Calcified And Decomposition Of Jarosite And Preparation Of Mortar From Gypsum Sediment

Jarosite is the main phase of jarosite slag.Jarosite slag is an industrial waste discharged in the process of wet zinc smelting,which is planned as a kind of hazardous solid waste.At present,more than 1 million tons of dangerous waste jarosite residue will be produced in China every year.A large amount of jarosite slag is treated by stacking,which wastes not only the rich metal resources in jarosite slag,but also a lot of land resources.Therefore,in this paper,calcium oxide is used to decompose jarosite,and its calcification product gypsum is used to prepare self-leveling mortar to realize its resource utilization.The effects of admixtures on the morphology of iron hydroxide and calcium sulfate dehydrate were researched by using Fe₂(SO₄)₃,ammonia and CaO as raw materials.Adding cetyltrimethyl ammonium bromide(CTAB),sodium dodecylbenzene sulfonate(SDBS)and citric acid(CA).It was found that CTAB can change the morphology of gypsum from needle or column to flake.The dispersion of ferric hydroxide colloid changed from good to bad with the increase of the amount of iron hydroxide.However,CTAB has no effect on the adsorption of iron hydroxide colloid on the surface of iron-bearing gypsum;after the addition of SDBS,fine gypsum grains increase and large particles decrease,and the dispersion of iron hydroxide colloid becomes better with the increase of SDBS addition.However,SDBS has no effect on the adsorption of iron hydroxide colloid on the gypsum surface in iron-containing gypsum;CA can change the gypsum morphology from needle or column to flake,and the dispersion of iron hydroxide colloid becomes better with the increase of adding amount,and the effect is the best at 1.5%.When the addition of CA is2.0%,the separation of iron and gypsum in iron-containing gypsum is obvious,and does not affect the growth of gypsum,so CA is the best admixture.The effect of Zn on the phase composition and morphology of jarosite were researched by using Fe₂(SO₄)₃ and(NH₄)₂SO₄ plus ZnSO₄ as raw materials,.It was found that there was little difference in composition,phase and morphology of the products,and only a small amount of Zn existed in jarosite crystals by EDS.Then the ammonium jarosite was decomposed by CaO calcification,and 2.0%CA was added.The effects of the amount of CaO and reaction time on the decomposition products were studied.The optimum dosage of CaO was 30%,and the reaction time was 12h.Then the calcification product is separated by heavy liquid and it was found that the upper separation product was dihydrate gypsum and the lower separation product was iron oxide.The process of preparing high strength gypsum by separating dihydrate gypsum from calcification products was studied.The optimum conditions were as follows:hydrothermal temperature 140?,hydrothermal time 3h,solid-liquid ratio 1:4.The compressive strength of high strength gypsum is 27.99 MPa.Finally,using high-strength gypsum as cementitious material,the effects of pozzolanic material,polyvinyl alcohol emulsion,protein retarder and silicone hydrophobic agent on the properties of gypsum-based self-leveling mortar were studied.The results show that when the optimum ratio(wt%)of pozzolanic material A,pozzolanic material B,PVA and protein retarder is 37.5: 12.5: 4: 0.12,the standard consistency of gypsum-based self-leveling mortar is 0.53,the initial setting time is 61 min,the final setting time is 126 min and 30 min,the 30 min fluidity is 140 mm,the compressive strength is 20.21 MPa,the absolute dry tensile bond is 1.17 MPa,and the dimensional shrinkage is 0.04%.All the indexes meet the requirements of JC/T1023-2021 standard,and the softening coefficient is 0.83.In order to further improve the water resistance of mortar,the effects of different waterproofing agents on the softening coefficient of gypsum-based self-leveling mortar were studied.It was found that the softening coefficient of organosilicon water-repellent agent could be increased to 0.9,reaching the super water-resistant grade.