Research On The Comprehensive Utilization Of Calcium Carbide Furnace Purification Ash Calcined Slag In Building Materials And Magnesium Sulfate Production

Calcium carbide furnace purification ash is a solid waste produced in the calcium carbide production process,the appearance of the purification ash is black,rich in carbon,calcium oxide,magnesium oxide and other substances.In addition,it also contains a certain amount of calcium carbide powder,sulfur,phosphorus and other impurities.The fineness of the purification ash is large,the ignition point is low,and spontaneous combustion is easy to occur after contact with air,which has high safety risks.At present,the main treatment method of calcium carbide industry for purifying ash is landfill.However,because of its flammable nature,transportation vehicles are often burned,and the purified ash is easily dispersed when discharged,seriously polluting the air.This thesis strives for the characteristics of purification ash,removes the carbon and other combustibles by high-temperature calcination,and prepares calcium-magnesium composite products,which are used in building materials and agriculture.The main research directions are as follows:(1)Preparation of concrete calcium magnesium composite expansion agent.Utilizing the rich characteristics of calcium oxide and magnesium oxide in purified ash calcined slag,it is prepared into a concrete expansion agent for use.Refer to the standard T/CECS 10082-2020 "Calcium magnesium composite expansion agent for concrete" to test the performance of purified ash calcined slag.Through research,it was found that the calcium expansion performance of purified ash calcined slag used as a calcium magnesium composite expansion agent did not meet the standard requirements.The experiment used a combination of5%-15% quicklime to improve the calcium expansion performance.The experimental results show that the limited expansion rate of the purified ash calcined slag after being mixed with 5% and 15% quicklime for 7days is 4.40 × 10-4 and 6.93 × 10-4;Limit the expansion rate to-0.9 after 28 days of air curing × 10-4 and1.75 × 10-4;The difference in the limited expansion rate between 3 and 28 days under 60 ℃ hydroponic conditions is 0.056 and 0.046,indicating that the calcium expansion performance and magnesium expansion performance meet the standard requirements.The 7-day compressive strength is 45.1MPa and 43.3MPa;The28 day compressive strength is 54.5MPa and 53.7MPa,which meets the standard requirements.(2)Prepare concrete admixtures.Purified ash calcined slag is rich in calcium oxide,which can provide sufficient calcium source for cement.However,due to the high content of magnesium oxide and its good expansion performance,it cannot replace a large amount of cement alone.Composite admixtures are prepared by combining purified ash calcined slag with fly ash.Through experiments,it was found that the appropriate proportion of purified ash calcined slag in the composite admixture is 10%-30%;The appropriate dosage of composite admixtures is between 5% and 15%;Composite admixtures can improve the adverse effect of fly ash alone on the early strength of the mortar.The experimental results show that the 7-day compressive strength of the composite 20% purified ash calcined slag is increased by 8.7% compared to the single fly ash group,respectively;Fly ash can inhibit the expansion performance of purified ash calcined slag.Compared with the rubber sand group containing 5% purified ash calcined slag and 20% fly ash,and the rubber sand group containing 5% purified ash calcined slag,the limited expansion rate decreased by 40.8%.(3)Preparation of magnesium sulfate fertilizer.Utilizing the rich calcium and magnesium characteristics of purified ash calcined slag,chemical methods are used to extract calcium and magnesium from it.Use ammonium chloride to leach calcium from solid,and use ammonium sulfate and sulfuric acid to leach magnesium from it.Through experimental exploration,it was found that at room temperature,the optimal conditions for leaching calcium were an ammonium chloride solution concentration of 1mol/L,a liquid-solid ratio of 40,and a reaction time of 60 minutes;When using ammonium sulfate to leach magnesium from filter residue,the leaching rate is too low at room temperature to meet the requirements;When sulfuric acid is used to leach magnesium from the filter residue,the magnesium leaching rate is 95.5% after 60 minutes of reaction.By studying the three treatment methods of calcined slag from purified ash,a new approach has been provided for the treatment of purified ash from calcium carbide furnaces,ultimately achieving the goal of comprehensive reuse of solid waste.