Precipitation formation

The hydrolysis of urea is strongly temperature-dependent, with the rate being negligible at room temperature. The rate of hydrolysis, and thus the rate of precipitate formation, can be controlled by adjusting the solution s temperature. Precipitates of BaCr04, for example, have been produced in this manner. 

Precipitate formation can occur upon contact of iajection water ions and counterions ia formation fluids. Soflds initially preseat ia the iajectioa fluid, bacterial corrosioa products, and corrosion products from metal surfaces ia the iajectioa system can all reduce near-weUbore permeability. Injectivity may also be reduced by bacterial slime that can grow on polymer deposits left ia the wellbore and adjacent rock. Strong oxidising agents such as hydrogen peroxide, sodium perborate, and occasionally sodium hypochlorite can be used to remove these bacterial deposits (16—18). 

Applicability/Limitations. In-situ treatment can be used when it is uneconomical to haul or when infeasible or uneconomical to dig or pump the contaminated waste matrix for treatment in a reactor. This approach should be used whenever excavation or removal causes an increased threat to human health. It can reduce the cost of a remediation program. Because chemicals are applied to the contaminated waste matrix, specifically soil and groundwater, a potential exists for reaction with the soil. Permeability problems can occur as the result of precipitate formation. This can result in inadequate mixing of the contaminant with the treatment chemical. Gas generation may also occur. 

Precipitate Formation Solubility Product Constant (ffsp)... 

Up to this point, we have focused on aqueous equilibria involving proton transfer. Now we apply the same principles to the equilibrium that exists between a solid salt and its dissolved ions in a saturated solution. We can use the equilibrium constant for the dissolution of a substance to predict the solubility of a salt and to control precipitate formation. These methods are used in the laboratory to separate and analyze mixtures of salts. They also have important practical applications in municipal wastewater treatment, the extraction of minerals from seawater, the formation and loss of bones and teeth, and the global carbon cycle. 

It is possible to observe effects of organotin(lV) compounds exposure such as inhibition of cleavage of fertilized eggs, interference with the formation of the mitotic spindle, damages affecting chromosome structure, and electron-dense precipitate formation in organelles. 

The section on tests for eations is used to illustrate the QATP. Students need to have tacit knowledge of the phenomena involved in qualitative analysis, reagents and apparatus, and to eonstruet explanations of the phenomena at the sub-microscopic level and to write equations to deseribe them. To help students understand precipitate formation, they are instraeted to compare the behaviom of two solutions, sodium chloride and iron(lll) ehloride when aqueous sodium hydroxide is added to the solutions (Fig. 6.1). The students will observe that there is no visible reaction with the sodium chloride solution, but a brown precipitate will be formed in the... 

Starting from molecular pre-catalysts some signs can pointed to the formation of metallic NPs colour changes during the reaction or precipitate formation are observed, or induction time is determined, or hard reaction conditions (high temperature and/or high pressure) are used, or potential stabilisers for metal nanoclusters are present... 

Reduced injectivity due to formation damage can be a significant problem in injection wells. Precipitate formation due to ions present in the injection water contacting counterions in formation fluids, solids initially present in the injection fluid (scaling), bacterial corrosion products, and corrosion products from metal surfaces in the injection system can all reduce permeability near the wellbore (153). The consequent reduced injection rate can result in a lower rate of oil production at offset wells. Dealing with corrosion and bacterial problems, compatibility of ions in the injection water and formation fluids, and filtration can all alleviate formation damage. 

In a recent study of the complexation of technetium with humic acid (HA) Sekine et al. [34,35] obtained interesting results which show competition between Tc,v-0(0H) i precipitate formation and Tcin-HA precipitate formation during a reduction process of pertechnetate with Sn2+. A weighable amount of... 

Dispersion during addition Use of alcohol solvents Stability and shelf life (gel and precipitate formation)... 

The separation between substrates in batch-produced CBD CdS is also a likely important factor for reproducibility. Arias-Carbajal Readigos et al.29 studied thin-film yield in the CBD technique as a function of separation between substrates in batch production. Based on a mathematical model, scientists proposed and experimentally verified that, in the case of CdS thin films, the film thickness reaches an asymptotic maximum with an increase in substrate separation. This behavior is explained on the basis of a critical layer of solution that exists near the substrate, within which the relevant ionic species have a higher probability of interacting with the thin-film layer than of contributing to precipitate formation. The critical layer depends on the solution composition and the temperature of the bath, as well as on the duration of deposition. 

Nielson, A.E., Precipitates Formation, Coprecipitation, and Aging, In Treatise on Analytical Chemistry,... 

Contaminant precipitation involves accumulation of a substance to form a new bulk solid phase. Sposito (1984) noted that both adsorption and precipitation imply a loss of material from the aqueous phase, but adsorption is inherently two-dimensional (occurring on the solid phase surface) while precipitation is inherently three-dimensional (occurring within pores and along solid phase boundaries). The chemical bonds that develop due to formation of the solid phase in both cases can be very similar. Moreover, mixtures of precipitates can result in heterogeneous solids with one component restricted to a thin outer layer, because of poor diffusion. Precipitate formation takes place when solubility limits are reached and occurs on a microscale between and within aggregates that constitute the subsurface solid phase. In the presence of lamellar charged particles with impurities, precipitation of cationic pollutants, for example, might occur even at concentrations below saturation (with respect to the theoretical solubility coefficient of the solvent). 

Admixture incompatibilities - Magnesium sulfate in solution may result in a precipitate formation when mixed with solutions containing Alcohol (in high concentrations) alkali carbonates and bicarbonates alkali hydroxides arsenates barium calcium clindamycin phosphate heavy metals hydrocortisone sodium succinate phosphates polymyxin B sulfate procaine hydrochloride salicylates strontium tartrates. 

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