Study On Modification Of Semi-coke And Its Adsorption Properties Of Dye In Waste Water

Dye wastewater seriously pollutes water quality and has been drawing more and more attention on its treatment because of its deep chroma, high concentration and complex composition, high salinity and strong toxicity. Semi-coke is one of the products during coal pyrolysis at 600-700℃. Large mount of abandoned fine semi-coke (FSC) which has a particle size less than 6 mm would be produced during the semi-coke producing, transporting and using. It is mostly disposed as low-grade fuel materials and abandoned in the rivers or fields, which not only wastes a huge amount of natural resources, but also seriously pollutes the environment.This article used the abandoned FSC as adsorbent to dispose of organic waste water with methyl orange (MO) or methylene blue (MB). First, the preparation conditions such as concentration of modifier, modification temperature, modification time, ratio of liquid to solid, calcination time and temperature on the performance of modified fine semi-coke (MFSC) were optimized by the single-factor experiment and fractional factorial design. The structural changes between FSC and MFSC were characterised by SEM, XRD and BET. The adsorption performance of MO on MFSC was studied by the static adsorption experiments and the adsorption thermodynamics and kinetics were analyzed.The results indicated that the FSC modified with HNO3 has the high adsorption capacity for MB. The significant factors on experimental design response were:HNO3 concentration, modification time,modification ratio of HNO3 to MFSC, calcination temperature, which were identified by the analysis of variance (ANOVA). The maximum adsorption capacity of MB is 40.8mg/g at 298K. The optimal modifying conditions for adsorbing MO were follows:FSC was modified by 0.5 mol/L ZnCl2 solution at 70 ℃ for 4 hours and the ratio of ZnCl2 to MFSC is 10 (mL/g). The maximum adsorption capacity of MO onto MFSC was 372.1 mg/g at 298K. The thermodynamic isotherms were seemed like’S’and there were an inflexion point on it. The equilibrium data of MO (low concentration) onto MFSC conformed to the Freundlich adsorption model, the adsorption process was non-favorable adsorption because of n> 1 and monolayer adsorption. The equilibrium data of MO (high concentration) onto MFSC conformed to the BET adsorption model, the adsorption process was multilayer adsorption and exothermic process. The adsorption of MO onto MFSC could be best described by the HO pseudo-second-order equation. The particle diffusion is the main control step. The apparent active energy of the adsorption process (Ea) was 19.21 kJ/mol.