| With the rapid development of the electricity and communication networks, the demand for iron tower is increasing. Dilute hydrochloric acid is often used to remove the tower component’s oxide layer on the surface before the anti-corrosive process. The pickling waste water, with high Zn2+, Fe2+ content, low pH value, strong corrosive, can’t be handle economically. Therefore, the recycling pickling waste liquor to produce high value-added products is more and more important. Base on the analysis of the basic composition and properties of the FeCl2 waste acid, provided by a tower steel structure factory, a new process has been developed to recycle FeCl2 waste acid. This process mainly includes three steps:extraction of FeCl2 from waste acid cooling by crystallization, preparation of FeCl2 crystal seed, and iron oxide yellow. The new process consumes less energy, with short production cycle, high yield, resource utilization, etc. This research contains three parts:(1)Concentrated heating-cooling crystallization method was used to FeCl2,By the simulation and optimization the Aspen Plus software, four effect evaporation-cooling crystallization was closed to prepare FeCl2. The first effect evaporator pressure is set up 5atm, vaporization rate is 0.09,and the second effect evaporator pressure is set up 3atm, temperature is 143.65℃, and the third one pressure is 1atm, temperature is 113.95 ℃, the last effect evaporator pressure is set up 0.2atm, temperature is 76.45 ℃. Then, cooling the temperature to 25℃ when those liquid go through the crystallizer, getting high purity FeCl2. This process greatly improves the energy efficiency of cooling crystallization by saving 67.4% energy compared with concentrated heating process, arid realizes the resource utilization of waste pickling liquor.(2)A new method was used to prepare iron oxide yellow. The method uses FeCl2 as raw material,5mol/L NaOH as alkali material, air as oxidant to synthesis α-FeOOH. The influences of temperature, pressure, and the initial concentration of Fe(OH)2 on crystal seed formation rate and the air flow rate, liquid flow rate, feed. concentration and reaction pressure, reducing Fe(OH)2 colloidal particle size, are conducive to the formation of iron oxide crystal seed in the three-phase reactor at room temperature. The optimized parameters of the three-phase reactor is:gas phase flow V=700 L/h, liquid flow rate L=70 L/h, initial pH=7.5, Fe(OH)2 particles 700 nm, the Fe(OH)2 initial concentration C=0.2～0.6mol/L. Control the reactor pressure P =0.1-0.5MPa, reaction temperature 20～30℃, than obtained the relationship between temperature, pressure, initial concentration of Fe(OH)2 and the iron oxide yellow seed generation rate. Controlling reaction temperature 120℃, reaction pressure 3atm, the yellow iron oxide products were characterized after it is pretreatment using the SEM and XRD. The result shows that those products get in line with China’s chemical industry standard level.(3)Designing and assembling a continuous production process for the synthetic of iron oxide yellow. Analyzing and studying the effect of ferrous hydroxide, initial concentration and feed flow rate and other parameters on the preparation of iron oxide yellow and discover that the optimum conditions are:Fe(OH)2 feed flow rate 20L/h, feed concentration 0.3mol/L, cell cycle circulation ratio 3-5, setting up the packed column at a temperature of 25 ℃, the pressure of 1atm during the seed preparation stage, and setting up the packed column at a temperature of 120℃, the pressure of 4atm during the seed growth stage. |
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