Study On The Technology And Performance Of α-hemihydrate Gypsum Prepared From Gypsum Solid Waste

Sulfuric acid,a basic chemical in the chemical industry,is used in all aspects of chemical production,and a relatively large amount of sulfuric acid waste stream is generated along with the production of chemicals.For the treatment of waste sulfuric acid,the neutralization method is generally used,which has the advantages of wide applicability and low treatment cost.Limestone is the most widely used neutralizing agent in the process.The use of limestone treatment will produce industrial by-product gypsum(gypsum dihydrate),which has low economic efficiency and no utilization value,and the conversion of gypsum dihydrate into α-hemihydrate gypsum is a more suitable method at present.In this paper,aramid gypsum and dye gypsum were studied,and finally,aramid gypsum was used as the reaction raw material to prepare α-hemihydrate gypsum in short column form by three methods: atmospheric pressure salt dissolution method,high pressure hydrothermal method and azeotropic reflux method.The experimental results show that:(1)the best process conditions for the preparation of α-hemihydrate gypsum by atmospheric salt solution method are 15% Na Cl solution,reaction temperature 95 ℃,slurry concentration 15%,p H 5,reaction time 3 h.When 0.03% succinic acid transcrystallizer is mixed,the transcrystallized product is α-hemihydrate gypsum with length-diameter ratio about 1:1,and the strength of transcrystallized product has a large increase,the flexural strength is 4.8 MPa,the drying compressive strength is 35 MPa,which meets the α30 strength standard in JC/T2038-2010 "α-type high-strength gypsum";(2)the best process conditions for the preparation of α-hemihydrate gypsum by high-pressure hydrothermal method are 3 h reaction time,130 ℃ reaction temperature,1:7 solid-liquid ratio,p H 5,when the transcrystallizing agent is 0.06% citric acid,the transcrystallization The strength of the trans-crystallized product is improved,the flexural strength is 4.3 MPa,and the drying compressive strength is 31 MPa in accordance with the α30 strength standard in JC/T2038-2010 "α-type high-strength gypsum";(3)the best process of preparing α-hemihydrate gypsum by azeotropic reflux method The azeotropic solvent is ethylene glycol,the transcrystallization temperature is 100 ℃,the transcrystallization time is 2 h,the crystalline water content of the reaction product is 6.1%,the compressive strength is 33 MPa,which meets the α30 strength standard in JC/T2038-2010 "α-type high-strength gypsum".The azeotropic solvent was recycled and reused three times for the transcrystallization reaction,and the drying compressive strength of the transcrystallized product was still up to 30.7 MPa.