Study On Preparation Of Thiourea Acetate Starch And Its Removal Performance To Heavy Metal

In this paper,a new natural polymer heavy metal adsorbent containing multiple functional groups,thiourea starch acetate?LNST?,was prepared by using food-grade corn starch as the matrix,followed by crosslinking,etherification,and grafting reactions.Taking 12.5 mg/L Cu???water sample as the treatment target,taking the removal rate and adsorption amount of Cu???as the evaluation index,the preparation of LNST was optimized through single factor,orthogonal and response surface test methods condition.By carrying out the adsorption time,the initial concentration of heavy metal ions in the water sample,the adsorption temperature,the pH value of the water sample,the LNST dosage,the coexistence turbidity effect test and the competitive adsorption test,the adsorption conditions on the LNST adsorption of Cu???,Pb???,The effect of Zn???performance,optimize the adsorption conditions of LNST,and conduct research on adsorption kinetics,adsorption isotherms and adsorption thermodynamics on the experimental results of three factors including adsorption time,initial concentration of heavy metal ions in water sample,and adsorption temperature to explore LNST Adsorption mechanism for Cu???,Pb???,Zn???.The research content and main test results are as follows:?1?The single-factor test shows that:the ratio of chloroacetic acid to anhydrous Na₂CO₃,the ratio of reactants(n _thiourea:n _CHCS),the reaction temperature and the reaction time affect the adsorption performance of LNST,all of which increase first and then decrease.the trend of.?2?Orthogonal test shows that the order of the influence of various factors in the preparation conditions of LNST is n _CHCS:n _thiourea:n _{chloroacetic acid}>reaction temperature>n _{chloroacetic acid}:n _{anhydrous Na2CO3}>reaction time,and there are influence factors among them certain interaction.?3?The response surface test showed that the amount ratio of thiourea to CHCS had the most significant effect on the removal of Cu???by LNST?P=0.0002<0.05?,followed by the amount of anhydrous Na₂CO₃ and chloroacetic acid.The effect of reaction temperature is not significant.The interaction between the quantity ratio of anhydrous Na₂CO₃ and chloroacetic acid and the reaction temperature is significant,and the interaction with other factors is not significant.?4?By comparing and analyzing the above test results,the best preparation conditions for LNST are determined:n CHCS:n thiourea:n chloroacetic acid=1:3.1:3.1,n anhydrous Na2CO3:n chloroacetic _acid=1:2.55,reaction Temperature T=80.73?,reaction time t=2 h.The removal rate of Cu???of LNST prepared under this condition is as high as 99.85%.?5?According to the infrared and scanning electron microscopy characterization analysis of LNST,it can be seen that there are-COOH,-NH-and C=S groups in the structure of LNST,and there are wrinkles and more obvious depressions on the surface,which are agglomerated,indicating successful starch modification.?6?The results of adsorption time test and adsorption kinetics study show that:for the samples with initial concentrations of 20,40,and 50 mg/L containing Cu???,Pb???,and Zn???,increase the adsorption time?10 min-71 h?,which can promote the adsorption of LNST to Cu???,Pb???,Zn???,and reach adsorption equilibrium at 4 h,4 h,and 7 h in sequence,and the adsorption rate order is:Cu???>Pb???>Zn???.The adsorption process of LNST to Cu???and Pb???conforms to the quasi-second-order kinetic model,which is chemisorption;the adsorption process to Zn???conforms to the Elovich and Power function kinetic model,which is the reaction activation energy with larger Complex heterogeneous diffusion process.?7?Adsorption concentration test and adsorption isotherm study show that when the dosage of LNST is 2 g/L,the initial concentration of Cu???,Pb???and Zn???will increase?5-100 mg/L?,To promote the adsorption of heavy metal ions by LNST,the order of saturation adsorption is Pb???>Cu???>Zn???.The adsorption process of Cu???by LNST conforms to the two isotherm models of Freundlich and Tempkin.There is a strong coordination chelation during the adsorption process,which belongs to the preferential adsorption of multi-molecular layer adsorption on uneven surfaces;The adsorption process of LNST adsorbs Zn???and Pb???conforms to the Tempkin isotherm model.There is a strong coordination chelation during the adsorption process,which belongs to uneven surface adsorption.?8?The pH test of the water sample showed that:for the initial concentration of 50 mg/L containing Cu???,Pb???or Zn???water samples.When the pH of the water sample rises,the adsorption of LNST to Cu???and Zn???is promoted;the process of adsorbing Pb???to LNST is first promoted and then inhibited.When pH=5,the maximum value is reached.?9?Adsorption temperature and adsorption thermodynamics research experiments show that:for the initial concentration of 50 mg/L containing Cu???,Pb???or Zn???water samples.At elevated temperature?25?-65??,the adsorption of LNST to Cu???and Pb???is a non-spontaneous exothermic reaction;the adsorption to Zn???is a spontaneous endothermic reaction.?10?The dosage test shows that:for the initial concentration of 200 mg/L of water samples containing Cu???,Pb???or Zn???.Increasing the dosage of LNST?1-7 g/L?can obviously promote the adsorption of Cu???and Zn???,the highest removal rates are 99.82%and 98.53%,respectively;The removal rate of Pb???has little effect,the highest removal rate is 98.37%.?11?Turbidity test results:for water samples containing Cu???,Pb???or Zn???with initial concentration of 50 mg/L.Increase the water sample turbidity?40-300 NTU?,the adsorption process of LNST for single metal is promoted and then suppressed,the optimal adsorption turbidity is 80,80,100 NTU in turn;the adsorption process of LNST for mixed metals is constantly being promoted until the adsorption is saturated,the optimal adsorption turbidity is200 NTU.?12?Competitive adsorption test shows that for the water samples containing Cu???,Pb???or Zn???with two initial concentrations?50,200 mg/L?,with the LNST dosage?1-8 g/L?,the change rate of the adsorption rate of single metal adsorption is:Pb???>Cu???>Zn???,Cu???>Pb???>Zn???,Cu???>Zn???>Pb???;the change of the adsorption rate of mixed metals is:Pb???&Zn???>Cu???,Cu???>Pb???&Zn???.