Preparation Of Metal-loaded Resin And Study On Stability Of Metal Ions During Decomplexation Of Ammonia Ligand

The ion exchange and adsorption method has the advantages of selectivity to ammonia nitrogen,the adsorbent can be regenerated and reused,and the process is simple.However,the salt environment has a great influence on the performance of the ion exchange adsorbent.The ligand exchange adsorption method utilizes the ability of transition metal ions to form complexes.The transition metal is loaded on a certain adsorbent carrier,and then using the special complexation between the target pollutant and the transition metal,the target pollutant is adsorbed on the adsorption,it can selectively adsorb ammonia nitrogen in high-salt wastewater.Ligand exchange adsorption method is used to treat high-salt ammonia-nitrogen wastewater.In the process of ammonia ligand decomplexation,the desorbent may destroy the stability between the carrier and the transition metal,causing the loaded metal to fall off the carrier,not only causing the metal pollution also reduces the separation performance of the adsorbent.Therefore,exploring the stability of the loaded metal and the metal utilization rate is very important for the recycling of high-salinity wastewater.In this study,the carrier resin and the loaded metal were screened,and the resin loaded metal was modified.By changing the existing form of the loaded metal on the resin,the adsorption performance and stability of the ligand exchange adsorbent were improved,so as to solve the problem of the loaded metal falling off in the process of the ligand exchange adsorbent.The main conclusions are as follows:（1）Three metal-loaded resins,Cu-D751,Cu+Ni-D751,and Cu+Zn-D751,were selected by investigating factors such as metal ion type,metal ion concentration,and loading time. When the initial p H of the solution is 11,the dosage of resin is 6 g/L,the initial concentration of ammonia nitrogen is 100 mg/L,and the concentration of NaCl is 4 g/L,the adsorption capacities of ammonia nitrogen treated by the three metal-loaded resins are:5.73mg/g,5.47mg/g,5.39mg/g.Using 1mol/L NaCl solution as the desorbent,Cu-D751 three desorption Cu²⁺shedding amount are:0.09%,0.09%,0.08%;In the three desorption processes of Cu+Ni-D751,the amount of Ni²⁺shedding is greater than 1%;During the first adsorption process of Cu+Zn-D751,Zn²⁺fell off more,up to 0.64%,the amount of Zn²⁺fell off by one desorption was as high as 4.08%,and the amount of Cu²⁺fell off was 0.06%,and the stability was poor.（2）Based on the problem of metal shedding during the desorption process,the above three metal-supported resins were modified to obtain Cu-D751-NaOH,Cu+Ni-D751-NaOH and Cu+Zn-D751-NaOH.When the initial p H of the solution is 11,the resin dosage is 6 g/L,the initial ammonia nitrogen concentration is 100 mg/L,the NaCl concentration is 4 g/L,and the reaction time is 2.5 h.The ammonia nitrogen adsorption capacity of the three modified metal-supported resins are respectively 6.58,10.53,9.04mg/g.Using 1mol/L NaCl solution as desorption agent,three kinds of metal loaded resins were desorbed and regenerated for three times.It was found that the amount of Cu²⁺shedding in Cu-D751-NaOH was always less than that in Cu-D751-NaOH,indicating that NaOH modification could improve the stability of Cu²⁺loading on D751 resin;For Cu+Ni-D751-NaOH,Cu²⁺fall off is always low,but Ni²⁺falls off more during the adsorption and desorption process,and the stability is poor.The possible reason is that the stability coefficient of Ni²⁺and the resin functional group is low;for Cu+Zn-D751-NaOH,NaOH modification can significantly improve the stability of Cu²⁺and Zn²⁺.FT-IR and XPS analysis shows that the metal supported on the modified metal-supported resin is mainly coordinated to adsorb ammonia nitrogen in the form of metal hydroxide.（3）Mechanism studies have shown that OH^-is a key factor to improve the adsorbent’s ammonia nitrogen adsorption performance when the metal loading is high.The modified metal-supported resin can supplement a certain amount of OH^-in the process of ammonia nitrogen treatment,which is conducive to more NH₄⁺convert into NH₃（aq）to improve the coordination and adsorption performance of the resin to ammonia nitrogen;High concentration NaCl is suitable as a desorbent.The material characterization results show that after the metal-supported resin is modified,the supported metal changes from coalescence to dispersion,which is beneficial to the combination of the supported metal and ammonia nitrogen and improves the metal utilization rate.The Freundlich isothermal model can better describe the adsorption balance of the modified metal-supported resin for highly salty ammonia-nitrogen wastewater.The reaction process conforms to the quasi-second-order kinetic model,and the correlation coefficients are all over 0.98,and the calculated equilibrium adsorption capacity q_eof the three resins is the closest to the experimental value.（4）The actual wastewater treatment results show that the adsorption performance of Cu-D751-NaOH、Cu+Ni-D751-NaOH and Cu+Zn-D751-NaOH is better,the primary adsorption capacity reaches 7.53,11.43,11.24 mg/g,respectively,and the adsorption performance of the actual high salt ammonia nitrogen wastewater is relatively stable.