Oxidation And Resource Utilization Of Industrial Wet Desulfurization Slag

Environmental protection is taken increasing attentions by the government and the society.With the stricter requirements of industrial waste gas emissions for the new environmental laws,the problem of waste treatment has emerged.In this paper,large amount of calcium sulfite exists in the desulfurization slag which is obtained from Hechi Wuji co.LTD was oxidized into dihydrate calcium sulphate with air used as an oxidation.We have found that the pH was the most important factor affects the calcium sulfite oxidation process.Combined with the results of single-factor experiments,the optimum operating parameters that pH of 4.0,air flow of 600 mL/min,temperature of 50 ? and the reaction time of 6 hours were determined.This oxidation solution is a stable,reliable and low cost operation.The further utilization of calcium sulfate dihydrate,which is an oxidation product of desulfurization waste residue,is explored.The method of preparation the high added value product,alpha half calcium sulfate and alpha calcium sulphate whisker was studied.We found that use hydrothermal method while the ratio of material 1:6,reaction would be better in the conversion to alpha calcium sulfate hemihydrate.While the reaction time was more than 6 h calcium sulfate dihydrate can be better dehydration into a-hemihydrate calcium sulfate,of which crystal was with the length/diameter ratio of 4 to 15 and crystalline perfection.It was also found that the addition of the crystal modifier,citric acid and sodium dodecyl benzene sulfonate(SDBS)would change the crystallization characteristics of calcium sulfate hemihydrate.At the same time,the influence of solvent on the crystallization of calcium sulfate hemihydrate was studied.It was found that under the 15%CaCl2(wt%)solution,the crystallization of calcium sulfate hemihydrate was not significant.The crystallization of ?-hemihydrate calcium sulfate would be thick while under the solution of 60%glycol.The crystallization was significantly different from the normal hydrothermal conditions.The dehydration time of calcium sulphate dihydrate has been shortened to about 30 min by microwave hydrothermal method,which is 90%shorter than the ordinary hydrothermal method.The influence of microwave environment on the crystallization of ?-hemihydrate calcium sulfate was also studied.It was found that the crystalline particles were finer when heated by microwave.The effects of citric acid,sodium dodecylbenzene sulfonate and aqueous solution of ethylene glycol on the morphology of ?-hemihydrate calcium sulfate were investigated.The alpha-hemihydrate calcium sulfate whisker could be obtained in ethylene glycol solution or pure ethylene glycol while heated by microwave.Compared with the ordinary hydrothermal method,the advantage of microwave hydrothermal method is not lower energy consumption but also faster reaction.This method has a broad application foreground.