Potential Precipitate

Scale prevention methods include operating at low conversion and chemical pretreatment. Acid injection to convert COs to CO2 is commonly used, but cellulosic membranes require operation at pH 4 to 7 to prevent hydrolysis. Sulfuric acid is commonly used at a dosing of 0.24 mg/L while hydrochloric acid is to be avoided to minimize corrosion. Acid addition will precipitate aluminum hydroxide. Water softening upstream of the RO By using lime and sodium zeolites will precipitate calcium and magnesium hydroxides and entrap some silica. Antisealant compounds such as sodium hexametaphosphate, EDTA, and polymers are also commonly added to encapsulate potential precipitants. Oxidant addition precipitates metal oxides for particle removal (converting soluble ferrous Fe ions to insoluble ferric Fe ions). 

Proteins modified with 2-iminothiolane are subject to disulfide formation upon sulfhydryl oxidation. This can cause unwanted conjugation, potentially precipitating the protein. The addition of a metal-chelating agent such as EDTA (0.01-0.1M) will prevent metal-catalyzed oxidation and maintain sulfhydryl stability. In the presence of some serum proteins (i.e., BSA) a 0.1M concentration of EDTA may be necessary to prevent metal-catalyzed oxidation, presumably due to the high contamination of iron from hemolyzed blood. 

From 1975 to 1990, scientists at the University of Kansas utilized a rational synthetic design for the definition of a new excipient, the SBE derivative of P-CD (SBE7-P-CD CAPTISOL ). Designing renal safety into the CD was approached by introducing anionic substituents onto the CD structure. This approach capitalized on the increased water solubility that would be realized with the introduction of an ionic substituent. Higher intrinsic water solubility was expected to help minimize the potential precipitation of the CD, if concentrated in the kidney cell, and the charged substituent was expected to capitalize on the ability of the kidney to efficiently excrete ionic compounds into the urine, thus reducing residence time and exposure of the kidney cells to the CD. 

CQ is the concentration of available sites for the crystallization of barium sulfate. This is equal to the sum of the initial concentration of already precipitated sulfate in the medium (Cg0) and of the potentially precipitable sulfate, equal to the concentration of that of the two reactants (Ba + or S0 2-) n stoichiometric defect. It was checked that the addition of EDTA did not change the rate of reaction. 

In conclusion, such a model is convenient to get an idea of the calcium oxalate concentration, CO2 pressure and conditions for potential precipitation of secondary calcium carbonate through oxalotrophic bacterial activity. It demonstrates that as long as calcium is available and oxalotrophic bacteria are present, transformation of oxalate into carbonate can occur under normal conditions found in soils and surficial sediments. Therefore, an oxalate-carbonate cycle, or at least pathway, must exist at the surface of continents (Verrecchia Dumont, 1996), explaining the absence of calcium oxalate accumulation in soils and the fossil record. 

Thus, dissolution of 0.25 mol of K-feldspar buffers sufficient acid to allow (potentially) precipitation of I mol of calcite. Buffering by silicates has been postulated as the primary control on subsurface pH (Hutcheon and Abercrombie, 1989,1990 Smith and Ehrenberg, 1989 Hutcheon etal, 1993), consistent with the observation that dissolution affecting feldspars typically leaves adjacent calcite cements and skeletal debris unaffected (Siebert et al, 1984). 

The alkanimidamide hydrochloride (0.01 mol) was dissolved in a mixture of benzene (40 mL) and H20 (10 mL). Into this solution 1 M NaOH (10 mL) and the aroyl isothiocyanate 24 (R1 = aryl, X = O 0.01 mol) in anhyd benzene (10 mL) were dropped simultaneously with vigorous stirring. Then additional 2M NaOH (10 mL) was added within 10 min. After 1 h, EtOH (10-20 mL) was added to dissolve the potential precipitate, and the organic phase was extracted with 2 M NaOH (10 mL). The combined alkaline extracts were acidified to pH 4- 5 with 1 M H,S04, and the precipitated triazines were collected by suction. 

The chemical composition of produced water was obtained through the simulation of the flow of water and solutes through the reservoir. With this data it was possible to estimate how much mineral can potentially precipitate at the production well (Figure 6). As comparison, a simulation considering conservative transport (without chemical reactions) was also performed. 

Figure 6. Minerals that potentially precipitate at production well as result of incompatible water mixing (a) produced mineral per day and (b) accumulated total mass...

Reactive transport simulation is more realistic because of the consideration of SrSOj and BaS04 precipitation in reservoir (Bertero et al., 1988), predicting a lower scaling in the production well than the conservative transport simulation (Figure 6). This can be justified by the fact that in a reactive transport simulation part of the mineral that could cause scale in the production well has already precipitated in the reservoir. For kinetic reasons, they are called potentially precipitated minerals because the local equilibrium assumption at the production well is not necessarily valid. Produced water can be SrSO and BaS04... 

Phosphorus adsorption typically occurs at low concentrations and reaches saturation level once all potential sorption sites are occupied. However, if the concentration of soil pore water is increased beyond the capacity of soil to adsorb phosphorus, the precipitation reactions may be involved in retaining phosphorus. When sorption isotherms are measured at high concentrations (Figure 9.26), it is hard to differentiate between adsorption and precipitation reactions. An example of potential precipitation reactions at high solution concentrations is shown in Figure 9.29. 

Besides electrolytes. H and OH also affect the stability of colloids. While OH" ions increase the negative zeta potential H ions have an opposite effect. Thus by var5 ng the value of zeta potentied to a critical potential , precipitation is facilitated. Various other physical and chemical agents which may bring about precipitation are heat, UV radiation, acids and alkalies. Also, mechanical disturbances like ultrasonic vibrations, high speed shaking or stirring can destroy the conformation of the colloidal particle and thus precipitate it. 

First of all, the column should be conditioned. Stabilizers and preservatives that might have been used during storage are washed out and the cartridge is adjusted to the desired pH (and salt content, etc.). In addition, potential precipitation problems that might occur during the mixing of mobile phase and sample can be solved. 

This information can indicate the nature of acid spending, whether overtreatment or undertreatment occurred, and whether iron and potential precipitation of reaction products are a concern. It also can indicate if acid mixtures injected might have been incompatible with formation fluids. It is imperative to patiently evaluate return samples before drawing any potentially incorrect conclusions about the treatment pumped. 

Due to the complexity of the precipitation process, the saturation index (SI) is calculated to estimate the calcium carbonate precipitation in water, and is used to describe the saturation state (from a thermodynamic point of view) of the aqueous phase composition versus different solids. It is widely used to estimate the potential precipitation of different solids from an equilibrated aqueous phase speciation. 

Figs. 69, 70, and 71 show that the use of lead-free solder (Sn-Ag-Bi-In) has not resulted in reliability problems. However, some joints have indicated a concern with the potential precipitation of bismuth from the alloy over time. Therefore the bismuth content of the solder used to assemble the MD player will be reduced from 2.5% bismuth to 0.5% bismuth with 6% indium. 

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