Study On Preparation And Properties Of Phosphogypsum Based Functional Foamed Gypsum

Phosphogypsum is the by-product in the wet processes of producing phosphoric acid,during which 4.5 5.5 tons of phosphogypsum will be formed for every ton of P₂O₅ production.It was reported that,the emission of phosphogypsum in China during 2016 is about 76 million tons,with a comprehensive utilization rate of 36.51%,and the total heap stock exceeds 400 million tons.The residues in phosphogypsum,such as strong acid,elements including P and F,organic matter and other impurities,enter into the ground together with the rainwater and have been polluting the soil and groundwater.Besides,phosphogypsum powders have been damaging the air condition.Therefore,how to deal with and utilize the phosphogypsum effectively has always been a worldwide problem.In order to improve the utilization rate of phosphogypsum,it is of great significance to prepare a kind of green building material with high added value.In this study,we prepared a kind of functional foam gypsum with good thermal insulation and sound absorption properties by using phosphorus building gypsum.And the bulk density and strength were expected to be controlled precisely.In addition,the effects of different dosage of calcium hydroxide on p H and strength of gypsum were studied,and the mechanism was explained.Also,retarder and water retention agent were studied on the influence of setting time of phosphorus building gypsum.What’s more,after adding SC and SA respectively and together,we studied the retarding effect under the condition of acid,weak alkali as well as strong alkali.And the optimal retarder in acidic and weakly alkaline conditions was respectively determined by comprehensive consideration of strength and setting time.Thereby,the preparation of foam gypsum by using sodium bicarbonate as foaming agents was studied and the problems were pointed out.Moreover,we primarily studied foaming process by hydrogen peroxide under the condition of acid and weak alkali,basing on which the influence of setting time,water temperature,water-gypsum ratio,p H,HPMC,Mn O₂,H₂O₂,K12 on foaming was considered.Finally,the functional modification of HPMC,K12,F10 and high strength gypsum is explored.The results showed that:1.Considering the setting time and the absolute dry strength,the SC is selected as retarder of phosphorus building gypsum in acidic conditions;under the condition of weak alkali,the mixed ratio of SC and SA was 4:1.With the increasing content of HPMC,the initial setting time of the phosphorus building gypsum increases,while the final setting time has no change.2.After adding high strength gypsum,the crystal structure of the dihydrate gypsum doesn’t change,while the setting time,bulk density and dry strength increase;Due to the difference of hydration rate,the crystallization of the two kinds of gypsum are separate and independent.Therefore,the internal stress is formed,which causes the fracture of the network part of the gypsum structure.The physical properties show that the compressive strength has a descent with its age increasing;with the content of high strength gypsum increasing,the linear expansion rate in two hours decreases first and then increases.3.The foaming effect of hydrogen peroxide is determined by multiple influencing factors rather a single one.For an excellent foaming effect,it’s essential to the balance between gas forming rate and setting rate.In weakly alkaline conditions,utilizing less catalyst can get better foaming effect which is more economical than that in acidic conditions.Thermal conductivity and absorption coefficient can be explained by the total influence of porosity,pore size and pore size rather than porosity alone.When the appearance density is same,the compressive strength of the foam gypsum is approximately the same,except which the strength is increased by using F10 and high strength gypsum.