Study On The Process Of Transforming Waste Iron Filings Into Schwertmannite By Biological/Chemical Mineralization Method

Schwertmannite is a kind of hydroxy iron sulfate mineral with weak crystallinity formed under acidic environment and rich in iron and sulfate.It has excellent adsorption performance for hexavalent chromium and trivalent arsenic,and it is also a kind of excellent performance The iron-based material used in the heterogeneous Fenton reaction has great environmental value.The machining industry often produces a large amount of waste iron filings,and long-term exposure of steel structures to the environment will also produce rust,resulting in a lot of waste of iron sources.Turning these discarded iron filings and rust into useful iron-containing environmental functional materials is a new way to turn waste into resources.Therefore,it is of great significance to transform scrap iron filings or rust into Schwertmannites,but research in this area is rarely reported.To this end,this article dissolves scrap iron scraps with acid,and then synthesizes Schwertmannites through chemical（H₂O₂ ferrous oxide）and biological methods（A.ferrooxidans ferrous oxide）to study the optimal synthesis of Schwertmannite with high efficiency Parameters;explore the adsorption capacity of the synthesized Schwertmannites for As（Ⅲ）and Cr（Ⅵ）under optimal conditions;finally try to build a large-scale synthesis process,which is the large-scale Schwertmannites using scrap iron filings and rust as raw materials Synthesizing provides technical support.The results obtained are as follows:（1）Use sulfuric acid to completely dissolve the scrap iron filings/rust,and determine the basic physical and chemical properties,so as to optimize the dissolution conditions of the scrap iron filings and rust acid.The results showed that the iron content of the three types of iron filings reached 80%to 90%,and contained a small amount of SiO₂,Fe₃O₄,and CaCO₃.After the acid solution is filtered,a clear green solution is obtained.Fe ions in the filtrate are mainly in the form of ferrous sulfate,and the Fe²⁺content is above 95%.Calculate the iron content of scrap iron scraps through complete acid dissolution,control Fe:H₂SO₄=0.97～0.98（molar ratio）,you can control the amount of sulfuric acid,and then calculate the amount of water added to the system to control the iron concentration of the dissolved solution,and the entire acid dissolution process to:Grind the iron-containing waste into particles less than 1cm,add dilute sulfuric acid（9.2 mol/L）,control the temperature at 40-60℃and stir at 50-100 rpm until it cannot be dissolved.The general reaction time is 1-2 hours.（2）The scrap iron filings/rust are completely dissolved in sulfuric acid,and the basic physical and chemical properties are measured,so as to optimize the dissolution conditions of the scrap iron filings and rust acid.The results showed that the iron content of the three types of iron filings reached 80%to 90%,and contained a small amount of SiO₂,Fe₃O₄,and CaCO₃.After filtering the acid solution,a clear green solution was obtained,which contained a large amount of FeSO₄.Calculate the iron content of scrap iron scraps through complete acid dissolution,control Fe:H₂SO₄=0.97～0.98（molar ratio）,you can control the amount of sulfuric acid,and then calculate the added amount of water system to control the iron concentration of the dissolved solution,and the entire acid dissolution process To:Grind the iron-containing waste into particles less than 1cm,add dilute sulfuric acid（9.2 mol/L）,control the temperature at 40-60℃,stir at 50-100 rpm until it cannot be dissolved,the general reaction time is 1-2 h.（3）Adsorption experiments were used to compare the adsorption effects of As（Ⅲ）and Cr（Ⅵ）on the synthesized Schwertmannites.Studies have found that the addition rate of H₂O₂ will affect the morphology and adsorption effect of minerals.A slow addition rate of H₂O₂ will allow minerals to have a better adsorption effect on heavy metals.Both Langmiur and Freundlich adsorption isotherm models can better describe the adsorption isotherm process of As（Ⅲ）and Cr（VI）,indicating that the entire adsorption process includes both single-layer adsorption and multi-layer adsorption.The maximum adsorption capacity of the synthesized Schwertmannites on As（Ⅲ）and Cr（Ⅵ）is 342.71 mg/g and 63.33 mg/g respectively,which is far better than the adsorption effect of traditional Schwertmannite.（4）Utilize the optimized acid dissolution conditions and mineral synthesis conditions to help the design of the large-scale synthesis process of Schwertmannite.The production scale is calculated at 10 t/d,which requires an investment of 484,000yuan in equipment and infrastructure,covering an area of 990m² and an installed capacity of 67.56 kw.The daily operating cost is 30,300 yuan,the output value is 50,000 yuan,and the daily income is 19,700 yuan.And draw the plan layout and elevation layout of the production facilities to provide theoretical guidance for the large-scale synthesis of Schwertmannite.