Preparation And Properties Of ?-gypsum-based Self-leveling Materials

Phosphogypsum is a by-product produced by the phosphate fertilizer industry during the wet process of phosphoric acid,4.5 ~ 5.5 tons Phosphogypsum are generated when per ton of P2O5 are produced.It is estimated that the accumulative Phosphogypsum is over 300 million tons all over the world every year,including our country's phoshpogysum emission about 80 million per year.Due to the influence of the harmful impurities in phosphogypsum,It is limited to use in chemical raw,subgrade,gesso building materials,Currently the mainly way of disposal phosphogypsum is stockpilling,This not only takes up a lot of lands and wastes of calcium and sulfur resource utilization in phosphogypsum,but also causes serious pollution of soil,groundwater and atmosphere for the phosphogypsum of phosphorus,fluorine and other harmful substances.The processing of phosphogypsum has become an important factor restricting the development of phosphate & compound fertilizer industry.At present,the preparation of using phosphorus gypsum based building materials is still in its primary stage for our country,It is urgent to use the industrial by-product gypsum of preparing high strength and high value-added gypsum materials with lacking the resources and the growing scarcity of energy,and the gypsum based products is the urgent need of social sustainable development and the important direction of gypsum.This subject is mainly impoved the process during wet-process phosphoric acid.Normally nitric acid is used to decompose phosphate rock,adding sulfuric acid to phosphate rock acid solution preparation of ?-calcium sulfate hemihydrate(?-HH),and use the ?-HH as the basic material preparation of ?-gypsum based self-leveling material,thus avoiding the discharge which plent of phosphorus gypsum created in the traditional wet-process phosphoric acid industry.This study comprehensivly research the atmospheric acidification process parameters and crystal agents which influence the ?-HH crystal morphology,it also study the ?-gypsum based self-leveling mortar which material compositions impact on its performance.Using XRD and SEM analyze the hydration products and hydration mechanism of the material.The results showed that:1.We can obtian the ?-HH that reaches JC / T 2038-2010 "?-type high-strength gypsum" in the provisions of ?25 levels when the atmospheric acidification processparameters: phosphoric acid concentration is 40%,the reaction temperature is 97 ?,the stirring intensity of 350 r/min,sulfuric acid concentration is 40%,the optimum content of OSM crystal agent is 0.2%,and the length to diameter ratio of the product is about 2 under this condition.2.We can get the three main surface energies of ?-HH crystals(111),(110)and(010)which respectively are 0.6991J/m2,1.3334J/m2 and 1.8309J/m2 through computer simulation.The order of three surfaces importance to ?-HH crystal morphology is(111)>(110)>(010).It is description that crystal agent control ?-HH crystal morphology mainly through adsorbing on the(111)crystal surface,thus inhibiting the lattice plane grow up fast and making the crystal growth rate and reducing the length to diameter ratio,and the crystal finally is short column.3.through the experiment of alpha gypsum based self-leveling material mixture ratio(quality percentage of components regard ?-HH and quartz's quality as a benchmark): basic material: ?-HH 60%;aggregate: quartz 40%;cement 6%;admixture: limestone powder 2%;Superplasticizer: PC 0.2%;retarder: sodium tripolyphosphate 0.1%;water retention agent: HPMC 0.15%;latex powder 1.5%;defoaming agent: organic silicone oil 0.1%.The gypsum based self-leveling material main performance parameters meet the request of JC/T1023-2007 "gypsum based self-leveling mortar",it is a kind of excellent performance of ground-leveling material.