What is the difference between dispersion and diffusion? Currently I believe, that diffusion is the mixture of molecules due to Brownian motion. So I read everywhere, that it happens with magnitude of the concentration gradient, and from higher concentration to lower concentration, cf. Fick's law.
It also seems that diffusion and dispersion happens always together, and that dispersion has something to do with the concentration gradient, and that the molecule transport by dispersion is of magnitudes bigger compared to diffusion.
What I am asking is, what exactly is dispersion with regard to molecule transport?