Solids precipitation, effect

Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

Cloth Blinding Continuous filters, except for precoats, generally use some type of medium to effect the separation of the solid and filtrate phases. Since the medium is in contact with the process solids, there is always the danger, and almost invariably the ac tual occurrence, of medium blinding. The term blinding refers to blockage of the fabric itself, either by the wedging of process solids or by solids precipitated in and around the yarn. 

Precipitates have important effects on the mechanical, electronic, and optical properties of solids. Precipitation hardening is an important process used to strengthen metal alloys. In this technique, precipitates are induced to form in the alloy matrix by carefully controlled heat treatment. These precipitates interfere with dislocation movement and have the effect of hardening the alloy significantly. 

DASPE-TFPB), respectively. The obtained solid precipitates were brightly emissive whereas that of the native DASPE-I were almost nonemissive (Fig. 7a the photo is taken under normal illumination and UV-light irradiation). This indicates that, in the solid of the ion-pair species between DASPE+ and TPB (or TFPB ), concentration quenching is effectively suppressed, and more importantly, these ion-pair complexes can generate fluorescent... 

However, other parameters, such as the salt concentration, ionic strength, and especially the natures of anions in the reacting solution, play essential roles in determining the properties of the precipitated solids. The effects of anions are related to their tendency to be incorporated in the solute complexes formed on aging, which in turn differ with each cation. These anion-containing solutes often act as precursors to the solid-phase formation, affecting the properties of the final products. Various phenomena are illustrated and discussed in the text that follows. 

Most of the important chemical phenomena associated with water do not occur in solution, but rather through interaction of solutes in water with other phases. Such interactions may involve exchange of solute species between water and sediments, gas exchange between water and the atmosphere, and effects of organic surface films. Substances dissolve in water from other phases, and gases are evolved and solids precipitated as the result of chemical and biochemical phenomena in water. 

Solids Precipitation. Although chloride concentration in the scrubber liquor has little effect on removal efficiency, it has a significant effect on the operation of the column. Chloride concentrations greater than about 6.6 percent (see Table III), lead to some deposit of salts in the scrubber column. Nevertheless, it appears that if chloride level is maintained below about... 

Commonly, different metals exhibit different solution pH of zero net charge. For this reason, different metals exhibit minimum solubility at different pH values, which makes it difficult to precipitate effectively two or more metals, as metal-hydroxides, simultaneously. Thus metal-hydroxide solubility as a function of pH displays a U-shaped behavior. The lowest point in the U-shaped figure signifies the solution pH of zero net charge and is demonstrated below. Consider the solid Fe(OH)2s,... 

Effects of Reactants The nature of the reactants can play a part in the rate at which a reaction takes place. Organic chemists often reflux (a careful method of boiling flammable compounds) their reactions for a number of hours to get covalently bonded compounds to react. Reactions involving aqueous ionic compounds will react instantly. For example, if the colorless solutions Pb(N03)2(aq) and KI(aq) are mixed, a yellow solid precipitates instantly. Covalently bonded substances have strong bonds that take time and energy to break in a controlled manner. Ionic compounds dissolved in solution have freed up their ions and they remain available to react with other substances in solution. 

As in the case of alum, the ions must be rapidly dispersed throughout the tank in order to effect the complete coagulation process. The solid precipitate Fe(OH)2(s) and complexes are formed and expressing in terms of equilibrium with the solid Fe(OH)2(s), the following reactions transpire (Snoeyink and Jenkins, 1980) ... 

Solubility and speciation. Minimum requirements for reliable thermodynamic solubility studies include (i) solution equilibrium conditions (ii) effective and complete phase separation (iii) well-defined solid phases and (iv) knowledge of the speciation/oxidation state of the soluble species at equilibrium. Ideally, radionuclide solubilities should be measured in both oversaturation experiments, in which radionuclides are added to a solution untU a solid precipitates, and undersaturation experiments, in which a radionuchde solid is dissolved in aqueous media. Due to the difference in solubilities of crystalline versus amorphous solids and different kinetics of dissolution, precipitation, and recrystalhzation, the results of these two types of experiments rarely agree. In some experiments, the maximum concentrahon of the radionuchde source term in specific water is of interest, so the sohd that is used may be SF or nuclear waste glass rather than a pure radionuclide solid phase. 

The establishment of hydrolysis equilibria is usually very fast, as long as the hydrolysis species are simple. Polynuclear complexes are often formed rather slowly. Many of these polynuclear hydroxo complexes are kinetic intermediates in the slow transition from free metal ions to solid precipitates and are tlius thermodynamically unstable. Some metal-ion solutions age, that is, tliey change their composition over periods of weeks because of slow structural transformations of the isopoly ions. Such nonequilibrium conditions can frequently be recognized if the properties of metal-ion solutions (electrode potentials, spectra, conductivity, light scattering, coagulation effects, sedimentation rates, etc.) depend on the history of the solution preparation. 

Adsorption is a common source of coprecipitation and is likely to cause significant contamination of precipitates with large specific surface areas—that is, coagulated colloids (see Feature 12-1 for definition of specific area). Although adsorption does occur in crystalline solids, its effects on purity are usually undetectable because of the relatively small specific surface area of these solids. 

Since solubility is the concentration of protein in solution at equilibrium with the solid phase, the state of protein in the solid phase affects the solubility in the solution phase. Theoretical treatment of the protein solubility problem has often ignored solid phase interactions of the protein due to its complexity. A crystalline solid phase is expected to render a lower solubility than the amorphous solid phase. However the complexity and the heterogeneity of the protein in the solid state (e.g. amorphous, gel, or crystalline, or precipitates of native or denatured forms) makes it difficult to directly assess solid state effects. 

Solids from the batch precipitation tests were also examined by scanning electron microscopy. In tests where no adipic acid was added, the calcium sulfite solids formed a single platelet crystal. However, upon addition of 3,000 ppm adipic acid prior to solids precipitation, the calcium sulfite crystals formed as platelet clusters or rosettes. As the concentration of adipic acid was increased the crystals became smaller and less plate-like until at 10,000 ppm adipic acid in the slurry solution the crystals were submicron in size and resembled popcorn shaped spheres (5). These results suggest that adipic acid effects the nuclea-tion rate of calcium sulfite and certainly can drastically change the particle size distribution and crystal morphology of precipitated solids. 

Case 2 This case should be compared with Case 1 to examine the effects of solid precipitation reaction to buffer the pH of mixed fluids. Slow increase of pH from 2.7 to 3.5 is caused by buffering of Fe(OH)3 (see Table 8.6). Rapid increase of pH from 3.5 to 5.5 is due to lack of buffering reactions. It should be noted that if the authors had allowed Al(OH)3 or kaolinite to precipitate in their simulations, the pH of the mixtures would be buffered at about 4.5 until most A1 is precipitated from the solutions (see Section 6.2). The authors measured A1 concentrations of about 200 mgL-1 in the pit lake. 

Figure 16,7 shows diagrammatically a vertical-tube, single-effect evaporator. The rate of steam flow and of condensate is m, that of the thin liquor, or feed, is jhy, and that of the thick liquor is m. The rate of vapor flow to the condenser, assuming that no solids precipitate from the liquor, is ifiy — m. Also, let T, be the condensing temperature of the steam, T the boiling temperature of the liquid in the evaporator, and 7 the temperature of the feed. 

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