Study On Preparation Of Zeolite/Bentonite Particle Adsorbent And Its Adsorption Of Heavy Metals

Due to its non-biodegradability and high toxicity,heavy metals have become the focus of environmental governance research.Bentonite and natural zeolite are often used to adsorb heavy metal ions because of their better ion exchange performance.However,the powdery bentonite and zeolite adsorption materials have a fine particle size,and are easy to disperse and powder after encountering water,resulting in difficulty in solid-liquid separation in subsequent processes and difficulty in recycling.At the same time,a large amount of sludge is generated,causing secondary pollution.In this paper,sodium-based bentonite and natural zeolite were used as raw materials.Two methods were used to prepare granular composite materials,which are extrusion-spheronization method and sol-gel method.The former adds modified orange peel powder to the raw materials to improve mechanical strength and enhance adsorption performance;the latter first loads chitosan on the raw materials,and then used the characteristics of cross-linking sodium alginate and calcium chloride to prepare adsorb particles.The prepared shaped particles were used for the adsorption of heavy metal ions Co²⁺and Cd²⁺.With the help of FT-IR,XRD,TGA-DTA,SEM,and BET analysis and detection methods,the prepared samples were characterized and analyzed,and the influence factors of adsorption were analyzed and screened.XPS and adsorption-related models were used to systematically study the adsorption mechanism.The main conclusions are as follows:?1?The preparation process of zeolite/bentonite/MOP?G1 and G2?were:roasting temperature 500°C,roasting time 70 minutes,the ratio of bentonite and zeolite was7:3,and the amount of modified orange peel powder?MOP?when Co²⁺was adsorbed was 45%;the amount of modified orange peel powder?MOP?when Cd²⁺was adsorbed was 40%.The best conditions for G1 adsorption of Co²⁺were:when the initial concentration of the solution was 150 mg·L^-1,pH=4,the dosage of adsorbent was 15g·L^-1 and the adsorption time was 6 hours,the adsorption rate of Co²⁺was 92.59%and the amount was 9.26 mg·g^-1.The best conditions for G2 adsorption of Cd²⁺were:the initial concentration of the solution was 150 mg·L^-1,pH=5,the amount of adsorbent added was 10 g·L^-1,and the adsorption time was 6 hours.The removal rate of Cd²⁺was96.88%.The adsorption capacity was 14.53 mg·g^-1.?2?The zeolite/bentonite/chitosan?G3?preparation conditions were:2%glacial acetic acid concentration,2.5%sodium alginate volume,and 1%CaCl2 mass fraction.The optimal adsorption conditions for G3 to adsorb Co²⁺were:the initial concentration of the solution was 100 mg·L^-1,pH=5,the amount of adsorbent added was 10 g·L^-1,and the adsorption time was 6 hours.The optimal adsorption conditions for G3 to absorb Cd²⁺were roughly the same as those for Co²⁺,with only a different dosage,5g·L^-1.When the adsorption reached equilibrium,the removal rate of Co²⁺was 75.47%;the removal rate of Cd²⁺was 86.57%,and the adsorption amount was 17.596 mg·g^-1.G3 has adsorption selectivity,and its ability to adsorb Cd²⁺is stronger than that of Co²⁺.?3?From the analysis of the parameters of the isothermal model equation,it can be obtained that the ability of the extrusion-spheronization composite microspheres to adsorb heavy metals increases with increasing temperature.The maximum adsorption capacity for heavy metals was at 318 K,and the maximum adsorption capacities for Co???and Cd???were 18.88 mg·g^-1 and 28.68 mg·g^-1,respectively.The adsorption capacity of gel-sol composite microspheres decreased with increasing temperature,the maximum adsorption capacity for heavy metals was 298 K,and the maximum adsorption capacities for Co???and Cd???were 25.38 mg·g^-1 and 74.68 mg·g^-1,respectively.These datas indicate the selectivity of composite microspheres for metal ions.The composite adsorption materials prepared by different methods have higher Cd²⁺adsorption than Co²⁺.?4?The adsorption processes of Co²⁺and Cd²⁺by the two composite adsorption materials were in good agreement with the pseudo-second-order kinetic model.In the adsorption isotherm model,the process of extrusion-spheronization composite microspheres adsorbing heavy metals had a high degree of fit with the Langmuir isothermal model,and the process of gel sol composite microspheres adsorbing heavy metals had a high degree of fit with Freundlich model.Through XPS analysis of composite particles and before and after adsorption,combined with kinetic and thermodynamic experimental results,it was found that the adsorption of heavy metal ions in solution by shaped adsorbent is not a single adsorption method,but through several single or mixed interaction what happens includes complexation,coordination,electrostatic attraction and ion exchange.