Experimental Study On Preparing Light CaCO₃with Sintering Plant FGD Ashes

At present, emissions of sulfur dioxide have caused serious pollution. The generation of SO2is mostly from sintering gas in our iron and steel industry. Therefore the desulphurization of sintering gas is necessary for achieving environmental protection requirement. Among the desulphurization technologies, the flue gas desulphurization process can be divided into wet, dry and semi-dry according to the form and characteristics of desulfurizer and desulfurization product. The technology of semi-dry gas desulfuration is widely used now. But if we do not make rational use of the desulfurized fly ash produced by semi-dry flue gas desulfurization technology, the desulfurized fly ash will become new pollutant, causing the second pollution. So the resource utilization of the desulfurized fly ash has become a problem to be solved.The sintering flue gas desulfurization ash of the experiment is from the factory in Anshan. We need to extract the calcium ions by ammonium chloride leaching solution, through the liquid-liquid and gas-liquid carbonization way to prepare light calcium carbonate respectively. This article studied the process characteristics of leaching and precipitation reactions, optimizes technological parameters and determines the appropriate technological conditions.This experiment mainly introduced the leaching process of desulfurization ash. It also emphasized the effects of factors like pretreatment methods、leaching time、leaching temperature and extent of the excess of ammonium chloride on leaching rate of calcium in the single factor experiment. The best condition is:900℃is the best high-temperature pretreatment leaching time is60min、temperature is25℃, the excessive dosage of NH4Cl is5%. Under the best condition, the leaching rate of calcium reachs76.26%.In the experiment of the liquid-liquid preparation of fine calcium carbonate, we mainly study the influence of pretreatment methods、different additives、additive dosage、 reaction temperature、Ca2+concentration and adding mode on the morphology and grain size of CaCO3. Best way of preparing fine calcium carbonate concluds that the solution is ammonium bicarbonate joining into calcium chloride, the dosage of citric acid is0.5%of calcium carbonate in mass, carbonizing temperature is15℃, calcium chloride concentration is0.57mol/L. Cube fine calcium carbonate is prepared with mean diameter140nm and homogeneity of grain size. The product from this way meets the standard of industrial fine precipitated CaCO3(HG/T2776-2010). In the experiment of the gas-liquid preparation of calcium carbonate, we mainly study the influence of different additives、 reaction temperature、additive dosage、carbon dioxide flow and Ca2+concentration on the morphology and grain size of CaCO3. Best way of preparing high-brightness white calcium carbonate concluds that the dosage of EDTA is4%of calcium carbonate in mass, carbonizing temperature is15℃, adding speed of ammonium carbonate is40mL/min, calcium chloride concentration is0.83mol/L. Rod-shaped calcium carbonate is prepared with mean diameter1μm, the ratio of length to radius is about3. The product from this way meets the standard of industrial precipitated CaCO3(HG/T2226-2000).