Studies on the kinetics of dissolution of a Nigerian lateritic soil in acids media including hydrochloric, nitric and sulphuric acids have been undertaken. The elemental and mineralogical characterization, loss of mas...Studies on the kinetics of dissolution of a Nigerian lateritic soil in acids media including hydrochloric, nitric and sulphuric acids have been undertaken. The elemental and mineralogical characterization, loss of mass on ignition, moisture content and pH of the material suspension in water were determined. The effects of acid concentration, process temperature, stirring rate and particle size on the dissolution rate were investigated. Experimental results indicated that laterite dissolution was greatly influenced by hydrogen ion concentration and the leaching data fitted a diffusion model. The linear dependence of the rate constant k on 1/ro 2 supported the proposed kinetic model. Values of 60.23 kJmol-1, 64.31 kJmol-1 and 67.53 kJmol-1 were obtained for the activation energies of laterite dissolution in hydrochloric, nitric and sulphuric acids respectively;and the order of reaction was approximately one with respect to each of the three acids.展开更多
Solidification/stabilization(S/S)technology has been widely used for remediation of the heavy metal contaminated soils.The heavy metal ions will be leached from the stabilized contaminated soil under sulfate erosion c...Solidification/stabilization(S/S)technology has been widely used for remediation of the heavy metal contaminated soils.The heavy metal ions will be leached from the stabilized contaminated soil under sulfate erosion conditions,which gives rise tosecondary contamination to the areas around the mine sites.The commonly used Portland cement,fly ash and quicklime were takenas binder raw materials with various mix proportions.And then,the sulphuric acid and nitric acid method was used to investigate theleaching characteristic of stabilized heavy metal contaminated soils.The effects of binder types and binder contents,sulfateconcentrations(1.5,3.0and6.0g/L)and erosion time(0,7,14and28d)on leached concentrations of heavy metal ions fromcontaminated soils were studied.Moreover,a parameter named immobilization percentage(IP)was introduced to evaluate theinfluence of erosion time and sulfate concentration on immobilization effectiveness for heavy metal ions.The results showed that,theleached heavy metal concentrations increased with sulfate concentration and erosion time.Comparatively speaking,the compositebinders that had calcium oxide in it exhibited the worst solidification effectiveness and the lowest immobilization percentage,withthe largest leached heavy metal concentration.展开更多
Sodium azide is a widely used inorganic compound. Besides the commonly used method of ＂Wislicenus process＂ which uses ammonia, nitrous and sodium as materials, the hydrazine hydrate route is also employed for the pr...Sodium azide is a widely used inorganic compound. Besides the commonly used method of ＂Wislicenus process＂ which uses ammonia, nitrous and sodium as materials, the hydrazine hydrate route is also employed for the preparation of sodium azide particularly in laboratory. However, because many species are involved in the reaction system, the reaction details for the hydrazine hydrate route are still unclear. A comprehensive understanding of the reaction mechanism may provide meaningful help for optimizing the production process. In this work, the reaction mechanism for the synthesis of sodium azide by hydrazine hydrate route has been studied using density function theory（DFT） method. On the basis of our calculations, the reaction details, including the energetics of ten elementary steps, the structures of intermediates and transition states as well as the influence of inorganic acids and alcohols, were illuminated at the atomistic level. Both the two steps, the generation of key intermediate（NH2-NH-NO） and the trans-cistransformation of NH2-NH-NO, are suggested to be the possible rate-limiting step, corresponding to the energy barriers of 20.3 and 22.7 kcal/mol, respectively. In the early reaction steps to generate NH2-NH-NO, the main role of sulphuric acid is to donate proton, which can be replaced by nitric acid or hydrochloric acid. From the energy point of view, isopropanol has similar reactivity as methanol and ethanol.展开更多
文摘Studies on the kinetics of dissolution of a Nigerian lateritic soil in acids media including hydrochloric, nitric and sulphuric acids have been undertaken. The elemental and mineralogical characterization, loss of mass on ignition, moisture content and pH of the material suspension in water were determined. The effects of acid concentration, process temperature, stirring rate and particle size on the dissolution rate were investigated. Experimental results indicated that laterite dissolution was greatly influenced by hydrogen ion concentration and the leaching data fitted a diffusion model. The linear dependence of the rate constant k on 1/ro 2 supported the proposed kinetic model. Values of 60.23 kJmol-1, 64.31 kJmol-1 and 67.53 kJmol-1 were obtained for the activation energies of laterite dissolution in hydrochloric, nitric and sulphuric acids respectively;and the order of reaction was approximately one with respect to each of the three acids.
基金Project(41472278) supported by the National Natural Science Foundation of ChinaProject(2015B071) supported by the Beijing Nova Program,ChinaProjects(53200859533,53200859536) supported by the Fundamental Research Funds for the Central Universities of China
文摘Solidification/stabilization(S/S)technology has been widely used for remediation of the heavy metal contaminated soils.The heavy metal ions will be leached from the stabilized contaminated soil under sulfate erosion conditions,which gives rise tosecondary contamination to the areas around the mine sites.The commonly used Portland cement,fly ash and quicklime were takenas binder raw materials with various mix proportions.And then,the sulphuric acid and nitric acid method was used to investigate theleaching characteristic of stabilized heavy metal contaminated soils.The effects of binder types and binder contents,sulfateconcentrations(1.5,3.0and6.0g/L)and erosion time(0,7,14and28d)on leached concentrations of heavy metal ions fromcontaminated soils were studied.Moreover,a parameter named immobilization percentage(IP)was introduced to evaluate theinfluence of erosion time and sulfate concentration on immobilization effectiveness for heavy metal ions.The results showed that,theleached heavy metal concentrations increased with sulfate concentration and erosion time.Comparatively speaking,the compositebinders that had calcium oxide in it exhibited the worst solidification effectiveness and the lowest immobilization percentage,withthe largest leached heavy metal concentration.
基金supported by the National Natural Science Foundation of China(21773138)
文摘Sodium azide is a widely used inorganic compound. Besides the commonly used method of ＂Wislicenus process＂ which uses ammonia, nitrous and sodium as materials, the hydrazine hydrate route is also employed for the preparation of sodium azide particularly in laboratory. However, because many species are involved in the reaction system, the reaction details for the hydrazine hydrate route are still unclear. A comprehensive understanding of the reaction mechanism may provide meaningful help for optimizing the production process. In this work, the reaction mechanism for the synthesis of sodium azide by hydrazine hydrate route has been studied using density function theory（DFT） method. On the basis of our calculations, the reaction details, including the energetics of ten elementary steps, the structures of intermediates and transition states as well as the influence of inorganic acids and alcohols, were illuminated at the atomistic level. Both the two steps, the generation of key intermediate（NH2-NH-NO） and the trans-cistransformation of NH2-NH-NO, are suggested to be the possible rate-limiting step, corresponding to the energy barriers of 20.3 and 22.7 kcal/mol, respectively. In the early reaction steps to generate NH2-NH-NO, the main role of sulphuric acid is to donate proton, which can be replaced by nitric acid or hydrochloric acid. From the energy point of view, isopropanol has similar reactivity as methanol and ethanol.
