Precipitation potential

Certain physical or chemical characteristics of the wastestream may limit the application of precipitation. For example, some organic compounds (as well as cyanide or other ions) may form organometallic complexes with metals, decreasing the precipitation potential. 

An aridity definition that takes account of the relation precipitation/potential evaporation is the Aridity Index used in the Atlas of Desertification (UNEP, 1993). Four different degrees of aridity can be recognized. These are best defined using the Aridity Index (AI), calculated as the ratio P/PET, where P stands for precipitation and PET for (potential) evapotranspiration. AI values of <1.0 indicate an average annual moisture deficit. According to this criterion, four subzones can be discussed ... 

The primary purpose of evaluating chugs as inhibitors of CYP enzymes in vitro is to determine their perpetrator or precipitant potential before advancing a candidate dmg to a late stage of development. However, identifying a dmg as an in vitro inhibitor of a given CYP enzyme does not imply that the dmg will necessarily cause clinically relevant dmg interactions. The clinical relevance of the inhibition must be considered in the following context ... 

In the preceding discussions, a criterion for stability was established using the equilibrium constant called K,p. At normal conditions, as especially used in the water works industry, specialized forms of water stability criteria have been developed. These are saturation pH, Langelier index, and the precipitation potential of a given water. 

Figure 11.1 shows a pipe that is almost completely blocked due to precipitation of CaC03. Precipitation potential is another criterion for water stability, and application of this concept can help prevent situations like the one shown in this figure. Understanding this concept requires prerequisite knowledge of the charge balance. 

CaCOspp,] is the precipitation potential of calcium carbonate. C pp in turn, can be obtained from the original calcium, minus the calcium at equilibrium, Ca r-... 

Solution The saturation pH is given as pHj = 10. The actual pH is 8.7, so the system is not saturated with calcium carbonate and no carbonate will precipitate the precipitation potential is therefore zero. At equilibrium at the Langelier saturation pH, the calcium ion concentration will remain the same at [Ca ] = 10 gmol/L. Ans... 

Precipitation potential—The amount of calcium carbonate that will precipitate when the solution is left by itself from its supersaturating condition. 

Precipitation-potential pH—The pH attained at the precipitation potential condition. 

Calcium ion concentration after occurrence of precipitation potential Calcium ion concentration before occurrence of precipitation potential... 

Precipitation potential of the calcium ion Precipitation potential of CaCOs Carbonate complex of calcium ion Bicarbonate complex of calcium ion Hydroxide complex of calcium ion... 

The degree and extent of precipitation will depend on the ability of a formulation to resist pH change when diluted. The pH change on dilution of one solution by another will depend on the initial pHs and buffer capacities of both solutions. Surakitbanharn et al. illustrated the affect of initial pH and phosphate buffer concentration on pH change when diluted with Sorensen s Phosphate Buffer. Myrdal et al. used the computational model of Surakitbanharn et al. as a means of selecting buffer concentration and initial pH to eliminate the precipitation potential of a weakly basic drug, levemopamil-HCl. Myrdal et al. showed that the unbuffered formulation precipitated upon dilution and resulted in phlebitis in vivo. 

Frequent liquor losses from the system, acting for all practical purposes as a frequently used purge stream, did not allow the examination of the full co-precipitation potential of the process. These liquor losses were the result of numerous piping and pump leaks and insufficient surge capacity. The poor condition of the equipment following three years of inactivity and a limited recommissioning were responsible for leaks and numerous other mechanical problems. Excessive inputs of seal water (needed to maintain worn out pumps in operation) combined with heavy rains and very limited surge capacity caused severe system volume balance problems. 

Nuijen, B., Bouma, M., Henrar, R.E.C., Manada, C., Bult, A., and Beijnen, J.H. (1999) Compatibility and stability of aplidine, a novel marine-derived depsipeptide antitumor agent, in infusion devices, and its hemolytic and precipitation potential upon i.v. administration, Anticancer Drugs, 10, 879-887. 

Precipitation Potential We can calculate the amount of CaC03(s) that will precipitate or dissolve as the water equilibrates by applying the two following principles to calculate equilibrium concentrations ... 

Calculate the precipitation potential for the water described in Example 6-18, taking ionic strength effects into account. 

List the equations required to determine the amount of CafOHIa required to produce a water with a theoretical precipitation potential of 5 mg/liter as CaCOs from one which has a negative Langelier Index. 

If ionic strength effects are not accounted for, the precipitation potential is 5.2 mg/1 as CaCOa (see Example 6-18). 

Gnpta JD, KneUer WA (1993) Precipitate potential of highway subbase aggregates (Report No FHWA/OH-94/004). Prepared for the Ohio Department of Transportation, Columbus, OH, p 132... 

Solubility product Solubility product constant, iQp, reflects the relationship between dissolved species and precipitated species. Each ionic compound has its own solubility limit, which is the maximum amount of the compound that can remain in solution. IQp is commonly used in solubility calculations to determine the precipitation potential of mineral salts. Certain combinations of cations and anions form sparingly soluble salts in water, and scaling in RO/NF may occur when the salts are concentrated beyond their solubility limits. See Table 6.10. 

Figure 5.5. (a) Schematic diagram of cell for recording the dissolution potential of electrolytes A, B, platinum electrodes a, solid phase (electrolyte embedded on the electrode undergoing dissolution) 3, layer of solution in the immediate vicinity of the solid phase 8, solvent phase, (b) Schematic diagram of ceU for the measurement of precipitation potentials A, B, platinum electrodes a, precipitating solid electrolyte ss, super-saturated solution of electrolyte. 

Table 5.1. Dissolution and precipitation potentials of some electrolytes.

Electrolyte Medium True dissolution potential Tme precipitation potential... 

Chapter 5. Non-equilibrium Phenomena in Continuous Systems 2. Precipitation potential... 

A crucial test was made in the context of dissolution and precipitation potential of KI in water and DMF. In one case f/+ < U while in the other case > U. Accordingly, one would expect difference in the sign of the potential in the two cases. Experimental results agree with this prediction [26]. Similarly, in solution of mixed electrolytes, the order of mobilities of cations and anions can be reversed as compared to the case of solution of a single electrolyte [26]. Effort has also been made to have a quantitative test of the theory. There is agreement between experimental and theoretically computed values of potentials as regards sign and order [29]. 

Precipitation potentials discussed in Chapter 6 are relevant in the context of injury potential [40]. It has been pointed out that precipitation of the electrolyte occurs at the negative electrode. In human body, the injured part of the protoplasmic structure is electrically negative with respect to the uninjured part. The sensation of injury seems to be associated with the clotting process, which involves the conversion of a soluble plasma protein, fibrinogen into an insoluble protein fibroin. When a blood vessel is damaged, the extrinsic clotting mechanism operates and fibrils of fibrin adhere to the injured vessel to form a clot. 

Thus, if the nucleation explanation is correct, it would only be too cold to snow when T decreases well below T /3. This would imply temperatures below 91 K, or -182 °C This is far colder than any recorded temperature on Earth, indicating that the nucleation factor is not an adequate explanation for snowfall suppression at frigid temperatures. The better explanation considers the water vapor capacity of the atmosphere, which decreases exponentially with decreasing temperature. Cold air holds exponentially less water vapor than warm air, and so the precipitation potential decreases dramatically as temperatures become more frigid. This is the main reason why warm snowstorms, where the air temperature is just slightly below the freezing point, typically produce the greatest snowfall rates. 

Designation of alloy family Composition Precipitate Precipitate potential with respect to alloy... 

A sandstone to be treated can be high in iron compounds such as siderite (iron carbonate), pyrite (iron sulfide), iron oxides, and iron chlorite clay. If this is the case, a separate acetic acid stage may be needed to reduce iron precipitation potential. The recommended acetic acid volume is 20-100 gal/ ft. Acetic acid reacts with carbonates and reduces reprecipitation of dissolved iron compounds through complexation. 

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