Study On Recovery Of Iron Resources From Waste Pickling Liquor Using Modified Co-precipitation Method

The steel industry produces a lot of waste pickling liquor?WPL?every year.The solutions would damage the environment due to the existence of ferrous salt and free residual acid.The conventional treatment method eliminates its impact on environment,but not gives consideration to environmental effects and economic benefits.A new recycling method,which can obtain high added-value product,is an inevitable choice that can realize the coordinated development of environment and economy.To solve this problem,a modified co-precipitation method is put forward for the recycling treatment for WPL to obtain Fe₃O₄ nanoparticles with high added-value and quality.With the analysis of merit and demerit of the conventional co-precipitation method and precipitation-oxidation method and the features of WPL,the highlight of the modified co-precipitation method is that Fe³⁺ as raw material transformed from Fe²⁺ in WPL by in-situ oxidation method.Oxidation-reduction potential?ORP?monitoring method is proposed to control Fe²⁺/Fe³⁺ mole ratio timely.By using standard curve method,the corresponding ORP value of the optimal Fe²⁺/ Fe³⁺ mole ratio is 522mVIn this study,two 3 factors and 4 levels orthogonal experiments are designed to obtain Fe₃O₄ nanoparticles.The Fe₃O₄ nanoparticles are characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?and vibrating sample magnetometer?VSM?.With research and analysis of particle size and saturation magnetization,the stirring rate,Fe²⁺/ Fe³⁺ mole ratio,terminal pH value,reaction temperature,aging temperature and aging time are analyzed to obtain the optimal technological conditions: stirring rate is 800r·min^-1,Fe²⁺/ Fe³⁺ mole ratio is 1:1.8,terminal pH value is 11,reaction temperature is 50?,aging temperature is 90?,aging time is 0.5h.The alternative promoters include sodium dodecyl sulfate?SDS?,sodium citrate,polyethylene glycol4000?PEG-4000?and anhydrous sodium metasilicate.In this study,the optimal technological conditions are applied to analyze the alternative promoters.The functions and effects of promoters on improving particle size,morphology,crystallinity and magnetic performance of Fe₃O₄ nanoparticles are analyzed by XRD pattern,TEM image and magnetic hysteresis curve.According to the research results,sodium citrate,PEG-4000 and anhydrous sodium metasilicate are used as a promoter combination to provide synergistic effects for the sake of improving the quality of Fe₃O₄ nanoparticles product.In this study,the optimal technological conditions and promoter combination are applied to validate the practicability of modified co-precipitation method by preparing Fe₃O₄ nanoparticles using simulation wastewater and WPL and characterizing.Fe₃O₄ nanoparticles preparing by simulation wastewater is spherical and has particle size with 30-50 nm.Its magnetic performances are: saturation magnetization is 81.523emu·g^-1,coercive force is 52.352 Oe.Fe₃O₄ nanoparticles preparing by WPL is spherical and has particle size with 20-40 nm.Its magnetic performances are: saturation magnetization is 80.206emu·g^-1,coercive force is 73.345 Oe.