Research On Preparation And Adsorption/desorption Properties Of Pb²⁺ By Carboxymethyl Salix Psammophila Powder Supported Nanoscale Zero-valent Iron

In recent years,as a new adsorbent,nanoscale zero-valent iron?NZVI?has received more and more attention in wastewater treatment,because of the larger specific surface area,greater reactivity and stronger reducibility and adsorption properties.However,due to its magnetic nature and small particles,NZVI is highly aggregated and chemically unstable.Therefore,in order to solve this shortcoming of NZVI,there are many studies have been made to fix NZVI on some kind of carrier so as to prevent its reunion and improve the use efficiency.In this paper,the carboxymethyl salix psammophila powder?CMS?was prepared by modification of salix psammophila powder?SPP?.And then the CMS as carrier,the carboxymethyl salix psammophila powder supported nanoscale zero-valent iron?NZVI/CMS?was prepared by using liquid phase reduction method.The optimum preparation conditions of CMS and NZVI/CMS were determined.The morphology and structure of SPP,CMS,NZVI,NZVI/CMS were inspected and analyzed by scanning electron microscope?SEM?,infrared spectroscope?FT-IR?,X-ray diffraction?XRD?,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?and Brunner-Emmet-Teller?BET?.On the optimum preparation conditions,the adsorption properties of SPP,CMS,NZVI,NZVI/CMS were investigated by changing the adsorption conditions.Furthermore,the adsorption kinetics,adsorption isotherm models and adsorption thermodynamics of SPP,CMS,NZVI,NZVI/CMS were determined.And the adsorption mechanism of SPP,CMS,NZVI,NZVI/CMS were also discussed.Subsequently,the desorption properties of SPP and CMS were studied by shaker method on the optimum adsorption conditions.The best desorption conditions of SPP and CMS were determined by changing the desorption conditions.The recycling performance of SPP,CMS,NZVI,NZVI/CMS were preliminary explored.The experimental results of this paper were summarized as follows:1.The adsorption/desorption properties of SPP for Pb²⁺The adsorption results showed that,the adsorption capacity of SPP reached a maximum of 30.64 mg/g as the dosage was 0.7 g,the initial concentration was 900 mg/L,the adsorption time was 120 min,the adsorption temperature was 30 oC and the p H was 5.Adsorption processes of SPP was in good agreement with the pseudo-second-order kinetic and Freundlich isotherm model,the adsorption rection was spontaneous,exothermic and decreased randomness.The desorption results showed that,the desorption efficiency of SPP was 85.45% after using desorption agent of 0.05 mol/L HNO3 at 30 oC and being performed on a thermostatted shaker for 60 minutes.The cyclic adsorption/desorption experiments showed that,the desorption efficiency reached 66.58% after for 4 times.2.The adsorption/desorption properties of CMS for Pb²⁺Preparation results showed that,the adsorption capacity of CMS reached 71.55 mg/g under the optimum preparation conditions,with the concentration of sodium hydroxide was 15%,the carboxymethylation reaction time was 2 h and reaction temperature was 60 oC.The characterization results showed,the surface of SPP is soomth and dense,the particle size is large.But the particle size of CMS is smaller than SPP,and its surface becomes loose and porous,and the crystal strcture has been changed,the carboxymethel were introdeced successfully into the CMS.The adsorption results showed that,the adsorption capacity of CMS reached a maximum of 71.55 mg/g as the dosage was 0.5 g,the initial concentration was 900 mg/L,the adsorption time was 120 min,the adsorption temperature was 30 oC and the p H was 4.Adsorption processes of CMS was in good agreement with the pseudo-second-order kinetic and Freundlich isotherm model,the adsorption rection was spontaneous,exothermic and decreased randomness.The desorption results showed that,the desorption efficiency of CMS was 81.83% after using desorption agent of 0.05 mol/L HNO3 at 30 oC and being performed on a thermostatted shaker for 90 minutes.The cyclic adsorption/desorption experiments showed that,the desorption efficiency reached 60.13% after for 4 times.3.The adsorption properties of NZVI for Pb²⁺The adsorption results showed that,the adsorption capacity of NZVI reached a maximum of 390.30 mg/g as the dosage was 0.05 g,the initial concentration of was 600 mg/L,the adsorption time was 120 min,the adsorption temperature was 30 oC and the p H of was 4.5.This adsorption reaction is exothermic andspontaneous,the adsorption processes was in good agreement with the pseudo-second-order kinetic and Langmuir isotherm model.The cyclic adsorption/desorption experiments showed that,the adsorption capacitiy of NZVI decreased from 390.3 mg/g to 98.6 mg/g after for 4 times,it can be seen the reusability of NZVI is poor.4.The adsorption properties of NZVI/CMS for Pb²⁺Preparation results showed that,the adsorption capacity of NZVI/CMS reached a maximum of 535.50 mg/g under the optimum preparation conditions,with the mass ratio of CMS to Fe3+ is 2/1 and BH4-to Fe3+ is 2/1.The characterization results showed,NZVI were aggregated into piles,but NZVI were scattered obviously after loaded on the CMS,the reunion phenomenon has been resolved effectively;The specific surface area of NZVI/CMS is 81.64 m2/g,which is significantly larger than 26.82 m2/g of NZVI,the size of NZVI became smaller after was loaded on CMS,CMS plays a role in dispersing NZVI particles.The adsorption results showed that,the adsorption capacity of NZVI/CMS reached a maximum of 535.50 mg/g as the dosage was 0.01 g,the initial concentration was 400mg/L,the adsorption time was 120 min,the adsorption temperature was 30 oC and the p H was 4.This adsorption reaction is spontaneous and exothermic.The cyclic adsorption/desorption experiments showed that,the adsorption capacitiy of NZVI/CMS reached 469.7 mg/g after for 4times,NZVI/CMS has better reusability than that of NZVI.