Preparation Of La/CTS/FA Composite Adsorbent And Its Adsorptive Characteristics For Acid Dyes

The full utilization of solid waste fly ash(FA)and abundant rare earth resource in Inner Mongolia Region,in this paper,La/CTS/FA adsorbent was prepared by loading a small amount of chitosan(CTS)and La(?)ion onto fly ash using the simple solution reaction method.The Various preparation conditions including the ratio of raw materials,stirring time and temperature and so on were optimized.The composite adsorbent was characterized by XRD,SEM,EDS,FT-IR and the specific surface area and pore size analysis.The La/CTS/FA adsorbent was used to remove acid lake blue A and weak acid dark blue 5R from aqueous solution,and the effects of various factors on adsorption were investigated.The adsorption kinetics and thermodynamics and the recycling of composite adsorbent were discussed.The detailed results are as follows:(1)A new adsorbent,La/CTS/FA adsorbent prepared by loading chitosan and La(?)ion onto fly ash was used to remove acid lake blue A and weak acid dark blue 5R.Optimized preparation conditions are as follows:La/CTS/FA adsorbent(using for adsorption of acid lake blue A)is obtained by2% of chitosan solution and fly ash(according to a certain mass ratio m(CTS):m(FA)=1:7.5)stirring for 1h at 60?(water bath conditions),and adding a certain amount of La(NO3)3 solution(according to the m(La):m(CTS):m(FA)=1:1:7.5)stirring for 1h,and the La/CTS/FA composite is obtained;La/CTS/FA adsorbent(using for adsorption of weak acid dark blue 5R)is obtained by 2% of chitosan solution and fly ash(according to a certain mass ratio m(CTS):m(FA)=1:7.5)stirring for 1h at room temperature,and adding a certain amount of La(NO3)3 solution(according to the m(La):m(CTS):m(FA)=1:1:7.5)stirring for 30 min,and the La/CTS/FA composite is obtained.The composite adsorbent was used to remove two kinds of acid dyes.The results show that obtaining La/CTS/FA adsorbent is much higher adsorption performance than FA,and the adsorbent with the best adsorption performance is used to remove acid dye.(2)The FA and composite adsorbent were characterized by SEM,EDS,XRD and the specific surface area and pore size analysis.The results show that CTS and La(?)have been successfully loaded on FA;And the specific surface area and pore size of La/CTS/FA composite is less than that of FA;Respectively La/CTS/FA adsorption process of acid dyes may be mainly completed through physical adsorption,hydrogen bonding or chemisorption.(3)The adsorption properties and influencing factors of La/CTS/FA composite adsorbent for the acid lake blue A and weak acid dark blue 5R were investigated.The results show that amount of adsorbent,oscillation frequency,solution pH,contact time and adsorption temperature are the main factors affecting the adsorption.The adsorbent dosage is 0.1g,the pH value of acid lake blue A dyes solution and weak acid dark blue 5R are 2.0 and natural acidity,shaking for 1h with oscillation frequency of 160 r/min.The best adsorption temperature of acid lake blue A and weak acid dark blue 5R on La/CTS/FA composite adsorbent is 25? with corresponding equilibrium adsorption capacity of 467.40 mg/g and 1202.50 mg/g?(4)Studies of adsorption kinetics show that the La/CTS/FA adsorbent has faster adsorption rate for two kinds of acid dyes from the aqueous solutions and adsorption can reach the basic equilibrium at 60 min.The adsorption process of La/CTS/FA for two kinds of acid dyes acid lake blue A and weak acid dark blue 5R at different temperatures(25?,40?and55?)can be well described by pseudo-second-order kinetic equation(R2>0.9995),the second-order kinetics rate constant k2 decreases with increasing temperature,indicating that the adsorption process of La/CTS/FA for two kinds of acid dyes was spontaneous exothermic process.The values of adsorption activation energy Ea of La/CTS/FA for the acid lake blue A and weak acid dark blue 5R are 9.7kJ/mol and 5.43 kJ/mol?(5)The isothermal adsorption studies show that the experimental isotherm data of La/CTS/FA for acid dyes acid lake blue A and weak acid dark blue 5R fit Langmuir adsorption isotherm model(R2>0.9934)at different temperatures(25?,40? and 55?),and the obtained maximum adsorption capacities of two kinds of acid dyes at room temperatures are 526.32mg/g and1250mg/g,respectively.The value of Langmuir adsorption coefficient b decreases with increasing temperature for two kinds of acid dyes,further indicting that the adsorption is of exothermic nature;The separation factor RL calculated by langmuir equation are in the range of 0.00039 to 0.0022,illustrating that the adsorption of two acid dyes on La/CTS/FA is very easy to occur.(6)Adsorption thermodynamics results show that thermodynamic parameters of acid dyes acid lake blue A obtained through the experiment and calculation at different temperatures(25?,40? and 55?)the thermodynamics free energy change ?G is in the range of-32.91~-35.64kJ/mol,enthalpy change ?H is-5.76kJ/mol,entropy change?S is 0.0911J/mol/K;thermodynamics parameters of weak acid dark blue 5R obtained ?G is in the range of-29.91~-30.6k J/mol,?H is-23.15kJ/mol,?S is 0.0227J/mol/K,indicating that the adsorption process of acid lake blue A and weak acid dark blue 5R on La/CTS/FA are spontaneous endothermic process and the adsorption process is controlled by physical adsorption.(7)The results of recycling performance show that the La/CTS/FA adsorbent saturated by acid lake blue A can be regenerated using HCl solutions of 0.01 mol/L though shaking 4h at 25? and the best regeneration rate can be achieved with the first regeneration rate of 100%.Acid lake blue A-saturated La/CTS/FA can be regenerated more than 4 times.