Adsorption Of Congo Red From Aqueous Solution By Modified Waste Tea

In this article,Raw tea is chosen as the biosorbent due to its characteristics of porous and high specific surface area and cheap and available.We use physical and chemical methods to modify the waste tea,and then study on the adsorption behavior of Congo red?CR?from aqueous solution by modified waste tea.The first method to modify the waste tea is to put the tea in the muffle furnace with300?for 2 hours after drying and smashing the tea.Then we get heating tea?HT?.researches show that the removal efficiency reached 98.4%when 0.4g/L modified tea?HT?was added to 50mg/L solution with a pH of 4.0 at 35?and the adsorption amount was123mg/g.The adsorption process fit to the Langmuir isothermal model and pseudo-second-order equation,the adsorption process is decided by chemisorption and physisorptions.Thermodynamic parameters suggest that the adsorption is spontaneous and endothermic in nature.The second method to modify the waste tea is to pyrolyze the tea at 500?without oxygen and then activate the waste tea with CO₂.Then we get activating tea?AT?.The results showed that the removal efficiency reached 97.5%when 0.3g/L modified tea?AT?was added to 50mg/L solution with a pH of 3.0 at 30?and the adsorption amount was162.5mg/g.The adsorption process fit to the Freundlich isothermal model and pseudo-first-order equation,the adsorption process is decided by chemisorption,we work out the average free energy is 1.1 kJ/mol from the D-R isothermal model.By studying the intraparticle diffusion,it is proved that the rate of adsorption is controlled by surface diffusion and intraparticle diffusion.Modifying HT and AT using CaCl₂ was also studied in this paper.Then we get CHT and CAT.The characterization analyses of the adsorbent show that they have more oxygen-containing functional group and more microporosity on the surface.The maximum material removal rate is 99.1%when we use CHT to remove CR,and the maximum material removal rate is 99.5%when we use CAT to remove CR.Then we study on removing cationic dye Methylene blue?MB?using the four kinds of adsorbent for comparing with anionic dye CR.The results show that the adsorption effect is ideal and the removal rate is above 96%when we use HT or AT to remove MB,and the adsorption effect is not ideal using CHT or CAT to remove MB.Finally,It can be said that the modified waste tea would be as effective and low-cost adsorbents for remove of Congo red from the printing and dyeing wastewater instead of active carbon.