| The electrolytic manganese residue (EMR) is a high water content residue from the production of manganese with manganese carbonate. It caused serious contamination to the environment and the residents'living. It has the features of the large capacity of drainage, which use to building materials is an effective way, but there is always a lack of breakthrough in the basic properties. What's more, there are lots of misunderstandings of some studies. Therefore, it is important to study the basic properties of EMR, especially the sulfate properties which use to the utilization of building materials.The basic properties of five different EMR samples collected from several different places were investigated by x-ray diffraction(XRD), scanning electron microscope(SEM), differential scan calorific(DSC), chemical analysis and so on. On this basis, the form and dissolution characteristics of sulfate contained in EMR were studied. Then the influence of some pretreatments for EMR on the main characteristics of sulfate was primarily studied. The results showed that:(1) The main chemical compositions of EMR are SiO2,Al2O3,CaO,SO3, it is a silica-aluminum material containing sulfate, and the main minerals of EMR are quartz, mullite, hematite, and dihydrate gypsum, which were investigated by chemical analysis and XRD. The SEM results testified that the EMR has a loose and porous microstructure and stacked up by amount of needle-like crystals and sediments.(2) EMR has much obvious gypsum peak, but the peak intensity is small, which indicated that the content of dihydrate gypsum is not high. The main forms of sulfate in EMR are dihydrate calcium sulphate, ammonium sulfate and manganese sulfate, and the slightly-dissolved dihydrate calcium sulphate accounts for 60%-70% of total sulfate of EMR.(3) In water and saturated lime water, the dissolution rate of the sulfate in EMR is rapid at primary stage, and the dissolved quantity appeared linear growth with residue-water ratio. With varies running water processing time, the content of manganese decreased significantly in seven days, the reduction value is 14.5% of undisturbed EMR. The main reason is dissolution of manganese sulfate.(4) Lime is not only beneficial to the dispersion of EMR, but also helpful to the transformation of other sulfates into dihydrate gypsum, and the increasing amount of dihydrate gypsum reached 43%. The ammonium sulfate and manganese sulfate were significantly decreased with the increase of lime and standing time. The content of ammonium sulfate and manganese sulfate approximately close to zero as the system incorporated with lime of 7%. So lime has better effect for the harmless pretreatment of EMR before comprehensive utilization.(5) After heat treatment, the main mineral compositions of the EMR are anhydrite and quartz. The thermal decomposition of sulfate is realized by stages in electrolytic manganese residue, with temperature increasing, different forms sulfate gradually decomposed. When temperatures reach 800℃, dihydrate gypsum with other impurities formed low melting compounds lead to decomposition temperature decrease and show stage. When temperatures reach 1000℃, 80% of the sulfate decomposition completely within the first five minutes, with heating time gradually decomposition also completed.(6) With the calcination temperature increased , the dissolved quantity decreased. At the same time, varies calcination age affects the dissolved quantity of sulfate in electrolytic manganese residue little. Meanwhile, when the incorporation is 7% with lime, and the calcining temperature is 200℃, the mechanical properties of EMR reached the maximum of 2.38MPa at 28 day of age. Compared with undisturbed EMR, chemical activity was significantly increased.The results indicated that detailed understanding of EMR is beneficial to its used for the building materials. |
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