Study On Preparation And Application Of Polypeptide Chelating Fertilizer Based On Leather Wastes

Waste leather shavings are solid wastes produced in the tanning process.The blue leather shavings are regarded as hazardous wastes because they contain heavy metal chromium,which seriously hinders the development of the tanning industry;currently the protein-based organic fertilizer is an urgent need for agriculture.The application of protein-based organic fertilizer is also an important method to solve agricultural soil pollution.The protein contained in the waste shavings can be prepared as a polypeptide chelated fertilizer containing different medium and trace elements,it can not only solve the pollution of the dangerous solid waste of the tanning,but also alleviate the urgent need for organic fertilizer in the current agriculture.This has far-reaching significance for the development of the tanning industry and agriculture.In this paper,three different molecular weight polypeptides were prepared using the hydrolysate of leather shavings by alkali,and the heavy metal chromium in the polypeptide was removed.The polypeptides,CaCl₂,Zn?CH₃COO?₂ and FeCl₂ were used as raw materials to synthesize calcium,zinc,iron organic chelated fertilizer with different structural properties by chelation reaction.The structures and properties of the compound peptide surfactants were analyzed in detail.It mainly includes the following aspects:First,the leather scraps were hydrolyzed by NaOH.The influence factors on the reaction such as NaOH dosage,temperature,time and liquid ratio were explored through the single factor experiment,different molecular weight polypeptide A,polypeptide B and polypeptide C hydrolysate were prepared;and heavy metal chromium was removed from polypeptides by CaO.The structure and properties were analyzed;the number average molecular weight is 2995 Da,1026 Da,680 Da,respectively;the concentrated polypeptide hydrolysate concentration is 0.3175 g/mL,and the chromium content is 38.9 ppm,47.5 ppm,49.5 ppm respectively;hydrolysis degree is 5.59%,15.25%,22.41%;nitrogen content is 14.27%,14.22%,14.23%.With the increase of NaOH,the OH^-concentration in the solution is increased,the hydrolysis reaction rate and the degree of hydrolysis are increased,and the molecular weight is decreased;the degree of hydrolysis is increased with increasing temperature in a certain range;time has less effect on hydrolysis reaction;the degree of hydrolysis is increased with the liquid-solid ratio in a certain range.Second,the effects of pH,polypeptide to metal mass ratio,temperature and time factors on the chelation reaction were investigated,and the optimal conditions for the chelation of three molecular weight polypeptide hydrolysates with three different elements were determined.It was found that with the decrease of molecular weight of peptide,the chelation rate increased gradually.The chelating rate of polypeptide and ions with the molecular weight of 680 Da was the highest.The highest chelation rates of polypeptide with Ca²⁺,Zn²⁺and Fe²⁺were 77.54%,75.22%and 75.77%,respectively.The larger the molecular weight of the polypeptide,the longer the polypeptide chain length,the greater the steric hindrance of the reaction,and the less free amino groups and carboxyl groups present in the solution,making the chelation difficult to increase.The chromium content of the chelate is satisfied with the national standard and can be used as a new type of functional organic fertilizer.Finally,the polypeptide chelated organic fertilizer was applied to rapeseed crops for fertilizer efficiency experiments.It is found that polypeptide chelated calcium organic fertilizer can increase the plant height and leaf width of rapeseed significantly.The polypeptide chelated zinc organic fertilizer can increase the plant weight of rapeseed significantly.The polypeptide chelated iron organic fertilizer can increase the chlorophyll content of rapeseed significantly.The polypeptide chelated fertilizer can promote the growth of rapeseed significantly.The highest increase of rapeseed plant height is 20.16%,and the maximum increase of rapeseed leaf width is 26.64%,and the highest increase of single gross weight is 14.34%when the fertilizer application rate is 97.18 mL/m².There was no significant difference in the effects of polypeptide chelated fertilizer and commercial amino acid chelated organic fertilizer on the growth of rapeseed.Applying hard-to-handle waste shavings to organic fertilizers in agriculture is of great significance for environmental protection and agricultural development.