Influence of different additives on the mechanical performance of a-hemihydrate gypsum from phosphogypsum

a-hemihydrate gypsum is synthesized from phosphogypsum and the influence of a CaO treatment, the solution pH and a maleic acid addition on the microstructure have been systematically investigated.The influence of the resolvable phosphorous on the microstructure of hemihydrates gypsum can be reduced by CaO treatment.The mid-diameter of the columnar crystals decreases and the crystal surface becomes smooth with the solution pH decrease.Moreover, the addition of maleic acid changed the crystal growth direction and equiaxed a-hemihydrates gypsum crystals were obtained in a pH=2 solution.Furthermore, the effect of different additives, such as Portland cement and circulating fluidized bed slag, on the morphology and mechanical properties of hemihydrates gypsum was also studied.It was observed that the compressive strength decreased after the addition of Portland cement and circulating fluidized bed slag.Keywords: phosphogypsum, a-hemihydrates gypsum, crystal morphology, Portland cement, circulating fluidized bed slag,mechanical performance Avtorji so sistemati~no raziskovali a-hemihidratni mavec (CaSO4•0,5H2O), ki so ga sintetizirali iz fosfatnega mavca.Analizirali so vpliv obdelave s CaO, kislosti (pH) raztopine in dodatka metanojske (mravljin~ne) kisline na mikrostrukturo.Vpliv topnega fosforja na mikrostrukturo hemihidratnega mavca se lahko zmanj{a s CaO obdelavo.Avtorji so ugotovili, da se povpre~ni premer stebri~astih kristalov zmanj{uje in kristalna povr{ina postaja bolj gladka z zman{evanjem pH raztopine.Nadalje ugotavljajo, da dodatek mravljin~ne kisline spremeni smer rasti kristalov in pri pH raztopine je enako 2, nastajajo enakoosni kristali a-hemihidratnega mavca.[tudirali so tudi vpliv drugih dodatkov, kot je dodatek Portland cementa in `lindre iz vrtin~aste plasti, na morfologijo in mehanske lastnosti mavca.Ugotavljajo, da se tla~na trdnost mavca zmanj{uje z dodatkom Portland cementa in `lindre izdelane v vrtin~asti lebde~i plasti.