Study On Fluoride Removal,Softening And Desalination Of Coking Wastewater

In this work, steamed ammonia wastewater from coking plant was studied.Several problems including fluoride removal from original ammonia wastewater,softening and desalination from the high hardness and salinity wastewater after degreasing, biological and membrane treatment were studied in detail through theory and experimental methods. The main work and conclusions are as follows:Calcium chloride was used as a precipitating agent to remove the fluoride ion form ammonia wastewater. On-line particle monitoring technology was applied to measure the batch crystallization kinetics data of calcium fluoride. Based on the two step crystallization theory of mass diffusion and surface reaction, precipitation crystallization kinetics model for fluorite was deduced and validated by experiments.The results indicate that the correlated data shows high satisfactory agreement with the experimental data. In addition, the model shows that surface reaction was a controlling step in the process of calcium fluoride precipitation. At a fixed concentration of calcium ion, the higher the initial concentration of fluoride ion is, the faster the fluoride ion concentration decline in the initial stage; Excessively high or low initial concentration of fluorite ion would eventually be unfavorable for obtaining lower fluoride ion concentration; Appropriate increase in operating temperature may promote fluorine ion purification, but too high temperature is negative. In the thesis, the fluoride ion purification experimental for stripping ammonia wastewater by continuous process had carried out. Through optimizing the process parameters, add to 2.6 times the theoretical amount of calcium fluoride is the preferred operating conditions for fluoride ion purification.Using the concentrated water from electrodialysis (EDR) and reverse osmosis(RO),the settling solid were calcium carbonate and magnesium hydrate. Combined solubility product constant and carbonate ionization constant analysis, wastewater agents softening mathematical model was presented based on the principle of the solubility product. Based on the batch experimental data, the parameters for the presented softening mathematical model and the six parameter interaction model were calculated. Among them, theoretical model has good physical and chemical significance. The six parameter interaction model shows good satisfactory with data.Besides, the contours of six parameter interaction hardness model and the contours of agent cost were analyzed. The results show that there is an optimal drug concentration and maximum softening effect under certain costs. Furthermore, continuous softening experiments showed: after wastewater being continuously softened 330 minutes, when the concentration of sodium carbonate and sodium hydroxide was 1.944, 1.457 kg·m-3 and 0.486 kg·m-3, respectively, the hardness of EDR wastewater in second floor maintained at about 0.35 mmol·L-1, when the concentration of sodium hydroxide was 1.457 kg ·m-3, the hardness of EDR wastewater in first floor and RO wastewater maintained at about 0.33 mmol·L-1 and 0.36 mmol·L-1, respectively.Desalination experiments for the concentrated water from electroosmosis (EDR)were carried out by electrodialysis and frozen crystallization, respectively. In the electrodialysis desalination experiments, the desalting efficiency and rules of high-salinity wastewater by home-made electrodialysis were investigated. The breakdown voltage of the softened wastewater was 2.8 V Finally, the influences of running time, voltage, flow rate of wastewater in the dilute compartment and the cathode and anode compartments on desalting efficiency were studied in detail. The results show that desalting efficiency was reduced with time, improved with the increase of voltage, enhanced with the decrease of the flow rate of wastewater in the dilute compartment and with the increase of the flow rate of sewage in the cathode and anode compartments. In batch freezing crystallization, the results show that the paddle-type has little effect on desalting effect, while freezing temperature has great influence on the desalination. The temperature of freezing crystallization is between-0.7 and -1.2 ?, the recovery rate of freshwater is from about 60 % to 80 %, the desalination efficiency is about 80 %, the desalination effect is good.