Effects Of Preparation Technology And Crystal Modifier On The Morphology And Mechanical Properties Of α-hemihydrate Gypsum

Phosphogypsum originates from the by-product of phosphorus chemical production.Due to the large amount of impurities and poor mechanical properties,it cannot be directly used to prepare gypsum products.The accumulation of a large amount of phosphogypsum not only causes serious damage to land and environmental resources,but also limits the The development of my country’s phosphorus chemical industry.In order to solve the problem that phosphogypsum is difficult to reuse,this project converts phosphogypsum into usable α-hemihydrate gypsum by pressurized aqueous solution method.The influence of mechanical properties was investigated,and then the regulation mechanism of crystal modifier on product morphology was discussed.The main research contents and r esults are as follows:1)Through the water washing-flotation-lime neutralization pretreatment process,the mechanical properties of the α-hemihydrate gypsum products prepared by the pressurized aqueous solution method can be improved.The order of influen ce of dry compressive strength is: autoclaving time > autoclaving temperature > water-material ratio.The α-hemihydrate gypsum samples were prepared when the autoclaving temperature was 130 °C,the holding time was 6 h,and the water-material ratio was0.5.Good mechanical strength and low energy consumption.2)Different crystal modifier have different effects on the morphology regulation of α-hemihydrate gypsum.The control effect is: carboxylate > inorganic salts >alcohols and macromolecules;the samples prepared with aluminum sulfate as crystal modifier,The crystals are large,uniform in size,and mostly long columnar in shape.When the dosage of sodium citrate is 0.3wt.%,crystals with an aspect ratio of 2:1 can be prepared.The α-hemihydrate gypsum crystal prepared by potassium oxalate is composed of A small amount of large crystals and many fine crystals are composed,while alcohols and their macromolecules,due to the adsorption of their hydroxyl groups,are mostly long fibrous crystals.3)Experiments show that metal cations do not adsorb on the crystal surface,carboxylates can control the growth rate of crystals by selectively adsorbing on different crystal planes,alcohols and macromolecules are not selectively adsorbed;except for sodium citrate,other kinds of crystal modifier can improve the mechanical strength of the prepared α-hemihydrate gypsum samples within a certain range.4)Based on aluminum sulfate,the conforming crystallizing agent prepared can effectively improve the crystal morphol ogy and mechanical properties of the preparedα-hemihydrate gypsum.When the total dosage of crystal modifier is 0.6wt.%,aluminum sulfate and oxalic acid The α-hemihydrate gypsum prepared when the potassium content ratio is 5:1 is the best,with smooth cr ystal surface and few defects.The 2h flexural strength and 2d dry compressive strength of the hydrated samples can reach 5.88 MPa and 36.90 MPa,respectively5)Using the existing horizontal autoclave and technology can be used as an effective way to realize the industrialized production of α-hemihydrate gypsum.