Preparation Of Calcium Sulfate Whisker By Semi-Dry Desulfurization Residues

In recent years,the treatment and comprehensive utilization of desulfurization residues attract more and more attentions.Desulfurization residues are mainly used in fields of building materials,subgrade construction,mine filling.But the majority of desulfurization residues are held in ash dams or similar dumps.If desulfurization residues can be effectively used,waste resources can be used,and environmental problems produced by solid waste accumulation can be solved,as well.Despite the uses above,desulfurization residues which contain high content of calcium sulfate can be used to prepare calcium sulfate whiskers.Calcium sulfate whiskers have lots of advantages.High strength,high modulus,high ductility,high insulation,anti-corrosionand innocuity are included.With excellent physical and chemical properties,calcium sulfate whiskers can be widely used inflexibilizer and functional filler,such as,resin,plastic,rubber,paint.Calcium sulfate whiskers can also be used as filter materials,insulation materials,insulating refractory materials.At first,pretreatment of semi-dry desulfurization residues was carried on to remove iron and change the calcium containing compounds to calcium sulfate.The compounds include calcium sulfite,calcium oxide and calcium hydroxide.Then semi-dry desulfurization residues after pretreatment was processed to prepare calcium sulfate whiskers by hydrothermal method.Preparation of calcium sulfate whiskers with and without additives was studied in the process of hydrothermal synthesis reaction.Without additives,the influence of slurry concentration,reaction temperature,initial pH value of slurry and reaction time on the morphology of calcium sulfate whisker was studied to obtain the optimum preparation conditions.It showed that optimum conditions of using semi-drydesulfurization residues to prepare calcium sulfate whiskers through the methods of hydrothermal synthesis reaction are slurry concentration of 3%,reaction temperature of 120?,initial pH value up to 9.25,reaction time of 120 min.And calcium sulfate whiskers with length of 89?m and aspect ratio of 29.67 were obtained.Then,sodium oleate,sodium dodecyl benzene sulfonate and sodium citrate were added to the process of preparation of calcium sulfate whisker respectively to investigate the impact of different additives on themorphology of calcium sulfate whiskers.Mechanisms of the additives were analyzed.It showed that calcium sulfate whisker with better morphology of length of 125?m and aspect ratio of 41.67 was obtained with adding 0.1%of sodium dodecyl benzene sulfonate.Finally,the crystal growth of calcium sulfate whiskers in the process of hydrothermal synthesis reaction was further investigated by means of thermodynamics and molecular dynamics simulation.Combining with crystal face parameters calculated by molecular dynamics simulation,analysis of crystal faces by XRD was conducted to analyze surface atomic distribution on parts of the crystal face.Simulations of the roles which different additives play on differentcrystal faces respectively were used to further illustrate the mechanisms of the additives.For the analysis of crystal faces,it has been showed that diffraction peak intensity of crystal faces of(400)and(200)increased under the influence of sodium oleate.It promoted the crystal growth along c-axis.The effect of sodium dodecyl benzene sulfonate was similar to that of sodium oleate.Crystal faces of(400),(200)and(020)are the faces which have the top three diffraction peak intensity.Results that molecular dynamics simulation of energy calculated are basically identical with the results of analysis of crystal faces.