Synthesis Of Lignin-based Slow-release Nitrogen And Phosphorus Fertilizer And Its Fertilization Efficiency Research

To cope with the global phosphorus crisis and address the eutrophication of water bodies,the recovery of phosphate from wastewater as a slow-release fertilizer to improve the slow-release performance of fertilizers is considered an effective way.In this study,amine-modified lignin(AL)was prepared using industrial alkaline lignin(L)for phosphate recovery from water bodies,and then the recovered phosphorus-rich aminated lignin(AL-P)was used as a slow-release N and P fertilizer,and the release pattern of N and P nutrients from AL-P was explored by water solubility and soil column drenching tests,and the response of alfalfa and soil to AL-P application was investigated by potting tests.The main findings were as follows.(1)Aminated lignin-based aqueous phosphate adsorbent materials were prepared from industrial alkali lignin by hydrothermal carbonization and amination modification.Scanning electron microscopy(SEM)and thermogravimetric analysis(TGA)showed that the AL-P material had a smooth surface and stable structure.Fourier transform infrared absorption spectroscopy(FTIR)showed that the aminated lignin successfully introduced nitrogen-containing groups.X-ray photoelectron spectroscopy(XPS)showed that the nitrogen-containing groups in aminated lignin(AL)promoted the adsorption of phosphate in water.Intermittent adsorption experiments showed that the adsorption process was consistent with quasi-secondary kinetics and the Langmuir model,with a maximum adsorption capacity of 46.28 mg P/g at 298 K and p H = 6.Ion competition and actual aqueous adsorption experiments showed that AL had good adsorption selectivity and removal capacity for phosphate in the water column.The adsorption mechanisms included electrostatic adsorption,ionic ligand exchange and cross-linked addition reaction.(2)The recovered phosphoramide-rich lignin(AL-P)had N and P contents of 9.99%and 3.89%,respectively,and a carbon to nitrogen ratio of 4.42,with low C/N favoring the mineralized release of AL-P nutrients.In the hydrostatic dissolution test,N and P of AL-P were able to be released slowly,which met the requirements of slow-release fertilizer.The release of N conformed to zero-level kinetics with constant nutrient release rate,and the release of phosphorus followed the Fickian diffusion mechanism.Soil column leaching tests showed that the release of N and P from AL-P in soil followed the Fickian diffusion mechanism.(3)The biomass,NP content,NP accumulation and P utilization of potted alfalfa were better than other treatments under the conditions of 1:2 application of calcium superphosphate fertilizer with AL-P.AL-P was effective in promoting the growth of potted alfalfa under the conditions of application with fast-acting chemical fertilizers,which was beneficial to the crop.The application of AL-P promoted the increase of soil cation exchange,soil organic matter,soil total nitrogen,soil total phosphorus and soil fast-acting phosphorus content,and did not cause changes in soil acidity and alkalinity while improving the fertility retention capacity of the soil.Therefore,amine-modified lignin-recycled spent aqueous phosphate as a slow-release fertilizer has great potential to improve the environment of water bodies,solve the global phosphorus crisis,improve nutrient utilization,promote plant growth and enhance soil fertility.