Batch Operation

In batch operation, a given amount (m) of ion exchanger is contacted with a given volume (V) of solution. The mixture is agitated until equilibrium has been attained. In typical binary batch process used for ion exchange studies (e.g. determination of kA/B as a function CA, Figure 1), the exchanger is initially in a homoionic form (e.g. the B form) and the solution initially contains only the ion A. Considering the simple uni-univalent exchange as an example, the ratio of ion concentrations at equilibrium is given by:

where ยง is the film thickness, Q the ion exchange capacity, D the film diffusion coefficient and C is the ion concentration. For particle diffusion (eqn [16]), the rate of exchange increases (i1/2 decreases) as the particle radius decreases, being proportional to 1/r0. For film diffusion (eqn [17]), the rate increases less strongly as r0 is decreased (the proportionality is to 1/r0). In film diffusion the exchange rate can also be increased by increasing the efficiency of agitation, which will decrease the film thickness. In real applications of ion exchange the exchange rates do not usually follow the simple relationships of eqns [16] and [17] and the equations are presented here just to give a simple view of the factors that can affect the ion exchange rates.

The values of film diffusion coefficients are of the same order of magnitude as the diffusion coefficients of ions in the external salt solution (D + 10~5cm2s~1). The values of particle diffusion coefficients depend strongly on the charge of the ion and on the structure and porosity of the exchanger matrix. In sulfonated polystyrene resins D decreases with increasing degree of cross-linking, being in the range of10~5-10~7 cm2 s"1 for univalent cations. For multivalent cations, the values are much lower, falling in the range of 107-10 10 cm2 s \ In weakly acidic resins and in crystalline inorganic

In general, to achieve a high conversion to the A form in a single batch equilibration, the selectivity coefficient kA/B and the ratio CA/BB must be high. In practice, the degree of conversion to the A form is controlled by adjusting the initial concentration of A (CA0) in the solution and the solution to solid ratio (V/m), often also called the batch factor (BF):

At constant CA0, the degree of conversion increases as V/m is increased (Figure 4). It is usually difficult to obtain a high conversion in a single batch equilibration, since the selectivity often decreases with increasing conversion and there is always ion B in the solution released from the exchanger. Removing B from the solution can enhance conversion. This can be achieved by equilibrating the ion exchanger successively with fresh portions of solution A.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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