Reactive tracers

Smoak JM, DeMaster DJ, Kuehl SA, Pope RH, McKee BA (1996) The behavior of particle-reactive tracers in a high turbidity environment " Th and °Pb on the Amazon continental shelf Geochim Cosmochim Acta 60 2123-2137... 

Initially, the aquifer contains a dilute Ca-HC03 groundwater, including a negligible amount of Pb++ as well as an equal quantity of Br, which serves in the calculation as a non-reactive tracer. At the onset of the simulation, water containing 1 mmolal Pb++ and Br- passes into the aquifer until half its pore volume has been displaced. At this point, the composition of water entering the aquifer changes to that of the initial fluid, uncontaminated water nearly devoid of lead and bromide. The simulation continues until water in the aquifer has been replaced 30 times. 

Fig. 32.1. Simulation of the contamination at 25 °C of an aquifer with inorganic lead. The 100-m long section of aquifer contains a small amount of Fe(OH)3, to which Pb++ sorbs. Aquifer is initially uncontaminated, but at t = 0 water containing 1 mmolal Pb++ and 1 mmolal Br , which serves as a non-reactive tracer, passes into the left side. Pb++ is taken to sorb according to surface complexation theory, and the amount of Fe(OH)3 is chosen so that migration of the metal is retarded by a factor of two relative to the groundwater flow. After half the groundwater has been displaced by the contaminated water (V2 p.v.), clean water is flushed through the aquifer.

Reactive Tracer. If the tracer is reactive, the measured concentrations reflect both mixing characteristics and decay of the tracer. Therefore, the data must be adjusted, such that the residence time distribution within the reactor can be obtained. Example 19-3 illustrates how to adjust the data following a step input of a reactive tracer. 

A pulse study was performed by adding 16.0 mg of a reactive tracer, A, which has a half-life of 25 s, to an inlet stream flowing at 0.625 L s-1. Determine E(t), t, and of from the following response data ... 

This equation is integrated with t = 5 and the plot is shown. For a non reactive tracer,... 

Residence time distributions can be determined in practice by injecting a non-reactive tracer material into the input flow to the reactor and measuring the output response characteristics in a similar manner to that described previously in Section 2.1.1. 

Ng and Assirelli have carried out a mixing study in batch stirred vessels with working volumes of 3 L to 20L using a fiber-optic UV-vis monitoring technique. Bromophenol blue sodium salt was used as a non-reactive tracer. The results on traditional Rushton turbines and 45° angled pitched blade turbines showed good agreement with a typical conductivity technique and a correlation proposed in literature. 

The simplest and most direct way of finding the E curve uses a physical or nonreactive tracer. For special purposes, however, we may want to use a reactive tracer. This chapter deals in detail with the nonreactive tracer, and for this all sorts of experiments can be used. Figure 11.7 shows some of these. Because the pulse and the step experiments are easier to interpret, the periodic and random harder, here we only consider the pulse and the step experiment. 

When we talk about tracers, we generally mean conservative tracers with no sources or sinks. This is opposed to gas tracers, with gas transfer to the atmosphere, and reactive tracers, with a reaction occurring. Tracer studies typically use a conservative tracer, input to the system in a highly unsteady manner, such as a pulse or a front. The pulse and front are typically a more stringent test of the model than a steady-state process with any variety of reactions. Thus, a model that properly simulates the output concentration curve of a pulse or front is assumed to be sufficient for most real conditions with reactions. 

Davenport, J. E., and H. B. Singh, Systematic Development of Reactive Tracer Technology to Determine Hydroxyl Radical Concentrations in the Troposphere, Atmos. Environ., 21, 1969-1981 (1987). 

When the flow through a reactor or any other type of process vessel is non-ideal, experiments with non-reactive tracers can provide most valuable information on the nature of the flow. The injection of a tracer and the subsequent analysis of the exit stream is an example of the general stimulus-response methods described under Process Control in Chapter 7. In tracer experiments various input signals can be... 

In order to investigate the dispersion characteristics of a reaction vessel, a non-reactive tracer is injected at a convenient location some way upstream from the inlet to the vessel. Subsequently, samples (taken over very short periods of time) are collected from two positions, one being the inlet pipe to the vessel, the other at the vessel outlet, with the following results ... 

For the non-reactive tracer tests, a solution containing KI was introduced to the bottom of the column (up-flow mode) using a Rainin Model SD-200 solvent delivery pump. The first non-reactive tracer test was performed after complete water saturation of a column. PCE was then introduced into the bottom of the column using a Harvard Apparatus Model 22 syringe pump at a flow rate of 0.33 mL/min. When approximately 70% of the pore volume... 

For the special case of a non-reactive tracer, integration of Equation 5 gives... 

The last point that will be discussed in this section is concerned with identification of micromixing by using reactive tracers. 

The reactive tracers were p-nitrophenyl acetate and sodium hydroxide which undergo a second-order reaction to produce p-nitrophen-ylate, an optically detectable product. In a poorly mixed CSTR, segregation was found to increase with viscosity but the interpretation of the experiments is difficult owing to an ill-defined RTD. 

Davis, J. A. et al., Multispecies reactive tracer test in an aquifer with spatially variable chemical conditions, Water Resour. Res., 36, 119, 2000. 

Using a high quality emissions dataset, TAPM performance is very good for the prediction of extreme pollution statistics, important for environmental impact assessments, for both non-reactive (tracer) and reactive (nitrogen dioxide, ozone and particulate) pollutants for a variety of sources (e.g. industrial stacks and surface or urban emissions) - see Luhar and Hurley (2003) Hurley et al. (2005). A study with the attention to detail that makes a big difference, is by Luhar et al. (2006a). Other findings include ... 

Several useful particle-reactive tracers are found within the natural uranium and thorium ( Th) decay series ... 

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