Adsorption and desorption properties of three types of agricultural humic acids for K

The experiment studied: The saturated adsorption and desorption of the 3 types(A,B,C) of agricultural humic acids for K+,and the effects of pH on the adsorption and desorption.Results showed that: Compared with A and B,potassium-saturated humic acid C exhibited stronger adsorption and desorption activities of its cation exchange capacity(CEC) 375.74 cmol/kg,the maximum desorption 71.00 mg/g.Besides,in the first 60 min of desorption reaction the capacity of desorption was very close to the maximum;the properties of humic acid A,B were similar in their K+ adsorption capacity.The adsorption saturation was reached in the first 60 min for humic acid A,and the adsorption quantity per unit was 10.2 mg/g.The adsorption saturation was reached in the first 20 min for humic acid B,and the adsorption quantity per unit was 7.72 mg/g.However,the adsorptive rate of K+ for humic acid B was faster than A,and B could reach saturated adsorption in a shorter period of time.All of the 3 types of humic acid had a strong buffering capacity to adapt to the changes in the medium pH.With the rise of pH value,the adsorptive quantity for K+ of humic acid A and B decreased within the effective buffering range,but the desorption of K+ for humic acid C appeared to reach a plateau after an ascent in pH range of 3-5.