Study On Gelling And Water-resistance Of Phosphogypsum By Fast-burning

Phosphogypsum(PG), mainly of CaSO4·2H2O,is an industrial by-product producedin the wet process of phosphoric-acid manufacture. The performance is similar tonatural gypsum(NG), but contains a small amount of impurities,which are notconducive to materials recycling use such as soluble phosphorus.UsingPhosphogypsumas gypsum cementitious material directly exist an adversely affected.Using the impurities of Phosphogypsum at high temperaturestransform into inertsubstance.With the method of fast burning to treat Phosphogypsum, to eliminate theeffects of soluble phosphorus impurities on the performance of phosphogypsum.Usingthe characteristics which partially dehydrated of phosphogypsum in the fast burning,tocombine removing impurity with preparing gypsum cementitious materials. Bystudying on the phase composition of the product which deal with by fast burning，Then analysis its gelling and water resistance, to provide a feasible way for thepreparation of phosphogypsum cementitious materials.Using fast burning to treat phosphogypsum with high-temperature furnace, Resultsshowed that the soluble phosphorus decrease obviously，but the total phosphoruscontent is constant,the content of soluble phosphorus reduced significantly,transforminto an inert substance called Ca(PO3)2to exist in the Phosphogypsum probably bymixing Ca(H2PO4)2.Using microscopic analysis methods such as x-raydiffraction (XRD), thermalgravimetric analysis (TG-DSC),X-ray fluorescence spectrometry (XRF) and scanningelectron microscope (SEM), To analysis the the phase composition of Phosphogypsumafter fast burning,dehydration performance and microstructure.The results showed thatFast burning also have a great influence on the dehydration temperature and the degreeof dehydration.It can produce the product which contains CaSO4·2H2O,β-CaSO4·1/2H2O, Ⅲ-CaSO4and II-CaSO4, product component has a good influenceon the fast burning system, Dehydration temperature has a regular change with thesoluble phosphorus content. The degree of dehydration was affected by phasecomposition of the product.and there are major changes of microstructure with thechange of phase composition.To research on the phosphogypsumof macroscopic physical properties after fastburning,The results showed that: phase composition have a good affects on setting timeand normal consistency.the more β-CaSO4·1/2H2O and Ⅲ-CaSO4, the greater ofnormal consistency.with the β-CaSO4·1/2H2O generated, setting time becomes shorter,with the II-CaSO4generated,setting time extended.with the increase of β-CaSO4·1/2H2Oin phosphogypsum, The strength of phosphogypsum after fast burning increase,II-CaSO4in the phosphogypsum can added the strength after fast burning.The humidity conditionsalso can affect the strength of phosphogypsum whichtreated by fast burning, The strength of15s fast burning phosphogypsum at96.5%humiditydecreased significantly,but30s fast burning phosphogypsum has somegrowth.the more II-CaSO4component, the greater the intensity of growth,indicating thatthe II-CaSO4in phosphogypsum can delay the strength loss in thehumid environments.K2SO4has a certain effect on the II-CaSO4which is generated after fastburning,the more II-CaSO4component,the strength of phosphogypsum increase more,especially for the product which treated by850℃、30s.Fast burning can impact on the water resistance of phosphogypsum,the fastburning product which time is30seconds have a better water resistance thanphosphogypsum which time is15s and150℃、4h,, II-CaSO4in phosphogypsum alsocan improve the water resistance of phosphogypsum.