Precipitation and accumulation

Precipitation and accumulation of clay. Precipitation of clay particles takes place at some depth in the soil as a result of 1. flocculation of clay particles, or 2. (mechanical) filtration of clay in suspension by fine capillary pores. 

Figure 6.2 Primary minerals containing Fe (e.g., pyroxenes and amphiboles in basaltic volcanic rocks) are weathered, releasing Fe into solution, which is then precipitated and accumulated in oxides as illustrated when examining the composition and percentage of clay and free oxides in Hawaiian soils. (Modified from Sherman, 1952.)...

The hydrological cycle interacts with the cycle of rocks. Minerals dissolve in or react with the water. Under different physicochemical conditions, minerals are precipitated and accumulate on the ocean floor and in the sediments of rivers and lakes. Dissolution and precipitation reactions impart to the water constituents that modify its chemical properties. Natural waters vary in chemical composition consideration of solubility relations aids in the understanding of these variations. This chapter sets forth principles concerning reactions between solids and water. Here again the most common basis is a consideration of the equilibrium relations. 

With drastic Eh increase is associated formation of bog iron ore and aggregations of native sulphur (Figure 3.35). The native sulphur accumulates in discharge surface locations of deep water with high IT S content. In mixing of this water with ground water containing O, with active bacterial participation forms insoluble in water native sulphur, which precipitates and accumulates in rock. 

Water resources in is evaluated mainly through the average flow of the river, poundage of the reservoir, the numbers of the reservoirs, accumulated precipitation and accumulated available water. About 5 main rivers and 17 large and mediumsized reservoirs are monitored in Beijing. 

Many salt deposits contain sulfides and hydrocarbon inclusions. When brine rises from the mine to the surface, noxious or hazardous gases can evolve in the pipeline or at the surface as the pressure decreases. These must be separated and disposed of safely. When temperatures in the mine are higher than those at the surface, dissolved salt may drop from solution. Process design should recognize the possibility of precipitation and accumulation of solids. In this connection, the pressure at the bottom of the well also increases the solubility of other compounds. Frear and Johnston [43] and Brandani et al. [44] have shown that the solubility of calcium species increases when the partial pressure of CO2 increases. A final consideration is on rates of solution. The very long residence time in a brine well allows more of the slower-dissolving materials to enter the brine, which is generally of lower quality than brine prepared at the plant from the same salt. 

The scheme of photoionization detection of atoms in a collinear accelerated atomic beam (Fig. 9.7(d)) is of interest for the ultrasensitive and ultraselective detection of ultratrace, very rare radioactive long-hved isotopes with a relative abundance of 10-i0-i0 20 There are a fairly large nrnnber of rare isotopes of cosmic origin, particularly those formed in the upper atmosphere as a result of nuclear reactions under the effect of cosmic rays. These isotopes form in the upper atmosphere, precipitate, and accumulate on the earth s surface and the ocean bottom. The rate of their precipitation in the ocean can be considered to remain constant for a long period of time, exceeding their half-life T1/2. 

Catalyst recovery is a major operational problem because rhodium is a cosdy noble metal and every trace must be recovered for an economic process. Several methods have been patented (44—46). The catalyst is often reactivated by heating in the presence of an alcohol. In another technique, water is added to the homogeneous catalyst solution so that the rhodium compounds precipitate. Another way to separate rhodium involves a two-phase Hquid such as the immiscible mixture of octane or cyclohexane and aliphatic alcohols having 4—8 carbon atoms. In a typical instance, the carbonylation reactor is operated so the desired products and other low boiling materials are flash-distilled. The reacting mixture itself may be boiled, or a sidestream can be distilled, returning the heavy ends to the reactor. In either case, the heavier materials tend to accumulate. A part of these materials is separated, then concentrated to leave only the heaviest residues, and treated with the immiscible Hquid pair. The rhodium precipitates and is taken up in anhydride for recycling. 

Industrial Wastewater Treatment. Industrial wastewaters require different treatments depending on their sources. Plating waste contains toxic metals that are precipitated and insolubiHzed with lime (see Electroplating). Iron and other heavy metals are also precipitated from waste-pidde Hquor, which requires acid neutralization. Akin to pickle Hquor is the concentrated sulfuric acid waste, high in iron, that accumulates in smokeless powder ordinance and chemical plants. Lime is also useful in clarifying wastes from textile dyeworks and paper pulp mills and a wide variety of other wastes. Effluents from active and abandoned coal mines also have a high sulfuric acid and iron oxide content because of the presence of pyrite in coal. 

Sorption and Desorption Processes. Sorption is a generalized term that refers to surface-induced removal of the pesticide from solution it is the attraction and accumulation of pesticide at the sod—water or sod—air interface, resulting in molecular layers on the surface of sod particles. Experimentally, sorption is characterized by the loss of pesticide from the sod solution, making it almost impossible to distinguish between sorption in which molecular layers form on sod particle surfaces, precipitation in which either a separate soHd phase forms on soHd surfaces, covalent bonding with the sod particle surface, or absorption into sod particles or organisms. Sorption is generally considered a reversible equdibrium process. 

Laudanine, C20H25O4N, was isolated by Hesse. The crude alkaloid is purified by recrj stallisation from dilute alcohol for the removal of small quantities of cryptopine, or it may be dissolved in acetic acid and the solution poured into dilute caustic soda, when this impurity is precipitated and laudanine may be recovered from the filtrate by addition of ammonium chloride. It still contains its isomeride laudanidine, which may be separated by repeated crystallisation of the hydrochlorides, laudanidine accumulating in the aqueous mother liquors. The base crystallises from dilute alcohol, or from a mixture of alcohol and chloroform in rhombic prisms, m.p. 166°, [a]o 0°. It dissolves in solutions of alkali hydroxides, fornung metallic derivatives, which are precipitated by excess of alkali, but is nearly insoluble in solution of ammonia. The salts crystallise well ... 

The transition from non-protective internal oxidation to the formation of a protective external alumina layer on nickel aluminium alloys at 1 000-1 300°C was studied by Hindam and Smeltzer . Addition of 2% A1 led to an increase in the oxidation rate compared with pure nickel, and the development of a duplex scale of aluminium-doped nickel oxide and the nickel aluminate spinel with rod-like internal oxide of alumina. During the early stages of oxidation of a 6% A1 alloy somewhat irreproducible behaviour was observed while the a-alumina layer developed by the coalescence of the rodlike internal precipitates and lateral diffusion of aluminium. At a lower temperature (800°C) Stott and Wood observed that the rate of oxidation was reduced by the addition of 0-5-4% A1 which they attributed to the blocking action of internal precipitates accumulating at the scale/alloy interface. At higher temperatures up to 1 200°C, however, an increase in the oxidation rate was observed due to aluminium doping of the nickel oxide and the inability to establish a healing layer of alumina. 

Phytostabilization (also known as in-place inactivation or phytoimmobilization) is the use of certain plant species to immobilize contaminants in the soil through absorption and accumulation by roots, adsorption onto roots, or precipitation, complexation, and metal valence reduction within the root zone. The following three mechanisms determine the fate of the contaminants within the phytostabilization process46 ... 

It will have a slope or drain system to permit removal of leaks, spills, and precipitation, and contain provisions for such accumulation to be removed. 

Smectite is the first secondary mineral to form upon rock weathering in the semi-arid to sub-humid tropics. Smectite clay retains most of the ions, notably Ca2+ and Mg2+, released from weathering primary silicates. Iron, present as Fe2+ in primary minerals, is preserved in the smectite crystal lattice as Fe3+. The smectites become unstable as weathering proceeds and basic cations and silica are removed by leaching. Fe3+-compounds however remain in the soil, lending it a reddish color aluminum is retained in kaolinite and A1-oxides. Leached soil components accumulate at poorly drained, lower terrain positions where they precipitate and form new smectitic clays that remain stable as long as the pH is above neutral. Additional circumstances for the dominance of clays are ... 

Different conditions are typical for Dry Tropical Wood, Dry Savanna and Dry Woody Shrub ecosystems in areas with precipitation rates of 400-600 mm and a prolonged dry season. The microbial activity is suppressed during a dry season. The soils of these ecosystems have no even periodic leaching, the formation by transpiration of a biogeochemical barrier in the upper soil layer favors the alkaline reaction and accumulation of soluble salts. This decreases also the intensity of exposure to different pollutants for living organisms. 

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