Precipitation rates

Schmidt and Anderson (op. cit.) and Anderson [Physics, 3, 23 (July 1932)] claim that resistivity of the collected dust may be a controlling factor which is very sensitive to moisture. They state that an increase in relative humidity of 5 percent may double the precipitation rate because of its effect on the conductivity of the collected dust layer. 

In the SFM the reactor is divided into three zones two feed zones fj and (2 and the bulk b (Figure 8.1). The feed zones exchange mass with each other and with the bulk as depicted with the flow rates mi 2, i,3 and 2,3 respectively, according to the time constants characteristic for micromixing and mesomix-ing. As imperfect mixing leads to gradients of the concentrations in the reactor, different supersaturation levels in different compartments govern the precipitation rates, especially the rapid nucleation process. 

The failure of conventional criteria may be due to the fact that it is not only one mixing process which can be limiting, rather for example an interplay of micromixing and mesomixing can influence the kinetic rates. Thus, by scaling up with constant micromixing times on different scales, the mesomixing times cannot be kept constant but will differ, and consequently the precipitation rates (e.g. nucleation rates) will tend to deviate with scale-up. 

Lasaga, A. C. (1995). Fundamental approaches in describing mineral dissolution and precipitation rates. In Chemical Weathering Rates of Silicafe Minerals" (A. F. White and S. L. Brantley, eds), Mineralogical Society of America, Washington, DC, Reviews in Mineralogy 31, 23-86. 

It was attempted to derive the relationships in the precipitated amounts of barite and quartz, flow rate and precipitation rate using the coupled fluid flow-precipitation... 

The above-mentioned consideration indicates that important factors controlling the precipitations of barite and silica are surface area/water mass ratio (A/M), temperature, precipitation rate constant (k) and flow rate (u), and the coupled fluid flow-precipitation models are applicable to understanding the distributions of minerals in submarine hydrothermal ore deposits. 

The calculations based on four reservoir models were made using equations (1-62)-(l-67) and precipitation rate constant k) for Si02 minerals by Rimstidt and Barnes (1980). 

Assuming the ranges of A/M, flow rate of mixed fluid, porosity and giving the precipitation rate of Si02 minerals (Rimstidt and Barnes, 1980), the relationship between dissolved silica concentration of mixed fluid and temperature was obtained (Fig. 1.142). It was found that the porosity does not change the results of calculations. 

Raised or Lowered average Precipitation Rates (e.g., central prairies 1999). 

UNSAT-H sets infiltration equal to the precipitation rate unless the surface soil becomes saturated. It does not simulate the soil crust that develops on the soil surface however, the user may describe a constant soil crust as a thin surface soil layer. It does not simulate runoff explicitly 80 however, it assigns excess precipitation that does not infiltrate into the soil as surface runoff. 

Fig. 6-6. The evolution of the lagoon s waters in response to oscillations in biological productivity. The results show the adjustment of the system from an initial composition equal to that of seawater. This figure shows dissolved carbon species, the saturation index, and the precipitation rate.

Figure 6-8 shows how the partial pressure of carbon dioxide in equilibrium with surface water oscillates in phase with the fluctuations in precipitation rate, saturation state, and temperature. The oscillations in alkalinity and bicarbonate concentrations have shifted in phase by about 90° because these quantities decrease when precipitation and evaporation are removing carbon from the system at above-average rates. 

Do the kinetic rate constants and rate laws apply well to the system being studied Using kinetic rate laws to describe the dissolution and precipitation rates of minerals adds an element of realism to a geochemical model but can be a source of substantial error. Much of the difficulty arises because a measured rate constant reflects the dominant reaction mechanism in the experiment from which the constant was derived, even though an entirely different mechanism may dominate the reaction in nature (see Chapter 16). 

The dissolution rate, according to the theory, does not depend on the mineral s saturation state. The precipitation rate, on the other hand, varies strongly with saturation, exceeding the dissolution rate only when the mineral is supersaturated. At the point of equilibrium, the dissolution rate matches the rate of precipitation so that the net rate of reaction is zero. There is, therefore, a strong conceptual link between the kinetic and thermodynamic interpretations equilibrium is the state in which the forward and reverse rates of a reaction balance. 

Given a specific application, we might also include precipitation kinetics in our calculations, as described in Chapter 16. Wat et al. (1992) present a brief study of the kinetics of barite formation, including the effects of scale inhibitors on precipitation rates. For a variety of reasons (see Section 16.2), however, it remains difficult to construct reliable models of the kinetics of scale precipitation. 

Application of calcite precipitation rate in predicting the utilization period of calcite scale affected wells, Philippines... 

KEYWORDS precipitation rate, calciting, saturation ratio, boiling temperatures, Mindanao Geothermal Production field... 

Rickard 1984 Compton Unwin 1990 Lebron 1996 Shiraki Brantley 1995) developed a precipitation rate equation for high salinity fluid in laboratory conditions at a temperature of 100°C using a reactor tank. This was modified through extrapolation to extend the application up to 300°C and currently used in the program code of FRACHEM (Andre et al. 2006). 

This paper evaluates the applicability of the modified precipitation rate equation in predicting the discharge duration of a calciting well compared to the observed utilization history and the results of the conservative method from direct deposition of excess calcite. Three wells in Mindanao Geothermal Production Field (MGPF) with documented output decline due to calcite deposition were studied, namely APOID, SP4D, and MD1D. 

Rate - precipitation rate, mole/kgw-s Kp - rate contant, mole/m2-s Q - saturation ratio (Q/K)... 

Akgw - Surface area for deposition per kilogram water in m2 Rp - Precipitation rate, mole/Kgw-s The following are the assumptions made in applying the precipitation rate equation ... 

The utilization periods for AP01D given by the direct deposition of the excess calcite method has a minimum of 1 month and maximum of 6 months as shown in Fig. 2. It should be noted that the calcite precipitation rate equation at a saturation ratio above 1.72 provided shorter utilization time than the direct deposition method, indicating that the rate law overestimated the amount of calcite deposited. At a saturation ratio below 1.72, however, the rate law indicated a longer utilization period, which was expected since the calcite deposition is kinetically controlled rather than instantaneous deposition of the excess calcite. 

The precipitation rate (Eq. 1) indicates comparable values for utilization period at calcite saturation ratio below 1.72 since the results are closer to the observed... 

The calcite precipitation rate (Eq. 1) should be further refined by calibrating the equation to the field condition particularly for saturation ratio above 1.72. 

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