| It is well known that both iron and steel are one of the most important structural and functional materials in our daily lives. In the current enterprises and electroplating industry of iron and steel, acid pickling is a necessary process which leads to a large number of pickling waste liquor(PWL). The corrosivity of pickling waste is strong and there is a great amount of Fe(II) in it. If it can not be properly dealt, pickle liquor will seriously affect the environment. In addition, the impertinent discharge will cause the waste of resources. It may even bring bad effects to human’s health. In view of pickling waste liquid treatment at present, the utilization of pickling waste liquor has always been paid attention. Our lab has been engaging in researching the synthesis and mechanism of iron oxides in solution, its application in wastewater treatment. In earlier research, pure chrysanthemum-like P-FeOOH micro-nano particles have been prepared using acid pickling liquor as raw materials. In this paper, based on the results of the element analysis to as-prepared β-FeOOH, the preparation process of P-FeOOH was simulated by using pure FeCl3 and FeCl2 as raw materials. The formation causes of the chrysanthemum-like P-FeOOH particle and formation mechanism were revealed. The optimal experimental conditions were found. At the same time, the application of as-prepared P-FeOOH in the field of water treatment was investigated. The study reflects the concept of waste resource utilization, and it has important theoretical significance and practical value. The main research work and results are summarized as follows:(1) P-FeOOH micro-nano structure was prepared using pure Fe(II) and Fe(III) reagents as raw materials. The influence of the initial pH value, the concentration of Fe(II) and Al(III), the dosage of urea, SO42- on the formation of flower-like p-FeOOH were studied in detail. To find the optimal reaction condition, the orthogonal experimental design was used. The results indicate that flower-like P-FeOOH with beautiful morphology can be obtained under the following conditions:pH=1.4, CFe(Ⅲ)/CFe(Ⅱ)=1:2, cAl(Ⅲ)=0.03, CSO42-=0.1 CCH4N2O=0.25.(2)To clarify the possible growth mechanism of the flower-like β-FeOOH, we carried out time-dependent experiments under different experimental conditions. The as-prepared samples were characterized by the technologies of XRD, IR, SEM, HRTEM, BET and TG-DSC. The existence of SO42- ions plays a key role on the formation of flower-like β-FeOOH. At the early stage, Fe(III) ions in solution can react with SO42- to form schwertmanite with "pin cushion" morphology based on a strong affinity between Fe(III) and SO42- ions. P-FeOOH is isostructural with schwertmannite and sulphate may also occupy the tunnel of β-FeOOH structure. Thus, when all SO42- ions were used up, β-FeOOH continues to grow along with the direction of "pin", which leads to the formation of flower-like P-FeOOH particles. The action of urea is to accelerate the hydrolysis of Fe(III) by decomposing to produce OH- under heating. The function of both Fe(II) and Al(III) is to supply a high ion strength which is favorable for the formation of P-FeOOH.(3) To investigate the adsorption performance of β-FeOOH, CAS was used as a model pollutant to beild a research system.The influence of pH, dose of absorbent, the initial concentration of pollutant and temperature on the adsorption properties of P-FeOOH to CAS was examined. Meanwhile, the adsorption thermodynamics and kinetics are studied. It was found that P-FeOOH shows a super high adsorption capacity for CAS and the adsorption rate of CAS decreases with the increase of pH value while the temperature does not have an obvious effect. The adsorption process of EBT, MY 10 and CAS on P-FeOOH was compared. The results show that the CAS’s high adsorption capacity is mainly due to CAS aggregation and formation of multimolecular layer adsorption. |
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