Preparation And Properties Of Lignin-based Multifunctional Slow/controlled Release Fertilizer

Mineral nutrients are needed for plant growth,but the nutrients in soil can meet only some plant’s needs.Therefore,slow/controlled release fertilizers were developed,which play a very important role in preserving soil fertility,increasing grain yield and improving the quality of agricultural products.Slow/controlled release fertilizer is a kind of fertilizer that can slow or control the release of nutrients in soil and be absorbed by plants for a long time by physical or chemical methods.However,compared with traditional fertilizers,the costs of slow/controlled release fertilizers are relatively high.In addition,most of materials used to prepare slow/controlled release fertilizers are synthetic polymers that are difficult to be degraded.With the release of nutrients,these synthetic polymers remain in soil and lead to soil environmental pollution.To solve the above problems,this thesis focused on the development of biodegradable,low-cost and environmentally friendly multifunctional biomass-based slow/controlled release fertilizers.Using lignin with low price and extensive source as the main raw material,four typse of lignin-based multifunctional slow/controlled release fertilizers with different morphologies and sizes were prepared by coating,crosslinking,electrostatic layer-by-layer self-assembly and adsorption methods.The nutrient contents,slow/controlled release behaviors and degradation of the four types of lignin-based multifunctional slow/release fertilizers were studied and evaluated systematically.The research contents are as follows:1.A lignin-based multifunctional slow release fertilizer was prepared based on urea granules entrapped in the lignin,attapulgite clay and ammonium zinc phosphate,cellulose acetate butyrate and liquid paraffin as inner coating and lignin-g-poly（acrylic acid-co-acrylamide）/attapulgite absorbent as outer coating.The addition of the outer absorbent can effectively improve the physical properties of soil,reduce the evaporation of water,improve water absorption（61.6%）and retention preperties（13.1%）.The nitrogen,phosphorus and zinc in the fertilizer had good sustained release behaviors,and the cumulative release rates were 70%,46.7%and60.1%,respectively.In addition,lignin as natural polymer can not only improve the degradation performance of fertilizer and avoid the secondary pollution of soil,but also adsorb and immobilize lead ions（91.7%）to prevents the accumulation of heavy metal ions in plants.2.A biodegradable fertilizer with high mechanical strength was prepared based on aminated lignin and sodium alginate by Schiff base reaction and crosslinking of iron ions,and reaction conditions were optimized.Compared with the sodium alginate-based fertilizer,the biodegradable fertilizer had higher mechanical strength,which benefits the transportation and storage of fertilizers.The addition of lignin and sodium alginate as biomass-based raw materials can reduce the production cost of fertilizer,alleviate the pollution of soil environment and improve the degradation performance of fertilizer.After 30 days,the degradation rate of the biodegradable fertilizer reached up to 55.6%.In addition,the biodegradable fertilizer had a good continuous release property due to the Schiff base bonds and crosslinking of iron ions.3.An environment-friendly and pH responsive fertilizer prepared by layer-by-layer self-assembly using chitosan and sodium lignosulfonate as polyelectrolytes on the surface of polydopamine-coated ammonium zinc phosphate,and the process and mechanism of layer-by-layer self-assembly were studied.The fertilizer had a good pH responsive release properties,and the release rates of nitrogen,phosphorus and zinc in fertilizer were different under acid or alkaline conditions.Pot experiments showed that the fertilizer can improve the nutrients utilization and promote the growth and development of maize.4.A lignin-based magnetic nanoparticle was prepared using aminated lignin by chelation of iron ions and loaded with Fe₃O₄ nanoparticles,and the structure and adsorption properties were characterized.The results showed that lignin-based magnetic nanoparticle had higher adsorption capacity and removal rate for H₂PO₄^-in wastewater,and the adsorption rate was faster and reached the adsorption equilibrium within 15 min.The adsorption kinetics of H₂PO₄^-onto nanoparticle was well described by pseudo-second-order model,and the adsorption isotherms of H₂PO₄^-onto nanoparticle was well described by Temkin model.After recovery and separation of H₂PO₄^-,and the lignin-based magnetic nanofertilizer was obtained.The release rates of iron and phosphorus reached 67.2%and 69.1%after 30 day,respectively.In addition,the lignin-based magnetic nanofertilizer showed excellent recyclability and reusability,and the adsorption capacity and removal rate remain above 83%and 62%respectively after 6 cycles,which can not only reduce the production cost of fertilizer,but also prevent the secondary pollution and improve the utilization efficiency of nutrients.