Mobilization of five different synthetic phosphate compounds by organic acids and its activation pathway

Effects of high-molecular-weight, humic acid and low-molecular-weight organic acid, citric acid, with different concentrations on phosphorus release from synthesized phosphates and its activation pathway was studied using lab-synthesis method and chemical extraction. The results show that both organic acids, humic acid and citric acid, improved phosphorus release from different synthesized phosphate compounds, and the activation intensified with the increasing of organic acid concentration. The ability of citric acid in mobilizing phosphorus from synthetic phosphate is stronger than that of humic acid. Humic acid could activate all three Ca phosphates, but had slight effect on Fe-P and Al-P. Citric acid increased the phosphorus releasing of Ca2-P, Ca8-P and Al-P through the combined action of proton and citric anion. Almost all the phosphorus mobilized from Ca10-P by citric acid was attributed to the proton effect, while under the low organic acid concentration, the phosphorus mobilized from Fe-P was caused by citric anion effect.