| With the rapid development of economy and technology in China, water waste is increasing dramatically, whereas the environmental capacity of receiving water waste is far insufficient. The water pollution become urgent problem demanding prompt solution. The Inner Mongolia Autonomous Region is located in the western area which is lack of water, and belonged to less developed surface water system with limited capacity of environment receiving water. In addition, the exists of a number of printing and dyeing enterprises such an Inner Mongolia Erdos Cashmere(Group) Co. Ltd. and King Deer Cashmere Company Limited make the purification treatment of printing and dyeing wastewater particularly important. In contrast, rich reserves of rare earth resources in this district and a plentiful of abandoned coal ashes produced by great quantity of large thermal power plants, has not been sufficiently utilized. Therefore, the aim of this research is to apply fly ash(FA) to the purification treatment wastewater. Based on the composition and structural properties of fly ash(FA), cheap and efficient Fe2O3/La2O3/ash sorbent(Fe2O3/La2O3/FA) has been prepared by sol- gel method, in which a small amount of rare earth elements(lanthanum) and other appropriate elements(iron) was added to FA. Direct dye wastewater is adsorbed and purified by the adsorbent above. The preparation conditions and structural performance of the adsorbent were optimized and characterized. Meanwhile, the adsorption properties and influencing factors of La/Fe/FA adsorbent for two kinds of reactive dyes such as Direct Fast Scarlet(DFS 4BS) and direct scarlet 4BE(CDR 4BE) from simulated wastewater were investigated. The adsorption kinetics and thermodynamics, heavy metals leaching and adsorption mechanism were further discussed. The detailed results are as below:(1) The study used solid waste fly ash(FA) as raw materials. After 4mol/L HCl treatment, the Fe2O3/La2O3/FA composite adsorbent is obtained using 10 g of acid-modified FA(m(FA):m(La2O3)=25: 1) by sol- gel method, and used direct acid red(DFS 4BS) as adsorption reaction model, won the Fe2O3/La2O3/FA adsorbent optimal conditions for the process: n[(NH4)2Fe(SO4) 2]: n[La(NO3)3]: n[C6H6O7] was 5:1:4. p H is adjusted to 9.0~10.0; the reaction temperature is 60 ℃;reaction time was 120min; then the Fe2O3/La2O3/FA adsorbent was prepared. The adsorbent could make the concentration of 6000mg/L DFS 4BS and CDR 4BE simulated dye wastewaters’ removal rate up to 90%, reflecting its good adsorption properties.(2) By studying Fe2O3/La2O3/FA adsorbent on the adsorption properties of two dye wastewater DFS 4BS and CDR 4BE and main factors, it is found that several factors affecting Fe2O3/La2O3/FA adsorbent properties including the oscillation frequency, p H, initial concentration, contact time and contact temperature etc. of simulated dye wastewater. When p H = 2.0, the adsorbent on two types simulated dye wastewater DFS 4BS and CDR 4BE adsorption capacity and removal rate reach maximum and are 598.58mg/g, 700mg/g and 99.76%, 100% respectively, when p H = 8.0 ~ 12.0, the adsorption capacity began to decline, when the p H is increased to 12.0, the adsorption capacity and removal rate both had a sharp decline to the lowest and are 224.74 mg/g, 195.6mg/g and 37.46%, 27.94% respectively; Fe2O3/La2O3/FA adsorbent on two types simulated dye wastewater DFS 4BS and CDR 4BE had a high removal rate, and the adsorption capacity increased with the concentration increasing, the removal rate decreased with the concentration increasing, When the concentration of two simulated dye wastewater DFS 4BS and CDR 4BE were 1000mg/L, the adsorption capacity of Fe2O3/La2O3/FA adsorbent on them are 99.91mg/g and 99.65mg/g, the removal rate were 99.91% and 99.65%, when the concentration of two types simulated dye wastewater increased to 7000 mg/L, the adsorption capacity of Fe2O3/La2O3/FA adsorbent on them are up to 483.95mg/g and 474.84mg/g,the removal rate are still as high as 67.40% and 61.28%.(3) Studies of adsorption kinetics show that the Fe2O3/La2O3/FA adsorbent have faster adsorption rate for DFS 4BSand CDR 4BE. From 0min to 30 min, the amplitude of increase with time is very fast, which indicated that the adsorption was fast adsorption. From 30 min to 60 min, the amplitude of increase is slow. From 60 min to 90 min, the adsorption capacity increases with time closed to zero, the adsorption achieved the dynamic equilibrium at 90 min. For example, when time is 90 min at 298 K, DFS 4BS simulated dye wastewater concentration is from 1000 mg/L to 6500 mg / L, the adsorption capacity of the adsorbent increased from 99.83mg/g to 583.95 mg / g, the removal rate is reduced to 99.83% from 89.83%. The concentration of CDR 4BE simulated dye wastewater is from 1000 mg / L to 6000mg/L, the adsorption capacity of the adsorbent increased from 99.96 mg / g to 595.12mg/g, the removal rate is reduced from 99.95% to 99.18%. At different temperatures(298K, 313 K, 328K), dynamics trend curve is basically at the same, Fe2O3/La2O3/FA adsorbent for the adsorption process and CDR 4BE and DFS 4BS dye wastewater pseudo second adsorption rate equation(R2> 0.999). Adsorption process is mainly controlled by diffusion within the particles, but it is also affected by external particle diffusion process; the adsorption activation energy Ea of adsorbent for DFS 4BS and CDR 4BE is 16.80 k J/mol and 31.18 k J/mol respectively which indicated that the adsorption process may be mainly completed through physical adsorption.(4) Isothermal adsorption studies showed that the isothermal adsorption experiment data of La/Fe/FA adsorbent for two kinds of reactive dyes DFS 4BS and CDR 4BE fit both of Langmuir and Freundlich isotherm adsorption model well at different temperature(298K~328K), from which the obtained maximum adsorption capacities of two kinds of reactive dyes at different temperature(298K~328K) are between 476.19~434.78mg/g and 434.78~666.67mg/g respectively. The adsorption capacities also correspondingly decreased, and that explained the adsorption process is an exothermic process. The obtained values of 1/n and equilibrium constant RL(from Freundlich isotherm adsorption model)also reflected that the adsorption is easy to occur.(5)Studies of adsorption thermodynamics showed that at different temperatures(298K ~ 328K), the adsorption thermodynamic parameters △ G of Fe2O3/La2O3/FA adsorbent for DFS 4BS and CDR 4BE adsorption is between-24.17 k J/mol ~-25.61 k J/mol and-30.85 k J/mol ~-31.50 k J/mol, indicating that the adsorption process of the absorbent for the two kinds of simulated dye wastewater, DFS 4BS and CDR 4BE,is a spontaneous process. The adsorption enthalpy △H of Fe2O3/La2O3/FA adsorbent for DFS 4BS and CDR 4BE adsorption is-16.03 k J / mol and 1.07 k J / mol respectively, indicating that it’s an exothermic reaction for DFS 4BS and it’s an endothermic reaction for CDR 4BE,which is consistent with the dynamics of the front.And the adsorption entropy change △S of Fe2O3/La2O3/FA adsorbent for DFS 4BS and CDR 4BE adsorption is 0.030 J/mol/K and 0.101J/mol/K respectively, indicating that the system is ordered reduced during absorption, and it’s mainly physical adsorption.The above results showed that Fe2O3/La2O3/FA adsorbent obtained from the lab can effectively remove the high concentration DFS 4BS and CDR 4BE. This method will have a great potential and future in treatment of reactive dyes wastewater particularly if combined with other method. The Fe2O3/La2O3//FA adsorbent not only can efficiently use solid waste fly ash but also can purify a high concentration of dye wastewater, which will benefit environment significantly. |
PDF Full Text Request