Humic acid sodium was used as an inhibitor to the secondary reaction in the process of clinker extraction.When the addition of humic acid sodium to clinker was up to about 0.43%

the extraction efficiency of alumina and caustic from clinker will be increased by 3.87% and 4.51%

respectively.Its inhibition mechanism was studied by the determination of infrared（NIR）spectra and the concentrations of SiO2 and Ca2+ in the extracted solution.The results showed that the big molecules of humic acid sodium enwrapped dicalcium silicate surface

which prevented dicalcium silicate from contacting with the solution.At the same time，the anions dissociating from humic acid sodium could combine with Ca2+，which resulted in the concentration reduction of Ca2+ in the solution.Therefore

it was inhibited to form hydrated aluminosilicate silicate which caused the loss of sodium aluminate.