黄铁矿(100)表面性质的密度泛函理论计算及其对浮选的影响

采用密度泛函理论(DFT)平面波赝势方法计算理想黄铁矿(100)表面的结构弛豫、原子的Mulliken布居以及电子结构,并解释黄铁矿体相中电荷分布异常的原因。从浮选角度分析表面结构和性质对黄铁矿浮选行为的影响。结果表明:黄铁矿(100)表面弛豫较小,表面Fe-S相互作用相对于体相增强;表面5配位的铁原子具有较高的活性;表面层铁硫原子的能隙降低;表面层的导电性强于体相的,表面的电化学活性增强。

含空位缺陷黄铁矿(100)表面吸附氢氧根和羟基钙的量子化学研究

采用密度泛函理论方法研究硫空位和铁空位缺陷对氢氧根和羟基钙在黄铁矿表面吸附的影响。计算结果表明,铁空位能减弱氢氧根的吸附,硫空位能促进氢氧根的吸附,而铁空位和硫空位缺陷都能增强羟基钙在黄铁矿表面的吸附。氢氧根在硫空位缺陷形成的活性铁原子上的吸附能力比在铁空位缺陷形成的活性硫原子上的吸附能力强。对于羟基钙分子,在硫空位缺陷存在的情况下氧原子与黄铁矿表面铁原子成键,在铁空位缺陷存在的情况下钙原子与周围的硫原子发生作用,从而促进了钙原子在黄铁矿表面空位缺陷处的吸附。

在煤的浮选中用磷酸盐抑制黄铁矿

利用各种无机的和有机的化学药品系统地研究了肯塔基9号煤层的黄铁矿的选择性抑制。所试验的大部分有机化学药品在抑制黄铁矿时选择性很小。发现在用燃料油作捕收剂时,正磷酸盐和焦磷酸盐对于煤浮选中含煤黄铁矿的选择性抑制是有效的。在相当低的焦磷酸盐浓度下,在宽广的pH范围内,含煤黄铁矿的浮游完全被抑制了,而煤的浮选保持不受影响。借助铁-磷酸盐-水体系的热力学计算和ξ-电位测定,解释了黄铁矿被磷酸盐选择性抑制的机理。发现焦磷酸盐与黄铁矿的铁离子在黄铁矿表面剧烈作用生成稳定的亲水的铁焦磷酸盐络合物。

Mineral cleavage nature and surface energy: Anisotropic surface broken bonds consideration

The population of surface broken bonds of some typical sulfide, oxide and salt-type minerals which may belong to cubic, tetragonal, hexagonal, or orthorhombic system, were calculated. In terms of the calculation results, the cleavage natures of these minerals were analyzed, and the relationship between surface broken bonds density and surface energy was also established. The results show that the surface broken bonds properties could be used to predict the cleavage nature of most of minerals, and the predicted cleavage planes agree well with those reported in previous literature. Moreover, this work explored a rule that, surface broken bonds density is directly related to surface energy with determination coefficient（R2） of over 0.8, indicating that the former is a dominant factor to determine the latter. Therefore, anisotropic surface broken bonds density can be used to predict the stability of mineral surface and the reactivity of surface atoms.

Surface characterization of chalcopyrite interacting with Leptospirillum ferriphilum

The alteration of surface properties of chalcopyrite after biological conditioning with Leptospirillum ferriphilum was studied by adsorption,zeta-potential,contact angle and bioleaching tests.The strains of L.ferriphilum cultured using different energy sources（either soluble ferrous ion or chalcopyrite） were used.The adhesion of bacteria to the chalcopyrite surface was a fast process.Additionally,the adsorption of substrate-grown bacteria was greater and faster than that of liquid-grown ones.The isoelectric point（IEP） of chalcopyrite moved toward that of pure L.ferriphilum after conditioning with bacteria.The chalcopyrite contact angle curves motioned diversely in the culture with or without energy source.The results of X-ray diffraction patterns（XRD）,scanning electron microscopy（SEM） and energy-dispersive X-ray spectroscopy（EDS） analysis indicate that the surface of chalcopyrite is covered with sulfur and jarosite during the bioleaching process by L.ferriphilum.Furthermore,EDS results imply that iron phase dissolves preferentially from chalcopyrite surface during bioleaching.The copper extraction is low,resulting from the formation of a passivation layer on the surface of chalcopyrite.The major component of the passivation layer that blocked continuous copper extraction is sulfur instead of jarosite.

Flotation and surface modification characteristics of galena,sphalerite and pyrite in collecting-depressing-reactivating system

The flotation tests and XPS analyses on galena,sphalerite and pyrite have been carried out in a collecting-depressing-reactivating system(hereafter referred as the CDR system).In this system,sulfide minerals were first collected and activated by the collector,and then depressed strongly by Ca(OH)2 in the strong alkaline solution,and finally reactivated by H2SO4.The flotation tests of pure minerals show that in this system the flotation behaviors of sphalerite and pyrite present irreversible characteristics along with the change of pulp potential.Furthermore,through the CDR system,considerable differences in the flotabilities between galena and sphalerite/pyrite are also observed.The XPS analysis results for galena,sphalerite and pyrite in a CDR system show that in the strong alkaline solution,some of the collectors,that have been already adsorbed on the mineral surface in the collecting process,are desorbed by Ca(OH)2.The XPS analysis results also show that in H2SO4 reactivating process,the surface hydroxides of galena are desorbed again by H2SO4 and replaced by diethyl dithiocarbamate,but those of sphalerite and pyrite are not desorbed.This flotation system may be applied to the bulk-differential flotation process of sulfur-bearing low-grade lead-zinc ores.

Investigation of pyrite surface state by DFT and AFM

The surface states of pyrite(Fe S2) were theoretically investigated using first principle calculation based on the density functional theory(DFT). The results indicate that both the(200) and(311) surfaces of pyrite undergo significant surface atom relaxation after geometry optimization, which results in a considerable distortion of the surface region. In the normal direction, i.e., perpendicular to the surface, S atoms in the first surface layer move outward from the bulk, while Fe atoms move toward the bulk, forming an S-rich surface. The surface relaxation processes are driven by electrostatic interaction, which is evidenced by a relative decrease in the surface energy after surface relaxation. Such a relaxation process is visually interpreted through the qualitative analysis of molecular mechanics. Atomic force microscopy(AFM) analysis reveals that only sulfur atom is visible on the pyrite surface. This result is consistent with the DFT data. Such S-rich surface has important influence on the flotation properties of pyrite.