Review of thermodynamic and kinetic investigations on lead recovery

Lead metallization in the course of processing of mineral and secondary raw materials of lead in a form of various chemical compounds (oxygen-containing and sulfur-containing) is investigated. The data on thermodynamics of lead reduction are presented for reduction from oxygen-containing compounds (oxides, sulfates, and silicates) by carbon, hydrocarbon, and sulfur-containing reducing agents at T = 298–1375 K; as well as from sulfide compounds by sulfide sulfur, hydrogen, and metal iron in the mentioned temperature range. The assumption is made on the lower energy consumption of lead reduction immediately from sulfides compared with the discussed oxygen-containing compounds. The literature data on the kinetics of preparation of metal lead are presented. It is found that the activation energy of lead reduction from the oxygen-containing compounds by natural gas is the lowest compared with reduction by carbon oxide, hydrogen, and their mixtures.     

Reduction of lead in the lead sulfide-molten sodium hydroxide system

Based on thermodynamic investigations of the reduction of lead from its sulfide compounds using the electron-donating properties of sulfur of its sulfide, we studied the effect of various factors on the reduction of lead (“metallization”) in molten sodium hydroxide. In the range of temperatures of smelting PbS with the alkali (470–510°C), there occurs a “burst” metallization reaching 95% at T = 550°C; at T = 650°C, the process is completed in 15 min; at 650–500°C, the reduction of the metal occurs in the diffusion region. The NaOH: PbS weight ratio (α) exerts a direct effect on the yield of the compact metal (‘lens’). At α = 1.8?0.8, the yield of the compact metal is 96–98%. It has been confirmed experimentally that the chemism of the utilization of elementary sulfur is related to a disproportionation of the latter with the accumulation of S^2? and SO ₄ ^2? ions and the possible formation of polysulfide sulfur S _n ^2? .     

Classification of petroleum origin and integrity by FTIR

A method was developed for classifying petroleum into four types according to their origin and integrity: marine, non-marine, degraded and thermally transformed. The method was based on the relative proportions of functional groups measured by FTIR spectroscopy. Twenty-one petroleum samples were used for model calibration and six for validation, which were pre-classified. Aliphatic functional group absorption maxima were used at 2919, 2856, 1457 and 1376 cm^?1, as well as at 1700  and 811 cm^?1 for aromatic groups, and at 1152 and 1030 cm^?1 for polar groups (sulphonyl and ether, respectively). Using hierarchical cluster and discriminate analyses, three canonic functions were obtained that classified the samples according to their origin and integrity, with a prediction efficiency of 100%, for both calibration and validation. The canonic functions derived from the discriminate analysis had correlation coefficients of 0.994, 0.900, and 0.867, among the variables studied and the classification factor. The method is efficient for the proposed classifications and can be useful for a range of applications.     

Skeletal Isomerization of n-Butene

In this review, the most relevant aspects of skeletal isomerization of n-butene to isobutene are discussed: the nature of the active sites, the prevailing mechanism of the skeletal isomerization, and the relation of this to that of n-butane. It is concluded that the prevailing mechanism of skeletal isomerization of n-butene is monomolecular (in contrast to butane isomerization) and requires Br?nsted acid (OH) active sites. The selectivity and catalytic stability can be influenced by the shape selectivity of zeolites and zeotypes. These effects are explained on the basis of the knowledge on the prevailing mechanism.