Study On Chemical Synthesis And Adsorption Properties Of Active Magnesium Oxide

Abstract:The concent of MgO and SiO2accounts for80%of the total amount of asbestos tailings, so extracting magnesium resource from asbestos tailings to prepare active MgO is not only good for the properly dispose of asbestos tailings, but also helpful for the ecological civilization construction. Taking MgSO4solution obtained from asbestos tailings after acid leaching and purification as the raw material, NaOH and CO(NH2)2as precipitating agent, Mg(OH)2and Mg5(CO3)4(OH)2·4H2O precursors were successfully synthesized by a simple liquid phase method. The precursors were annealing at low temperature to obtain the active magnesium oxide. The active magnesium oxide prepared by Mg(OH)2precursor was used as the adsorbent, and the adsorption behaviors of the active magnesium oxide to Congo Red azo dye were studied. The main results of this paper are as follows:(1) Optimal conditions for the preparation of active magnesium oxide by Mg(OH)2precursor are as follows. The reaction temperature is40℃,the concentration of NaOH is3mol/L, the molar ratio of OH-/Mg2is2.4, aging time is2h and the calcinations condition is350℃for2h. Under this condition, the active magnesium oxide sample is cubic system MgO, its specific surface area is83.39m2/g, pore volume is0.5003cm3/g, average pore diameter is22.94nm, and the iodine number can be reached up to260mg/g(2) Optimal conditions for the preparation of active magnesium oxide by Mg5(CO3)4(OH)2·4H2O precursor are as follows. The reaction temperature is120℃, the concentration of CO(NH2)2is3mol/L, the molar ratio of CO(NH2)2and MgSO4is18, aging time is6h and the calcinations condition is500℃for2h. The decomposition of the precusor is two-step process. The first step is the loss of crystallization water and the following step are dehydroxylation and decarbonization, the precursor can be well decomposed to MgO after these two steps. And the most probale mechanism models of the two steps are An and D3, respectively. The obtained active magnesium oxide sample is cubic system MgO, its specific surface area is57.53m2/g, pore volume is0.227cm3/g, average pore diameter is15.78nm, and the iodine number can be reached up to220mg/g.(3) The active magnesium oxide exhibits excellent Congo Red removal performance, and the maximum adsorption capacity is2740mg/g. The adsorption isotherm curve can be well correlated by Langmuir equation, and the adsorption process is satisfied with pseudo-second order model.