Abstract: The purpose of this research is to offer basic data for the utilization of brown coal and the production of humic acid slow-release fertilizers. The effects of K⁺ concentration, equilibrium time, ratio of solid to liquid and pH value on adsorption characteristics of the K⁺ humic acid extracted from brown coal and its absorptive regularity were studied by isothermal adsorption methods. Results show that pH value increase of medium was of great advantage of K⁺ adsorption and could improve the velocity of adsorption reaction. Under the condition of pH<4.4, physical adsorption was dominant. However, under the condition of 7.12
+ on humic acid could be well described by Langmuir equation and its kinetics adsorption fitted Elovich equations best. The adsorption capacity of the experimental humic acid treated by nitric was higher than that of the brown coal without treated. Suitable ratio of solid to liquid could increase the unit adsorption, when the ratios were 0.06 and 0.04, the unit adsorptions can reach maximum being 0.079 g/g and 0.094 g/g, respectively.