Preparation Of Mn₃O₄and Its Adsorption Property

(1)The effects of preparative and rinsing conditions for hydrolysate on its sulfatecontent were investigated in the production of high-purity Mn₃O₄by two-step methodfrom MnSO4. The sulfate contents of hydrolysate and Mn₃O₄prepared under differentfeeding sequence, ratio of ammonia to manganese, concentration of manganese sulfatesolution, temperature and feeding rate of ammonia solution were determined. Thehydrolysates were washed with ammonia, ammonia nitrate solution and waterrespectively, and their sulfate contents of hydrolysate washed by homogenate andrinsing method were determined. The experimental results show that the hydrolysateand Mn₃O₄exhibit lower sulfate content by the addition of ammonia to manganesesolution and the yield of manganese is86.1%, the hydrolysis is preferably conductedunder following conditions: MnSO4concentration0.5mol/L, temperature60℃，ammonia to manganese ratio3:1, feeding time20min. The sulfate contents ofhydrolysate decrease sharply using homogenate washing method, which is better thanrinsing method, the sulfate content of Mn₃O₄washed with2%ammonia for2times canlower to0.09%.（2）The hydrolysis of manganese in aqueous solution of ammonium halide wasstudied. The percent of conversion was determined by the amount of released hydrogenin hydrolysis. The results show that all ammonium halide can catalze the hydrolysis ofmanganese, and the percents of conversion ascend with increasing concentration ofammonium halide. Except for NH4Br，NH4I, the conversion of system increase withelevating temperature. The percent of conversion is91⁹2%,78.81%and22.86%at40℃in0.3739mol/L NH4Br，NH4I，NH4Cl and NH4F solution, respectively.（3）Mn₃O₄was prepared by two step method using NH4Cl,（NH4）2SO4andHCOONH4as catalyst. The effects of the kind of catalyst, concentration andtemperature on catalytic reaction and products were investigated. The order of catalystand overall apparent activation energy for reaction were determined. The results showthat all above catalysts can catalyze the hydrolysis of manganese. The reaction exhibitsfirst order for catalyst at lower catalyst concentration, and it deviates from first order athigher catalyst concentration. The apparent activation energy of reaction is about20kJ/mol, indicates that reaction rate is less independent on temperature and controlled bydiffusion. Other organic ammonium carboxylates were also employed as catalysts, therates of catalytic process indicate the ammonium lactate, ammonium tartrate are moreeffective catalyst than ammonium chloride, and ammonium succinate show similarcatalytic efficiency with ammonium chloride, whereas the ammonium salt ofnitrilotriacetic acid, propionic acid, n-pentanoic acid, p-amino phenylsulfonic acid and benzoic acid show less catalytic efficiency than ammonium chloride.（4） porous Mn₃O₄was prepared by hydrolysis-oxidation method usingmanganese sulfate as raw material, the product was characterized by XRD,SEM andspecific surface area analysis. Its adsorptive manners for Cd（Ⅱ） in water under differentpH, time, dosage and temperature were investigated, as well as kinetic andthermodynamic parameters of adsorption process. The results indicate that the preparedMn₃O₄is of body-centred tetragonal, its primary size of crystallite is45.8nm，andexhibits porous structure with specific surface area of40.27m2/g. The experimentsshow that adsorptions attain equilibrium after12h with saturated adsorptive capacity of12.8mg/g at293K and pH5.5. The adsorption manner coincides with quasi-secondaryorder pattern, and its activation energy of adsorption is2.743kJ/mol. The adsorptionisotherms fit fairly with Langmuir equation, the enthalpy and entropy change are ofpositive, whereas Gibbs free energy change is of negative, which indicate a endothermicand spontaneous process.（5）The absorption of lead ion by Mn₃O₄was studied, the effects of pH ofsolution, absorbent dosage, temperature and time on absorption of lead were examined.The experimental results absorption rate for lead ion is95.3%. The lower temperature isfavorable for absorption, and absorption patterns accord with HO pseudo-second ordermodel and particle inner diffusion model and Langmuir absorption isothermic equation.△G、△H、△Sare all negative, indicating absorption is a spontaneous and exothermicprocess. and absorption activation energy is21.550kJ/mol, the absorption is based onphysical interaction.