Limestones solution rates

Table 7.5. Calculated solution rates for small limestone islands. (After Anthony et al., 1989.)...

Table III shows the results of titrating 0.5 ml of each limestone solution. The mean relative error of -6 indicates about a -4 error in the dissolution procedure, since the instrumental error amounted to approximately 2% The determinations listed are representative. Variation in instrumental parameters, such as titrant delivery rate (5 1), difference...

The reaction of C2S with CaO to form C S depends on dissolution of the lime Hi the clinker Hquid. When sufficient Hquid is present, the rate of solution is controUed by the size of the CaO particles, which depends Hi turn on the sizes of the particles of ground limestone. Coarse particles of siHca or calcite fail to react completely under commercial burning conditions. The reaction is governed by the rate of solution (10) ... 

Fig. 1.27. Direct injection of solution of limestone sample. Conditions Supelco LC-18 DB column concentration and pH gradient program at a flow rate of 1.5 ml/ min from 0.06 mol/1 HIBA at pH 3.8 to 0.5 mol/1 HIBA at pH 4.5 11 min modifier, 0.02 mol/1 1-octanesulfonate detection as for Fig. 1.23 sample injection, 50 pi sample...

There were three sets of experiments. The first set consisted of measurements of the surface absorption coefficient of americium and plutonium on basalts and limestones. In these experiments, disks of the stone were immersed 1n solutions of 4 x 10 5 M Pu(NO3)if or 10 7 M Am(N03)3- Small aliquots (0.05%) of the solutions were removecT, dried on tantalum planchets, and then placed in an internal alpha proportional counter. When the counting rate of samples taken at 12 hour intervals had become constant, this was regarded as evidence of the attainment of equilibrium. It was... 

Limestone (CaCC>3) dissolution is an important phenomenon in stack gas desulfurization processes using limestone slurry to absorb SC>2 and produce CaSC>3/CaS04 waste solids (1). The rate of dissolution directly determines the need for excess limestone and interacts strongly with SC>2 removal and scale-free operation in the absorber. There is a need to know the dependence of dissolution rates on both solution composition and the type and grind of limestone. This paper presents a mass transfer model and... 

Figures 5, 6, and 7 demonstrate the effect of organic acids on the dissolution rate at 25°C. Additives that provide buffer capacity between the bulk solution pH (4.0 to 5.5) and the pH at the limestone surface (5.5 to 8.0) enhance dissolution rate by providing an additional means of diffusing acidity to the limestone surface. Figure 5 shows that at pH 5.0, 3 mM total acetic acid enhances the dissolution rate a factor of 7. This enhancement is somewhat greater at higher pH, where H+ diffusion is much more limited.

The dissolution of limestone is known to be controlled by both diffusion of ions in solution and surface reaction rates. The pH value influences which of these steps dominates in the limestone dissolution. For example, at pH values less than 5 the diffusion process dominates the dissolution with little dependence on surface reaction. On the other hand, at pH values greater than 7 the reaction at the limestone surface begins to dominate the dissolution process. In the pH range between 5 and 7 both dissolution steps can influence the overall rate. 

The bulk of the limestone dissolution in most SO2 scrubbers occurs in the 5-6 pH range. Thus, both solution mass transfer properties and the nature of the limestone must be considered at typical operating conditions. Therefore, the pH, solution composition, solution buffer capacity, and the nature of the limestone are important considerations when designing for maximum limestone utilization. This paper deals primarily with the measurement of the influence of limestone properties on the overall dissolution rate. 

The next day the filtered solution is then used as the initial charge to the reactor. In this way, the initial reactor composition will be approximately the same in the beginning as during the run. The pH controller is then set to the desired value. The pH controller is used to meter scrubber feed liquor (pH 2) into the reactor to maintain a constant reactor pH. After the stirring rate has been set and the desired temperature reached, 10.00 g of sized limestone are added to the reactor. 

The buffering activity of adipic acid limits the drop in pH that normally occurs at the gas-liquid interface during SO2 absorption, and the resultant higher concentration of SO2 at the interface significantly accelerates the liquid-phase mass transfer. The capacity of the bulk liquor for reaction with SO2 is also increased by the presence of calcium adipate in solution. Thus, the SO2 absorption becomes less dependent on the dissolution rate of limestone or calcium sulfite in the absorber to provide the necessary alkalinity. 

Buffer Reaction Mechanism. The mechanism by which adipic acid buffers the pH is simple. It reacts with lime or limestone in the effluent hold tank to form calcium adipate. In the absorber, calcium adipate reacts with absorbed S02(H2S03) to form CaS03 and simultaneously regenerates adipic acid (the buffer reaction). The regenerated adipic acid is returned to the effluent hold tank for further reaction with lime or limestone. With a sufficiently high concentration of calcium adipate in solution, usually on the order of 10 m-moles/liter to react with the absorbed S02, the overall reaction rate is no longer controlled by the dissolution rate of limestone or calcium sulfite. 

The presence of sodium sulfate and sodium chloride is principally the result of secondary absorption reactions. Sodium sulfate is formed by the oxidation of sodium sulfite via reaction with oxygen absorbed from the flue gas. Oxidation also occurs in other parts of the system where process solutions are exposed to air however, the amount of oxidation is small relative to the oxidation which occurs in the absorber. At steady state, the sulfate must leave the system either as calcium sulfate or as a purge of sodium sulfate at the rate at which it is being formed in the system. Although a practical limit for the level of oxidation that can be tolerated by the limestone dual alkali system has not yet been established, it appears that oxidation rates equivalent to 15 to 20% of the S02 removed might be accommodated without intentional purges of sodium sulfate. 

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