprecipitate that involves co-ions dissolved from the adsorbent and a precipitate formed on the surface composed of ions from the bulk solution, or their hydrolysis products (5,15,33,62,69). The two latter products are examples of surface precipitates. 

Chain architecture also plays a role in determining the adsorption characteristics of copolymers. For instance, if we consider triblock ABA-type copolymers the relative positions of the anchor and buoy blocks become important. When there are two buoy blocks and a central anchor block, the copolymers show diblock AB-type behavior (see Fig. 9 and 10). If, however, there are two anchor blocks and a central buoy block, surface precipitation of the polymer molecule at the particle surface is generally observed. This precipitation (or multilayer formation) process is due to strong interaction between the anchor blocks themselves and manifests itself in the form of an ever-increasing adsorption isotherm (i.e., there is no plateau) of the type shown in Figure 11. When compared with... 

---