Preparation And Characterization Of Citric Acid Chelated Zinc,Copper And Manganese Compounds

Trace elements are indispensable in the process of plant growth.Inorganic salt trace elements are vulnerable to the antagonistic effect of p H value,phosphate and other factors,which will reduce their effectiveness,while chelated trace elements are not affected by this.At present,the commonly used chelated trace elements mainly include amino acids and EDTA,but they still have some shortcomings,such as high price and environmental problems,so they are not suitable for promotion in the field of fertilizer.Citric acid is a cheap and environment-friendly organic acid,which can be used as chelating agent and trace element chelating agent.Therefore,citric acid was chosen to chelate with trace elements to prepare citric acid chelated trace elements.Zinc citrate chelate was prepared from citric acid and zinc nitrate,and the product was separated and purified with anhydrous ethanol.Through single factor and orthogonal experiments,the optimum preparation conditions were as follows:zinc nitrate 0.1 mol/L,p H 6,reaction temperature 60℃,reaction time 1.5 h,molar ratio of citric acid and zinc nitrate 1:1,the chelation rate could reach more than 96%.The purified product was characterized by infrared spectrum,X-ray powder diffraction,element analysis and thermogravimetric analysis.The results showed that the chelated zinc citrate was formed by the reaction of citric acid and zinc nitrate,and its chemical formula was Zn C₆H₁₁O₈N.The solubility of chelated zinc citrate was 2.54 g/（100 g water）at 20℃.The stability constant of zinc citrate chelate was determined by the method of equimolar continuous change,and its stability constant lg K=5.21.Copper citrate chelate was prepared with citric acid and copper nitrate as raw materials.The results of single factor experiments showed that the optimum conditions were 0.1 mol/L copper nitrate,p H 6,reaction temperature 60℃,reaction time 60 min,molar ratio of citric acid to copper nitrate 1,and the chelation rate could reach 94%.The infrared spectrum and X-ray diffraction of the purified copper citrate chelate show that there is a chelating reaction between citric acid and copper nitrate,and the chemical formula is Cu C₆H₁₁O₈N.The solubility of copper citrate chelate at 20℃is 28.77 g/（100g water）,and its stability constant lg K is 3.71.Manganese citrate chelate was prepared with citric acid and manganese nitrate as raw materials.The single factor experiment showed that the chelation rate of manganese could reach 98%when manganese nitrate was 0.1 mol/L,p H was 5,reaction temperature was 60℃,reaction time was 30 min,molar ratio of citric acid and manganese nitrate was1.The chelation reaction was proved by infrared spectrum and X-ray diffraction.The chemical formula was Mn C₆H₁₁O₈N.The solubility of chelated manganese citrate at 20℃is 1.1 g/（100 g water）,and its stability constant lg K is 5.73.Different concentrations of citric acid chelate microelement seed soaking solution and nitrate seed soaking solution were prepared to soak wheat seeds.The results showed that the germination potential,germination rate,root length,bud length,pod and cat activities of wheat seeds soaked with seed soaking solution were improved compared with those of water control group,The results showed that the increasing range of each index of wheat soaked with citric acid chelate microelement seed soaking solution was greater than that of nitrate seed soaking solution.