Study on iron removal and phase transition behavior of titanium gypsum in acidic solution
Objectives This study aims to address the issue of impurities in titanium gypsum and investigate the phase transformation behavior of gypsum under atmospheric pressure.Methods Industrial solid waste ti-tanium gypsum was used as the raw material and treated with an acidic solution leaching method.The phase composition and chemical composition of the reaction products were analyzed using X-ray diffraction(XRD)and X-ray fluorescence(XRF),respectively.The phases of the products were identified,and the iron removal rate and gypsum content were quantitatively evaluated to characterize the efficiency of iron re-moval.The effects of various factors,including raw material preparation,the type and concentration of acidic solutions,reaction temperature,and reaction time,were investigated to determine the iron removal efficiency and the phase transformation behavior of titanium gypsum.An ultra-depth-of-field microscope was employed to observe the microstructure of raw materials and products,thereby verifying the iron removal effect of titanium gypsum in acidic solutions.Results Sulfuric acid demonstrated the best iron removal perfor-mance compared to hydrochloric acid,oxalic acid,and nitric acid,without generating other impurities.With increasing acid concentration,the phase transformation from gypsum dihydrate to anhydrite occurred in sulfuric acid solutions,while the transformation from gypsum dihydrate to hemihydrate gypsum was ob-served in both nitric acid and hydrochloric acid solutions.In oxalic acid solutions,calcium oxalate was ulti-mately formed.For reactions in sulfuric acid,higher acid concentration,reaction temperature,and reaction time promoted the transformation of gypsum dihydrate to anhydrite.When untreated(unmilled and un-dried)raw materials were used,the phase transformation was not affected,reducing the operational steps and energy consumption in raw material preparation and thereby lowering the pretreatment cost of titanium gypsum.Conclusions This study provides an effective method to remove impurities from titanium gypsum,reduce energy consumption and costs,and elucidate the phase transformation pathways between gypsum di-hydrate,hemihydrate gypsum,and anhydrite.The findings supplement the understanding of gypsum perfor-mance variations and broaden the potential applications of gypsum resource reutilization.
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