Preparation Of Humic Acid Based On Rice Straw In Northeast China And Its Application In Environmental Remediation

Humic acid（HA）,a macromolecular organic matter widely present in nature,is mainly produced by microorganisms decomposing the remains of plants and animals.Humic acid contains a large number of active functional groups and a variety of physical and chemical properties,and is widely used in agriculture,pharmaceuticals,cosmetics,environmental protection and other fields.At present,most commercial humic acid（CHA）on the market comes from non-renewable resources such as peat,lignite,and weathered coal,and the cost is high.Therefore,an attempt can be made to prepare biomass humic acid（BHA）from renewable biomass resources.Northeast China,as an important rice planting area in our country,has a large amount of rice straw output every year.In order to avoid resource waste and environmental pollution and realize high-value utilization of rice straw,the rich rice straw resources in Northeast China were used as waste biomass raw materials to extract and prepare rice straw-based biomass humic acid（BHA）.Based on the rich functional groups and various physical and chemical properties of BHA,various environmental remediation applications can be realized by preparing and synthesizing different composite materials.The BHA was extracted from northeast rice straw by hydrothermal reaction,and the optimal preparation process was explored.The BHA-loaded magnetic nanoparticles（MNPS）were used to improve the adsorption efficiency of the adsorbent for heavy metals in water.The composite remediation material was prepared by BHA and bentonite to fix heavy metals in contaminated soil.The research is as follows:（1）The biomass humic acid（BHA）was extracted and prepared from rice straw in northeast China by using hydrothermal reaction to simulate the process of soil humification.The preparation process and synthesis mechanism were explored by single factor experiment and orthogonal experiment.The BHA was characterized and analyzed by infrared spectrum,scanning electron microscope and ultraviolet spectrum,and compared with commercial humic acid.The results showed that the hydrothermal method could successfully extract BHA from rice straw.The maximum BHA yield of 10.24%could be obtained under the hydrothermal reaction conditions of 2%alkali concentration,2 hours hydrothermal time,1:9 solid-liquid ratio and 200℃hydrothermal temperature.The N/C and O/C ratios of BHA are higher than those of CHA,indicating that the maturity of humization of BHA is higher,and BHA also contains more oxygen-containing functional groups and stronger electron transfer ability.（2）By using the complexation effect of BHA on metal,the magnetic nanoparticle MNP was modified by the improved co-precipitation method,and a new magnetic composite material BHA@MNP was prepared.The characterization analysis of BHA@MNP was carried out by infrared spectrum,scanning electron microscope,transmission electron microscope,XRD and VSM.The adsorption performance was investigated by heavy metal adsorption experiments in water.The results show that BHA is well loaded on MNP to form a coating structure.BHA adds rich functional groups to the surface of MNP,reduces the aggregation and oxidation of MNP,and improves the adsorption performance of MNP.The adsorption and removal of Cd²⁺,Pb²⁺and Ni²⁺by BHA@MNP were very efficient,and the theoretical maximum adsorption capacity was 290.81 mg·g^-1,374.99 mg·g^-1 and 296.85 mg·g^-1,respectively.The removal efficiency of heavy metals was significantly better than that of bare MNP.BHA@MNP has strong magnetic properties,which can be quickly and easily separated and recycled from wastewater,and can be recycled and reused for multiple cycles at the same time.The adsorption of Cd²⁺,Pb²⁺and Ni²⁺ions in the complex environment of simulated wastewater also showed better removal efficiency.（3）Based on the interlayer structure and ion exchange ability of bentonite,BHA was introduced into the surface and interlayer of bentonite to compound modify bentonite,enrich the functional groups of bentonite surface,improve the ability of bentonite to fix heavy metals in the soil,and the biomass humic acid-bentonite composite repair agent（BHA@B）was prepared.For remediation of cadmium,lead,and nickel contaminated soils.BHA@B was characterized by infrared spectrum,SEM,and XRD.Through the remediation experiment of heavy metal contaminated soil,the fixing effect of BHA@B on heavy metals in soil was evaluated by BCR continuous extraction method.The results show that BHA is successfully combined with bentonite,and deformation and peeling occur on the bentonite surface,resulting in a large number of pores,but the addition of BHA does not affect the crystal structure of bentonite itself.Based on the experimental data of single-element heavy metal contaminated soil remediation,the results showed that the BHA@B treatment reduced the weak acid extracted state and reducible state of cadmium,lead,and nickel by 22.5%and 8.1%,17%and 11.4%,and 19.8%and 14%,respectively,compared with the blank treatment.Compared with unmodified bentonite,the BHA@B treatment also showed excellent soil remediation ability in the experiment of multiple heavy metal contaminated soil in the simulated environment.