Influence of purification and storage conditions on the flocculation of modified larch tannin

A typical plant polyphenol,larch tannin,was chosen to study the influence of purification and storage on the flocculation when it was modified as flocculant.The variability of stability was analyzed by the relative viscosity and Fourier transform infrared spectrometer(FT-IR).The results showed that the optimum dosage of modified tannin without purification was 10 mg · L-1 to 1 g · L-1 Kaolin suspension,whereas it achieved 1 mg · L-1 when it was purified by filtration,extraction and centrifugation.After such purification step,the modified tannin could be stored for 30 days at 4 ℃ or 25 ℃ in either solid or liquid forms,and the flocculation ability was not affected.If tannin was purified only by filtration and centrifugation,the flocculation ability was affected obviously,unless stored at 4 ℃.However,if tannin was purified only by filtration and extraction,or only by filtration,the modified tannin lost its flocculation ability unless stored at 4 ℃ and in solid form.Additionally,if modified tannins were stored at 4 ℃ in solid form,there was little variation of their relative viscosities.The smaller the relative viscosity change,the better the stability of flocculation ability.FT-IR showed that the larch tannin contained a large number of phenolic hydroxyl groups,and the tertiary amine groups were added to the aromatic ring after modification.But there was little difference between the modified tannin before and after preservation.