The Study Of Simultaneous Removal Of Iron,Manganese And Hardness By Chemical Crystallization Circulating Pellet Fluidized Bed Reactor

In recent years,the coexistence of iron,manganese and hardness in water was becoming increasingly serious,and there were huge potential safety hazards.Aimed to solve the problems of complicated process and difficult operation management in the present water treatment process,it was necessary to develop a process that could effectively remove such complex contaminants.Chemical crystallization circulating pellet fluidized bed（CPFB）reactor has been widely concerned in the field of water treatment due to its low consumption,high efficiency and no secondary pollution.In this study,the effects of simultaneous removal of iron,manganese and hardness in water by CPFB and its influencing factors were investigated,and the relevant technological conditions were determined through static,pilot-scale and full-scale experimental study.At the same time,the physical morphology and elemental changes of particle surface before and after crystallization were analyzed by means of SEM and EDS.The chemical composition of particle surface was analyzed by XPS,and the mechanism of simultaneous removal of iron,manganese and hardness by the system was further explored.This study has a good reference value for developing a new technology of simultaneous removal of iron,manganese and hardness in water.The main research results and conclusions were as follows:（1）In static beaker experiment,induced crystallization method could effectively remove iron,manganese and hardness.The results showed that when the average concentration of iron,manganese and hardness in influent water were 3.83,3.94 and296 mg/L,the dosage of Na OH was 100 mg/L,the p H was 9.59,the removal rate of total hardness was 57.8%,the removal rate of iron and manganese were 99%and 98.8%respectively,and the quality of effluent water could fulfill the standards.Calcite crystal seeds had certain adsorption capacity for iron and manganese in raw water,it could remove 91.8%iron and 21.9%manganese by adsorbing in the mixing process.Increasing the stirring intensity and time in a certain range could make the crystal seeds fully in contact with ions,improve the crystal growth environment,and further improve the removal efficiency of contaminants.Seed addition was helpful for the removal of contaminants.Seed addition amount and size affected the removal ability by affecting the seed surface area.When the dosage of seed up to 60 g/L and the seed size was less than 0.09 mm,the removal effect was the best.（2）The results of the pilot-scale experiment showed that when the average concentration of iron,manganese and hardness in influent water were 0.90,1.90 and300 mg/L,the height of crystal seed was 50 cm and the dosage of Na OH was 100 mg/L,the effluent water quality could meet the related standards and became better with the running extension.Most of the contaminants could be removed efficiently from the bottom of the fluidized bed at 0-30 cm and the removal rates of iron,manganese and hardness were up to 70.6%,96.7%and 59%,respectively,and the effluent p H value was9.6.In addition,the manganese removal by fluidized bed became difficult with the increase of influent hardness.By the analyzing the structural changes of seeds by SEM,EDS and XPS methods after long-term operation,it was found that a compact layer of crystallized product,which were a mixture of Ca CO₃,Fe OOH,Fe₃O₄,Mn₃O₄and Mn O₂appeared on its surface.（3）In the full-scale experimental study of thermal power plant,the stable removal of iron,manganese and hardness in the make-up water of circulating water with reservoir as water source could be achieved by CPFB.The contents of iron,manganese and hardness in influent water were 0.38,0.16 and 270.2 mg/L,respectively.The optimum operating p H value was 10.6,the total hardness was reduced by 57%,and the removal rate of iron and manganese were 42.1%and 45.6%,respectively.At this situation,the unite cost of water treatment was 0.65 yuan/m³.The mass of Ca CO₃removed by crystallization in the fluidized bed was about 520 kg per day,and the mass of iron and manganese removed were about 0.623 and 0.292 kg per day,respectively.Crystalline particles were hard and the proportion of Ca CO₃was more than 95%.This part of high purity limestone could be used as raw material for wet flue gas desulfurization process,which can turn waste into treasure and truly realize zero emission.