Studies On Synthesis Of Layered Double Hydroxide Using Steel Slag As Material And Application In Printing And Dyeing Wastewater Treatment

Layered double hydroxide(LDHs), belonging to hydrotalcite compounds, has been widely applied in adsorption, catalysis, medicine, photoelectric materials and functional polymer materials for its special acid-base double function, memory effect, interlayer anionic exchangeability and thermal stability.In this paper, Ca-Mg-Al-Fe quaternary LDHs was successfully synthesized using steel slag as raw material via coprecipitation, and the influences of p H, crystallization temperature and crystallization time on the synthesis process were investigated. Then the samples were characterized by XRD, XRF, SEM, FT-IR, TEM, DTA/TG and BET. The results showed that p H is the dominant factor for the synthesis of LDHs, and pure LDHs could be synthesized when p H value was controlled in the range of 10.5-11.8 during coprecipitation process. Crystallization temperature and time are important factors influencing the crystal cell parameters and layer spacing. As the crystallization temperature and time increased, lattice parameters a, c and the spacing of layer first reduce and then increase. Crystal grain size of LDHs along the axis of a is larger than that along the axis of c. After optimization, when LDHs was synthesized at the conditions of p H of11.8, crystallization temperature of 150 o C and crystallization time of 16 h, it presents well-defined structure and crystal shape, clear layered structure, large aperture and well thermal stability.The Ca-Mg-Al-Fe quaternary LDHs was applied for absorption materials in simulated wastewater containing cationic red or acid orange. The influence of adsorbent concentration, initial p H, adsorption temperature, adsorption time and initial concentration were discussed and the data were fitted in adsorption thermodynamics models and kinetic models. The results of cationic red simulated wastewater adsorption showed that removal rate has no significant change with adsorbent concentration. The adsorption effect has no significant change when p H = 3-10. With the temperature increased, the adsorbance increases. When C0 =500 ppm, the adsorbance is 425.69 mg·g-1, indicading that the LDHs has excellent treatment effect for cationic red dye wastewater. The adsorption of cationicred can be best described by langmuir thermodynamic model and pseudo-second-order kinetics model.The result of acid orange simulated wastewater adsorption showed that the removal rate increases with the increasement of adsorbent concentration. The adsorption effect has no significant change when p H = 4-10. As the temperature increased, adsorbance increases.When the temperature is 343.15 K, the adsorbance is 212.08 mg·g-1, indicading that LDHs has well treatment effect for acid orange dye wastewater. With the increasement of initial concentration, the adsorbance increases at first and then stabilizes. The adsorption of acid orange can be best described by langmuir thermodynamic model and pseudo-second-order kinetic model. Ca-Mg-Al-Fe quaternary LDHs synthesized by coprecipitation using steel slag as raw material has well adsorption effect for both cationic dye waste water and anionic dye wastewater, means that it has a well potential application value.