| Magnesium slag is a kind of industrial waste of silicothermic process,mainly composed of SiO2, CaO and MgO. Silicothermic process is highlyenergy-consuming and highly polluting.To obtain1ton of pure magnesium,11tons of dolomite, about10tons of coal and1.2tons of ferrosilicon are needed,and at the same time,35tons of CO2and0.20ton of SO2will be released. In2014, China’s magnesium production was873.8thousand tons and more than600tons of Magnesium slag was produced.Magnesium slag can be pulverized easily.It’s water solution is alkaline,which can seriously pollute the environment. The increasing discharge andaccumulation of magnesium slag, not only waste a lot of resources, but also takeup a lot of lands and destroy vegetations and landforms. Besides, magnesiumslag flow with rain into rivers and lakes, which has a negative influence on cropsand surrounding environment and poses a serious threat to the health of humanand crop growth. At the same time, magnesium slag is rich in elements of whichsoil is in urgent need but these sustances can not be directly absorbed by crops.To solve problems above,research about feasibility of using magnesium slag to produce silicon,calcium and magnesium compound fertilizer was done,and then experiments to figure out the percentage of silicon in magnesium slagwas conducted and in the end XRD, SEM and UV spectrum were used toanalyze experimental results and mechanism. The conclusion is:(1) Based on many documents and the physical and chemical properties ofmagnesium slag, draw up the craft process and technological route of usingmagnesium slag to produce silicon, calcium and magnesium compoundfertilizer.(2) Containing silicon calcium and magnesium elements needed by crops,the components of magnesium slag can meet the basic elements and content thatcompound fertilizer requires. Also they are low in heavy metal elements so canmeet the basic requirements to produce compound fertilizer.(3) Add quartz sand into magnesium slag and roast their compound, phasechange will occur, with the less reactive Ca2SiO4converted into higher reactiveCaSiO3, which can be easily dissolved in HCl. During the roasting, when adding13.53%quartz sand, which means that content of SiO2in magnesium slag is43%, the lowest temperature is required as1460℃.(4) When magnesium slag is acidleached, the lowest concentration of HClneeded is4mol/L. In this concentration, MgO, CaO and Fe2O3can be dissolvedthoroughly into the solution.4mol/L of HCl is accessible, and cost-effective.(5) When the acidleached slag is roasted in the temperature of140℃to400℃, H2SiO3is divided into SiO2and the lattice structure of part of the amorphous SiO2is destroyed with lattice reconstruction taking place. When thetemperature is below140℃, only physical adsorption water is removed; whenthe temperature is above400℃, amorphous SiO2in acidleached slag isconverted into chemically stable SiO2crystal. To improve the content ofavailable SiO2, temperature should be controlled between140℃and400℃.(6) The results of orthogonal test showed that the optimum craft conditionsto improve the content of available silicon in acidleaching was in the200℃,roasting6hours with the additive KOH. The content of available SiO2is up to25.62%, which compared with that in untreated acidleached slag(3.62%)increased by6.1times and which compared with that in the original magnesiumslag (4.35%) increased by4.8times.(7) Using ammonia to control the pH of the filtered solution, we canseparate trivalent Fe element, and76%of Fe can be removed. |
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