Freundlich Equation

The most common shape of the graph of amount adsorbed per unit weight of adsorbent versus the concentration in the fluid in equilibrium is:

Typical Adsorption Isotherm

This graph very closely resembles that for microbial specific growth rate coefficient versus substrate concentration. These data often fit nicely the empirical equation proposed by Freundlich:

                                        q = Kf  Cn

where: Kf and n are coefficients

 q = weight adsorbed per unit wt of adsorbent

 C = concentration in fluid

 Taking logs and rearranging:

                      log q = log Kf + n log C

The coefficients Kf and n can be estimated from slopes and by substituting values from a line fitted to a graph of log q versus log C. With a personal computer handy, the method of least squares can be used to get a statistical fit, however outlying data points are not as obvious as with a graph.
Step-by-step example of finding Freundlich coefficients.

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