Utilization of waste lignin to prepare controlled-slow release urea

Purpose The present work reports an economicallyattractive improvement in the area of producing particulateslow release nitrogen fertilizer using lignin as a wasteeffluent of pulp and paper manufacturing process.Methods An improved coating of modified lignin wasapplied on the surfaces of the individual urea particles. TheKraft and Sulfite black liquors obtained from two differentpaper pulping units and were used as sources of sulfate andsulfite lignin, respectively. Chemical modification ofextracted lignin was performed through acetylation reactionby acetic acid/sodium metabisulfite to increase itshydrophobicity character. In a separate experiment, a thinlayer of synthesized acetylated lignin was coated ongranular urea by fluidized-bed technique. The nitrogenrelease of synthesized fertilizer in the water and soil wasexamined by the Kjeldahl method.Results The analysis of FTIR spectra indicated the changesin the functional groups of acetylated lignin. Petrographicphotography and scanning electron microscopy (SEM)analyses demonstrated a uniform and homogeneous coveringof the urea surface. The 7 day nitrogen release rate ofurea coated by acetylated lignin in soil was obtained 36.3and 45.3 % for Kraft and Sulfite lignin, respectively,whereas this value was 59 % for sulfur coated urea.Conclusions Using industrial wastewater as source of ligningives satisfactory results for industrial applications andyields a quality green fertilizer product with reducedoperation difficulties while considerably preserving theenvironment.