Three methods are developed for the calculation of adsorption isotherms in precipitate and adsorbing colloid flotation. The Gouy-Chapman model is used in all three, with corrections for the effective volumes of the ions in the ionic atmosphere and of the floc particles. The theories all predict a weak dependence of adsorption isotherm on temperature and a stronger dependence on ionic strength; increasing either variable decreases the surface adsorption. The effects of film surface potential, floc zeta potential, ion and floc effective volumes, and floc-floc screening are examined.