Adsorption Effect And Mechanism Of Cr³⁺ On Modified 5A Zeolite In Water

In recent years,with the acceleration of economic development and industrialization,industrial wastewater containing heavy metal ions has been discharged continuously,and heavy metal ions pose a serious threat to human health.In this paper,waste water containing Cr³⁺heavy metals was studied.Na OH base modification,Fe³⁺modification and Na OH-Fe³⁺composite modification were used to modify5A zeolite for treating this kind of waste water.The adsorption and removal effect of molecular sieve on trivalent chromium ions in water was investigated.The results are as follows:1.When the wastewater contains Cr³⁺30mg/L concentration,additive amount of molecular sieves is 0.9 g/L,the calculation of the unmodified of Cr³⁺5A molecular sieve adsorption capacity of 20.88 mg/g,alkali modified molecular sieve adsorption capacity of Cr³⁺Na OH was 25.29mg/g,less modified molecular sieve adsorption capacity increased21.12%,Fe³⁺modified molecular sieve of Cr³⁺adsorption capacity of 21.56 mg/g,adsorption capacity increased by 3.25%,The adsorption capacity of Cr³⁺by Na OH-Fe³⁺composite modified zeolite was 31.97mg/g,which increased by 53.11%.2.The adsorption of modified zeolites before and after modification conforms to the Langmuir adsorption isothermal model,indicating that the adsorption process is mainly monolayer adsorption at a certain temperature.The adsorption rate conforms to Lagergren quasi-second order rate equation,indicating that the adsorption process of Cr³⁺by zeolite is diffusion process.3.XRD test shows that the characteristic diffraction peak of modified zeolite has not changed significantly compared with that of unmodified zeolite,indicating that the modification has not damaged the crystal structure of zeolite.4.NaOH base modification can reduce the Si-Al ratio of molecular sieve and increase the compensation cation,so as to improve the adsorption capacity of Cr³⁺.After modified by Fe^3+,the removal of Cr³⁺by zeolite in water not only results in ion exchange,but also results in complexation reaction between Cr³⁺and iron hydroxide on the surface of zeolite.The pore diameter of 5A zeolite will increase to some extent after alkali modification,which is conducive to the formation of more iron hydroxides in the Fe³⁺modification process,thus improving the complexing effect between Cr³⁺and ferric hydroxide,so that the adsorption capacity of Na OH-Fe³⁺composite modified zeolite for Cr³⁺is significantly improved compared with that of unmodified zeolite.