Research On The Preparation Of Hydrophobic Phosphor Gypsum And It Properties

Phosphor gypsum(PG), a byproduct of high-concentration phosphate fertilizer, phosphate fertilizer or wet processed phosphoric acid, has high content of CaSO4·2H2O, and a small quantity of some impurities such as phosphorite, phosphoric acid, calcium fluoride, alumina, ferric oxide and organism. Similar to nature gypsum, the hard product of PG is a porous material, which has strong ability of absorbing water. After hard product of PG absorbs water, the crystal node of PG would dissolve in water, resulting to the recrystallization among crystals and decreased strength of PG products. Thus it would influence the application of the hard product of PG. The aim of this thesis are improving hydrophobicity of the hard product of PG, and expanding the application.This thesis starts on the preparation of a stable paraffin emulsion。The combination of O-D emulsified and PIT method is adopted. The factors, such as HLB value, the dosage of emulsifier, the way of adding emulsifying water, emulsifying time, emulsifying temperature, stirring method and rate are studied when liquid paraffin is used as raw material, Span80 and Tween80 as complex emulsifier, and 1.3-BDL as auxiliary emulsifier. Furthermore, the condition of preparation of paraffin emulsion is optimized through the orthogonal experiment using the great function of design and data analysis in SPSS16.0. The optimum emulsifying conditions were obtained. Under this condition, the average size of the prepared emulsion is 0.169μm, and the stability and dispersion are quite good when the value of HLB is 10.6, the dosage of emulsifier(M乳化剂/M石蜡) is 30%, the water-oil ratio(M水/M石蜡)is 3.5, the stirring rate(ω)is 800r/min, the emulsification temperature is 75℃,and the pH value is 10.0.Effects of the prepared paraffin emulsion,Nano-organosilicon,salt water-reducing agents,(polyvinyl alcohol)PVA,triethanolamine,hydrophobization agent A on improving water absorptivity of PG are discussed through single factor experiment. Based on this, influence of paraffin emulsion,Nano-organosilicon,triethanolamine,hydrophobization agent A on improving water absorptivity and compression strength of PG is investigated through SPSS16.0. The hardened PG is prepared under the best matching condition through orthogonal experiment, the best matching condition is obtained when the quantity of paraffin emulsion is 8%, Nano-organosilicon 1.8%, salt water-reducing agent 0.3%,PVA 0.3%,triethanolamine 0.7%,hydrophobization agent A 1.8%. Under this condition, the water absoptivity of prepared PG is 1.89%, and the compressive strength is 5.4MPa. Such performance indexes could meet the national standards.The comparative experiment between the bland PG product and modified hardened PG is conducted. By analyzing the water absorptivity, compressive strength, and SEM figure, the influence of compound repelling agent on the crystal growth,degree of density,strength of PG is investigated.