Modified alkali lignin chelated zinc fertilizer and preparation method thereof

The invention discloses a modified alkali lignin chelated zinc fertilizer and a preparation method thereof. The preparation method comprises the following steps: adding alkali lignin powder into water, regulating the pH value, and dissolving to obtain a 30-40 wt% water solution; adding amino acid, dropwisely adding epoxy chloropropane, heating to 75-95 DEG C, and reacting for 2-3 hours; regulating the pH value to 10-12, dropwisely adding bromoacetic acid, and reacting at 70-90 DEG C for 1-2 hours; and finally, regulating the pH value of the system to 5-7 with a dilute hydrochloric acid solution, adding zinc sulfate, and carrying out chelation reaction at 50-70 DEG C for 0.5-2 hours, thereby obtaining the modified alkali lignin chelated zinc fertilizer after the reaction finishes. The chelated microelement fertilizer molecules have abundant hydroxy and carboxyl groups, and the N atom has lone electron pairs which can form composite coordination with metallic ions; and thus, the fertilizer has high chelation capacity, and the maximum complexation quantity for zinc ions is approximate to the level of EDTA (ethylene diamine tetraacetic acid); and the pot incubation test indicates that the fertilizer has an obvious yield increase action on crops.